Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
  • C08L23/08—Copolymers of ethene
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B9/00—Power cables
  • H01B9/02—Power cables with screens or conductive layers, e.g. for avoiding large potential gradients
  • H01B9/027—Power cables with screens or conductive layers, e.g. for avoiding large potential gradients composed of semi-conducting layers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
  • C08L23/08—Copolymers of ethene
  • C08L23/0846—Copolymers of ethene with unsaturated hydrocarbons containing atoms other than carbon or hydrogen
  • C08L23/0853—Ethene vinyl acetate copolymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/02—Elements
  • C08K3/04—Carbon
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
  • C08L23/08—Copolymers of ethene
  • C08L23/0846—Copolymers of ethene with unsaturated hydrocarbons containing atoms other than carbon or hydrogen
  • C08L23/0869—Copolymers of ethene with unsaturated hydrocarbons containing atoms other than carbon or hydrogen with unsaturated acids, e.g. [meth]acrylic acid; with unsaturated esters, e.g. [meth]acrylic acid esters
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/10—Homopolymers or copolymers of propene
  • C08L23/12—Polypropene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/10—Homopolymers or copolymers of propene
  • C08L23/14—Copolymers of propene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
  • C08L33/04—Homopolymers or copolymers of esters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
  • H01B1/20—Conductive material dispersed in non-conductive organic material
  • H01B1/24—Conductive material dispersed in non-conductive organic material the conductive material comprising carbon-silicon compounds, carbon or silicon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
  • H01B13/22—Sheathing; Armouring; Screening; Applying other protective layers
  • H01B13/24—Sheathing; Armouring; Screening; Applying other protective layers by extrusion
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2203/00—Applications
  • C08L2203/20—Applications use in electrical or conductive gadgets
  • C08L2203/202—Applications use in electrical or conductive gadgets use in electrical wires or wirecoating
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2205/00—Polymer mixtures characterised by other features
  • C08L2205/02—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2207/00—Properties characterising the ingredient of the composition
  • C08L2207/10—Peculiar tacticity
  • C08L2207/14—Amorphous or atactic polypropylene
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/002—Inhomogeneous material in general
  • H01B3/004—Inhomogeneous material in general with conductive additives or conductive layers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2933—Coated or with bond, impregnation or core

Definitions

• the present invention relates to a semi-conductive polymer composition, to a wire or cable comprising said semi-conductive polymer composition, and to the use of said composition for the production of a layer, preferably a semiconducting shield layer of a wire or cable.
• a typical electrical power cable or wire generally comprises one or more conductors in a cable core, which is surrounded by one or more insulation layers or sheaths of polymeric material.
• the core is typically copper or aluminium but it may also be non-metallic, surrounded by a number of different polymeric layers, each serving a specific function, e.g. a semiconducting shield layer, an insulation layer, a metallic tape shield layer and a polymeric jacket.
• Each layer can provide more than one function.
• low voltage wire or cable are often surrounded by a single polymeric layer that serves as both an insulating layer and an outer jacket, while medium to extra-high voltage wire and cable are often surrounded by at least separate insulating and jacket layers.
• a power cable core may for example be surrounded by a first polymeric semiconducting shield layer, a polymeric insulating layer, a second polymeric semiconducting shield layer, a metallic tape shield, and a polymeric jacket.
• Generally semi-conductive shields are used to provide layers of intermediate conductivity between the high potential conductor and the primary insulation, and between the primary insulation and the ground.
• Semi-conductive shields may be either bonded to the insulation layer or strippable.
• the inner semi-conductive shield is usually bonded to the insulation layer whereas the outer semi-conductive shield is often strippable.
• Typical inner semi-conductive shield layers comprise a polar ethylene copolymer, such as ethylene-vinyl acetate copolymer (EVA), ethylene methylacrylate copolymer (EMA), ethylene ethylacrylate copolymer (EEA), ethylene butylacrylate copolymer (EBA) and conductive filler, such as carbon black.
• EVA ethylene-vinyl acetate copolymer
• EMA ethylene methylacrylate copolymer
• EAA ethylene ethylacrylate copolymer
• EBA ethylene butylacrylate copolymer
• conductive filler such as carbon black
• NBR highly polar acrylonitrile-butadiene rubber
• Another approach for making a semi-conductive layer strippable is to use high amounts of ethylene polar copolymer.
• high amounts of ethylene polar copolymer combined with a high amount of filler are particularly difficult to extrude, due to the high viscosity of the composition. High production costs have to be faced.
• EP 2128195 proposes adding a secondary polymer phase to the polymer composition comprising an ethylene copolymer comprising polar co-monomer units and a conductive filler.
• the secondary polymer phase is an olefin copolymer comprising propylene monomer units and ethylene monomer units wherein the olefin copolymer has a melting point of 110°C or less and it is prepared using a metallocene polymerization catalyst.
• the melting point of the first polymer phase and the second polymer phase should differ by at most ⁇ 10°C to ensure good processing ability (i.e. both phases of the composition melt and flow together at the same physical form). This imposes great restrictions on the selection of the secondary polymer phase.
• the amount of conductive filler is decreased as even small changes may dramatically affect compounding efficiency and consistency during full scale production.
• the present invention provides a semi-conductive polymer composition comprising:
• the olefin homo- or copolymer (B) has a degree of crystaliinity below 12%, more preferably equal or below 10%, even more preferably below 5%, 2%, 1 % or 0.8%. Even more preferably the olefin homo- or copolymer (B) has a degree of crystaliinity below 0.5%.
• the melting temperature of the two polymers (A) and (B) has to be quite similar (usually within 10°C).
• the level of crystaliinity of component (B) is low, the need for restrictions on the melting temperature of component (B) in comparison with component (A) is eliminated.
• the olefin homo- or copolymer (B) is a propylene homo- or copolymer, more preferably is atactic-polypropylene or an ethylene ⁇ - propylene copolymer (EPP).
• the olefin homo- or co-polymer (B) is preferably present in the composition in an amount between 5 and 25% based on the total weight of the polymer composition.
• the amount of (B) should be selected to preserve the mechanical strength and the melt strength of the polymer composition.
• the polar co-monomer in the ethylene copolymer (A) is selected from the group consisting of acrylic acids, methacrylic acids, acrylates, methacrylates, and vinyl esters.
• the ethylene copolymer (A) is a vinyl acetate, acrylate or methacrylate copolymer, even more preferably the ethylene copolymer (A) is an acrylate more preferably an ethylene-methyl acrylate copolymer (EMA).
• EMA ethylene-methyl acrylate copolymer
• the conductive filler is present in the composition in an amount below 37% based on the total weight of the polymer composition.
• the conductive filler (C) is carbon black.
• the conductive filler is preferentially located in the ethylene copolymer (A).
• the MFR (2 1.6 g i3o°c) of the polymer composition satisfies the following relationship:
• the polymer composition of the invention preferably has a MFR (2 1 .6 Kg i3o°c) higher than 15 g/10min.
• the present invention provides a wire or cable comprising the polymer composition of the invention.
• the wire or cable comprises a conductor layer, an insulation layer and at least one semi- conductive layer, wherein said semi-conductive layer comprises the polymer composition of the invention.
• the present invention is directed to the use of the polymer composition of the invention in the production of a semi ⁇ conductive layer of a wire or cable.
• the present invention is also directed to a process for producing of a wire or cable comprising extruding a semi-conductive layer with the composition of the invention.
• the semi-conductive polymer composition according to the present invention comprises an ethylene copolymer (A) comprising polar co-monomer units.
• the polar co-monomers are selected from the group consisting of acrylic acids, methacrylic acids, acrylates, methacrylates, and vinyl esters.
• the polar co-monomers are selected from the group consisting of acrylic acids; alkyl acrylates, preferably Ci- to C 6 -alkyl acrylates or of Ci- to C 4 -alkyl acrylates; alkyl methacrylates, preferably C-i- to C 6 -alkyl methacrylates or of C-i- to C 4 -alkyl methacrylates; and vinyl acetate.
• the polar co-monomers may be selected from the group of alkylesters of (meth)acrylic acid, such as methyl, ethyl and butyl(meth)acrylate and vinyl acetate.
• the ethylene copolymer (A) is selected from the group consisting of ethylene vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene- ethyl acrylate copolymer (EEA), ethylene butyl acrylate copolymer (EBA), ethylene- methacrylic acid copolymer (EMAA) and ethylene acrylic acid copolymer (EAA) most preferably the ethylene copolymer (A) is an ethylene-methyl acrylate copolymer (EMA).
• EVA ethylene vinyl acetate copolymer
• EMA ethylene-methyl acrylate copolymer
• EAA ethylene- ethyl acrylate copolymer
• EBA ethylene butyl acryl
• the ethylene copolymer (A) comprising polar co-monomer units is prepared by copolymerizing ethylene and at least a polar co-monomer mentioned above. However, it may also be produced by grafting the polar co-monomer onto the homo- or copolymer backbone.
• the polar copolymer is prepared by copolymerizing ethylene with a polar co-monomer, this is preferably affected in a high pressure process resulting in low density ethylene copolymer.
• component (A) has a polar co-monomer content from 5 to 35 wt%, more preferably from 10 to 30 wt% or even more preferably from 15 to 25 wt%.
• component (A) has a melt flow rate MFR (2.16 kg, 190°C) of 0.1 to 100 g/10 min, more preferably of 1 to 60 g/10 min and most preferably of 5 to 50 g/10 min, and most preferably 15 to 50 g/10 min.
• the amount of component (A) is from 30 to 75 wt.% of the total polymer composition, more preferably is from 40 to 70 wt.% and most preferably is from 45 to 65 wt.%.
• the ethylene copolymer (A) comprising polar co-monomer units may further comprise unit containing an epoxy group.
• unit is referred herein as an "epoxy-group-containing monomer unit” and means an unsaturated compound comprising an epoxy group.
• Such compounds can be used as co- monomers for copolymerising epoxy-containing monomers units to the ethylene copolymer (A) or can be grafted to the ethylene copolymer (A), as well known in the polymer field. Grafting and copolymerizing of epoxy-group containing monomer units can be made according to or analogously to the methods described in the literature.
• the ethylene copolymer (A) containing epoxy groups as well as the epoxy-group-containing monomer units are very well known (mentioned e.g. in JP 06-116362 of Nippon Petrochem Co. LTD and WO 2010040964 of Arkema France) and commercially available.
• epoxy-containing monomer units e.g.
• aliphatic esters and glycidyl ethers such as an allyl glycidyl ether, a vinyl glycidyl ether, a maleate or itaconate of glycidyl, a (meth)glycidyl acrylate, and alicyclic esters and glycidyl ethers, such as a 2-cyclohexene-1 - glycidylether, a cyclohexene-4,5-diglycidyl carboxylate, a cyclohexene-4 glycidyl carboxylate, a 5-norbornene-2-methyl-2-glycidyl carboxylate and a endo cis- bicyclo (2,2,1) - 5-heptene-2,3-diglycidyl dicarboxylate, can be mentioned.
• component (A) even lower production cost may be achieved.
• the MFR of component (A) is often of almost irrelevance to the final composition, as the high MFR of component (B), e.g. ethylene-propylene copolymer and atactic-polypropylene, will boost the final value of the mixture.
• component (B) e.g. ethylene-propylene copolymer and atactic-polypropylene
• component (A) in co-polar co-monomer content is believed to affect predominantly the crystallinity of the system.
• Such an effect can be controlled by adjusting the conductive filler levels to appropriate values in order to ensure that volume resistivity levels and other mechanical properties are kept within the required range.
• the polymer composition of the present invention further comprises an olefin homo- or copolymer (B) having a degree of crystallinity when measured by differential scanning calorimetry (DSC), below 20%, preferably below 12%, more preferably equal or below 10%, even more preferably below 5%, 2%, 1% or 0.8%.
• DSC differential scanning calorimetry
• the olefin homo- or copolymer (B) has a degree of crystallinity below 0.5%.
• the olefin homo- or copolymer (B) has a degree of crystallinity below 0.8%.
• the degree of crystallinity measures the fraction of the ordered molecules in a polymer.
• Methods to evaluate the degree of crystallinity include density measurement, differential scanning calorimetry (DSC), X-ray diffraction (XRD), infrared spectroscopy and nuclear magnetic resonance (NMR). The measured value depends on the method used, which is therefore quoted together with the degree of crystallinity.
• DSC differential scanning calorimetry
• XRD X-ray diffraction
• NMR nuclear magnetic resonance
• the measured value depends on the method used, which is therefore quoted together with the degree of crystallinity.
• the distribution of crystalline and amorphous regions can be visualized with microscopic techniques, such as polarized light microscopy and transmission electron microscopy.
• the olefin homo- or copolymer (B) is highly amorphous at room temperature. Preferably it has a glass transition temperature below 5°C.
• the olefin homo- or copolymer (B) preferably has a melt flow rate (MFR) of 50 higher.
• MFR melt flow rate
• the average molecular weight (Mw) of the olefin homo- or copolymer (B) is preferably- below 50 000. Even more preferably the Mw of the olefin homo- or copolymer (B) is preferably below 35 000. Indeed, it has been found that when the Mw is below the mentioned values, the polymer composition may be processed more easily and better properties are achieved.
• component (B) is a homo- or copolymer of a C 2 -C 4 olefin.
• the olefin homo- or copolymer (B) is a propylene homo- or copolymer.
• the propylene homo- or copolymer (B) is atactic-polypropylene (aPP) or an ethylene-propylene copolymer (EPP).
• atactic-polypropylene means a propylene homopolymer having an atactic component higher than 50%, preferably higher than 60%, even more preferably higher than 65, most preferably equal or higher than 70%.
• EPP ethylene-propylene copolymer
• ethylene-propylene copolymer a copolymer comprising at least 50%, preferably at least 65, more preferably at least 80, most preferably at least 90 wt% of polypropylene units.
• the ethylene-propylene copolymer (EPP) preferably has an isotactic component higher than 50%, preferably higher than 60%, even more preferably higher than 70%, most preferably equal higher than 75%.
• aPP suitable for the polymer composition of the present invention has a cost significantly reduced with respect to most of polymer used as component (A). Atactic polypropylene may also be a waste product of different polymeric processes, and would therefore be recycled. Therefore by adding aPP to component (A) and to the conductive filler processing improvement are achieved, for a small sacrifice in electrical performance, at a substantially reduced cost.
• the melting point of the ethylene copolymer comprising polar co- monomer units (A) and the melting point of the olefin homo- or copolymer (B) should differ by at most of ⁇ 10°C. If a polymer composition according to claim 1 is used there may be greater differences in melting temperature between component A and B.
• the olefin homo- or copolymer (B) is present in the polymer composition in an amount between 1 and 30 wt%, preferably between 3 and 20 wt%, even more preferably between 5 and 10 wt% of the total polymer composition.
• the semi-conductive polymer composition of the invention further comprises conductive filler, preferably carbon black.
• conductive filler preferably carbon black. Any carbon black may be used which is electrically conductive. Examples of carbon blacks include furnace blacks and acetylene blacks. Furnace blacks are particularly preferred.
• Suitable furnace blacks may have a primary particle size less than 29 nm measured according to ASTM D-3849. Many suitable furnace blacks of this category are characterized by an iodine number between 60 and 300 mg/g according to ASTM D-1510 and an oil absorption number between 50 and 200 ml/100g according to ASTM D-2414.
• Suitable furnace blacks may have a primary particle size of greater than 28nm measured according to ASTM D-3849. Many suitable furnace blacks of this category are characterized by an iodine number between 30 and 200 mg/g according to ASTM D-1510 and an oil absorption number between 80 and 300 ml/1 OOg according to ASTM D-2414.
• Suitable carbon blacks for semi-conductive cable layers are preferably characterized by their cleanliness. Therefore, preferred carbon blacks have an ash-content of less than 0.2 wt% measured according to ASTM-1506, a 325 mesh sieve residue of less than 30 ppm according to ASTM D-1514 and have less than 1 wt% total sulphur according to ASTM-1619.
• extra-clean furnace carbon blacks having an ash-content of less than 0.05 wt.% measured according to ASTM-1506, a 325 mesh sieve residue of less than 15 ppm according to AST D-1514 and have less than 0.05 wt.% total sulphur -according to ASTM-1619.
• the amount of the conductive filler is at least such that a semiconducting composition is obtained. Depending on the desired use and conductivity of the composition, the amount of the conductive filler may vary.
• the polymer composition comprises 10 to 50 wt% of the total polymer composition of conductive filler. More preferably the amount of conductive filler is lower than 37 wt%, even more preferably the amount of conductive filler is 36 wt% or lower, 35 wt% or lower and most preferably lower it is than 33 wt%.
• the conductive filler is present in an amount of at least 10 wt%, preferably at least 20 wt% even more preferably in an amount of at least 30 wt%.
• component (A) and (B) Based on AFM (Atomic Force Microscopy) results, it appears that the inherent immiscibility between component (A) and (B) creates a two phase system in which the conductive filler exhibits preferential localization in the component (A) phase.
• preferential localization it is meant that the major part of the conductive filler is located in component (A). This localization constrains the mobility and dynamics of component (A).
• the conductive filler particles well dispersed in the component (A) create a conductive pathway that allows current to flow.
• the component (B) areas act as insulators since it is energetically not favourable for the conductive filler particles to localise themselves.
• the polymer composition of the present invention does not comprise NBR, which has a chewing-gum like consistency and thus gives rise to handling and dosing problems. Further in compositions containing NBR processing aids, parting agents are necessary to obtain a homogeneous final tree flowing composition.
• NBR non-reactive polymer
• the disadvantages due to the stickiness of NBR are overcome, thus the above additives may be omitted or their amount may be reduced.
• the semi-conductive polymer composition may further comprise a cross- linking agent.
• the cross-linking agent e.g. peroxide, is preferably added in an amount of less than 3.0 wt%, preferably of less than 2 wt% based on the total polymer composition.
• Suitable peroxides used for cross-linking are: di- tert-amylperoxide, 2,5-di(tert-butylperoxy)-2,5-dimethyl-3-hexyne, 2,5-di(tert- butylperoxy)-2,5-dimethylhexane, tert-butylcumylper-oxide, di(tert- butyl)peroxide, dicumylperoxide, di(tert-butylperoxy-isopropyl)benzene, butyl-4,4-bis(tert-butylperoxy)valerate, 1 ,1-bis(tert-butylperoxy)-3,3,5- trimethylcyclohexane, tert-butylperoxybenzoate, diben-zoylperoxide.
• the semi-conductive polymer composition may comprise further additives.
• additives antioxidants, scorch retarders, cross-linking boosters, stabilisers, processing aids, flame retardant additives, acid scavengers, inorganic fillers, voltage stabilizers, additives for improving water tree resistance, or mixtures thereof can be mentioned.
• fillers can also act as an acid scavenger. If for example, ethylene vinylacetate is used as a copolymer in the semi-conductive formulation, above 150°C forms acid which provokes an increased risk for corrosion of processing equipment.
• Basic, preferably inorganic fillers neutralise the acid and reduce the acid corrosion attack.
• Suitable filler materials may be selected from the group consisting of calcium carbonate, talc, mica, wollastonite, barium sulfate, calcite, and hydrotalcite.
• the polymer composition of the present invention feature increased performance in terms of processing with and decrease of costs.
• the polymer composition of the invention preferably has a MFR (2 1.6 Kg 130°C) higher than 15 g/10min.
• polymer composition of the present invention features comparable volume resistivity (VR) despite lower conductive filler concentration.
• the MFR(21.6 Kg -i 3o e c) of the polymer composition of the present invention satisfies the following relationship:
• the semi-conductive polymer composition according to the invention is preferably prepared by mixing together the components by using any suitable means such as conventional compounding or blending apparatus, e.g. a Banbury Mixer, a 2-roll rubber mill or a twin screw extruder, Buss co- kneader, etc.
• the compounding temperature is typically in a range of 120°C to 200°C.
• the present invention also pertains to an electric power cable comprising a semiconducting layer formed by the semi-conductive composition as described above.
• a wire or cable is defined to be a cable transferring energy operating at any voltage.
• the voltage applied to the cable can be alternating (AC), direct (DC), or transient (impulse).
• the multilayered article is a wire or cable operating at voltages higher than 1 kV, preferably higher than -23 kV.
• the semi-conductive polymer composition according to the invention is preferably extruded to form a semi-conductive layer of a wire or cable. This is preferably done at a line speed of at least 20 m/min, more preferably at least 50 m/min.
• the pressure used for the extrusion is 50 to 500 bar.
• the polymer composition can be applied onto the metallic conductor and/or on at least one coating layer thereof, e.g. an insulating layer.
• the inventive semi-conductive copolymer composition is contained in at least one of said semi-conductive layers.
• the power cable comprising the semi-conductive copolymer composition of the present invention may further comprise additional layers such as water barrier layers and a sheath layer.
• At least the outermost semi-conductive layer of a power cable is formed by the composition as described above.
• the present invention relates to the use of a semiconducting polymer composition as described above for the production of a semi-conductive layer of an electric power cable, preferably a medium to high voltage electric power cable.
• the melt flow rate (MFR) is determined according to ISO 1133.
• the MFR is measured with a load of 21.6 Kg at 190°C and /or with a load of 2.16 Kg at 130°C.
• FTIR Quantitative Fourier transform infrared
• N k1 (A / R) + k2
• A is the maximum absorbance defined of the co-monomer band
• R is the maximum absorbance defined as peak height of the reference peak ⁇ "> and with k1 and k2 the linear constants obtained by calibration.
• the band used for ethylene content quantification is selected depending if the ethylene content is random (730 cm “1 ) or block-like (as in heterophasic PP copolymer) (720 cm “1 ).
• the absorbance at 4324 cm “1 is used as a reference band.
• Co-monomer content (wt%) is determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) determination calibrated with quantitative nuclear magnetic resonance (NMR) spectroscopy.
• FTIR Fourier transform infrared spectroscopy
• NMR quantitative nuclear magnetic resonance
• Film samples of the polymers is prepared for the FTIR measurement: 0.5-0.7 mm film thickness is used for ethylene butyl acrylate and ethylene ethyl acrylate and 0.10 mm film thickness for ethylene methyl acrylate in amount of >6wt%. Films are pressed using a Specac film press at 150°C, approximately at 5 tons, 1-2 minutes, and then cooled with cold water in a not controlled manner. The accurate thickness of the obtained film samples is measured.
• the absorbance peak for the co-monomer is normalised with the absorbance peak of polyethylene (e.g. the peak height for butyl acrylate or ethyl acrylate at 3450 cm “1 is divided with the peak height of polyethylene at 2020 cm "1 ).
• the NMR spectroscopy 10 calibration procedure is undertaken in the conventional manner as well documented in the literature.
• a 0.10 mm thick film sample is prepared. After the analysis the maximum absorbance for the peak for the methylacrylate at 3455 cm “1 is subtracted with the absorbance value for the base line at 2475 cm “1 (Amethylacrylate - A2475). Then the maximum absorbance peak for the polyethylene peak at 2660 cm “1 is subtracted with the absorbance value for the base line at 2475 cm “1 (A2660 - A2475). The ratio between (Amethylacrylate-A2475) and (A2660-A2475) is then calculated in the conventional manner as well documented in the literature. The weight-% may be converted to mol-% by calculation as well documented in the literature.
• the co-monomer content is determined by quantitative nuclear magnetic resonance (NMR) spectroscopy after basic assignment (e.g. "NMR Spectra of Polymers and Polymer Additives", A. J. Brandolini and D. D. Hills, 2000, Marcel Dekker, Inc. New York). Experimental parameters is adjusted to ensure measurement of quantitative spectra for this specific task (e.g “-2G0 and More NMR Experiments: A Practical Course", S. Berger and S. Braun, 2004, Wiley-VCH, Weinheim). Quantities are calculated using simple corrected ratios of the signal integrals of representative sites in a manner known in the art.
• NMR nuclear magnetic resonance
• Co-monomer content (wt%) is determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) determination calibrated with quantitative nuclear magnetic resonance (NMR) spectroscopy.
• FTIR Fourier transform infrared spectroscopy
• NMR quantitative nuclear magnetic resonance
• the weight-% may be converted to mol-% by calculation as well documented in the literature.
• This setup is chosen primarily for the high resolution and quantitatively needed for accurate ethylene content quantification.
• Standard single-pulse excitation is employed without NOE, using an optimised tip angle, 1 s recycle delay and a bi-level WALTZ16 decoupling scheme ⁇ Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225; Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., acromol. Rapid Commun. 2007, 28, 1128 ⁇ .
• a total of 6144 (6k) transients are acquired per spectra.
• Figure 2 reports graphically the VR versus CB of the samples in Table !
• the semi-conductive polymer compositions of EVA, EBA, EPP and CB have the following advantageous feature:
• the ethylene-propylene copolymer (EPP) used has a polyethylene content of 8.6 wt% and a polypropylene content of 91.4wt%. It has a 21.78% of atactic component and 78.22% isotactic component. It has M w of 17000 and M n of 8000. It features a degree of crystallinity of 10% and a melting temperature of 80.1 °C.
• the trade name for the ethylene-propylene copolymer (EPP) used is LicoceneTM PP 1502 from Clariant, made by a metallocene type catalyst.

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