Cable

Abstract

A cable comprising a conductor surrounded in this order by at least an inner semiconductive layer, an insulating layer, and an outer semiconductive layer, wherein the inner semiconductive layer and / or the outer semiconductive layer contains an LDPE homopolymer or an LDPE copolymer, an antioxidant, carbon black, and a peroxide selected from the group consisting of a saturated aliphatic monofunctional peroxide and a saturated aliphatic difunctional peroxide; and wherein the insulating layer contains an LDPE homopolymer or an LDPE copolymer and a peroxide selected from the group consisting of an aliphatic monofunctional peroxide, an aliphatic difunctional peroxide, and a monofunctional peroxide containing an aromatic group, the above cable.

Description

Technical Field

[0001] The present invention relates to a cable, for example, a cross-linked power cable in which the electrical DC conductivity of an insulating layer is reduced by carefully designing a surrounding semiconductive layer.

Background Art

[0002] A standard power cable comprises a conductor surrounded in this order by an inner semiconductive shield (also called a conductor shield), an insulating layer, and an outer semiconductive shield (also called an insulation shield). The cable may also be further provided with additional layers, such as a jacket, as is well known in the art.

[0003] The electrical DC conductivity of such a cable (hereinafter referred to as DC conductivity in this specification) should be controlled low in order to mitigate thermal runaway of a cable system when used at various operating temperatures and electrical stresses, particularly high temperature and electrical stress.

[0004] The inventors have found that an increase in the DC conductivity of the insulating layer in such a cable may be related to the composition of the semiconductive layer in contact with the insulating material.

[0005] It will be understood that the layers within a power cable are often cross-linked. The cross-linking reaction is typically initiated using a peroxide. It is known that the decomposition products of the peroxide used in the insulating layer may impair DC conductivity. The peroxide is typically incorporated into the material layer before or during extrusion of one or more layers onto the conductor. After formation of the layered cable, it is exposed to an elevated temperature and radical formation is initiated, thereby achieving cross-linking.

[0006] The decomposition products of peroxides in the insulating layer and the semiconductive layer may include decomposition products and / or volatile decomposition products that adversely affect the electrical properties of the cable. Therefore, the decomposition products are customarily reduced or removed after crosslinking. Such a removal process is generally known as a degassing step.

[0007] DC conductivity is an important material property, for example, for insulating materials for high voltage direct current (HV DC) cables. First, the temperature dependence and electric field dependence of this property affect the resulting electric field within the cable. The second problem is the fact that heat is generated within the insulator due to leakage current flowing between the inner semiconductive layer and the outer semiconductive layer. This leakage current depends on the electric field and DC conductivity of the insulator. A high DC conductivity of the insulating material can even cause thermal runaway under high stress / high temperature conditions. Therefore, in order to avoid thermal runaway during operation, the DC conductivity must be sufficiently low.

[0008] There is a high demand to increase the voltage of power cables to achieve an increase in power transmission. There remains a need to find alternative polymer compositions that result in a reduction in DC conductivity in the cable. Such polymer compositions should preferably also have the good mechanical properties required for demanding power cable embodiments. Summary of the Invention Problems to be Solved by the Invention

[0009] The peroxide decomposition products of certain peroxides in the semiconductive layer may affect the DC conductivity in the insulating layer. These decomposition products may migrate from the semiconductive layer to the insulating layer, thereby seemingly having an adverse effect on performance. Therefore, it is important to carefully select the peroxides used in the semiconductive shield. Therefore, the inventors designed a cable having specific components in the insulating layer and the semiconductive layer and minimizing the DC conductivity in the insulating layer by ensuring that the semiconductive layer contains only certain peroxides.

Means for Solving the Problems

[0010] From one aspect, the present invention is a cable comprising a conductor surrounded in this order by at least an inner semiconductive layer, an insulating layer, and an outer semiconductive layer, wherein the inner semiconductive layer and / or the outer semiconductive layer contains an LDPE (low density polyethylene) homopolymer or an LDPE copolymer, an antioxidant, carbon black, and a peroxide selected from the group consisting of a saturated aliphatic monofunctional peroxide and a saturated aliphatic difunctional peroxide; and the insulating layer contains an LDPE homopolymer or an LDPE copolymer and a peroxide selected from the group consisting of an aliphatic monofunctional peroxide, an aliphatic difunctional peroxide, and a monofunctional peroxide containing an aromatic group and provides the above cable.

[0011] From one aspect, the present invention is a cable comprising a conductor surrounded in this order by at least an inner semiconductive layer, an insulating layer, and an outer semiconductive layer, wherein the inner semiconductive layer and the outer semiconductive layer independently contain an LDPE homopolymer or an LDPE copolymer, an antioxidant, carbon black, and a peroxide selected from the group consisting of a saturated aliphatic monofunctional peroxide and a saturated aliphatic difunctional peroxide; and The insulating layer contains an LDPE homopolymer or an LDPE copolymer and a peroxide selected from the group consisting of an aliphatic monofunctional peroxide, an aliphatic difunctional peroxide, and a monofunctional peroxide containing an aromatic group. To provide the cable described above.

[0012] The cable of the present invention is crosslinkable.

[0013] From another perspective, the present invention provides a crosslinked cable that can be obtained by crosslinking the cable defined above in this specification.

[0014] From another perspective, the present invention provides a crosslinked power cable that can be obtained by crosslinking the cable defined above in this specification.

[0015] From another perspective, the present invention is a method for manufacturing a cable comprising a conductor sequentially surrounded by at least an inner semiconductive layer, an insulating layer, and an outer semiconductive layer, Extruding or co-extruding the inner semiconductive layer, the insulating layer, and the outer semiconductive layer onto the conductor; and Crosslinking one or more of the inner semiconductive layer, the insulating layer, and the outer semiconductive layer Including the steps of, wherein the inner semiconductive layer and the outer semiconductive layer independently contain an LDPE homopolymer or an LDPE copolymer, an antioxidant, carbon black, and a peroxide selected from the group consisting of a saturated aliphatic monofunctional peroxide and a saturated aliphatic difunctional peroxide; The insulating layer contains an LDPE homopolymer or an LDPE copolymer and a peroxide selected from the group consisting of an aliphatic monofunctional peroxide, an aliphatic difunctional peroxide, and a monofunctional peroxide containing an aromatic group. To provide the method described above.

Embodiments for Carrying Out the Invention

[0016] The present invention provides a cable comprising a conductor surrounded by at least an inner semiconductive layer, an insulating layer, and an outer semiconductive layer. The present invention also relates to a crosslinked cable comprising a conductor surrounded by at least an inner semiconductive layer, an insulating layer, and an outer semiconductive layer.

[0017] Inner semiconductive layer and outer semiconductive layer

[0018] The inner semiconductive layer and the outer semiconductive layer can be the same or different, preferably the same. As used herein, the same means that the chemical compositions of the inner semiconductive layer and the outer semiconductive layer before crosslinking are the same. Both layers can include one or more LDPE homopolymers or one or more LDPE copolymers, an antioxidant, carbon black, and a peroxide selected from saturated aliphatic monofunctional peroxides or saturated aliphatic difunctional peroxides. The following discussion can apply to either or both of the above semiconductive layers.

[0019] It is also possible to use a combination of a polyethylene plastomer and a low-density polyethylene (LDPE) homopolymer or LDPE copolymer.

[0020] Low-density polyethylene (LDPE) homopolymer or LDPE copolymer

[0021] The term "LDPE" is an abbreviation for low-density polyethylene, but it is understood to include LDPE-like high pressure (HP) polyethylene and does not limit the density range. The term "LDPE" describes and differentiates only the properties of HP polyethylene having different branched structures compared to polyethylene produced in the presence of an olefin polymerization catalyst, for example. The term "LDPE" as used herein means a low-density homopolymer of ethylene (referred to herein as an LDPE homopolymer) or a low-density copolymer of ethylene and one or more comonomers (referred to herein as an LDPE copolymer).

[0022] The LDPE used in the inner semiconductive layer and / or the outer semiconductive layer can be an LDPE homopolymer, but preferably is an LDPE copolymer with one or more comonomers. It is also possible to use a mixture of low-density polyethylene (LDPE) homopolymer or LDPE copolymer in the inner semiconductive layer and / or the outer semiconductive layer.

[0023] Preferably, the LDPE copolymer used in the inner semiconductive layer and / or the outer semiconductive layer contains one or more polar comonomers. As the polar comonomer for the LDPE copolymer, one or more comonomers containing a carboxyl group and / or one or more ester groups are used. Even more preferably, one or more polar comonomers of the LDPE copolymer are selected from the group consisting of one or more acrylates, one or more methacrylates or one or more acetates or combinations thereof.

[0024] When present in the LDPE copolymer, the one or more polar comonomers are preferably selected from the group consisting of alkyl acrylate, alkyl methacrylate or vinyl acetate, or combinations thereof. Even more preferably, the one or more polar comonomers are selected from C1-~C6-alkyl acrylate, C1-~C6-alkyl methacrylate or vinyl acetate. Even more preferably, the LDPE copolymer used in the inner semiconductive layer and / or the outer semiconductive layer is a copolymer of ethylene and C1-~C4-alkyl acrylate, such as methyl acrylate, ethyl acrylate, propyl or butyl acrylate, or vinyl acetate.

[0025] The use of ethylene methyl acrylate (EMA) copolymer, ethylene methyl methacrylate (EMMA) copolymer, ethylene ethyl acrylate (EEA) copolymer, ethylene ethyl methacrylate (EEMA), ethylene butyl methacrylate (EBMA), ethylene butyl acrylate (EBA) copolymer or ethylene vinyl acetate (EBA) copolymer is preferred.

[0026] The use of ethylene methyl acrylate (EMA), ethylene butyl acrylate (EBA) or ethylene ethyl acrylate (EEA) is preferred.

[0027] When the LDPE is a copolymer, it preferably contains 0.001 to 40% by weight, more preferably 0.05 to 40% by weight, more preferably 0.05 to 30% by weight, still more preferably 1 to 30% by weight, of one or more comonomers. When there is a polar comonomer, the polar comonomer content is preferably 5 to 30% by weight, 7 to 30% by weight, 10 to 30% by weight, 5 to 25% by weight, 5 to 20% by weight, for example 7 to 20% by weight. In some embodiments, 10 to 20% by weight or 12 to 25% by weight of one or more comonomers may be present.

[0028] Preferably, the LDPE homopolymer or LDPE copolymer has a melt flow rate MFR2 of 0.1 to 50 g / 10 min, more preferably 1.0 to 30 g / 10 min, still more preferably 2.0 to 25 g / 10 min, most preferably 5.0 to 22 g / 10 min. Alternatively, the LDPE homopolymer or LDPE copolymer has a melt flow rate MFR2 of 10 to 22 g / 10 min.

[0029] Any LDPE homopolymer or LDPE copolymer may have a density of 910 to 940 kg / m 3 , preferably 915 to 935 kg / m 3 For example, 915 to 930 kg / m 3 of.

[0030] The LDPE homopolymer or LDPE copolymer can be produced by any conventional polymerization process. Preferably, it is produced by radical polymerization, such as high-pressure radical polymerization. The high-pressure polymerization can be carried out in a tubular reactor or an autoclave reactor. Preferably, it is a tubular reactor. Generally, the pressure can be in the range of 1200 to 3500 bar, and the temperature can be in the range of 100 °C to 350 °C. Further details regarding high-pressure radical polymerization are given in Encyclopedia of Polymer Science and Engineering, Vol. 6 (1986), pp 383-410 and Encyclopedia of Materials: Science and Technology, Elsevier Science Ltd.: “Polyethylene: High-pressure, R. Klimesch, D. Littmann and F.-O. Mahling pp. 7181-7184. 2001, which is incorporated herein by reference.

[0031] For example, propylene can be used as a comonomer, or as a chain transfer agent (CTA), or both, whereby it is well known that it can contribute to the total amount of C-C double bonds, preferably to the total amount of vinyl groups. In the present specification, when a compound that can also act as a comonomer, such as propylene, is used as a CTA for providing double bonds, the copolymerizable comonomer is not calculated in the comonomer content.

[0032] The inner semiconductive layer and / or the outer semiconductive layer can comprise at least 50 wt% of the LDPE homopolymer or LDPE copolymer, such as at least 60 wt%. When a blend of LDPE homopolymer or LDPE copolymer is used, this percentage refers to the total of the LDPE homopolymer or LDPE copolymer present.

[0033] In some embodiments, at least 65 wt% of an LDPE homopolymer or an LDPE copolymer is present. The LDPE generally forms the balance of the layer when the other components of the semiconductive layer are selected.

[0034] Insulating layer

[0035] The cable of the present invention includes an insulating layer comprising an LDPE homopolymer or an LDPE copolymer and a peroxide selected from an aliphatic monofunctional peroxide, an aliphatic difunctional peroxide, or a monofunctional peroxide containing an aromatic group. The insulating layer may include a mixture of an LDPE homopolymer or an LDPE copolymer.

[0036] The LDPE is preferably an LDPE homopolymer or an LDPE copolymer having at least one polyunsaturated comonomer. In one embodiment, the LDPE of the insulating layer comprises less than 5 wt% of a polar comonomer, such as less than 5 wt% of a comonomer containing a carboxyl group or an ester group, such as an acrylate monomer or an acetate monomer. In one embodiment, the LDPE homopolymer or LDPE copolymer of the insulating layer comprises less than 3.0 wt%, preferably less than 2.0 wt%, particularly less than 1.0 wt%, of a polar comonomer, such as less than 3.0 wt%, preferably less than 2.0 wt%, particularly less than 1.0 wt%, of a comonomer containing a carboxyl group or an ester group, such as an acrylate monomer or an acetate monomer.

[0037] When the LDPE homopolymer or LDPE copolymer is a copolymer, it preferably comprises at least one polyunsaturated comonomer and optionally one or more other comonomers. Preferably, the LDPE copolymer is a binary copolymer of ethylene and a single polyunsaturated comonomer.

[0038] The polyunsaturated comonomer preferably consists of a straight-chain carbon having at least 8 carbon atoms and at least 4 carbons between non-conjugated double bonds, at least one of which is terminal. The polyunsaturated comonomer is preferably a diene, for example, a diene containing at least 8 carbon atoms, where the first carbon-carbon double bond is terminal and the second carbon-carbon double bond is non-conjugated to the first carbon-carbon double bond, which is a diene selected from C8-~C 14 -dienes selected from non-conjugated dienes or mixtures thereof, for example, dienes selected from 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, 7-methyl-1,6-octadiene, 9-methyl-1,8-decadiene or combinations thereof, for example dienes selected from 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, or any combination thereof.

[0039] When the LDPE is an LDPE copolymer, it preferably contains one or more comonomers in an amount of 0.001 to 40% by weight, preferably 0.05 to 40% by weight, more preferably 0.05 to 30% by weight, still more preferably 1.0 to 30% by weight, still more preferably 1.0 to 20% by weight. When a polyunsaturated comonomer is present, the content of the polyunsaturated comonomer is preferably 0.001 to 10% by weight, preferably 0.01 to 10% by weight, more preferably 0.01 to 5.0% by weight, still more preferably 0.01 to 3.0% by weight, particularly 0.01 to 2.0% by weight, more particularly 0.1 to 2.0% by weight. In some embodiments, the only comonomer present is the polyunsaturated comonomer.

[0040] Preferably, the LDPE homopolymer or LDPE copolymer has a melt flow rate MFR2 of 0.1 to 50 g / 10 min, preferably 0.3 to 20 g / 10 min, more preferably 0.3 to 15 g / 10 min, even more preferably 0.50 to 15 g / 10 min, or 0.50 to 10 g / 10 min. In some embodiments, MFR2 is 0.50 to 8.0 g / 10 min, preferably 0.50 to 6.0 g / 10 min, and most preferably 0.50 to 4.0 g / 10 min.

[0041] Any LDPE homopolymer or LDPE copolymer may have a density of 905 to 935 kg / m 3 For example, 910 to 928 kg / m 3 Preferably, 915 to 925 kg / m 3

[0042] The insulating layer preferably does not contain carbon black. It may contain at least 80% by weight, for example at least 90% by weight, of LDPE homopolymer or LDPE copolymer. In some embodiments, at least 95% by weight of LDPE homopolymer or LDPE copolymer is present. When a blend of LDPE homopolymer or LDPE copolymer is used, this percentage refers to the total of the LDPE homopolymer or LDPE copolymer present.

[0043] When other components are calculated, the LDPE homopolymer or LDPE copolymer generally forms the balance of the layer. The insulating layer preferably contains 99.95% by weight or less of LDPE homopolymer or LDPE copolymer.

[0044] Carbon black

[0045] According to the present invention, the inner semiconductive layer and the outer semiconductive layer further contain carbon black.

[0046] ​The semiconductor properties are due to the added carbon black. Accordingly, the amount of carbon black is an amount such that at least a semiconductive layer is obtained. Preferably, the inner semiconductive layer and / or the outer semiconductive layer contains 10 to 48% by weight of carbon black. In other preferred embodiments, the amount of carbon black is 10 to 45% by weight, 15 to 45% by weight, 20 to 45% by weight, 25 to 45% by weight, 25 to 40% by weight, or 25 to 35% by weight based on the weight of the semiconductive layer.

[0047] Examples of suitable carbon blacks include acetylene black.

[0048] Acetylene carbon black can be produced by the acetylene black process by thermal decomposition of acetylene gas by reaction of acetylene with an unsaturated hydrocarbon, as described, for example, in U.S. Patent No. US4340577.

[0049] Acetylene black can have an average primary particle size of greater than 20 nm, for example 20 to 80 nm. The average primary particle size is defined as the number average particle diameter according to ASTM D3849-95a. Suitable acetylene blacks in this category have an iodine adsorption amount of 30 to 300 mg / g, for example 30 to 150 mg / g, according to ASTM D1510. Further, the oil absorption amount (of this category) is, for example, 80 to 300 ml / 100 g, for example 100 to 280 ml / 100 g, which is measured according to ASTM D2414. Acetylene black is a generally recognized term and is very well known and is supplied, for example, by Denka.

[0050] Mixtures can also be used. When a mixture of carbon blacks is used, this percentage refers to the total amount of carbon black present.

[0051] Peroxide - Semiconductive Layer

[0052] The peroxide is preferably added to the inner semiconductive layer and / or the outer semiconductive layer in an amount of 3.0 wt%, more preferably 0.1 to 2.5 wt%, even more preferably 0.3 to 2.5 wt%, based on the weight of the semiconductive layer. In some embodiments, the peroxide is present in an amount of 0.5 to 2.5 wt% based on the weight of the semiconductive layer. In one embodiment, 0.5 to 2.0 wt% of peroxide is present based on the weight of the semiconductive layer. When a blend of peroxides is used, this percentage refers to the total of the peroxides present.

[0053] The peroxide is a saturated aliphatic monofunctional peroxide or a saturated aliphatic difunctional peroxide. Combinations of peroxides may be used. The term "monofunctional" is used herein to define a peroxide in which a single O - O group is present. The term "difunctional" represents a peroxide in which two O - O groups are present.

[0054] Since the peroxide is aliphatic, it should not contain aromatic groups, such as a phenyl ring. Also, the peroxide should not contain three or more O - O groups. Therefore, peroxides such as 1,4 - bis[2-(tert - butylperoxy)propan - 2 - yl]benzene or 1,3 - bis[2-(tert - butylperoxy)propan - 2 - yl]benzene are excluded.

[0055] The term "saturated" is used herein to define a peroxide that does not contain carbon - carbon double or triple bonds.

[0056] In one embodiment, it is preferable that the inner semiconductive layer and the outer semiconductive layer of the cable of the present invention do not contain a peroxide containing an aromatic group, such as a phenyl ring. In one embodiment, it is preferable that the inner semiconductive layer and the outer semiconductive layer of the cable of the present invention do not contain a peroxide containing three or more O—O groups. In one embodiment, it is preferable that the inner semiconductive layer and the outer semiconductive layer of the cable of the present invention do not contain a peroxide containing a carbon-carbon double bond or triple bond, such as a hexene group or a hexyne group. Ideally, it is preferable that the inner semiconductive layer and the outer semiconductive layer of the cable of the present invention do not contain all such peroxides.

[0057] The peroxide may be added to the semiconductive composition used to form the semiconductive layer during the compounding step (i.e., when the polyolefin is mixed with carbon black), or in a separate step after the compounding step, or when the semiconductive composition is extrusion molded.

[0058] The peroxide is preferably liquid at a temperature of 20 to 45°C, preferably 25 to 40°C (atmospheric pressure).

[0059] The following peroxides can be mentioned as peroxides used for crosslinking: di-tert-amyl peroxide, 2,5-di(tert-butylperoxy)-2,5-dimethylhexane, di(tert-butyl) peroxide, and butyl-4,4-bis(tert-butylperoxy) valerate.

[0060] Preferably, the peroxide is selected from 2,5-di(tert-butylperoxy)-2,5-dimethyl-hexane, di(tert-butyl) peroxide, or a combination thereof.

[0061] Peroxide-insulating layer

[0062] As peroxides used for crosslinking the insulating layer, the following compounds can be mentioned: di-tert-amyl peroxide, 2,5-di(tert-butylperoxy)-2,5-dimethyl-3-hexyne, 2,5-di(tert-butylperoxy)-2,5-dimethylhexane, tert-butyl cumyl peroxide, di(tert-butyl) peroxide, dicumyl peroxide, butyl-4,4-bis(tert-butylperoxy) valerate, tert-butyl peroxybenzoate, dibenzoyl peroxide.

[0063] Preferably, the peroxide is selected from 2,5-di(tert-butylperoxy)-2,5-dimethyl-hexane, dicumyl peroxide, tert-butyl cumyl peroxide, di(tert-butyl) peroxide, or combinations thereof. Most preferably, the peroxide is tert-butyl cumyl peroxide, dicumyl peroxide or 2,5-di(tert-butylperoxy)-2,5-dimethyl-hexane.

[0064] It is preferred that dicumyl peroxide or 2,5-di(tert-butylperoxy)-2,5-dimethyl-hexane is used in the insulating layer.

[0065] The peroxide is preferably added to the insulating layer in an amount of less than 3.0% by weight, more preferably 0.1 - 2.5% by weight, even more preferably 0.3 - 2.5% by weight, 0.4 - 2.0% by weight, 0.4 - 1.5% by weight, 0.4 - 1.0% by weight, based on the weight of the insulating layer. When a blend of peroxides is used, this percentage refers to the total of the peroxides present.

[0066] Antioxidant

[0067] Any layer of the cable core can contain an antioxidant. Examples of antioxidants that can be mentioned are sterically or semi-sterically hindered phenols, aromatic amines, aliphatic sterically hindered amines, organic phosphates, thio compounds, polymerized 2,2,4-trimethyl-1,2-dihydroquinoline, and combinations thereof.

[0068] More preferably, the antioxidant is selected from the group consisting of 4,4'-bis(1,1'-dimethylbenzyl)diphenylamine, para-oriented styrenated diphenylamine, 4,4'-thiobis(2-tert-butyl-5-methylphenol), polymerized 2,2,4-trimethyl-1,2-dihydroquinoline, or derivatives thereof.

[0069] More preferably, the antioxidant is selected from the group consisting of 4,4'-bis(1,1'-dimethylbenzyl)diphenylamine, para-oriented styrenated diphenylamine, 4,4'-thiobis(2-tert.butyl-5-methylphenol), 2,2'-thiobis(6-t-butyl-4-methylphenol), distearyl thiodipropionate, 2,2'-thio-diethyl-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), polymerized 2,2,4-trimethyl-1,2-dihydroquinoline, or derivatives thereof, but is not limited thereto.

[0070] The amount of the antioxidant, optionally a combination of two or more antioxidants, can be in the range of 0.005 to 2.5 wt%, for example 0.01 to 2.5 wt%, preferably 0.01 to 2.0 wt%, more preferably 0.03 to 2.0 wt%, particularly 0.03 to 1.5 wt%, more particularly 0.05 to 1.5 wt%, or 0.1 to 1.5 wt%, based on the weight of the semiconductive layer.

[0071] The insulating layer may also contain an antioxidant, for example an antioxidant defined for the semiconductive layer. The antioxidant used in the insulator is preferably different from the antioxidant used in the inner semiconductive layer and / or the outer semiconductive layer. The amount of antioxidant, optionally a combination of two or more antioxidants, based on the weight of the insulating layer, can be in the range of 0.005 to 2.5 wt%, preferably 0.01 to 2.5 wt%, more preferably 0.01 to 2.0 wt%, particularly 0.03 to 2.0 wt%, more particularly 0.03 to 1.5 wt%. In some embodiments, the amount of antioxidant is 0.04 to 1.5 wt%, preferably 0.04 to 1.0 wt%, more preferably 0.04 to 0.8 wt%, particularly 0.04 to 0.6 wt%, more particularly 0.04 to 0.5 wt%, based on the weight of the insulating layer.

[0072] Other components

[0073] The inner semiconductive layer and / or the outer semiconductive layer, or the insulating layer, may contain further additives. Possible additives that can be mentioned are scorch retarders, crosslinking boosters, stabilizers, processing aids, flame retardant additives, acid scavengers, inorganic fillers, voltage stabilizers, or combinations thereof.

[0074] A "scorch retarder" is defined as a compound that reduces premature crosslinking, i.e., the formation of scorch during extrusion. In addition to the scorch retarding properties, the scorch retarder can simultaneously result in a further effect of boosting, i.e., enhancing, the crosslinking performance. It is particularly preferred to use a scorch retarder in the insulating layer.

[0075] Useful scorch retardants can be selected from unsaturated dimers of aromatic alpha-methylalkenyl monomers, substituted or unsubstituted diphenylethylene, quinone derivatives, hydroquinone derivatives (e.g., 2,5-di-tert-butylhydroquinone), monofunctional vinyl-containing esters and ethers, or combinations thereof. More preferably, the scorch retardant is selected from unsaturated dimers of aromatic alpha-methylalkenyl monomers, such as 2,4-diphenyl-4-methyl-1-pentene, substituted or unsubstituted diphenylethylene, or combinations thereof. A highly preferred option is 2,4-diphenyl-4-methyl-1-pentene.

[0076] Preferably, the amount of the scorch retardant is in the range of 0.005 to 1.0% by weight, more preferably in the range of 0.01 to 0.80% by weight. Even more preferred ranges are 0.03 to 0.75% by weight, 0.05 to 0.70% by weight, and 0.050 to 0.50% by weight, based on the total weight of the layer in question.

[0077] In a further embodiment of the present invention, the scorch retardant is not used in the manufacture of the inner semiconductive layer and / or the outer semiconductive layer.

[0078] In a further embodiment of the present invention, the scorch retardant is not used in the manufacture of the insulating layer.

[0079] The crosslinking booster may be a compound containing at least two unsaturated groups, such as an aliphatic or aromatic compound, ester, ether, amine, or ketone, and it contains a compound containing at least two unsaturated groups, such as cyanurate, isocyanurate, phosphate, orthoformate, aliphatic or aromatic ether, or allyl ester of benzenetricarboxylic acid. Examples of esters, ethers, amines, and ketones are diacrylate, triacrylate, tetraacrylate, triallyl cyanurate, triallyl isocyanurate, 3,9-divinyl-2,4,8,10-tetra-oxaspiro[5,5]-undecane (DVS), triallyl trimellitate (TATM), or N,N,N',N',N",N"-hexaallyl-1,3,5-triazine-2,4,6-triamine (HATATA), or any mixture thereof. The crosslinking promoter can be added in an amount such that it is less than 2.0 wt%, such as less than 1.5 wt%, such as less than 1.0 wt%, such as less than 0.75 wt%, such as less than 0.5 wt%, based on the total weight of the layer in question, and its lower limit is, based on the total weight of the layer in question, such as at least 0.05 wt%, such as at least 0.1 wt%.

[0080] In a further embodiment of the present invention, the crosslinking promoter is not used in the manufacture of the inner semiconductive layer and / or the outer semiconductive layer.

[0081] In a further embodiment of the present invention, the crosslinking promoter is not used in the manufacture of the insulating layer.

[0082] Conductor

[0083] The cable of the present invention includes a conductor. The conductor can be made from any suitable conductive metal, typically copper or aluminum.

[0084] Cable

[0085] A power cable is defined as a cable that transmits energy operating at any voltage, typically operating at a voltage higher than 1 kV. The voltage applied to the power cable is alternating current (AC), direct current (DC), or transient (impulse).

[0086] As used herein, the term "cable" is intended to refer to a cable having at least one cable core, optionally two or three cable cores. Each "cable core" used herein comprises a conductor surrounded by at least an inner semiconductive layer, an insulating layer, and an outer semiconductive layer. One or more cable cores within the cable may be surrounded by at least one reinforcing layer and / or an armouring layer adapted for mechanical protection of the cable. The armouring layer may include metallic wires, a braid, a sheath, or a low loss armour. These variations and cable structures are well known to those skilled in the art. The armouring layer may extend over a portion of the cable.

[0087] The term "DC cable" refers to a direct current (DC) cable generally having one or more cable cores, preferably one or two cable cores.

[0088] The cable according to the invention is very advantageously a DC power cable, which can be, for example, a low voltage (LV), medium voltage (MV), high voltage (HV) or extra high voltage (EHV) or ultra-high voltage (UHV) DC cable, these terms being well known and indicating the level of the operating voltage. The DC power cable may operate at a voltage of at least 30 kV and can be, for example, an HVDC cable. In the case of an HVDC cable, the operating voltage is defined herein as the voltage between the ground and the conductor of the high voltage cable.

[0089] The cable may be an HVDC power cable operating at a voltage of 40 kV or more, further at a voltage of 50 kV or more, and further at a voltage of 60 kV or more. In some embodiments, the operating voltage may be more than 80 kV. The upper limit is not limited. A practical upper limit can be up to 1100 kV. Most preferred are HVDC power cables operating at 80 - 320 kV, or HVDC power cables operating at 320 - 525 kV or 320 - 640 kV.

[0090] As is well known, the cable can optionally comprise further layers, such as a layer surrounding an outer semiconductive layer, such as one or more screens, jacket layers, one or more other protective layers, or any combination thereof.

[0091] The cable is the following step (a): preparing and mixing a crosslinkable first semiconductive composition for the inner semiconductive layer, for example by melt mixing in an extruder, preparing and mixing a crosslinkable insulating composition for the insulating layer, for example by melt mixing in an extruder, preparing and mixing a second semiconductive composition for the outer semiconductive layer, for example by melt mixing in an extruder, the following step (b): For example, by coextrusion, applying onto a conductor, melting and mixing the first semiconductive composition obtained from step (a) to form the inner semiconductive layer, melting and mixing the insulating layer composition obtained from step (a) to form the insulating layer, and melting and mixing the second semiconductive composition obtained from step (a) to form the outer semiconductive layer, and Step (c): Optionally, crosslinking one or more of the insulating layer, the inner semiconductive layer, and the outer semiconductive layer of the obtained cable under crosslinking conditions can be manufactured by a process including one or more of the above steps.

[0092] When a peroxide is used in the manufacture of the layers of the cable, such layers are preferably crosslinked. Therefore, the cable of claim 1 is crosslinkable and defines the cable before crosslinking.

[0093] The first semiconductive composition for the inner semiconductive layer, the crosslinkable insulating composition for the insulating layer, and the second semiconductive composition for the outer semiconductive layer comprise the components necessary to form the respective inner layer, insulating layer, and outer layer of the cable.

[0094] During the preparation of the polymer composition, the components can be blended, for example, melt mixed in a compounding apparatus. Preferably, the process does not involve the use of a peroxide. Typically, the process involves heating to a temperature of at least 150°C, preferably at least 160°C, for example at least 170°C. The process generally involves heating to 300°C or less, for example 250°C or less.

[0095] It is understood that all of the definitions and preferred embodiments described above apply equally to all further embodiments as described below. In one embodiment, the insulating layer composition of the present invention may contain a crosslinking agent before the composition is used for cable manufacturing, whereby the polymer component and the crosslinking agent are added to the melt of the polymer composition by any conventional mixing process, for example in an extruder, and by adsorption onto a solid composition of the polymer, such as its pellets, of a liquid peroxide, a peroxide in liquid form or a peroxide dissolved in a solvent. Next, the resulting insulating layer composition of the components, for example, among others, the polymer composition, one or more antioxidants, and the crosslinking agent, are used for the preparation process of a molded article, such as a cable core.

[0096] In another embodiment, the crosslinking agent may be added, for example, in a process during the preparation of a crosslinkable molded article, and forms an insulating layer composition as used in the cable core of the present invention. Next, when the crosslinking agent is added during the preparation process of the molded article, for example, the crosslinking agent as described herein is added in liquid form at ambient temperature, or preheated above its melting point, or dissolved in a carrier medium, as is well known in the art.

[0097] The insulating layer composition used in the cable core of the present invention may also contain one or more further additives, or one or more further additives may be blended into the polymer composition during the preparation process of a molded article containing the insulating layer composition. It is understood that one or more further additives, such as any antioxidant, crosslinking agent, scorch retardant, may be added in the form of a masterbatch, as is well known in the art.

[0098] In certain embodiments, the semiconductive layer used in the cable core of the present invention can be obtained by several means using several different manufacturing techniques, such as internal mixers (e.g., Banbury or Bolling), continuous single screw (e.g., BUSS), or continuous twin screw (e.g., Farrel or Werner & Pfleiderer). The type of mixer and the selected operating conditions for the preparation of the semiconductive compound have a direct impact on the melt quality and also affect the final compound properties, such as melt flow rate, volume resistivity, and surface smoothness. Particularly useful is the co-kneader technology (BUSS, X-compound). In the preparation of the semiconductive layer, the conductive filler can be added to the molten polymer while completely controlling the manufacturing temperature. With this technique, a blend with sufficient dispersive and distributive mixing can be achieved by those skilled in the art.

[0099] It is understood that the crosslinking agent is generally added to the semiconductive layer composition in the same manner as in the case of the insulating layer composition, as detailed in the above embodiments.

[0100] It is preferred that all layers are crosslinked. Therefore, the present invention further provides a crosslinked cable obtained by crosslinking the cable defined herein.

[0101] The curing procedure can be carried out at elevated temperatures, such as above 150 °C, for example 160 - 350 °C.

[0102] Melt mixing means mixing above the melting point of at least one of the major polymer components of the resulting mixture, and is typically carried out at a temperature at least 10 - 15 °C higher than the melting point or softening point of one or more polymer components.

[0103] As used herein, the term "coextrusion" means that all or part of one or more layers are formed simultaneously using one or more extrusion heads. For example, triple extrusion can be used to form three layers.

[0104] In a further embodiment of the present invention, the insulating layer in the crosslinked cable of the present invention has a DC conductivity of 80 fS / m or less; 70 fS / m or less; or alternatively, 5 to 64 fS / m or less as determined based on the DC conductivity method at 70 °C.

[0105] Moreover, the first semiconductive composition and the second semiconductive composition may be the same, for example.

[0106] The thickness of the insulating layer of a power cable, such as a DC cable, such as an HVDC or EHVDC power cable, is typically 2 mm or more, for example at least 3 mm, for example at least 5 to 100 mm, for example 5 to 50 mm, when measured from the cross-section of the insulating layer of the cable.

[0107] The thickness of the inner semiconductive layer and / or the outer semiconductive layer of the power cable is typically 0.5 mm or more, for example 0.7 mm to 5.0 mm, when measured from the cross-section of the layer.

[0108] Viewed from another aspect, the present invention is a cable comprising a conductor surrounded in this order by at least an inner semiconductive layer, an insulating layer, and an outer semiconductive layer, wherein the inner semiconductive layer and / or the outer semiconductive layer, comprises at least 50 wt% of an LDPE homopolymer or LDPE copolymer, 0.005 to 2.5 wt% of one or more antioxidants, 25 to 48 wt% of carbon black; and, 0.1 to 2.5 wt% of a peroxide selected from the group consisting of saturated aliphatic monofunctional peroxides and saturated aliphatic difunctional peroxides and; and, wherein the insulating layer, At least 80% by weight of an LDPE homopolymer or LDPE copolymer; and, 0.1 to 2.5% by weight of a peroxide selected from the group consisting of an aliphatic monofunctional peroxide, an aliphatic difunctional peroxide, and a monofunctional peroxide containing an aromatic group comprising providing the above cable.

[0109] Viewed from another aspect, the present invention is a cable comprising a conductor surrounded in this order by at least an inner semiconductive layer, an insulating layer, and an outer semiconductive layer, wherein the inner semiconductive layer and / or the outer semiconductive layer comprises at least 55% by weight of an LDPE homopolymer or LDPE copolymer, 0.1 to 1.5% by weight of one or more antioxidants, 25 to 41% by weight of carbon black; and, 0.5 to 2.0% by weight of a peroxide selected from the group consisting of a saturated aliphatic monofunctional peroxide and a saturated aliphatic difunctional peroxide comprising; and, the insulating layer comprises at least 95% by weight of an LDPE homopolymer or LDPE copolymer; and, 0.4 to 2.0% by weight of a peroxide selected from the group consisting of an aliphatic monofunctional peroxide, an aliphatic difunctional peroxide, and a monofunctional peroxide containing an aromatic group comprising providing the above cable.

[0110] The present invention will be described herein with reference to the following non-limiting examples.

[0111] Determination method

[0112] Unless otherwise specified in the detailed description or experimental part of the invention, the following methods were used for the determination of properties.

[0113] wt%: % by weight

[0114] Melt flow rate

[0115] The melt flow rate (MFR) is determined in accordance with ISO 1133 and is expressed in g / 10 min. The MFR is an indicator of the polymer's fluidity and, by extension, its processability. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR is determined for polyethylene at 190 °C and can be determined under different loads, for example 2.16 kg (MFR2) or 21.6 kg (MFR 21 ).

[0116] Density

[0117] The density was measured in accordance with ISO 1183-1 / Method A. The sample preparation was carried out in accordance with Table 3Q of ISO 1872-2 (compression molding).

[0118] Preparation of Crosslinked Plaques for Heat Set

[0119] The crosslinked plaques were prepared from pellets of the semiconductive polymer composition for testing and were compression molded using the following conditions: First, the pellets were melted at 120 °C for 1 minute under a pressure of 61 N / cm 2 . Next, the temperature was raised to 180 °C at a rate of 18 K / min while the pressure was raised to 614 N / cm 2 . The temperature was maintained at 180 °C for 26 minutes. Next, the plaques were crosslinked by the peroxide present in the semiconductive polymer composition. After completion of crosslinking, the crosslinked plaques, i.e., here the crosslinked semiconductive polymer composition, were cooled to room temperature at a cooling rate of 15 K / min while under pressure. The thickness of the plaques is 1 mm.

[0120] Heat Set

[0121] For the crosslinked plaques, i.e., the samples taken from the crosslinked semiconductive polymer compositions according to the present invention and the crosslinked semiconductive polymer compositions of the comparative examples, the hot set elongation and the permanent deformation were determined. These properties were determined in accordance with IEC 60811-507:2012. In the hot set test, a weight corresponding to 20 N / cm 2 was attached to the dumbbell of the material being tested and marked at a reference length of 20 mm. This test piece was placed in an oven at 200 °C, and after 15 minutes, the distance between the reference marks was measured, and the hot set elongation was calculated. Subsequently, the weight was removed, and the sample was left for 5 minutes. Next, the sample was taken out of the oven and cooled to room temperature. The distance between the reference marks was measured, and the permanent deformation was calculated.

[0122] The crosslinked plaques were prepared as described in the section "Preparation of Crosslinked Plaques", and dumbbell specimens were prepared from the crosslinked plaques with a thickness of 1 mm in accordance with ISO 527-2 / 5A:2012.

[0123] DC conductivity method

[0124] Plaques were separately compression molded from both the pellets of the insulating polymer composition and the pellets of the semiconductive polymer composition, using a Teflon (登録商標) press film for both plaques. The insulating composition plaque made of the polymer composition to be tested had a thickness of 1 mm and a diameter of 330 mm, and the plaque made of the semiconductive polymer composition had a thickness of 0.3 mm and a diameter of 260 mm. The plaque made of the insulating polymer composition and the plaque made of the semiconductive polymer composition were prepared by press molding according to steps 1 to 8 in the following table.

[0125]

Table 0

[0126] Immediately after compression molding, a conditioning process was initiated, and one plaque made of a cross-linked insulating polymer composition and one plaque made of a semiconductive polymer composition to be tested were stored at 70 °C for 24 hours in a sealed aluminum bag in direct contact with each other. After the conditioning process, DC conductivity measurements were performed on a sandwich structure combining the insulating plaque and the semiconductive plaque to be tested.

[0127] A high voltage source was connected to the upper electrode, and a voltage was applied to a test sample, i.e., a sandwich structure, made of a cross-linked polymer composition of the semiconductive plaque facing the high voltage electrode to be tested. The current resulting through the sample was measured using an electrometer / picoammeter. The measurement cell was a three-electrode system of brass electrodes placed in a heating oven. The diameter of the measurement electrode was 100 mm. Care was taken to avoid flashover from the round edge of the electrode. The applied voltage was +30 kV DC, the average electric field was 30 kV / mm, and the temperature was 70 °C for 24 hours, 30 °C for 10 hours, and 95 °C for 10 hours. The current value at 70 °C was recorded 24 hours after the end of the 70 °C plateau, and the value at 95 °C was recorded 44 hours after the end of the 95 °C plateau. These values were used to calculate the DC conductivity of the test samples at two different temperatures consisting of the cross-linked insulating polymer composition and the semiconductive composition.

[0128] The conductivity σ is defined as the current density J divided by the applied electric field E. Therefore, the relationship between the measured current I flowing through the sample and the conductivity σ can be expressed in SI units as follows.

Equation

[0129] Experimental section

[0130] The following materials were used in these examples: EBA is an ethylene copolymer of butyl acrylate produced in a high-pressure radical process. MFR2 is 18 g / 10 min, and the density is 924 kg / m 3 is. Carbon black: acetylene black Peroxide 1 for comparative example: 1,4-bis[2-(tert-butylperoxy)propan-2-yl]benzene and / or 1,3-bis[2-(tert-butylperoxy)propan-2-yl]benzene CAS 25155-25-3 Peroxide 2: 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane CAS 78-63-7 SRA1: 2,4-diphenyl-4-methyl-1-pentene CAS 6362-80-7 The insulating layer is LS4258DCE commercially available from Borealis and contains the peroxide of claim 1.

[0131] The semiconductive polymer composition is prepared in a co-kneader (BUSS, X-compounds) where conductive filler can be added to the polymer in the molten state while fully controlling the production temperature.

[0132] The crosslinking agent was added to the semiconductive polymer composition after compounding.

[0133] The following precursor semiconductive compositions were prepared (all values are in wt%):

[0134] [Table 1]

[0135] Next, the precursor semiconductive composition in Table 1 is used to prepare the following semiconductive compositions in Tables 2 to 3 below.

[0136]

Table 2

[0137]

Table 3

[0138] The above data show that when the semiconductive composition of the present invention having a defined peroxide contacts the insulating layer composition defined herein, the DC conductivity in the insulating layer decreases as compared with the comparative example. The design of the semiconductive layer is assumed to reduce the species that impair the DC conductivity migrating from the semiconductive composition of the present invention to the insulating layer. Therefore, by carefully designing both the semiconductive layer and the insulating layer, the performance of the cable is improved.

Claims

1. A cable comprising a conductor surrounded in this order by at least an inner semiconductive layer, an insulating layer, and an outer semiconductive layer, wherein the inner semiconductive layer and / or the outer semiconductive layer contains an LDPE homopolymer or an LDPE copolymer, an antioxidant, carbon black, and a peroxide selected from the group consisting of a saturated aliphatic monofunctional peroxide and a saturated aliphatic difunctional peroxide; and the insulating layer contains an LDPE homopolymer or an LDPE copolymer and a peroxide selected from the group consisting of an aliphatic monofunctional peroxide, an aliphatic difunctional peroxide, and a monofunctional peroxide containing an aromatic group, said cable.

2. The cable according to claim 1, wherein the peroxide used in the inner semiconductive layer and / or the outer semiconductive layer is liquid at a temperature of 20 to 45°C, preferably 25 to 40°C.

3. The cable according to claim 1 or 2, wherein the peroxide used in the inner semiconductive layer and / or the outer semiconductive layer is 2,5-di(tert-butylperoxy)-2,5-dimethyl-hexane.

4. The cable according to any one of claims 1 to 3, wherein the inner semiconductive layer has the same chemical composition as the outer semiconductive layer.

5. The cable according to any one of claims 1 to 4, wherein the inner semiconductive layer and / or the outer semiconductive layer contains an ethylene alkyl acrylate or an ethylene vinyl acetate copolymer.

6. The cable according to claim 5, wherein the inner semiconductive layer and / or the outer semiconductive layer contains ethylene methyl acrylate, ethylene ethyl acrylate, or ethylene butyl acrylate.

7. The cable according to any one of claims 1 to 6, wherein the inner semiconductive layer and / or the outer semiconductive layer contains 0.1 to 2.0% by weight of a peroxide.

8. The cable according to any one of claims 1 to 7, wherein the insulating layer contains an LDPE homopolymer or an LDPE copolymer of ethylene and a polyunsaturated comonomer.

9. The inner semiconductive layer and / or the outer semiconductive layer is at least 50% by weight of an LDPE homopolymer or an LDPE copolymer; 0.005 to 2.5% by weight of one or more antioxidants; 15 to 48% by weight of carbon black; and 0.1 to 2.5% by weight of a peroxide selected from the group consisting of a saturated aliphatic monofunctional peroxide and a saturated aliphatic difunctional peroxide comprising; and, wherein the insulating layer comprises at least 80% by weight of an LDPE homopolymer or LDPE copolymer; and, 0.1 to 2.5% by weight of a peroxide selected from the group consisting of aliphatic monofunctional peroxides, aliphatic difunctional peroxides, and monofunctional peroxides containing an aromatic group comprising, A cable according to any one of claims 1 to 8, comprising a conductor surrounded in this order by at least an inner semiconductive layer, an insulating layer, and an outer semiconductive layer.

10. A crosslinked cable obtainable by crosslinking a cable according to any one of claims 1 to 9.

11. The crosslinked cable according to claim 10, wherein the DC conductivity of the insulating layer is less than 64 fS / m when measured according to the DC conductivity method at 70°C.

12. The crosslinked cable according to claim 10 or 11, which is a direct current (DC) power cable.

13. A method of manufacturing a cable comprising a conductor surrounded in this order by at least an inner semiconductive layer, an insulating layer, and an outer semiconductive layer, comprising: extruding an inner semiconductive layer, an insulating layer, and an outer semiconductive layer onto the conductor; and, crosslinking one or more of the inner semiconductive layer, the insulating layer, and the outer semiconductive layer including the steps of, wherein the inner semiconductive layer and the outer semiconductive layer independently comprise an LDPE homopolymer or LDPE copolymer, an antioxidant, carbon black, and a peroxide selected from the group consisting of saturated aliphatic monofunctional peroxides and saturated aliphatic difunctional peroxides; the insulating layer comprises an LDPE homopolymer or LDPE copolymer and a peroxide selected from the group consisting of aliphatic monofunctional peroxides, aliphatic difunctional peroxides, and monofunctional peroxides containing an aromatic group; the method.

14. The method according to claim 13, further comprising crosslinking at least the semiconductive layer and the insulating layer, for example by exposing the cable to heat.

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