EA040293B1 - CABLE WITH LOW CONDUCTIVITY INSULATION - Google Patents

Description

The invention relates to the use of blends containing low density polyethylene (LDPE) polymers in insulating layers of cables such as DC cables. In particular, the present invention relates to the combination of LDPE with small amounts of a recycled polymer selected from LLDPE, PESP or UHMWPE to provide a surprisingly established method for producing extremely low conductivity cable insulation layers.

The blends of the present invention may be used in cross-linked or non-cross-linked form, the latter eliminating the need for a cross-linking agent and eliminating the need for a post-cross-linking degassing procedure to remove cross-linking by-products.

For both crosslinked and non-crosslinked blends, the conductivity of the resulting composition, and therefore of the insulation layer, is lower compared to using LDPE alone.

State of the art

High pressure (HP) process polyolefins are widely used in applications where polymers are highly demanding, where polymers must meet high mechanical and/or electrical requirements. For example, in power cables, in particular medium voltage (MV) cables, and especially high voltage (HV) and extra high voltage (EHV) cables, the electrical properties of the polymer composition used in the cable are important. In addition, important electrical properties may differ in different cable applications, such as the difference between AC and DC cable applications.

A typical power cable comprises a conductor surrounded by at least an inner semi-conductive layer, an insulating layer, and an outer semi-conductive layer, in that order. Cables are usually made by extruding layers onto a conductor.

The polymeric material in one or more of these layers is often crosslinked to improve, for example, heat and deformation resistance, creep characteristics, mechanical strength, chemical resistance, and abrasion resistance. During the crosslinking reaction, crosslinks (bridges) are predominantly formed. Crosslinking can be done by using, for example, a free radical generating compound, which is typically included in the material layer prior to extrusion of the layer(s) onto the conductor. After the cable layers are formed, the cable is subjected to a crosslinking step to initiate the formation of radicals and thus the crosslinking reaction.

Peroxides are widely used as compounds providing the formation of free radicals. The resulting peroxide degradation products may include volatile by-products, which are generally undesirable because, for example, they can have a negative effect on the electrical properties of the cable. Therefore, the formation of volatile decomposition products such as methane is usually minimized or removed after the crosslinking and cooling steps. Such a removal step, commonly known as a degassing step, is time consuming and energy intensive, resulting in additional costs. It should be borne in mind that the crosslinked polyethylene material is thermosetting.

LDPE is also an ideal cable material in terms of cleanliness. LDPE can be obtained in a very pure form without impurities. On the contrary, low pressure polymers usually contain more gel and catalyst residues, which can lead to cable defects.

To increase the capacity of extruded high voltage direct current (HVDC) cables, the voltage needs to be increased. In HVDC cables, the insulation is heated by the leakage current. Heating is proportional to insulation conductivity x voltage ² . Thus, if the voltage increases, more heat is generated. This can lead to thermal breakdown followed by electrical breakdown. Thus, to increase the transmission capacity, an insulating material with very low electrical conductivity is required. In one embodiment, the voltage can be increased from the highest currently used voltage of 320 to 640 kV or more.

The authors of the present invention investigated the possibility of reducing the conductivity using a combination of LDPE with a secondary polymer. At the same time, the secondary polymer is usually a polymer obtained using an olefin polymerization catalyst, and therefore the content of catalyst residues may be high. This results in a greater risk of mechanical failure compared to cross-linked polyethylene. However, the present inventors have surprisingly found that the combination of small amounts of LDPE or LLDPE and LDPE made using a single site catalyst results in a marked decrease in conductivity in thermoplastic and crosslinked insulation layers even at very low polymer levels.

Thermoplastic LDPE has a number of advantages as cable insulation compared to thermoset cross-linked PE. Because the polymer is non-crosslinked, there is no possibility of peroxide-initiated scorch. In addition, no degassing step is required to remove peroxide decomposition products. Eliminating the crosslinking and degassing steps can lead to a faster, less complicated and more economical way to make a cable. However, the absence of a crosslinked material may lead to a decrease in heat resistance and, therefore,

- 1 040293 significant creep problems. Thus, in order to provide a polymeric material that can be used without crosslinking in the cable insulation layer, better thermomechanical properties are needed.

The present inventors have found that the combination of LDPE with a small amount of single site catalyzed LLDPE, single site PESP catalyst or UHMWPE material can provide a blend, such as a thermoplastic blend, that is ideal for cable production. Surprisingly, these mixtures have a much lower conductivity compared to the corresponding individual LDPE and are characterized by the absence of dielectric breakdown.

The use of LDPE in the present invention is not in itself new and has been previously proposed in the literature. In addition, the possibility of using non-crosslinked LDPE in the cable insulation layer is not new. WO2011/113685 proposes an LDPE with a density of 922 kg/m ³ and an MFR _{2 of} 1.90 g/10 min for use in cable insulation. WO 2011/113685 also proposes the use of other individual polymers in a non-crosslinked cable insulation layer.

In WO 2011/113686, a mixture of LDPE and HDPE is used to make a crosslinked polymer composition that can be used in a cable insulation layer.

The present inventors have found that certain LDPEs can be combined with small amounts of LLDPE, PESP, or UHMWPE to form a blend that has excellent electrical properties. In particular, the present inventors have found that the mixtures of the present invention have extremely low conductivity in both uncrosslinked and crosslinked forms.

Thus, these mixtures are ideally suited for use in the insulating layer of direct current (DC) power cable, and such mixtures allow the use of cables at higher voltages than currently possible.

Brief description of the invention

Thus, in one aspect of the present invention, there is provided a cable comprising one or more conductors surrounded by at least an inner semi-conductive layer, an insulating layer, and an outer semi-conductive layer, in that order, wherein said insulating layer contains at least 90 wt. compositions, and the specified polymer composition contains (I) from 80.0 to 99.9 wt.% homopolymer or copolymer of LDPE; and (II) from 0.1 to 20.0 wt.%:

(i) an ultra-high molecular weight polyethylene having a Mw of at least 1,000,000; or (ii) medium density polyethylene (MDPE) produced using a single site catalyst and having a density of 925 to 940 kg/m ³ or linear low density polyethylene (LLDPE) obtained using a single site catalyst and having a density of 910 to 925 kg / m ³ ;

and where the polymer composition of the insulating layer has a conductivity of 20.0 fS/m or less, determined by method C at an average electric field strength of 80 kV/mm and 70°C.

In all embodiments according to the present invention, it is preferred that the polymer composition of the insulating layer has a conductivity of 10 fS/m or less, preferably 5.0 fS/m or less, more preferably 2.0 fS/m or less, when measured in accordance with the method DC conductance measurements as described in section Method A.

In all embodiments according to the present invention, it is preferable that the insulating layer has a conductivity of 10 fS/m or less, preferably 5.0 fS/m or less, when measured in accordance with the DC conductivity measurement method as described in Determination Method A.

In all embodiments, it is preferred that the conductivity of the resin composition of the insulating layer be 1.0 x 10' ¹⁴ S/cm or less when measured in accordance with the dc conductivity measurement method as described in Methods of Determination B.

In another aspect of the present invention, a cable is provided comprising one or more conductors surrounded by at least an inner semi-conductive layer, an uncrosslinked insulating layer, and an outer semi-conductive layer, in that order, wherein said insulating layer contains at least 90 wt. compositions, and the specified polymer composition contains (I) from 80.0 to 99.9 wt.% homopolymer or copolymer of LDPE, preferably having a density of from 927 to 940 kg/m ³ ; and (II) from 0.1 to 20.0 wt.% ultra-high molecular weight polyethylene having a Mw of at least 1,000,000.

In this embodiment, it is preferable that the conductivity of the resin composition of the insulating layer is 1.0 x 10' ¹⁴ S/cm or less, for example, 1.0 x 10' ¹⁶ S/cm or less when measured according to the DC conductivity measurement method. , as described in the section Methods for determining B.

Preferably, the insulating layer in said embodiment is non-crosslinked, and hence the conductivity measurement is carried out on the non-crosslinked insulating layer.

In another aspect of the present invention, there is provided a cable comprising one or more conductors surrounded by at least an inner semiconductive layer, a crosslinked insulating layer, and an outer semiconductive layer, in that order, wherein said insulating layer comprises at least 90% by weight of a polymer composition, wherein the specified polymer composition contains (I) from 80.0 to 99.9 wt.% homopolymer or copolymer of LDPE; and (II) from 0.1 to 20.0 wt.% of medium density polyethylene (MDPE) obtained using a single-site catalyst and having a density of from 925 to 940 kg/m ³ or linear low density polyethylene (LLDPE) obtained with using a single-center catalyst and having a density of 910 to 925 kg/m ³ .

In another aspect of the present invention, a cable is provided comprising one or more conductors surrounded by at least an inner semi-conductive layer, a non-crosslinked insulating layer, and an outer semi-conductive layer, in that order, wherein said insulating layer contains at least 90% by weight of a polymer composition, moreover, the specified polymer composition contains (I) from 80.0 to 99.9 wt.% homopolymer or copolymer of LDPE; and (II) from 0.1 to 20.0 wt.% linear low density polyethylene (LLDPE), obtained using a single-site catalyst and having a density of from 910 to 925 kg/m ³ .

In another aspect of the present invention, there is provided a cable comprising one or more conductors surrounded by at least an inner semiconductive layer, a crosslinked insulating layer, and an outer semiconductive layer, in that order, wherein said insulating layer comprises at least 90% by weight of a polymer composition, wherein the specified polymer composition contains (I) from 80.0 to 99.9 wt.% homopolymer or copolymer of LDPE; and (II) from 0.1 to 20.0 wt.% medium density polyethylene (MDPE), obtained using a single-site catalyst and having a density of from 925 to 940 kg/m ³ .

Preferably, the cross-linked or non-cross-linked polymer composition of the insulating layer in said embodiment has a conductivity of less than 5.0 fS/m, preferably less than 2.0 fS/m, when measured in accordance with the dc conductivity measurement method as described in Methods for Determination A .

Preferably, the cross-linked or non-cross-linked polymer composition of the insulating layer in this embodiment has a conductivity of 20 fS/m or less, such as 10 fS/m or less, when measured in accordance with the method for measuring DC conductivity as described in Methods for Determining C .

Preferably, the crosslinked or non-crosslinked polymer composition of the insulating layer in this embodiment has a conductivity of 10 fS/m or less, such as 5.0 fS/m or less, when measured in accordance with the DC conductivity measurement method as described in the Methods section. definitions D.

In particular, the cable according to the present invention is a direct current (DC) power cable, preferably operating or capable of operating at 320 kV or more, such as 650 kV or more.

In another aspect of the present invention, a method for manufacturing a cable is provided, comprising the steps of applying one or more conductors, preferably by (co)extrusion, an inner semi-conductive layer, an insulating layer, and an outer semi-conductive layer, in that order, wherein the insulating layer comprises a polymer composition as previously defined. herein, and optionally crosslinking the insulating layer.

Definitions

As used herein, the term molecular weight Mw refers to the weight average molecular weight. Used in this document, the term molecular weight Mv denotes the nominal viscous molecular weight.

Uncrosslinked polymer compositions or cable layers are considered thermoplastic.

In this document, the polymer composition according to the present invention may also be referred to as a polymer mixture. These terms are used interchangeably.

The low density polyethylene, LDPE, of the present invention is a polyethylene produced by a high pressure process. Typically, the polymerization of ethylene and optional additional comonomer(s) in a high pressure process is carried out in the presence of an initiator(s). The meaning of the term LDPE is well known and presented in the literature. The term LDPE describes and distinguishes high pressure polyethylene from polyethylenes prepared in the presence of an olefin polymerization catalyst. LDPEs have certain typical distinguishing features, such as a different branched structure.

The term SSC denotes a product obtained using a single site catalyst.

Detailed description of the invention

The present invention requires the use of a certain polymer composition containing low density polyethylene (LDPE) and small amounts of ultra-high molecular weight polyethylene (UHMWPE) or LLDPE/LDPE single site catalyst in the insulating layer of a cable, especially a power cable such as a DC power cable (DC). Surprisingly, the combination of small amounts of UHMWPE or SSC LDPE/LLDPE with LDPE makes it possible to obtain an insulating layer that has a reduced, i. low electrical conductivity. The terms reduced or low electrical conductivity, used interchangeably herein, mean that the value obtained from a DC conductivity measurement, as defined below in the Determination Method section, is low, i. lowered. The low electrical conductivity is beneficial in minimizing unwanted heat generation in the cable insulation layer.

Additionally, and unexpectedly, some of the polymer compositions of the present invention, and hence the cable insulation layer of the present invention, have low electrical conductivity without the need for crosslinking. In addition, the non-crosslinked insulation still has the mechanical properties required for an insulating layer of a cable, preferably a DC power cable, such as low flexural modulus, good tensile modulus and good crack stress.

LDPE

The low density polyethylene, LDPE, of the present invention is a polyethylene produced by a high pressure process. Typically, the polymerization of ethylene and optional additional comonomer(s) in a high pressure process is carried out in the presence of an initiator(s). The meaning of the term LDPE is well known and presented in the literature. The term LDPE describes and distinguishes high pressure polyethylene from polyethylenes produced in the presence of an olefin polymerization catalyst. LDPEs have certain typical distinguishing features, such as a different branched structure.

The LDPE used in the composition according to the present invention may have a density from 915 to 940 kg/m ³ , preferably from 918 to 935 kg/m ³ , especially from 920 to 932 kg/m ³ , for example, from about 922 to 930 kg/ m ³ .

The LDPE polymer of the present invention may be a polymer having a high density. The density of the LDPE polymer is preferably 927 to 940 kg/m ³ , preferably 928 to 935 kg/m ³ , especially 929 to 932 kg/m ³ , for example about 930 kg/m ³ . In particular, when the polymer composition according to the present invention contains UHMWPE, the use of high density LDPE is preferred, i.e. LDPE with a density of 927 to 940 kg/m ³ .

The MFR ₂ (2.16 kg, 190° C.) of the LDPE polymer is preferably 0.05 to 30.0 g/10 min, more preferably 0.1 to 20 g/10 min, and most preferably 0.1 to 10 g/10 min, especially 0.1 to 5.0 g/10 min. In a preferred embodiment, the MFR ₂ LDPE is 0.1 to 4.0 g/10 min, especially 0.5 to 4.0 g/10 min, especially 1.0 to 3.0 g/10 min.

If the LDPE is a high density LDPE, it is preferred that the MFR ₂ be 0.1 to 2.0 g/10 min, especially 0.1 to 1.0 g/10 min.

The LDPE may have a tensile modulus (1 mm/min ISO527-2) of at least 300 MPa, eg at least 325 MPa. Values up to 600 MPa are possible.

The LDPE may have a flexural modulus (ISO 178) of at least 300 MPa, for example at least 320 MPa. Values up to 600 MPa are possible.

A mixture of several LDPEs can be used in the polymer composition according to the present invention, however, it is preferable to use a single LDPE.

The LDPE can be a low density ethylene homopolymer (referred to herein as an LDPE homopolymer) or a copolymer of low density ethylene with one or more comonomers (referred to herein as an LDPE copolymer). The one or more comonomers of the LDPE copolymer are preferably selected from polar comonomer(s), non-polar comonomer(s), or a mixture of polar comonomer(s) and non-polar comonomer(s). Furthermore, said LDPE homopolymer or LDPE copolymer may optionally be unsaturated.

As a polar comonomer for the LDPE copolymer, comonomer(s) containing(s) hydroxyl(s) group(s), alkoxy group(s), carbonyl(s) group(s), carboxyl(s) group(s), simple(s) ether(s) group(s), ester(s) group(s) or a mixture thereof. More preferably, comonomer(s) containing carboxyl(s) and/or ester(s) group(s) are used as said polar comonomer. More preferably, the polar comonomer(s) of the LDPE copolymer are selected from the group of acrylate(s), methacrylate(s), acetate(s), or any mixtures thereof.

When present in said LDPE copolymer, the polar comonomer(s) are preferably selected from the group of alkyl acrylates, alkyl methacrylates or vinyl acetate, or mixtures thereof. More preferably, said polar comonomers are selected from C ₁ -C ₆ alkyl acrylates, C ₁ -C ₆ alkyl methacrylates or vinyl acetate. More preferably, said LDPE copolymer is a copolymer of ethylene with a CrCl alkyl acrylate such as methyl, ethyl, propyl or butyl acrylate, or vinyl acetate, or any mixture thereof.

As non-polar(s) comonomer(s) for the LDPE copolymer, comonomer(s) other than the above polar comonomers can be used. Preferably non-polar comonomers are other than comonomer(s) containing(s) hydroxyl(s) group(s), alkoxy(s), carbonyl(s) group(s), carboxyl(s) group(s), simple(s) ether(s) group(s) or ester(s) group(s). One group of preferred non-polar comonomers comprises, preferably consists of monounsaturated(s) (= one double bond) comonomer(s), preferably olefins, preferably alpha olefins, more preferably C ₃ -C ₁₀ alpha olefins such as propylene, 1- butene, 1-hexene, 4-methyl-1-pentene, styrene, 1-octene, 1-nonene; polyunsaturated(s) (=more than one double bond) comonomer(s); comonomer(s) containing(their) silane group; or any mixtures thereof. The polyunsaturated(e) comonomer(s) are described(s) below in relation to unsaturated LDPE copolymers.

If the LDPE polymer is a copolymer, it preferably contains from 0.001 to 35% by weight, more preferably less than 30% by weight, more preferably less than 25% by weight of one or more comonomer(s). Preferred ranges include a range of 0.5 to 10% by weight, such as 0.5 to 5% by weight, of comonomer.

The LDPE polymer may optionally be unsaturated, i. may contain carbon-carbon double bonds (-C=C-). Preferred unsaturated LDPEs contain carbon-carbon double bonds/1000 carbon atoms in a total amount of at least 0.4/1000 carbon atoms. If a non-crosslinked LDPE is used in the final cable, then the LDPE is usually not unsaturated as defined above. By non-unsaturated is meant that the C=C content is preferably less than 0.2/1000 carbon atoms, for example 0.1/1000 carbon atoms or less.

As is well known, unsaturation of the LDPE polymer can be provided by comonomers, low molecular weight (Mw) additives such as crosslinking enhancer, CTA or scorch retarding additive, or any combination thereof. The total number of double bonds refers herein to double bonds introduced by any means. If two or more of the above sources of double bonds are selected to provide unsaturation, then the total number of double bonds in the LDPE polymer is the sum of the double bonds present. Any double bond measurements are made prior to optional crosslinking.

The term total carbon-carbon double bonds refers to the combined number of double bonds that are derived from vinyl groups, vinylidene groups, and transvinylene groups, if present.

If the LDPE homopolymer is unsaturated, then unsaturation can be provided, for example, by a chain transfer agent (CTA) such as propylene and/or by polymerization conditions. If the LDPE copolymer is unsaturated, then unsaturation can be provided by one or more of the following methods: using a chain transfer agent (CTA), using one or more polyunsaturated comonomers, or using polymerization conditions. It is well known that selected polymerization conditions, such as maximum temperatures and pressures, can affect the degree of unsaturation. In the case of an unsaturated LDPE copolymer, it is preferably an unsaturated ethylene LDPE copolymer with at least one polyunsaturated comonomer and optionally other(s) comonomer(s), such as polar(s) comonomer(s) which(s) preferably selected from acrylate(s) or acetate(s) comonomer(s). More preferably, the unsaturated LDPE copolymer is an unsaturated ethylene LDPE copolymer with at least polyunsaturated comonomer(s).

The polyunsaturated comonomers suitable for the unsaturated second polyolefin (b) preferably consist of a straight carbon chain with at least 8 carbon atoms and at least 4 carbon atoms between non-conjugated double bonds, of which at least one is terminal, more preferably said the polyunsaturated comonomer is a diene, preferably a diene, which contains at least eight carbon atoms, wherein the first carbon-carbon double bond is terminal and the second carbon-carbon double bond is unconjugated to the first. Preferred dienes are selected from C ₈ -C ₁₄ non-conjugated dienes or mixtures thereof, more preferably selected from 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13tetradecadiene, 7-methyl-1,6-octadiene , 9-methyl-1,8-decadiene or mixtures thereof. More preferably, the diene is selected from 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, or any mixture thereof, however, it is not limited to the above dienes.

It is well known that, for example, propylene can be used as a comonomer, or as a chain transfer agent (CTA), or both, whereby it can contribute to the total number of carbon-carbon double bonds, preferably to the total number of vinyl groups. Herein, when a compound that can act as a comonomer, such as propylene, is used as a CTA to produce double bonds, said copolymerizable comonomer is not included in the comonomer content.

If the LDPE polymer is unsaturated, it preferably has a total number of carbon-carbon double bonds, which are derived from vinyl groups, vinylidene groups and transvinylene groups, if present, greater than 0.4/1000 carbon atoms, preferably greater than 0.5/1000 carbon atoms. The upper limit of the number of carbon-carbon double bonds present in the polyolefin is not limited and may preferably be less than 5.0/1000 carbon atoms, preferably less than 3.0/1000 carbon atoms.

In some embodiments, for example, in which a higher degree of crosslinking at a low peroxide content is desirable, the total carbon-carbon double bonds that are derived from vinyl groups, vinylidene groups, and trans-vinylene groups, if present, in the unsaturated LDPE is preferably is more than 0.40/1000 carbon atoms, preferably more than 0.50/1000 carbon atoms, preferably more than 0.60/1000 carbon atoms.

If the LDPE is an unsaturated LDPE as defined above, it preferably contains at least vinyl groups, and the total vinyl groups are preferably greater than 0.05/1000 carbon atoms, more preferably greater than 0.08/1000 carbon atoms, and most preferably greater than 0.11/1000 carbon atoms. Preferably the total number of vinyl groups is less than 4.0/1000 carbon atoms. More preferably, the second polyolefin (b) before crosslinking contains vinyl groups in a total amount of more than 0.20/1000 carbon atoms, more preferably more than 0.30/1000 carbon atoms.

However, it is preferred if the LDPE according to the present invention is not unsaturated and contains less than 0.2 C=C/1000 carbon atoms, preferably less than 0.1 C=C/1000 carbon atoms.

Preferably, the LDPE is a homopolymer. If the insulating layer is not cross-linked, it is particularly preferred if the LDPE is a homopolymer. If the insulating layer is crosslinked, then the LDPE may be an LDPE copolymer.

The LDPE polymer can have a high melting point, which can be important, especially for thermoplastic insulation material. Melting points of 112°C or more are contemplated, eg 114°C or more, especially 116°C or more, eg 112 to 125°C. LDPE with such high melting points can be used in combination with UHMWPE in particular.

The LDPE polymer is produced at high pressure by free radical initiated polymerization (referred to as high pressure (HP) radical polymerization). The high pressure reactor can be, for example, the well-known tubular or autoclave reactor or a mixture thereof, preferably a tubular reactor. High pressure polymerization (HP) and control of process conditions to provide other properties of the polyolefin depending on the desired end use are well known and described in the literature and can be easily used by a person skilled in the art. Suitable polymerization temperature is up to 400°C, preferably 80 to 350°C, and pressure is 70 MPa, preferably 100 to 400 MPa, more preferably 100 to 350 MPa. The pressure can be measured at least after the compression stage and/or after the tubular reactor. The temperature can be measured at several points in all stages.

After separation, the resulting LDPE is usually in the form of a polymer melt, which is usually mixed and pelletized in a pelletizing section, such as a pelletizing extruder, connected to a high pressure reactor system. Optionally, additive(s) such as antioxidant(s) may be added to said mixer in a known manner.

Further details of the process for preparing ethylene (co)polymers by high pressure radical polymerization can be found in particular in Encyclopedia of Polymer Science and Engineering, Vol. 6 (1986), pp 383-410 and Encyclopedia of Materials: Science and Technology, 2001 Elsevier Science Ltd.: Polyethylene: High-pressure, R. Klimesch, D. Littmann and F.-O. Mahling pp. 7181-7184.

As is known, in the preparation of an unsaturated ethylene LDPE copolymer, the amount of carbon-carbon double bonds can be controlled by polymerization of ethylene, for example in the presence of one or more polyunsaturated comonomers, chain transfer agents, or both, using a target ratio between the monomer, preferably ethylene, and the polyunsaturated comonomer and/or chain transfer agent depending on the nature and amount of C-C double bonds desired for the unsaturated LDPE copolymer. In particular, document WO 9308222 describes the radical polymerization of ethylene with polyunsaturated monomers at high pressure. As a result, unsaturation can be evenly distributed along the polymer chain in accordance with the statistical

- 6 040293 the nature of the copolymerization.

The polymer composition according to the present invention preferably contains from 81.0 to

99.5 wt.%, for example, from 82.0 to 99.0 wt.%, LDPE. Preferably the composition contains from 84.0 to

99.0 wt.%, for example, from 85.0 to 98.0 wt.%, LDPE, more preferably from 85.0 to 98.0 wt.%

LDPE.

UHMWPE

The composition according to the present invention may contain a UHMWPE component. Said component may be an ethylene copolymer or an ethylene homopolymer. Preferably, UHMWPE is a homopolymer.

It is generally observed that an increase in molecular weight is important to provide better dimensional stability (ie creep resistance). The exceptional dimensional stability due to the higher molecular weight may be due to the increased likelihood of cross chain formation and the high melt viscosity of UHMWPE.

SVM copolymer component

The composition according to the present invention may contain component (II), which is a CBM polyethylene copolymer component. The use of UHMWPE copolymer can be advantageous because it forms cross chains between crystals and thus improves creep characteristics. It may be present in an amount from 0.5 to 19.0 wt.%, for example, from 1.0 to 18.0 wt.%, for example, from 1.0 to 16.0 wt.%, preferably from 2.0 up to 15.0 wt.%. In particular, if UHMWPE is present, its amount can be from 4.0 to 15.0 wt.%, preferably from 4.0 to 12.0 wt.% of the mixture, especially from 4.0 to 11.0 wt.%. The amounts of LDPE present can be up to 100% complementary.

The comonomer present in said component is at least one C _3-20 olefin. Preferred comonomers are alpha-olefins, especially those with 3-8 carbon atoms. Preferably the comonomer is selected from the group consisting of propene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1,7-octadiene and 7-methyl-1,6-octadiene. Most preferred is the use of 1-hexene or 1-butene. Ideally, only one comonomer is present. Especially preferred is the use of hexene.

The comonomer content is preferably 0.5 to 3 mol%. The amount of comonomer is usually adapted to achieve the intrinsic viscosity required in the present invention.

The CBM polyethylene copolymer component of the blends of the present invention preferably has a nominal viscosity molecular weight (Mv) of at least 1,000,000 g/mol, preferably at least 1,500,000 g/mol, more preferably at least 2,000,000 g/mol. In all embodiments, it is preferred that the CBM polyethylene has an Mv of less than 10,000,000 g/mol, more preferably less than 9,000,000 g/mol.

The CBM polyethylene copolymer component of the blends of the present invention preferably has a weight average molecular weight (Mw) of at least 1,000,000 g/mol, preferably at least 1,500,000 g/mol, more preferably at least 2,000,000 g/mol. In all embodiments, it is preferred that the CBM polyethylene has a Mw of less than 12,000,000 g/mol, more preferably less than 10,000,000 g/mol. A particularly preferred range is from 3000000 to 10000000, for example from 4000000 to 9000000 g/mol.

The UHMWPE copolymer may have a reduced viscosity of 1500 to 4500 (ISO 1628-3), preferably 2000 to 4000.

The UHMWPE copolymer component preferably has an intrinsic viscosity of at least 7 dl/g, preferably at least 9 dl/g, such as at least 12 dl/g, even at least 14 dl/g. The intrinsic viscosity of the UHMWPE copolymer component should preferably be at most 30 dl/g, more preferably at most 28 dl/g. It should be understood that intrinsic viscosity is a measure of molecular weight in the art.

The UHMWPE copolymer component is also preferably unimodal. This means that it has one peak in the GPC chromatogram. Ideally, it is formed by one component, and, therefore, it is obtained using one production step.

The density of the UHMWPE copolymer component may range from 900 to 930 kg/m ³ , preferably from 905 to 925 kg/m ³ .

Said component has a very low MFR, for example MFR21 less than 0.5 g/10 min, especially MFR21 less than 0.1 g/10 min, especially less than 0.05 g/10 min.

The CBM copolymer component can be obtained by catalysis using a Ziegler-Natta catalyst, for example using vanadium tetrachloride. The CBM copolymer is usually produced in the gas phase in the absence of hydrogen to provide a high Mw. In the case of gas phase reactors, the reaction temperature used is typically in the range of 60 to 115°C, for example 70 to 110°C, the pressure in the reactor is typically in the range of 10 to 25 bar, and the residence time in the reactor is typically ranges from 1 to 8 hours. UHMWPE copolymers are commercially available polymers.

SVM homopolymer component

Alternatively, the composition according to the present invention may contain a CBM polyethylene homopolymer component. Said component may be present in an amount of from 0.5 to 19.0 wt.%, for example from 1.0 to 18.0 wt.%, for example from 1.0 to 16.0 wt.%, preferably from 2.0 to 15.0 wt%. In particular, if UHMWPE is present, its amount can be from 4.0 to 15.0 wt.%, preferably from 4.0 to 12.0 wt.% of the mixture, especially from 4.0 to 11.0 wt.%. The amounts of LDPE present can be up to 100% complementary.

The CBM polyethylene homopolymer has a nominal viscosity molecular weight (Mv) of at least 1,000,000 g/mol, preferably at least 1,500,000 g/mol, more preferably at least 2,000,000 g/mol. In all embodiments, it is preferred that the CBM polyethylene has an Mv of less than 8,000,000 g/mol, more preferably less than 7,000,000 g/mol.

The CBM polyethylene homopolymer component of the blends of the present invention preferably has a nominal viscosity molecular weight (Mv) of at least 1,000,000 g/mol, preferably at least 1,500,000 g/mol, more preferably at least 2,000,000 g/mol. In all embodiments, it is preferred that the CBM polyethylene homopolymer has an Mv of less than 10,000,000 g/mol, more preferably less than 9,000,000 g/mol.

The CBM polyethylene homopolymer component of the blends of the present invention preferably has a weight average molecular weight (Mw) of at least 1,000,000 g/mol, preferably at least 1,500,000 g/mol, more preferably at least 2,000,000 g/mol. In all embodiments, it is preferred that the CBM polyethylene homopolymer has a Mw of less than 12,000,000 g/mol, more preferably less than 10,000,000 g/mol. A particularly preferred range is from 3000000 to 10000000, for example from 4000000 to 9000000 g/mol.

The UHMWPE homopolymer may have a reduced viscosity of 1500 to 4500 (ISO 1628-3), preferably 2000 to 4000.

The UHMWPE homopolymer component preferably has an intrinsic viscosity of at least 7 dl/g, preferably at least 9 dl/g, eg at least 12 dl/g, even at least 14 dl/g. The intrinsic viscosity of the UHMWPE homopolymer component should preferably be at most 30 dl/g, more preferably at most 28 dl/g. It should be understood that intrinsic viscosity is a measure of molecular weight in the art.

The CBM polyethylene homopolymer component is preferably unimodal. This means that it has one peak in the GPC chromatogram. Ideally, it is formed by one component, and, therefore, it is obtained using one production step.

The CBM density of the homopolymer component may range from 920 to 960 kg/m ³ , preferably from 930 to 950 kg/m ³ .

Said component has a very low MFR, for example MFR21 less than 0.5 g/10 min, especially MFR21 less than 0.1 g/10 min, especially less than 0.05 g/10 min.

The UHMWPE homopolymer component can be obtained by catalysis using a Ziegler-Natta catalyst, for example using vanadium tetrachloride. The CBM homopolymer is usually produced in the gas phase in the absence of hydrogen to provide a high Mw. In the case of gas phase reactors, the reaction temperature used is typically in the range 60 to 115°C, for example 70 to 110°C, the reactor pressure is typically in the range 10 to 25 bar, and the residence time in the reactor is typically 1 to 8 ocloc'k. Said homopolymers are commercially available polymers, for example in DSM.

UHMWPE can be combined with LDPE for use in crosslinked or non-crosslinked insulation layers, preferably non-crosslinked. In any embodiment, it is preferred that the conductivity of the polymer composition of the insulating layer be 1.0 x 10 ^-14 S/cm or less when measured in accordance with the DC conductivity measurement method as described in Methods for Determination B. More preferably, the conductivity of the polymer composition of the insulating layer is 9.0 x 10 ^-15 S/cm or less when measured according to the DC conductivity measurement method as described in Determination Methods B, for example, 5.0 x 10 ^-15 S/cm or less .

LLDPE or PESP

In another embodiment, the implementation of the LDPE according to the present invention is combined with LLDPE or PESP obtained using a single site catalyst. In addition, it is preferred that the LDPE/LLDPE/PESP blend does not contain an acid scavenger. In this embodiment, it is preferred that the insulating layer is crosslinked, especially if the polymer is PESP.

Said PESP or LLDPE may be present in an amount of from 0.5 to 19.0 wt.%, for example, from 1.0 to 18.0 wt.%, for example, from 1.0 to 16.0 wt.%, preferably from 2.0 to 15.0 wt.%. In the case of using PESP, the preferred amounts are from 4.0 to 15.0 wt.%, preferably from

4.0 to 12.0% by weight of the mixture, especially 5.0 to 10.0% by weight. In the case of LLDPE, the preferred amounts are from 1.5 to 6 wt.%, especially from 2.0 to 5.0 wt.%. The amount of LDPE can be adjusted until a total of 100% is obtained.

The LLDPE according to the present invention have a density of 910 to 925 kg/m ³ . Ideally, the polymer has a density of at least 912 kg/m ³ . A preferred density range may be 912-922 kg/m ³ , especially 915 to 921 kg/m ³ . This density is achievable by polymerization of ethylene polymer catalyzed by a single site catalyst and has several advantages.

PESP according to the present invention have a density of 925 to 940 kg/m ³ . Ideally, the polymer has a density of at least 928 kg/m ³ . A preferred density range may be 928-938 kg/m ³ , especially 930 to 937 kg/m ³ . This density is achievable by polymerization of ethylene polymer catalyzed by a single site catalyst and has several advantages.

The PESP or LLDPE polymer of the present invention preferably has an MFR21 of 5-50 g/10 min, more preferably 10 to 40 g/10 min, especially 20 to 35 g/10 min. MFR ₂ values may vary from 0.1 to 10.0 g/10 min, for example from 0.5 to 5 g/10 min. Ideally, the MFR ₂ value is in the range of 0.5 to 3 g/10 min.

The SSC ethylene polymers of the present invention preferably have a molecular weight, Mw, of at least 80,000, preferably at least 100,000. A very high Mw is undesirable. Mw should be no more than 250000, for example no more than 200000.

Mw/Mn depends on the modality, but can vary from 2 to 12, for example, from 2 to 10, for example, from 2 to 5.

The LLDPE or PESP of the present invention may be unimodal or multimodal. Unless otherwise indicated, as used herein, the term multimodal refers to multimodality in terms of molecular weight distribution and therefore includes a bimodal polymer. Usually multimodal refers to a polyethylene composition containing at least two polyethylene fractions, which are obtained under different polymerization conditions, leading to different (weight average) molecular weights and molecular weight distributions of the fractions. The prefix multi refers to a number of different polymer fractions present in a polymer. Thus, for example, a multimodal polymer comprises a so-called bimodal polymer consisting of two fractions. The shape of the molecular weight distribution curve, i.e. As a plot of the mass fraction of a polymer versus its molecular weight, a multimodal polymer exhibits two or more maxima or usually expands markedly compared to the curves for individual fractions. For example, if a polymer is produced in a sequential multi-stage process using reactors connected in series and using different conditions in each of the reactors, each of the polymer fractions produced in the different reactors will have its own molecular weight distribution and weight average molecular weight. When recording the molecular weight distribution curve of such a polymer, the individual curves corresponding to the fractions usually together form an extended molecular weight distribution curve for the entire resulting polymer product.

Unless otherwise noted, a unimodal polymer is unimodal in terms of molecular weight distribution and therefore contains a single peak in its GPC curve.

PESP/LLDPE is a copolymer and can therefore be made from ethylene with at least one other comonomer, for example a C ₃ _ ₂₀ olefin. Preferred comonomers are alpha-olefins, especially those with 3-8 carbon atoms. Preferably the comonomer is selected from the group consisting of propene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1,7-octadiene and 7-methyl-1,6-octadiene. Most preferred is the use of 1-hexene or 1-butene.

The polymer may contain one monomer, two monomers or more than 2 monomers. The use of a single comonomer is preferred. In case two comonomers are used, it is preferred that one comonomer is a C ₃ _ ₈ alpha-olefin and the other comonomer is a diene as defined above.

The amount of comonomer is preferably such that it is 0-3 mol%, more preferably 0.5-3.0 mol% LLDPE/PESP. Values less than 1.0 mol% are also contemplated, for example from 0.1 to 1.0 mol%. They can be determined by NMR.

The LLDPE or PESP polymer according to the present invention is obtained by polymerization catalyzed by a single site catalyst. The use of a polyethylene polymer prepared using a single site catalyst provides better conductivity compared to, for example, a Ziegler-Natta catalyst. In addition, the use of a polymer produced using a single site catalyst allows the use of a lower amount of crosslinking agent to achieve the desired degree of crosslinking compared to, for example, a Ziegler-Natta catalyst. More importantly, SSC PE is a purer polymer, which means the cable is characterized

- 9 040293 fewer impurities and less chance of defects. LLDPE or PESP, as defined above, can be made using any conventional single site catalyst, including metallocenes and non-metallocenes well known in the art.

Preferably, said catalyst is a metal-containing catalyst coordinated by one or more η-bonding ligands. Such η-bonded metals are typically Group 3-10 transition metals, such as Zr, Hf or Ti, especially Zr or Hf. The η binding ligand is typically an n ⁵ -cyclic ligand, i.e. a homo- or heterocyclic cyclopentadienyl group, optionally with fused or pendant substituents. Such single site, preferably metallocene, procatalysts have been widely described in the scientific and patent literature over the past twenty years. As used herein, procatalyst refers to the specified transition metal complex. The metallocene procatalyst may have the formula II:

(Cp)mRnMXq (II) where each Cp is independently an unsubstituted or substituted and/or fused homo- or heterocyclopentadienyl ligand, for example a substituted or unsubstituted cyclopentadienyl, substituted or unsubstituted indenyl, or a substituted or unsubstituted fluorenyl ligand;

one or more optional substituents are independently selected, preferably from halo, hydrocarbon substituent (e.g., C1- _C20 alkyl, _C2-C20 alkenyl, _C2 - _C20 alkynyl, _C3 - _C12 cycloalkyl, C6- _C20 -aryl or C ₇ -C ₂₀ -arylalkyl), C ₃ -C ₁₂ -cycloalkyl, which contains 1, 2, 3 or 4 heteroatoms in the ring fragment, C6-C ₂₀ -heteroaryl, C1-C ₂₀ -haloalkyl, -SiR ₃ , -OSiR ₃ , -SR, -PR ₂ or -NR2, each R independently represents hydrogen or a hydrocarbon substituent, for example, C1-C ₂₀ -alkyl, C ₂ -C ₂₀ -alkenyl, C ₂ -C ₂₀ -quinil , C ₃ -C ₁₂ -cycloalkyl or C6 -C ₂₀ -aryl; or, for example, in the case of -NR''2, the two substituents R may form a ring, for example a five- or six-membered ring, together with the nitrogen atom to which they are attached;

R is a bridge of 1-7 atoms, e.g. a bridge of 1-4 carbon atoms and 0-4 heteroatoms, where the heteroatom(s) may be, for example, atom(s) of Si, Ge and/or O where each of the bridging atoms may independently have substituents such as C _1-20 alkyl, tri(C _1-20 alkyl)silyl, tri(C _1-20 alkyl)siloxy or C _6-20 aryl substituents ; or a bridge of 1-3, for example one or two, heteroatoms such as silicon, germanium and/or oxygen atom(s), for example -SiR1 ₂ -, where each R ¹ is independently C _1-20 -alkyl, C _6-20 aryl or tri(C _1-20 alkyl)silyl residue such as trimethylsilyl;

M is a transition metal of 3-10 groups, preferably 4-6 groups, for example 4 groups, for example Ti, Zr or Hf, especially Hf;

each X is independently a sigma ligand such as H, halogen, C _1-20 alkyl, C _1-20 alkoxy, C ₂ -C ₂₀ alkenyl, C ₂ -C ₂₀ alkynyl, C ₃ -C ₁₂ - cycloalkyl, C ₆ -C ₂₀ -aryl, C ₆ -C ₂₀ -aryloxy, C ₇ -C ₂₀ arylalkyl, C ₇ -C ₂₀ -arylalkenyl, -SR, -PR ₃ , -SiR ₃ , -OSiR ₃ , -NR ₂ or -CH2-Y, where Y is C ₆ -C ₂₀ -aryl, C ₆ -C ₂₀ -heteroaryl, C1 -C ₂₀ -alkoxy, C ₆ -C ₂₀ -aryloxy, NR ₂ , -SR, -PR'S , -SiR ₃ or -OSiR ₃ ;

each of the above ring moieties, individually or as part of another moiety, as a substituent for Cp, X, R or R1 may be further substituted, for example, with C1- _C20 alkyl which may contain Si and/or O atoms;

n is 0, 1 or 2, such as 0 or 1, m is 1, 2 or 3, such as 1 or 2, q is 1,2 or 3, such as 2 or 3, where m+q is equal to the valency of M.

Accordingly, in each X as -CH ₂ -Y, each Y is independently selected from C ₆ -C ₂₀ -aryl, NR ₂ , SiR ₃ or -OSiR ₃ . Most preferably X as -CH2-Y is benzyl. Each X other than -CH2-Y is independently halogen, C1- _C20 alkyl, C1- _C20 alkoxy, _C6 - _C20 aryl, _C7 - _C20 -arylalkenyl, or _-NR2 as as defined above, eg -N(C1-C ₂₀ -alkyl) ₂ .

Preferably q is 2, each X is halogen or -CH ₂ -Y, and each Y is independently as defined above.

Cp is preferably cyclopentadienyl, indenyl, tetrahydroindenyl or fluorenyl optionally substituted as defined above.

In a suitable subgroup of compounds of formula II, each Cp independently contains 1, 2, 3 or 4 substituents as defined above, preferably 1, 2 or 3, for example 1 or 2 substituents, which are preferably selected from C 1 -C ₂₀ -alkyl, C ₆ -C ₂₀ -aryl, C ₇ -C ₂₀ -arylalkyl (wherein the aryl ring, individually or as part of another moiety, may be further substituted as above), -OSiR ₃ where R is as above, preferably C1- _C20 alkyl.

R, if present, is preferably a methylene, ethylene or silyl bridge, by which silyl can be displaced as defined above, eg (dimethyl)Si=, (methylphenyl)Si= or (trimethylsilylmethyl)Si=; n is 0 or 1; m is 2 and q is two. Preferably R is other than hydrogen.

A specific subgroup includes the well-known Zr, Hf and Ti metallocenes with two η-5 ligands, which may be bridged or unbridged cyclopentadienyl ligands, optionally substituted with e.g. siloxy or alkyl (e.g. _{C1_6} alkyl), as defined above, or with two indenyl ligands, bridged or unbridged, optionally substituted on any of the ring moieties, e.g., siloxy or alkyl, as defined above, e.g., in 2-, 3-, 4- and/or 7 -provisions. Preferred bridges are ethylene or -SiMe ₂ .

The preparation of metallocenes can be carried out according to or similar to methods known in the literature and is within the skill of a person skilled in the art. Thus, for the preparation see, for example, EP-A-129 368, for examples of compounds in which the metal atom carries an NR ₂ ligand, see in particular WO-A-9856831 and WO-A-0034341. See also, for example, documents EP-A-260 130, WO-A-9728170, WO-A-9846616, WO-A-9849208, WO-A-9912981, WO-A-9919335, WO-A- 9856831, WO-A-00/34341, EP-A-423 101 and EP-A-537 130.

Alternatively, in another subgroup of metallocene compounds, the metal bears a Cp group as defined above and additionally an η1 or η2 ligand, where said ligands may or may not be bridged to each other. Such compounds are described, for example, in WO-A9613529, the contents of which are incorporated herein by reference.

Other preferred metallocenes include metallocenes of formula (I)

Cp' ₂ M'X' ₂ where each X' represents halogen, C1_ ₆ alkyl, benzyl or hydrogen;

M' is Hf or Zr;

Cp' is a cyclopentadienyl or indenyl group optionally substituted with a C1-10 hydrocarbon group or groups and optionally bridged, for example via ethylene or dimethylsilyl.

Particularly preferred catalysts are bis-(n-butylcyclopentadienyl) hafnium dibenzyl and bis-(n-butylcyclopentadienyl) zirconium dichloride.

Metallocene protocatalysts are typically used as part of a catalyst system that also includes a catalyst activator, also referred to as a cocatalyst. Suitable activators are, among others, aluminum compounds such as aluminum alkoxy compounds. Suitable aluminum alkoxy activators are, for example, methylalumoxane (MAO), hexaisobutylaluminum and tetraisobutylaluminum. In addition, boron compounds can be used as activators (for example, fluoroboron compounds such as triphenylpentafluoroboron or triphentylcarbenium tetraphenylpentafluoroborate ((C ₆ H ₃ ) ₃ B+B-(C ₆ F ₅ ) ₄ ). Cocatalysts and activators, as well as obtaining such catalyst systems are well known in the art For example, in the case of using an aluminum alkoxy compound as the activator, a suitable Al/M molar ratio of the catalyst system (Al is the aluminum from the activator and M is the transition metal from the transition metal complex) is between 50 up to 500 mol/mol, preferably from 100 to 400 mol/mol Ratios below or above the above ranges are also possible, but the above ranges are usually the most suitable.

If a procatalyst is required, a procatalyst/cocatalyst mixture or a procatalyst/cocatalyst reaction product in supported form (eg, on a silica or alumina support), unsupported form, or it can be deposited and used as such can be used. One of the possible ways to obtain a catalytic system is based on emulsion technology, in which no external support is used, and a solid catalyst is formed by solidification of catalyst droplets dispersed in a dispersion medium. The method of curing and other possible metallocenes are described, for example, in document WO 03/051934, which is incorporated herein by reference.

It is also possible to use combinations of different activators and procatalysts. In addition, as is known in the art, additives, modifiers, and the like can be used.

Any catalytically active system containing a procatalyst, such as a metallocene complex, is referred to herein as a single site or metallocene catalyst (system). Methods for preparing these polymers are well known.

It is particularly preferred if the PESP/LDPE combination described herein is cross-linked. The crosslinked resin composition of the insulating layer according to this aspect of the present invention may have a conductivity of less than 3.0 fS/m (measured using the DC Conductivity A method defined herein).

It is particularly preferred if the LLDPE/LDPE combination described herein is non-crosslinked.

Preferably the SSC PE is PESP.

- 11 040293

Polymer composition

The polymer composition used in the insulating layer according to the present invention contains components (I) and (II). In a more preferred embodiment, the polymer composition preferably consists essentially of components (I) and (II). The term consists essentially of meaning that no other polymer components are present in the composition. It should be understood that the polymer composition may contain standard polymer additives, described in more detail below. The term consists essentially of being used to exclude the presence of other polymeric components, but it implies the possibility of additives being present.

Conductivity

In all embodiments according to the present invention, it is preferable that the conductivity of the polymer composition or the conductivity of the insulating layer is 10.0 fS/m or less, for example, 6.0 fS/m or less, especially 5.0 fS/m or less, when determining using method A. In some embodiments, the conductivity of the composition or the conductivity of the insulating layer may be 2.0 fS/m or less, for example, 1.0 fS/m or less, when determined using method A (30 kV, 70°C ).

In all embodiments according to the present invention, it is preferred that the conductivity of the composition or the conductivity of the insulating layer is 20.0 fS/m or less, for example 15.0 fS/m or less, especially 10.0 fS/m or less. The indicated values are measured according to measurement method C (80 kV, 70°C).

In all embodiments according to the present invention, it is preferred that the conductivity of the composition or the conductivity of the insulating layer is 10.0 fS/m or less, for example 5.0 fS/m or less, especially 4.0 fS/m or less. The indicated values are measured according to the measurement method D (60 kV, 70°C).

The LDPE and LDPE/LLDPE composition described herein may have a conductivity in S/cm of less than 1.0x10' ¹⁴ , for example, when determined according to the DC V measurement method, for example, 9.0x10' ¹⁵ S/cm or less, especially 5.0 x 10' ¹⁵ S/cm or less, for example, 1.0 x 10' ¹⁶ S/cm or less or 5.0 x 10 ^-16 or less. In some embodiments, the conductivity may be 9.0 x 10 ^-17 S/cm or less.

In one embodiment, the LDPE of the present invention is combined with UHMWPE. When LDPE is blended with UHMWPE, the resulting mixture has significantly improved electrical conductivity compared to pure LDPE at low levels of UHMWPE, indicating a charge carrier mobility constraint due to the locally more regular morphology of UHMWPE.

The composition of LDPE and UHMWPE described herein may have a conductivity in S/cm of less than 1 x 10 ^-14 , for example, when determined according to the DC V measurement method.

Cables

The cable according to the present invention is preferably a DC cable. A DC power cable is defined as a DC cable capable of transmitting power and operating at any voltage level, typically operating at voltages greater than 1 kV. The DC power cable may be a low voltage (LV), medium voltage (MV), high voltage (HV) or extra high voltage (EHV) DC cable, where the terms given are well known to indicate the operating voltage level. The polymer is even more preferably used in the insulating layer of a DC power cable operating at voltages greater than 36 kV, such as an HV DC cable. For HV DC cables, the operating voltage is defined in this document as the electrical voltage between earth and the conductor of the high voltage cable.

Preferably, the HV DC cable according to the present invention is a cable operating at voltages of 40 kV or more, even at voltages of 50 kV or more. More preferably, the HV DC power cable operates at voltages of 60 kV or more. The invention is also well suited to very demanding cable applications, and other cables according to the present invention are HV DC power cables operating at voltages greater than 70 kV. Target voltages are 100 kV or more, such as 200 kV or more, more preferably 300 kV or more, especially 400 kV or more, especially 500 kV or more. Voltages of 640 kV or more, such as 700 kV, are also provided. The upper limit is not limited. A practical upper limit may be up to 1500 kV, for example up to 1100 kV. Thus, the cables of the present invention perform well in UHV DC power cable applications in high demand areas at voltages from 400 to 850 kV, eg 650 to 850 kV.

A cable, such as a DC cable, comprises an inner semi-conductive layer containing a first semi-conductive composition, an insulating layer containing a polymer composition

- 12 040293 according to the present invention, and the outer semi-conductive layer containing the second semi-conductive composition, in that order.

The polymer composition according to the present invention is used in the insulating layer of the cable. Ideally, the insulating layer contains at least 95 wt.%, for example, at least 98 wt.%, of the polymer composition according to the present invention, for example, at least 99 wt.%, for example, consists of a polymer composition. Therefore, it is preferable that the polymer composition according to the present invention is the only component other than additives used in the insulating layer of the cables according to the present invention. Thus, it is preferable that the insulating layer consists essentially of the composition according to the present invention. The term consists essentially of being used herein to mean that only the specified polymer composition is present. It should be understood that the insulating layer may contain standard polymeric additives such as scorch inhibitors, water treeing inhibitors, antioxidants, and the like. They are not excluded by the term consists essentially of. It should also be noted that these additives can be added as part of the masterbatch and therefore transferred to the polymer carrier. The use of masterbatch additives is not excluded by the term consists essentially of.

The insulating layer may have low electrical conductivity when it is crosslinked with a crosslinking agent. Thus, the insulating layer of the cables according to the present invention may optionally be crosslinkable.

The term crosslinkable means that the insulating layer can be crosslinked using a crosslinking agent before use. To be crosslinkable, the insulating layer must contain a crosslinking agent, typically a free radical generating agent. The crosslinked polymer composition has a typical network structure, in particular interpolymer crosslinks (bridges), well known in the art.

If the insulating layer is crosslinked, any parameter of the insulating layer other than conductivity is ideally measured prior to crosslinking, unless otherwise specified. In embodiments in which the insulating layer does not contain a crosslinking agent, the electrical conductivity, as described in the Determination Method section, is measured based on a sample of the polymer composition forming the insulating layer that is not crosslinked (i.e. does not contain a crosslinking agent and is not crosslinked). crosslinking agent). In embodiments in which the insulating layer is cross-linked with a cross-linking agent, the electrical conductivity is measured based on a sample of the cross-linked polymer composition (i.e., the sample of the polymer composition is first cross-linked with the initially present cross-linking agent, and then the electrical conductivity is measured based on the resulting cross-linked sample). Measurement of the conductivity of a sample of a non-crosslinked or crosslinked polymer composition is described in the Methods section.

The amount of crosslinker used, if present, may vary, preferably within the ranges indicated below. Preferably, peroxide is used in an amount of 0 to 110 mmol -O-O-/kg polymer composition of the insulating layer, preferably 0 to 90 mmol -O-O-/kg polymer composition (corresponding to the range of 0 to 2.4 wt.% peroxide dicumyl based on polymer composition), preferably from 0 to 37 mmol -O-O- / kg of polymer composition, preferably from 0 to 35 mmol -O-O- / kg of polymer composition, preferably from 0 to 34 mmol -O-O -/kg polymer composition, preferably 0 to 33 mmol -O-O-/kg polymer composition, more preferably 0 to 30 mmol -O-O-/kg polymer composition, more preferably 0 to 20 mmol -O-O -/kg polymer composition, more preferably 0 to 10.0 mmol O-O-/kg polymer composition, more preferably 0 to 7.0 mmol -O-O-/kg polymer composition, more preferably less than 5.0 mmol -O-O-/kg polymer composition, most preferably the polymer composition does not contain a crosslinking agent (= 0 wt.% added crosslinking agent). Thus, in the ideal case, the insulating layer does not contain by-products of peroxide decomposition.

The lower limit of the content of the cross-linking agent, if present, is not limited and may be at least 0.1 mmol -O-O- / kg polymer composition in the insulating layer, preferably at least 0.5 mmol -O-O - / kg polymer composition, more preferably at least 5.0 mmol -O-O- / kg polymer composition. A lower peroxide content can reduce the required degassing step, if necessary, of the resulting and crosslinked cable.

The units mmol -O-O-/kg of polymer composition herein means the content (mmol) of peroxide functional groups per kg of polymer composition when measuring the polymer composition before crosslinking. For example, 35 mmol -O-O-/kg of the polymer composition corresponds to 0.95 wt.% of the well-known dicumyl peroxide, based on the total amount (100 wt.%) of the polymer composition.

Such a polymer composition may contain one type of peroxide or two or more different types of peroxides, and in this case, the amount (in mmol) -O-O- / kg of polymer composition, as defined above, below or in the claims, is the sum of the amounts -О-О- 13 040293 /kg polymer composition of each type of peroxides. As non-limiting examples of suitable organic peroxides, mention may be made of di-tert-amyl peroxide, 2,5-di(tert-butylperoxy)-2,5-dimethyl-3-hexine, 2,5-di(tert-butylperoxy)-2.5 -dimethylhexane, tert-butylcumylperoxide, di(tert-butyl)peroxide, dicumylperoxide, butyl-4,4-bis(tert-butylperoxy)valerate, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, tert-butylperoxybenzoate, dibenzoyl peroxide, bis(tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 1,1-di(tert-butylperoxy)cyclohexane, 1,1-di(tert- amylperoxy)cyclohexane or any mixtures thereof. Preferably, the peroxide is selected from 2,5-di(tert-butylperoxy)-2,5-dimethylhexane, di(tert-butylperoxyisopropyl)benzene, dicumyl peroxide, tert-butylcumyl peroxide, di(tert-butyl)peroxide, or mixtures thereof. Most preferably, the peroxide is dicumyl peroxide.

If the mixture component is PESP, it is preferred that the insulating layer is crosslinked.

If the mixture component is UHMWPE, it is preferred that the insulating layer is non-crosslinked.

If the insulating layer is not crosslinked, it is preferable that the insulating layer does not contain a crosslinking agent. In this way, the disadvantages of the prior art relating to the use of a crosslinking agent in the cable layer can be avoided. Naturally, the non-crosslinked layer embodiment also simplifies the cable manufacturing process. Because no crosslinker is required, raw material costs are lower. In addition, degassing of the crosslinked cable layer is usually required after crosslinking to remove peroxide by-products. If the material is not crosslinked, this degassing step is not required.

In addition to the mixture of LDPE and optional peroxide, the insulating layer may contain additional component(s), such as additives (for example, any antioxidant(s), scorch inhibitor(s), enhancer (i) cross-linking, stabilizer(s), processing aid(s), flame retardant(s), water treeing inhibitor(s), acid or ion scavenger(s), inorganic filler(s), and stabilizer (s) stresses), known in the field of polymers.

Thus, the insulating layer may contain additive(s) commonly used for wires and cables, such as one or more antioxidants and optionally one or more scorch retarders, preferably at least one or more antioxidants. The amounts of additives used are conventional and well known to the person skilled in the art, for example from 0.1 to 1.0% by weight.

As non-limiting examples of antioxidants, mention may be made, for example, of hindered or semi-hindered phenols, aromatic amines, aliphatic hindered amines, organic phosphites or phosphonites, thio compounds, and mixtures thereof.

Preferably, the insulating layer does not contain carbon black. It is also preferred that the insulating layer does not contain fire retardant(s), such as additives containing metal hydroxides, in flame quenching amounts.

The cable according to the present invention also contains inner and outer semi-conductive layers. They can be made from any conventional material suitable for use in said layers. The compositions of the inner and outer semi-conductive layers may be different or the same and may contain a polymer(s), which(e) is(are) preferably a polyolefin or a mixture of polyolefins, and a conductive filler, preferably carbon black. Suitable polyolefin(s) are, for example, low pressure process polyethylene or high pressure process polyethylene (LDPE). The carbon black may be any conventional carbon black used in the semi-conductive layers of a DC power cable, preferably in the semi-conductive layer of a DC power cable. Preferably, the carbon black has one or more of the following properties: a) a primary particle size of at least 5 nm, which is defined as the number average particle diameter in accordance with dispersion procedure D of ASTM D3849-95a, b) an iodine number of at least at least 30 mg/g in accordance with ASTM D1510, c) an oil absorption number of at least 30 ml/100 g, which is measured in accordance with ASTM D2414. Non-limiting examples of carbon black are, for example, acetylene black, furnace black and Ketjen black, preferably furnace black and acetylene black. Preferably, the polymer composition contains from 10 to 50 wt.% carbon black, based on the weight of the semiconductive composition.

In a preferred embodiment, the outer semiconductive layer is crosslinked. In another preferred embodiment, the inner semi-conductive layer is preferably non-crosslinked. Thus, in general, it is preferable that the inner semiconductive layer and the insulating layer remain uncrosslinked, and the outer semiconductive layer is crosslinked. Therefore, the peroxide crosslinker can only be present in the outer semiconductive layer.

A conductor contains one or more wires. In addition, the cable may contain one or more of these conductors. Preferably the conductor is an electrical conductor and contains one or more metallic wires. Preferred is C and wire.

As is well known, the cable may optionally contain additional layers, for example, a shield(s) layer(s), sheath layer(s), other(s) protective(s) layer(s), or any combination thereof.

Cable production

The present invention also provides a method for manufacturing a cable, comprising the steps of applying one or more conductors, preferably by (co)extrusion, an inner semi-conductive layer, an insulating layer and an outer semi-conductive layer, in that order, where the insulating layer contains a mixture as described herein . The insulating layer may or may not be crosslinked.

The method may optionally include the steps of crosslinking one or both of the inner semiconductive layer or the outer semiconductive layer without crosslinking the insulating layer. Preferably the outer semi-conductive layer is crosslinked without crosslinking the insulating layer. Also preferably, the inner semi-conductive layer is non-crosslinked. Thus, it is preferred that the semiconductive layer contains a peroxide which allows the semiconductive composition to be crosslinked.

More preferably, the cable is produced by a method comprising the steps of (a) providing and mixing, preferably melt mixing in an extruder, an optionally crosslinkable first semiconductive composition comprising a polymer, carbon black and optionally additional component(s) for the inner semiconductive layer, providing and blending, preferably melt blending in an extruder, an optional crosslinkable low density polyethylene (LDPE) blend of the present invention; and providing and mixing, preferably melt mixing in an extruder, a second semiconductive composition that is optionally crosslinkable and contains a polymer, carbon black, and optionally additional component(s) for the outer semiconductive layer;

(b) depositing one or more conductors, preferably by co-extrusion, of the meltblown first semiconductive composition obtained in step (a) to form an inner semiconductive layer of the meltblown resin composition of the present invention obtained in step (a) to form an insulating layer, and a mixed melt of the second semiconductive composition obtained in step (a) to obtain an outer semiconductive layer, and (c) optionally crosslinking under crosslinking reaction conditions one or both of the first semiconductive composition of the inner semiconductive layer and the second semiconductive composition of the outer semiconductive layer obtained cable and optionally crosslinking the insulating layer, more preferably without crosslinking the insulating layer.

Preferably in step (c) the second semiconductive polymer composition of the outer semiconductive layer is crosslinked, more preferably crosslinked without crosslinking the insulating layer. Further preferably, the second semiconductive resin composition of the outer semiconductive layer is crosslinked without crosslinking the insulating layer or the first semiconductive composition of the outer semiconductive layer.

Melt blending means mixing above the melting temperature of at least the main polymer(s) component(s) of the resulting mixture and conducting, for example, without limitation, at a temperature of at least 15° C. above the melting or softening temperature of the polymer(s). ) component(s).

The term (co)extrusion in this document means that in the case of two or more layers, said layers may be extruded in separate stages, or at least two or all of said layers may be coextruded in one extrusion stage, as is well known in the art. technology. Also, the term (co)extrusion as used herein means that all or part of the layers are formed simultaneously using one or more extrusion dies. For example, triple extrusion can be used to form three layers. In the case of forming a layer using more than one extrusion die, the layers can be extruded, for example, using two extrusion dies, with the first die used to form the inner semi-conductive layer and the inner part of the insulating layer, and the second die used to form the outer insulating layer and an outer semi-conductive layer.

As is well known, the polymer of the present invention and the optional and preferred first and second semiconductive compositions can be made before or during the cable manufacturing process.

Preferably, the polymers required for the production of the cable according to the present invention are used in the cable production process in the form of powder, grains or granules. Granules as used herein generally refer to any polymer product that is made from a reactor-produced polymer (derived directly from the reactor) by post-reactor modification to form solid polymer particles.

The mixing step (in the melt) of (a) the proposed polymer composition according to the present

- 15 040293 of the invention and the preferred first and second semi-conductive compositions are preferably carried out in a cable extruder. Step a) of the cable production process may optionally include a separate mixing step, for example in a mixer connected to and upstream of the cable extruder in the cable production line. Mixing in a separate upstream mixer can be carried out by mixing the component(s) with or without external heating (heating with an external source).

Any crosslinking agent can be added prior to the cable manufacturing process or during the mixing (melt) step (a). For example, preferably a crosslinking agent, as well as optional(e) additional(e) component(s), such(s) as an additive(s), may already be present in the polymers used. The crosslinker is added, preferably by impregnation, to the polymer solids, preferably the granules.

Preferably, the melt blended polymer composition obtained in the (melt blending) step (a) consists of a polyolefin (a) and optionally a second polyolefin (b), if present, according to the present invention as the sole polymer(s) component(s). Optional(s) and preferred(s) additive(s) can be added to the polymer composition as such or as a mixture with a polymer carrier, i. in the form of the so-called masterbatch.

Optional crosslinking can be carried out at an elevated temperature, which is well known to be chosen depending on the type of crosslinking agent. For example, temperatures above 150° C., such as 160 to 350° C., are typical, however temperatures are not limited to these values.

Temperatures and processing devices are well known in the art, for example conventional mixers and extruders such as single or twin screw extruders are suitable for the process of the present invention.

Advantages of the most preferred embodiment of having an uncrosslinked inner semiconductive layer and an insulating layer in combination with an outer semiconductive layer that is crosslinked include:

optimum electrical performance of HV DC cable insulation system, easy cable connection due to non-crosslinked thermoplastic insulation composition, no need to wait and transfer heat through the insulating and inner semi-conductive layers as they are not crosslinked.

The overall production efficiency is improved, especially in HV applications with a thick insulating layer, since there is no need to crosslink the inner semi-conductive layer and the insulating layer. Crosslinking the inner and outer semiconductive and insulating layers typically takes at least 1 hour, while only the outer semiconductive layer takes less than 8 minutes to crosslink, reliable high-speed extrusion is possible, resulting in longer periods of stable operation at higher speeds and extrusion quality due to the absence of the risk of vulcanization (undesired premature crosslinking) in the inner semi-conductive and insulating layers, the possibility of reducing the outgassing step and thus speeding up the entire cable production process, since any unwanted by-products, i.e. The degradation products formed from the crosslinker are easier to remove, i.e. to degas, only from the outer layer, unexpectedly sufficient mechanical protection of the insulating layer by the cross-linked outer semi-conductive layer against mechanical and thermal cracking, expressed as TSCR (thermal stress cracking).

The thickness of the insulation layer of a cable, more preferably a DC power cable such as an HV DC power cable, is usually 2 mm or more, preferably at least 3 mm, preferably at least 5 to 100 mm, more preferably 5 to 50 mm and usually from 5 to 40 mm, for example from 5 to 35 mm, when measuring the cross-section of the insulating layer of the cable.

The thickness of the inner and outer semi-conductive layers is usually less than the thickness of the insulating layer, and in a HV DC power cable, it can be, for example, more than 0.1 mm, for example, from 0.3 to 20 mm, from 0.3 to 10 mm for the inner semiconductive and outer semiconductive layers. The thickness of the inner semi-conductive layer is preferably 0.3-5.0 mm, preferably 0.5-3.0 mm, preferably 0.8-2.0 mm. The thickness of the outer semi-conductive layer is preferably 0.3 to 10 mm, such as 0.3 to 5 mm, preferably 0.5 to 3.0 mm, preferably 0.8 to 3.0 mm. It will be appreciated by one skilled in the art that the thickness of the DC cable layers depends on the expected voltage level in the end use of the cable and can be selected accordingly.

The most interesting HVDC cables according to the present invention may have an insulating layer of 20 mm or more, for example 20 to 40 mm. Operating voltages over 320 kV are possible. Transmission capacities of more than 1000 MW are also envisaged.

Preferred embodiments of the polymer composition of the present invention may be combined with each other to further define preferred embodiments of the present invention.

Further, the present invention is defined with reference to the following non-limiting examples and figures.

In FIG. 1 shows conductivity versus voltage at 70° C. for cross-linked polyethylene and cross-linked polyethylenes modified with SSC-PESP.

In FIG. 2 shows the dependence of conductivity on the content of UHMWPE.

In FIG. 3 you can see a visual representation of the results presented in table.5. It can be seen from these results that the value of DC conductivity drops by ~2 orders of magnitude upon modification of pure LDPE.

Methods for determining

Unless otherwise indicated in the description or experimental part, the following methods were used to determine the properties.

Wt %: % by weight.

Melt flow index.

The melt flow index (MFR) was determined according to ISO 1133 and reported as g/10 min. The MFR is an indicator of the flowability and, accordingly, the workability of the polymer. The higher the melt flow index, the lower the viscosity of the polymer. MFR was determined at 190°C for polyethylene and at 230°C for polypropylene. MFR can be determined at various loads such as 2.16 kg (MFR ₂ ) or 21.6 kg (MFR ₂₁ ).

Molecular mass.

Mz, Mw, Mn and MWD were measured by gel permeation chromatography (GPC) according to the following method: weight average molecular weight Mw and molecular weight distribution (MWD=Mw/Mn, where Mn is number average molecular weight and Mw is weight average molecular weight; Mz is z-average molecular weight) was determined in accordance with ISO 16014-4:2003 and ASTM D 6474-99. A Waters GPCV2000 instrument equipped with a refractive index detector and in-line viscometer was used with 2x GMHXLHT columns and 1x G7000HXL-HT TSK-gel column from Tosoh Bioscience and 1,2,4trichlorobenzene (TCB stabilized at 250 mg/L 2,6-di-tert -butyl-4-methylphenol) as a solvent at 140°C and at a constant flow rate of 1 ml/min. Injected 209.5 μl of sample solution for analysis. The column set was calibrated using universal calibration (according to ISO 160142:2003) with at least 15 narrow MWD polystyrene (PS) standards ranging from 1 kg/mol to 12000 kg/mol. Mark-Houwink constants were used as specified in ASTM D 6474-99. All samples were prepared by dissolving 0.5-4.0 mg of polymer in 4 ml (at 140° C.) of stabilized TCB (similar to mobile phase) and holding for max. 3 hours at a maximum temperature of 160°C with continuous gentle shaking before sampling and feeding into the GPC instrument.

Content of comonomers.

a) Comonomer content of polypropylene random copolymer.

Quantitative Fourier transform infrared spectroscopy (FTIR) was used to quantify the amount of comonomer. Calibration was provided by correlation with comonomer content determined by quantitative nuclear magnetic resonance (NMR) spectroscopy.

The calibration procedure based on the results of quantitative ¹³ C-NMR spectroscopy was carried out in the usual way, well described in the literature.

The amount of comonomer (N) was determined as a mass percent (wt.%), according to the equation:

N = kl (A/R) + k2 where A is the maximum absorbance determined for the comonomer band, R is the maximum absorbance determined as the height of the reference peak, and k1 and k2 are linear constants obtained by calibration. The band used to quantify the ethylene content was chosen depending on whether the ethylene content is random (730 cm ^-1 ) or block (as in a heterophasic PP copolymer) (720 cm ^-1 ). The absorbance at 4324 cm ^-1 was used as a reference band.

b) Quantification of alpha-olefin content in linear low density polyethylene and low density polyethylene by NMR spectroscopy.

Comonomer content was determined by quantitative ¹³ C nuclear magnetic resonance (NMR) spectroscopy after basic line assignment (J. Randall JMS - Rev. Macromol. Chem. Phys., C29(2&3), 201-317 (1989)). The experimental parameters were adjusted to provide quantitative spectra for the particular specified task.

In particular, solution NMR spectroscopy was used using a Bruker Avance III 400 spectrometer. Homogeneous samples were prepared by dissolving approximately 0.200 g of polymer in 2.5 ml of deuterated tetrachlorethylene in 10 mm sample tubes using a thermostat and a rotary tube oven at 140°C. Single-pulse ^13C NMR spectra decoupled from protons with NOE (in full-scan suppression mode) were recorded using the following acquisition parameters: vector tilt angle 90°, 4 blank scans, 4096 transitions at exposure time 1.6 s, spectral width 20 kHz, temperature 125°C, two-level decoupling from WALTZ protons, and a relaxation delay of 3.0 s. The resulting FSI signal was processed using the following processing parameters: zero-filling up to 32k points and apodization using a Gaussian windowed function; automatic phase correction of zero and first order and automatic correction of the baseline using a fifth order polynomial, limited to the region of interest.

Scores were calculated using simple adjusted ratios of the integrals of the representative area signals using methods well known in the art.

c) Content of polar comonomers in low density polyethylene.

(1) Polymers containing > 6% by weight of polar comonomer units.

The content of comonomers (wt.%) was determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) with calibration based on quantitative nuclear magnetic resonance spectroscopy (NMR). Below are examples of the determination of the content of polar comonomers for copolymers of ethylene with ethyl acrylate, ethylene with butyl acrylate and ethylene with methyl acrylate. Polymer film samples were prepared for FTIR measurements: a thickness of 0.5-0.7 mm was used for copolymers of ethylene with butyl acrylate and ethylene with ethyl acrylate, and a film with a thickness of 0.10 mm was used for a copolymer of ethylene with methyl acrylate in an amount of more than > 6 wt.%. The films were pressed using a Specac film press at 150° C., with a load of about 5 tons for 1-2 minutes, and then cooled with cold water in an uncontrolled manner. The exact thickness of the obtained film samples was measured.

After FTIR analysis, baselines were determined for the analyzed peaks in absorption mode. The comonomer absorption peak was normalized to the polyethylene absorption peak (eg, the peak height of butyl acrylate or ethyl acrylate at 3450 cm ^-1 divided by the peak height of polyethylene at 2020 cm ^-1 ). The calibration procedure using NMR spectroscopy was carried out in the usual way, which is well described in the literature and explained below.

To determine the content of methyl acrylate, a film sample 0.10 mm thick was prepared. After analysis, the absorbance for the baseline at 2475 cm ^-1 (Amethyl acrylate - A2475) was subtracted from the maximum absorption peak of methyl acrylate at 3455 cm ^-1 . The absorbance for the baseline at 2475 cm ^-1 (A2660 - A ₂₄₇₅ ) was then subtracted from the maximum of the polyethylene absorption peak at 2660 cm ^-1 . The ratio between (A _{methyl acrylate} - A ₂₄₇₅ ) and ^(A 2660 ^- A2475) was then calculated in the usual manner, which is well described in the literature.

Wt.% can be converted to mol.% by calculation. This is well described in the literature.

Quantitative determination of copolymer content in polymers by NMR spectroscopy.

Comonomer content was determined by quantitative nuclear magnetic resonance (NMR) spectroscopy after basic line assignment (eg, NMR Spectra of Polymers and Polymer Additives, A. J. Brandolini and D. D. Hills, 2000, Marcel Dekker, Inc. New York). Experimental parameters were adjusted to provide quantitative spectra for a particular specified task (eg, 200 and More NMR Experiments: A Practical Course, S. Berger and S. Braun, 2004, Wiley-VCH, Weinheim). Scores were calculated using simple adjusted ratios of the integrals of the representative area signals using methods well known in the art.

(2) Polymers containing 6% by weight or less of polar comonomer units.

The content of comonomers (wt.%) was determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) with calibration based on quantitative nuclear magnetic resonance spectroscopy (NMR). Below are examples of determining the content of polar comonomers for copolymers of ethylene with butyl acrylate and ethylene with methyl acrylate. For FTIR measurements, film samples with a thickness of 0.05 to 0.12 mm were prepared as described above in method 1). The exact thickness of the obtained film samples was measured.

After FTIR analysis, baselines were determined for the analyzed peaks in absorption mode. From the peak absorption peak of the comonomer (eg, methyl acrylate at 1164 cm ^-1 and butyl acrylate at 1165 cm ^-1 ), the absorption value for the baseline at 1850 cm ^-1 (Apolar comonomer - A1850) was subtracted. The absorbance for the baseline at 1850 cm ^-1 (A2660 -A ₁₈₅₀ ) was then subtracted from the polyethylene absorbance maximum at 2660 cm ^-1 . The ratio between (Ac _omonomer - A ₁₈₅₀ ) and (A ₂₆₆₀ A ₁₈₅₀ ) was then calculated. The calibration procedure using NMR spectroscopy was carried out in the usual way, which is well described in the literature, as described above in method 1).

Wt.% can be converted to mol.% by calculation. This is well described in the literature.

The following is an example of how the content of polar comonomer obtained by the above method (1) or (2), depending on its amount, can be converted to micromole or

- 18 040293 mmol per g of polar comonomer, as indicated in the definitions in the text and claims:

Calculations in millimoles (mmol) and micromoles were performed as described below.

For example, in the case of 1 g of ethylene-butyl acrylate copolymer, which contains 20 wt.% butyl acrylate, the specified material contains 0.20/M _{butyl acrylate} (128 g/mol) = 1.56x10 ^-3 mol. (= 1563 micromoles).

The content of polar comonomer units in the polar copolymer, C _{polar comonomer} , was expressed in mmol/g (copolymer). For example, a polar ethylene-butyl acrylate copolymer that contains 20 wt% butyl acrylate sonomer units has a C _{polar comonomer of} 1.56 mmol/g.

Applicable molecular weights: M-butyl acrylate = 128 g/mol, Methyl acrylate = 100 g/mol, M-methyl acrylate = 86 g/mol.

Density.

Low density polyethylene (LDPE): Density was measured according to ISO 1183-2. Sample preparation was carried out in accordance with ISO 1872-2, Table 3 Q (injection molding).

Low pressure polyethylene: Polymer density measured according to ISO 1183/1872-2B.

A method for determining the amount of double bonds in a polymer composition or in a polymer.

A) Determination of the number of carbon-carbon double bonds by IR spectroscopy.

Quantitative infrared (PC) spectroscopy was used to determine the amount of carbon-carbon (C=C) double bonds. Calibration was carried out by preliminary determination of the molar extinction coefficient of C=C functional groups in representative low molecular weight model compounds of known structure.

The number of each of these groups (N) was determined as the number of carbon-carbon double bonds per thousand carbon atoms (C=C/1000C), according to the equation:

N = (A x 14)/(E x L x D), where A is the maximum absorbance as determined by the height of the peak, E is the molar extinction coefficient of the test group (l-mol+mm ^-1 ), L is the thickness film (mm), and D is the density of the material (g-cm ^-1 ).

The total number of C=C bonds per thousand carbon atoms can be calculated by summing N for individual components containing C=C.

For solid polyethylene samples, infrared spectra were recorded using an FTIR spectrometer (Perkin Elmer 2000) on thin films (0.5-1.0 mm) obtained by injection molding with a resolution of 4 cm ^-1 and analyzed in absorption mode.

1) Polymer compositions containing homopolymers and copolymers of polyethylene, with the exception of polyethylene copolymers with > 0.4 wt.% polar comonomer.

For polyethylenes, three types of functional groups containing C=C were quantified, each of which has a characteristic absorption, and each of which was calibrated against different model compounds to obtain individual extinction coefficients:

vinyl (R-CH=CH2) at 910 cm^-1 calculated on 1-decene [dec-1-ene] to give E = 13.13 l-mol 1 mm^-1;

vinylidene (RR'C=CH2) at 888 cm ^-1 in terms of 2-methyl-1-heptene [2-methylhept-1-ene] to give E = 18.24 l-mol ^-1 -mm ^-1 ;

trans-vinylene (R-CH=CH-R') at 965 cm ^-1 in terms of trans-4-decene[(E)-dec-4-ene] to give E = 15.14 l-mol-1- mm ^-1 .

For polyethylene homopolymers or copolymers with <0.4 wt% polar comonomer, a linear baseline correction between about 980 and 840 cm ^-1 was applied.'

2) Polymer compositions containing polyethylene copolymers with >0.4 wt% polar comonomer.

For polyethylene copolymers with >0.4 wt.% polar comonomer, two types of functional groups containing C=C were quantified, each of which has a characteristic absorption, and each of which was calibrated against different model compounds to obtain individual extinction coefficients:

vinyl (R-CH=CH2) at 910 cm^-1 calculated on 1-decene [dec-1-ene] to give E = 13.13 l-mol 1mm 1;

vinylidene (RR'C=CH2) at 888 cm ^-1 in terms of 2-methyl-1-heptene [2-methylhept-1-ene] to give E = 18.24 l-mol-1-mm ^-1 ;

EVE:

for ethylene-butyl acrylate (EVA) copolymer systems, a linear baseline correction between about 920 and 870 cm ^-1 was applied.

EMA:

for ethylene-methyl acrylate (EMA) copolymer systems, a linear baseline correction between about 930 and 870 cm ^-1 was applied.

- 19 040293

3) Polymer compositions containing unsaturated low molecular weight molecules.

For systems containing low molecular weight substances containing C=C, a direct calibration was carried out using the molar extinction coefficient of C=C absorption of the low molecular weight substances themselves.

C) Quantification of molar extinction coefficients by IR spectroscopy.

Molar extinction coefficients were determined according to the procedure given in ASTM D3124-98 and ASTM D6248-98. Infrared spectra for solutions were recorded using an FTIR spectrometer (Perkin Elmer 2000) equipped with a liquid sample cuvette with a path length of 0.1 mm at a resolution of 4 cm ^-1 .

The molar extinction coefficient (E) was determined as l-mol ^-1 -mm ^-1 according to the equation:

E = A/(C x L), where A is the maximum absorbance as determined by the peak height, C is the concentration (mol-l ^-1 ), and L is the thickness of the cuvette (mm).

Used at least three 0.18 mol-l ^-1 solution in carbon disulfide (CS ₂ ) and determined the average value of the molar extinction coefficient.

Methods for measuring conductivity in direct current.

Method A.

Plates were obtained from the granules of the tested polymer composition by injection molding. The end plates were 1 mm thick and 200x200 mm in size. The conductivity measurement can be carried out using a test polymer composition that does not contain or contains an optional cross-linking agent. In the absence of a crosslinker, the conductivity was measured on an uncrosslinked wafer sample using the procedure described below. If the polymer composition to be tested contained a crosslinking agent, crosslinking took place during the preparation of the wafer samples, whereby the conductivity was then measured according to the procedure described below on the resulting crosslinked wafer sample. The crosslinker, if present in the polymer composition prior to crosslinking, is preferably a peroxide as defined herein.

The plates were obtained by molding under pressure at 130°C for 12 min with a gradual increase in pressure from 2 to 20 MPa. The temperature was then increased to reach 180° C. after 5 minutes. The temperature was then held constant at 180° C. for 15 minutes, during which time the plate became fully cross-linked under the action of peroxide, if present in the polymer composition under test. Finally, the temperature was lowered at a cooling rate of 15° C./min until room temperature was reached, at which point the pressure was released. Immediately after the pressure was released, the plates were wrapped in metal foil to prevent the loss of volatile compounds.

If degassing of the plates is expected (ie, they are cross-linked), the plates were kept in a ventilated oven at atmospheric pressure for 24 hours at 70°C. The plates were then wrapped again with metal foil to prevent further exchange of volatiles between the plate and the environment.

A high voltage source was connected to the top electrode to energize the test sample. The resulting current passing through the sample was measured using an electrometer. The measuring cell was a three-electrode system with brass electrodes. Brass electrodes were equipped with heating tubes connected to a heating circulator to facilitate measurement at elevated temperature and to ensure a uniform temperature of the test sample. The measuring electrode diameter was 100 mm. Silicone rubber insulation was placed between the ends of the brass electrodes and the test specimen to prevent sparks from the rounded ends of the electrodes.

The applied DC voltage was 30 kV, which means an average electric field strength of 30 kV/mm. The temperature was 70°C. The current passing through the plate was recorded throughout the experiments lasting 24 hours. The current after 24 hours was used to calculate the conductivity of the insulation.

This method and the schematic diagram of the measuring setup for measuring conductivity are described in detail in the publications presented in Nordic Insulation Symposium 2009 (Nord-IS 09), Gothenburg, Sweden, June 15-17, 2009, page 55-58: Olsson et al, Experimental determination of DC conductivity for XLPE insulation.

Direct current B method for measuring conductivity (values in S/cm).

Broadband dielectric spectroscopy (BDS).

Samples (40x100 mm) were prepared by hot pressing at 250°C and a press force of 100 kN. To control the thickness, spacers 0.1 mm thick were used. Then, disk-shaped samples were cut from the plates.

All measurements were carried out on disk-shaped samples with a diameter of 40 mm and a thickness of ~0.1 mm. Conductivity measurements were carried out using a dielectric spectrometer.

- 20 040293

Broadband dielectric spectroscopy (BDS) was performed using a Novocontrol Alpha spectrometer in the frequency range from 10 ^-2 to 10 ⁷ Hz at various temperatures in the range of 253383K (from -20 to 110°C) with an error of ±0.1K (±0.1° C) at atmospheric pressure and in a nitrogen atmosphere. For selected temperatures, frequency scanning was also performed to study the local and ion dynamics. The sample cell consisted of two silver coated electrodes 40 mm in diameter and a sample about 0.1 mm thick. The complex permittivity , where £ is the real part and £ is the imaginary part, usually depends on the frequency ω, temperature T, and pressure P ¹ , although only the dependence on frequency and temperature was investigated here. The complex permittivity c* can also be calculated from the complex ^permittivity function £ as 1^ . This means that the conductivity data is an effective representation of the permittivity, yet reflects different features of the dielectric behavior, as described below. The analysis was carried out using the empirical equation of Havriliak (Havriliak) and Negami (Negami) ² .

₌ __________1__________ “ _[ 1 + (/^(7,7))^]^ is the permittivity at extremely high frequencies, and α, γ (0 < α, αγ < 1) describe, respectively, the symmetric and asymmetric broadening of the distribution of relaxation times. The relaxation times at maximum loss (T _max ) presented herein were analytically obtained by substituting the data from the relaxation spectra into the Havriliak-Negami (HN) equation as follows:

Direct current conductivity measurement method C.

Method A was repeated, but the applied DC voltage was 80 kV, which means an average electric field strength of 80 kV/mm.

Direct current conductivity measurement method D.

Method A was repeated, but the applied DC voltage was 60 kV, which means an average electric field strength of 60 kV/mm.

Experimental part.

The following materials were used in the examples:

LDPE1 - LDPE homopolymer with a density of 922 kg/m ³ and MFR ₂ 2.0 g/10 min.

LDPE2 - LDPE homopolymer having properties from table. 1:

Table 1. Polymer properties

Base Resin Properties LDPE MFR ₂ , 190°C [g/10 min] 0.3 Density [kg/ ^m3 ] 930 Tensile modulus 350 MPa Modulus of elasticity in bending 330 MPa

UHMWPE1: Mw = 4.6x106 Da, reduced viscosity 2200 (ISO1628-3).

The UHMWPE polymer was a homopolymer.

PESP1 - single-center copolymer of ethylene with a density of 930 kg/m ³ and MFR ₂ 2.2 g/10 min.

PESP2 - single-center copolymer of ethylene with a density of 935 kg/m ³ and MFR ₂ 1.2 g/10 min.

SSC LLDPE is a single center ethylene copolymer with a density of 918 kg/m ³ and an MFR _{2 of} 1.5 g/10 min.

Preparation of Polymer Compositions: Each of the polymer components of the polymer composition under study was added as individual pellets to a pilot extruder (Prism TSE 24TC) along with additives, if not present in the pellets, other than the crosslinker. The resulting mixture was melt-blended under the conditions shown in the table below, and extruded in the usual way to obtain granules.

Setpoints for HS temperatures] extruder Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 RPM Output [kg/h] Pressure [bar] Filter [mesh] 80 155 165 175 175 180 225 7.5 60 325

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Claims (15)

A crosslinking agent, herein a peroxide, if present, was added to the granules and the resulting granules were used in the experimental part. Crosslinking conditions are determined in conductivity tests. Example 1 Cross-linked mixtures. Prepared the following mixtures. Table 3 CE1 IE1 IE2 LDPE1 [wt.%] 99.92 84.92 84.92 Santonox R [wt%]* 0.08 0.08 0.08 PESP1 [wt.%] 0 15 0 PESP2 [wt.%] 0 0 15 Peroxide - DCP [wt%] +0.55 +0.55 +0.55 * antioxidant DCP - dicumyl peroxide. The results are shown in FIG. 1 and summarized in Table 4. As can be seen, both PESP-modified cross-linked blends exhibit extremely low voltage dependence and have a conductivity of less than 10 fS/m at 80 kV/mm. In comparison, the material with 0% PESP shows more than 10 times higher conductivity. Table 4 Material Wt% SSCwsp Conductivity [fS/m] ² (30 kV/mm) Conductivity [fS/m] ⁴ (60 kV/mm) Conductivity [fS/m] ³ (80 kV/mm) CE1 0 14.2 49.6 IE1 15 0.2 3.8 8D IE2 15 oh, s 2.5 7.3 ‘Method A (30 kV). ³ Method C (80 kV). ⁴ Method D (60 kV). Example 2. Not stitched. All blends were prepared on the Prism blender described above. Table 5 CE2 IE3 IE4 LDPE2 (wt%) 100 98 95 SSC LLDPE (wt%) 2 5 DC Conductivity (S/cm), Method B Ι,ΙΟΕ-14 3.27E-17 5D2E-17 These results are shown in Fig. 3. Example 3. Not stitched. Mixtures in the table. 6 was prepared by melt blending the components at 160° C. for 10 min in a Haake Mini twin screw extruder, followed by hot pressing at 250° C. and a press force of 100 kN. Film samples had dimensions of 40x100 mm. To control the thickness, spacers 0.1 mm thick were used. Then, disk-shaped samples were cut from the films. To control the thickness, spacers 0.1 mm thick were used. Table 6 SEZ IE5 LDPE2 mass% 100 95 UHMWPE wt.% 5 DC Conductivity (S/cm)* Ts64E-12 6D1E-15 *(method B). In FIG. 2 you can see a visual representation of the results from table.6. It can be seen from these results that the value of DC conductivity drops by ~2 orders of magnitude when pure LDPE is modified with UHMWPE. In this example, all measurements were carried out on disk-shaped samples with a diameter of 40 mm and a thickness of ~0.1 mm. CLAIM 1. A cable containing one or more conductors surrounded by at least an inner semi-conductive layer, an insulating layer and an outer semi-conductive layer, in this order, where the specified insulating layer contains at least 90 wt.% of the polymer composition, and the specified polymer composition contains ( I) from 80.0 to 99.9 wt.% LDPE homopolymer or copolymer; and (II) from 0.1 to 20.0 wt.%: (i) an ultra-high molecular weight polyethylene having a Mw of at least 1,000,000; or (ii) medium density polyethylene (MDPE) prepared using a single site catalyst and having a density of 925 to 940 kg/m ³ , or linear low density polyethylene - 22 040293 (LLDPE), obtained using a single-site catalyst, and having a density from 910 to 925 kg / m ³ ; and where the polymer composition of the insulating layer has a conductivity of 20.0 fS/m or less, measured by the method of determining C at an average electric field strength of 80 kV/mm and 70°C. 2. The cable according to claim 1, containing one or more conductors surrounded by at least an inner semi-conductive layer, a cross-linked insulating layer and an outer semi-conductive layer, in this order, where the specified insulating layer contains at least 90 wt.% of the polymer composition, and the specified polymer composition contains (I) from 80.0 to 99.9 wt.% homopolymer or copolymer of LDPE; and (II) from 0.1 to 20.0 wt.% of medium density polyethylene (MDPE), obtained using a single-site catalyst, and having a density of from 925 to 940 kg/m ³ or linear low density polyethylene (LLDPE), obtained using a single-center catalyst, and having a density of 910 to 925 kg/m ³ . 3. A cable according to any one of the preceding claims, characterized in that the polymer composition of the insulating layer has a conductivity of 10 fS/m or less, such as 5.0 fS/m or less, such as 2.0 fS/m or less, when measured in according to the DC conductance measurement method as described in Determination Methods A. 4. Cable according to any one of the preceding claims, characterized in that the polymeric composition of the insulating layer has a conductivity of 15.0 fS/m or less, for example 10.0 fS/m or less, measured by the C method at an average electric field strength of 80 kV/ mm and 70°C. 5. Cable according to any one of the preceding claims, characterized in that the polymer composition of the insulating layer has a conductivity of 10.0 fS/m or less, such as 5.0 fS/m or less, such as 4.0 fS/m or less, measured by the method determination of D at an average electric field strength of 60 kV/mm and 70°C. 6. Cable according to claim 1, containing one or more conductors surrounded by at least an inner semi-conductive layer, an insulating layer and an outer semi-conductive layer, in this order, where the specified insulating layer contains at least 90 wt.% of the polymer composition, and the specified the polymer composition contains (I) from 80.0 to 99.9 wt.% homopolymer or copolymer of LDPE, having a density of from 927 to 940 kg/m ³ ; and (II) from 0.1 to 20.0 wt.% ultra-high molecular weight polyethylene having a Mw of at least 1,000,000. 7. The cable according to any of the preceding claims, characterized in that the conductivity of the polymer composition of the insulating layer is 1.0 x 10' ¹⁴ S/cm or less, for example, 1.0 x 10' ¹⁶ S/cm or less when measured in accordance with the method for measuring conductivity according to direct current, as described in the section Methods for determining B. 8. Cable according to claim 1 or 6, characterized in that the insulating layer is non-crosslinked. 9. A cable according to any one of the preceding claims, which is a direct current (DC) power cable, such as a cable operating or capable of operating at 320 kV or more, such as 650 kV or more. 10. Cable according to claim 1 or 2, characterized in that component (II) is an SSC PESP. 11. Cable according to claim. 1 or 2, characterized in that the component (II) is a PESP and is from 4.0 to 15.0 wt.% of the polymer composition. 12. Cable according to claim 1 or 2, characterized in that the component (II) is LLDPE and constitutes from 1.5 to 6 wt.% of the polymer composition. 13. Cable according to claim 1 or 6, characterized in that the component (II) is UHMWPE and constitutes from 5.0 to 10.0 wt.% of the polymer composition. 14. Cable according to any one of claims 1, 2, 10 or 11, characterized in that the PESP has a density of 930 to 937 kg/m ³ and MFR ₂ of 0.5 to 3.0 g/10 min. 15. A method for manufacturing a cable, comprising the steps of applying one or more conductors, preferably by (co)extrusion, an inner semi-conductive layer, an insulating layer and an outer semi-conductive layer, in that order, where the insulating layer contains a polymer composition according to any one of claims 1 to 14 , and optionally crosslinking the insulating layer. -