RU2803930C1 - Semiconducting polymer composition - Google Patents

Abstract

FIELD: semiconductive polymer composition.

SUBSTANCE: present invention is related to a group of inventions: a semiconductive polymer composition, a product, a method for producing a semiconductive polymer composition, a method for producing a cable, and the use of polyethylene wax. The semiconductive polymer composition contains an ethylene-vinyl acetate copolymer base polymer, at least 25 wt.% carbon black, 5-15 wt.% polyethylene wax, and 0.1-5 wt.% acid absorber. Semiconductive polymer composition is obtained by mixing the components in a mixing equipment. Polyethylene wax is used to reduce energy consumption when mixing a semiconductive polymer composition. The product is a layer in a multilayer cable or a cable. The method for producing a cable includes applying to one or more conductors a layer containing the semiconductive polymer composition.

EFFECT: development of a semiconductive polymer composition providing lower energy consumption during mixing without loss of mixing performance.

19 cl, 2 tbl, 4 ex

Description

FIELD OF THE INVENTION

The present invention relates to a semiconductive polymer composition containing a base polymer of ethylene vinyl acetate, EVA, a conductive component of carbon black and polyethylene wax. The present invention further relates to a layer in a multilayer cable, such as, for example, an associated semiconducting layer in a power cable containing a semiconducting polymer composition, methods for producing and/or manufacturing a semiconducting polymer composition, and a cable containing a semiconducting layer that is obtained from a semiconducting polymer composition, and the use of a semiconducting polymer composition to reduce energy consumption in preparing the mixture.

BACKGROUND OF THE ART

In wire and cable (W&C) applications, a typical cable contains at least one conductor surrounded by one or more layers of polymeric materials. In power cables, including medium voltage (MV), high voltage (HV), and extra high voltage (EHV) applications, the conductor is surrounded by several layers, including an inner semiconducting layer, an insulating layer, and an outer semiconducting layer, in that order. To these layers may be added additional layer(s), such as shielding layer(s) and/or auxiliary barrier layer(s), i.e. e. one or more waterproof layer(s) and one or more shell layer(s). In addition, the electrical properties that are important may differ between different cable applications, as in the case of alternating current (AC) cables and direct current (DC) cables.

The insulating layer and semiconducting layers usually consist of homo- and/or copolymers of ethylene, which are preferably cross-linked. LDPE (low density polyethylene, i.e. polyethylene obtained by radical polymerization at high pressure), cross-linked with peroxide, i.e. Dicumyl peroxide in combination with cable extrusion is the predominant material for cable insulation layer.

Conventional cables are usually produced by extruding layers on a conductor. Such polymer semiconducting layers are well known and widely used in dielectric power cables rated for voltages greater than 6 kV. Such layers are used to create intermediate resistivity layers between conductor and insulation, and between insulation and ground or neutral potential.

In addition, it is also known that cross-linking of polymers, i.e. polyolefins, significantly contributes to increasing the heat resistance and resistance to deformation, mechanical strength, chemical resistance and abrasion resistance of the polymer. Therefore, cross-linked polymers are widely used in various end applications, for example, for the specified application in the production of wires and cables (W&C).

Semiconducting layers are widely used in dielectric power cables for voltages above 6 kV. The purpose of the semiconducting layer is to provide a smooth interface with the electric field in the insulation, thereby extending the service life, that is, the long-term viability of the power cable, incl. by preventing partial discharges at the interface between the conductive and dielectric layers.

When preparing a semiconductive polymer composition for use in such a semiconductive layer, the composition is mixed during the mixing process using suitable mixing equipment, for example, using internal mixers such as Banbury or Bolling, single continuous screws such as BUSS mixers, or twin continuous screws. action, such as Farrel, or continuous mixers, such as Werner & Pfleiderer. The composition contains, for example, a polymer, a conductive component such as carbon black, and optionally other additives. If a semiconducting polymer composition is to be used in a cross-linked layer, peroxide may be added to the composition, i.e. at the impregnation stage, which is carried out after mixing. After a mixing and optional impregnation step, cables are typically produced by extruding various layers of conductor.

During the mixing process, the composition is mixed at elevated temperatures. For this and other reasons, the mixing process consumes a lot of energy, and more energy-efficient production of semiconducting polymer compositions would be desirable.

BRIEF DESCRIPTION OF THE INVENTION

The inventors of the present invention have discovered that by adding polyethylene wax to a semiconducting polymer composition, it is possible to achieve lower energy consumption during mixing without loss of mixing performance. The composition of the present invention contains polyethylene wax to reduce energy consumption when mixing the semiconducting polymer composition compared to a conventional semiconducting polymer composition without such additive. Without wishing to be bound by theory, it is believed that the composition provides a process advantage either due to the composition itself or through improved interaction between the mixing equipment and the composition, which reduces the energy consumption of the mixing equipment during the mixing process.

Thus, in one aspect, the present invention relates to a semiconducting polymer composition comprising:

(a) a base polymer of ethylene-vinyl acetate copolymer,

(b) at least 25 wt. % soot and

(c) from 1 to 15 wt. % polyethylene wax.

The authors of the present invention unexpectedly discovered that when adding from 1 to 15 wt. % polyethylene wax due to the main polymer, energy consumption during the mixing process is reduced by approximately 10%. This is usually achieved without the need to adjust other compounds in the composition (such as, for example, soot content). Thus, processes following the mixing stage, such as cable production, can be carried out without additional equipment. Thus, polyethylene wax can be referred to as an energy consumption reducing component resulting in lower energy consumption during mixing of a semiconductive polymer composition compared to a corresponding composition containing no polyethylene wax or containing a different amount of polyethylene wax.

Moreover, it is also known that at elevated temperatures, the EVA copolymer is susceptible to thermal decomposition, which leads to the formation of acetic acid and unsaturation on the polymer backbone (B. Sultan et. al, J. App. Pol. Sci., Vol 43, Issue 9 , p. 1737). The formation of acetic acid is undesirable, as it can lead to corrosion of production equipment. Reducing the energy consumption of the mixing process may result in a reduction in the temperature of the mixing equipment and therefore a reduction in acetic acid production.

In yet another aspect, the present invention relates to an article comprising semiconducting layer(s) that are derived from a semiconducting polymer composition as defined above, where the article is, for example, a layer in a multilayer cable, for example, a layer of a power cable or cable, such as a power cable. Thus, the article may be a multilayer cable layer, for example a power cable layer, wherein said layer comprises a semiconducting polymer composition as defined above. The layer may, for example, be a bonded layer in said multilayer cable.

In another aspect, the present invention relates to a method for preparing a semiconducting polymer composition, as defined above, by mixing. The mixing process typically involves heating said polymer composition to a temperature above the melting point of at least the major polymer component(s) of the composition, which typically occurs at a temperature greater than 10° C. higher, preferably more than 25°C above the melting temperature of the polymer component(s) and below the undesirable decomposition temperature of the components.

The present invention also relates to a method for making a cable, comprising the steps of: coating one or more conductors with a layer containing a semiconducting polymer composition as defined above.

In one aspect, the present invention relates to the use of polyethylene wax to reduce energy consumption during mixing of a semiconducting polymer composition, as defined above.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

By semiconducting polymer composition as used herein, it is meant that the polymer composition contains a conductive filler, such as, for example, carbon black in an amount that provides semiconductivity. The expression "semiconducting polymer composition" is well known for polymer compositions used in semiconducting materials, such as semiconducting layers of cables, as is well known to those skilled in the art.

Polyethylene wax, as used herein, means a polyethylene polymer having an average molecular weight between 600 and 8000 g/mol, preferably between 800 and 6000 g/mol, or between 800 and 5000 g/mol, more preferably between 1000 and 4000 g/mol .

The term "wax" may additionally or alternatively be considered as a polymer having an MFR ₂ value (melt flow rate at 2.16 kg load) greater than 1200 g/10 min. Thus, as used herein, the term "polyethylene wax" may be replaced by the term "polyethylene copolymer having an MFR ₂ greater than 1200 g/10 min."

The term "polyethylene" means an ethylene-based polymer, i.e. one that contains at least 50 wt. % ethylene based on the total weight of the polymer. The terms "polyethylene" and "ethylene-based polymer", as used herein, are used interchangeably and mean a polymer that contains a majority of polymerized ethylene monomer by weight (based on the total weight of polymerizable monomers) and optionally may contain at least one polymerized comonomer. The ethylene-based polymer may include more than 50, or more than 60, or more than 70, or more than 80, or more than 90 wt. % units derived from ethylene (based on total weight of ethylene-based polymer).

The low density polyethylene, LDPE, of the present invention is a polyethylene produced by a high pressure process. Typically, polymerization of ethylene and optional additional comonomer(s) in a high pressure process is carried out in the presence of initiator(s). The meaning of the term LDPE is well known and described in the literature. The term LDPE describes and distinguishes high-density polyethylene from low-density polyethylene produced in the presence of an olefin polymerization catalyst. LDPEs have some typical features, such as different branching architectures. The typical density range of LDPE is from 0.900 to 0.960 g/cm ³ .

The term "conductor", as used herein, means a conductor containing one or more wires. The wire can be for any application and be, for example, an optical, telecommunications or electrical wire. Moreover, the cable may contain one or more such conductors. The conductor is preferably an electrical conductor and contains one or more metal wires.

Ethylene-vinyl acetate copolymer (a)

The copolymer of ethylene and vinyl acetate (a) in the context of the present invention is polyethylene, i.e. contains ethylene as the main monomer component. The polyethylene copolymer (a) contains vinyl acetate as a comonomer and may contain one or more additional comonomers. As is well known, "comonomer" refers to the copolymerizable comonomer units.

The ethylene vinyl acetate copolymer(s) is produced by a high pressure polymerization process, preferably by radical polymerization in the presence of initiator(s). Thus, copolymer (a) is low density polyethylene (LDPE). It should be noted that high pressure polyethylene (HPPE) is referred to herein as LDPE, a term that has a well-known meaning in the polymer field. Although the term LDPE is an abbreviation for low-density polyethylene, the term is not intended to be limiting to a range of densities, but to cover low-, medium-, and high-density LDPE-like HDPEs. The term LDPE describes and characterizes only the nature of high-density polyethylene with typical characteristics such as a high degree of branching.

The preferred ethylene vinyl acetate copolymer (a) is an LDPE copolymer, i.e. a low density copolymer of ethylene, vinyl acetate and optionally one or more other comonomers (referred to herein as EVA copolymer). One or more other comonomers of the EVA copolymer, if present, are preferably selected from polar comonomer(s), non-polar comonomer(s), or a mixture of polar comonomer(s) and non-polar comonomer(s) as defined below. In addition, said EVA copolymer may be unsaturated. It should be understood that if one or more other comonomers are present, the vinyl acetate comonomer constitutes a majority of any other comonomer present in the composition.

In one preferred embodiment, the one or more other comonomers include a polar comonomer. By “polar” comonomer is meant a comonomer containing at least one polar bond and having a net electric dipole, that is, a net positive charge region and a net negative charge region.

As the polar comonomer related to one or more other polar comonomers, compounds containing hydroxyl groups, alkoxy groups, carbonyl groups, carboxyl groups, ether groups or ester groups or a mixture thereof can be used. More preferably, said polar comonomer, if present, is comonomer(s) containing carboxyl group(s) and/or ester group(s). Even more preferably, the optional polar comonomer(s) of the EVA copolymer is selected from the acrylate(s), methacrylate(s) or acetate(s) groups or any mixtures thereof.

Polar comonomer(s), if present in said EVA copolymer, are preferably selected from the group of alkyl acrylates, alkyl methacrylates, or mixtures thereof. More preferably, said polar comonomer(s) is selected from C1-C6 alkyl acrylates, C1-C6 alkyl methacrylates. Even more preferably, said polar EVA copolymer is a copolymer of ethylene and a C1-C4 alkyl acrylate, for example methyl, ethyl, propyl or butyl acrylate, or any mixture thereof, more preferably a copolymer of ethylene and methyl, ethyl or butyl acrylate or any mixtures of them.

As an optional non-polar comonomer(s) for the EVA copolymer, comonomer(s) other than the above-mentioned polar comonomers can be used as the preferred copolymer(s). Preferably, the non-polar comonomers are other than comonomer(s) containing hydroxyl group(s), alkoxy group(s), carbonyl group(s), carboxyl group(s), group(s). s) ether or ester. One group of preferred non-polar comonomers includes, preferably consists of, monounsaturated (i.e., one double bond) comonomers, preferably olefins, preferably alpha olefins, more preferably C3-C10 alpha olefins such as propylene, 1-butene, 1- hexene, 4-methyl-1-pentene, polyunsaturated (i.e. with more than one double bond) comonomers such as 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene , 7-methyl-1,6-octadiene, 9-methyl-1,8-decadiene or mixtures thereof, silane group containing comonomer(s), or any mixtures thereof.

As mentioned above, the EVA copolymer may not necessarily be unsaturated, i.e. may contain carbon-carbon double bonds (-C=C-). Unsaturation may be provided by one or more of the following: a chain transfer agent (CTA), one or more polyunsaturated comonomer(s), or polymerization conditions.

As used herein, the fact that an ethylene vinyl acetate copolymer (a) is “unsaturated” means that the copolymer contains carbon-carbon double bonds. Carbon-carbon double bonds mean unsaturation in the context of this document. Polyethylene, as used herein, may contain vinyl groups, for example allyl groups. Vinyl groups are functional groups containing carbon-carbon double bonds. As used herein, the term "vinyl group" has its generally accepted meaning, i.e. fragment "-CH=CH2". In addition, polyethylene may additionally contain other functional groups also containing carbon-carbon double bonds. Other functional groups also containing carbon-carbon double bonds may be, for example, vinylidene groups and/or vinylene groups. The vinylene group has a cis or trans configuration. For the avoidance of doubt, vinylidene groups and vinylene groups are not vinyl groups as used herein. Typically, these unsaturated polyolefins have a double bond content of greater than 0.1 double bonds/1000 carbon atoms.

Another embodiment in accordance with the present invention relates to a semiconducting polymer composition, wherein the ethylene-vinyl acetate copolymer (a) optionally contains unsaturation provided, for example, by copolymerizing ethylene and vinyl acetate and at least one polyunsaturated comonomer (i.e., to produce a terpolymer ) and/or, for example, using a chain transfer agent, for example propylene.

It is well known that, for example, propylene can be used as a comonomer or as a chain transfer agent (CAA), or both, and it can contribute to unsaturation, for example, the number of vinyl groups in polyethylene. As used herein, when using a copolymerizable APC such as propylene, the copolymerized APC is not calculated based on the original comonomer content.

Polyunsaturated comonomers suitable for the optional unsaturated copolymer of ethylene and vinyl acetate (a) 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 polyunsaturated comonomer is a diene, preferably a diene containing at least eight carbon atoms, wherein the first carbon-carbon double bond is terminal and the second carbon-carbon double bond is not conjugated to the first. Preferred dienes are selected from C8-C14 non-conjugated dienes or mixtures thereof, more preferably selected from 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, 7-methyl-1,6-octadiene , 9-methyl-1,8-decadiene or mixtures thereof. Even more preferably, the diene is selected from 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, or any mixture thereof.

Typically, and preferably in wire and cable (W&C) applications, the density of the copolymer(s), preferably the preferred EVA copolymer, is greater than 900 kg/m ³ . Preferably, the density of the copolymer, preferably the preferred EVA copolymer, does not exceed 960 kg/m ³ . Typically, densities range from 900 to 960 kg/m ³ , for example from 910 to 950 kg/m ³ , for example from 920 to 945 kg/m ³ .

The MFR ₂ (2.16 kg, 190°C) of copolymer (a), preferably the preferred EVA copolymer, depends on the desired end use, as is well known to those skilled in the art. Preferably, the MFR ₂ (2.16 kg, 190° C.) of copolymer (a), preferably the preferred EVA copolymer, is up to 150 g/10 min, for example up to 100 g/10 min. Typical ranges are 0.01 to 50, preferably 0.05 to 40 g/10 min, more preferably 0.1 to 30 g/10 min, e.g. 0.5 to 20 g/10 min, e.g. from 1 to 15 g/10 min.

Ideally, the MFR ₂ value of ethylene vinyl acetate copolymer (a) is less than the MFR ₂ value of polyethylene wax (c).

The melting point of the copolymer (a) is usually above 50°C, more preferably above 60°C, and most preferably 80°C or above. The melting point of the copolymer (a) is preferably below 125°C, more preferably below 120°C, more preferably below 115°C.

Although, within the scope of the present invention, the ethylene vinyl acetate copolymer(a) may contain one or more comonomers in addition to vinyl acetate, it is preferred that the sole comonomer be vinyl acetate, i.e. The copolymer consists of ethylene and vinyl acetate monomer units. If other comonomers are present, they may be selected from those described above as optional "polar" or "nonpolar" comonomers. Preferably, the ethylene-vinyl acetate copolymer (a) is not a mixture or mixture of different ethylene-vinyl acetate copolymers.

The total comonomer content of the copolymer (a), preferably the EVA copolymer as the preferred copolymer (a), is preferably up to 70 wt. %, more preferably up to 60 wt. %, for example, up to 50 wt. %. Typically the comonomer content is from 0.001 to 50 wt. %, more preferably from 0.05 to 40 wt. %, even more preferably less than 35 wt. %, even more preferably less than 30 wt. %, more preferably less than 25 wt. % to the total mass of the copolymer. Typically the content is from 0.5 to 40 wt. %, preferably from 1 to 35 wt. % preferably from 2 to 30 wt. %, for example from 3 to 25 wt. %, for example from 5 to 20 wt. % of the total amount of the specified copolymer.

The content of vinyl acetate in the copolymer (a) is preferably from 1 to 35 wt. %, more preferably from 1.5 to 32 wt. %, more preferably from 2 to 28 wt. %, more preferably from 2.5 to 25 wt. %, even more preferably from 3 to 22 wt. %, for example from 4 to 20 wt. %, especially from 5 to 19 wt. %, for example from 10 to 18 wt. %, for example from 12 to 16 wt. % relative to the total weight of the copolymer.

Accordingly, the preferred ethylene-vinyl acetate copolymer (a) of the present invention is a LDPE copolymer, and is preferably produced at high pressure by free radical polymerization (called high pressure radical polymerization (HP)). The high pressure reactor may be, for example, a well known tubular or autoclave reactor or a combination thereof, preferably a tubular reactor. High pressure (HP) polymerization and adjustment of process conditions to further develop 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 one skilled in the art. Suitable polymerization temperatures are up to 400°C, preferably from 80 to 350°C, and pressure from 70 MPa, preferably from 100 to 400 MPa, more preferably from 100 to 350 MPa. The pressure can be measured at least after the compression stage and/or after the tubular reactor. Temperature can be measured at several points during all stages.

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

Additional information on the preparation of ethylene (co)polymers by high-pressure radical polymerization can be found, in particular, in the publications 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. Mähling pp. 7181-7184.

The ethylene-vinyl acetate copolymer (a) is present in the semiconducting polymer composition of the present invention in an amount of at least 30 wt. %, or at least 40 wt. %, or at least 50 wt. % relative to the total weight of the composition as a whole. Preferred amounts may range from 30 to 73 wt. %, more preferably from 30 to 70 wt. %, for example from 32 to 68 wt. %, for example from 35 to 65 wt. % or from 45 to 60 wt. %

Ethylene vinyl acetate used as component (a) is different from polyethylene wax (c).

Soot (b)

The semiconducting polymer composition of the present invention contains at least 25 wt. % soot. Depending on the desired application, the conductivity of the carbon black and the conductivity of the composition, the amount of carbon black may vary. The semiconducting polymer composition contains, for example, from 25 to 60 wt. %, preferably from 28 to 55 wt. %, more preferably from 30 to 50 wt. %, for example from 35 to 45 wt. % carbon black based on the total weight of the semiconducting polymer composition.

According to at least one illustrative embodiment, the amount of soot is at least 25 wt. %, for example at least 30 wt. % or at least 35 wt. %, relative to the total mass of semiconducting compositions. Preferably, the soot content in semiconducting compositions does not exceed 45 wt. % or does not exceed 40 wt. % relative to the total mass of semiconducting compositions. Thus, the amount of soot can be from 25 to 45 wt. %, or from 25 to 40 wt. %, or from 30 to 45 wt. %, or from 30 to 40 wt. %, or from 34 to 41 wt. % relative to the total mass of semiconducting compositions.

Any electrically conductive carbon black can be used. Typically, the carbon black is a special carbon black or P-type carbon black. Non-limiting examples of suitable carbon blacks include furnace black and acetylene black.

The carbon black may have a nitrogen adsorption surface area (NSA) of from 5 to 400 m ² /g, for example from 10 to 300 m ² /g, i.e. from 30 to 200 m ² /g when determined in accordance with ASTM D6556-19. In addition, the carbon black may have one or more of the following properties: i) a primary particle size of at least 5 nm, for example from 10 to 30 nm or from 11 to 20 nm, which is defined as the average particle diameter in accordance with ASTM D3849- 14, ii) iodine value of at least 10 mg/g, for example from 10 to 300 mg/g, for example from 30 to 250 mg/g, for example from 60 (or 61) to 200 mg/g, or from 80 to 200 mg/g, or 100 to 170 mg/g, when determined in accordance with ASTM D-1510-19, and/or iii) an oil absorption number (OAN) of at least 30 ml/100 g, e.g. 50 to 300 ml/100 g, for example from 50 to 250 ml/100 g, for example from 70 to 200 ml/100 g, for example from 90 to 130 ml/100 g or from 70 to 119 (or 120) ml/100 g when measured in accordance with ASTM D 2414-19.

One group of suitable types of furnace black has a primary particle size of 28 nm or less. Particularly suitable furnace blacks in this category may have an iodine value between 60 and 300 mg/g. In addition, a suitable oil absorption number (of this category) is between 50 and 225 ml/100 g, e.g. between 50 and 200 ml/100 g.

Other suitable types of carbon black may be produced by any other process or subjected to further processing. Suitable carbon blacks for semiconducting cable layers are characterized by their purity. Therefore, suitable carbon blacks have an ash content of less than 0.2 wt. %, measured in accordance with ASTM D1506, 325 mesh sieve residue less than 30 parts per million (ppm) in accordance with ASTM D1514 and less than 3 wt. %, preferably less than 1 wt. % total sulfur according to ASTM D1619.

Furnace black is a generally accepted term for a well-known type of soot produced in a furnace-type reactor. As examples of carbon black, its production process and reactors, reference may be made in particular to EP629222 from Cabot, US 4391789, US 3922335 and US 3401020. Examples of commercial furnace blacks include grades N115, N351, N293, N220 and N550. To improve the usefulness of such types of carbon black in semiconducting compounds, modifications of such types of commercial carbon black, for example, from the point of view of purity, granule properties and surface area are preferred. Furnace black is generally distinguished from acetylene black, which is another type of carbon black suitable for semiconducting polymer compositions.

Acetylene blacks are produced by the acetylene black production process as described in US Pat. No. 4,340,577. In particular, acetylene blacks may have a particle size greater than 20 nm, for example from 20 to 80 nm. The average primary particle size is defined as the average particle diameter according to ASTM D3849-14. Suitable acetylene blacks in this category have an iodine value between 30 and 300 mg/g, for example between 30 and 150 mg/g according to ASTM D1510. In addition, the absorption number of the oil (of this category) is, for example, between 80 and 300 ml/100 g, i.e. between 100 and 280 ml/100 g and measured according to ASTM D2414. The term acetylene black is generally accepted and well known, supplied by Denka.

Polyethylene wax (c)

The polyethylene wax (c) may be high-density polyethylene, typically high-density LDPE, prepared in a manner similar to that described above for ethylene-vinyl acetate copolymer (a) (except using vinyl acetate as the comonomer). The polyethylene wax can be selected from homopolymers of polyethylene as well as copolymers of polyethylene with one or more comonomers and can be produced by a high pressure or low pressure process. Thus, the polyethylene wax (c) is selected from a homopolymer or copolymer of ethylene obtained in the presence of a coordination catalyst or obtained by a high pressure polymerization process. Polyethylene may be unimodal or multimodal in terms of molecular weight distribution and/or comonomer distribution, these expressions having a well-known meaning.

In at least one exemplary embodiment, the polyethylene wax (c) is polyethylene produced in the presence of an olefin polymerization catalyst. "Olefin polymerization catalyst" as used herein preferably means a conventional complex catalyst. It is preferably selected from a Ziegler-Natta catalyst, a single site catalyst that includes a metallocene and a non-metallocene catalyst, or a chromium catalyst, or any mixture thereof. The terms have a commonly known meaning. Polyethylene polymerized in the presence of an olefin polymerization catalyst is also often called "low-pressure polyethylene" to clearly distinguish it from polyethylene produced at high pressure. Both terms are well known in the polyolefin field. Low-density polyethylene can be produced through a polymerization process that includes: in bulk, suspension, solution or gas phase or any combination thereof. The olefin polymerization catalyst is typically a coordination catalyst as defined above.

If the polyethylene wax (c) is a low-density polyethylene (PE), the low-density PE is preferably selected from a very low density ethylene copolymer (VLDPE), a linear low density ethylene copolymer (LLDPE), a medium density ethylene copolymer (MDPE) or a homopolymer or high density ethylene copolymer (HDPE). These well-known types are named according to their area density. The term VLDPE includes, as used herein, polyethylenes, which are also known as plastomers and elastomers and have a density between 850 and 909 kg/m ³ . LLDPE has a density of 909 to 930 kg/m ³ , preferably 910 to 929 kg/m ³ or 910 to 925 kg/m ³ , more preferably 915 to 929 kg/m ³ . PESP has a density of 930 to 945 kg/m ³ , preferably 931 to 945 kg/m ³ . HDPE has a density greater than 945 kg/m ³ , preferably greater than 946 kg/m ³ , preferably 946 to 977 kg/m ³ , more preferably 946 to 965 kg/m ³ .

More preferably, such low pressure ethylene copolymer for polyethylene wax (c) is copolymerized with at least one comonomer selected from a C3-20 alpha olefin, more preferably from a C4-12 alpha olefin, more preferably from a C4-8 alpha olefin, for example with 1-butene, 1-hexene or 1-octene or a mixture thereof. The amount of comonomer(s) present in the PE copolymer ranges from 0.1 to 15 mol%, typically from 0.25 to 10 mol%.

Moreover, when the polyethylene wax (c) is a low pressure PE polymer, then such PE may be unimodal or multimodal in terms of molecular weight distribution (MWD=Mw (weight average molecular weight)/Mn (number average molecular weight). Generally, a polymer consisting of at least two polymer fractions that have been produced under different polymerization conditions (including, but not limited to, any process parameters, feedstock feeds, process control agent feeds, and catalyst system feeds) resulting in different (weighted average) molecular weights and molecular weight distributions for the fractions are called "multimodal". The prefix "multi" refers to the number of different polymer fractions present in the polymer. For example, a multimodal polymer includes a so-called "bimodal" polymer consisting of two fractions. Shape of the curve molecular weight distribution, i.e., the appearance of a graph of the mass fraction of a polymer versus its molecular weight, a multimodal polymer will have two or more maxima or, as a rule, a distinct expansion compared to the curves for individual fractions.

Unimodal low-pressure PE can be produced, for example, by one-step polymerization in one reactor in a well-known and documented manner. Multimodal (eg, bimodal) low-density polyethylene can be produced, for example, by mechanical mixing of two or more separate polymer components or, preferably, by in-situ mixing during the polymerization process of the components. Both mechanical mixing and in situ mixing are well known in the art. In situ mixing means polymerization of polymer components under different polymerization conditions, e.g. two or more stages of the polymerization process, or using two or more different polymerization catalysts, in a single-stage polymerization process, or using a combination of a multi-stage polymerization process and two or more different polymerization catalysts. The polymerization zones can be operated under bulk, slurry, solution, or gas phase conditions, or any combination thereof, as is known in the art.

According to another embodiment, the polyethylene wax (c) is polyethylene produced by a high pressure polymerization process, preferably by radical polymerization in the presence of initiator(s). More preferably, the polyethylene wax (c) is low density polyethylene (LDPE). It should be noted that high pressure polyethylene (HPPE) is referred to herein generally as LDPE, and this term has a well-known meaning in the polymer field as previously described. Although the term LDPE is an abbreviation for low-density polyethylene, the term is not intended to limit a range of densities, but rather to cover LDPE-like high-density polyethylenes of low, medium and high density. The term LDPE describes and characterizes only the nature of high-density polyethylene with typical features, such as a high degree of branching, compared to PE obtained in the presence of an olefin polymerization catalyst.

The semiconducting polymer composition of the present invention contains from 1 to 15 wt. % polyethylene wax (c). The semiconducting polymer composition contains, for example, from 2 to 15 wt. %, or from 2 to 10 wt. %, or from 1 to 10 wt. %, for example from 1 to 9 wt. %, for example from 2 to 8 wt. %, or from 3 to 7 wt. %, or about 5 wt. %, or from 1 to 5 wt. %, or from 1 to 3 wt. % polyethylene wax based on the weight of the semiconducting polymer composition. According to at least one illustrative embodiment, the polyethylene wax is present in an amount of at least 3 wt. %, for example at least 5 wt. % or at least 7 wt. %, relative to the total mass of semiconducting polymer compositions. Preferably, the content of polyethylene wax in semiconducting polymer compositions does not exceed 15 wt. % relative to the total mass of semiconducting polymer compositions. Thus, polyethylene wax may be present in an amount of from 3 to 15 wt. %, or from 5 to 15 wt. %, or from 7 to 15 wt. %, or from 10 to 15 wt. % relative to the total mass of semiconducting polymer compositions.

In at least one exemplary embodiment, the polyethylene wax (c) has an MFR ₂ (2.16 kg, 190°C) of at least 1200 g/10 min.

The polyethylene wax may, according to at least one exemplary embodiment, have an average molecular weight between 600 and 8000 g/mol, for example between 800 and 6000 g/mol or between 1000 and 5000 g/mol, for example between 1000 and 4000 g /mol, for example between 2000 and 4000 g/mol or between 3000 and 4000 g/mol, for example about 3500 g/mol.

The polyethylene wax may, in at least one illustrative embodiment, have a softening or melting point of from 90 to 130°C or from 100 to 130°C, for example from 100 to 120°C or from 100 to 110°C.

Polymer composition

In addition to components (a)-(c) described above, the semiconducting polymer composition of the present invention may contain additional components, typically additives, such as antioxidants, crosslinking accelerators, polymerization retarders, processing aids, fillers, coupling agents, ultraviolet absorbers radiation, stabilizers, antistatic agents, nucleators, glidants, plasticizers, lubricants, viscosity adjusting agents, tackifying agents, release agents, surfactants, extender oils, acid scavengers and/or metal deactivators. These additives are well known in the industry and one skilled in the art will be familiar with their use. Any additives present may be added as isolated raw materials or in mixture with the carrier polymer, i.e. the so-called masterbatch.

In a particularly preferred embodiment, the composition of the present invention contains an acid scavenger that includes compounds that are metal salts of long chain carboxylic acids, such as metal stearates, lactates, natural or synthetic silicates, such as hydrotalcites, metal oxides (for example, magnesium oxide, calcium, zinc oxide), metal carbonates (eg calcium carbonate) and metal hydroxides. Ideally, the acid scavenger is a metal stearate such as calcium stearate, zinc stearate, sodium stearate, lithium stearate or magnesium stearate. Zinc stearate is particularly preferred.

The acid scavenger, if present, is typically at least 0.1 wt. % of the total weight of the composition as a whole. Thus, the approximate amount of acid scavenger is from 0.1 to 5.0 wt. %, preferably from 0.2 to 4.0 wt. %, more preferably from 0.3 to 3.0 wt. %, for example from 0.4 to 2.0 wt. %, or from 0.2 to 2.0 wt. %, or from 0.2 to 1 wt. %, relative to the total weight of the polymer composition.

In yet another preferred embodiment, the composition contains an antioxidant. Examples of such antioxidants include, but are not limited to: hindered phenols such as tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane, bis[(beta-(3,5-di-tert -butyl-4-hydroxybenzyl)-methylcarboxyethyl)]sulfide, 4,4'-thiobis(2-methyl-6-tert-butylphenol), 4,4'-thiobis(2-tert-butyl-5-methylphenol), 2 ,2'-thiobis(4-methyl-6-tert-butylphenol), 2,2'-thiodiethylenebis-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate, 4,6-bis(octylthiomethyl) -o-cresol and thiodiethylene bis(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate, phosphites and phosphonites such as tris(2,4-di-tert-butylphenyl)phosphite and di-tert-butylphenylphosphonite, thio compounds such as dilauryl thiodipropionate, dimyristyl thiodipropionate and distearyl thiodipropionate, various siloxanes; polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), n,n'-bis(1,4-dimethylpentyl-p-phenylenediamine), alkylated diphenylamines, 4,4'-bis(1,1' -alpha,alpha-dimethylbenzyl)diphenylamine, diphenyl-p-phenylenediamine, mixed diaryl-p-phenylenediamines, 2,2'-oxamidobis-(ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate ) and other hindered amines that prevent decomposition or stabilizers. A more preferred antioxidant is 4,4'-bis(1,1'-dimethylbenzyl)diphenylamine. A particularly preferred antioxidant is TMX.

Antioxidants can be used in amounts from 0.1 to 5.0 wt. %, preferably from 0.1 to 2 wt. % or from 0.15 to 2 wt. %, more preferably from 0.2 to 2 wt. % or from 0.2 to 1.5 wt. %, even more preferably from 0.25 to 1.0 wt. %, for example from 0.3 to 0.8 wt. %, especially from 0.35 to 0.7 wt. %, based on the weight of the composition.

Examples of filler additives include: clays, precipitated silica and silicates, colloidal silicon dioxide, calcium carbonate, ground minerals and other types of carbon black. Fillers can be used in amounts from less than about 0.01 to more than about 40 wt. % based on the weight of the composition.

In embodiments where the semiconducting polymer composition is a crosslinkable composition, it may also contain a crosslinking agent. Typical amounts of crosslinking agent range from 0.01 to 4.0 wt. %, preferably from 0.02 to 2.0 wt. %, more preferably from 0.03 to 1.5 wt. %, for example from 0.05 to 1.2 wt. %, especially from 0.1 to 1.0 wt. %, relative to the total weight of the composition.

The preferred crosslinking agent is a peroxide. Non-limiting examples are organic peroxides such as di-tert-amyl peroxide, 2,5-di(tert-butylperoxy)-2,5-dimethyl-3-hexine, 2,5-di(tert-butylperoxy)-2,5 -dimethylhexane, tert-butylcumyl peroxide, di(tert-butyl)peroxide, dicumyl peroxide, butyl-4,4-di(tert-butylperoxy)-valerate, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane , tert-butylperoxybenzoate, dibenzoyl peroxide, di(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-butyl cumyl peroxide, di(tert-butyl) peroxide or mixtures thereof.

Scene retarders that can be used in the present invention include unsaturated dimers of aromatic alpha-methylalkenyl monomers such as 2,4-di-phenyl-4-methyl-1-pentene, substituted or unsubstituted diphenylethylene, quinone derivatives, hydroquinone derivatives, monofunctional vinyl-containing esters and ethers, monocyclic hydrocarbons having at least two or more double bonds, or mixtures thereof. For example, the scorch retarder may be selected from 2,4-diphenyl-4-methyl-1-pentene, substituted or unsubstituted diphenylethylene, or mixtures thereof.

Typically, ethylene vinyl acetate copolymer (a) and polyethylene wax (c) are the only polymer components present in the polymer composition. However, it should be understood that the polymer composition may contain additional components, such as additives, which may optionally be added to the mixture with the carrier polymer, i.e. into the so-called masterbatch.

According to at least one exemplary embodiment, the semiconductive polymer composition is substantially free of or does not include rubber, such as, for example, ethylene propylene rubber or ethylene propylene non-conjugated diene terpolymer. Therefore, the semiconductive composition of the present invention is preferably substantially free of rubber (eg, less than 0.5 wt% rubber, preferably less than 0.1 wt% rubber, e.g. less than 0.05 wt% rubber, based on total weight of the composition). Even more preferably, the semiconductive composition does not contain added rubber (ie, contains 0 wt.% rubber relative to the total weight of the composition). In other words, said semiconducting resin composition is preferably a semiconducting resin composition not containing rubber.

According to at least one exemplary embodiment, the content of vinyl acetate in component (a) is between 3.0 and 25 wt. %, the amount of component (c) is between 1.0 and 10 wt. % and the amount of carbon black (b) in the semiconducting polymer composition is between 34 and 41 wt. %. According to another embodiment, the vinyl acetate content of component (a) is between 5.0 and 25 wt. %, the amount of component (c) is between 1.0 and 7 wt. % and the amount of carbon black (b) in the semiconducting polymer composition is between 34 and 41 wt. % According to another embodiment, the content of vinyl acetate in component (a) is between 5.0 and 20 wt. % and the amount of component (c) is between 2.0 and 8 wt. % and the amount of carbon black (b) in the semiconducting polymer composition is between 34 and 41 wt. % According to another embodiment, the content of vinyl acetate in component (a) is between 10 and 20 wt. % and the amount of component (c) is between 3 and 7 wt. % and the amount of carbon black (b) in the semiconducting polymer composition is between 34 and 41 wt. % According to another embodiment, the vinyl acetate content of component (a) is between 11 and 19 wt. % and the amount of component (c) is between 3 and 7 wt. % and the amount of carbon black (b) in the semiconducting polymer composition is between 34 and 41 wt. %

Preparation of a polymer composition

In yet another aspect, the present invention relates to a method for preparing a semiconducting polymer composition comprising:

(a) a base polymer of ethylene-vinyl acetate copolymer,

(b) at least 25 wt. % soot and

(c) from 1 to 15 wt. % polyethylene wax.

The method may, for example, include mixing components (a) to (c) at a temperature of less than 240°C.

Another embodiment of the present invention relates to a method for producing a semiconducting polymer composition, as defined herein, comprising mixing and/or combining (eg, mixing) components (a)-(c) at a temperature below 240°C. Preferred temperatures are from 155 to 235°C, for example from 160 to 230°C.

Such elevated temperature mixing is generally referred to as melt mixing and is typically carried out at a temperature greater than 10°C, preferably greater than 25°C, above the melting temperature of the polymer component(s) and below the undesirable decomposition temperature components.

The specified temperature is usually the highest temperature encountered during the mixing stage, such as, for example, in a drum mixer of mixing equipment after all the carbon black has been added, but before the composition is discharged to subsequent functions.

The most preferred production method involves mixing the various components, usually by extrusion.

Preferably, said method of producing the invention further includes the step of granulating the resulting polymer mixture. The granulation can be influenced in a well known manner using conventional granulation equipment, such as preferably a conventional granulation extruder which is built into said mixing device. The method of the present invention can be carried out in a batch or continuous manner.

The devices used to carry out the method of the present invention are, for example, a single-screw or twin-screw mixer, or a mixing extruder, or a combination thereof, which are preferably integrated into the granulation device. The device(s) may be operated in batch mode or, preferably, in continuous mode. The method may include an additional subsequent screening step prior to the preferred granulation step, which is also commonly used in the prior art in the preparation of semiconducting polymer compositions to limit the number of large particles.

According to at least one exemplary embodiment, such a device may be a mixer including a drum mixer where the composition melt is mixed, for example, with one or more carbon black addition hoppers and a discharge extruder or gear pump located downstream of the mixer body. The mixer may, for example, be a single-screw machine that oscillates axially once per revolution, where fixed pins in the mixer body of the device interact with gaps in the screw. This provides elongation mixing, which provides effective dispersive mixing in a relatively short drum. The temperature can be controlled by adding carbon black to the polymer melt in one or more bins. The output can, for example, be 3.5 t/h and 750 rpm.

When adding from 1 to 15 wt. % polyethylene wax, the energy consumption of mixing equipment, such as a mixer, is reduced compared to mixing corresponding semiconducting polymer compositions containing no polyethylene wax or containing a different amount of polyethylene wax. The reduction in energy consumption may, for example, be at least 1%, or at least 3%, or at least 5%, or at least 7%, or at least 9%, or at least 11%.

End uses

Another embodiment of the present invention relates to an article, preferably a cable (eg, a power cable), comprising at least one layer, wherein said layer comprises a semiconducting polymer composition as described herein. Another embodiment of the present invention relates to a layer in a multilayer cable, such as a power cable layer, wherein said layer comprises a semiconducting polymer composition as described herein. The multilayer cable may, for example, have at least 3 layers, for example an inner semiconducting layer, an outer semiconducting layer and an insulating layer located between them.

Said cable layer containing the semiconducting polymer composition is preferably a semiconductive layer and thus are used interchangeably herein.

In addition, the cable of the present invention may be, for example, a power cable comprising a conductor surrounded by at least a semiconducting layer containing, preferably consisting of, a polymer composition of the present invention.

Ideally, a cable will comprise a conductor surrounded by at least an inner semiconducting layer, an insulating layer and an outer semiconducting layer in a given order, wherein the semiconducting layer(s) contains, preferably consists of, semiconductive polymer composition as described herein. The present invention includes a semiconducting polymer composition of inner and outer semiconducting layers, which may be the same or different.

According to another embodiment of the power cable, the semiconductive layer(s) may be removable or non-removable, preferably non-removable, i.e. connected. These terms are known and describe the peelability of a layer, which may or may not be desirable depending on the end application. Thus, according to at least one exemplary embodiment, said layer is a bonded layer in said multilayer cable, such as, for example, an inner or outer semiconductive layer located in contact with the conductor of the cable.

In the case of a release semiconducting layer, the EVA copolymer of the present invention is more polar with a polar comonomer content of at least 20.0 wt. %, for example at least 25.0 wt. %, preferably at least 26.0 wt. %, more preferably from 27.0 to 35.0 wt. % based on the weight of said EVA copolymer and may contain additional polar polymer components that contribute to peelability. Preferably, the permanent semiconductive layer (eg, the inner or outer layer) has a polar comonomer content of less than 25.0 wt. %, preferably less than 20.0 wt. %, more preferably from 10.0 to 18.0 wt. %. In some embodiments, a polar comonomer content of from 6.0 to 15.0 wt may be desirable. % in terms of the specified EVA copolymer. Thus, according to at least one illustrative embodiment, the semiconducting polymer composition has a polar comonomer content of less than 25.0 wt. %, preferably less than 20.0 wt. %, more preferably from 10.0 to 18.0 wt. % or from 6.0 to 15.0 wt. % in terms of the specified EVA copolymer. In both removable and non-removable cases, the layer is preferably crosslinkable.

According to at least one exemplary embodiment, the semiconductive layer of the invention has a wire wrap tension of 8 kN/m or more, preferably more than 10 kN/m. The method used to measure such wire tension during wrapping is well known and is, for example, described in the methods section ("Strip force 90") in WO 2019002449.

The term "conductor" as used herein above and below means that a conductor contains one or more wires. Moreover, the cable may contain one or more such conductors. Preferably the conductor is an electrical conductor and contains one or more metal wires.

The cable of the present invention is preferably a power cable selected from medium voltage, high voltage and extra high voltage cables. The cable is preferably a medium voltage cable, a high voltage cable or an extra high voltage cable.

Insulating layers for medium or high voltage power cables are usually at least 2 mm thick, usually at least 2.3 mm, and the thickness increases with the voltage for which the cable is rated.

As is well known, the cable may optionally further comprise additional layers, for example layers surrounding an insulating layer or, if present, outer semiconducting layers such as shield layer(s), cladding layer(s), etc. protective layer(s) or any combination thereof.

The cable of the present invention may be stitchable. Accordingly, an even more preferred cable is a cross-linked cable, wherein at least one semiconductive layer contains a cross-linkable polymer composition of the present invention, which is cross-linked before subsequent end use.

The most preferred cable of the present invention is a power cable, preferably a stitchable one. Such a power cable ideally comprises a conductor surrounded by at least an inner semiconducting layer, an insulating layer and an outer semiconducting layer in a given order, the semiconducting layer(s) comprising, preferably consisting of: of a semiconducting polymer composition as described herein. Preferably, at least the inner semiconductive layer contains a polymer composition of the present invention, as defined above or below, or in the claims, including preferred embodiments. In this preferred embodiment of the cable, the outer semiconductive layer may optionally contain a polymer composition of the present invention, which may be identical or different from the polymer composition of the inner semiconductive layer. Moreover, at least the polymer composition of the present invention of the inner semiconductive layer is crosslinkable, preferably crosslinkable with peroxide, and crosslinking is carried out before subsequent final use. Preferably also the insulating layer is cross-linkable and the cross-linking is carried out before the subsequent final use. The outer semiconductive layer may not necessarily be crosslinkable and thus may be uncrosslinked or crosslinked, depending on the desired end application.

The present invention further relates to a method for producing a cable, preferably a power cable, comprising the following steps:

applying to one or more conductors a layer containing a semiconductive composition as described herein.

According to at least one exemplary embodiment, a method for producing a cable includes the following steps:

(i) preparing and mixing, preferably melt mixing in an extruder, a polymer composition, preferably in the form of granules, as defined above,

(ii) applying the melt mixture of the polymer composition obtained in step (i), preferably by (co)extrusion, onto the conductor to form at least one semiconducting layer, and

(iii) optionally and preferably cross-linking the resulting at least one semiconducting layer in the presence of a cross-linking agent.

In yet another embodiment, the present invention relates to a method for producing a cable, preferably a power cable, comprising the following steps:

(i) preparing and mixing, preferably melt mixing in an extruder, a first semiconductive composition as defined above, preferably in the form of granules, for the inner semiconductive layer,

- preparing and mixing, preferably melt mixed in an extruder, a polymer composition for the insulating layer,

- preparing and mixing, preferably melt mixing in an extruder, a polymer composition for the insulating layer,

- preparing and mixing, preferably melt mixing in an extruder, a second semiconductive composition comprising a polymer, carbon black and optionally additional component(s), preferably in the form of granules, for the outer semiconductive layer,

(ii) applying to the conductor, preferably by coextrusion,

- a melt mixture of the first semiconducting composition obtained in step (i) to form an internal semiconducting layer,

- a melt mixture of the polymer composition obtained in step (i) to form an insulating layer, and

- a melt mixture of the second semiconducting composition obtained in step (i) to form an outer semiconducting layer,

wherein at least one of the first semiconducting composition of the resulting inner semiconductive layer and the second semiconducting composition of the resulting outer semiconducting layer, preferably at least the first semiconducting composition of the resulting inner semiconducting layer comprises, preferably consists of, a polymer composition of the present invention.

The term "(co)extrusion", as used herein, 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 co-extruded in the same extrusion stage , as is well known in the art. The term "(co)extrusion" also means that all or part of the layer(s) are formed simultaneously using one extrusion head or sequentially using more than one extrusion head.

As is known, a melt mixture of a polymer composition or component(s) thereof is applied to form a layer. The mixing step can be carried out in a cable extruder. The melt mixing step may include a separate mixing step in a separate mixer, i.e. mixer located in the connection and preceding the cable extruder of the cable production line. Mixing in the preceding separate mixer can be accomplished by mixing with or without external heating (external source heating) of the component(s).

Typically, carbon black (b) and polyethylene wax (c) are mixed with ethylene vinyl acetate copolymer (a), i.e. by melt mixing, and the resulting melt mixture is granulated into granules for use in the cable production methods described above. Granules as used herein generally mean any polymer product formed from a reactor-produced polymer (obtained directly from the reactor) by post-reactor modification to solid polymer particles. Granules can be of any size and shape. The resulting granules are then used to produce cables.

All or a portion of optional other components, such as additional polymer component(s) or additive(s), may be present in the polymer composition prior to submission to the mixing step (i) of the cable preparation process or may be added, for example, by the cable manufacturer at the mixing stage (i) of the cable production process.

If, and preferably, the polymer composition is cross-linked after formation of the cable, the cross-linking agent is preferably a peroxide, which can be mixed with the components of the polymer composition before or during the mixing step (i). Preferably, a crosslinking agent, preferably a peroxide, is impregnated into the solid polymer granules of the polymer composition. The resulting granules then enter the cable production stage.

Most preferably, the polymer composition of the present invention is supplied to the mixing step (i) of the cable manufacturing process in a suitable product form, such as a granular product.

If the polymer composition is cross-linked with silane, then the cross-linking agent is usually not added to the polymer composition before forming the cable, but the cross-linking agent is usually added to the insulating layer composition, and after the cable is formed, the cross-linking agent migrates during the cross-linking step into the semi-conductive layer containing the polymer composition of the present invention .

In a preferred method for producing a cable, the resulting cable is stitched in step (iii).

As already mentioned, the polymer composition is preferably crosslinkable, and preferably the granules of the polymer composition also contain peroxide before being supplied to the cable production line.

In the crosslinking step (iii) described above, the crosslinking conditions may vary depending on, incl. depending on the stitching method used and cable size. The crosslinking according to the present invention is carried out, for example, in a known manner, preferably at elevated temperature. One skilled in the art can select suitable crosslinking conditions, for example, radical crosslinking or hydrolyzable silane groups. By way of non-limiting example, suitable crosslinking temperatures are, for example, at least 150°C and typically at most 360°C.

Determination methods

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

wt. % = mass percent

Melt Flow Rate: Melt Flow Rate (MFR) is determined in accordance with ISO 1133 and is expressed in g/10 min. MFR is an indicator of the flowability and therefore processability of a polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR value is determined at 190°C for polyethylene. MFR can be determined at different loads such as 2.16 kg (MFR ₂ ) or 21.6 kg (MFR ₂₁ ).

Density: Low Density Polyethylene (LDPE): Density measured in accordance with ISO 1183-2. Samples are obtained in accordance with ISO 1872-2, Table 3 Q (compression pressing).

experimental part

The following components are used:

EVA copolymer (a): Commercially available ethylene vinyl acetate copolymer (Elvax 550A), produced in a tubular reactor by high pressure polymerization, MFR (190°C, 2.16 kg) 8 g/10 min, vinyl acetate (VA) containing 15 wt. %

Carbon black (b): commercially available P-type furnace black (Printex Alpha A) with the following properties:

Iodine value: 112 to 124 (mg/g) (ASTM D1510-19)

Oil Absorption Number: 92 to 104 (ml/100g) (ASTM D2414-19)

Average primary particle size: 11 to 20 nm (ASTM D3849-14)

Polyethylene wax (c): Commercially available polyethylene wax from BASF (Luwax AL 3 Powder), which is an ethylene homopolymer wax with the following properties:

Melting point (DSC): 102 to 108°C (ASTM D-3418).

Dropping point (Ubbelohd): 101 to 112°C (ASTM D-3954).

Ball hardness at 23°C (Fischer): from 10 to 20 N/mm ²

Melt viscosity at 120°C: 135 to 240 mm ² /s (ASTM D-2162)

Density at 23°C: 0.910 to 0.925 g/cm ³ (ASTM D-792)

Molar mass approximately 3500 g/mol

Acid scavenger: commercially available soluble zinc stearate (Zinkum). In this particular experimental portion, the aforementioned EVA(a) copolymer uses a zinc stearate masterbatch containing 20% pure zinc stearate, brand Zinkum.

Antioxidant: TMH: polymerized 2,2,4-trimethyl-1,2-dihydroquinoline, melting point: 80 to 135°C, CAS:26780-96-1.

Four compositions of the present invention and one reference composition are prepared with the components shown in Table 1. The compositions are prepared by methods known to those skilled in the art. In these examples, the mixing equipment used is an X-Compound CK 45 (mixer). The mixer power required during mixing of compositions 1 to 4 of the present invention as well as the reference composition is shown in Table 2. Surprisingly, it has been found that when preparing a semiconducting polymer composition containing polyethylene wax, the mixer power requirement is reduced. The productivity (25 kg/h at 500 rpm) of the mixer is the same for all compositions.

Table 1. Examples of the present invention and comparative examples (all contents expressed in wt.%).

Base polymer EVA Soot Acid absorber Polyethylene wax Antioxidant Reference composition 58.35 39 2 - 0.65 Composition 1 56.35 39 3 1 0.65 Composition 2 54.35 39 3 3 0.65 Composition 3 52.35 39 3 5 0.65 Composition 4 50.35 39 3 7 0.65

Table 2. Power consumption for various compositions.

Examples Mixer power consumption (kW) Reference composition 8.9 Composition 1 8.9 Composition 2 8.7 Composition 3 7.8 Composition 4 7.9

Claims (29)

1. Semi-conducting polymer composition containing: (a) a base polymer of ethylene-vinyl acetate copolymer, (b) at least 25% by weight carbon black, (c) from 5 to 15% by weight polyethylene wax; and (d) from 0.1 to 5 wt.% acid scavenger. 2. Semiconducting polymer composition according to claim 1, additionally containing (e) from 0.1 to 5 wt.% antioxidant. 3. Semiconducting polymer composition according to claims. 1 or 2, wherein the ethylene vinyl acetate copolymer (a) is present in an amount of at least 30% by weight, preferably 30 to 70% by weight, more preferably 32 to 68% by weight, even more preferably 35 to 65% by weight .% or from 45 to 60 wt.% relative to the total mass of semiconducting polymer compositions. 4. Semi-conducting polymer composition according to any one of paragraphs. 1-3, wherein the polyethylene wax (c) is present in an amount of 7 to 15 wt%, or 7 to 9 wt%, or 5 to 10 wt%, for example 5 to 9 wt%, or from 5 to 7 wt.%, or from 10 to 15 wt.% relative to the total weight of the semiconducting polymer compositions. 5. Semi-conducting polymer composition according to any one of paragraphs. 1-4, wherein the ethylene-vinyl acetate copolymer (a) has a vinyl acetate content of from 1 to 35 wt.%, preferably from 1.5 to 32 wt.%, more preferably from 2 to 28 wt. %, more preferably from 2.5 to 25 wt.%, even more preferably from 3 to 22 wt.%, for example from 4 to 20 wt.%, especially from 5 to 19 wt.%, based on the total weight of the copolymer. 6. Semi-conducting polymer composition according to any one of paragraphs. 1-5, wherein the ethylene vinyl acetate copolymer (a) has an MFR ₂ (melt flow rate at 2.16 kg load) of 0.01 to 50 g/10 min, more preferably 0.05 to 40 g/10 min , even more preferably from 0.1 to 30 g/10 min. 7. Semi-conducting polymer composition according to any one of paragraphs. 1-6, wherein the carbon black (b) is present in an amount of 25 to 60% by weight, preferably 28 to 55% by weight, more preferably 30 to 50% by weight. 8. Semi-conducting polymer composition according to any one of paragraphs. 1-7, where the carbon black has an iodine value of at least 10 mg/g, for example from 10 to 300 mg/g, for example from 30 to 250 mg/g, for example from 80 to 200 mg/g or from 100 to 170 mg/g when determined in accordance with ASTM D-1510-19, and/or an oil absorption number of at least 30 ml/100 g, for example 50 to 300 ml/100 g, for example 50 to 250 ml /100 g, eg 70 to 200 ml/100 g, eg 90 to 130 ml/100 g when measured according to ASTM D 2414-19. 9. Semi-conducting polymer composition according to any one of paragraphs. 1-8, where polyethylene wax has an average molecular weight from 600 to 8000 g/mol. 10. Semi-conducting polymer composition according to any one of paragraphs. 1-9, does not contain rubber. 11. Semi-conducting polymer composition according to any one of paragraphs. 1-10, wherein the polyethylene wax is an energy reducing component that results in reduced energy consumption during mixing of the semiconductive polymer composition compared to a corresponding composition containing no polyethylene wax or containing a different amount of polyethylene wax. 12. An article comprising semiconducting layer(s) derived from a semiconducting polymer composition as defined above, wherein the article is a layer in a multilayer cable or a cable. 13. The article according to claim 12, where the article is a layer in a power cable, and the cable is a power cable. 14. Method for producing a semiconducting polymer composition containing: (a) a base polymer of ethylene-vinyl acetate copolymer, (b) at least 25% by weight carbon black and (c) from 5 to 15% by weight polyethylene wax, (d) from 0.1 to 5% by weight of an acid scavenger, wherein said method comprises mixing (a) to (d) in mixing equipment. 15. The method according to claim 14, where the mixing equipment is a mixer. 16. The method of claim 14, wherein the energy consumption of the mixing equipment is reduced compared to mixing the corresponding semiconducting polymer compositions of claim 15 containing no polyethylene wax or containing a different amount of polyethylene wax, wherein said reduction in energy consumption is at least 1%, or at least 3%, or at least 5%, or at least 7%, or at least 9%, or at least 11%. 17. Method according to any one of paragraphs. 15 or 16, wherein the semiconducting polymer composition is as defined in any one of paragraphs. 2-11. 18. A method for producing a cable, comprising the stages of: applying to one or more conductors a layer containing a semiconducting polymer composition, as defined in any of paragraphs. 1-11 or obtained according to any of paragraphs. 15-17. 19. The use of polyethylene wax to reduce energy consumption when mixing a semiconducting polymer composition, which is defined in any of paragraphs. 1-11.