RU2827725C1 - Semiconductor polymer composition - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: present invention relates to a semiconductor polymer composition used to produce a power cable. Disclosed is a semiconductor polymer composition containing, wt.%: 30–73 copolymer of ethylene and vinyl acetate (a), 25–60 carbon black (b) and 2–30 copolymer of ethylene and vinyl acetate with MFR2 from 100 to 1200 g/10 min (c), provided that components (a) and (c) are different; method of producing the disclosed semiconductor polymer composition and an article which is a cable or power cable and contains a semiconductor polymer composition.

EFFECT: obtaining a semiconductor composition having sufficient smoothness, while obtaining a power cable at the stage of swelling compounding requires less temperature and power consumption.

14 cl, 4 tbl, 12 ex

Description

AREA OF TECHNOLOGY

The present invention relates to a semiconductor polymer composition, to an optionally crosslinkable cable containing said composition, and, if said cable is crosslinkable, to a crosslinked cable containing said composition, as well as to a method for producing a cable containing said composition, including an optional step of crosslinking the cable. The present invention also relates to a method for producing a semiconductor polymer composition.

LEVEL OF TECHNOLOGY

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

Typical cables are usually produced by extruding layers onto the conductor. Such polymer semiconductor layers are well known and widely used in dielectric power cables rated for voltages above 6 kV. These layers are used to provide intermediate resistivity layers between the conductor and the insulating material and between the insulating material and earth potential or ground potential.

In addition, it is also known that crosslinking of polymers, such as polyolefins, greatly contributes to improving the thermal and deformation resistance, mechanical strength, chemical resistance, and abrasion resistance of the polymer. Accordingly, crosslinked polymers are widely used in various end applications, such as the aforementioned wire and cable (W&C) applications.

The purpose of the semiconductor layer is to provide a smooth interface with the electric field in the insulating material, thereby extending the service life, i.e. the long-term viability, of the power cable, among other things, by preventing partial discharge at the interface between the conductive and dielectric layers.

Semiconductor composites are produced by a compounding process in which polymer, carbon black and other additives are compounded at elevated temperatures. The resulting semiconductor polymer composites are subject to high demands in terms of smoothness.

Semiconductor compositions using ethylene vinyl acetate copolymer (EVA) as one of the polymer components are well known in the art. It is also known that at elevated temperatures, the EVA copolymer is subject to thermal decomposition, which leads to the formation of acetic acid and unsaturations in the polymer backbone (B. Sultan et. al, J. App. Pol. Sci., Vol 43, Issue 9, p. 1737). The formation of acetic acid is undesirable, since it can lead to corrosion of production equipment. Unsaturation in the polymer backbone is also undesirable, since such fragments are sensitive to thermal-oxidative degradation.

Another important characteristic is the smoothness of the semiconductor composition. The smoothness is partially influenced, among other things, by the carbon black (CB), which is usually used in such compositions. An uneven distribution of the carbon black particles by size, for example, can reduce the smoothness of the surface and cause a localized concentration of electrostatic voltage, which is a defect that can initiate a phenomenon known as fan treeing. In addition, the smoothness of the surface of the semiconductor layer of a power cable can be influenced by the surface properties and the size of the carbon black particles. For example, it is known that the larger the carbon black particles, the smoother the surface of the semiconductor layer. However, increasing the size of the carbon black particles to improve the smoothness, in turn, worsens, i.e. increases the specific resistance of the semiconductor layer material. Thus, these properties often need to be balanced, especially in the case of so-called furnace black.

In order to overcome the above-mentioned disadvantages of current EVA-containing semiconductor compositions, it is desirable to provide a composition that can be produced at lower compounding temperatures without any loss in compounding productivity. Ideally, such a composition should have sufficient smoothness to be considered suitable for use in power cables. In this regard, the inventors of the present invention have surprisingly found that it is advantageous to include acid scavengers such as stearates and/or an ethylene vinyl acetate copolymer with an MFR ₂ of at least 100 g/10 min in semiconductor polymer compositions.

ESSENCE OF THE INVENTION

Thus, according to a first aspect, the present invention provides a semiconductor polymer composition comprising:

(a) at least 30% by weight of an ethylene-vinyl acetate copolymer;

(b) at least 25% by weight of carbon black; and

(c) at least 2% by weight of an ethylene-vinyl acetate copolymer with an MFR ₂ of at least 100 g/10 min;

provided that components (a) and (c) are different.

According to a specific embodiment, the present invention also provides a semiconductor polymer composition as defined above, further comprising at least 0.1% by weight of an acid absorber.

According to a second aspect, the present invention provides an article comprising a semiconductor layer(s) obtained from a semiconductor polymer composition as defined above, wherein said article is, for example, a cable, for example a power cable.

According to a further aspect, the present invention provides a method for producing a semiconductor polymer composition comprising:

at least 30% by weight of ethylene-vinyl acetate copolymer;

at least 25% by weight of carbon black; and

at least 2% by weight of an ethylene-vinyl acetate copolymer with an MFR ₂ of at least 100 g/10 min and/or at least 0.1% by weight of an acid scavenger.

wherein said method comprises compounding (a) - (c) at a temperature of less than 240°C, provided that the ethylene-vinyl acetate copolymer (c), if present, is different from the ethylene-vinyl acetate copolymer (a).

According to a final aspect, the present invention provides the use of an ethylene-vinyl acetate copolymer with an MFR ₂ of at least 100 g/10 min and/or an acid scavenger to reduce the compounding temperature of a semiconductor polymer composition.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

In this document, a semiconductor polymer composition means that said polymer composition contains a conductive filler, such as, for example, carbon black, in an amount that provides semiconductor properties. The term "semiconductor polymer composition" is a well-known expression for polymer compositions used in semiconductor products, such as semiconductor layers of cables, as well known to those skilled in the art.

It should be understood that the term "polyethylene" means an ethylene-based polymer, i.e. a polymer containing at least 50% by weight of ethylene based on the total weight of the polymer as a whole. In this document, the terms "polyethylene" and "ethylene-based polymer" are used interchangeably and mean a polymer containing a majority by weight of polymerized ethylene monomer (based on the total weight of polymerizable monomers), while it may optionally contain at least one polymerized comonomer. The ethylene-based polymer may contain more than 50, or more than 60, or more than 70, or more than 80, or more than 90 weight percent of units derived from ethylene (based on the total weight of the ethylene-based polymer).

Low density polyethylene, LDPE, according to the present invention is a polyethylene obtained in 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 documented in the literature. The term LDPE describes and distinguishes between high pressure polyethylene and low pressure polyethylene obtained in the presence of an olefin polymerization catalyst. LDPEs have some typical properties, such as a specific branching architecture. A typical density range of LDPE is from 0.900 to 0.960 g/cm ³ .

In this document, the term "conductor" means a conductor comprising one or more wires. The wire may have any application and may be, for example, an optical, telecommunications or electrical wire. In addition, a cable may comprise one or more such conductors. Said conductor is preferably an electrical conductor and comprises one or more metal wires.

The mass content of components (a) - (c) indicated in the description and claims is based on the total mass of the semiconductor polymer composition.

Copolymer (a) of ethylene and vinyl acetate

The copolymer (a) of ethylene and vinyl acetate in the context of the present invention is a 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 comonomer(s). As is well known, "comonomer" refers to copolymerizable units of the comonomer.

The copolymer (a) of ethylene and vinyl acetate is obtained by a high-pressure polymerization process, preferably by radical polymerization in the presence of an initiator(s). The copolymer (a) is thus a low-density polyethylene (LDPE). It should be noted that polyethylene obtained under high pressure (HP) is generally referred to herein as LDPE, which term has a well-known meaning in the field of polymers. Although the term LDPE is an abbreviation for low-density polyethylene, it is understood that said term does not limit the density range, but includes LDPE-like high-pressure polyethylenes of low, medium and higher density. The term LDPE describes and characterizes only the nature of high-pressure polyethylene with typical properties such as a high degree of branching.

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

According to one preferred embodiment, one or more other comonomers comprise a polar comonomer. By "polar" comonomer is meant a comonomer comprising at least one polar bond and having a net electric dipole, i.e. a net positive charge region and a net negative charge region.

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

If polar comonomer(s) are(are) present in said EVA copolymer, said polar comonomer(s) is(are) preferably selected from the group consisting of alkyl acrylates, alkyl methacrylates or a mixture thereof. More preferably, said polar comonomer(s) is(are) selected from _C1 - _C6 alkyl acrylates, _C1 - _C6 alkyl methacrylates. Even more preferably, said polar EVA copolymer is a copolymer of ethylene with a _C1 - _C4 alkyl acrylate, such as methyl-, ethyl-, propyl- or butyl acrylate, or any mixture thereof, more preferably is a copolymer of ethylene with methyl-, ethyl- or butyl acrylate or any mixture thereof.

As the optional non-polar comonomer(s) for the EVA copolymer, comonomer(s) other than the above-listed polar comonomers can be used as the preferred copolymer (a). Such non-polar comonomers are preferably different from comonomer(s) containing hydroxyl group(s), alkoxy group(s), carbonyl group(s), carboxyl group(s), ether group(s) or ester group(s). One group of the preferred non-polar comonomer(s) comprises, preferably consists of, monounsaturated (=one double bond) comonomer(s), preferably olefins, preferably alpha-olefins, more preferably _C3 - _C10 alpha-olefins, such as propylene, 1-butene, 1-hexene, 4-methyl-1-pentene; polyunsaturated (=more than one double bond) comonomer(s) 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; comonomer(s) containing a silane group; or any mixtures thereof.

As mentioned above, the EVA copolymer may optionally be unsaturated, i.e. it may contain carbon-carbon double bonds (-C=C-). The unsaturation may be provided by one or more of the following methods: by means of a chain transfer agent (CTA), by means of one or more polyunsaturated comonomer(s), or by means of polymerization conditions.

The fact that the copolymer of (a) ethylene and vinyl acetate is "unsaturated" means in this context that said copolymer contains carbon-carbon double bonds. In the present document, carbon-carbon double bonds mean unsaturations. The polyethylene described in the present document may contain vinyl groups, for example, allyl groups. Vinyl groups are functional groups containing carbon-carbon double bonds. In the context of the present document, the term "vinyl group" has the generally accepted meaning, i.e. it is a fragment "-CH=CH ₂ ". In addition, the 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 either a cis- or a trans-configuration. For the avoidance of doubt, vinylidene groups and vinylene groups are not vinyl groups as used in this document. Typically, the double bond content of these unsaturated polyolefins is more than 0.1 double bond/1000 C atoms.

In another embodiment, the present invention provides a semiconductor polymer composition in which the ethylene-vinyl acetate copolymer (a) optionally comprises unsaturation, provided, for example, by copolymerizing ethylene with vinyl acetate and at least one polyunsaturated comonomer (i.e., to form a terpolymer) and/or, for example, by using a chain transfer agent, such as propylene.

It is well known that, for example, propylene can be used as a comonomer or as a chain transfer agent (CTA), or in both cases, whereby it can contribute to the unsaturation, for example, to the amount of vinyl groups in polyethylene. In this document, when using a copolymerizable CTA, such as propylene, the copolymerized CTA is not calculated on the basis of the initial comonomer content.

Polyunsaturated comonomers suitable for the optional unsaturated copolymer (a) of ethylene and vinyl acetate 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 with the first double bond. 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, said 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 (a), preferably the preferred EVA copolymer, is greater than 900 kg/ ^m3 . The density of the copolymer, preferably the preferred EVA copolymer, is preferably not greater than 960 kg/ ^m3 . Typical density ranges are from 900 to 960 kg/ ^m3 , such as from 910 to 950 kg/ ^m3 , such as from 920 to 945 kg/ ^m3 .

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

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

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

Although it is within the scope of the present invention when the ethylene-vinyl acetate copolymer (a) comprises one or more comonomers in addition to vinyl acetate, it is preferred that the only comonomer is vinyl acetate, i.e. said copolymer consists of monomer units of ethylene and vinyl acetate. In the case of other comonomers being present, they may be selected from any of the comonomers which have been described above as optional "polar" or "non-polar" comonomers. The ethylene-vinyl acetate copolymer (a) is preferably not a mixture or combination 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% by weight, more preferably up to 60% by weight, for example up to 50% by weight. Typically, the comonomer content is from 0.001 to 50% by weight, more preferably from 0.05 to 40% by weight, even more preferably less than 35% by weight, even more preferably less than 30% by weight, more preferably less than 25% by weight, relative to the total weight of the copolymer. Typical ranges include from 0.5 to 40% by weight, preferably from 1 to 35% by weight, more preferably from 2 to 30% by weight, for example from 3 to 25% by weight, for example from 5 to 20% by weight, relative to the total amount of said copolymer.

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

Accordingly, the preferred ethylene-vinyl acetate copolymer (a) according to the present invention is an LDPE copolymer, wherein it is preferably obtained at high pressure by free radical polymerization (called high pressure (HP) radical polymerization). The high pressure reactor can 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 the process conditions for further adjustment of other properties of the polyolefin depending on the desired end use are well known and described in the literature and can be easily applied by a person skilled in the art. Suitable polymerization temperatures are up to 400°C, preferably from 80 to 350°C, wherein the pressure is 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 step and/or after the tubular reactor. Temperature can be measured at multiple points throughout all stages.

After separation, the obtained LDPE is usually in the form of a polymer melt, which is usually 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 said mixer in a known manner.

Further information on the preparation of ethylene (co)polymers by high-pressure radical polymerization can be found, among other things, 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.

The ethylene-vinyl acetate copolymer (a) is present in the semiconductor polymer compositions according to 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 be from 30 to 73 wt.%, more preferably from 30 to 70 wt.%, such as from 32 to 68 wt.%, such as from 35 to 65 wt.% or from 45 to 60 wt.%.

Soot (b)

The semiconductor polymer composition according to the present invention comprises at least 25% by weight of carbon black. 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 semiconductor polymer composition comprises, for example, from 25 to 60% by weight, preferably from 28 to 55% by weight, more preferably from 30 to 50% by weight, for example from 35 to 45% by weight of carbon black based on the total weight of the semiconductor polymer composition.

According to at least one exemplary embodiment, the carbon black is present in an amount of at least 25 wt.%, such as at least 30 wt.%, or at least 35 wt.%, relative to the total weight of the semiconductor compositions. The carbon black content in the semiconductor compositions preferably does not exceed 45 wt.%, or does not exceed 40 wt.%, relative to the total weight of the semiconductor compositions. Thus, the carbon black can be present in an amount of 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 weight of the semiconductor compositions.

Any carbon black that is electrically conductive may be used. Typically, the carbon black is a specialty carbon black or a P-type carbon black. Non-limiting examples of suitable carbon blacks include furnace blacks and acetylene blacks. The carbon black may have a nitrogen adsorption surface area (NSA) of 5 to 400 ^m2 /g, such as 10 to 300 ^m2 /g, i.e., 30 to 200 ^m2 /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, such as from 10 to 30 nm, or from 11 to 20 nm, which is determined as the average particle diameter according to ASTM D3849-14, ii) an iodine adsorption number of at least 10 mg/g, such as from 10 to 300 mg/g, such as from 30 to 250 mg/g, such as from 60 (or 61) to 200 mg/g, or from 80 to 200 mg/g or from 100 to 170 mg/g when determined according to ASTM D-1510-19; and/or iii) an oil absorption number (OAN) of at least 30 ml/100 g, such as from 50 to 300 ml/100 g, such as from 50 to 250 ml/100 g, such as from 70 to 200 ml/100 g, such as from 90 to 130 ml/100 g or from 70 to 119 (or 120) ml/100 g when measured according to ASTM D 2414-19.

The primary particle size of one of the groups of suitable furnace blacks is 28 nm or less. Particularly suitable furnace blacks of this category may have an iodine adsorption number of 60 to 300 mg/g. In addition, it is advisable for the oil absorption number (in this category) to be from 50 to 225 ml/100 g, for example from 50 to 200 ml/100 g.

Other suitable carbon blacks may be obtained by any other method or may be further processed. Suitable carbon blacks for semiconductor cable layers are accordingly characterized by their purity. Thus, suitable carbon blacks have an ash content of less than 0.2% by weight, measured according to ASTM D1506, a residue on a 325 mesh sieve of less than 30 ppm according to ASTM D1514 and contain less than 3% by weight, preferably less than 1% by weight of total sulfur according to ASTMD1619.

The term "furnace black" is a generally recognized term for a well-known type of carbon black which is produced in a furnace-type reactor. As examples of various types of carbon black, their production process and reactors, reference may be made, inter alia, to EP 629222 Cabot, US 4391789, US 3922335 and US 3401020. As examples of industrial grades of furnace black, mention may be made of N115, N351, N293, N220 and N550. In order to further improve the suitability of such carbon blacks in semiconductor compounds, modifications of said industrial grades of carbon black are preferred, for example with respect to purity, granule properties and surface area. Furnace blacks are generally distinguished from acetylene blacks, which are another type of carbon black suitable for a semiconductor polymer composition.

Acetylene blacks are obtained in a process for producing acetylene carbon black, for example as described in US 4,340,577. In particular, the particle size of the acetylene blacks can be greater than 20 nm, for example from 20 to 80 nm. The average primary particle size is determined as the average particle diameter according to ASTM D3849-14. The iodine adsorption number of suitable acetylene blacks of this grade is from 30 to 300 mg/g, for example from 30 to 150 mg/g according to ASTM D1510. In addition, the oil absorption number (of this grade) is, for example, from 80 to 300 ml/100 g, for example from 100 to 280 ml/100 g, said number being measured according to ASTM D2414. Acetylene black is a generally recognized term, is very well known and is supplied, for example, by Denka.

Ethylene vinyl acetate (c)

Ethylene vinyl acetate (c) is a copolymer of ethylene and vinyl acetate with an MFR ₂ (2.16 kg, 190°C) of at least 100 g/10 min. Typically, the MFR ₂ of ethylene vinyl acetate (c) is up to 1200 g/10 min, such as up to 1000 g/10 min, preferably up to 800 g/10 min. Thus, preferred ranges may comprise from 100 to 1200, preferably from 150 to 1000, more preferably from 200 to 800 g/10 min, such as from 250 to 600 g/10 min, such as from 350 to 550 g/10 min.

The ethylene vinyl acetate (c) may be a high-pressure polyethylene as defined above for the copolymer (a) of ethylene and vinyl acetate, for example with additional polar comonomers. However, as a rule, it is a high-pressure LDPE obtained by a process similar to the process described above for the copolymer (a) of ethylene and vinyl acetate.

The ethylene vinyl acetate used as component (c) is different from the copolymer (a) of ethylene and vinyl acetate. Thus, the copolymer (a) of ethylene and vinyl acetate does not have to be identical to the copolymer (c) of ethylene and vinyl acetate.

The copolymer (c) of ethylene and vinyl acetate may contain one or more additional comonomers defined above for the copolymer (a). According to one preferred embodiment, the ethylene vinyl acetate (c) consists of the monomers ethylene and vinyl acetate.

A typical content of vinyl acetate in ethylene vinyl acetate (c) is from 1 to 45% by weight, preferably from 1 to 35% by weight, more preferably from 2 to 30% by weight, even more preferably from 3 to 25% by weight, for example from 5 to 20% by weight, in particular from 10 to 20% by weight, for example from 11 to 19% by weight, relative to the total weight of ethylene vinyl acetate.

Ethylene vinyl acetate (c) is present in the semiconductor polymer compositions according to the present invention in an amount of at least 2% by weight relative to the total weight of the composition as a whole. Preferred amounts may be from 2 to 30% by weight, more preferably from 2 to 20% by weight, for example from 5 to 15% by weight.

Ideally, ethylene vinyl acetate (c) is not ethylene vinyl acetate wax. For example, the average molecular weight can be more than 8000 g / mol.

Polymer composition

In addition to the components (a) to (c) described above, the semiconductor polymer composition according to the present invention may contain further components, typically additives such as antioxidants, crosslinking accelerators, premature polymerization inhibitors, processing aids, fillers, coupling agents, ultraviolet absorbers, stabilizers, antistatic agents, nucleating agents, slip agents, plasticizers, lubricants, viscosity regulators, tackifiers, anti-adhesives, surfactants, extender oils, acid scavengers and/or metal deactivators. These additives are well known in the industry and their use is known to those skilled in the art. Any additives that are present may be added as a separate raw material or in a mixture with the carrier polymer, i.e. in a so-called masterbatch.

According to a particularly preferred embodiment, the composition of the present invention comprises an acid scavenger, which comprises compounds that are metal salts of long-chain carboxylic acids, such as stearates, lactates, natural or synthetic metal silicates such as hydrotalcites, metal oxides (e.g. magnesium oxide, calcium oxide, zinc oxide), metal carbonates (e.g. 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, typically constitutes at least 0.1% by weight relative to the total weight of the composition as a whole. Thus, a typical amount of the acid scavenger is from 0.1 to 5.0% by weight, preferably from 0.2 to 4.0% by weight, more preferably from 0.3 to 3.0% by weight, such as from 0.4 to 2.0% by weight, or from 0.2 to 2.0% by weight, or from 0.2 to 1% by weight relative to the total weight of the polymer composition.

According to another preferred embodiment, the proposed composition comprises an antioxidant. Examples of such antioxidants include, but are not limited to, the following compounds: sterically 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; the polymer isoform 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), n,n'-bis(1,4-dimethylpentyl-p-phenylenediamine), alkylated diphenylamines, 4,4'-bis(1,1'-diethylbenzyl)diphenylamine, diphenyl-p-phenylenediamine, mixed diaryl-p-phenylenediamines, 2,2'-oxamido-bis-(ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and other sterically hindered amine antidegradants or stabilizers. A more preferred antioxidant is 4,4'-bis(1,1'-dimethylbenzyl)diphenylamine. A particularly preferred antioxidant is TMQ.

Antioxidants can be used in amounts of from 0.1 to 5.0 wt.%, preferably from 0.15 to 2 wt.%, more preferably 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.%, in particular from 0.35 to 0.7 wt.% based on the weight of the composition.

Examples of fillers as additives include: clays, precipitated silica and silicates, colloidal silica, calcium carbonate, ground minerals, and additional carbon blacks. Fillers can be used in amounts ranging from less than about 0.01 to more than about 40 percent by weight based on the weight of the composition.

According to embodiments in which the semiconductor polymer composition is a crosslinkable composition, said composition may also contain a crosslinking agent. Typical amounts of the crosslinking agent are from 0.01 to 4.0 wt. %, preferably from 0.02 to 2.0 wt. %, more preferably from 0.03 to 1.5 wt. %, such as from 0.05 to 1.2 wt. %, in particular from 0.1 to 1.0 wt. % relative to the total weight of the composition.

The preferred crosslinking agent is peroxide. Non-limiting examples include organic peroxides such as di-tert-amyl peroxide, 2,5-di(tert-butylperoxy)-2,5-dimethyl-3-hexyne, 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-butyl peroxybenzoate, 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. The peroxide is preferably 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.

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

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

According to at least one exemplary embodiment, the vinyl acetate content in component (a) is from 3.0 to 25 wt.%, and the vinyl acetate content in component (c) is from 3.0 to 25 wt.%, wherein the amount of carbon black (b) in the semiconductor polymer composition is from 34 to 41 wt.% According to another embodiment, the vinyl acetate content in component (a) is from 5.0 to 25 wt.%, and the vinyl acetate content in component (c) is from 5.0 to 25 wt.%, wherein the amount of carbon black (b) in the semiconductor polymer composition is from 34 to 41 wt.%. According to another embodiment, the vinyl acetate content in component (a) is from 5.0 to 20 wt.%, and the vinyl acetate content in component (c) is from 5.0 to 20 wt.%, wherein the amount of carbon black (b) in the semiconductor polymer composition is from 34 to 41 wt.% According to another embodiment, the vinyl acetate content in component (a) is from 10 to 20 wt.%, and the vinyl acetate content in component (c) is from 10 to 20 wt.%, wherein the amount of carbon black (b) in the semiconductor polymer composition is from 34 to 41 wt.%. According to another embodiment, the vinyl acetate content in component (a) is from 11 to 19% by weight, and the vinyl acetate content in component (c) is from 11 to 19% by weight, while the amount of carbon black (b) in the semiconductor polymer composition is from 34 to 41% by weight.

Obtaining a polymer composition

According to a further aspect, the present invention provides a method for producing a semiconductor polymer composition comprising:

(a) at least 30% by weight of an ethylene-vinyl acetate copolymer;

(b) at least 25% by weight of carbon black; and

(c) at least 2% by weight of an ethylene-vinyl acetate copolymer with an MFR ₂ of at least 100 g/10 min and/or at least 0.1% by weight of an acid scavenger, wherein said method comprises compounding (a) - (c) at a temperature of less than 240°C, provided that the ethylene-vinyl acetate copolymer (c) is different from the ethylene-vinyl acetate copolymer (a).

According to a further embodiment of the present invention, a method for producing a semiconductor polymer composition as defined herein is provided, comprising mixing and/or combining (e.g., compounding) components (a) to (c) at a temperature below 240°C. Preferred temperature ranges include from 155 to 235°C, such as from 160 to 230°C.

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

The temperature indicated is usually the temperature defined in the Measured Temperature paragraph in the Determination Methods section.

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

Said method of production according to the present invention preferably further comprises a step of granulating the obtained polymer mixture. Granulating can be carried out in a generally known manner by using conventional granulating equipment, such as preferably a conventional granulating extruder built into said mixing device. The method according to the present invention can be carried out in a batch or continuous mode.

The devices used to implement the method according to the present invention are, for example, a single-screw or twin-screw mixer or a kneading extruder or a combination thereof, which are preferably integrated into a granulation device. The apparatus(es) can be operated in a batch or, preferably, in a continuous mode. In order to limit the amount of large particles, the proposed method can include an additional subsequent sieving step before the preferred granulation step, which is also commonly used in the prior art for the production of semiconductor polymer compositions.

According to at least one of the illustrative embodiments, such a device can be a combined kneading machine comprising a mixing drum in which the melt mixing of the proposed composition is carried out, for example, with one or more receiving bins for adding carbon black, and a discharge extruder or a gear pump located after the mixing drum. The combined kneading machine can be, for example, a single-screw machine performing an axial movement once per revolution, in which fixed pins in the mixer housing of the said device interact with gaps in the screw. In this way, kneading is carried out in the longitudinal direction, ensuring effective dispersion and distribution mixing in a relatively short drum. The temperature can be adjusted by adding carbon black to the polymer melt in one or more bins. The throughput can be, for example, 3.5 tons/hour at a speed of 750 rpm.

End Applications

According to another embodiment of the present invention, there is provided an article, preferably a cable (for example, a power cable), comprising at least one layer comprising the semiconductor polymer composition described in this document. According to a further embodiment of the present invention, there is provided a layer in a multilayer cable, such as a layer of a power cable, comprising the semiconductor polymer composition described in this document. The multilayer cable may, for example, comprise at least 3 layers, such as, for example, an inner semiconductor layer, an outer semiconductor layer and an insulating layer located therebetween.

At least one layer of the cable containing the semiconductor polymer composition is preferably a semiconductor layer.

Furthermore, the cable according to the present invention may be, for example, a power cable comprising a conductor surrounded by at least a semiconductor layer comprising, preferably consisting of, the polymer composition according to the present invention.

Ideally, the cable should comprise a conductor surrounded by at least an inner semiconductor layer, an insulating layer and an outer semiconductor layer in a given order, wherein said semiconductor layer(s) comprises, preferably consists of, a semiconductor polymer composition described in this document. It is within the scope of the present invention when the semiconductor polymer composition of the inner and outer semiconductor layers is identical or different.

According to another embodiment of the power cable, the semiconductor layer(s) may be removable or non-removable, preferably non-removable, i.e. attached. Such terms are known and describe the peeling property of the layer, which may be desirable or undesirable depending on the end use. Thus, according to at least one of the illustrative embodiments, said layer is an attached layer in said multilayer cable, such as, for example, an inner or outer semiconductor layer located in contact with the cable conductor.

In the case of a removable semiconductor layer, the EVA copolymer according to 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 improve the ability to remove the layer. The content of polar comonomers in the non-removable semiconductor layer (for example, the inner or outer layer) is preferably less than 25.0 wt. %, preferably less than 20.0 wt. %, more preferably from 10.0 to 18.0 wt. %. According to some embodiments, a polar comonomer content of from 6.0 to 15.0 wt. %, based on said EVA copolymer, may be desirable. Thus, according to at least one of the exemplary embodiments, the content of polar comonomers in the semiconductor polymer composition is less than 25.0 wt.%, preferably less than 20.0 wt.%, more preferably from 10.0 to 18.0 wt.%, or only from 6.0 to 15.0 wt.%, based on said EVA copolymer. In both the case of a removable and non-removable layer, said layer is preferably crosslinkable.

According to at least one exemplary embodiment, the semiconductor layer proposed in the present invention has a pull-off force of 8 kN/m or more, preferably more than 10 kN/m. The method used to measure such a pull-off force is well known and is described, for example, in WO 2019002449 in the section devoted to the method entitled "Pull-off force at an angle of 90°".

The term "conductor" as used herein above and below means that said conductor comprises one or more wires. Furthermore, a cable may comprise one or more such conductors. Said conductor is preferably an electrical conductor and comprises one or more metal wires.

The cable according to the present invention is preferably a power cable selected from medium voltage, high voltage or 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 generally have a thickness of at least 2 mm, typically at least 2.3 mm, the said thickness increasing with increasing voltage for which the cable is designed.

As is well known, the cable may optionally comprise additional layers, such as layers surrounding the insulating layer or, if present, outer semiconducting layers such as shield(s), jacket layer(s), other protective layer(s) or any combination thereof.

The cable according to the present invention may be crosslinkable. Accordingly, it is even more preferable if the cable is a crosslinked cable, in which at least one semiconductor layer comprises a crosslinkable polymer composition according to the present invention, which is crosslinked before subsequent final use.

The most preferred cable according to the present invention is a power cable, preferably crosslinkable. Such a power cable ideally comprises a conductor surrounded by at least an inner semiconductor layer, an insulating layer and an outer semiconductor layer, in this order, wherein said semiconductor layer(s) comprises, preferably consists of, a semiconductor polymer composition described in this document. At least the inner semiconductor layer preferably comprises a polymer composition according to the present invention, as defined above or below or in the claims, including in its preferred embodiments. According to such a preferred embodiment of the cable, the outer semiconductor layer may optionally comprise a polymer composition proposed in the present invention, which may be identical to the polymer composition of the inner semiconductor layer or different from it. Moreover, at least the polymer composition according to the present invention of the inner semiconductor layer is crosslinkable, preferably crosslinkable with a peroxide, wherein said composition is crosslinked before the subsequent final use. The insulating layer is also preferably crosslinkable, wherein said layer is crosslinked prior to subsequent end use. The outer semiconductor layer may optionally be crosslinkable and thus may be uncrosslinked or crosslinked depending on the desired end use.

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

applying to one or more conductors a layer containing a semiconductor composition as defined herein.

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

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

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

(iii) optionally and preferably crosslinking the obtained at least one semiconductor layer in the presence of a crosslinking agent.

According to a further embodiment, the present invention includes a method for producing a cable, preferably a power cable, comprising the following steps:

(i) obtaining and mixing, preferably melt mixing in an extruder, a first semiconductor composition as defined above, preferably in the form of pellets, for the inner semiconductor layer,

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

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

(ii) applied to a conductor, preferably by co-extrusion,

- mixing in a melt the first semiconductor composition obtained in stage (i) to form an internal semiconductor layer,

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

- mixing in the melt the second semiconductor composition obtained in stage (i) to form an outer semiconductor layer,

wherein at least one composition of the first semiconductor composition of the obtained internal semiconductor layer and the second semiconductor composition of the obtained external semiconductor layer, preferably at least the first semiconductor composition of the obtained internal semiconductor layer, comprises, preferably consists of, a polymer composition according to the present invention.

In this document, the term "(co)extrusion" 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. In this document, the term "(co)extrusion" also means that all or part of the layer(s) are formed simultaneously using one extrusion die or sequentially using more than one extrusion die.

As is well known, a molten mixture of a polymer composition or its component(s) is applied to form a layer. The mixing step can be carried out in a cable extruder. The melt mixing step can include a separate mixing step in a separate mixer, such as a kneading machine, connected to the cable extruder of the cable production line and located before it. Mixing in the preceding separate mixer can be carried out by mixing said component(s) with or without external heating (heating by an external source).

In general, carbon black (b) and ethylene vinyl acetate (c) are mixed with the ethylene-vinyl acetate copolymer (a), such as by melt mixing, and the resulting molten mixture is pelletized to form pellets for use in the cable production methods described above. In this document, pellets generally mean any polymer product made from reactor-produced polymer (obtained directly from the reactor) by post-reactor modification to form solid polymer particles. The pellets may be of any size and shape. The resulting pellets are then used to produce cable.

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

If and preferably the polymer composition is crosslinked after the cable is produced, the crosslinking agent is preferably a peroxide, which can be mixed with the components of the polymer composition before or during the mixing step (i). The solid polymer granules of the polymer composition are preferably impregnated with a crosslinking agent, preferably a peroxide. The resulting granules are then fed to the cable production step.

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

In the case where the polymer composition can be crosslinked using a silane, the crosslinking agent is usually absent from said polymer composition before the cable is produced, but such a crosslinking agent is usually added to the insulating layer composition, and after the cable is produced, said crosslinking agent migrates in the crosslinking step to the semiconductor layer containing the polymer composition according to the present invention.

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

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

In the above-described step (iii) of the crosslinking process according to the present invention, the crosslinking conditions may vary depending, among other things, on the crosslinking method used and the size of the cable. The crosslinking according to the present invention is carried out, for example, in a known manner, preferably at an elevated temperature. A person skilled in the art can select suitable crosslinking conditions, for example for crosslinking by means of a radical reaction or by means of hydrolyzable silane groups. As a non-limiting example of a suitable crosslinking temperature range, for example at least 150°C and usually not higher than 360°C.

Methods of determination

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

% mass = mass percent

Melt Flow Index: The melt flow index (MFR) was determined according to ISO 1133 and is given in g/10 min. MFR is an indicator of the flowability and therefore the processability of the polymer. The higher the melt flow index, the lower the viscosity of the polymer. In the case of polyethylene, the MFR was determined at 190°C. 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 was measured according to ISO 1183-2. Sample preparation was carried out according to ISO 1872-2, Table 3Q (compression molding).

Surface Smoothness: In the surface smoothness analysis (SSA) method, a tape sample consisting of a semiconductor polymer composition described below was used, and the said method is a well-known method used in the prior art for determining the surface smoothness of semiconductor polymer materials.

Surface Smoothness Analysis (SSA) is designed to measure and record surface irregularities, called protrusions, on extruded semiconductor material. This method is used for analysis directly related to production, the so-called operational analysis. SSA equipment allows measuring and sorting protrusions of different sizes based on the width at half the height. Depending on the product, each size classification has a certain maximum number of protrusions. The principle of detecting protrusions using SSA is to measure the shadow of the tape above the horizon. The extruded tape passes through a shear pin, which is illuminated from one side by a light source. If there is a protrusion or other defect on the surface, a shadow is created, which is recorded using a one-dimensional camera located on the other side of the tape. The camera consists of light-sensitive pixels that measure the height and width of the defect. The height of the amount of light passing through the horizon and the width by the number of shadowed pixels are recorded and defined as protrusions. The detected protrusions are recorded as the width at half the height (W50) and the height (h) of different sizes with a single number of protrusions per square of the analyzed tape (number/ ^m2 ). The determination of the width at half the height is the width of the protrusions having half the height. Such a test system as a whole is also described, for example, in WO 0062014 Semyre.

Receiving a tape sample

About 4 kg of the semiconductor polymer composition pellets were taken and extruded in the form of a tape sample using a Collin 20 mm single screw extruder and a 25D extruder (supplied by Collin) under the following temperature conditions at different sections starting from the inlet of the extruder: 95°C, 120°C, 120°C and 125°C to ensure a polymer melt temperature of 125°C. The pressure before the extrusion plate was typically 260 bar (26 MPa), the residence time was maintained at a level of 1 to 3 minutes, while the typical screw speed was 50 rpm depending on the polymer material, as is known to those skilled in the art.

Extruder head hole: 30mm×1mm

Tape thickness: 500±20 µm

Tape width: 18 mm

The tape was air-cooled until completely cured before being introduced into the scanning (detection) zone of the SSA instrument camera, located 50 cm from the head outlet.

Measurement area: The camera of the SSA device scanned the surface of the belt while the belt moved at a given speed. The scanning width was set to exclude the edge area of the belt. Scanning was performed along the belt according to the measurement area of 1 m ² . More detailed information is given below.

Investigation of a tape sample using SSA

The test was based on optical inspection of the obtained extruded tape, which was passed in front of an optical scanner capable of scanning even a large surface at high speed and good resolution. The SSA device was fully computerized and during operation it automatically stored information about the positions and sizes of the detected protrusions for statistical evaluation. In this document, a "protrusion" means a reduced build-up, the height of which is at least one order of magnitude greater than the surrounding background roughness. It is located in isolation in a limited number per unit surface area.

The height is the distance between the baseline (= belt surface) and the highest point of the projection. The half-height was defined as the width of the projection at 50% of its height (W50), measured relative to the baseline. For measuring the half-height, the surface of the belt sample was taken as the baseline. In this document, above and below, the projection is called "a particle protruding from the surface of the belt". And thus, the term "half-height of said particle protruding from the surface of the belt sample" used in the description and claims herein represents the said width at half-height (W50).

The instrument was an SSA analysis instrument from Semyre Photonic Systems AB, Sweden.

Hardware: PC via Image Pre Processor

Software: NOPINIT

Camera type: Dalsa spectrophotographic camera with 2048 pixels. It was an interactive camera with a scan rate of 5000.

Light source: red LED with adjustable intensity.

Resolution of the protrusion width (particle): 10 µm

Resolution of the protrusion height (particle): 1.5 µm

Tape speed in the device for SSA: 50 mm/sec

The horizon for the tape surface was created by a rotating metal shaft. The light source and camera were directly aligned, ensuring the absence of a false reflected signal with a focal point on the horizon.

The scanning results were related to a tape area of 1 ^m2 and expressed as

- the number of particles per ^m2 having a width greater than 150 µm at half the height of the specified particle protruding from the surface of the belt (= baseline),

- the number of particles per ^m2 having a width greater than 200 µm at half the height of the said particle protruding from the surface of the belt (= baseline), and

- the number of particles per ^m2 having a width greater than 500 µm at half the height of the specified particle protruding from the surface of the belt (= baseline).

The values given represent the average number of particles determined for 10 tape samples obtained and analyzed for the semiconductor composition under study.

Measured temperature: The temperature of the semiconductor polymer composition was measured in the compounding device (BUSS MX 140 mixer) after adding carbon black and before the discharge extruder. The temperature was measured at a throughput of 2000 kg/h and a rotation speed of about 430 rpm.

Experimental part

The following components were used:

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

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

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

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

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

Ethylene vinyl acetate (c): commercially available high MFR EVA (Repsol Primeva P18500) with a VA comonomer content of 18 wt% and an MFR (190°C, 2.16 kg) of 500 g/10 min.

Ethylene vinyl acetate (d) was prepared as described below.

A mixture of fresh ethylene and recycled ethylene, chain transfer agent (1-propylene) and vinyl acetate was compressed to achieve an initial reactor pressure of 2600 bar. The total capacity of the hypercompressor was about 30 tons/hour. In the compressor zone, propylene was added as a chain transfer agent in quantities that allowed maintaining an MFR ₂ value of about 500 g/10 min. Vinyl acetate was also added here in quantities that ensured that 15 wt.% of vinyl acetate in ethylene-vinyl acetate was achieved. The compressed mixture was heated to 135°C in a preheat section before being fed to a two-zone tubular reactor with branched-flow feed with L/D (length/diameter) varying from 17,300 to 30,400. Mixtures of commercially available peroxide radical initiators dissolved in an inert solvent were introduced after the preheat section and at another location along the reactor in amounts sufficient to achieve peak exothermic polymerization temperatures of 262°C and 262°C, respectively, with cooling to 155°C in between. The reaction mixture was depressurized using a pressure regulating valve, the mixture was cooled, and the polymer was separated from the unreacted gas.

The resulting polymer contained VA comonomer in an amount of 15% by weight and had an MFR ₂ (190°C, 2.16 kg) of 500 g/10 min.

Acid scavenger: commercially available zinc stearate (Zinkum)

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

Antioxidant 2: 4,4'-bis(1,1'-dimethylbenzyl)diphenylamine, melting point: 98-100°C, AS: 10081-67-1

Four compositions according to the present invention and one reference composition were prepared with the components listed in Table 1. The resulting compositions were compounded using methods known to those skilled in the art. In these examples, the compounding equipment included a BUSS MX 140 continuous single-screw mixer. The compounding temperatures for compositions 1, 2, and 4 according to the present invention, as well as the reference composition, are given in Table 2. The smoothness result for composition 3 according to the present invention is given in Table 3.

The measured surface smoothness of 9.9 given in Table 3 is suitable for a semiconductor polymer composition intended for commercial cable applications.

Eight additional compositions according to the present invention and one more reference composition with the components listed in Table 4 were prepared. These compositions were compounded on an X-Compound CK 45 machine (25 kg/h and 300 rpm). The kneading machine power required during compounding is also listed in Table 4. Surprisingly, it was found that when preparing a semiconductor composition containing an EVA component with a high MFR value, the required kneading machine power was reduced. The kneading machine capacity was the same for all compositions.

Claims (24)

1. A semiconductor polymer composition containing: a) from 30 to 73% by weight of ethylene-vinyl acetate copolymer; b) from 25 to 60% by weight of carbon black; and c) from 2 to 30% by weight of ethylene-vinyl acetate copolymer with MFR ₂ from 100 to 1200 g/10 min; provided that components (a) and (c) are different. 2. The semiconductor polymer composition of claim 1, wherein the carbon black has an iodine adsorption number of at least 10 mg/g, such as from 10 to 300 mg/g, such as from 30 to 250 mg/g, such as from 80 to 200 mg/g or from 100 to 170 mg/g when determined according to ASTM D-1510-19; and/or an oil absorption number of at least 30 ml/100 g, such as from 50 to 300 ml/100 g, such as from 50 to 250 ml/100 g, such as from 70 to 200 ml/100 g, such as from 90 to 130 ml/100 g when measured according to ASTM D 2414-19. 3. The semiconductor polymer composition according to claim 1, wherein the copolymer (a) of ethylene and vinyl acetate comprises vinyl acetate in an amount of from 1 to 35% by weight, preferably from 1.5 to 32% by weight, more preferably from 2 to 28% by weight, more preferably from 2.5 to 25% by weight, even more preferably from 3 to 22% by weight, for example from 4 to 20% by weight, in particular from 5 to 19% by weight, for example from 10 to 18% by weight, for example from 12 to 16% by weight, relative to the total weight of the copolymer. 4. The semiconductor polymer composition according to claim 1, wherein the ethylene-vinyl acetate copolymer (a) has an MFR ₂ lower than the MFR ₂ of the ethylene-vinyl acetate copolymer (c), preferably has an MFR ₂ of 0.01 to 50, more preferably of 0.05 to 40 g/10 min, even more preferably of 0.1 to 30 g/10 min, such as 0.5 to 20 g/10 min, such as 1 to 15 g/10 min. 5. The semiconductor polymer composition according to claim 1, wherein the copolymer (a) of ethylene and vinyl acetate is present in an amount of from 30 to 70% by weight, preferably from 32 to 68% by weight, more preferably from 35 to 65% by weight or from 45 to 60% by weight. 6. The semiconductor polymer composition of claim 1, wherein the carbon black (b) is present in an amount of from 28 to 55 wt.%, preferably from 30 to 50 wt.%, such as from 35 to 45 wt.% or from 34 to 41 wt.%; and/or ethylene vinyl acetate (c) is present in an amount of from 2 to 20% by weight, preferably from 5 to 15% by weight. 7. The semiconductor polymer composition of claim 1, further comprising at least 0.1% by weight of an acid scavenger, preferably a metal stearate, such as zinc stearate, and/or additionally containing an antioxidant and/or cross-linking agent. 8. The semiconductor polymer composition according to claim 1, wherein the ethylene vinyl acetate (c) comprises vinyl acetate in an amount of from 1 to 45% by weight, preferably from 1 to 35% by weight, more preferably from 2 to 30% by weight, even more preferably from 3 to 25% by weight, for example from 5.0 to 20% by weight, in particular from 10 to 20% by weight, for example from 11 to 19% by weight, relative to the total weight of the ethylene vinyl acetate. 9. The semiconductor polymer composition of claim 1, wherein the ethylene vinyl acetate (c) has an MFR ₂ (2.16 kg, 190 °C) of 100 to 1000 or 100 to 800 g/10 min, such as 250 to 600 g/10 min, such as 350 to 550 g/10 min. 10. An article comprising a semiconductor layer(s) obtained from a semiconductor polymer composition as defined above, wherein said article is a cable or a power cable. 11. A method for producing a semiconductor polymer composition comprising: a) from 30 to 73% by weight of ethylene-vinyl acetate copolymer; b) from 25 to 60% by weight of carbon black; and c) from 2 to 30% by weight of an ethylene-vinyl acetate copolymer with an MFR ₂ of 100 to 1200 g/10 min and, optionally, at least 0.1% by weight of an acid scavenger, wherein said method comprises compounding (a)-(c) at a temperature of less than 240 °C, provided that the copolymer (c) of ethylene and vinyl acetate differs from the copolymer (a) of ethylene and vinyl acetate. 12. The method according to claim 11, wherein the semiconductor polymer composition comprises both a copolymer of ethylene and vinyl acetate with an MFR ₂ of 100 to 1200 g/10 min and an acid absorber as component (c). 13. The method of claim 12, wherein the acid scavenger is a metal stearate, preferably zinc stearate. 14. The method according to claim 11, wherein the semiconductor polymer composition is a composition defined in claim 2.