RU2377677C1 - Power cable embedding dielectric fluid and mixture of thermoplastic polymers - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention refers to power cable embedding electrical conductor and extruded protective overlayer including thermoplastic polymer material mixed with dielectric fluid where thermoplastic polymer material includes;(a) at least 75% wt in relation to total weight of thermoplastic polymer material, at least one copolymer of at least two a-olefinic comonomers, at that enthalpy of fusion of mentioned copolymer is less than 25 J/g; and (b) quantity equal or less than 25% wt in relation to total weight of thermoplastic polymer material, of at least one homopolymer of propylene or copolymer of propylene with at least one a-olefin, besides enthalpy of fusion of at least one homopolymer of propylene or copolymer of propylene exceeds 25 J/g, and fusion temperature exceeds 130°C. Enthalpy of fusion of protective overlayer is equal or less than 40 J/g, and weight content of dielectric fluid in thermoplastic polymer material is less than concentration of saturation of dielectric fluid in thermoplastic polymer material.

EFFECT: invention allows to improve cable flexibility not deteriorating its thermomechanical behaviour.

49 cl, 1 dwg, 3 tbl, 8 ex

Description

BACKGROUND OF THE INVENTION

This invention relates to a power cable. In particular, the invention relates to a cable for transmitting or distributing medium or high voltage electrical energy, in which an extruded protective coating based on a thermoplastic polymer material is mixed with a dielectric fluid, which simultaneously allows, in particular, the use of high operating temperatures and provides a cable with increased flexibility.

The specified cable can be used to transfer or distribute both direct current (DC) and alternating current (AC).

Currently, requirements for high environmental safety of products made of materials that not only do not harm the environment during their manufacture or use, but which can be easily recycled at the end of their service life, are universally accepted for electric or telecommunication cables.

However, the use of environmentally friendly materials is determined by the need to limit the cost and at the same time, for practical use, to maintain productivity equal to or greater than that for standard materials.

In the case of medium and high voltage energy transmission cables, the various insulating layers around the conductor typically consist of a crosslinked polymer based on a polyolefin, in particular crosslinked polyethylene (XLPE) or elastomeric copolymers of ethylene / propylene (EPR) or ethylene / propylene / diene (EPDM) also crosslinked. Crosslinking after the polymer material has been extruded onto the conductor gives the material satisfactory mechanical and electrical properties both during prolonged use and over current, even at high temperatures.

However, it is well known that cross-linked materials cannot be recycled, therefore production waste and cable insulation material at the end of their service life can only be destroyed by incineration.

Description of the Related Art

Applications WO 02/03398 and WO 02/27731, both filed in the name of the Applicant, disclose cables comprising at least one electrical conductor and at least one extruded protective coating based on a thermoplastic polymer material mixed with a dielectric fluid, where the thermoplastic material includes a propylene homopolymer or a propylene copolymer with at least one olefin comonomer selected from ethylene and an α-olefin other than propylene, said copolymer or copolymer has a temperature lavleniya greater than or equal to 140 ° C, and a melting enthalpy of from 30 J / g to 100 J / g. Alternatively, as the main thermoplastic material, as indicated previously, a propylene homopolymer or copolymer can be used in a mechanical mixture with a low crystallinity polymer, generally with a melting enthalpy of less than 30 J / g, which mainly increases the flexibility of the material. The amount of low crystallinity polymer is generally less than 70% by weight and preferably 20 to 60% by weight of the total weight of the thermoplastic material.

WO 04/066318, filed in the name of the Applicant, relates to a cable comprising at least one electrical conductor and at least one extruded protective coating based on a thermoplastic polymer material mixed with a dielectric fluid, wherein said thermoplastic polymer material is selected from:

(a) at least one propylene homopolymer or at least one propylene copolymer with at least one olefin comonomer selected from ethylene and an α-olefin other than propylene, wherein said copolymer or copolymer has a melting point greater than or equal to 130 ° C, and a melting enthalpy of 20 J / g to 100 J / g;

(b) a mechanical mixture comprising at least one propylene homopolymer or copolymer (a) and at least one ethylene elastomeric copolymer (c) with at least one aliphatic α-olefin and optionally a polyene. The elastomeric ethylene copolymer (c) has a melting enthalpy of less than 30 J / g. The amount of said elastomeric copolymer (c) is generally less than 70% by weight, preferably from 20% by weight to 60% of the total weight of the base thermoplastic material.

US 6,562,907 to Sumitomo Chemical Co. Ltd., relates to a resin composition consisting essentially of 70 parts by weight of an olefin polymer and 30 parts by weight of one polypropylene resin selected from the group consisting of the following polymers (A) and (B), where (A) is ethylene-propylene a copolymer having a crystal melting enthalpy of 87 ± 5 J / g, measured in accordance with JIS K7122 using a differential scanning calorimeter (DSC), and (B) is a propylene-ethylene copolymer having a crystal melting enthalpy of 60 ± 5 J / g, measured in accordance and with JIS K7122 using a differential scanning calorimeter (DSC). Mineral oil softeners such as naphthenic oil or paraffin mineral oil can be added to the thermoplastic resin. The resin can be used in areas such as the manufacture of electrical wires, for example, plastic cables, insulating and protective materials for wires.

The applicant noted that power cables with a protective coating in accordance with the prior art demonstrate good thermomechanical properties, but have relatively low flexibility, inter alia, due to the stiffness of the polymer material for the protective coating (protective coatings) of the cables. Flexibility is especially important during cabling operations or the installation of equipment associated with them. This characteristic is associated with the crystallinity of the material, since as the proportion of the amorphous polymer fraction increases, the material becomes softer and more flexible. However, the elastic modulus of the polyolefin material decreases with increasing temperature; therefore, a decrease in crystallinity is also accompanied by a deterioration in mechanical properties at high temperatures. This can be a problem in harsh environments such as overload. Thus, it was expected that melting enthalpy values lower than the minimum values known from the prior art would not be sufficient to provide suitable necessary thermal and bar resistance.

SUMMARY OF THE INVENTION

Currently, the Applicant has found that it is possible to improve the flexibility of the cable without compromising its thermomechanical characteristics by manufacturing a cable with at least one protective coating that includes the first thermoplastic copolymer having low crystallinity (expressed in melting enthalpy) as the main material of the polymer base , and as a secondary polymer material, a second thermoplastic polymer or copolymer having crystallinity greater than that of the first copolymer, and those Melting perature exceeding 130 ° C.

The resulting protective coating results in a cable with excellent flexibility without compromising thermomechanical and electrical characteristics, which makes it particularly suitable for use in the manufacture of a power cable, for example, as an electrical insulating layer of a medium or high voltage cable at a high operating temperature of at least 90 ° C and above, in particular at operating temperatures up to 110 ° C for continuous use and up to at least 130 ° C in case of overcurrent.

In accordance with a first aspect, the present invention relates to a power cable comprising at least one electrical conductor and at least one extruded protective coating comprising a thermoplastic polymer material mixed with a dielectric fluid, wherein said thermoplastic polymer material includes:

(a) at least 75%, relative to the total weight of the thermoplastic polymer material, of at least one copolymer of at least two α-olefin comonomers, said copolymer having a melting enthalpy of less than 25 J / g; and

(b) an amount equal to or less than 25%, relative to the total weight of the thermoplastic polymer material, of at least one propylene homopolymer or propylene copolymer with at least one α-olefin, said at least one propylene homopolymer or propylene copolymer having an enthalpy a melting point exceeding 25 J / g and a melting point exceeding 130 ° C;

and where

- the specified protective coating has a melting enthalpy equal to or less than 40 J / g, and

- the mass content of said dielectric fluid in said thermoplastic polymer material is lower than the saturation concentration of said dielectric fluid in said thermoplastic polymer material.

For the purposes of this description and the claims following it, unless otherwise indicated, all numbers expressing doses, amounts, percentages, etc., should be understood to be supplemented in all cases by the term “approximately”. Additionally, all ranges include any combination of the disclosed maximum and minimum values and include any intermediate ranges that may or may not be indicated separately.

As used herein and in the claims, the term “in mixture” means that the thermoplastic polymer material and the dielectric liquid are mixed together to obtain a substantially homogeneous distribution of the liquid in the polymer matrix (single phase).

In this description and the following claims, “conductor” means a conductive element as such, elongated and made, preferably, of a metal material in the form of a rod or a multicore cable, more preferably aluminum or copper, or a conductive element of the type as described above covered with a semiconducting layer.

In this description and the claims, “protective coating” means a polymer coating of a conductor, for example, an electrically insulating layer, a semiconducting layer, a braid, a protective layer, said protective layer being optionally foamed, a waterproof layer or a layer having several functions, for example, a protective conductive filler layer.

By “electrical insulating layer” is meant a protective coating made of a material having insulating properties, namely, having a dielectric strength of at least 5 kV / mm, preferably greater than 10 kV / mm.

By “semiconducting layer” is meant a protective coating made of a material having semiconductor properties, such as a polymer matrix filled with, for example, carbon black. For example, the amount of carbon black needed to add a volume resistance of less than 500 Ohm · m, preferably less than 20 Ohm · m at room temperature is added to the polymer matrix. Typically, the amount of carbon black can vary from 1 to 50% by weight, preferably from 3 to 30% by weight of the polymer.

According to a first embodiment, the extruded protective coating based on said thermoplastic polymer material mixed with said dielectric fluid is an electrically insulating layer.

According to yet another embodiment, the extruded protective coating based on said thermoplastic polymer material mixed with said dielectric fluid is a semiconducting layer.

The melting enthalpy (ΔH _m ) can be determined using the differential scanning calorimetry (DSC) method.

Preferably, the copolymer (a) is present in an amount of from 80% by weight to 95% by weight of the total weight of the thermoplastic polymer material. A larger amount of copolymer (a) in the thermoplastic cable material of the present invention can lead to an undesirable decrease in heat and pressure resistance.

Preferably, the copolymer (a) has a melting enthalpy of 15 J / g to 10 J / g. The melting enthalpy of the copolymer (a) may also be below 10 J / g, for example, 0 J / g.

The copolymer (a) can be supplied in the form of either granules or briquettes. When the melting enthalpy of the copolymer (a), for example, is below 10 J / g, the copolymer is generally supplied in the form of briquettes. The copolymer (a) in granular form is preferred in accordance with this invention because of its ease of processing.

Advantageously, the flexural modulus of the copolymer (a) is from 80 MPa to 10 MPa, more preferably from 40 MPa to 20 MPa. The bending modulus of the copolymer (a) can also be lower than 10 MPa, for example 1 MPa.

At least two α-olefin comonomers of at least one copolymer (a) can be selected from ethylene or an α-olefin of the formula CH ₂ = CH-R, where R is a linear or branched C ₁ -C ₁₀ alkyl group, which selected, for example, from propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, preferably ethylene, propylene, butene and octene.

Most preferred are propylene-ethylene copolymers.

Preferably, at least one of the at least two α-olefin comonomers is propylene.

The copolymer (a) for the cable of this invention may be a random copolymer or a heterophasic copolymer.

By “statistical copolymer” is meant a copolymer in which the monomers are randomly distributed across the polymer chain.

By “heterophasic copolymer” is meant a copolymer in which elastomeric domains, for example, ethylene propylene elastomer (EPR), are formed and distributed over a homopolymer or copolymer matrix.

Preferably, the copolymer (a) is selected from:

(a ₁ ) a random copolymer of propylene with at least one comonomer selected from ethylene and an α-olefin other than propylene;

(a ₂ ) a heterophasic copolymer comprising a propylene-based thermoplastic phase and an ethylene-based elastomeric phase copolymerized with an α-olefin, preferably propylene, in which the elastomeric phase is preferably present in an amount of at least 45% by weight heterophasic copolymer.

Particularly preferred from said class (a ₁ ) is a propylene copolymer with at least one olefin comonomer selected from ethylene and an α-olefin other than propylene, said copolymer having:

- melting point from 130 ° C to 170 ° C; and

a melting enthalpy of less than 20 J / g.

For example, class (a ₂ ) heterophasic copolymers are prepared by sequential copolymerization of: i) propylene, possibly containing small amounts of at least one olefin comonomer selected from ethylene and an α-olefin other than propylene; and then: ii) a mixture of ethylene with an α-olefin, in particular propylene and possibly a minor amount of diene.

A heterophasic copolymer in which the elastomeric phase consists of an elastomeric ethylene-propylene copolymer comprising from 15% to 50% ethylene and from 50% to 85% propylene relative to the weight of the elastomeric phase is particularly preferred from said class (a ₂ ).

Examples of commercially available products of class (a ₁ ) are Vistalon ™ 404, Vistalon ™ 606, Vistalon ™ 805 (Exxon Chemicals).

Examples of commercially available class (a ₂₎ represents a product Softell ^® CA02A; Hifax ^® CA07A; Hifax ^® CA10A (all supplied by Basell).

According to one preferred embodiment, the melting enthalpy of the propylene homopolymer or propylene copolymer with at least one α-olefin (b) exceeds 30 J / g, more preferably 50 to 80 J / g. The amount of said propylene homopolymer or propylene copolymer (b) is preferably from 5% by weight to 25% of the total weight of the base thermoplastic material.

In accordance with one preferred embodiment, the copolymer (b) has a melting point of from 140 ° C to 170 ° C.

Advantageously, the flexural modulus of the homopolymer or copolymer (b) is equal to or greater than 100 MPa, more preferably from 200 MPa to 1500 MPa.

Advantageously, the homopolymer or copolymer (b) is a heterogeneous copolymer obtained by sequential copolymerization of: (i) propylene optionally containing at least one α-olefin comonomer other than propylene; and then (ii) a mixture of propylene with an α-olefin, in particular ethylene, and optionally a diene. Copolymerization is usually carried out in the presence of Ziegler-Natta catalysts based on halogen-containing titanium compounds supported on magnesium chloride. Details regarding the preparation of these copolymers are given, for example, in EP-A-0400333, EP-A-0373660 and US-A-5286564.

The term "α-olefin" refers to ethylene or olefin of the formula CH ₂ = CH-R ', where R' represents a linear or branched alkyl group containing from 2 to 10 carbon atoms. Said α-olefin may be selected, for example, from 1-butene, 1-pentene, 1-hexene, 1-octene, 1-dodecene, and the like.

Advantageously, the thermoplastic phase of the heterogeneous copolymer includes a propylene homopolymer or a crystalline propylene copolymer with an olefin comonomer selected from ethylene and α-olefins other than propylene. Preferably, the olefin comonomer is ethylene. The amount of olefin comonomer is preferably less than 10 molar percent relative to the total number of moles of the thermoplastic phase.

As a comonomer, diene is optionally present. The specified diene, in the General case, contains from 4 to 20 carbon atoms and, preferably, selected from linear (un) conjugated diolefins, for example, 1,3-butadiene, 1,4-hexadiene, 1,6-octadiene, etc. .; monocyclic or polycyclic dienes, for example, 1,4-cyclohexadiene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene and the like.

Advantageously, said single-phase thermoplastic homopolymer or copolymer of propylene has a microscopic homogeneous structure and can be obtained by homopolymerization of propylene or copolymerization of propylene with ethylene or α-olefin other than propylene in the presence of a low stereospecific Ziegler-Natta catalyst. In particular, the catalyst mainly includes:

a) a solid catalyst comprising titanium tetrahalide (e.g. titanium tetrachloride) supported on MgCl ₂ , optionally mixed with aluminum trihalide (e.g. aluminum trichloride);

b) a cocatalyst comprising trialkylaluminum, where the alkyl groups are C ₁ -C ₉ groups (for example triethylaluminum or triisobutylaluminum);

c) a Lewis base in an amount generally not exceeding 10 molar percent of the total moles of trialkylaluminum.

The addition of a Lewis base in a predetermined amount allows you to control the stereoregularity of the obtained polymer. The Lewis base is generally selected from esters of aromatic acids and alkoxysilanes, for example ethyl benzoate, methyl p-toluate, diisobutyl phthalate, diphenyldimethoxysilane or mixtures thereof. The cocatalyst is added in a large excess with respect to the solid catalyst. The molar ratio of titanium halide to aluminum trialkyl is generally from 50: 1 to 600: 1.

Dielectric fluid suitable for use in the protective coating for the cables of this invention mainly has various features.

It was found that the use of a dielectric fluid increases the breakdown strength (dielectric strength) of the protective coating. For example, it was found that the use of a dielectric fluid, as will be described later, allows to increase the breakdown strength of the insulating layer based on polypropylene from about 30 kV / mm in the absence of a dielectric fluid up to more than 50 kV / mm, and values in excess of 80 were also achieved kV / mm.

Preferably, a suitable dielectric has a breakdown strength of at least 3 kV / mm, more preferably greater than 9 kV / mm.

According to a preferred embodiment, the dielectric constant of the dielectric fluid at 25 ° C is less than or equal to 3.5, more preferably less than 3 (measured in accordance with IEC 247).

Other advantageous features of a dielectric fluid suitable for use in the framework of the present invention are heat resistance, gas absorption ability, in particular hydrogen absorption, and partial discharge resistance.

Advantageously, the boiling point of the dielectric fluid should be higher than the temperature to which the cable can become hot during use and during overcurrent. Preferably, the boiling point of the dielectric liquid is above 130 ° C, more preferably above 250 ° C.

Suitable dielectric fluid is compatible with thermoplastic polymer material. “Compatibility” means that the chemical composition of the liquid and the thermoplastic polymer material is such that it results in a microscopic homogeneous distribution of the dielectric liquid in the polymer material after mixing the liquid and the polymer, similar to a plasticizer.

Preferably, the dielectric fluid is mixed with the thermoplastic polymer material in amounts less than the saturation concentration of the dielectric fluid in the thermoplastic polymer material. It was found that these amounts, described in detail below, do not impair the thermomechanical characteristics of the protective coating and prevent the specified dielectric fluid from reaching the surface of the thermoplastic polymer material.

The saturation concentration of the dielectric fluid in the thermoplastic polymer material can be determined using the method of absorption of fluid in the sample-eight, as described, for example, in WO 04/066317.

The weight ratio of the dielectric liquid to the thermoplastic polymer material according to this invention in the General case is from 1:99 to 25:75, preferably from 2:98 to 20:80.

It is also worth noting that the use of a dielectric fluid with a relatively low melting point or low pour point (for example, boiling point or pour point does not exceed 80 ° C) simplifies the handling of a dielectric fluid that can be melted without additional and complex stages of the production process (for example, dielectric fluid melting steps) and / or devices for mixing a fluid with a polymer material.

According to another preferred embodiment, the melting point or the pour point of the dielectric fluid is from -130 ° C to + 80 ° C.

The melting point can be determined using known methods, such as, for example, differential scanning calorimetry (DSC).

In accordance with another preferred embodiment, the dielectric fluid has a predetermined viscosity to prevent rapid diffusion of the fluid into the insulating layer and, therefore, to go beyond it, as well as to ensure easy incorporation of the dielectric fluid into the thermoplastic polymer material and mixing with it. In general, the dielectric fluid of the present invention at 40 ° C has a viscosity of 10 cSt to 800 cSt, preferably 20 cSt to 500 cSt (measured in accordance with ASTM D445-03).

For example, the dielectric fluid is selected from mineral oils, for example, naphthenic oils, aromatic oils, paraffin oils, polyaromatic oils, said mineral oils optionally containing at least one heteroatom selected from oxygen, nitrogen or sulfur; liquid saturated hydrocarbons; vegetable oils, for example, soybean oil, linseed oil, castor oil; oligomeric aromatic polyolefins; paraffin waxes, for example, polyethylene waxes, polypropylene waxes; synthetic oils, e.g., silicone oils, alkylbenzenes (e.g., dodecylbenzene, di (octylbenzyl) toluene), aliphatic esters (e.g., pentaerythritol tetraesters, sebacic acid esters, phthalic acid esters), olefinic polyol oligomers (e.g., isobutene polybutenes or ; or mixtures thereof. Paraffin oils and naphthenic oils are particularly preferred.

Mineral oils as dielectric fluid may include polar compound (s). The amount of polar compound (s) is preferably up to 2.3% by weight. Such a low content of polar compounds allows for low dielectric loss.

The amount of polar compounds in a dielectric fluid can be determined in accordance with ASTM D2007-02.

Alternatively, the dielectric fluid may include at least one alkylaryl hydrocarbon of the structural formula:

where R1, R2, R3, R4, the same or different, represent hydrogen or a methyl group;

n1 and n2, the same or different, are 0, 1 or 2, provided that the sum of n1 + n2 is less than or equal to 3.

As another alternative, the dielectric fluid includes at least one diphenyl ether with the following structural formula:

where R5 and R6 are the same or different and represent hydrogen, a phenyl group unsubstituted or substituted by at least one alkyl group, or an alkyl group unsubstituted or substituted by at least one phenyl group. By alkyl group is meant a linear or branched C ₁ -C ₂₄ , preferably C ₁ -C ₂₀ , hydrocarbon radical.

A dielectric fluid suitable for use in the cable sheath of the present invention is described, for example, in WO 02/027731, WO 02/003398 or WO 04/066317, all filed in the name of the Applicant.

Preferably, the protective coating for the power cable of the present invention has a melting enthalpy of equal to or less than 35 J / g, and more preferably of 30 to 5 J / g.

Preferably, the protective coating has a melt flow index (MFI), measured at 230 ° C with a load of 21.6 N in accordance with ASTM D1238-00, ranging from 0.05 dg / min to 10.0 dg / min, more preferably from 0.4 dg / min to 5.0 dg / min.

A thermoplastic polymeric material that, together with a dielectric fluid, forms a protective coating for the cable of this invention and which includes

(a) at least 75%, relative to the total weight of the thermoplastic polymer material, of at least one copolymer of at least two α-olefin comonomers, said copolymer having a melting enthalpy of less than 25 J / g; and

(b) an amount equal to or less than 25%, relative to the total weight of the thermoplastic polymer material, of at least one propylene homopolymer or propylene copolymer with at least one aliphatic α-olefin, said at least one propylene homopolymer or propylene copolymer having a melting enthalpy in excess of 25 J / g and a melting temperature in excess of 130 ° C;

has a melting enthalpy substantially equal to or less than 40 J / g.

In accordance with one preferred embodiment, the cable of the present invention has at least one extruded protective coating with electrical insulation properties obtained from a thermoplastic polymer material mixed with a dielectric fluid, as described above.

In accordance with another preferred embodiment, the cable of the present invention has at least one semiconductor extruded protective coating obtained from a thermoplastic polymer material mixed with a dielectric fluid, as described above. To obtain a semiconducting layer, a conductive filler is generally added to the polymer material. In order to provide a suitable distribution of the conductive filler in the thermoplastic polymer material, the latter is preferably selected from homopolymers or copolymers of propylene comprising at least 40% of the amorphous phase relative to the total polymer weight.

In accordance with another aspect, the present invention relates to a polymer composition comprising a thermoplastic polymer material mixed with a dielectric fluid, wherein said thermoplastic polymer material includes

(a) at least 75%, relative to the total weight of the thermoplastic polymer material, of at least one copolymer of at least two α-olefin comonomers, said copolymer having a melting enthalpy of less than 25 J / g; and

(b) an amount equal to or less than 25%, relative to the total weight of the thermoplastic polymer material, of at least one propylene homopolymer or propylene copolymer with at least one aliphatic α-olefin, said at least one propylene homopolymer or propylene copolymer having a melting enthalpy in excess of 25 J / g and a melting temperature in excess of 130 ° C;

- the specified protective coating has a melting enthalpy equal to or less than 40 J / g, and

- the mass content (concentration) of said dielectric fluid in said thermoplastic polymer material is lower than the saturation concentration of said dielectric fluid in said thermoplastic polymer material.

In accordance with another aspect, the present invention relates to the use of a polymer composition, as described above, as the main polymer material for the manufacture of a cable sheath with electrical insulation properties or for the manufacture of a cable sheath with semiconductor properties.

Upon receipt of the protective coating for the cable according to this invention, other standard components can be added to the above polymer composition, such as antioxidants, process improvers, water-tree degradation inhibitors, or mixtures thereof.

Standard antioxidants suitable for this purpose are, for example, distearyl or dilauryl thiopropionate and pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] or mixtures thereof.

Substances for improving technological properties that can be added to the polymer composition include, for example, calcium stearate, zinc stearate, stearic acid, or mixtures thereof.

Polymeric materials, as indicated above, can advantageously be used to produce an insulating layer, especially in the case of medium or high voltage cables. Thermal and bar resistance, obtained by applying an insulating layer, such as the layer according to this invention, allow power cables of medium or high voltage, which they are part of, operate at 90 ° C or higher temperature without compromising performance and provide excellent flexibility in compared with the known power cables based on thermoplastic polypropylene.

If the protective coating of this invention is a semiconductor layer, a conductive filler, in particular carbon black, is generally distributed over the base polymer material in an amount sufficient to impart semiconductor characteristics to the material (i.e., sufficient to achieve a resistance of less than 5 Ohm · m at room temperature). This amount generally lies in the range from 5% to 80% and, preferably, from 10% to 50% of the total weight of the mixture.

The use of the same basic polymer composition for both the insulating layer and the semiconducting layers is particularly advantageous in the manufacture of medium or high voltage cables in which it provides excellent adhesion between adjacent layers and, therefore, good electrical characteristics, in particular, at the boundary between the insulating layer layer and the inner semiconducting layer, where the electric field and, therefore, the risk of partial discharge is higher.

The polymer composition for cable sheeting of the present invention can be prepared by mixing together a thermoplastic polymeric material, a dielectric fluid, and any other additives that may be present using methods known in the art. Mixing can be carried out, for example, using an internal mixer with tangential type rotors (Banbury) or with interpenetrating rotors; in a continuous mixer such as Ko-Kneader (Buss), in a twin-screw mixer with screws of the same or opposite rotation; or in a single screw extruder.

The thermoplastic polymer material may be prefabricated in the polymerization reactor or by introducing components (a) and (b) together with the dielectric fluid into the mixing apparatus for the polymer composition, an example of which was given above.

Alternatively, the dielectric fluid of the present invention can be added to the thermoplastic polymer material during the extrusion process by direct injection into the extruder barrel, as disclosed, for example, in international patent application WO 02/47092, filed in the name of the Applicant.

Higher compatibility was also found between the dielectric fluid and the thermoplastic polymer material of this invention than in the case of similar mixtures of the same polymer material with other dielectric fluids known in the art. This higher compatibility leads, among other things, to a lower exit of the dielectric fluid to the surface. Due to the high operating temperature and their low dielectric loss, the cables of the present invention can carry, at the same voltage, a power of at least equal to or even greater than that transmitted with a standard XLPE-coated cable.

For the purposes of this invention, the term “medium voltage” generally means a voltage from 1 kV to 35 kV, while “high voltage” means voltages in excess of 35 kV.

Although this description is primarily directed to the manufacture of cables for transmitting or distributing medium or high voltage energy, the polymer composition of this invention can be used to coat electrical devices in general, and in particular various types of cables, for example low voltage cables (i.e. cables carrying voltage less than 1 kV), telecommunication cables or combined power / telecommunication cables, or auxiliary equipment used in electrical circuits, t FIR both connection points, spikes, connectors or the like

Brief Description of the Drawings

Additional characteristics will become apparent from the detailed description below, with reference to the accompanying drawing, which provides a perspective view of an electric cable, especially suitable for medium or high voltage in accordance with this invention.

Detailed Description of Preferred Embodiments

In the drawing, the cable (1) includes a conductor (2), an inner layer with semiconductor properties (3), an intermediate layer with insulating properties (4), an outer layer with semiconductor properties (5), a metal shield (6) and an outer braid ( 7).

The conductor (2) generally consists of metal wires, preferably of copper or aluminum, twisted together using standard methods, or of a solid aluminum or copper rod. At least one protective coating selected from the insulating layer (4) and the semiconducting layers (3) and (5) includes the composition of this invention, as previously defined. Around the outer semiconducting layer (5) is usually a shield (6) in the general case of conductive wires or strips wound in a spiral. This screen is then coated with a braid (7) made of a thermoplastic material, such as, for example, non-crosslinked polyethylene (PE).

The cable can also be equipped with a protective structure (not shown), the main role of which is to mechanically protect the cable from shock or crushing. This protective structure may be, for example, a metal edging or a layer of foamed polymer, as described in WO 98/52197, filed in the name of the Applicant.

The drawing shows only one use case of the cable in accordance with this invention. Suitable modifications may be made to this embodiment in accordance with specific technical needs and application requirements without departing from the scope of the invention.

The protective layer or layers of thermoplastic material for the cable in accordance with this invention can be made in accordance with known methods, for example, by extrusion. The extrusion is preferably carried out in one stage, for example, using a tandem method in which the individual extruders are arranged in series, or by coextrusion using a multi-section head of the extruder.

The following examples illustrate the invention but do not limit it.

Examples 1-8

Cables were manufactured with a protective coating in accordance with this invention and a control protective coating.

The protective coatings in accordance with this invention had the composition shown in Table 1.

Table 1. Example one 2 3 four 5 6 Softell CA 02 A 80 85 90 80 90 80 Moplen RP 310D twenty fifteen 10 - - Moplen RP 210G - - - twenty 10 Borsoft SA 233 CF - - - - twenty

The amount shown in Table 1 is expressed in mass percent relative to the total weight of the thermoplastic polymer material.

- Softell ^® CA 02 A: heterophasic copolymer EPR, melting point 143 ° C, melting enthalpy 12.4 J / g, MFI 0.6 dg / min and bending modulus 20 MPa (commercial product Basell);

- Moplen ^® RP 210G: propylene-ethylene random copolymer, melting point 146 ° C, melting enthalpy 65.1 J / g, MFI 1.8 dg / min and bending modulus 800 MPa (commercial product Basell);

- Moplen ^® EP 310 D: heterophasic propylene copolymer EPR, melting point 165 ° C, melting enthalpy 71.8 J / g, MFI 0.8 dg / min and bending modulus 1050 MPa (commercial product Basell);

- Borsoft ^® SA 233 CF: statistical propylene-ethylene copolymer with heterophasic copolymer EPR, melting point 142 ° C, melting enthalpy 65 J / g, MFI 0.8 dg / min and bending modulus 400 MPa (commercial product Borealis).

As a dielectric fluid, Jarylec® EXP3 (boiling point 390 ° C, sold by Arkema) was added to each thermoplastic mixture in an amount of 6% by weight of the protective coating composition.

The control protective coatings have the composition shown in Table 2.

Table 2. Example 7 8 Moplen RP 210G 70 - Hifax 7320 thirty - Adflex Q200 F one hundred

The amount shown in Table 2 is the same as in Table 1.

- Moplen ^® RP 210G: propylene-ethylene random copolymer, melting point 146 ° C, melting enthalpy 65.1 J / g, MFI 1.8 dg / min and bending modulus 800 MPa (commercial product Basell);

- Hifax ^® 7320: ethylene-propylene heterophase copolymer with melting point 165 ° C, melting enthalpy 27.0 J / g, MFI 2.5 dg / min and flexural modulus 200 MPa (commercial product of Basell);

- Adflex ^® Q200 F: a propylene heterophasic copolymer with a melting point of 165 ° C, a melting enthalpy of 30 J / g, an MFI of 0.8 dg / min and a bending modulus of 150 MPa (commercial product Basell).

The compositions of examples 7 and 8 contained Jarylec® EXP3 dielectric fluid in an amount of 6% by weight of the protective coating composition.

The polymer compositions of Tables 1 and 2 were used as insulating layers in the manufacture of power cables in accordance with the following.

Each polymer base was introduced directly into the receiving opening of the extruder. Then, the dielectric fluid pre-mixed with antioxidants was injected under high pressure into the extruder. An extruder was used with a diameter of 80 mm and a ratio of screw length to extruder barrel diameter (L / D) of 25. Injection was carried out during extrusion at a distance of 20 D from the extruder screw through three injection points located on the same section with a gap of 120 ° between them. Dielectric fluid was injected at a temperature of 70 ° C and a pressure of 250 bar.

The cable emerging from the extruder head was cooled to room temperature by passing it through cold water.

The resulting cable consisted of an aluminum conductor (150 mm ² in cross section), an internal semiconducting layer with a thickness of approximately 0.5 mm, an insulating layer of one of the polymer compositions of Tables 1 or 2 with a thickness of approximately 4.5 mm and an external semiconducting layer with a thickness of approximately 0 5 mm.

Cable Flexibility Measurement

The flexibility of the cables was measured in accordance with the method of TC20 / WG9 of the European Committee for Electrotechnical Standards (CENELEC), which contains all the information about the equipment, sample preparation and test procedure. The results are presented in Table 3.

Melting point measurement (T _m ), enthalpy of melting (ΔH) and heat and bar resistance.

The melting temperature (T _m ) and the melting enthalpy (ΔH) of the insulating layers of each of the studied power cables were determined using differential scanning calorimetry (DSC) using a differential scanning calorimeter Mettler Toledo DSC 820. The temperature program below was applied to all samples that It was necessary to analyze:

- cooling from room temperature to 10 ° C;

- heating from 10 ° C to 190 ° C at a speed of 10 ° C / min;

- maintaining a temperature of 190 ° C for 5 minutes;

- cooling to 10 ° C at a speed of 10 ° C / min;

- maintaining a temperature of 10 ° C for 10 minutes;

- heating to 190 ° C at a speed of 10 ° C / min.

The thermal and bar resistance of each test power cable was measured in accordance with CEI EN 60811-3-1 Par. 8.

The results are shown in Table 3.

Table 3. Example Flexural modulus (kg) Thermal and bar resistance at 120 ° C (%) Melting temperature
(T _m ) (° C)

H) (Дж/г)Enthalpy of melting (

H) (J / g) one 16.3 80.6 162 21,2 2 14.9 75,2 162 18.2 3 15.6 72.0 160 14.1 four 14.3 79.0 146 23.1 5 15.1 60.0 150 11.9 6 17,2 81.0 145 20,0 7 32,4 90.9 157 42.5 8 18.1 80.0 164 25.0

The results presented in Table 3 show that the protective layer for the cable according to this invention is a cable with increased flexibility with respect to previously known cables while maintaining thermal and bar resistance practically unchanged.

Thermal and bar resistance is especially important for measuring the performance and reliability of a power cable, since this characteristic indicates the ability of a cable (insulating layer) to withstand deformation at high temperatures, for example, at a temperature reached under overvoltage conditions.

Claims (49)

1. A cable comprising at least one electrical conductor and at least one extruded protective coating comprising a thermoplastic polymer material mixed with a dielectric fluid, wherein said thermoplastic polymer material includes:
(a) at least 75% by weight relative to the total weight of the thermoplastic polymer material of at least one copolymer of at least two α-olefin comonomers, said copolymer having a melting enthalpy of less than 25 J / g; and
(b) an amount equal to or less than 25 wt.% with respect to the total weight of the thermoplastic polymer material of at least one propylene homopolymer or propylene copolymer with at least one α-olefin, said at least one propylene homopolymer or propylene copolymer has a melting enthalpy in excess of 25 J / g and a melting point in excess of 130 ° C;
and where
said protective coating having a melting enthalpy equal to or less than 40 J / g, and
the mass content (concentration) of said dielectric fluid in said thermoplastic polymer material is lower than the saturation concentration of said dielectric fluid in said thermoplastic polymer material. 2. The cable according to claim 1, in which the extruded protective coating based on the specified thermoplastic polymer material in a mixture with the specified dielectric fluid is an insulating layer. 3. The cable according to claim 1, in which the extruded protective coating based on the specified thermoplastic polymer material in a mixture with the specified dielectric fluid is a semiconducting layer. 4. The cable according to claim 1, where the copolymer (a) is present in an amount of from 80 to 95 wt.% Of the total weight of the thermoplastic polymer material. 5. The cable according to claim 1, in which the copolymer (a) has a melting enthalpy of 15 to 10 J / g 6. The cable according to claim 1, in which the copolymer (a) has a modulus of elasticity in bending from 80 to 10 MPa. 7. The cable according to claim 6, in which the copolymer (a) has a modulus of elasticity in bending from 40 to 20 MPa. 8. The cable according to claim 1, in which at least two a-olefin comonomers of at least one copolymer (a) are selected from ethylene or a-olefin of the formula CH ₂ = CH-R, where R is a linear or branched C ₁ A C ₁₀ alkyl group. 9. The cable according to claim 1, in which the copolymer (a) is a propylene-ethylene copolymer. 10. The cable according to claim 1, in which at least one of the at least two a-olefin comonomers is propylene. 11. The cable according to claim 1, in which the copolymer (a) is a random copolymer or heterophasic copolymer. 12. The cable according to claim 1, in which the copolymer (a) is a random copolymer (a ₁ ) of propylene with at least one comonomer selected from ethylene and a-olefin other than propylene. 13. The cable according to claim 1, in which the copolymer (a) is a heterophasic copolymer (a ₂ ) comprising a thermoplastic phase based on propylene and an elastomeric phase based on ethylene copolymerized with a-olefin. 14. The cable according to item 13, in which the a-olefin is propylene. 15. The cable according to item 13, in which the elastomeric phase is present in an amount of at least 45% of the total mass of the heterophasic copolymer. 16. The cable of claim 12, wherein (a ₁ ) is a propylene copolymer with at least one olefin comonomer selected from ethylene and an a-olefin other than propylene, said copolymer having
melting point from 130 to 170 ° C; and
enthalpy of fusion less than 20 J / g. 17. The cable according to item 13, in which (a ₂ ) is a heterophasic copolymer in which the elastomeric phase consists of an elastomeric copolymer of ethylene and propylene, comprising from 15 to 50% ethylene and from 50 to 85% propylene relative to the total weight elastomeric phase. 18. The cable according to claim 1, wherein the propylene homopolymer or propylene copolymer with at least one aliphatic a-olefin (b) has a melting enthalpy exceeding 30 J / g. 19. The cable according to claim 18, wherein the propylene homopolymer or propylene copolymer with at least one α-olefin (b) has a melting enthalpy of 50 to 80 J / g. 20. The cable according to claim 1, in which the copolymer (b) has a melting point from 140 to 170 ° C. 21. The cable according to claim 1, in which the amount of said propylene homopolymer or propylene copolymer (b) is from 5 to 20 wt.% Of the total weight of the main thermoplastic material. 22. The cable according to claim 1, in which at least one a-olefin (b) is selected from ethylene or an olefin of the formula CH ₂ = CH-R ', where R' is a linear or branched alkyl group containing from two to ten carbon atoms. 23. The cable of claim 22, wherein the a-olefin is ethylene. 24. The cable according to claim 1, in which the amount of a-olefin (b) is less than 10 mol.% Of the total number of moles of the thermoplastic phase. 25. The cable according to claim 1, in which in (b) there is a diene. 26. The cable according to claim 1, in which the dielectric fluid has a breakdown strength equal to at least 3 kV / mm 27. The cable according to claim 26, wherein the dielectric fluid has a breakdown strength exceeding 9 kV / mm. 28. The cable according to claim 1, in which the boiling point of the dielectric fluid is higher than 130 ° C. 29. The cable according to claim 28, wherein the boiling point of the dielectric liquid is above 250 ° C. 30. The cable according to claim 1, in which the melting temperature or the temperature of the beginning of the flow of the dielectric fluid is from -130 to + 80 ° C. 31. The cable according to claim 1, in which the dielectric constant of the dielectric fluid at 25 ° C is less than or equal to 3.5. 32. The cable according to p, in which the dielectric constant of the dielectric fluid at 25 ° C is less than 3. 33. The cable according to claim 1, in which the viscosity of the dielectric fluid at 40 ° C is from 10 to 800 cSt. 34. The cable according to clause 33, in which the viscosity of the dielectric fluid at 40 ° C is from 20 to 500 cSt. 35. The cable according to claim 1, in which the dielectric fluid is a mineral oil, including up to 2.3% of the polar compounds by weight. 36. The cable according to claim 1, in which the dielectric fluid is selected from paraffin oils and naphthenic oils. 37. The cable according to claim 1, in which the dielectric fluid includes at least one alkylaryl hydrocarbon with the structural formula

where R1, R2, R3 and R4, the same or different, represent hydrogen or a methyl group;
n1 and n2, the same or different, are 0, 1 or 2, provided that the sum of n1 + n2 is less than or equal to 3. 38. The cable according to claim 1, in which the dielectric fluid includes at least one diphenyl ether with the following structural formula

where R ₅ and R _{6 are the} same or different and represent hydrogen, a phenyl group unsubstituted or substituted by at least one alkyl group, or an alkyl group unsubstituted or substituted by at least one phenyl group, where the alkyl group is a linear or branched C ₁ -C ₂₄ , preferably C ₁ -C ₂₀ , a hydrocarbon radical. 39. The cable according to claim 1, in which the dielectric fluid is present in a weight ratio to the thermoplastic polymer material, comprising from 1:99 to 25:75. 40. The cable according to claim 1, in which the dielectric fluid is present in a weight ratio to the thermoplastic polymer material, comprising from 2:98 to 20:80. 41. The cable according to claim 1, in which the melting enthalpy of the protective coating is equal to or less than 35 J / g 42. The cable according to paragraph 41, in which the melting enthalpy of the protective coating is from 30 to 5 J / g 43. The cable according to claim 1, in which the protective coating has a melt flow index (MFI), measured at 230 ° C with a load of 21.6 N in accordance with ASTM D1238-00, ranging from 0.05 to 10.0 dg / min 44. The cable according to item 43, in which the protective coating has a melt flow index (MFI), measured at 230 ° C with a load of 21.6 N in accordance with ASTM D1238-00, ranging from 0.4 to 5.0 dg / min 45. The cable according to claim 1, in which at least one extruded protective coating has electrical insulating properties. 46. The cable according to claim 1, where the cable is selected from a medium or high voltage cable. 47. A polymer composition comprising a thermoplastic polymer material mixed with a dielectric fluid, wherein said thermoplastic polymer material includes:
(a) at least 75 wt.% with respect to the total weight of the thermoplastic polymer material of at least one copolymer of at least two α-olefin comonomers, said copolymer having a melting enthalpy of less than 25 J / g; and
(b) an amount equal to or less than 25 wt.% with respect to the total weight of the thermoplastic polymer material of at least one propylene homopolymer or propylene copolymer with at least one aliphatic a-olefin, said at least one propylene homopolymer or copolymer propylene has a melting enthalpy in excess of 25 J / g and a melting point in excess of 130 ° C;
said protective coating having a melting enthalpy equal to or less than 40 J / g, and
the mass content (concentration) of said dielectric fluid in said thermoplastic polymer material is lower than the saturation concentration of said dielectric fluid in said thermoplastic polymer material. 48. Thermoplastic polymer material, including:
(a) at least 75% by weight relative to the total weight of the thermoplastic polymer material of at least one copolymer of at least two α-olefin comonomers, said copolymer having a melting enthalpy of less than 25 J / g; and
(b) an amount equal to or less than 25% relative to the total weight of the thermoplastic polymer material of at least one propylene homopolymer or propylene copolymer with at least one aliphatic a-olefin, said at least one propylene homopolymer or propylene copolymer has a melting enthalpy in excess of 25 J / g and a melting point in excess of 130 ° C;
having a melting enthalpy equal to or less than 40 J / g. 49. The use of the polymer composition specified in paragraph 47, as the main polymer material for the manufacture of a protective coating of a cable with electrical insulating properties.