High tracking-resistant polyethylene composition for wire and cable applications

Abstract

The present invention relates to a crosslinkable polymer composition comprising a copolymer of ethylene and hexene, the copolymer being a multimodal polyethylene in which there are at least two polymer fractions in the polymer, each polymer fraction having a different weight average molecular weight, the copolymer having a crystallinity of at least 40% as determined by DSC as described herein, based on the total weight of the polymer composition, the polymer composition further comprising a carbon black content of not more than 4% by weight, wherein the polymer composition does not contain a silane-modified polymer component, and the polymer composition has passed the tracking resistance test according to IEC 60587 (2007) method 2A on a molded plate prepared according to ISO 11357 at least at 4.5 kV for 1 hour and then at 4.75 kV for 1 hour. The present invention further relates to a tracking-resistant wire or cable comprising at least one layer of the above polymer composition or to the use of the polymer composition in a wire or cable for improving tracking resistance, flame retardancy and / or heat resistance. The present invention also relates to a method for manufacturing the above polymer composition.

Description

Technical Field

[0001] The present invention relates to a polymer composition having improved tracking resistance comprising a copolymer of ethylene and hexene for use in electric wires and cables, its use for improving tracking resistance in an electric wire or cable, a tracking-resistant electric wire and cable comprising a layer of the polymer composition, and a method for producing such a polymer composition. Background Art

[0002] In overhead lines (OH) with covered conductors that are vulnerable to damage due to fire, voltage drop, power outage, and mechanical damage (such as fallen trees or contact with flying objects), there is a particular need for materials with improved tracking resistance. On the other hand, compared with AC cables laid underground, overhead lines with covered conductors have many advantages because cable capacitance limits the length of AC cables. Higher voltage cables limit the cable length and shorten the line length. Depending on the system voltage, AC cables are limited to a shorter net length. The higher the system voltage, the shorter the net length. The net length of the cable can be extended by compensating reactors, but this increases costs and installation and increases losses in the cable network. These limitations apply to system voltages above 10 kV. Therefore, for long-distance power grids, overhead lines still dominate.

[0003] The phase-to-phase distance of the covered conductors can be very narrow, so it can better withstand trees falling on the conductors. Such power lines can be built close to trees without having to clear forest areas. There is also a problem in dusty areas that in addition to the insulators, tracking can deteriorate or damage the conductors, and the conductors may break and fall to the ground.

[0004] The voltage drop in the conductor depends on the resistance of the conductor and the inductance between the conductors. For rural overhead lines, the inductive voltage drop may be the dominant factor in the conductor.

[0005] The narrow distance between the conductors also reduces the inductance of the overhead line, so the inductive voltage drop of the covered conductor is reduced by about 50% compared with bare wires. Longer cable lines with a lower system voltage can be built. This makes network design easier and reduces costs.

[0006] Covered conductors in cable lines are common and have been used for more than 30 years. It has been found that during long-term use, sparks will appear on the cable surface, especially in areas where there is conductive dust and / or trees / branches in contact with the cable line. These sparks on the cable surface, also known as tracking, will damage the insulation of the cable, cause the conductor to burn, and ultimately lead to cable failure. Therefore, there is a great need for higher tracking resistance in the network and power plant utilities. Nowadays, there is a need for a power grid that can increase the tracking resistance on OH lines to greater than 3 kV up to 5.75 kV tracking resistance or even more. A further desire is to improve the fire resistance so that fire does not spread along the line.

[0007] To improve the reliability of power distribution and transmission, plastic-coated overhead conductors, PAS, and BLL / BLX conductors without metal sheaths have been developed. These coated conductor systems can also save a large amount of space, as the required space is reduced by approximately 40% compared to standard bare wires. Considering the advantages compared to traditional bare wire structures, the construction cost of coated conductor (CC) wires is moderate.

[0008] Polymer compositions that meet the 4.5 kV tracking resistance are known, mainly those containing carbon black. However, those black compositions heat up in sunlight and may increase the above-mentioned tracking problems or even cause fires due to low heat resistance.

[0009] An optical cable contains optical fibers for transmitting signals for any form of communication, data exchange, or control purposes. For example, one type of such optical cable is described in GB A2 2193583. In addition to the optical fibers, the optical cable also includes an outer sheath that protects these optical fibers. The outer sheath is usually based on polymeric materials, such as polyolefins, especially polyethylene or ethylene copolymers, where the ethylene monomer constitutes a large part of the total mass of the polymer. The cable sheath must meet the requirements of easy production and good mechanical properties (such as tensile strength and elongation at break, especially at high temperatures up to 100 °C). In addition, the outer sheath should also have low heat distortion and good tracking resistance.

[0010] In particular, good tracking resistance of the sheath is highly concerned because, for practical reasons, optical cables are usually installed adjacent to power cables. These power cables, due to their high voltage, especially exceeding 130 kV, generate strong electric fields, which can cause voltage to pass through the sheath area of the adjacent optical cable. This leads to creep current through tracking and further causes local breakdown of the sheath, especially under humid conditions, which is called dry arc. Tracking is defined as the process of generating tracking marks due to the action of an arc. The arc concentrates sufficient energy to generate tracking marks and sufficient energy for tracking growth. Failure occurs when the tracking extends far enough to bridge the remaining distance between two electrodes or a ground connection and thus becomes a local degradation path on the surface of the insulating material. The tracking resistance is measured according to the inclined plane tracking test. Details of the test procedure applied according to this method are given in the arc in the Examples section.

[0011] EP 1267189 A1 discloses a tracking-resistant optical cable that includes at least one optical fiber and an outer sheath, the outer sheath containing a polymeric material, preferably a bimodal ethylene-butene copolymer, characterized in that the polymeric material forms a matrix for the sheath and consists of a multimodal olefin polymer obtained by coordination catalytic polymerization, and the total composition of the sheath includes 15 - 40% by weight of magnesium hydroxide and / or aluminum hydroxide and 0.01 - 0.9% by weight of carbon black.

[0012] WO 93 / 05424 A1 discloses a tracking resistant optical cable, which includes at least one optical fiber and a polymeric material outer sheath, characterized in that the polymeric material forms a matrix, the matrix consists of a blend of linear polyethylene and 0 wt% to at most 20 wt% of branched LDPE based on the weight of the linear polyethylene, and further characterized in that the total composition of the outer sheath material contains 15 - 30 wt% of magnesium hydroxide or aluminum hydroxide.

[0013] JP - 2004 - 010864 A discloses a tracking resistant water - crosslinkable polymer composition, which contains 8 to 50 pbw of magnesium hydroxide (B) and 0.2 to 1.1 pbw of carbon black (C) added to 100 pbw of an ethylene - based polymer (A) mainly composed of an ethylene - α - olefin copolymer. The polymer composition contains 0.1 to 10 pbw of an unsaturated alkoxysilane (D), 0.01 to 1 pbw of an organic peroxide (E) and 0.001 to 1 pw of a silanol condensation catalyst (F).

[0014] Each of the above - mentioned polymer compositions and cables has problems of low heat resistance, electrical safety, voltage drop, short - circuit and breakage, and mechanical problems such as insufficient tensile strength and elongation at break. In addition, there is a strong demand in the related market for improving the tracking resistance of materials.

[0015] The object of the present invention is to design a tracking resistant polymer composition for wire and cable applications and its use in the layer of a wire or cable, the polymer composition having improved tracking resistance as well as good mechanical properties, ultraviolet resistance and heat resistance. It is also necessary to reduce the carbon black in the cable to reduce the visibility of the cable in the landscape. Summary of the Invention

[0016] The present invention has found that the above object can be achieved by a crosslinkable polymer composition comprising a copolymer of ethylene and hexene, the copolymer being a multimodal polyethylene having at least two polymer fractions in the polymer, each polymer fraction having a different weight average molecular weight, the copolymer having a crystallinity of at least 40% as determined by DSC as described herein, based on the total weight of the polymer composition, the polymer composition further comprising a carbon black content of not more than 4% by weight, wherein the polymer composition does not contain a silane-modified polymer component, and the polymer composition has passed the tracking resistance test according to IEC 60587 (2007) method 2A on a molded plate prepared according to ISO 11357 and as described in the experimental section below at least at 4.5 kV for 1 hour and then at 4.75 kV for 1 hour. Preferably, the crosslinkable polymer composition has passed the tracking resistance test according to IEC 60587 (2007) method 2A on a molded plate prepared according to ISO 11357 at least at 5.75 kV for 1 hour and then at 6 kV for 1 hour.

[0017] These objects can also be achieved by a tracking-resistant wire or cable comprising at least one layer of the above polymer composition or the use of the polymer composition in a wire or cable for improving tracking resistance, flame retardancy and / or heat resistance.

[0018] The present invention further relates to a method for manufacturing the above polymer composition, which comprises polymerizing at least two polymer components in different reaction stages of a multi-stage polymerization process in the presence of a polymerization catalyst, wherein the polymer components formed in the previous polymerization stage are present in the subsequent polymerization stage. Detailed Description

[0019] The crosslinkable polymer composition of the present invention comprises a copolymer of ethylene and hexene. The copolymer of ethylene and hexene is a multimodal polyethylene having at least two polymer fractions in the polymer, each polymer fraction having a different weight average molecular weight. The expression "peak state of the polymer" refers to the form of its molecular weight distribution (MWD) curve, i.e., the appearance of the graph of the polymer weight fraction as a function of its molecular weight. If the polymer is produced in a sequential step process (e.g., by using reactors connected in series and using different conditions in each reactor), the different polymer fractions produced in different reactors will each have their own molecular weight distribution, and these distributions may be significantly different from each other. The molecular weight distribution curve of the resulting final polymer can be regarded as the superposition of the molecular weight distribution curves of the polymer fractions, which will correspondingly show two or more different maxima, or at least be significantly broader compared to the curve of a single fraction. A polymer showing such a molecular weight distribution curve is called "multimodal". Multimodal polymers can be produced according to several methods, such as those described in WO 92 / 12182. It is known to produce multimodal (especially bimodal) olefin polymers, preferably ethylene polymers, in two or more reactors connected in series. Examples thereof are described in EP 040992, EP 041796, EP 022376, EP 0887379 and WO 92 / 12182. According to the disclosures of these documents, each polymerization stage can be carried out in the liquid phase, slurry or gas phase.

[0020] In the crosslinkable polymer composition according to the present invention, the copolymer of ethylene and hexene preferably has a density of 920 to 970 kg / m 3 and a melt flow rate MFR2 measured according to ISO 1133 at 190 °C under a load of 2.16 kg of less than 0.4 g / 10 min. More preferably, the copolymer may have a density of 930 to 960 kg / m 3 , and even more preferably 945 to 955 kg / m 3 and a melt flow rate MFR2 of not more than 0.4 g / 10 min, more preferably not more than 0.2 g / 10 min, and even more preferably not more than 0.1 g / 10 min.

[0021] Furthermore, preferably in a polyethylene composition without carbon black, the base resin preferably may have a density of at least 945 kg / m 3 , more preferably 946 to 950 kg / m 3 , and most preferably 946.5 to 949 kg / m 3 .

[0022] The multimodal copolymer of ethylene and hexene is preferably at least bimodal. Such a multimodal polymer comprises at least two polymer fractions present in the polymer, each polymer fraction having a different weight average molecular weight. These fractions are sometimes hereinafter referred to as fraction (A) and fraction (B) respectively.

[0023] In this regard, an ethylene copolymer means a polymer comprising at least 50% by weight of ethylene monomer units.

[0024] Fraction (A) can be a homopolymer of ethylene in the fraction or an ethylene copolymer with the lowest comonomer content. Preferably, fraction (A) is a homopolymer of ethylene.

[0025] A homopolymer of ethylene thus means a polymer consisting essentially of ethylene monomer units. Due to the requirements of large-scale polymerization, the homopolymer of ethylene may contain a small amount of comonomer units, which is usually less than 0.1 mol% of the homopolymer of ethylene, preferably less than 0.05 mol% of the homopolymer of ethylene, and most preferably less than 0.01 mol% of the homopolymer of ethylene.

[0026] In a preferred embodiment of the present invention (sometimes hereinafter referred to as embodiment A), the copolymer of ethylene and hexene can be bimodal, consisting of polymer fractions (A) and (B), and optionally further containing a prepolymer fraction in an amount up to 10% by weight of the total polymer, preferably up to 7% by weight of the total polymer, and most preferably up to 5% by weight of the total polymer. Those skilled in the art will understand that the presence of stabilizers is required for the measurement of polymer properties.

[0027] In embodiment A, fraction (A) of the copolymer can be a homopolymer or copolymer of ethylene. Fraction (A) preferably has a density of 960 to 980 kg / m 3 ³.

[0028] In addition, preferably, fraction (A) of the copolymer has an MFR2 measured according to ISO 1133 of 150 to 600 g / 10 min, more preferably 175 to 550 g / 10 min, and most preferably 200 to 550 g / 10 min.

[0029] Fraction (A) and / or fraction (B) can consist of a single polymer fraction prepared in one reactor, or can consist of two or more partial fractions prepared in different reactors.

[0030] Preferably, fraction (A) and / or fraction (B) consists of two partial fractions or a single fraction.

[0031] Most preferably, fraction (A) consists of a single fraction or two partial fractions (preferably produced in one or two loop reactors respectively), while fraction (B) consists of a single fraction (preferably produced in a gas phase reactor).

[0032] If one or more fractions of the base resin consist of partial fractions produced in different reactors, it is preferred to select the reaction conditions such that substantially the same polymers are produced therein. This means that if, for example and preferably, the base resin consists of fractions (A) and (B), and fraction (A) is produced as two partial fractions in two different loop reactors under conditions such that substantially the same or identical polymers are produced therein, the polymer will still be a bimodal resin since it consists of fractions of two different polymers.

[0033] Furthermore, in the polyethylene composition, the copolymer of ethylene and hexene preferably has a weight average molecular weight Mw of 150,000 to 350,000 g / mol, more preferably 200,000 to 320,000 g / mol.

[0034] The copolymer of ethylene and hexene preferably has a molecular weight distribution Mw / Mn of 20 to 35, more preferably 22 to 31.

[0035] Preferably, the copolymer of ethylene and hexene accounts for at least 10% by weight of the polyethylene composition, more preferably at least 20% by weight, still more preferably at least 40% by weight.

[0036] The copolymer of ethylene and hexene has a crystallinity of at least 40%, preferably at least 45%, more preferably at least 50%, even more preferably at least 55% as determined by DSC as described in the following experimental section. The crystallinity of the copolymer can further be at least 60% or at least 65%. These crystallinity values apply to pure copolymers of ethylene and hexene without additives. The presence of a larger amount of filler can significantly reduce the crystallinity of the polymer composition, which is evident from the examples shown below.

[0037] The crosslinkable polymer composition according to the invention may further comprise an ethylene polymer or copolymer grafted or copolymerized with an unsaturated carboxylic acid or its derivative, and / or an elastomeric ethylene copolymer.

[0038] The unsaturated carboxylic acid may be selected from maleic acid or its anhydride. The elastomeric ethylene copolymer may be, for example, a very low density copolymer of ethylene and 1-octene. It preferably has a density in the range of 860 to 910 kg / m 3 and an MFR2 in the range of 0.1 to 50 g / 10 min.

[0039] On the other hand, the multimodal copolymer of ethylene and hexene may alternatively constitute all of the polymer components in the polyethylene composition according to the invention, typically constituting at least 90% by weight of the total composition.

[0040] In addition to the multimodal copolymer of ethylene and hexene, common additives used with polyolefins, such as pigments (e.g., carbon black), stabilizers (e.g., antioxidants) and / or ultraviolet absorbers, antistatic agents, and processing aids (e.g., processing aids) reagents, can be present in the polyethylene composition. Preferably, the amount of these additives is 10% by weight or less of the composition, more preferably 8% by weight or less, and most preferably 5% by weight or less.

[0041] Preferably, the composition contains no more than 4% by weight, more preferably no more than 3% by weight, even more preferably no more than 2.5% by weight or no more than 1% by weight of carbon black. Based on the weight of the total composition, carbon black can also be included in the composition in an amount of 0.1 to 0.8% by weight. Any of the above ranges or limits can be combined. The carbon black content can also be as low as 0.002% by weight or even 0.001% by weight.

[0042] In addition, preferably, in the polyethylene composition containing carbon black, the copolymer of ethylene and hexene can have a content of units derived from 1-hexene of 0.9 to 1.45 mol%, more preferably 0.95 to 1.30 mol%, still more preferably 1.0 to 1.25 mol%, still more preferably 1.03 to 1.24 mol%, and particularly preferably 1.04 to 1.23 mol%.

[0043] Furthermore, preferably, in the polyethylene composition containing carbon black, the copolymer of ethylene and hexene can have a number average molecular weight of 9,000 g / mol or more, preferably 9,300 g / mol or more.

[0044] Preferably, in the polyethylene composition containing carbon black, the base resin has a total content of units derived from 1-hexene of 0.50 to 0.70 mol%, preferably 0.52 to 0.69 mol%, and more preferably 0.54 to 0.67 mol%.

[0045] In a further embodiment of the present invention, the polyethylene composition does not contain carbon black.

[0046] The crosslinkable polymer composition of the present invention can preferably further contain a filler selected from aluminum oxide, metal carbonate, calcium oxide, and / or metal hydroxide. Preferred fillers can be ground or precipitated magnesium hydroxide or calcium carbonate. Another preferred filler is calcium carbonate, which can be coated with stearic acid and has an average particle size of 0.1 to 20 μm, more preferably 0.5 to 10 μm, and even more preferably 1 to 3 μm. Based on the total weight of the composition, the content of the filler is preferably 10 to 65% by weight, more preferably 20 to 30% by weight, and even more preferably at least 25% by weight. The above upper and lower limits can be combined with each other in various combinations.

[0047] The crosslinkable polymer composition according to the invention may preferably further comprise an ultraviolet stabilizer and / or an antioxidant and / or a pigment.

[0048] The ultraviolet stabilizer may be a hindered amine light stabilizer (HALS), selected from 944, 622, 770 and mixtures thereof. In addition, any ultraviolet stabilizer may be used, preferably the HALS compounds listed in EP 3622541 A1. Two or more ultraviolet stabilizers may be combined. Any of the above ultraviolet stabilizers may also be combined with one or more ultraviolet absorbers (such as benzotriazoles, benzophenones, triazines or phenolic compounds). Any ultraviolet absorber listed in EP19191837.4 may be used.

[0049] Based on the total weight of the composition, the content of the ultraviolet stabilizer may be 0.1 to 2% by weight, more preferably 0.2 to 1.5% by weight, even more preferably 0.3 to 1% by weight.

[0050] The antioxidant may be selected from, for example, hindered phenols (such as Irganox 1010 (CAS No. 128-37-0), Irganox1076 (CAS No. 2082-79-3), Irganox 1035 (Cas No. 41484-359), sulfur-containing antioxidants (such as Irganox PS 802 (Cas No. 693-36-7), Irganox PS 800 (Cas No. 2500-88-1), phosphites / phosphonites (such as Irgafos 168 (Cas No. 31570-04-4), Irgafos P-EPQ (Cas No. 38613-77-3), nitrogen-containing antioxidants (such as Naugard 445 (Cas 10081 -67-1), Vulcanox HS / LG (cas No. 26780-96-1). Combinations of two or more may be used.

[0051] Based on the total weight of the composition, the content of the antioxidant may be 0.1 to 2% by weight, more preferably 0.2 to 1% by weight, even more preferably 0.3 to 0.5% by weight.

[0052] The pigment may be selected from, for example, blue, green or orange pigments. A particularly preferred pigment is titanium dioxide. Preferably, the total amount of pigments other than carbon black present in the polyethylene composition may be less than 1% by weight of the total composition, more preferably 0.001 to 2% by weight. A preferred pigment is carbon black. In the case of carbon black, its content may be 0.001 - 5% by weight.

[0053] The present invention also relates to a process for producing a polyethylene composition according to any one of the above embodiments, wherein the multimodal copolymer of ethylene and hexene is produced in a multistage process.

[0054] The multimodal copolymer of ethylene and hexene comprises at least two or more ethylene homopolymer or copolymer fractions as described above.

[0055] Optionally, the multimodal copolymer of ethylene and hexene further comprises a prepolymer fraction as described above.

[0056] The multistage polymerization process represents a process in which a polymer comprising two or more fractions is produced by polymerizing each of the at least two polymer fractions in separate reaction stages, typically with different reaction conditions in each stage comprising a polymerization catalyst. A compounding step is preferably carried out after polymerization.

[0057] Preferably, fractions (A), (B) and optionally an additional fraction (C) are polymerized in any order in different stages of the multistage process. Thus, it is preferred that fractions (A), (B) and (C) are polymerized in successive stages. More fractions can also be produced in the copolymer.

[0058] Preferably, the multimodal polyethylene in the polymer composition according to the present invention is polymerized in at least one slurry phase reactor and at least one gas phase reactor.

[0059] In a preferred embodiment, fraction (A) is polymerized in a slurry phase reactor, preferably a loop reactor, and fraction (B) is polymerized in a gas phase reactor, in any order. If a copolymer comprising fractions (A), (B) and (C) is produced, it is preferred that fractions (A) and (B) are polymerized in a slurry phase reactor, preferably a loop reactor, and fraction (C) is polymerized in a gas phase reactor. The multistage process may preferably further include a prepolymerization stage.

[0060] In any order means that there is no preferred arrangement of the order of the successive polymerization stages of the multistage process.

[0061] In a preferred embodiment of the process according to the present invention, fraction (A) is polymerized in the first reaction stage.

[0062] Thus, it is preferred that fraction (B) is polymerized in the second reaction stage in the presence of fraction (A).

[0063] If fraction (C) is present, it is preferably polymerized in the third reaction stage in the presence of fractions (A) and (B).

[0064] Preferably, the multi-stage process consists of a reaction stage carried out in a slurry-phase reactor followed by a reaction stage carried out in a gas-phase reactor. Thus, optionally, a prepolymerization stage precedes the reaction stage carried out in the slurry-phase reactor. In a preferred embodiment, the multi-stage process consists of two consecutive reaction stages carried out in the slurry phase (preferably a loop reactor) followed by a reaction stage carried out in a gas-phase reactor. The detailed conditions are described in EP 1655333 A1.

[0065] A low molecular weight polymer (e.g., fraction (A)) can be prepared in the first polymerization step, and a high molecular weight 1-hexene copolymer (e.g., fraction (B)) can be prepared in the second polymerization step. This can be referred to as the normal mode and is preferred.

[0066] The HMW copolymer fraction (B) can also be prepared in the first polymerization step, while the LMW polymer fraction (A) is prepared in the second polymerization step. This can be referred to as the reverse mode.

[0067] If the LMW fraction is produced in the first polymerization step, the melt flow rate of the first ethylene fraction (A) can be measured directly as described herein. If the LMW fraction is produced in the second polymerization step, the melt flow rate of the LMW ethylene fraction (A) can be calculated based on the weight ratio of the LMW fraction and the HMW fraction and the molecular weight of the total polyethylene composition.

[0068] In addition, when the fractions of each polymer are known, subtracting GPC curves can also be used to determine the melt flow rate of the polymer produced in the second stage of the multi-stage polymerization process.

[0069] The slurry and gas-phase stages can be carried out using any conventional reactor known in the art. The slurry-phase polymerization can be carried out, for example, in a continuously stirred tank reactor; a stirred tank reactor operated batchwise or a loop reactor. Preferably, the slurry-phase polymerization is carried out in a loop reactor. In such a reactor, the slurry is circulated at high speed along a closed pipe using a circulation pump. Loop reactors are generally known in the art and examples are given, for example, in US 4,582,816 A, US 3,405,109 A, US 3,324,093 A, EP 479186 A and US 5,391,654 A.

[0070] The art-recognized gas-phase reactors include any mechanically mixed fluidized bed reactor, fast fluidized bed reactor or settling bed reactor or a gas-phase reactor having two independent zones, such as a combination of a fluidized bed and a settling bed zone. Preferably, the gas-phase reactor used for the second polymerization step is a fluidized bed reactor.

[0071] As the catalyst system, a system of any catalyst suitable for polymerizing polyethylene resins and an optional cocatalyst can be used. Particularly suitable is a Ziegler-Natta catalyst system. In a preferred embodiment, the polymerization is carried out in the presence of a Ziegler-Natta catalyst. Suitable Ziegler-Natta catalysts preferably comprise a magnesium compound, an aluminum compound, and a titanium compound supported on a particulate carrier.

[0072] A particularly preferred catalyst system and its preparation are described in EP 1378528 A1.

[0073] The crosslinkable polymer composition of the present invention can be used in wires or cables to improve tracking resistance. Accordingly, the present invention further relates to a tracking-resistant wire or cable, preferably a power cable or an optical fiber cable, comprising at least one layer comprising the above-described crosslinkable polymer composition. Preferably, the layer is an insulating layer, a jacket layer, or a sheath layer.

[0074] More preferably, the ethylene polymer is present in the sheath of the wire or cable in the highest possible amount, i.e., in addition to optional other components such as the above-described fillers, stabilizers, and / or carbon black.

[0075] When producing wire or cable materials, preferably sheath materials, their components, such as ethylene polymers, magnesium hydroxide, and / or aluminum hydroxide, carbon black, and optional additives, should be thoroughly mixed to obtain as uniform a composition as possible to produce, in a preferred embodiment, the outer sheath of an optical fiber cable.

[0076] Preferably, the kneading of the sheath material is carried out according to the method described in WO 98 / 15591. According to this method, the filler and carbon black can be mixed into the polymer material by passing the polymer through the viscosity crossover stage two or more times in two or more separate steps, i.e., each step means a separate kneading operation in a mixer or an extruder. The two components in the form of fine powder are added in the required proportions to obtain the best results and to incorporate these components into the sheath material as uniformly as possible. Kneading can also be carried out in a conventional kneading unit (such as a twin-screw kneader, such as those commonly provided by Werner & Pfleiderer and Berstorf, a Banbury mixer, a Farrel Pominis FCM mixer, or a Buss co-kneader).

[0077] The powder should have as small a size as possible. Thus, the filler, preferably magnesium hydroxide, can preferably have a median particle size d of 1 to 10 μm, more preferably 1.5 to 6 μm. 50 . The carbon black can preferably have a nominal particle size of 10 - 30 nm, more preferably 20 nm. The particle size can be determined according to the method described in the experimental section.

[0078] The crosslinkable polymer composition according to the invention may preferably have a tensile strength, determined according to ISO 527-2, of at least 12.5 MPa, more preferably at least 21.5 MPa.

[0079] The crosslinkable polymer composition according to the invention may preferably have an elongation at break, determined according to ISO 527-2, of at least 50%, more preferably at least 100%, even more preferably at least 300%.

[0080] The crosslinkable polymer composition according to the invention may preferably have a UV resistance with an elongation of at least 50%, more preferably at least 100% after 1000 h of aging, determined according to the Sepap UV aging test, measured on a 1 mm plate according to NFC62-062-2.

[0081] The crosslinkable polymer composition of the invention may be crosslinked in the presence of a crosslinking agent or in the presence of moisture and a condensation catalyst. Known techniques for moisture curing in the presence of a condensation catalyst are described, for example, in U.S. Patent No. 4,117,195, US 3,646,155 or EP 0193317 A1.

[0082] The tracking-resistant polymer composition of the invention can be used as a thermoplastic material or a crosslinked material by using, for example, a direct peroxide injection (DPI) process, in which peroxide is injected into an extruder to obtain a cable, which then enters a heated and pressurized vulcanization tube to cure the cable. An alternative to injecting peroxide into the extruder is to impregnate the granules with peroxide before extrusion. The tracking-resistant polymer composition of the invention can also be crosslinked by moisture curing, for example, by the processes described in U.S. Patent No. 4,117,195, US 3,646,155.

[0083] Experimental section

[0084] A. Measurement methods

[0085] Unless otherwise defined, the following definitions of terms and determination methods apply to the above general description of the invention and the following examples.

[0086] (1) Melt flow rate (MFR)

[0087] The MFR can be measured according to ISO 1133 (Davenport R-1293 from Daventest Ltd). The MFR value can be measured at 190 °C under three different loads of 2.16 kg (MFR 2.16 ), 5 kg (MFR5) and 21.6 kg (MFR 21 ).

[0088] (2) Density

[0089] The density can be measured according to ISO 1183-1 - Method A (2019). The sample preparation can be completed by compression molding according to ISO 1872-2:2007.

[0090] (3) Tracking test

[0091] The tracking test is carried out according to IEC 60587 (2007) Method 2A “Step-by-step tracking voltage method” and failure judgment criterion A. IEC 60587 (2007) stipulates that exceeding 60 mA does not occur earlier than the third voltage level. For all materials, five plates are measured, and the passing percentage is calculated based on the number of plates passing through the corresponding kV level. The test is carried out at 4.5 kV for 1 hour and at 4.75 kV for 1 hour or at 5.75 kV for 1 hour and at 6 kV for 1 hour, with the current not exceeding 60 mA.

[0092] According to ISO 293, plates (6 x 200 x 200 mm) are prepared by compression molding (Collin R 1358, version: 2 / 060510) for the tracking test. An ordinary strip about 1.2 mm thick is extruded and used in the plates. The pellets or strips are extruded between two Mylar film sheets and placed in a steel frame (200 x 200 x 6 mm). The sample is pressed by applying a pressure of 20 bar at 200 °C for 1 minute, and then a pressure of 200 bar at the same temperature for 5 minutes. The remaining compression is carried out at the same high pressure at a cooling rate of 15 °C / min for 9 minutes. The amount of pellets or strips used for each plate is calculated using the density of the material, with a 10% weight excess. According to the standard dimensions of the tracking test, the plates are sawn and drilled.

[0093] The tracking test in the examples was completed with non-crosslinked samples.

[0094] (4) Flame retardancy test

[0095] The covered conductor aerial cable is made of the tracking-resistant blend IE4 (as shown in Table 2 below). The cable is tested according to the single-wire vertical flame test in accordance with EN60332-1 and the single-wire flame test in UL 1581 and meets the requirements of both standards.

[0096] The covered conductor aerial cable consists of 7 aluminum conductors with a diameter of 7.8 mm and a length of 50 mm 2 . The blend of IE4 forms an insulating layer, and the average thickness of the tracking-resistant layer is 6.8 mm. The cable has a diameter of 21.4 mm.

[0097] (5) Median particle size (d 50 )

[0098] Median particle size d 50 It can be measured by laser diffraction (ISO 13320), dynamic light scattering (ISO 22412) or sieving analysis (ASTM D1921-06). For the metal hydroxides used in the working examples, the median particle size d 50 was determined by laser diffraction according to ISO 13320.

[0099] (6) Manufacture of strips for determining tensile strength, elongation at break, tracking and UV ageing

[0100] For the determination of tensile strength and elongation at break, strips (1.8 mm) were produced on a Collin TeachLine E20T strip extruder with a 4.2:1, 24D compression screw of 20 mm diameter. The temperature profile for the polymer was 150 / 180 / 200 °C and the screw speed was 55 rpm.

[0101] (7) Tensile testing

[0102] Tensile testing was carried out using an Alwetron TCT 10 tensile tester in accordance with ISO 527-1 and ISO 527-2. Ten test specimens were punched from the sheet using ISO 527-2 / 5A samples and placed in a climatic chamber at a relative humidity of 50 ± 5% and a temperature of 23 °C for at least 16 h before testing. The test specimens were placed vertically between grips at a distance of 50 ± 2 mm, the distance between the extensometer grips was 20 mm and the load cell was 1 kN. Before testing, the exact width and thickness of each specimen were measured and recorded. Each specimen bar was subjected to a tensile test at a constant speed of 50 mm / min until fracture, and at least 6 approved parallel tests were carried out. In highly filled systems, the results usually vary, so the median was used to obtain a single value for elongation at break (%) and tensile strength (MPa).

[0103] (8) UV ageing

[0104] UV ageing was carried out on 1 mm thick dumbbells in accordance with NFC62-062-2. Thus, it was carried out in a Sepap (mercury lamp) oven at 60 °C.

[0105] (9) Comonomer content of the polymer

[0106] Quantitative nuclear magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymer.

[0107] Hexene content

[0108] Using for 1H and 13 Quantitative 13 C{ 1 H} NMR spectra were recorded in the molten state on a Bruker Advance III 500 NMR spectrometer operating at 500.13 and 125.76 MHz for 13 C, respectively. All spectra were recorded at 150 °C using a

[0109] Quantitative 13 C{ 1 13 C optimized 7 mm magic angle spinning (MAS) probe and nitrogen was used for all pneumatic devices. Approximately 200 mg of the material was loaded into a zirconia MAS rotor with an outer diameter of 7 mm and spun at a frequency of 4 kHz. This setting was chosen mainly because of the high sensitivity required for rapid identification and accurate quantification (Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382., Parkinson, M., Klimke, K., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2007; 208:2128., Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373). Transient NOE with a short recycle delay of 3 s (Pollard, M., Klimke, K., Graf, R., Spiess, H.W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004; 37:813., Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382.) and the RS-HEPT decoupling scheme (Filip, X., Tripon, C., Filip, C., J. Mag. Resn. 2005, 176, 239, Griffin, J.M., Tripon, C., Samoson, A., Filip, C., and Brown, S.P., Mag. Res. in Chem. 2007 45, S1, S198) were used with standard single pulse excitation. A total of 16384 (16k) transients were acquired for each spectrum. This setting was chosen because it is highly sensitive to low comonomer content.

[0109] For quantitative 13 C{ 1The 1H NMR spectra were processed, integrated, and quantitative characteristics were determined using a custom spectral analysis automation program. All chemical shifts were referenced internally to the bulk methylene signal (δ+) at 30.00 ppm (J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201).

[0110] Characteristic signals corresponding to 1 - hexene incorporation were observed (J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201.), and all amounts were calculated relative to all other monomers present in the polymer.

[0111] Characteristic signals resulting from isolated 1 - hexene incorporation (i.e., EEHEE comonomer sequences) were observed. The integration of the signal at 38.29 ppm assigned to the *B4 site, which reports the number of sites per comonomer, was used to quantify isolated 1 - hexene incorporation:

[0112] H = I *B4

[0113] When characteristic signals resulting from consecutive 1 - hexene incorporation (i.e., EHHE comonomer sequences) were observed, the integration of the signal at 40.46 ppm assigned to the ααB4B4 site, which reports the number of sites per comonomer, was used to quantify this consecutive 1 - hexene incorporation:

[0114] HH = 2*I ααB4B4

[0115] When characteristic signals resulting from non - consecutive 1 - hexene incorporation (i.e., EHEHE comonomer sequences) were observed, the integration of the signal at 24.7 ppm assigned to the ββB4B4 site, which reports the number of sites per comonomer, was used to quantify this non - consecutive 1 - hexene incorporation:

[0116] HEH = 2*I ββB4B4

[0117] Due to the overlap of the signals from the *B4 and *ββB4B4 sites of 1 - hexene from isolated (EEHEE) and non - consecutive incorporations (EHEHE) respectively, the total amount of isolated 1 - hexene incorporation was corrected based on the amount of non - consecutive 1 - hexene present:

[0118] H = I *B4 - 2*I ββB4B4

[0119] In the case where no other signals indicating other comonomer sequences (i.e., 1-hexene chain initiation) are observed, the total 1-hexene comonomer content is calculated based only on the amounts of sequences containing isolated (EEHEE), consecutive (EHHE), and non-consecutive (EHEHE) 1-hexene comonomers:

[0120] H 总 = H + HH + HEH

[0121] Characteristic signals generated by saturated end groups are observed. The content of such saturated end groups is quantified using the average of the integrals of the signals at 22.84 and 32.23 ppm assigned to the 2s and 3s sites, respectively:

[0122] S = (1 / 2) * (I 2S + I 3S )

[0123] The relative content of ethylene is quantified using the integral of the bulk methylene (δ+) signal at 30.00 ppm:

[0124] E = (1 / 2) * I δ++

[0125] The total ethylene comonomer content is calculated based on the bulk methylene signal and taking into account the ethylene units present in other observed comonomer sequences or end groups:

[0126] E 总 = E + (2 / 2) * H + (1 / 4) * HH + (3 / 4) * HEH + (3 / 2) * S

[0127] Then the total mole fraction of 1-hexene in the polymer is calculated as follows:

[0128] fH = (H 总 / (E 总 + H 总 )

[0129] The comonomer incorporation of total 1-hexene in mole percentage is calculated from the mole fraction in the usual way:

[0130] H [mol%] = 100 * fH

[0131] The comonomer incorporation of total 1-hexene in weight percentage is calculated from the mole fraction in the standard way:

[0132] H [wt%] = 100 * (fH* 84.16) / ((fH * 84.16)+((1 - fH) * 28.05))

[0133] Butene content

[0134] Use for 1 H and 13 C respectively running at 500.13 and 125.76 MHz, the Bruker Advance III 500 NMR spectrometer records quantitative 13 C{ 1 H} NMR spectra. All spectra are used 13The C optimized 7 mm magic angle spinning (MAS) probe was recorded at 150 °C and nitrogen was used for all pneumatic devices. Approximately 200 mg of the material was loaded into a zirconia MAS rotor with an outer diameter of 7 mm and spun at a frequency of 4 kHz. This setting was chosen mainly because of the high sensitivity required for rapid identification and accurate quantification (Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207: 382., Parkinson, M., Klimke, K., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2007; 208: 2128., Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373). The transient NOE with a short recycle delay of 3 s (Pollard, M., Klimke, K., Graf, R., Spiess, H.W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004; 37: 813., Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207: 382.) and the RS-HEPT decoupling scheme (Filip, X., Tripon, C., Filip, C., J. Mag. Resn. 2005, 176, 239, Griffin, J.M., Tripon, C., Samoson, A., Filip, C., and Brown, S.P., Mag. Res. in Chem. 2007 45, S1, S198) were used with standard single pulse excitation. A total of 1024 (1k) transients were acquired for each spectrum. This setting was chosen because it is highly sensitive to low comonomer content.

[0135] For quantification 13 C{ 1 H} NMR spectra were processed, integrated, and the quantitative characteristics were determined using a custom spectral analysis automation program. All chemical shifts were internally referenced to the bulk methylene signal (δ+) at 30.00 ppm (J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201).

[0136] Characteristic signals corresponding to 1-butene incorporation were observed (J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201.). All amounts are calculated relative to all other monomers present in the polymer.

[0137] Characteristic signals resulting from isolated 1-butene incorporation (i.e., EEBEE comonomer sequences) were observed. Quantification of the isolated 1-butene incorporation was carried out using the integration of the signal at 93.84 ppm at the *B2 site, which indicates the reported number of sites per comonomer:

[0138] B = I *B2

[0139] When characteristic signals resulting from consecutive 1-butene incorporation (i.e., EBBE comonomer sequences) were observed, quantification of this consecutive 1-butene incorporation was carried out using the integration of the signal at 39.4 ppm at the ααB2B2 site, which indicates the reported number of sites per comonomer:

[0140] BB = 2*I ααB2B2

[0141] When characteristic signals resulting from non-consecutive 1-butene incorporation (i.e., EBEBE comonomer sequences) were observed, quantification of this non-consecutive 1-butene incorporation was carried out using the integration of the signal at 24.7 ppm at the ββB2B2 site, which indicates the reported number of sites per comonomer:

[0142] BEB = 2*I ββB2B2

[0143] Since the *B2 and *βB2B2 sites of 1-butene from isolated (EEBEE) and non-consecutive incorporation (EBEBE) overlap respectively, the total amount of isolated 1-butene incorporation was corrected based on the amount of non-consecutive 1-butene present:

[0144] B = I *B2 - 2*I ββB2B2

[0145] In the case where no other signals indicating other comonomer sequences (i.e., 1-butene chain initiation) were observed, the total 1-butene comonomer content was calculated based only on the amounts of isolated (EEBEE), consecutive (EBBE), and non-consecutive (EBEBE) 1-butene comonomer sequences:

[0146] B 总 = B + BB + BEB

[0147] Characteristic signals generated by saturated end groups were observed. The content of such saturated end groups was quantified using the average of the integrals of the signals at 22.84 and 32.23 ppm, which were respectively assigned to the 2s and 3s sites:

[0148] S = (1 / 2) * (I 2S + I 3S )

[0149] The relative content of ethylene was quantified using the integral of the bulk methylene (δ+) signal at 30.00 ppm:

[0150] E = (1 / 2) * I δ++

[0151] Based on the bulk methylene signal and considering the ethylene units present in other observed comonomer sequences or end groups, the total ethylene comonomer content was calculated:

[0152] E 总 = E + (5 / 2) * B + (7 / 2) * BB + (9 / 2) * BEB + (3 / 2) * S

[0153] Then the total mole fraction of 1-butene in the polymer was calculated as:

[0154] fB = (B 总 / (E 总 + B 总 )

[0155] The total comonomer incorporation of 1-butene in mole percentage was calculated from the mole fraction in the usual way:

[0156] B [mol%] = 100 * fB

[0157] The total comonomer incorporation of 1-butene in weight percentage was calculated from the mole fraction in the standard way:

[0158] B [wt%] = 100 * (fB * 56.11) / ((fB * 56.1

[0159] (10) Crystallinity

[0160] Crystallinity was determined by differential scanning calorimetry (DSC). The DSC experiments were run on a Mettler Toledo DSC 3+ device calibrated with indium, zinc, and tin according to ISO 11357 / 1. For the first heating run, cooling run, and second heating run, a heating / cooling / heating cycle with a scan rate of 10 °C / min between -60 °C and 180 °C was performed on 5 ± 1 mg samples in a nitrogen atmosphere (50 mL min -1 ). The melting and crystallization temperatures were specified as the peak temperatures in the second heating and cooling scans, respectively. The enthalpy of fusion (ΔH m ) was obtained by integrating the second heating run between 0 °C and 140 °C. The crystallinity was obtained by dividing this enthalpy by 290 J / g (i.e., the enthalpy of 100% crystalline polyethylene (ΔH 100％ )):

[0161] Crystallinity % = 100xΔH m / ΔH 100％

[0162] B. Materials

[0163] Polymer A

[0164] The polymer is a natural bimodal high-density polyethylene. Its melt flow rates are: MFR2 is 0.45 g / 10 min, MFR5 is 1.75 g / 10 min, and MFR 21 is 38 g / 10 min. The density is 942 kg / m 3 and it is produced using 1-butene as a comonomer (2 wt%).

[0165] Polymer B

[0166] Polymer B is a natural bimodal high-density polyethylene. Its melt flow rates are: MFR2 < 0.1 g / 10 min, MFR5 is 0.21 g / 10 min, MFR 21 is 6.2 g / 10 min. The density is 949 kg / m 3 and it is produced using 1-hexene as a comonomer (1.4 wt%). The production of Polymer B is described below.

[0167] Polymer production

[0168] Preparation of catalysts for polymers A and B

[0169] Complex preparation

[0170] 87 kg of toluene was added to the reactor. Then, 45.5 kg of BomagA in heptane was also added to the reactor. Then, 161 kg of 99.8% 2-ethyl-1-hexanol was introduced into the reactor at a flow rate of 24 - 40 kg / h. The molar ratio between BOMAG-A and 2-ethyl-1-hexanol was 1:1.83.

[0171] Preparation of solid catalyst components

[0172] 275 kg of silica (ES747JR from Crossfield, with an average particle size of 20 μm) activated in nitrogen at 600 °C was charged into the catalyst preparation reactor. Then, at room temperature, 411 kg of 20% EADC (2.0 mmol / g of silica) diluted in 555 liters of pentane was added to the reactor within one hour. Then the temperature was raised to 35 °C while the treated silica was stirred for one hour. The silica was dried at 50 °C for 8.5 hours. Then, 655 kg of the complex prepared as described above (2 mmol of Mg / g of silica) was added at 23 °C within 10 minutes. At 22 °C, 86 kg of pentane was added to the reactor within 10 minutes. The slurry was stirred at 50 °C for 8 hours. Finally, 52 kg of TiCl4 was added at 45 °C within 0.5 hour. The slurry was stirred at 40 °C for 5 hours. Then the catalyst was dried by purging with nitrogen.

[0173] Polymer A

[0174] Polymer A was produced according to Example 1 of EP 1327664 B1.

[0175] Polymer B

[0176] A loop reactor with a volume of 50 dm 3 operated at a temperature of 70 °C and a pressure of 57 bar. Ethylene, propane diluent, and hydrogen were fed into the reactor. The solid Ziegler-Natta polymerization catalyst produced as described above was also introduced into the reactor together with a triethylaluminum cocatalyst such that the Al / Ti molar ratio was about 15. The estimated production split was 2 wt%.

[0177] The slurry stream was continuously withdrawn and introduced into a loop reactor with a volume of 150 dm 3 operating at a temperature of 95 °C and a pressure of 55 bar. Additional ethylene, propane diluent, and hydrogen were further fed into the reactor such that the ethylene concentration in the fluid mixture was 3.9 mol% and the ratio of hydrogen to ethylene was 390 mol / kmol. The estimated production split was 16 wt%. The ethylene homopolymer withdrawn from the reactor had an MFR2 of 280 g / 10 min.

[0178] The slurry stream from the reactor is withdrawn intermittently and introduced into a loop reactor operating at a temperature of 95 °C and a pressure of 52 bar. Fresh propane, ethylene, and hydrogen are further added to the reactor such that the ethylene concentration in the fluid mixture is 3.7 mol% and the molar ratio of hydrogen to ethylene is 370 mol / kmol. The ethylene homopolymer withdrawn from the reactor has an MFR2 of 282 g / 10 min. The estimated production split ratio is 27 wt%. 3

[0179] The slurry is withdrawn intermittently from the loop reactor and introduced into a flash vessel operating at a temperature of 50 °C and a pressure of 3 bar. From there, the polymer is introduced into a fluidized bed gas phase reactor operating at a pressure of 20 bar and a temperature of 85 °C. Additional ethylene and 1-hexene comonomers, nitrogen as an inert gas, and hydrogen are added such that the molar ratio of hydrogen to ethylene is 7 mol / kmol and the molar ratio of 1-hexene to ethylene is 46 mol / kmol. The estimated production split ratio is 55 wt%. The polymer has a melt flow rate MFR5 of 0.22 g / 10 min and a density of 949 kg / m 3 .

[0180] Preparation of Polymer Compositions

[0181] The polymer compositions of the examples according to the invention (IE1 to IE6) and the comparative examples (CE1 and CE2) are prepared by mixing the components in a BUSS co-kneader (MDK / E 46-B) at a screw speed of 225 rpm and with the temperature set at 40, 160, 180, 200 °C in the kneading section and 200 °C in the granulation extruder. The mixer screw is heated to 120 °C. The extruder screw temperature is 160 °C, the barrel is heated to 170 °C, and the speed is 4 rpm. The amounts of the different components and the properties of the polymer compositions of the examples according to the invention and the comparative examples are shown in Tables 2 and 3 below.

[0182] CE2 contains 74.35 wt% of the CE1 composition shown in Table 2 below and additional additives. IE2 and IE3 contain 75 wt% of the IE1 composition shown in Table 2 and additional additives. IE5 and IE6 contain the respective amounts of IE1 given in Table 3 below and additional additives / materials.

[0183] Additives / Materials

[0184] 944, 2020, and 783 are hindered amine light stabilizers commercially available from BASF. ​

[0185] 1010 and 168 is a heat stabilizer commercially available from BASF.

[0186] Calcium stearate is available from commercially available.

[0187] The carbon black used is commercially available from Orion.

[0188] MDH-1 is a coated precipitated magnesium hydroxide ( H5HV) commercially available from Huber, with a particle size of 1.6 - 2.0 μm determined by laser diffraction and a BET surface area of 5 m 2 / g.

[0189] MDH-2 is a stearic acid-coated ground magnesium hydroxide commercially available from Europiren B.V. (Netherlands), ( 3,5C), with a particle size (D 50 ) of 3.5 μm determined by laser diffraction and a BET surface area of 7 - 10 m 2 / g.

[0190] CaCO3 is a stearic acid-coated calcium carbonate (EXh1 SP) commercially available from Omya AG, Switzerland, with a particle size of 1.4 μm determined by laser diffraction.

[0191] GE300C is a linear low density polyethylene grafted with maleic anhydride, commercially available from HDC Hyundai EP Co., Ltd. under the trade name GE300C (maleic anhydride content = 0.5 to 1.0 wt%, MFR2 = 2.0 g / 10 min, density = 930 kg / m 3 ).

[0192] QUEO 8201 is a very low density polyethylene copolymer commercially available from Borealis AG (Austria) under the name Queo 8201, with a density of 883 kg / m 3 , and an MFR2 of 1.1 g / 10 min.

[0193] Table 2

[0194]

[0195]

[0196] Table 3

[0197]

[0198]

[0199] Comparative examples CE1 and CE2 in Table 2 above show that the addition of magnesium hydroxide as a filler significantly improves tracking resistance. However, the polymer composition containing 25 wt% magnesium hydroxide according to CE2 also did not pass the tracking test at the 6 kV level but was limited to 4.75 kV. Surprisingly, the polymer composition (IE1) according to the present invention passed the tracking test at 4.75 kV, had a passing percentage of 40% at 6 kV without the addition of magnesium hydroxide and additionally showed good mechanical properties.

[0200] A mixture of CaCO3 and Mg(OH)2 can also provide good tracking and flame retardant properties. Even when using a higher filler content in IE4 to IE6, it not only results in excellent tracking properties but also satisfactory mechanical properties.

[0201] By incorporating fillers into the polymer formulation IE1 of the present invention, as done in IE2, IE3, IE4, IE5 and IE6, a passing percentage of 100% can be achieved at the highest tracking level (6 kV). This level can also be reached using calcium carbonate. In addition, the fillers used in IE2 and IE3 have a significant cost advantage over the filler used in CE2. It can also be seen that compared with the composition (CE2) containing magnesium hydroxide as a filler, the IE3 composition containing calcium carbonate as a filler has less reduction in mechanical and electrical properties. In highly filled materials, optionally using a polymer with filler acceptability can improve mechanical properties.

[0202] For IE4, a flame retardant test was also carried out. The coated conductor containing the IE4 composition was tested according to the vertical burning test according to EN60332-1 and the single wire burning test of UL 1581. The cable meets the requirements of both standards. The material composition containing fillers in IE4 can achieve the required fire protection performance for cables and coated conductors and can suppress or reduce the spread of fire.

[0203] The polymer composition according to IE1 further gives acceptable performance in the Sepap ultraviolet aging test, reaching an absolute elongation of 50% after 1000 hours of aging. This shows that even without the addition of carbon black, the material shows sufficient long-term stability without brittleness. The results further show that although it does not contain carbon black, the composition of IE1 can still be advantageously used in overhead power cables, having sufficient heat resistance to sunlight and improved ultraviolet resistance. Therefore, power loss can be reduced compared with black cables. In addition, the visibility of the cable will be reduced, especially if it is grey.

[0204] Accordingly, the multimodal hexene-based polymer compositions of the present invention exhibit surprisingly improved tracking resistance even in the absence of fillers in the polymeric material, making them highly suitable for high-end wire and cable applications, especially fiber optic cables or overhead power cables. In addition to the improved tracking resistance, the filled polymer compositions of the present invention are further improved in heat resistance and UV resistance, showing good mechanical properties. Moreover, the compositions of the present invention containing fillers, especially metal hydroxides or metal carbonates, also exhibit flame retardant properties, reducing the risk of spreading bushfires.

Claims

1. A crosslinkable polymer composition comprising a copolymer of ethylene and hexene, said copolymer being a multimodal polyethylene having at least two polymer fractions in the polymer, each polymer fraction having a different weight average molecular weight, said copolymer having a crystallinity of at least 40% as determined by DSC, based on the total weight of the polymer composition, the polymer composition further comprises a carbon black content of 0 wt% to not more than 4 wt%, wherein the copolymer of ethylene and hexene has a content of units derived from 1 - hexene of 0.50 to 0.70 mol%, wherein the copolymer of ethylene and hexene has a density of 920 to 970 kg / m 3 and a melt flow rate MFR2 determined according to ISO 1133 at 190 °C under a load of 2.16 kg of less than 0.4 g / 10 min, wherein the polymer composition does not contain a silane-modified polymer component, and the polymer composition has passed the tracking resistance test according to IEC60587(2007) method 2A on a molded plate prepared according to ISO 11357 at least at 4.5 kV for 1 hour and then at 4.75 kV for 1 hour.

2. The crosslinkable polymer composition according to claim 1, wherein the polymer composition has passed the tracking resistance test according to IEC60587(2007) method 2A on a molded plate prepared according to ISO 11357 at least at 5.75 kV for 1 hour and then at 6 kV for 1 hour.

3. The crosslinkable polymer composition according to claim 1 or 2, further comprising a filler selected from aluminum oxide, metal carbonate, calcium oxide and / or metal hydroxide, and / or further comprising an ultraviolet stabilizer and / or an antioxidant and / or a pigment, and / or further comprising an ethylene polymer or copolymer grafted or copolymerized with an unsaturated carboxylic acid or its derivative, and / or an elastomeric ethylene copolymer.

4. The crosslinkable polymer composition according to claim 3, wherein based on the total weight of the polymer composition, the content of the filler is at least 25 wt%.

5. The crosslinkable polymer composition according to claim 3, wherein the ultraviolet stabilizer is a hindered amine light stabilizer (HALS).

6. The crosslinkable polymer composition according to claim 1 or 2, having a tensile strength of at least 12.5 MPa as determined by ISO527 - 2, and / or the polymer composition has an elongation at break of at least 300% as determined by ISO 527 - 2, and / or the polymer composition has ultraviolet resistance in terms of at least 50% elongation after 1000 h aging as determined by the Sepap ultraviolet aging test measured on a 1 mm plate according to NFC62 - 062 - 2.

7. The crosslinkable polymer composition according to claim 1 or 2, which has been crosslinked in the presence of a crosslinking agent or in the presence of moisture and a condensation catalyst.

8. A tracking - resistant cable comprising at least one layer of the polymer composition according to any one of claims 1 to 7.

9. The cable according to claim 8, which is a power cable or an optical fiber cable.

10. The cable according to claim 8 or 9, wherein the at least one layer is an insulating layer, or a jacket layer or a sheath layer.

11. Use of a polymer composition according to any one of claims 1 to 7 in an electric wire or cable for improving tracking resistance and / or for improving flame retardancy along the length of the electric wire or cable.

12. A method of manufacturing a polymer composition according to any one of claims 1 to 7, which comprises polymerizing at least two polymer components in different reaction stages of a multi-stage polymerization process in the presence of a polymerization catalyst, wherein the polymer components formed in the preceding polymerization stages are present in the subsequent polymerization stages.

13. The method according to claim 12, wherein the polymerization is carried out in the presence of a Ziegler-Natta catalyst.

Images