Crosslinkable stabilized polymer composition

Abstract

The present invention relates to a crosslinkable polyethylene composition comprising an additive composition consisting of a mixture of polyethylene glycol and a mixture of 4, 4 '-thiobis (2-tert-butyl-5-methylphenol) plus thio-diethylene bis [3-(3, 5-di-tert-butyl-4-hydroxyphenyl) propionate], and a method for producing the crosslinkable polyethylene composition.

Description

Technical Field

[0001] The present invention relates to stabilizable polymer compositions which can be crosslinked. Such compositions are used in particular as insulating layers for cables, especially for cables exposed to water. Background Art

[0002] Typical power cables generally comprise one or more conductors in a cable core, which is surrounded by several layers of polymeric materials, which layers include an inner semiconductive layer, followed by an insulating layer, and then an outer semiconductive layer. These layers are generally crosslinked. Other layers such as a metal tape or a metal wire shield or screen can be added on these layers, and finally a sheath layer is added. In electro-strained polymeric materials, in the presence of water, so-called "water treeing" may occur. This is a degradation mechanism that can lead to a lower electrical breakdown strength Eb of the insulation system. Crosslinking by peroxides can lead to the formation of so-called "scorch", i.e., non-uniformities, surface irregularities and possible discoloration. Therefore, any significant decomposition of the free radical former during extrusion should be avoided, and thus an anti-scorch agent is used as an additive. An "anti-scorch agent" is a component that reduces the formation of scorch during the extrusion of a polymer composition, compared to the same polymer composition extruded without said component, typical examples of which are 2,4-diphenyl-4-methyl-1-pentene, substituted or unsubstituted diphenylethylene, quinone derivatives, hydroquinone derivatives, esters and ethers containing a monofunctional vinyl group, or mixtures thereof. In addition to good anti-scorch properties, a high degree of crosslinking and good thermo-oxidative stability are also important for applications such as cables.

[0003] EP3045496 relates to a crosslinked polyethylene resin composition comprising a) 100 parts by weight of low density polyethylene (LDPE), which can be a homopolymer of ethylene or a copolymer of ethylene, wherein the comonomer is selected from the group consisting of propylene, 1-butene, 1-pentene, 1-hexene and 1-octene, b) 0.1 to 10 parts by weight of a crosslinking agent, c) 0.1 to 5 parts by weight of a crosslinking promoter selected from the group consisting of, for example, 2,4-diphenyl-4-methyl-1-pentene, 1,4-hydroquinone and hydroquinone derivatives, d) 0 to 5 parts by weight of a treeing inhibitor such as polyethylene glycol, and e) more than 0.3 parts by weight and 5 parts by weight or less of an antioxidant which is a mixture of, for example, a thio-bisphenol-based antioxidant and a thio-propionate-based antioxidant. The low density polyethylene (LDPE) does not contain polar groups.

[0004] EP966003 describes 100 parts by weight of polyethylene and 0.3 to 0.6 parts by weight of an antioxidant selected from 4,4'-thiobis(2-methyl-6-tert-butylphenol), 4,4'-thiobis(2-tert-butyl-5-methylphenol), or 2,2'-thiobis(6-tert-butyl-4-methylphenol) and 0.4 to 1 part by weight of polyethylene glycol having a weight average molecular weight of 1000 to 100000.

[0005] CA2650428 relates to a composition comprising i) 100 parts by weight of polyethylene which is a homopolymer prepared by free-radical initiated reaction in a tubular reactor or autoclave reactor at high temperature and high pressure, or alternatively a copolymer prepared by copolymerizing ethylene and a comonomer at low temperature and low pressure using a Ziegler-Natta catalyst or a metallocene catalyst, or a copolymer of at least one α-olefin selected from the group consisting of 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene; and based on 100 parts by weight of polyethylene, ii) 1 to 4 parts by weight of a chemical crosslinking agent; iii) 0.3 to 0.8 parts by weight of an antioxidant; and iv) 0.3 to 1.0 part by weight of polyethylene glycol having a molecular weight in the range of 5000 to 50000. Further, the anti-treeing, crosslinkable polyolefin composition may further comprise 0.1 to 1.0 part by weight of 2,4-diphenyl-4-methyl-1-pentene. CA2650428 teaches the use of a mixture comprising 4,4'-thiobis(2-tert-butyl-5-methylphenol) and at least one selected from the group consisting of tetrakis[methylene(3,5-di-tert-butyl-4-hydroxy-hydrocinnamate)]methane, 4,6-bis(octylthio)butyl)-o-cresol, and 2,2'-thiobis[ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)]propionate as the antioxidant.

[0006] EP1731564 discloses a crosslinkable polymer composition comprising: (i) an unsaturated polyolefin having a total of vinyl / 1000 carbon atoms greater than 0.37, and (ii) at least one additive containing an ether and / or ester group selected from the group consisting of polyethylene glycol, glyceride compounds, polypropylene glycol, fatty acid esters containing an amide group, ethoxylated and / or propoxylated pentaerythritol, α-tocopherol esters, ethoxylated and / or propoxylated fatty acids and their derivatives. EP1731564 further relates to the use of an antioxidant and optionally a mixture of two or more antioxidants, only mentioning sterically hindered or semi-sterically hindered phenols, aromatic amines, aliphatic hindered amines, organophosphates, sulfur compounds, and mixtures thereof.

[0007] There is still a need for a crosslinkable composition that provides a good balance of water tree retardancy, degree of crosslinking, resistance to coking, thermo-oxidative stability, and storage stability (i.e., low migration of additives to the pellet surface during storage). SUMMARY OF THE INVENTION

[0008] The present invention provides

[0009] a crosslinkable polymer composition comprising

[0010] i) a low density polyethylene (LDPE) copolymer having at least one polyunsaturated comonomer, preferably one polyunsaturated comonomer, said at least one polyunsaturated comonomer optionally combined with one or more other comonomers; and

[0011] ii) an additive composition consisting of a mixture of polyethylene glycol and 4,4'-thiobis(2-tert-butyl-5-methylphenol) plus thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; and

[0012] iii) a peroxide crosslinking agent; and

[0013] iv) an anti-scorch agent.

[0014] Thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is also known as 2,2'-thiodiethylidenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0015] The present invention further relates to a material obtained by crosslinking the crosslinkable polymer composition as described herein.

[0016] In yet another aspect, the present invention relates to the use of the crosslinkable polymer composition according to the present invention for cables.

[0017] The present invention further relates to a cable comprising a material as described herein.

[0018] "Crosslinkable" means that the polymer composition can be crosslinked using an incorporated peroxide crosslinking agent(s) prior to use in its final application.

[0019] After crosslinking, a crosslinked polymer composition having a typical network (especially polymer-polymer crosslinks (bridges) well known in the art) is obtained.

[0020] "Unsaturated ethylene acrylate polymer" means a copolymer containing at least units derived from ethylene as a monomer and units derived from an acrylate monomer (such as an alkyl acrylate and / or an alkyl methacrylate).

[0021] "Antiscorching agent" is a compound that reduces premature crosslinking (i.e., "scorch" formation during extrusion). In addition to the antiscorching property, the antiscorching agent can also produce other effects simultaneously, such as an enhancing effect, i.e., improving the crosslinking property.

[0022] It is obvious to those skilled in the art that the crosslinked polymer composition can be and is defined herein as having characteristics that exist in the polymer composition, polymer (i) before or after crosslinking, as described or obvious in the context.

[0023] Preferably, a low-density polyethylene (LDPE) copolymer having at least one polyunsaturated comonomer, optionally combined with one or more other comonomers, preferably one polyunsaturated comonomer, is an unsaturated ethylene acrylate polymer.

[0024] Further preferably, a low-density polyethylene (LDPE) copolymer having at least one polyunsaturated comonomer, optionally combined with one or more other comonomers, particularly one polyunsaturated comonomer, has a total of greater than 0.30, preferably 0.40 (as described herein), more preferably greater than 0.43, and even more preferably 0.46 vinyl groups per 1000 carbon atoms. In addition, preferably, a low-density polyethylene (LDPE) copolymer having at least one polyunsaturated comonomer, optionally combined with one or more other comonomers, particularly one polyunsaturated comonomer, has a total of less than 2.0, less than 1.7, less than 1.5, less than 1.3, less than 1.0 vinyl groups / 1000 carbon atoms.

[0025] A low-density polyethylene (LDPE) copolymer having at least one polyunsaturated comonomer, optionally combined with one or more other comonomers, preferably one polyunsaturated comonomer, particularly an unsaturated ethylene acrylate polymer combination is preferably a terpolymer.

[0026] In a preferred aspect, the unsaturated ethylene acrylate polymer is selected from the list consisting of unsaturated ethylene methyl acrylate polymer, unsaturated ethylene ethyl acrylate polymer, unsaturated ethylene butyl acrylate polymer, and mixtures thereof. More preferably, the unsaturated ethylene acrylate polymer is an ethylene butyl acrylate terpolymer. Most preferably, the unsaturated ethylene acrylate polymer is an unsaturated ethylene acrylate non-conjugated diene terpolymer.

[0027] The non-conjugated diene is preferably selected from the group consisting of 1,7-octadiene, 1,9-decadiene, 1,11-dodecadiene, 1,13-tetradecadiene, 7-methyl-1,6-octadiene, 9-methyl-1,8-decadiene, and mixtures thereof. In a particularly preferred embodiment, the unsaturated ethylene acrylate polymer is an ethylene-1,7-octadiene-butyl acrylate terpolymer.

[0028] In a preferred embodiment, the unsaturated ethylene acrylate polymer comprises 0.001 to 40% by weight, more preferably 0.001 to 30% by weight, 0.001 to 20% by weight, 0.001 to 15% by weight, 0.001 to 10% by weight, 0.001 to 5.0% by weight, 0.001 to 3.0% by weight of acrylate based on the total weight of the unsaturated ethylene acrylate polymer.

[0029] The crosslinkable polymer composition according to the invention preferably comprises

[0030] i) a low density polyethylene (LDPE) copolymer, preferably an unsaturated ethylene acrylate polymer, having at least one polyunsaturated comonomer optionally combined with one or more other comonomers, in an amount greater than 95.5% by weight, more preferably greater than 96.0% by weight, based on the total weight of the crosslinkable polymer composition, and

[0031] ii) an additive composition in an amount of 0.50 to 1.65% by weight, more preferably 0.90 to 1.20% by weight, based on the total weight of the crosslinkable polymer composition, the additive composition consisting of a mixture of polyethylene glycol and 4,4'-thiobis(2-tert-butyl-5-methylphenol) plus thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate];

[0032] iii) a peroxide crosslinking agent in an amount of at most 1.80% by weight, more preferably at most 1.70% by weight, most preferably at most 1.60% by weight, such as 0.50 to 1.60% by weight, based on the total weight of the crosslinkable polymer composition; and

[0033] iv) an anti-scorching agent in an amount of 0.1 to 0.5% by weight, more preferably 0.30 to 0.50% by weight, most preferably 0.35 to 0.50% by weight, based on the total weight of the crosslinkable polymer composition.

[0034] In a preferred embodiment, the crosslinkable polymer composition according to the invention preferably comprises

[0035] i) A low-density polyethylene (LDPE) copolymer, preferably an unsaturated ethylene acrylate polymer, greater than 96.0 wt% based on the total weight of the crosslinkable polymer composition, the low-density polyethylene (LDPE) copolymer having at least one polyunsaturated comonomer optionally combined with one or more other comonomers, and

[0036] ii) An additive composition of 0.90 to 1.20 wt% based on the total weight of the crosslinkable polymer composition, the additive composition consisting of polyethylene glycol and a mixture of 4,4'-thiobis(2-tert-butyl-5-methylphenol) plus thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate];

[0037] iii) A peroxide crosslinking agent of at most 1.80 wt%, more preferably at most 1.70 wt%, most preferably at most 1.60 wt%, such as 0.50 to 1.60 wt% based on the total weight of the crosslinkable polymer composition; and

[0038] iv) A scorch retarder of 0.1 to 0.5 wt%, more preferably 0.30 to 0.50 wt%, most preferably 0.35 to 0.50 wt% based on the total weight of the crosslinkable polymer composition.

[0039] More preferably, the crosslinkable polymer composition (as described exactly above) is characterized in that, in addition to the components contained in the additive composition (ii) and / or in addition to the scorch retarder iv), the total amount of additive v) is less than 0.40 wt%, particularly less than 0.3 wt%, such as less than 0.10 wt%, based on the total weight of the crosslinkable polymer composition, and

[0040] wherein components i), ii), iii), iv) and v) total 100 wt%. Particularly preferably, component i) is the balanced component totaling 100 wt%. The abbreviation "v)" represents "additives" in addition to the components contained in the said additive composition ii) and in addition to the components contained in the scorch retarder iv).

[0041] In an independent and particularly preferred aspect, 4,4'-thiobis(2-tert-butyl-5-methylphenol) is present in an amount of 0.12 to 0.22 wt% relative to the total crosslinkable polymer composition.

[0042] In yet another and also independently preferred aspect, thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is present in an amount of 0.10 to 0.40 wt%, preferably 0.15 to 0.25 wt% relative to the total crosslinkable polymer composition.

[0043] Most preferably, 4,4'-thiobis(2-tert-butyl-5-methylphenol) is present in an amount of 0.12 to 0.22% by weight relative to the total crosslinkable polymer composition, and

[0044] thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is present in an amount of 0.10 to 0.40% by weight, particularly 0.15 to 0.25% by weight relative to the total crosslinkable polymer composition.

[0045] In yet another aspect, polyethylene glycol is present in an amount of 0.30 to 1.00% by weight and preferably 0.40 to 0.80% by weight relative to the total crosslinkable polymer composition.

[0046] The present invention also relates to the use of the crosslinkable polymer composition described herein for cables.

[0047] In another aspect, the present invention relates to a material obtained by crosslinking the crosslinkable polymer composition described herein.

[0048] Preferably, the material is characterized in that the extruded model cable has a breakdown strength of at least 75.0 kV / mm, preferably at least 80.0 kV / mm and more preferably at least 85.0 kV / mm measured after 1000 hours of wet aging as described in the specification, which breakdown strength is represented by the Weibull 63.2% value and is referred to as Eb(63%) in the present invention.

[0049] The present invention also relates to a cable comprising the material described herein. The cable is preferably a power cable. Detailed Description

[0050] Hereinafter, several preferred embodiments will be described. These embodiments can be combined with any of the preferred aspects discussed above as appropriate.

[0051] The first preferred embodiment is a crosslinkable polymer composition comprising

[0052] i) an unsaturated ethylene acrylate polymer having a total of more than 0.40 vinyl groups per 1000 carbon atoms (as described herein), wherein the unsaturated ethylene acrylate polymer is an unsaturated ethylene acrylate non-conjugated diene terpolymer; and

[0053] ii) an additive composition consisting of a mixture of polyethylene glycol and 4,4'-thiobis(2-tert-butyl-5-methylphenol) plus thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; and

[0054] iii) A peroxide crosslinking agent; and

[0055] iv) A scorch retarder.

[0056] A second preferred embodiment is a crosslinkable polymer composition comprising

[0057] i) An unsaturated ethylene acrylate polymer greater than 96.0% by weight based on the total weight of the crosslinkable polymer composition, the unsaturated ethylene acrylate polymer having a total of greater than 0.40 vinyl groups per 1000 carbon atoms (as described herein); and

[0058] ii) An additive composition of 0.90 to 1.20% by weight based on the total weight of the crosslinkable polymer composition, the additive composition consisting of a mixture of polyethylene glycol and 4,4'-thiobis(2-tert-butyl-5-methylphenol) plus thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; and

[0059] iii) A peroxide crosslinking agent of at most 1.80% by weight, more preferably at most 1.70% by weight, most preferably at most 1.60% by weight, such as 0.50 to 1.60% by weight based on the total weight of the crosslinkable polymer composition; and

[0060] iv) A scorch retarder of 0.1 to 0.5% by weight, more preferably 0.30 to 0.50% by weight, most preferably 0.35 to 0.50% by weight based on the total weight of the crosslinkable polymer composition.

[0061] A third particularly preferred embodiment is a crosslinkable polymer composition comprising

[0062] i) An unsaturated ethylene acrylate polymer greater than 96.0% by weight based on the total weight of the crosslinkable polymer composition, the unsaturated ethylene acrylate polymer having a total of greater than 0.40 vinyl groups per 1000 carbon atoms (as described herein), wherein the unsaturated ethylene acrylate polymer is an unsaturated ethylene acrylate non-conjugated diene terpolymer; and

[0063] ii) An additive composition of 0.90 to 1.20% by weight based on the total weight of the crosslinkable polymer composition, the additive composition consisting of a mixture of polyethylene glycol and 4,4'-thiobis(2-tert-butyl-5-methylphenol) plus thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; and

[0064] iii) a peroxide crosslinking agent of up to 1.80 wt%, more preferably up to 1.70 wt%, most preferably up to 1.60 wt%, such as 0.50 to 1.60 wt% based on the total weight of the crosslinkable polymer composition; and

[0065] iv) an anti-scorching agent of 0.1 to 0.5 wt%, more preferably 0.30 to 0.50 wt%, most preferably 0.35 to 0.50 wt% based on the total weight of the crosslinkable polymer composition.

[0066] A fourth particularly preferred embodiment is a crosslinkable polymer composition comprising

[0067] i) an unsaturated ethylene acrylate polymer of greater than 96.0 wt% based on the total weight of the crosslinkable polymer composition, the unsaturated ethylene acrylate polymer having a total of greater than 0.40 vinyl groups per 1000 carbon atoms (as described herein), wherein the unsaturated ethylene acrylate polymer is an unsaturated ethylene acrylate non-conjugated diene terpolymer; and

[0068] ii) an additive composition of 0.90 to 1.20 wt% based on the total weight of the crosslinkable polymer composition, the additive composition consisting of a mixture of polyethylene glycol and 4,4'-thiobis(2-tert-butyl-5-methylphenol) plus thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate];

[0069] wherein

[0070] 4,4'-thiobis(2-tert-butyl-5-methylphenol) is present in an amount of 0.12 to 0.22 wt% relative to the total crosslinkable polymer composition; and

[0071] wherein

[0072] thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is present in an amount of 0.10 to 0.40 wt% relative to the total crosslinkable polymer composition;

[0073] and

[0074] iii) a peroxide crosslinking agent of up to 1.80 wt%, more preferably up to 1.70 wt%, most preferably up to 1.60 wt%, such as 0.50 to 1.60 wt% based on the total weight of the crosslinkable polymer composition; and

[0075] iv) an anti-scorching agent of 0.1 to 0.5 wt%, more preferably 0.30 to 0.50 wt%, most preferably 0.35 to 0.50 wt% based on the total weight of the crosslinkable polymer composition.

[0076] A further preferred embodiment is a material obtained by crosslinking the crosslinkable polymer compositions described in the preferred embodiments above. A further particularly preferred embodiment is a cable comprising these materials.

[0077] The specific embodiments mentioned above can be combined with any of the generally described preferred ranges disclosed.

[0078] Experimental Section

[0079] Measurement Methods

[0080] Unless otherwise defined, the following definitions of terms and measurement methods apply to the above general description of the invention and the following examples.

[0081] a) Melt Flow Rate

[0082] The melt flow rate (MFR) is determined according to ISO 1133 and expressed in g / 10 min. The MFR represents the fluidity of the polymer and thus represents the processability of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. For polyethylene, the MFR is determined at 190 °C and can be determined at different loads, such as 2.16 kg (MFR2) or 21.6 kg (MFR 21 )

[0083] b) Density

[0084] The density is measured according to ISO 1183-1 / Method A. Sample preparation is carried out by compression molding according to ISO 17855-2:2016.

[0085] c) Crosslinking of Plates

[0086] The crosslinked plates are prepared from the pellets of the test polymer composition or from the extruded tapes of the test polymer composition, i.e., the polymer compositions comprising the polymer composition according to the invention and the polymer compositions comprising the comparative polymer composition, which are compression molded under the following conditions: First, the pellets are melted at 120 °C under a pressure of 61 N / cm 2 for 1 min. Then, the temperature is raised to 180 °C at a rate of 18 °C / min, and simultaneously the pressure is raised to 614 N / cm 2This temperature is maintained at 180 °C for 8 min. The total crosslinking time is 12 min, which includes the time for raising the temperature from 120 °C to 180 °C. After completion of the crosslinking, the crosslinked plates (i.e., the crosslinked polymer compositions according to the invention and the crosslinked comparative polymer compositions) are still cooled to room temperature under pressure at a cooling rate of 15 °C / min. For the crosslinked plates used for heat setting measurement, the final thickness of the crosslinked plates is about 1.0 mm. Details of the samples for extrusion tape are described below in "Sample Preparation and Thermal Oxidation Aging for Thermal Oxidation Aging".

[0087] d) Heat setting method for samples from crosslinked plates

[0088] The heat setting elongation and the permanent deformation are determined on samples taken from the crosslinked plates (i.e., the crosslinked polymer compositions containing the polymer compositions according to the invention and the crosslinked polymer compositions containing the comparative compositions). These properties are determined according to IEC 60811-507:2012. In the heat setting test, the dumbbell-shaped test material is equipped with a weight corresponding to 20 N / cm 2 . First, the specimen is marked with reference lines. Starting from the middle of the specimen, two reference lines are made (one reference line on each side). The distance L0 between the two lines is 20 mm. The specimen is placed in an oven at 200 °C, where the weight corresponds to 20 N / cm 2 , and after 15 min, the heat setting elongation is measured as follows. After 15 min at 200 °C, the distance between the reference lines is called L1 and is measured. Then, the elongation after 15 min is calculated as follows: Heat setting elongation (%) = ((L1 * 100) / L0) - 100. Subsequently, the weight is removed and the sample is allowed to relax at 200 °C for 5 min. Then, the sample is taken out of the oven and cooled to room temperature. After cooling, the distance L2 between the two reference lines is measured, and the permanent deformation is calculated as follows: Permanent deformation (%) = ((L2 * 100) / L0) - 100.

[0089] The crosslinked plates are prepared as described in the preparation of crosslinked plates (i.e., the method for crosslinked plates), and the dumbbell-shaped specimens are prepared from the crosslinked plates with a thickness of about 1.0 mm according to ISO 527-2 / 5A.

[0090] e) Monsanto scorch

[0091] The anti-scorch formation of different formulations was evaluated in a Monsanto MDR2000 rheometer. The experiment was carried out using a compression-molded circular plate with a thickness of about 3 mm. The circular plate was pressed at 120 °C for 2 min without pressure, followed by pressing at a pressure of 5 tons for 2 min. Then, the plate was cooled to room temperature. The torque increase with time was monitored in the Monsanto rheometer. The time required to reach a certain torque increase was determined. In this case, the time taken from the start of the test until the torque increased by 1 dNm from the minimum value in the torque curve was reported. The longer the time taken, the stronger the resistance of the test formulation to scorch formation. For the polymer compositions of the present invention and the comparative polymer compositions, a temperature of 135 °C was used to generate data.

[0092] f) Sample preparation for thermal oxidative aging and thermal oxidative aging

[0093] Using a Collin Teach-Line E 20T tape extruder with the following temperature settings: 60 °C (zone 1), 115 °C (zone 2), 120 °C (zone 3), and 125 °C (zones 4 to 6), the pellets containing the polymer compositions of the present invention and the pellets containing the comparative polymer compositions were respectively extruded into tapes with a thickness of about 0.6 to 0.7 mm. Then, by placing all the tapes in one direction, and then according to the description of "crosslinking of plates" given above, these tapes with the corresponding compositions were used to prepare crosslinked plates, where the thickness changed to about 2 mm instead of the floor. Dumbbell-shaped specimens were prepared from the crosslinked plates according to ISO527-2 / 5A. Before thermal oxidative aging, the dumbbell-shaped specimens were conditioned at 70 °C for 24 h. Then, the dumbbell-shaped specimens were placed in a cell oven at 150 °C and aged with different aging times with 15 air changes per hour. "Zero" samples were collected after the conditioning step for determining the tensile properties of the compositions of the present invention and the comparative compositions before the start of thermal oxidative aging. The thermal oxidative aging performance was monitored by performing tensile tests on samples taken out of the oven at different aging times. Before the tensile test, the samples were kept in a constant room (23 °C and 50% relative humidity) for at least 16 h. For each sample taken out (aging time), 6 to 8 samples were subjected to tensile tests at a tensile speed of 250 mm / min. The tensile tests were carried out at 23 °C and 50% relative humidity.

[0094] g) Determination of the additive content on the pellet surface

[0095] For storage studies, 150 g of pellets of the crosslinkable inventive composition were placed in sealed aluminum bags. One bag of pellets was prepared for each sample taken. The bags containing the pellets were stored at 23 °C for 12 months and at 35 °C for 12 months, respectively. The content of the components on the pellet surface was determined by placing 100 g of pellets in an 800 ml beaker with a magnetic stirrer. 100 ml of methanol was added, and then the pellets were stirred in methanol for 5 min. A 5 ml sample was taken from the solvent using a syringe. When the solution was transferred from the syringe to a vial for HPLC analysis, the solution passed through a filter placed at the tip of the syringe. The content of the components (DCP, antioxidant, and scorch retarder) in the solution was determined by HPLC analysis. This test was carried out on the "zero" sample at the start of the storage test and on the pellets after storage at 23 °C for 12 months and at 35 °C for 12 months, respectively. HPLC analysis was carried out using a C18-SB (150×4.6 mm) column (such as Zorbax). The injection volume of the methanol solution was 10 μl. Isocratic elution was carried out at 28 °C with a methanol-water mixture (89:11 % by volume) at 1 ml / min.

[0096] f) Wet ageing

[0097] The wet ageing test is based on the procedures described in the papers by H.G. Land and H. "Model Cable Test for Evaluating the Ageing Behaviour under Water Influence of Compounds for Medium Voltage Cables", Proceedings of the Jicable 91 Conference, Versailles, France, 24 - 28 June 1991, and by U.H. Nilsson, "The Use of Model Cables for Evaluation of the Electrical Performance of Polymeric Power Cable Materials", Proceedings of the NORD-IS Conference, Trondheim, Norway, 13 - 15 June 2005.

[0098] The wet aging performance was evaluated on model cables. These model cables consisted of Cu wires with a diameter of 1.38 mm. An inner semiconductive layer, an insulating layer, and an outer semiconductive layer were applied to the Cu wires by extrusion. The model cable had the following structure: an inner semiconductive layer of 0.70 mm, an insulating layer of 1.50 mm, and an outer semiconductive layer of 0.15 mm. The crosslinkable composition of the present invention was used as the insulating material, and LE0592 (supplied by Borealis) was used as the inner semiconductive layer and the outer semiconductive layer. The cable was extruded and vulcanized in a dry curing CCV production line, i.e., the material was crosslinked after cable production. The wire speed used was 15 m / min. Thereafter, the crosslinked model cable was pre-conditioned at 80 °C for 72 h.

[0099] Then, the Cu wire used during extrusion was removed and replaced with a thinner Cu wire in order to fill the conductor region with water. The cable was placed in a water bath and aged at 9 kV voltage, at an ambient water temperature of 70 °C and a conductor temperature of 85 °C at 50 Hz for 1000 h. The initial electrical breakdown strength and the breakdown strength after 1000 h of wet aging were determined. Cables were prepared and aged as described below.

[0100] - Dry pre-conditioning (degassing): 80 °C, 72 h in an oven

[0101] - Applied voltage: 9 kV / 50 Hz

[0102] - Electrical stress (maximum): 9 kV / mm

[0103] - Electrical stress (average): 6 kV / mm

[0104] - Conductor temperature: 85 °C

[0105] - Water bath temperature: 70 °C

[0106] - Aging time: 1000 h

[0107] - Water quality inside and outside the conductor: deionized

[0108] From the extruded cable length, 10 cable specimens with an effective length of 0.5 m were collected and aged. After wet aging, these ten cable specimens were subjected to an AC breakdown test with a voltage ramp of 100 kV / min at ambient temperature until breakdown occurred. The Weibull 63.2% value of the breakdown strength (field stress at the inner semiconductive layer) after 1000 h of wet aging was reported as Eb63%, 1000 h. Another five unaged cable specimens, also with an effective length of 0.5 m, were similarly subjected to an AC breakdown test under the same conditions as described above to determine the initial Eb, Eb63%, 0 h.

[0109] h) Comonomer content

[0110] a) Quantifying the α-olefin content in low-density polyethylene by NMR spectroscopy: The comonomer content is determined by quantitative 13 13C nuclear magnetic resonance (NMR) spectroscopy after basic assignment (J. Randall, JMS-Rev. Macromol. Chem. Phys., Vol. 29 (Issues 2 and 3), pp. 201 - 317 (1989)). The experimental parameters are adjusted to ensure the measurement of quantitative spectra for this specific task.

[0111] Specifically, solution-state NMR spectroscopy is used with a Bruker Avance III 400 spectrometer. A homogeneous sample is prepared by dissolving approximately 0.200 g of the polymer in 2.5 ml of deuterated tetrachloroethylene in a 10 mm sample tube using a heating block and a spinning tube furnace at 140 °C. The following acquisition parameters are used to record proton-decoupled 13 13C single-pulse NMR spectra: 90-degree flip angle, 4 dummy scans, 4096 transients, 1.6 s acquisition time, 20 kHz spectral width, 125 °C temperature, double-stage WALTZ proton decoupling scheme, and 3.0 s relaxation delay. The resulting FID is processed using the following processing parameters: zero-filled to 32k data points and apodized using a Gaussian window function; automatic zero-order and first-order phase correction, and automatic baseline correction using a fifth-order polynomial limited to the region of interest.

[0112] Based on methods well-known in the art, the quantity is calculated using a simple correction ratio of signal integrals at representative sites.

[0113] b) Determination of the comonomer content of polar comonomers in low-density polyethylene: The comonomer content (wt%) is determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) measurements calibrated with quantitative nuclear magnetic resonance (NMR) spectroscopy.

[0114] The film is pressed using a Specac film press at 150 °C and approximately 5 tons for 1 - 2 min, and then cooled with cold water in an uncontrolled manner. The exact thickness of the resulting film sample is measured.

[0115] After FTIR analysis, a baseline of the absorbance pattern is drawn for the peaks to be analyzed. The absorbance peaks of the comonomer are normalized with the absorbance peaks of polyethylene. The FTIR peak height ratio is correlated with the polar comonomer content of the reference material determined by NMR. The NMR spectral calibration procedure is carried out in a conventional manner well-documented in the literature.

[0116] Quantification of the content of polar comonomers in polymers by NMR spectroscopy

[0117] The content of polar comonomers is determined by quantitative nuclear magnetic resonance (NMR) spectroscopy after basic assignment (e.g., "NMR Spectra of Polymers and Polymer Additives", A.J. Brandolini and D.D. Hills, 2000, Marcel Dekker, Inc., New York).

[0118] The experimental parameters are adjusted to ensure the measurement of quantitative spectra for this specific task (e.g., "200 and More NMR Experiments: A Practical Course", S. Berger and S. Braun, 2004, Wiley-VCH, Weinheim). In a manner known in the art, a simple correction ratio of signal integrals at representative sites is used to calculate the quantity.

[0119] The determination of the content of polar comonomers in ethylene ethyl acrylate, ethylene butyl acrylate, and ethylene methyl acrylate is illustrated below as an example.

[0120] The weight % can be converted to mole % by calculation. This is well documented in the literature.

[0121] (1) Ethylene copolymers containing butyl acrylate

[0122] A thin film sample of the polymer is prepared for FTIR measurement: for ethylene butyl acrylate with a butyl acrylate content > 6 wt%, a thickness of 0.5 to 0.7 mm is used, and for ethylene butyl acrylate with a butyl acrylate content < 6 wt%, a thickness of 0.05 to 0.12 mm is used.

[0123] After FT-IR analysis, for butyl acrylate > 6 wt%, the maximum absorbance of the peak at 3450 cm -1 is subtracted from the absorbance value of the baseline at 3510 cm -1 (A 丙烯酸丁酯 - A 3510 ). Then, the maximum absorbance peak of the polyethylene peak at 2020 cm -1 is subtracted from the absorbance value of the baseline at 2120 cm -1 (A 2020 - A 2120 ). Then, (A 丙烯酸丁酯 - A 3510 ) and (A 2020-A 2120 The ratio between

[0124] The maximum absorbance of the peak at 1165 cm of butyl acrylate comonomer < 6 wt% minus the absorbance value of the baseline at 1865 cm -1 at (A -1 -A 丙烯酸丁酯 -A 1865 ). Then, the maximum absorbance peak of the polyethylene peak at 2660 cm -1 minus the absorbance value of the baseline at 1865 cm -1 at (A 2660 -A 1865 ). Then, calculate the ratio between (A 丙烯酸丁酯 -A 1865 ) and (A 2660 -A 1865 ).

[0125] (2) Ethylene copolymer containing ethyl acrylate

[0126] Prepare a thin film sample of the polymer for FTIR measurement: For ethylene ethyl acrylate, a thickness of 0.5 mm was used.

[0127] After FT-IR analysis, the maximum absorbance (A -1 ) of the peak at 3450 cm of ethyl acrylate was determined, where linear baseline correction was applied between approximately 3205 and 3295 cm 丙烯酸乙酯 . Then, the maximum absorbance peak (A -1 ) of the polyethylene peak at 2020 cm was determined, where linear baseline correction was applied between approximately 1975 and 2120 cm -1 . Then, calculate the ratio between (A 2020 ) and (A -1 ) in a conventional manner well documented in the literature. 丙烯酸乙酯 The ratio between (A 2020 ) and (A

[0128] (3) Ethylene copolymer containing methyl acrylate

[0129] Prepare a thin film sample of the polymer for FTIR measurement: For ethylene methyl acrylate with a methyl acrylate content > 8 wt%, a thickness of 0.1 mm was used, and for ethylene methyl acrylate with a methyl acrylate content < 8 wt%, a thickness of 0.05 mm was used.

[0130] After analysis, the maximum absorbance of the peak at 3455 cm of methyl acrylate > 8 wt% minus the absorbance value of the baseline at 3510 cm -1 at (A -1 ​丙烯酸甲酯 -A 3510 )。Then, subtract the absorbance value of the baseline at 2450 cm -1 from the maximum absorbance peak of the polyethylene peak at 2675 cm -1 (A 2675 -A 2450 ). Then, calculate the ratio between (A 丙烯酸甲酯 -A 3510 ) and (A 2675 -A 2450 ) in a conventional manner well documented in the literature.

[0131] For a copolymer with less than 8 wt% methyl acrylate comonomer, subtract the absorbance value of the baseline at 1850 cm -1 from the maximum absorbance of the peak at 1164 cm -1 (A 丙烯酸甲酯 -A 1850 ). Then, subtract the absorbance value of the baseline at 1850 cm -1 from the maximum absorbance peak of the polyethylene peak at 2665 cm -1 (A 2665 -A 1850 ). Then, calculate the ratio between (A 丙烯酸甲酯 -A 1850 ) and (A 2665 -A 1850 ).

[0132] i) Methods ASTM D3124-98 and ASTM D6248-98 for determining the amount of double bonds in polymers (i.e., polyethylene)

[0133] Methods ASTM D3124-98 and ASTM D6248-98 are applicable for determining the double bonds in the LDPE component (i). The LDPE component (i) in the description of this method is referred to as "polymer".

[0134] The methods ASTM D3124-98 and ASTM D6248-98 include, on the one hand, procedures for determining the amount of double bonds per 1000 C-atoms, which are based on the ASTM D3124-98 method. In the ASTM D3124-98 method, a detailed description for determining vinylidene per 1000 C-atoms is given based on 2,3-dimethyl-1,3-butadiene. In the ASTM D6248-98 method, detailed descriptions for determining vinyl per 1000 C-atoms and trans-vinylidene per 1000 C-atoms are given based on 1-octene and trans-3-hexene, respectively. The sample preparation procedures described therein have been applied herein for determining vinyl per 1000 C-atoms, vinylidene per 1000 C-atoms, and trans-vinylidene per 1000 C-atoms in the present invention. The ASTM D6248-98 method suggests that the bromination procedure of the ASTM D3124-98 method may be included, but the samples of the present invention were not brominated. In order to determine the extinction coefficients of these three types of double bonds, the following three compounds have been used: 1-decene for vinyl, 2-methyl-1-heptene for vinylidene, and trans-4-decene for trans-vinylidene, and, with the exceptions mentioned above, the procedures described in ASTM D3124-98 and ASTM D6248-98 were followed.

[0135] The total amounts of vinyl bonds, vinylidene bonds, and trans-vinylidene double bonds of the "polymer" are analyzed by means of IR spectroscopy and given as the amounts of vinyl bonds per 1000 carbon atoms, vinylidene bonds per 1000 carbon atoms, and trans-vinylidene bonds per 1000 carbon atoms.

[0136] The polymer to be analyzed is pressed into a film with a thickness of 0.5 to 1.0 mm. The actual thickness is measured. FT-IR analysis is carried out on a PerkinElmer Spectrum One. Two scans are recorded, with a resolution of 4 cm -1 .

[0137] 1) A polymer composition comprising a polyethylene homopolymer and copolymer or a polyethylene homopolymer and copolymer other than a polyethylene copolymer with a comonomer > 0.4 wt%.

[0138] For polyethylene, three types of C=C-containing functional groups are quantified, each type of C=C-containing functional group has a characteristic absorption, and each type of C=C-containing functional group is calibrated to a different model compound, thereby yielding their respective extinction coefficients:

[0139] · Vinyl (R-CH=CH2), via 910 cm -1, based on 1-decene [dec-1-ene], E = 13.13 l·mol was obtained -1 ·mm -1

[0140] ·vinylidene (RR’C=CH2), via 888 cm -1 , based on 2-methyl-1-heptene [2-methylhept-1-ene], E = 18.24 l·mol was obtained -1 ·mm -1

[0141] ·trans-vinylidene (R-CH=CH-R’), via 965 cm -1 , based on trans-4-decene [(E)-dec-4-ene], E = 15.14 l·mol was obtained -1 ·mm -1

[0142] For polyethylene homopolymers or copolymers with a polar comonomer < 0.4 wt%, a linear baseline correction is applied between approximately 980 and 840 cm -1

[0143] 2) Polymer compositions comprising polyethylene copolymers (such as terpolymers) or polyethylene copolymers with a polar comonomer > 0.4 wt%

[0144] For polyethylene copolymers with a polar comonomer > 0.4 wt%, two types of C=C-containing functional groups were quantified, each type of C=C-containing functional group having a characteristic absorption and each type of C=C-containing functional group being calibrated to a different model compound, thus yielding their respective extinction coefficients:

[0145] ·vinyl (R-CH=CH2), via 910 cm -1 , based on 1-decene [dec-1-ene], E = 13.13 l·mol was obtained -1 ·mm

[0146] ·vinylidene (RR’C=CH2), via 888 cm -1 , based on 2-methyl-1-heptene [2-methylhept-1-ene], E = 18.24 l·mol was obtained -1 ·mm -1

[0147] For the ethylene-butyl acrylate system, a linear baseline correction is applied between approximately 920 and 870 cm -1

[0148] For the ethylene-ethyl acrylate system, a linear baseline correction is applied between approximately 920 and 825 cm -1 ​​Apply linear baseline correction between them.

[0149] For ethylene-methyl acrylate systems, apply linear baseline correction between approximately 930 and 870 cm -1 Apply linear baseline correction between them.

[0150] On the other hand, methods ASTM D3124-98 and ASTM D6248-98 also include procedures for determining the molar extinction coefficient. Use at least three 0.18 mol·l -1 solutions in carbon disulfide (CS2) and use the average value of the molar extinction coefficient.

[0151] The amount of vinyl groups derived from polyunsaturated comonomers per 1000 carbon atoms is determined and calculated as follows:

[0152] The polymer to be analyzed and the reference polymer have been produced in the same reactor, substantially using the same conditions, i.e., similar peak temperatures, pressures, and productivities, but the only difference is that a polyunsaturated comonomer was added during the polymerization of the polymer to be analyzed, while no polyunsaturated comonomer was added during the polymerization of the reference polymer. The total amount of vinyl groups in each polymer is determined by FT-IR measurements as described herein.

[0153] For both the reference polymer and the polymer to be analyzed, it is assumed that the baseline levels of vinyl groups formed naturally by the process and vinyl groups formed by a chain transfer agent (if present) are the same. Then, this baseline level is subtracted from the measured amount of vinyl groups in the polymer to be analyzed, resulting in the amount of vinyl groups / 1000 C-atoms produced by the polyunsaturated comonomer.

[0154] Experiments

[0155] Raw materials:

[0156]

[0157] Process details of low-density polyethylene (LDPE) copolymers having at least one polyunsaturated comonomer optionally combined with one or more other comonomers

[0158] Typically, high-pressure free-radical initiated polymerization of ethylene can be achieved in a tubular reactor or an autoclave reactor at pressures in the range of 1200 to 3500 bar and at temperatures in the range of 120 to 350 °C. Further details on high-pressure free-radical polymerization are given in Volume 6 (1986), pages 383 to 410 of the Encyclopedia of Polymer Science and Engineering and in the Encyclopedia of Materials: Science and Technology, Elsevier Science Ltd.: "Polyethylene: High-pressure", R. Klimesch, D. Littmann and F.-O. Pages 7181 to 7184 (2001), which are incorporated herein by reference.

[0159] An ethylene-1,7-octadiene-butyl acrylate terpolymer having at least one polyunsaturated comonomer, optionally combined with one or more other comonomers (such as those used in the examples), used as a low-density polyethylene (LDPE) copolymer is produced in a tubular reactor by polymerizing ethylene together with 1,7-octadiene and butyl acrylate and (one or more) chain transfer agents to achieve the described polymer properties, such as vinyl content and MFR value.

[0160] Preparation of Polymer Compositions

[0161] By laboratory-scale compounding, via melt mixing followed by pelletizing, (one or more) antioxidants and polyethylene glycol are added to polyethylene pellets. Also on a laboratory scale, a crosslinking agent is added to the pellets of the prepared composition. The crosslinking agent is added to the polyethylene composition by distributing the crosslinking agent (DCP in molten form) onto the pellets of the composition prepared by compounding at 70 °C. The pellets are kept at 80 °C until the pellets are dry. The amounts of crosslinking agents used to crosslink different compositions are presented in the description of the compositions of the present invention and the comparative compositions. The scorch retardant (CAS No. 6362-80-7; 2,4-diphenyl-4-methyl-1-pentene) is added in a similar manner to the crosslinking agent.

[0162]

[0163] After preparing the crosslinked plates, the heat setting values are determined. The results are shown below. Results:

[0164]

[0165] It can be seen that the thermal oxidative aging performance of the embodiments of the present invention is very good and is further achieved with a lower level of peroxide crosslinking agent. Compared with the comparative examples, the compositions of the present invention also show significantly better Monsanto scorch. The thermal oxidative stability in terms of breaking stress and breaking strain is improved.

[0166] In further experiments, the long-term storage stability (of the embodiments of the present invention) was evaluated by storing the pellets under different conditions (time and temperature), and the amount of (one or more) antioxidants, peroxides, and scorch retardants migrated to the pellet surface was determined. The results at time zero and after storing for one year at 23 °C and 35 °C respectively are presented below:

[0167]

[0168] The results show low migration to the surface level of the components. Surprisingly, there is no migration of 4,4'-thiobis(2-tert-butyl-5-methylphenol) at both +23 °C and +35 °C.

[0169] In further experiments, the water tree resistance performance of the embodiments of the present invention was evaluated by the so-called model cable test. In this test, small cable cores were extruded and crosslinked. The core consists of a conductor, an inner semiconductor layer, an insulating layer, and an outer semiconductor layer. The breakdown strength, denoted as Eb(63%), represented by the Weibull 63.2% value, was measured on these model cables before wet aging and when the cable cores had been exposed for 1000 h in the wet aging test.

[0170] Results (embodiments of the present invention):

[0171] Eb(63%, 0 h) ≥ 98.7 kV / mm

[0172] Eb(63%, 1000 h) = 90.9 kV / mm.

[0173] These results show that after exposing the material to 1000 h of wet aging, the breakdown strength, denoted as Eb(63%), represented by the Weibull 63.2% value, remains at the same level as before wet aging.

Claims

1. A crosslinkable polymer composition comprising i) a low density polyethylene (LDPE) copolymer having at least one polyunsaturated comonomer, preferably one polyunsaturated comonomer, said at least one polyunsaturated comonomer optionally combined with one or more other comonomers; and ii) an additive composition consisting of a mixture of polyethylene glycol and 4,4'-thiobis(2-tert-butyl-5-methylphenol) plus thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; and iii) a peroxide crosslinking agent; and iv) an anti-scorching agent.

2. The crosslinkable polymer composition according to claim 1, wherein the low density polyethylene (LDPE) copolymer is an unsaturated ethylene acrylate polymer, preferably an ethylene-1,7-octadiene-butyl acrylate terpolymer.

3. The crosslinkable polymer composition according to claim 1 or 2, wherein the low density polyethylene (LDPE) copolymer, preferably the unsaturated ethylene acrylate polymer, has a total of more than 0.40 vinyl groups per 1000 carbon atoms (as described herein).

4. The crosslinkable polymer composition according to any one of the preceding claims, comprising i) an unsaturated ethylene acrylate polymer having a total of more than 0.40 vinyl groups per 1000 carbon atoms (as described herein); and ii) an additive composition consisting of a mixture of polyethylene glycol and 4,4'-thiobis(2-tert-butyl-5-methylphenol) plus thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; and iii) a peroxide crosslinking agent; and iv) an anti-scorching agent.

5. The crosslinkable polymer composition according to claim 4, wherein the unsaturated ethylene acrylate polymer is a terpolymer.

6. The crosslinkable polymer composition according to claim 4 or 5, wherein the unsaturated ethylene acrylate polymer is an ethylene-butyl acrylate terpolymer.

7. The crosslinkable polymer composition according to any one of claims 4 to 6, wherein the unsaturated ethylene acrylate polymer is an unsaturated ethylene acrylate non-conjugated diene terpolymer.

8. The crosslinkable polymer composition according to any one of the preceding claims, comprising i) greater than 95.5 wt%, more preferably 96.0 wt% of the low density polyethylene (LDPE) copolymer, preferably the unsaturated ethylene acrylate polymer, based on the total weight of the crosslinkable polymer composition, said low density polyethylene (LDPE) copolymer having at least one polyunsaturated comonomer optionally combined with one or more other comonomers, and ii) An additive composition based on 0.50 to 1.65% by weight, preferably 0.90 to 1.20% by weight, of the total weight of the crosslinkable polymer composition, the additive composition consisting of a mixture of polyethylene glycol and 4,4'-thiobis(2-tert-butyl-5-methylphenol) plus thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; iii) A peroxide crosslinking agent based on at most 1.80% by weight of the total weight of the crosslinkable polymer composition; and iv) An anti-scorching agent based on 0.1 to 0.5% by weight, more preferably 0.30 to 0.50% by weight, most preferably 0.35 to 0.50% by weight of the total weight of the crosslinkable polymer composition.

9. The crosslinkable polymer composition according to claim 8, wherein, in addition to the components contained in the additive composition (ii) and / or in addition to the anti-scorching agent (iv), the additive (v) is present in a total amount of less than 0.40% by weight based on the total weight of the crosslinkable polymer composition, and wherein the components (i), (ii), (iii), (iv) and (v) total 100% by weight.

10. The crosslinkable polymer composition according to any one of claims 1 to 9, wherein 4,4'-thiobis(2-tert-butyl-5-methylphenol) is present in an amount of 0.12 to 0.22% by weight relative to the total crosslinkable polymer composition.

11. The crosslinkable polymer composition according to any one of claims 1 to 10, wherein thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] is present in an amount of 0.10 to 0.40% by weight, preferably 0.15 to 0.25% by weight relative to the total crosslinkable polymer composition.

12. The crosslinkable polymer composition according to any one of claims 1 to 11, wherein polyethylene glycol is present in an amount of 0.40 to 0.80% by weight relative to the total crosslinkable polymer composition.

13. Use of the crosslinkable polymer composition according to any one of claims 1 to 12 for a cable.

14. A material obtained by crosslinking a crosslinkable polymer composition according to any one of claims 1 to 12, preferably characterized in that: The extruded model cable has a breakdown strength, designated Eb(63%), as represented by the Weibull 63.2% value of at least 75.0 kV / mm, preferably at least 85.0 kV / mm, after 1000 hours of wet aging as described in the specification.

15. A cable comprising the material according to claim 14.

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