BR112019026497B1 - RETICULABLE COMPOSITION, ARTICLE AND METHOD FOR CONDUCTING ELECTRICITY - Google Patents

Abstract

The copolymerization of ethylene (E) and methoxypolyethylene glycol methacrylate (MPEGMA) produces the co-E-MPEGMA copolymer. These copolymers are different from polyethylene, for example low density polyethylene (LDPE) grafted with MPEGMA, i.e. g-E-MPEGMA, and are useful in preparing insulation sheaths for medium, high and extra high voltage cables. These cables exhibit good retardation in water trees.

Description

Field of invention

[0001] The present invention relates to ethylene-methoxypolyethylene glycol methacrylate copolymers.

Background of the invention

[0002] It is known that water trees in the insulation layers of medium to extra high voltage power cables (produced from peroxide cross-linked low density polyethylene, LDPE) cause the occurrence of electrical trees, which lead to failure of the cable. Solutions to inhibit aquatic trees involve incorporating small amounts of a polar copolymer, such as ethylene butyl acrylate (EBA), or polyethylene glycol (PEG). The mechanism for using PEG with a maximum weight-average molecular weight (Mw) of 20,000 grams per mole (g/mol) as a water tree retardant (WTR) is believed to be that the PEG is mobile enough to Move to the region of greatest stress and fill the tops of the trees.

[0003] USP 4,812,505 and 9,058,918 and EP 0 966 003 and 1 731 565 teach PEG or a combination of PEG and glycerol fatty acid esters as WTR additives in combination. Documents USP 6,274,239 and 8,269,109, US 2012/0031641 and EP 0 179 565 and 2 439 234 teach the use of various polar copolymers, such as ethylene-vinyl acetate (EVA), ethylene-ethyl acrylate (EEA) or a combination of them for WTR properties.

[0004] Document WO 2016204949 A1 teaches a composition comprising an ethylene-based polymer with high melt strength and cross-linked with peroxide, which is produced in a tubular reactor. The composition has a dissipation factor measured at 130 °C (60 Hz, 2 kV) or 120 °C (60 Hz, 8 kV) or 100 °C (60 Hz 8 kV) less than or equal to 0.5%.

[0005] USP 4,370,517 teaches that polyethylene grafted with methoxypolyethylene glycol 400 methacrylate (MPEG 400 MA) suppresses aquatic tree, in which the polyolefin contains from 0.01 to 0.888% by weight of ester groups. In this invention, polyethylene was produced as usual, and MPEG 400 MA was grafted to it through reactions that were carried out during the molding of the composition, generally with peroxide initiators.

Summary of the invention

[0006] In one embodiment, the invention is a copolymer of ethylene reactor and methoxypolyethylene glycol methacrylate (co-E-MPEGMA).

[0007] In one embodiment, the invention is a crosslinkable composition comprising co-E-MPEGMA. In one embodiment, the co-E-MPEGMA ranges from greater than 0 to less than or equal to (<) 10 weight percent (wt%), or >0 to <5 wt%, or >0 to <1% by weight, or >0 to <0.5% by weight of units derived from methoxypolyethylene glycol methacrylate (MPEGMA).

[0008] In one embodiment, the invention is a crosslinkable composition comprising in weight percentage (% by weight) based on the weight of the composition: (A) 1 to < 100% by weight of co-E-MPEGMA; (B) >0 to 90% by weight of an ethylene-based polymer other than co-E-MPEGMA or a grafted ethylene-methoxypolyethylene glycol methacrylate (g-E-MPEGMA); (C) 0 to <5% by weight of a water tree retardant (WTR); (D) 0 to <2% by weight of an antioxidant; and (E) 0 to <3% by weight of a crosslinking agent; wherein the weight of the composition is 100% by weight.

[0009] In one embodiment, the co-E-MPEGMA comprises > 0 to <10% by weight, or > 0 to <5% by weight, or > 0 to <1% by weight, or > 0 to <0, 5% by weight MPEGMA.

[0010] In one embodiment, the composition comprises > 0 to < 99% by weight, or > 0 to < 90% by weight, or > 0 to < 80% by weight, or > 0 to < 70% by weight, or >0 to <60% by weight, or >0 to <50% by weight, or >0 to <40% by weight, or >0 to <30% by weight, or >0 to <20% by weight, or >0 to <10% by weight, or >0 to <5% by weight, or >0 to <2% by weight, or >0 to <1% by weight, co-E-MPEGMA or g-E-MPEGMA.

[0011] In one embodiment, the composition comprises greater than or equal to (>) 1% by weight to < 100% by weight, or >2% by weight to < 100% by weight, or >5% by weight to < 100 % by weight or >10% by weight to < 100% by weight, or >20% by weight to < 100% by weight, or >30% by weight to < 100% by weight, or >40% by weight to < 100% by weight, or >50% by weight to < 100% by weight, or >60% by weight to < 100% by weight, or >70% by weight to < 100% by weight, or >80% by weight to < 100% by weight, ethylene-based polymer other than co-E-MPEGMA or g-E-MPEGMA. In one embodiment, the ethylene-based polymer is a polyethylene. In one embodiment, the polyethylene is low density polyethylene (LDPE).

[0012] In one embodiment, the WTR is present in an amount greater than zero (> 0)% by weight. In one embodiment, the composition comprises >0 to 5% by weight, or greater than or equal to (>)0.1 to 5% by weight, or >0.5 to 5% by weight, or >1 to 5% by weight, or >2 to less than or equal to (<) 4.5% by weight, or >2 to <4% by weight of WTR. In one embodiment, the water tree retardant is a polyolefin glycol, e.g., polyethylene glycol (PEG) or polypropylene glycol (PPG).

[0013] In one embodiment, the antioxidant is present in an amount greater than zero (> 0)% by weight. In one embodiment, the composition comprises >0 to 2% by weight, or greater than or equal to (>)0.01 to 2% by weight, or >0.05 to 2% by weight, or >0.1 to < 1% by weight antioxidant. In one embodiment, the antioxidant is a hindered phenol or a hindered thiophenol.

[0014] In one embodiment, the crosslinking agent is present in an amount greater than zero (> 0)% by weight. In one embodiment, the composition comprises >0 to 3% by weight, or greater than or equal to (>)0.01 to 3% by weight, or >0.05 to 3% by weight, or >0.1 to < 2% by weight or >0.1 to < 1% by weight crosslinking agent. In one embodiment, the crosslinking agent is a peroxide. In one embodiment, the peroxide is an organic peroxide, for example, dicumyl peroxide.

[0015] In one embodiment, the invention is an article comprising co-E-MPEGMA. In one embodiment, the article is an insulation layer of a wire or cable construction, particularly an insulation layer of a medium to extra high voltage power cable. In one embodiment, the article is a sheathed conductor comprising a conductive core and an insulation layer that at least partially covers the conductive core, wherein the insulation layer comprises co-E-MPEGMA.

[0016] Surprisingly, PEG in non-mobile form (i.e., non-grafted copolymers of ethylene and methoxypolyethylene glycol methacrylate or co-E-MPEGMA) can also provide WTR properties when used as a polymer to produce peroxide-crosslinked electrical insulation compositions .

[0017] Surprisingly, also, co-E-MPEGMA (in which the methoxypolyethylene glycol methacrylate content is 0.5% by weight) exhibits greater resistance to combustion under extrusion conditions (i.e., ts1 greater at 140 ° C ) than another co-E-MPEGMA (in which the methoxypolyethylene glycol methacrylate content was 2.3% by weight), at similar melt index values of the two copolymers. ts1 refers to the time for a torque increase of 0.11 N-m (1 inch-pound (1 lb-in)) as measured by the Moving Matrix Rheometer (MDR).

[0018] Another surprise is that a blend of LDPE with co-E-MPEGMA (in which the methoxypolyethylene glycol methacrylate content is 0.5% by weight) exhibits synergistic resistance to combustion under extrusion conditions (i.e., higher ts1 at 140 °C) than predicted from a linear combination of the two polymers. On the other hand, the use of co-E-MPEGMA (in which the methoxypolyethylene glycol methacrylate content is 2.3% by weight) in a blend with LDPE does not generate synergy in the combustion resistance characteristics.

[0019] In one embodiment, the compositions of this invention are useful in the manufacture of insulation sheaths for medium voltage cables. In one embodiment, the compositions of this invention are useful in the manufacture of insulation sheaths for high and extra high voltage cables. In one embodiment, the compositions of the invention are useful in direct peroxide injection (DPI) processes.

Brief description of the drawings

[0020] Figure 1 is a line graph of the retardant properties of water trees for all examples.

[0021] Figure 2 is a line graph of hot creep and combustion performance (ts1 at 140 °C) for all examples.

Detailed description of the preferred modalities Definitions

[0022] For purposes of United States patent practice, the contents of any referenced patent, patent application, or publication are incorporated by reference in their entirety (or the equivalent U.S. version thereof is incorporated by reference) especially with respect to the disclosure of definitions (so long as they are consistent with any definitions provided in this disclosure) and general knowledge in the art.

[0023] Unless otherwise stated, implied from the context or customary in the art, all parts and percentages are based on weight, and all test methods are current as of the filing date of this disclosure.

[0024] The numerical ranges disclosed in this document include all values from the lowest value to the highest value, inclusive. For ranges that contain have explicit values (e.g., 1 or 2; or 3 to 5; or 6; or 7) any subrange between any two explicit values is included (e.g., 1 to 2; 2 to 6; 5 to 7 ; 3 to 7; 5 to 6; etc.).

[0025] The terms “which comprises”, “which includes”, “which has” and their derivatives are not intended to exclude the presence of any additional component, step or procedure, regardless of whether it is specifically disclosed or not. For the avoidance of doubt, all compositions claimed through the use of the term “comprising” may include any additional additive, adjuvant or compound, whether polymeric or not, unless otherwise stated. essentially consists of” excludes from the scope of any subsequent recitation any other component, step or procedure, except those that are not essential to operability. The term “consists of” excludes any component, step or procedure that is not specifically delineated or listed. The term “or”, unless otherwise stated, refers to the elements listed individually as well as in any combination.Use of the singular includes use of the plural and vice versa.

[0026] "Composition" and similar terms mean a mixture or mixture of two or more components.

[0027] “Mix” and similar terms mean an intimate physical mixture (i.e., without reaction) of two or more substances, for example, two or more polymers, or a polymer and a catalyst or an additive, etc. A mixture may or not be miscible (not phase separated at the molecular level). A mixture may or may not be phase separated. A mixture may or may not contain one or more domain configurations, as determined from transmission electron spectroscopy, light scattering , X-ray scattering and other methods known in the art. Blending can be effected by physically mixing the two or more substances at the macro level (e.g., melt blending resins or compound formation) or at the micro level (e.g. example, simultaneous formation within the same reactor).

[0028] “Ethylene-based polymer" and similar terms refer to a polymer that contains, in polymerized form, a greater weight percentage of ethylene-derived units, based on the total weight of the polymer. Non-limiting examples of Ethylene-based polymers include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), very low-density polyethylene (VLDPE), ultra-low-density polyethylene (ULDPE), medium-density polyethylene (MDPE), polyethylene high-density polyethylene (HDPE), and functionalized polyethylene, for example, ethylene-vinyl acetate (EVA), ethylene-ethyl acrylate (EEA) and the like.

[0029] “Cable”, “power cable” and similar terms refer to at least one wire or optical fiber within an insulation, jacket or protective sheath. A "sheath" is a generic term and is used in relation to cables, it includes coverings or layers of insulation, protective jackets and the like. Typically, a cable is made up of two or more wires or optical fibers joined together in a common protective jacket. The individual threads or fibers within the shirt may be bare, covered or insulated. Combination cables can contain both electrical wires and optical fibers. The cable can be designed for low, medium, high and extra high voltage applications. "Extra high voltage cable" refers to cable rated to carry 161 or more kilovolts (kV). "High voltage cable" refers to cable rated to withstand voltages greater than or equal to (>) 36 kV and less than or equal to (<) 160 kV. "Medium voltage cable" refers to cable rated to carry voltages of > 6 to < 36 kV. "Low voltage cable" refers to cable rated to carry voltages <6 kV. Typical cable designs are illustrated in USP documents 5,246,783, 6,496,629, and 6,714,707.

[0030] “Conductor” and similar terms mean a metal wire or cable, typically copper or aluminum, used to transmit electrical energy and/or electrical signals. The conductor may be uncoated or coated with one or more polymeric sheaths, e.g., semiconductor coating or layer, coating or insulation layer, etc. In one embodiment, a conductor is an optical fiber for transmitting data and/or other information.

[0031] "Cross-linkable", "curable" and similar terms mean that the polymer, before or after forming into an article, is not cured or cross-linked and has not been subjected to or exposed to treatment that has induced substantial cross-linking, although the polymer comprises additive (or additives) or functionality that will cause, promote or permit substantial cross-linking upon subjection or exposure to such treatment (e.g. exposure to peroxide).

[0032] MPEGMA means methoxypolyethylene glycol methacrylate.

[0033] co-E-MPEGMA means a reactor copolymer resulting from the copolymerization of ethylene and methoxypolyethylene glycol methacrylate. It is also referred to as an ungrafted copolymer of ethylene and methoxypolyethylene glycol methacrylate to distinguish it from g-E-MPEGMA.

[0034] g-E-MPEGMA means polyethylene grafted with methoxypolyethylene glycol methacrylate.

[0035] E-MPEGMA means one of, or both, co-E-MPEGMA and g-E-MPEGMA, as required by the context in which E-MPEGMA is used.

[0036] "Free of E-MPEGMA" and similar terms means that the polymer does not contain, or contains only an inconsequential amount, incorporated or grafted into its main structure, of E-MPEGMA.

[0037] "Copolymerization conditions" and similar terms generally refer to temperature, pressure, monomer concentrations, catalyst concentration, cocatalyst concentration and the like necessary for the reaction of monomer and comonomer with respect to a copolymer.

Methoxypolyethylene glycol ethylene-methacrylate reactor copolymer (CO-E- MPEGMA)

[0038] Co-E-MPEGMA is formed from the copolymerization of ethylene and MPEGMA. The structure of MPEGMA is shown by Formula 1 below: (Formula 1) where n is an integer from 1 to 80, from 3 to 60 or from 5 to 45. MPEGMA is a known compound produced by known methods, for example, it is commercially available from BASF. The number average molecular weight (Mn) of MPEGMA used in the practice of this invention is typically 144 to 3,600, or 230 to 2,750, or 320 to 2,100 grams per mole (g/mol).

[0039] MPEGMA is copolymerized with ethylene under conventional copolymerization conditions to form co-E-MPEGMA, the structure of which is shown by Formula 2 below: (Formula 2)

[0040] This structure provides an important benefit to the water retardant property of co-E-MPEGMA in relation to gE-MPEGMA prepared by grafting MPEGMA onto a polyethylene, the structure of which is shown by Formula 3 below: (Formula 3)

[0041] In co-E-MPEGMA, the alpha and beta carbon atoms of the methacrylate group of MPEGMA are incorporated into the main structure of polyethylene. In contrast, the alpha carbon atom of the methacrylate group of g-E-MPEGMA is not incorporated into the main structure of polyethylene.

[0042] Without being bound by theory, for an aquatic tree retardant to work effectively, it must capture and bind to water molecules that have entered the polymer matrix. This capture and binding typically requires that the polymer's capturing and binding group be flexible and unhindered. In relation to co-E-MPEGMA, the functional or binding group of g-E-MPEGMA is more flexible than co-E-MPEGMA, since it has a lower steric hindrance due to its alpha carbon atom of the methacrylate group being exo to, that is, outside the main structure of the polymer. Due to the fact that the alpha carbon atom of the methacrylate group of co-E-MPEGMA is incorporated into the polyethylene backbone, the structure is less flexible and more sterically hindered and thus is less susceptible to capture and binding with water. The fact that co-E-MPEGMA works effectively as a water tree retardant (WTR) is surprising.

[0043] The minimum amount of MPEGMA incorporated into co-E-MPEGMA is typically at least 0.1% by weight, or 0.15% by weight, or 0.20% by weight, or 0.25% by weight, based on the weight of co-E-MPEGMA. The maximum amount of MPEGMA incorporated into co-E-MPEGMA can vary according to convenience and is generally a function of diminishing returns and practicalities of the process. Typically, the maximum amount does not exceed 10% by weight, or 5% by weight, or 1% by weight, or 0.5% by weight, based on the weight of the co-E-MPEGMA.

[0044] In one embodiment, co-E-MPEGMA containing 0.5% by weight or less of MPEGMA-derived groups exhibits greater resistance to combustion under extrusion conditions (ts1 at 140 ° C) than a co-E- MPEGMA with similar melt index value, but containing more than 0.5% by weight of MPEGMA-derived groups.

[0045] In one embodiment, a blend of co-E-MPEGMA containing 0.5% by weight or less of MPEGMA-derived groups and an ethylene-based polymer, particularly a low-density polyethylene, exhibits synergistic resistance to combustion in extrusion conditions (ts1 at 140 °C) than that predicted from a sum of individual resistances to combustion of the two polymers. In one embodiment, a blend of co-E-MPEGMA containing 0.5% by weight or less of MPEGMA-derived groups and an ethylene-based polymer, particularly a low-density polyethylene, exhibits synergistic resistance to combustion under extrusion conditions. (ts1 at 140 ° C) than a similar mixture in all respects, except that the MPEGMA content of co-E-MPEGMA was greater than 0.5% by weight, for example, 2.3% by weight.

Ethylene-based polymer

[0046] In one embodiment, the invention is a composition (i.e., blend) comprising co-E-MPEGMA and one or more E-MPEGMA-free ethylene-based polymers. Polyethylene, an ethylene-based polymer and, as that term is used herein, is a homopolymer of ethylene or a copolymer of ethylene and a minor proportion of one or more alpha-olefins having 3 to 12 carbon atoms and, preferably, 4 to 8 carbon atoms and, optionally, a diene, or a mixture of such homopolymers and copolymers. The mix can be a mechanical mix or an in situ mix. Examples of alpha-olefins are propylene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene.

[0047] Polyethylene can be homogeneous or heterogeneous. Homogeneous polyethylenes generally have a polydispersity (Mw/Mn) in the range of 1.5 to 3.5 and an essentially uniform comonomer distribution and are characterized by unique and relatively low differential scanning calorimetry (DSC) melting points. Heterogeneous polyethylenes, on the other hand, have a molecular mass dispersion (DM = Mw/Mn) greater than 3.5 and do not have a uniform distribution of comonomers. Mw is defined as weight average molecular weight, and Mn is defined as number average molecular weight. The density of polyethylenes can be in a range of 0.860 or less to 0.950 or more grams per cubic centimeter (g/cm3), but they typically have a density in the range of 0.870 to 0.930 g/cm3. They generally have a melt index in the range of 0.1 to 50 grams per 10 minutes (g/10 min). Density is measured in accordance with ASTM D792, and melt index is measured in accordance with ASTM D1238 (190 °C/2.16 kg).

[0048] Polyethylenes can be produced by low or high pressure processes. They can be produced in the gas phase or in the liquid phase in solutions or fluid pastes using conventional techniques. Low pressure processes are typically run at pressures below 6.89 MPa (1,000 pounds per square inch (psi)), while high pressure processes are typically run at pressures above 103.42 MPa (15,000 psi).

[0049] Typical catalytic systems (if required) that are used to prepare these polyethylenes include the following: magnesium/titanium-based catalyst systems, which are exemplified by the catalyst system described in USP 4,302,565 (heterogeneous polyethylenes); vanadium-based catalyst systems, such as those described in USP 4,508,842 (heterogeneous polyethylenes) and 5,332,793; 5,342,907; and 5,410,003 (homogeneous polyethylenes); a chromium-based catalyst system such as that described in USP 4,101,445; a metallocene catalyst system such as those described in UPS documents 4,937,299 and 5,317,036 (homogeneous polyethylenes); or other transition metal catalyst systems. Many of these catalyst systems are often referred to as Ziegler-Natta catalyst systems or Phillips catalyst systems. Catalyst systems using chromium or molybdenum oxides on silica-alumina supports may be included in this document. Typical processes for preparing polyethylenes are also described in the aforementioned patents. Typical in situ polyethylene blends and processes and catalyst systems are described in USP documents 5,371,145 and 5,405,901. The various polyethylenes may include low-density ethylene homopolymers (LDPE) produced by high-pressure processes (HP-LDPE), linear low-density polyethylenes (LLDPE), very low-density polyethylenes (VLDPE), medium-density polyethylenes (MDPE ), high-density polyethylene (HDPE) with a density greater than 0.940 g/cm3. The last four polyethylenes are generally produced by low pressure processes. A conventional high pressure process is described in Introduction to Polymer Chemistry, Stille, Wiley and Sons, New York, 1962, pages 149 to 151. High pressure processes are typically free radical initiated polymerizations conducted in a tubular reactor or in a agitated autoclave or a combination of the two. In the stirred autoclave, the pressure is typically in the range of 68.95 to 206.8 MPa (10,000 to 30,000 psi), and the temperature is typically in the range of 175 to 250 °C, and in the tubular reactor, the pressure is typically in the range from 172.4 to 310.3 MPa (25,000 to 45,000 psi), and the temperature is in the range of 200 to 350 °C. LDPE, particularly HP-LDPE, are preferred polyethylenes for use in the practice of this invention.

Water Tree Retarder (WTR)

[0050] In one embodiment of the invention, co-E-MPEGMA or a composition comprising co-E-MPEGMA can be used in combination with a water tree retardant (WTR). Any compound that inhibits the formation of aquatic trees in the cross-linked polymer, i.e., co-E-MPEGMA or a composition comprising co-E-MPEGMA, under its end-use conditions, can be used as an aquatic tree retardant in the practice of this invention. . For immersion or diffusion into the polymer, a tree water-resistant agent of low melting point, for example, less than 70 °C, preferably less than 50 °C and more preferably less than 35 °C, is preferred. Furthermore, a high molecular weight eutectic mixture, e.g., not exceeding 1,000,000, preferably not exceeding 100,000, and most preferably not exceeding 50,000, gram average molar mass weight per mole (g/mol) that is a solid at 23 ° C, and a low molecular weight, for example, less than 2000, preferably less than 1000 and more preferably less than 500, g/mol that is liquid at 23 ° C can be used. Representative aquatic tree resist agents include an alcohol of 6 to 24 carbon atoms (USP 4,206,260), an organosilane, e.g., a silane containing an epoxy-containing radical (USP 4,144,202), an inorganic ionic salt of a strong acid and a strong Zwitter ion compound (USP 3,499,791), a ferrocene compound and a substitute quinoline compound (USP 3,956,420), a polyhydric alcohol and a silicone fluid (USP document 3,795. 646). Polyglycols are a preferred class of aquatic tree retardants. Polyethylene glycol (PEG) having a weight average molar mass of less than 2,000, preferably less than 1,200 and more preferably less than 800, is a particularly preferred water tree resistant agent, particularly for use with polyethylene, especially with LDPE. Vinyl-capped PEG is a particularly preferred tree-resistant agent.

[0051] High molecular weight aquatic tree resistant agents that are solids at 23°C can be introduced into the polymer, e.g. LDPE, by pre-compounding the agent in a polymer masterbatch or intermediate product, e.g. before soaking liquid additives, which is then pelletized. If a master batch, the granules can then be added directly to the polymer in the extruder to facilitate agent incorporation whilst reducing the impact on extrusion efficiency, for example screw slippage. PEG having a weight average molar mass of less than 1,000,000, preferably less than 50,000 and more preferably less than 25,000 g/mol is a preferred agent for use in product master or intermediate batch procedures, especially with polyethylene, particularly with LDPE.

Cross-linking agent

[0052] The co-E-MPEGMA or composition comprising co-E-MPEGMA and an ethylene-based polymer can be crosslinked by adding a crosslinking agent to the co-E-MPEGMA or the composition. In one embodiment, the production of an article comprises crosslinking the co-E-MPEGMA or composition comprising co-E-MPEGMA, and typically the co-E-MPEGMA or composition comprising co-E-MPEGMA is crosslinked through the action of a peroxide.

[0053] The crosslinking of polymers with free radical initiators such as, but not limited to, a peroxide is well known. Generally, the peroxide, typically an organic peroxide, is incorporated into the polymer by melt blending in a roller mill, a twin-axial screw kneading extruder, or a BANBURYTM or BRABENDERTM mixer at a temperature lower than the initial temperature for significant decomposition. of peroxide. Peroxides are judged for decomposition based on their half-life temperatures, as described in the Plastic Additives Handbook, Gachter et al., 1985, pages 646 to 649. An alternative method for incorporating organic peroxide into a polymer compound is mixing liquid peroxide and polymer pellets in a blending device, such as a HENSCHELTM mixer, or an immersion device, such as a simple drum cup, which are maintained at temperatures above the freezing point of organic peroxide and below the decomposition temperature organic peroxide and polymer melting temperature. After incorporation of organic peroxide, the polymer/organic peroxide mixture is then, for example, introduced into an extruder, in which it is extruded around an electrical conductor at a temperature lower than the decomposition temperature of the organic peroxide to form a cable. The cable is then exposed to higher temperatures at which organic peroxide decomposes to provide free radicals, which cross-link the polymer.

[0054] Suitable crosslinking agents are organic peroxides, such as dicumyl peroxide; 2,5-dimethyl-2,5-di(t-butylperoxy)hexane; t-butyl cumyl peroxide; and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane. In one embodiment, dicumyl peroxide is a preferred organic peroxide. In Direct Peroxide Injection (DPI) processes, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane is a preferred organic peroxide, as it is liquid under ambient conditions (23 °C and atmospheric pressure).

[0055] Peroxide curing agents are used in amounts of at least 0.5% by weight, based on the weight of the composition. In various embodiments, the peroxide curing agent is used in an amount of 0.5 to 10, or 0.7 to 5, or 1 to 3% by weight, based on the weight of the composition. Peroxides can be used alone or in combination with various other known curing coagents, enhancers, and retarders, such as triallyl isocyanurate; ethoxylated bisphenol A dimethacrylate; α-methylstyrene dimer (AMSD); and other coagents described in USP documents 5,346,961 and 4,018,852.

[0056] As an alternative, or in addition, to the use of peroxides for crosslinking the compositions of this invention, other approaches to crosslinking polymers can be used to effect the desired degree of crosslinking. Such approaches and technologies are well known to those skilled in the art and include, but are not limited to, radiation crosslinking, moisture crosslinking, bisulfonyl azide crosslinking, hydroxyl terminated polydimethylsiloxane (PDMS) crosslinking, etc. In some cases, it would be necessary for the polymers used in the practice of this invention to be appropriately functionalized to allow cross-linking (for example, with alkoxysilanes in the case of moisture cross-linking or cross-linking with hydroxyl-terminated PDMS).

Additions

[0057] Conventional additives, other than WTR and crosslinking agents, are exemplified by antioxidants, coupling agents, ultraviolet absorbers or stabilizers, antistatic agents, pigments, dyes, nucleating agents, reinforcing fillers or polymeric additives, carbon black smoke, gliding agents, plasticizers, processing aids, lubricants, viscosity control agents, tackifiers, antiblocking agents, surfactants, extender oils, metal deactivators, voltage stabilizers, flame retardant fillers and additives, intensifiers and catalysts, and smoke suppressants. Fillers and additives can be added in amounts ranging from less than about 0.1 to more than about 200 parts by weight for every 100 parts by weight of the base resin, e.g., co-E-MPEGMA alone or in combination with one or more ethylene-based resins.

[0058] Examples of antioxidants are: hindered phenols, such as tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane; bis kbeta-(3,5-ditert-butyl-4-hydroxy-benzyl)-methylcarboxyethyl)]sulfone; 4,4'-thiobis(2-t-butyl-5-methylphenol) and thiodiethylene bis(3,5-di-tert-butyl-4-hydroxy)-hydrocinnamate; phosphites and phosphonites, such as tris(2,4-di-tert-butylphenyl)phosphite and di-tert-butylphenyl-phosphonite; thio compounds such as dilaurylthiodipropionate, dimyrysylthiodipropionate and distearylthiodipropionate; various siloxanes; and various amines, such as polymerized 2,2,4-trimethyl-1,2-dihydroquinoline and alkylated diphenylamines. Antioxidants can be used in amounts of 0.1 to 5 parts by weight per 100 parts by weight based on the weight of the base resin, for example, co-E-MPEGMA alone or in combination with a polyethylene.

Compound formation, manufacturing and articles of manufacture

[0059] Compound formation of the mixed compositions of this invention can be carried out by standard means known to those skilled in the art. Examples of compounding equipment are internal batch mixers, such as a BANBURYTM or BOLLINGTM internal mixer. Alternatively, single- or twin-screw continuous mixers can be used, such as a FARREL™ continuous mixer, a WERNER and PLFEIDERER™ twin-screw mixer, or a BUSS™ continuous kneading extruder. The type of mixer used and the operating conditions of the mixer can affect the properties of the composition, such as viscosity, volume resistivity and extruded surface smoothness.

[0060] The compounding temperature for the polymer blend and any additives/fillers is typically the melting point of polyethylene, for example, 120 °C, to 220 °C, more typically 160 to 210 °C. The various components of the final composition can be added to and compounded with each other in any order, or simultaneously, but typically the polymer blend is first compounded, followed by incorporation of the additive package.

[0061] In some embodiments, the additives are added as a pre-mixed master batch. Such master batches are commonly formed by dispersing the additives, separately or together, in an inert plastic resin, for example, one of a plastic matrix component or a low-density polyethylene. Master batches are conveniently formed by melt compounding methods.

[0062] In one embodiment, the polymer composition of this invention can be applied as a covering to a cable, for example, as a sheath or insulation layer, in known amounts and by known methods (e.g., with the equipment and methods described in USP documents 5,246,783 and 4,144,202). Typically, the polymeric composition may be prepared in an extruder reactor equipped with a cable coating mold and, after the components of the composition are formulated, the composition is extruded onto the cable as the cable is extracted through the mold. The sheath is then typically subjected to a curing period that occurs at ambient temperatures up to above the polymer's melting point (but below the polymer's decomposition point) until the article achieves the desired degree of cross-linking. Curing can begin in the extruder-reactor.

[0063] In one embodiment, the compositions of this invention are useful in the Direct Peroxide Injection (DPI) process for the manufacture of cable insulation and protective jackets. In one embodiment, the DPI process consists of a mixer, e.g., a LICO Spa turbomixer, and an extruder, e.g., a single-screw manufacturing extruder. In this process, which is well known in the art (e.g. EP 0 472 949 A1), peroxide (typically a liquid organic peroxide) and, optionally, other additives, typically liquid additives, e.g. one or more liquid antioxidants, are measured and mixed into the polymer in the mixer, and then the polymer blended with peroxide and optional additives continuously feeds into the extruder. The DPI process eliminates the need to compound peroxide and optional additives at compounders, thereby saving raw material cost for cable manufacturers.

[0064] In one embodiment, the invention is a method or process of preparing an insulation sheath for a cable, the method comprising the steps of (1) feeding co-E-MPEGMA into an extruder, (2) injecting peroxide in the extruder and co-E-MPEGMA, (3) mix the peroxide and co-E-MPEGMA in the extruder to form a mixture of peroxide and co-E-MPEGMA, and (4) extrude the mixture of (3) into a coated or uncoated conductor.

[0065] Other articles of manufacture that can be prepared from the polymeric compositions of this invention include fibers, ties, sheets, tapes, pellets, tubes, pipes, caulking, seals, gaskets, foams, shoes and bellows. These articles can be manufactured using known equipment and techniques.

[0066] The invention is described in more detail through the following examples. All parts and percentages are by weight unless otherwise noted.

Examples Test Methods

[0067] Hot creep is measured to determine the degree of curing (crosslinking), and hot forming is used to measure the relaxation of the sample after hot creep stretching. The test is based on the ICEA-T-28-562-2003 method for power cable insulation materials. The hot creep test is performed on 1.3 mm (50 mil) thick samples in an oven with a glass door at 150 °C or 200 °C with a tensile force of 0.2 MPa applied stress at the bottom of the specimens. Three test specimens for each specimen are cut using ASTM D 412 type D drawbars. The specimens are stretched for 15 minutes, in which the percentage increases in length are measured, and the average values of the three specimens are reported as "creep at warm". Hot forming values are obtained for the same samples subjected to hot creep tests, after removing the filler for 5 minutes under heat and cooling it at room temperature for 10 minutes. A sample is considered to have "failed" if it breaks during testing or produces hot creep greater than (>) 175%.

[0068] Moving matrix rheometer (MDR) analyzes are performed on compounds using the Alpha Technologies Model 2000 Rheometer MDR unit. The test is based on the ASTM D 5289 procedure, “Standard Test Method for Rubber - Property Vulcanization Using Rotorless Cure Meters”. MDR analyzes are performed using 4 to 5 grams of material. Samples are tested at 182°C for 12 minutes or at 140°C for 120 or 180 minutes with an arc swing of 0.5 degrees for both temperature conditions. Samples are tested from material that contains all necessary additives, including cross-linking agents. Resistance to premature cross-linking under extrusion (“combustion”) conditions is evaluated by ts1 (time to torque increase of 0.11 N-m (1 lb-in)) at 140 °C. The final degree of crosslinking is reflected by MH (maximum torque) - ML (minimum torque) at 182 °C.

[0069] Aquatic tree growth rate testing is performed in accordance with the ASTM D6097 test standard. The sample in the test has a diameter of 25.4 mm (1 inch), a thickness of 6.35 mm (250 mil) and a standard conical defect in which the water tree can grow. After conditioning in a vacuum oven at 80 °C for 7 days, the specimen is placed in a 0.01 N sodium chloride (NaCl) solution under 2 kilovolts (kV) at 1 kilohertz (kHz) for 30 days of aging. Then the specimen is removed from the NaCl solution and stained with a dye (e.g. methylene blue). Slices with a thickness of between 0.25 and 0.65 mm are cut along the conical defect. The slices are then placed on a 25.4 mm (1 inch) x 76.2 mm (3 inch) ground glass microscope slide, from which optical microscopic images are obtained. The water tree length (Lt) is measured for each sample. Ten samples are tested, and the average Lt is reported.

[0070] The Dissipation Factor (DF) and dielectric constant (DC) test is performed on 1.3 mm (50 mil) cured plates. The plates are degassed in a vacuum oven at 60 °C for five days. The DF test is performed in accordance with ASTM D150 at 60 Hz on a GUILDLINETM High Voltage Capacitance Bridge Unit, Model 9920A, with a TETTEXTM Specimen Holder and an AG Instruments TETTEXTM Temperature Control Unit. Samples are tested at 60 Hz and applied voltage of 2 kV at temperatures of 25 °C, 40 °C, 90 °C and 130 °C.

[0071] AC breaking strength ("ACBD"), also known as AC dielectric strength, is tested on specimens cut from nominal 1.016 mm (40 mil) thick crosslinked plates using a Dielectric Strength Tester D-149 HIPOTRONICSTM series AC adapter with external cell (electrode configuration: top - 12.7 mm (0.5 inch) diameter, bottom - 25.4 mm (1 inch) diameter), at a voltage rating of 0.5 kV/second ramp for three temperatures (23 °C, 90 °C and 120 °C).

Inventive Examples 1 to 4 (IE1 to IE4) and Comparative Examples 1 to 2 (CE1 to CE2)

[0072] The compositions are shown in Table 2. The polymers are as follows: LDPE (available from The Dow Chemical Company) of 0.922 g/cm3 density (ASTM D792) and 1.8 g/10 min index fusion (I2) (ASTM D1238); co-E-MPEGMA copolymers are produced in a mini-autoclave plant from ethylene and methoxypolyethylene glycol methacrylate. The chain transfer agent (CTA) is propylene. Methoxypolyethylene glycol (MPEGMA) monomer or oligomer has a number average molecular weight (Mn) of 500 g/mol. The co-E-MPEGMA copolymer, 0.5% by weight, has an MPEGMA level of 0.5% by weight and a melt index of 3.74 g/10 min, while the co-E-MPEGMA copolymer, 2, 3% by weight, has an MPEGMA level of 2.3% by weight and a melt index of 3.67 g/10 min. The melt index refers to that at 190 °C using 2.16 kg of charge.

CO-E-MPEGMA synthesis details

[0073] Monomer - Undiluted poly(ethylene glycol) methyl ether methacrylate is loaded into a 316 stainless steel container and diluted with ethyl acetate, to produce a final concentration of 8.0% by weight. This container is purged with nitrogen for three hours before use and maintained on a 0.48 MPa (70 pounds per square inch (psig)) nitrogen pad during operation.

[0074] Initiators - The peroxide initiator tert-butyl peroxyacetate (TPA, 20% by weight solution in H ISOPARTM) and the peroxide initiator di-tert-butyl peroxide (DTBP, 20% by weight solution in H ISOPARTM) are combined with E ISOPARTM in a second 316 stainless steel supply vessel to produce 8,500 mass ppm TPA and 1,881 mass ppm DTBP, a ratio of 5:1 mol TPA/mol DTBP. The container is padded and unpadded five times with 0.48 Mpa (70 psig) nitrogen before use and kept under a nitrogen pad during operation.

[0075] MPEGMA-modified LDPE (co-E-MPEGMA, 0.5% by weight) - Ethylene is injected at 5,444 grams per hour (g/h) (194 mol/h), at a pressure of 193 MPa ( 1,930 bar), in a stirred (1,600 rpm) 300 ml continuous stirred tank reactor (CSTR) autoclave, with an external heating jacket set at about 215 °C. Propylene (chain transfer agent or "CTA") is added to the ethylene stream at a pressure of 6.2 MPa (62 bar) and a rate of 94.7 g/h (2.25 mol/h), before that the mixture is compressed to 193 MPa (1,930 bar) and injected into the reactor. The MPEGMA solution in ethyl acetate is pumped at a pressure of 193 MPa (1,930 bar) and at a rate of 52.5 ml/h into the ethylene-propylene mixture, before said mixture is injected into the reactor. The peroxide initiator is added directly to the reactor, through the side wall, at a pressure of 193 MPa (1,930 bar) and at a rate of 22.0 x 10-2 g/h (1.66 millimol/hour (mmol/ h)) of TPA and 4.8 x 10-2 g/h (0.33 mmol/h) of DTBP. The conversion of ethylene to polymer is 12.1% by weight, based on the mass of ethylene entering the reactor, and the average reaction temperature is 244 °C. An ethylene-based polymer with a melt index (I2) of 3.74 g/10 min is formed.

[0076] Monomer - Undiluted poly(ethylene glycol) methyl ether methacrylate is loaded into a 316 stainless steel container and diluted with ethyl acetate, to produce a final concentration of 30.0% by weight. This container is purged with nitrogen for three hours before use and maintained on a 0.48 MPa (70 pounds per square inch (psig)) nitrogen pad during operation.

[0077] Initiators - The peroxide initiator tert-butyl peroxyacetate (TPA, 20% by weight solution in H ISOPARTM) and the peroxide initiator di-tert-butyl peroxide (DTBP, 20% by weight solution in H ISOPARTM) are combined with E ISOPARTM in a second 316 stainless steel supply vessel to produce 8,500 mass ppm TPA and 1,881 mass ppm DTBP, a ratio of 5:1 mol TPA/mol DTBP. The container is padded and unpadded five times with 0.48 Mpa (70 psig) nitrogen before use and kept under a nitrogen pad during operation.

[0078] LDPE modified with MPEGMA (co-E-MPEGMA, 2.3% by weight) - Ethylene is injected at 5,444 grams per hour (g/h) (194 mol/h), at a pressure of 193 MPa ( 1,930 bar), in a stirred (1,600 rpm) 300 ml continuous stirred tank reactor (CSTR) autoclave, with an external heating jacket set at about 215 °C. Propylene (chain transfer agent or "CTA") is added to the ethylene stream at a pressure of 6.2 MPa (62 bar) and a rate of 65.8 g/h (1.56 mol/h), before that the mixture is compressed to 193 MPa (1,930 bar) and injected into the reactor. The MPEGMA solution in ethyl acetate is pumped at a pressure of 193 MPa (1,930 bar) and at a rate of 80.2 ml/h into the ethylene-propylene mixture, before said mixture is injected into the reactor. The peroxide initiator is added directly to the reactor, through the side wall, at a pressure of 193 MPa (1,930 bar) and at a rate of 22.0 x 10-2 g/h (1.66 millimol/hour (mmol/ h)) of TPA and 4.8 x 10-2 g/h (0.33 mmol/h) of DTBP. The conversion of ethylene to polymer is 13.1% by weight, based on the mass of ethylene entering the reactor, and the average reaction temperature is 246 °C. An ethylene-based polymer with a melt index (I2) of 3.67 g/10 min is formed.

[0079] LUPEROXTM 101 peroxide (peroxide decomposing at high temperature with half-life temperatures for 1 hour (h) and 10 h of 140.3 °C and 120.3 °C, respectively, measured in dodecane, and available together with Arkema) is used as a cross-linking agent. LOWINOXTM TBM-6 stabilizer, a hindered thiophenol, is used as an antioxidant (AO) in formulations.

[0080] All components (except peroxide) are mixed in a 420 ml BRABENDERTM container with CAM blades at 30 rotations per minute (rpm) rotor speed at a jacket temperature of 180 ° C for one minute (after loading ). The jacket temperature is then increased to 190°C, and the melt is flowed and compounded for 3 minutes to obtain a homogeneous mixture. The polymer melt is removed from the mixing bowl, flattened in a cold press, cut into small strips using a guillotine plate cutter, and then pelletized into small pieces by a BERLYNTM pelletizer. These small pieces feed into a BRABENDERTM single screw extruder at 40 rpm, with a 120°C/130°C/140°C/150°C barrel profile, a 20/40 sieve pack and a single screw conveyor. conventional. The resulting polymer yarn is cut into uniform pellets using the BERLYNTM pelletizer.

[0081] The composite pellets are heated in an oven at 70 °C for at least 4 hours. LUPEROX TM 101 is transferred to the pellets in a glass vial using a syringe. The jar is shaken well and then placed in the stoneware cup at 30 rpm for 10 minutes, until all liquids are absorbed by the pellets. Completed compounds are placed in an oven at 70°C overnight. The resulting pellets are evaluated as such (or compression molded into various thicknesses for testing).

[0082] The pellets are tested in a moving matrix rheometer at 140 °C or 182 °C (to evaluate crosslinking characteristics). For measuring the growth of aquatic trees, the compositions are compression molded under the following conditions: 3.5 MPa (500 pounds per square inch (psi)) at 180 °C for 5 minutes, followed by 17 MPa (2,500 psi) at same temperature for 5 minutes, slowly cooling to 30°C at this pressure and opening the press to remove the molded plate. For hot creep and electrical measurements, the compositions are compression molded under the following conditions to produce fully crosslinked samples of different thicknesses: 3.5 MPa (500 psi) at 125 °C for 3 minutes, followed by 17 MPa (2,500 psi) at this temperature for 3 minutes, and 17 MPa (2,500 psi) at 180 °C for 12 minutes, cooling to 30 °C at this pressure and opening the printer to remove the molded plate.

[0083] The properties of the compositions are given in Table 2. CE1 is a single LDPE formulation that is known to exhibit poor WTR properties. CE2 involved PEG 20000 as a WTR additive in the LDPE-based formulation. IE1 to IE4 did not contain PEG. IE1 consisted of 50 wt% co-E-MPEGMA, 0.5 wt% copolymer, and 49.625 wt% LDPE, while IE2 contained 50 wt% co-E-MPEGMA, 2.3% by weight of copolymer and 49.625% by weight of LDPE. IE3 and IE4 are based solely on co-E-MPEGMA copolymers. When using co-E-MPEGMA copolymers in formulations, the length of the water tree (Lt) decreases unexpectedly, as shown in IE1 to IE4 relative to CE1 (Figure 1).

[0084] All hot creep values are desirably less than 175%. From the results of the moving matrix rheometer and hot creep, the use of co-E-MPEGMA blend, 0.5 wt%/LDPE (IE1) presents better resistance to combustion than co-E-MPEGMA blend. MPEGMA, 2.3 wt%/LDPE (IE2), while the curing performances of the two are similar (Figure 3). In Figure 3, two baselines from CE1 to IE3 and IE4 are drawn. The curing and combustion balance is improved if the blend of co-E-MPEGMA and LDPE is above the baseline and vice versa. Unexpectedly, IE1 is far above baseline 1, while IE2 is slightly below baseline 2. Table 1 Polymers and their properties Table 2 Compositions and properties of CE1 to CE2 and IE1 to IE

Claims (10)

1. Crosslinkable composition, characterized by the fact that it comprises in percentage by weight based on the weight of the composition: (A) 1 to < 100% by weight of a co-E-MPEGMA with the co-E-MPEGMA consisting of (i ) ethylene and (ii) methoxypolyethylene glycol methacrylate (MPEGMA); (B) >0 to 90% by weight of an ethylene-based polymer other than co-E-MPEGMA or a grafted ethylene-methoxypolyethylene glycol methacrylate g-E-MPEGMA; (C) 0 to < 5% by weight of a water tree retardant (WTR); (D) 0 to < 2% by weight of an antioxidant; and (E) 0 to < 3% by weight of a crosslinking agent; the weight of the composition being 100% by weight. 2. Crosslinking composition according to claim 1, characterized in that the ethylene-based polymer is a low density polyethylene (LDPE). 3. Crosslinkable composition according to claim 1, characterized in that the WTR is a polyethylene glycol. 4. Crosslinkable composition according to claim 1, characterized in that the crosslinking agent is a peroxide. 5. Crosslinkable composition according to claim 1, characterized in that MPEGMA contains from 1 to 80 repeating units of ethylene glycol. 6. Article, characterized by the fact that it comprises: - a coated conductor comprising a conductive core and an insulation layer at least partially covering the conductive core, the insulation layer comprising co-E-MPEGMA consisting of (i) ethylene and (ii) methoxypolyethylene glycol methacrylate (MPEGMA). 7. Article according to claim 6, characterized in that the co-E-MPEGMA consists of 0.1% by weight to 10% by weight of units derived from MPEGMA and from 50 to 99.1% by weight of units derived from ethylene. 8. Article according to claim 6, characterized in that the insulation layer is an insulation layer of a medium to extra high voltage power cable. 9. Article according to claim 6, characterized in that the MPEGMA contains from 1 to 80 repeating units of ethylene glycol. 10. Method for conducting electricity, the method being characterized by the fact that it comprises the step of applying a voltage along the conductive core of the coated conductor, as defined in claim 6, so as to generate a flow of electricity through the conductive core.