Polyethylene composition with improved rheological properties

Abstract

This invention relates to a polyethylene composition that improves rheological properties while maintaining thermal and mechanical properties, wherein the polyethylene composition has an MFR5 (5.0 kg, 190 °C, ISO 1133) of 0.1 g / 10 min to 4.0 g / 10 min, and a viscosity η at a constant shear stress of 747 Pa. 747 The polyethylene composition having a strength equal to or greater than 130 kPas can be obtained by a method comprising the following steps or by a method comprising the following steps: a) providing a polyethylene matrix resin (A) having an MFR5 (5.0 kg, 190 °C, ISO 1133) of 0.1 g / 10 min to 3.0 g / 10 min, and optionally comprising one or more C3 to C4 compounds in a weight of 1 wt.-% to 10 wt.-% based on the total weight of the polyethylene matrix resin (A). 12 The invention comprises: a) further melting the polyethylene matrix resin (A) in an extruder using an α-olefin comonomer; b) mixing the polyethylene matrix resin (A) in an amount of 73.5 wt.-% to 99.99 wt.-% based on the total weight of the resulting mixture with an amount of 0.01 wt.-% to 1.5 wt.-% free radical initiator (B), the free radical initiator (B) being selected from peroxides according to formulas (I) to (III) and any mixture thereof, preferably in a melt-mixing apparatus, such as an extruder; and c) reacting the polyethylene matrix resin (A) with the free radical initiator (B) at a temperature range of 150°C to 300°C to obtain the polyethylene composition. The invention also relates to a method for producing the polyethylene composition, articles comprising the polyethylene composition, and the use of the polyethylene composition in the manufacture of articles, preferably in the manufacture of pipe or auxiliary pipe articles.

Description

Technical Field

[0001] This invention relates to a polyethylene composition that has improved rheological properties while maintaining thermal and mechanical properties. Background Technology

[0002] Melt strength is directly related to the rheological properties of polyolefin compositions. Therefore, the polymerization catalyst used to polymerize polyolefin resins imposes certain limitations on rheological properties such as melt flow rate or viscosity. In particular, Ziegler-Natta catalysts typically only allow the polymerization of polyolefin resins with certain molecular weight limitations. Furthermore, continuous multi-stage polymerization processes employing two or more polymerization reactors connected in series to allow for the polymerization of multi-peak polyolefin resins impose limitations on the melt strength of the polyolefin composition. To increase the molecular weight of the polyolefin resin in a multi-stage process, the proportion of the high molecular weight polyolefin component in the polymerization stage (typically the gas-phase reactor stage) must be increased. However, increasing the proportion in the gas-phase reactor to improve the molecular weight and melt strength of the polyolefin composition can adversely affect other properties of the polyolefin composition, such as mechanical strength or impact resistance.

[0003] To increase the constant shear stress (η) at 747 Pa 747 To reduce polymer viscosity, a lower melt flow rate (MFR) is required. However, further reductions in MFR are limited by the molecular weight potential (hydrogen responsiveness) of the catalyst. Due to this limitation in the polymer production process, polymer design is restricted to higher gas-phase reactor (GPR) partitioning ratios to provide minimal hydrogen flow control for melt flow control. This limits the minimum melt flow that a multi-stage process can produce. The limitation on GPR partitioning ratios also constrains the required performance balance between short-term hydrostatic strength, an indicator of mechanical strength, and slow crack growth resistance.

[0004] For example, it is known from WO 2004 / 055068 A1, WO 2004 / 055069 A1 and EP 0 810 235 A1 for improving anti-sagging properties (in η). 747 The Ziegler-Natta (ZN) catalyst is measured. A particularly preferred Ziegler-Natta catalyst is described in EP 2 894 195 B1.

[0005] Therefore, there is a need to develop new methods and processes to overcome the limitations faced by ZN catalysts. A further objective is to simplify the processing and manufacturing of various products.

[0006] Therefore, one way to overcome the above limitations is to use a heat- and shear-induced twin-screw blending process with specific additives. It has been proposed to modify the viscosity of polyolefins through this heat- and shear-induced blending process.

[0007] Crosslinking technology is an important technique for improving the properties of polyethylene (PE). This technology utilizes free radical chemistry. One type of process modifies the polymer backbone by subjecting the polymer to high-energy irradiation, where CH bonds break on the main chain, generating reactive free radicals. However, the commercial limitations of this technology lie in the high capital investment required for expensive irradiation equipment and the limitations in achieving uniform crosslinking for product thickness and irregularly shaped products.

[0008] Another technique for modifying polymer backbones is through chemical modification. Using free radical initiators such as organic peroxides generates secondary or tertiary free radicals, thereby promoting backbone modification. However, these methods rely on the random binding of so-called backbone radicals to modify the backbone, and there is a competition between branching, grafting, and chain scission. It is also known that chain scission can lead to the formation of numerous byproducts and many undesirable oxygen-containing byproducts, which may also be potentially toxic. Therefore, identifying suitable peroxide molecules that do not decompose into toxic byproducts is crucial, especially for drinking water or food contact applications.

[0009] Suitable peroxides, typically organic peroxides compatible with polyolefin monomers, are used for crosslinking. Examples of such organic peroxides include alkyl peroxides, alkenyl peroxides, and alkynyl peroxides. Exemplary organic peroxides that can be used in the polymer pipes of this invention include di-tert-butyl peroxide (Trigonox® B) and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3 (Trigonox® B). ® 145), 3,3,5,7,7-pentamethyl-1,2,4-trioxane (Trigonox) ® 311), 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (Trigonox) ® 101) and 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxyhexacyclononane (Trigonox ® 301). Summary of the Invention

[0010] To overcome the aforementioned drawbacks, it was discovered that an improved polyethylene composition can be obtained by mixing and reacting a polyethylene matrix resin with a specific free radical initiator, thereby achieving the above objective and overcoming the limitations imposed by the expensive irradiation equipment required to achieve uniform crosslinking of polyethylene.

[0011] Therefore, the present invention provides a polyethylene composition having an MFR5 (5.0 kg, 190 °C, ISO 1133) of 0.1 g / 10 min to 4.0 g / 10 min, and a viscosity η at a constant shear stress of 747 Pa. 747(Measured as described in the experimental section below) equal to or greater than 130 kPa s, the polyethylene composition can be obtained by a method comprising the following steps or by a method comprising the following steps: a) Provides a polyethylene matrix resin (A) having an MFR5 (5.0 kg, 190°C, ISO 1133) of 0.1 g / 10 min to 3.0 g / 10 min, and optionally comprising one or more C3 to C4 compounds in an amount of 1 wt.-% to 10 wt.-% based on the total weight of said polyethylene matrix resin (A). 12 α-olefin comonomer, preferably further melted in an extruder in the polyethylene matrix resin (A); b) Mix the polyethylene matrix resin (A) in an amount of 73.5 wt.-% to 99.99 wt.-% based on the total weight of the resulting mixture with a free radical initiator (B) in an amount of 0.01 wt.-% to 1.5 wt.-% selected from peroxides of formulas (I) to (III) below and any mixture thereof. (I), (II), and (III), R1 and R2 are each independently selected from alkyl groups having 4 to 30 carbon atoms, and the alkyl groups can be cyclic, linear, branched, or unbranched. R1 and R2 can be the same or different. Preferably, the polyethylene matrix resin (A) and the free radical initiator (B) are melt-mixed in a melt-mixing apparatus (e.g., an extruder). c) The polyethylene matrix resin (A) is reacted with the free radical initiator (B) in a temperature range of 150°C to 300°C, preferably 160°C to 280°C, more preferably 180°C to 260°C, to obtain the polyethylene composition.

[0012] The above objective is also achieved by a method for producing a crosslinkable polyethylene composition, the method comprising steps a) to c) above.

[0013] The above objective is also achieved by articles comprising the above-described polyethylene composition, preferably pipes, auxiliary pipe products or membranes, wherein the articles preferably have improved hydrostatic pressure resistance.

[0014] The above-mentioned objective is also achieved by using the above-mentioned polyethylene composition in the manufacture of articles, preferably in the manufacture of pipes or auxiliary pipe articles. Detailed Implementation

[0015] Surprisingly, a novel polyethylene composition has been discovered to address the aforementioned problems, which is obtainable or produced in the presence of a specific free radical initiator. This initiator is an FDA-approved organic peroxide, ideally suited for the production of low-density polyethylene, preferably foam. Preferably, specific additives can be added to the polyethylene composition of the present invention. These additives can be at least one conjugated or non-conjugated, linear or branched diene. When shear-induced blending process conditions are employed, the limitation of using expensive irradiation equipment is overcome for achieving uniform crosslinking of polyethylene.

[0016] The polyethylene resin according to the present invention refers to a polymer derived from at least 50 mol% ethylene monomer units and additional comonomer units.

[0017] Therefore, ethylene homopolymers refer to polymers that are essentially composed of ethylene monomer units. Due to the requirements of large-scale polymerization, ethylene homopolymers may contain a small amount of comonomer units, the content of which is usually less than 0.1 mol%, preferably less than 0.05 mol%, and most preferably less than 0.01 mol%.

[0018] Ethylene copolymers refer to polymers composed of ethylene monomer units and comonomer units in a content of at least 0.1 mol%. In ethylene random copolymers, the comonomer units are randomly distributed in the polymer chain.

[0019] Polyethylene matrix resin (A) The polyethylene matrix resin (A) can be unimodal, bimodal, or multimodal.

[0020] Multimodal resins are widely used, for example, in the production of pipes, due to their excellent physical and chemical properties, such as mechanical strength, corrosion resistance, and long-term stability. Such compositions are described, for example, in EP 0 739 937 and WO 02 / 102891. The term "molecular weight" as used herein generally refers to the weight-average molecular weight (Mw).

[0021] Typically, polyolefin resins used in piping or injection molding applications contain at least two polyolefin components produced under different polymerization conditions, resulting in different weight-average molecular weights, a phenomenon known as "multimodal." The prefix "multimodal" relates to the number of different polymer components that make up the composition. Thus, for example, a polyolefin resin consisting of only two components is called "bimodal."

[0022] The molecular weight distribution curve of such multi-peak polyolefins (i.e., the graph of the polymer weight fraction as a function of its molecular weight) will show two or more maximum values, or be at least significantly wider than the curve of a single component.

[0023] For example, if a polymer is produced in a continuous, multi-stage process using reactors connected in series and each reactor operating under different conditions, the polymer components produced in each reactor will each have their own molecular weight distribution and weight-average molecular weight. When recording the molecular weight distribution curves of such a polymer, superimposing these individual curves onto the molecular weight distribution curve of the final polymer product typically yields a curve with two or more distinct maximum values.

[0024] Polyolefin resins containing polyolefin components with the same molecular weight but different comonomer contents are also called "multimodal". Therefore, polyolefin resins with two components having different comonomer contents are also called "bimodal".

[0025] Monomeric polyolefin resins contain only one polyolefin component, which cannot be distinguished by molecular weight or comonomer content. Typically, monomeric polyolefin resins are polymerized in a single polymerization stage.

[0026] The polyethylene matrix resin (A) is preferably a copolymer of ethylene and one or more α-olefin comonomers, more preferably ethylene and one or more C4 to C4 copolymers. 10 Copolymers of α-olefin comonomers.

[0027] Preferably, the comonomer is selected from 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, and 1-decene. Most preferably, the comonomer is 1-butene and / or 1-hexene.

[0028] Based on the total weight of the polyethylene matrix resin (A), the one or more C4 to C 12 The content of α-olefin comonomer can be from 1 wt.-% to 10 wt.-%, preferably from 1.5 wt.-% to 8 wt.-%, more preferably from 2.0 wt.-% to 7.5 wt.-%.

[0029] Furthermore, the polyethylene matrix resin (A) is preferably a multi-peak polyethylene resin, and more preferably a bi-peak polyethylene resin.

[0030] Preferably, the polyethylene matrix resin (A) is composed of two polyethylene components, one having a lower weight-average molecular weight (MAM) and the other a higher MMA. Both components can be homopolymers and / or copolymers.

[0031] The polyethylene matrix resin (A) has an MFR5 (5.0 kg, 190°C, ISO 1133) of 0.1 g / 10 min to 3.0 g / 10 min, preferably 0.5 g / 10 min to 3.0 g / 10 min, and more preferably 0.6 g / 10 min to 2.0 g / 10 min.

[0032] Preferably, the polyethylene matrix resin (A) has an MFR 21.6 (21.6 kg, 190°C, ISO 1133) is 1 g / 10 min to 100 g / 10 min, more preferably 2 g / 10 min to 50 g / 10 min, and even more preferably 5 g / 10 min to 40 g / 10 min.

[0033] The flow rate ratio of the polyethylene matrix resin (A) used to indicate the molecular weight distribution width of the polymer is FRR. 21 / 5 (i.e., MFR) 21.6 The ratio of MFR5 to MFR5 is preferably 5 to 60, more preferably 15 to 55, and even more preferably 20 to 50.

[0034] Preferably, the polyethylene matrix resin (A) has a density of 920 kg / m³. 3 More, preferably 930 kg / m 3 More, or even more preferably 940 kg / m 3 More, or even more preferably 950 kg / m 3 Or more. The density may also be 920 kg / m³. 3 Up to 960 kg / m 3 between.

[0035] The polyethylene resin may be selected from linear low-density polyethylene (LLDPE) resin, medium-density polyethylene (MDPE) resin, and high-density polyethylene (HDPE) resin.

[0036] Free radical initiator (B) The polyethylene composition of the present invention can be obtained by mixing and reacting the above-mentioned polyethylene matrix resin (A) with a free radical initiator (B) or by mixing and reacting the above-mentioned polyethylene matrix resin (A) with a free radical initiator (B), wherein the free radical initiator (B) is selected from the peroxide compounds of formulas (I) to (III) and any mixture thereof, wherein R1 and R2 are each independently selected from alkyl groups having 4 to 30 carbon atoms, and the alkyl groups may be cyclic, linear, branched or unbranched; wherein R1 and R2 may be the same or different.

[0037] The free radical initiator is preferably selected from di(2-ethylhexyl) peroxide dicarbonate, di(4-tert-butylcyclohexyl) peroxide dicarbonate, dihexadecyl peroxide dicarbonate, ditetradecyl peroxide dicarbonate, and mixtures thereof. Particularly preferred is dihexadecyl peroxide dicarbonate as the free radical initiator.

[0038] The polyethylene composition of the present invention can be obtained by mixing and reacting a free radical initiator (B) or by mixing and reacting a free radical initiator (B) in an amount of 0.01 wt.-% to 1.5 wt.-%, preferably 0.1 wt.-% to 1.5 wt.-%, more preferably 0.5 wt.-% to 1.2 wt.-%, with the amount of each free radical initiator (B) based on the total weight of the resulting mixture.

[0039] The aforementioned free radical initiators can be liquid or solid at room temperature.

[0040] The aforementioned free radical initiator can be added to the polyethylene matrix resin (A) in the form of a dispersion. The medium in which the initiator according to the invention is dispersed is preferably inert and polar to the initiator, such that the initiator is almost insoluble therein, and the polyethylene matrix resin (A) is incompatible with the medium.

[0041] The aforementioned free radical initiator is preferably dispersed in water or alcohol.

[0042] The polyethylene matrix resin (A) can preferably be physically mixed with the initiator or initiator dispersion in a manner known to those skilled in the art, below the decomposition temperature of the initiator, for example, in a mixer with low or high shear forces. The temperature of the initiator is preferably selected below a temperature at which the initiator half-life is 0.1 hours. Preferably, both the polyethylene matrix resin (A) and the initiator dispersion are maintained at a temperature below a temperature at which the initiator half-life is 10 hours.

[0043] Preferably, the initiator dispersion is mixed with the polyethylene matrix resin (A) below the decomposition temperature, during and / or thereafter the temperature is increased so that the free radical initiator can decompose and react with the polyethylene matrix resin (A) before the matrix resin is completely melted.

[0044] Various additives may preferably be incorporated into the initiator or initiator dispersion to ensure the chemical and / or physical stability of the dispersion. Such additives may include freezing point inhibitors, pH buffers, bactericides, chemical stabilizers, thickeners, and / or surfactants. For example, such additives are described in WO 97 / 49759 A1.

[0045] The aforementioned free radical initiator can be added to the polyethylene matrix resin (A) in the amount described above or in the form of a so-called masterbatch (MB), wherein the free radical initiator is contained in a concentrated form in the carrier polymer in the masterbatch.

[0046] When the free radical initiator is added in the form of a masterbatch, based on the total weight of the resulting mixture, in the mixing step b), the masterbatch containing the free radical initiator and the carrier polymer is present in an amount of 0.05 wt.-% to 5.0 wt.-% in the above mixing step b), wherein the amount of the masterbatch is selected such that the amount of the free radical initiator (B) is within the above range.

[0047] Additives (C) The polyethylene composition of the present invention can preferably be obtained by further mixing an additive (C) in step b) above, wherein the additive (C) is at least one conjugated or non-conjugated, straight-chain or branched diene, more preferably a diene selected from 1,3-butadiene, 2,4-octadiene, 1,7-octadiene, 1,9-decadiene or any mixture thereof, and even more preferably 1,7-octadiene.

[0048] Other preferred dienes suitable as adjuvants (C) are disclosed in WO 2009 / 146926 A1.

[0049] The amount of the additive (C) added is preferably 0.1 wt.% to 5 wt.%, more preferably 0.1 wt.% to 2.0 wt.%, relative to the ethylene content in the resulting mixture.

[0050] Surprisingly, the aforementioned diene auxiliaries were found to enhance and modulate the rheological properties of the crosslinkable polyethylene compositions of the present invention, for example, through η. 747 The measured viscosity increases, melt strength improves, shear thinning is enhanced, and anti-sagging properties are improved.

[0051] Polyethylene composition The polyethylene composition of the present invention has an MFR5 (5.0 kg, 190°C, ISO 1133) of 0.1 g / 10 min to 4.0 g / 10 min, and a viscosity η at a constant shear stress of 747 Pa. 747 (Measured as described in the experimental section below) equal to or greater than 130 kPa s.

[0052] The MFR5 (5.0 kg, 190°C, ISO 1133) of the polyethylene composition is preferably from 0.1 g / 10 min to 3.0 g / 10 min, more preferably from 0.15 g / 10 min to 2.0 g / 10 min.

[0053] The viscosity η of the polyethylene composition of the present invention under constant shear stress of 747 Pa 747 Preferably equal to or greater than 150 kPa s, more preferably at 150 kPa s to 1100 kPa Within the range of s, or even more preferably within 150 kPa s to 900 kPa Within the range of s.

[0054] The melting temperature Tm of the polyethylene composition of the present invention (determined by differential scanning calorimetry (DSC) as described in the experimental section below) is preferably 122°C to 135°C, more preferably 123°C to 135°C.

[0055] The shear thinning index (SHI) of the polyethylene composition of the present invention 5 / 300 Preferably equal to or greater than 50, more preferably in the range of 55 to 160; the SHI 5 / 300 The determinations were made in accordance with ISO 6721-1 and ISO 6721-10 and as described in the Experimental section below.

[0056] The flow rate of the polyethylene composition of the present invention is higher than that of FRR. 21 / 5 Preferably, the flow rate is equal to or greater than 20. Preferably, the flow rate ratio is equal to or greater than FRR. 21 / 5 The flow rate ratio is equal to or less than 36. 21 / 5 Melt Flow Rate (MFR) 21.6 The ratio to MFR5 (5.0 kg, 190 °C, ISO 1133). Flow rate ratio FRR 21 / 5 Used to indicate the molecular weight distribution width of a polymer.

[0057] The polyethylene composition of the present invention preferably has a strength of not less than 915 kg / m³ as determined according to ISO 1183-1:2012. 3 The density is more preferably 915 kg / m³. 3 Up to 965 kg / m 3 Within the range, or even more preferably within 920 kg / m 3 Up to 960 kg / m 3 Within the range. Therefore, the polyethylene can be selected from linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE).

[0058] In addition to the polyethylene matrix resin (A) and the free radical initiator (B), in step b) above, commonly used additives for polyolefins may be incorporated, such as stabilizers (e.g., antioxidants), metal scavengers and / or UV stabilizers, antistatic agents, and processing aids (e.g., processing aids), more preferably one or more antioxidants. Preferably, based on the total weight of the resulting mixture, the amount of these additives is 10 wt.% or less, more preferably 8 wt.% or less, even more preferably 5 wt.% or less, for example, in the range of 0.1 wt.% to 10 wt.%

[0059] The polyethylene composition of the present invention can preferably be obtained in the presence of carbon black, wherein the amount of carbon black is 1.0 wt.-% to 10 wt.-% based on the total amount of the resulting mixture, preferably 1.5 wt.-% to 9.0 wt.-%, more preferably 1.8 wt.-% to 8.0 wt.-%, even more preferably 1.8 wt.-% to 7.0 wt.-%, even more preferably 1.8 wt.-% to 5.0 wt.-%, even more preferably 1.8 wt.-% to 4.5 wt.-%, and even more preferably 1.8 wt.-% to 4.0 wt.-%.

[0060] Carbon black may be added to the above mixing step b) either as is (pure) or in the form of a so-called masterbatch (MB), wherein the carbon black and optionally other additives defined above are present in a concentrated form in the carrier polymer.

[0061] Aggregation methods Preferably, the polyethylene matrix resin (A) is an "in-situ" blend. Such a blend is preferably produced in a multi-stage process. However, an "in-situ" blend can also be produced in a single reaction stage by using two or more different types of catalysts.

[0062] Polymerization catalysts used to produce polyethylene matrix resin (A) include transition metal coordination catalysts, such as Ziegler-Natta (ZN) catalysts, metallocene catalysts, non-metallocene catalysts, chromium-based catalysts, etc. The catalyst can be supported, for example, on conventional supports, including silica, aluminum-containing supports, and magnesium dichloride-based supports. Preferably, the catalyst is a ZN catalyst, more preferably a non-silica-supported ZN catalyst, and most preferably a MgCl2-based ZN catalyst.

[0063] The Ziegler-Natta catalyst is further preferably composed of Group 4 (group number according to the new IUPAC system) metal compounds, preferably including titanium, magnesium dichloride and aluminum.

[0064] The catalyst may be commercially available or prepared according to literature or similar literature. For the preparation of preferred catalysts that can be used in this invention, refer to Borealis WO 2004 / 055068, WO 2004 / 055069 and EP 0 810235. Particularly preferred Ziegler-Natta catalysts are described in EP 0 810 235 and WO 99 / 51646.

[0065] Methods for polymerizing ethylene or copolymerizing ethylene with the aforementioned comonomers are known in the art. Such polymerization methods typically comprise at least two consecutive polymerization stages. Polymerization in each stage is typically carried out in solution, slurry, bulk, or gas phase. In one specific embodiment, the method comprises at least one slurry reactor stage and at least one gas phase reactor stage, each stage comprising at least one reactor, and all reactors are arranged in series. In a particularly preferred embodiment, the polymerization method comprises at least one bulk reactor and at least one gas phase reactor, arranged in this order. In some preferred methods, the method comprises one bulk reactor and at least two gas phase reactors, such as two or three gas phase reactors. The method may also include a pre-reactor and a post-reactor. The pre-reactor typically comprises a pre-polymerization reactor. In this method, relatively high polymerization temperatures are typically used to obtain specific properties of the polymer. Typical temperatures in all methods are 70°C or higher, preferably 80°C or higher, more preferably 85°C or higher. The high polymerization temperatures described above are typically applied to some or all of the reactors in a reactor series.

[0066] The method of the present invention can also be carried out by two- or more-stage polymerization or by using two or more different polymerization catalysts in a single-stage polymerization. Multi-site or dual-site catalysts can also be used. More preferred options are disclosed, for example, in WO 2009 / 146926A1.

[0067] Production of polyethylene compositions According to the present invention, the polyethylene composition of the present invention can be produced by a method comprising the following steps: a) Provides a polyethylene matrix resin (A) having an MFR5 (5.0 kg, 190°C, ISO 1133) of 0.1 g / 10 min to 3.0 g / 10 min, and optionally comprising one or more C3 to C4 compounds in an amount of 1 wt.-% to 10 wt.-% based on the total weight of said polyethylene matrix resin (A). 12 α-olefin comonomer; b) Mix the polyethylene matrix resin (A) in an amount of 73.5 wt.-% to 99.99 wt.-% based on the total weight of the resulting mixture with a free radical initiator (B) in an amount of 0.01 wt.-% to 1.5 wt.-% selected from peroxides of formulas (I) to (III) below and any mixture thereof. (I), (II), and (III), R1 and R2 are each independently selected from alkyl groups having 4 to 30 carbon atoms, and the alkyl groups can be cyclic, linear, branched, or unbranched. R1 and R2 can be the same or different. Preferably, the polyethylene matrix resin (A) and the free radical initiator (B) are melt-mixed in a melt-mixing apparatus (such as an extruder). c) The polyethylene matrix resin (A) is reacted with the free radical initiator (B) at a temperature range of 150°C to 300°C, preferably 160°C to 280°C, more preferably 180°C to 260°C, to obtain the polyethylene composition; the polyethylene composition has an MFR5 (5.0 kg, 190°C, ISO 1133) of 0.1 g / 10 min to 4.0 g / 10 min, and a viscosity η at a constant shear stress of 747 Pa. 747 (As measured in this article) equal to or greater than 130 kPa s.

[0068] Preferably, step b) is performed by melt-mixing the polyethylene matrix resin (A) with the free radical initiator (B) in a melt-mixing apparatus (such as an extruder).

[0069] More preferably, the mixing or extrusion step b) is carried out in the presence of at least one conjugated or non-conjugated, straight-chain or branched diene, as described above, in the presence of 0.1 wt.-% to 5.0 wt.-%, more preferably 0.1 wt.-% to 2.0 wt.-%.

[0070] Particularly preferred is that, in step b), the polyethylene matrix resin (A) and the free radical initiator (B) are melt-mixed in a melt-mixing apparatus, and in step c), the reaction is carried out in a temperature range of 150°C to 300°C, more preferably in a barrel temperature range of 160°C to 280°C, and even more preferably in a range of 180°C to 280°C.

[0071] The mixing or extrusion step b) can preferably be carried out in a single-screw extruder or a twin-screw extruder.

[0072] Particularly preferred is that the extruder is a shear-induced extruder.

[0073] Products Furthermore, the present invention relates to an article comprising the polyethylene composition of the present invention or an article obtained by the method of the present invention. Preferably, based on the total weight of the article, the article comprises at least 90 wt.-%, more preferably 95 wt.-%, and even more preferably 99 wt.-%, of the polyethylene composition of the present invention, and even more preferably the article is composed of the polyethylene composition of the present invention.

[0074] Preferably, the article is selected from pipes, auxiliary pipe articles, membranes, blow-molded articles or any other extruded articles.

[0075] According to ISO 1167-1:2006, under a stress of 12.0 MPa and a temperature of 20°C, the article preferably has hydrostatic resistance with a failure time of at least 150 h, more preferably at least 200 h, and even more preferably at least 300 h; and / or According to ISO 1167-1:2006, at a stress of 5.4 MPa and a temperature of 80°C, the article preferably has hydrostatic resistance with a failure time of at least 100 h, more preferably at least 200 h, and even more preferably at least 248 h.

[0076] use The present invention also relates to the use of the polyethylene composition according to the invention for manufacturing articles by blending the polyethylene composition with optional additives as described above, preferably by extrusion, preferably for manufacturing pipes or supplementary pipe articles.

[0077] Preferably, the polyethylene composition according to the invention can be extruded in the presence of a rheology modifier (e.g., a maleimide derivative, more preferably hexamethylene-1,6-dimaleimide). Other additives used with the polyolefin may also be present, such as stabilizers (e.g., antioxidants), metal scavengers and / or UV stabilizers, antistatic agents, and application agents (e.g., processing aids).

[0078] Based on the total weight of the reactive polyolefin composition, the rheology modifier is present in the polyethylene composition in an amount of up to 0.5 wt.% or less. The other additives mentioned above are preferably present in the polyethylene composition in an amount of up to 10 wt.% or less.

[0079] Based on the total weight of the polyethylene composition, the polyethylene composition may preferably also contain 1.0 wt.-% to 10 wt.-% carbon black.

[0080] Further preferred embodiments of the above-mentioned components, dosages, and methods of blending and / or extruding the crosslinkable polyethylene compositions according to the present invention can be found in WO2019 / 219902 A1.

[0081] Improving melt strength is crucial for many high-end applications because it is directly related to the rheological properties of the polymer and the performance of the final product. This invention discovers that by using a specific free radical initiator (B) in the blending process for preparing polyethylene compositions, optionally in combination with a diene auxiliary agent (C), polyethylene compositions according to the invention exhibiting excellent rheological properties can be obtained.

[0082] The free radical initiator (B) according to the present invention can act as a chain extender and / or a branching initiator and / or a partial crosslinking agent, thus increasing the viscosity η of the polymer under a constant shear stress of 747 Pa. 747 And melt strength. In shear-induced extrusion processes, the use of equipment such as twin-screw blenders to blend polyolefins improves the rheological properties of the polyethylene composition, for example, by adjusting the rheological properties of the polyethylene composition according to the density of the polyethylene used, with η... 747 The measured viscosity increased by up to 7 times. For polymers produced using a multi-peak process, η 747 It is a function of the melt flow rate. According to the present invention, for a given melt flow rate, the η of the polyethylene composition can be increased. 747 In other words, the improvement of this invention lies in the higher viscosity η. 747 This also reduces the polymer's melt flow rate. This surprising property overcomes the limitations of the catalyst's molecular weight potential.

[0083] Therefore, the desired increase in polymer molecular weight can be achieved without relying on the specific design of the polymerization catalyst. Conventional catalysts and polymerization conditions, typically used to control polymer microstructure, limit the improvement of the rheological properties of polyolefins. Therefore, this invention surprisingly overcomes these limitations, improving the rheological properties of polyolefins while simultaneously obtaining a desirable polymer microstructure. Increased η 747 The increased melt strength further improves the anti-sagging properties of the compositions of the present invention. This improvement is achieved even at different densities and melt flow rates.

[0084] The present invention is further illustrated by the experimental section and examples given below.

[0085] Example A. Testing Methods a) Melt flow rate Melt flow rate (MFR) is determined according to ISO 1133 and expressed in g / 10 min. MFR indicates polymer flowability and therefore represents the polymer's processability. A higher melt flow rate generally indicates a lower polymer viscosity. The MFR5 of polyethylene was measured at 190°C and a 5 kg load. 2.16 (Also known as MFR2) is the MFR of polyethylene measured at a temperature of 190°C and a load of 2.16 kg. 21 It was measured at a temperature of 190°C and a load of 21.6 kg. FRR (Flow Rate Ratio) represents the ratio of flow rates under different loads. Therefore, FRR... 21 / 5 MFR 21 The value of / MFR5.

[0086] b) Density The density of the polymer was measured on a compression-molded specimen prepared according to EN ISO 1183-1:2004 Method A, and expressed in kg / m³. 3 Provided.

[0087] c) Comonomer content The content of the comonomer (1-hexene) was measured using Fourier transform infrared spectroscopy (FTIR), as described in EP 2 228 394A1. 13 C-NMR calibration.

[0088] d) Dynamic shear measurement (frequency scan measurement) Characterization of the polymer melt by dynamic shear measurements conformed to ISO standards 6721-1 and 6721-10. Measurements were performed on an Anton Paar MCR301 stress-controlled rotational rheometer equipped with a 25 mm parallel plate geometry. Measurements were taken on a compression-molded plate under a nitrogen atmosphere, with strain set within the linear viscoelastic range. Oscillatory shear tests were conducted at 190 °C, with a frequency range of 0.0154 rad / s to 500 rad / s and a 1.2 mm gap.

[0089] In dynamic shear experiments, the probe undergoes uniform deformation under sinusoidally varying shear strain or shear stress (strain and stress control modes, respectively). In controlled strain experiments, the sinusoidal strain experienced by the probe can be expressed as... γ(t) = γ0sin(ωt) (1) If the applied strain is within the linear viscoelastic range, the resulting sinusoidal stress response can be expressed as: σ(t) = σ0sin(ωt +δ)(2) Where σ0 and γ0 are the stress and strain amplitudes, respectively; ω is the angular frequency; δ is the phase shift (the loss angle between the applied strain and the stress response); and t is time.

[0090] Dynamic test results are typically represented by several different rheological functions, namely, shear storage modulus G', shear loss modulus G'', complex shear modulus G*, complex shear viscosity η*, dynamic shear viscosity η', the heterogeneous component of complex shear viscosity η'', and loss tangent tanδ. These can be expressed as follows: G' = cosδ [Pa](3) G" = sinδ [Pa](4) G* = G' + iG'' [Pa](5) η * = η ' - iη" [Pa·s](6) η' = [Pa·s] (7) η'' = [Pa·s](8) In addition to the rheological functions mentioned above, other rheological parameters were determined, such as the so-called elasticity index EI(x). The elasticity index EI(x) is the value of the storage modulus G', which is determined when the loss modulus G'' is x kPa, and can be described by Equation 9.

[0091] EI(x) = G' (G'' = x kPa) [Pa](9) For example, EI (5 kPa) is defined by the value of the storage modulus G', which is determined when the value of G' is equal to 5 kPa.

[0092] The so-called shear thinning coefficient is determined as described in Equation 10.

[0093] (10) For example, SHI (0.05 / 300) It is defined as the complex viscosity (in Pa·s) measured when G* is equal to 0.05 kPa, divided by the complex viscosity (in Pa·s) measured when G* is equal to 300 kPa. Correspondingly, SHI (5 / 200) It is defined as the complex viscosity value (in Pa.s) measured when G* equals 5 kPa, divided by the complex viscosity value (in Pa.s) measured when G* equals 200 kPa. Correspondingly, SHI... (2.7 / 210)It is defined by dividing the complex viscosity value (in Pa.s) measured when G* is equal to 2.7 kPa by the complex viscosity value (in Pa.s) measured when G* is equal to 210 kPa.

[0094] Obtain the values ​​of storage modulus (G'), loss modulus (G''), complex modulus (G*), and complex viscosity (η*) as functions of frequency (ω).

[0095] Therefore, for example, η* 300rad / s (eta*) 300rad / s η* is used as an abbreviation for complex viscosity at a frequency of 300 rad / s. 0.05rad / s (eta*) 0.05rad / s () is used as an abbreviation for complex viscosity at a frequency of 0.05 rad / s.

[0096] These values ​​were determined using a single-point interpolation procedure defined in the Rheoplus software. In cases where a given G* value was not reached in the experiment, the value was determined by extrapolation using the same procedure as before. In both cases (interpolation or extrapolation), the options in Rheoplus's "Interpolate y-values ​​to x-values ​​from parametric interpolation" and "Logarithmic interpolation type" were applied.

[0097] References: [1] Rheological characterization of polyethylene fractions” Heino, EL, Lehtinen, A., Tanner J., Seppälä, J., Neste Oy, Porvoo, Finland, Theor.Appl. Rheol., Proc. Int. Congr. Rheol, 11th (1992), 1, 360-362. [2] The influence of molecular structure on some rheologicalproperties of polyethylene”, Heino, EL, Borealis Polymers Oy, Porvoo, Finland, Annual Transactions of the Nordic Rheology Society, 1995.). [3]Definition of terms relating to the non-ultimate mechanicalproperties of polymers, Pure&Appl. Chem., Vol. 70, No. 3, pp. 701-754, 1998. e)η 747 A method closely related to and used in conjunction with this invention relates to the rheology of polymers, and is based on determining the viscosity of the polymer under constant shear stress. The shear stress chosen for this method is 747 Pa. The viscosity of the polymer under this shear stress was measured at a temperature of 190°C, and it was found to be inversely proportional to the gravitational flow of the polymer; that is, the higher the viscosity, the lower the gravitational flow.

[0098] Viscosity at a shear stress of 747 Pa was determined using a rotational rheometer, which can be a constant-stress rheometer, such as the Anton Paar MCR series rheometer. The rheometer and its functions are described in the "Encyclopedia of Polymer Science and Engineering," 2nd edition, Vol. 14, pp. 492-509. Measurements were taken under constant shear stress (constant rotation direction) between two plates with a diameter of 25 mm. The gap between the plates was 1.2 mm.

[0099] The sample was conditioned before measurement. Measurement was performed at 190°C. After temperature conditioning, measurement was initiated by applying a predetermined stress of 747 Pa. The stress was maintained for 1860 s during the measurement period. η 747 The parameters were calculated by averaging the last five points of the measured transient shear viscosity. These five points were found to be located between 1620 s and 1860 s. Therefore, η 747 It was determined at the corresponding time point of 1740 s.

[0100] The measurement principle involves applying a certain torque to a plate shaft using a precision motor. This torque is then converted into shear stress in the sample. This shear stress remains constant. The rotational speed at which the shear stress is generated is recorded and used to calculate the sample's viscosity.

[0101] f) Tensile modulus (23℃) As a measure of stiffness, the tensile modulus (E modulus) of the composition was measured at 23°C for the compression-molded specimens, according to ISO 527-2:1993. Specimens (Type 1B) were cut from a 4 mm thick plate prepared by compression molding, according to ISO 293:2004, using the conditions defined in Chapter 3.3 of ISO 1872-2:2007. The modulus was measured at a speed of 1 mm / min.

[0102] g) Tensile properties (23℃) According to ISO 527-1 (crosshead rate of 50 mm / min), the tensile strength and elongation at break (i.e., tensile strain at break) are measured at 23°C.

[0103] h) Charpy notch impact strength According to ISO 179 / 1eA:2000, at -20°C (Charpy impact strength (-20°C)) and 23°C (Charpy impact strength (23°C)), for 80*10*4 mm... 3 Charpy impact strength was determined using V-shaped cut samples. Samples were cut from 4 mm thick plates prepared by compression molding, according to ISO 293:2004 and using the conditions defined in Chapter 3.3 of ISO 1872-2:2007.

[0104] i) Melting temperature (Tm) and crystallization temperature (Tcr) The melting temperature of the polymer used was measured according to ISO 11357-3. T was measured on a 3 ± 0.5 mg sample using a TA Instruments Q2000 differential scanning calorimeter (DSC). m and T cr Crystallization and melting curves were obtained during cooling and heating scans at 10 °C / min from 0 °C to 200 °C. The melting temperature and crystallization temperature were considered as endothermic and exothermic peaks, respectively.

[0105] j)F 30 melt strength The tests described herein follow ISO 16790:2005. The apparatus shown in Figure 1 conforms to ISO 16790:2005.

[0106] The strain hardening behavior was determined using the method described by MH Wagner in his article "Rheotens - Mastercurves and Drawability of Polymer Melts" in Volume 36, pp. 925-935 of *Polymer Engineering & Science*. The strain hardening behavior of the polymer was analyzed using a Rheotens apparatus (a product of Göttfert GmbH, Siemensstr. 2, 74711 Buchen, Germany), in which the melt strip was stretched to elongation at a specified acceleration.

[0107] Rheotens experiments simulated industrial spinning and extrusion processes. In principle, the melt was extruded through a circular die, and the resulting strip was then drawn out. Stress on the extrudate was recorded as a function of melt properties and measured parameters (particularly the ratio of yield to draw speed, which is essentially a measure of elongation). For the results given below, the material was extruded using a laboratory Göttfert X-trude 300 extruder and a gear pump equipped with a cylindrical die (L / D = 6.0 / 2.0 mm). To measure the F30 melt strength and v30 melt ductility, the pressure at the extruder outlet (i.e., the gear pump inlet) was set to 30 bar by bypassing a portion of the extruded polymer.

[0108] The gear pump was pre-adjusted to a strip extrusion rate of 5 mm / s, and the melt temperature was set to 200°C. The length of the spun yarn between the die and the Rheoten wheel was 100 mm. At the start of the experiment, the take-up speed of the Rheoten wheel was adjusted to match the speed of the extruded polymer strip (with zero tensile force). The experiment was then initiated by slowly increasing the take-up speed of the Rheoten wheel until the polymer filament broke. The acceleration of the roller was sufficiently small to allow for measurement of the tensile force under quasi-steady-state conditions. The acceleration of the stretched melt strip was 120 mm / s². 2 Rheoten is used in conjunction with a PC program (rheometer). This is a real-time data acquisition program used to display and store the measured tensile force and tensile speed data. The endpoint of the Rheotens curve (the relationship between force and roller speed) at which the polymer strip breaks is taken as the F30 melt strength and tensile speed.

[0109] k)g strain hardening The strain hardening test is a modified tensile test performed on specially prepared thin samples at 80°C. Strain hardening modulus (MPa) <gp>It is calculated from the true strain-true stress curve; by using the slope of the curve in the true strain region, λ is between 8 and 12.

[0110] The actual strain λ is calculated from the length l (mm) and the gauge length l0 (mm), as shown in Equation 1.

[0111] (1) Where Δl is the increase in length (mm) between the gauge marks of the specimen. The true stress σ is calculated according to Equation 2. 真实 (MPa), assuming volume conservation between gauge length markers: σ 真实 =σ n λ(2) Where σ n For engineering stress.

[0112] The Neo-Hookean constitutive model (Equation 3) was used to fit the actual strain-stress data, and the values ​​for 8 < λ < 12 were calculated from them. <gp>(MPa).

[0113] (3) Where C is the mathematical parameter of the constitutive model, used to describe the yield stress extrapolated to λ=0.

[0114] Initially, five samples were measured. If... <gp>If the coefficient of variation is greater than 2.5%, two additional samples will be measured. If the test bar undergoes strain in the fixture, the test result will be discarded.

[0115] According to the stress parameters provided in Table 2 of ISO 1872-2, the PE granules of the material are compressed into sheets with a thickness of 0.30 mm.

[0116] After compression molding, the sheet is annealed to eliminate any orientation or thermal history and maintain its isotropy. Annealing is performed in an oven at (120±2)℃ for 1 hour, followed by slow cooling to room temperature by closing the temperature chamber. The sheet is allowed to move freely during this process.

[0117] Next, the specimen is punched out from the pressed sheet. The specimen geometry is based on the improved ISO 37:1994 Type 3 (Figure 3).

[0118] This sample has a large clamping area to prevent the clamp from slipping, and its dimensions are shown in the table below.

[0119] Table: Dimensions of Type 3 Specimens (Improved ISO 37:1994)

[0120] The stamping process is carried out in such a way that there are no deformations, cracks or other irregular defects in the sample.

[0121] The thickness of the sample is measured at three points in the parallel region of the sample; the lowest of these thickness measurements is used for data processing.

[0122] Perform the following steps on a general tensile testing machine equipped with a temperature control chamber and a non-contact elongation meter: 1. Before starting the test, acclimate the sample in a temperature-controlled chamber at (80 ± 1) ℃ for at least 30 min.

[0123] 2. Clamp the sample onto the upper fixture.

[0124] 3. Turn off the temperature control box.

[0125] 4. After the temperature reaches (80 ± 1) ℃, close the lower clamp.

[0126] 5. Before applying the load and starting the measurement, allow the specimen to balance between the fixtures for 1 minute.

[0127] 6. Apply a preload of 0.5 N at a speed of 5 mm / min.

[0128] 7. Stretch the specimen along its long axis at a constant transverse speed (20 mm / min) until the specimen breaks.

[0129] During the test, a load cell with a range of 200 N was used to measure the load on the sample. A non-contact elongation meter was used to measure the elongation.

[0130] B. Materials The inventive embodiments (IE) and comparative embodiments (CE) are prepared according to the following steps and using the components shown below.

[0131] The following ethylene polymers were used in the examples and comparative examples: Matrix resin PE1 According to section b of "2. Examples" in WO2022 / 144275A1, a multi-stage polymerization process including a prepolymerization step, a slurry cyclic polymerization step, and a gas-phase polymerization step was carried out in the presence of the Ziegler-Natta catalyst prepared as described in Example 1 of EP1378528A1 and a TEA cocatalyst. The reaction conditions and properties of the obtained matrix resin PE1 are shown in Table 1 below.

[0132] Table 1

[0133] Matrix resin PE2 Following the description in section "2. Materials" b of WO2019 / 219902A1, a multi-stage polymerization process was carried out, including a prepolymerization step, a slurry cyclic polymerization step, and a gas-phase polymerization step, and the polymerization was conducted in the presence of the Ziegler-Natta catalyst prepared as described in Example 1 of WO99 / 51646A1. The reaction conditions and properties of the obtained matrix resin PE2 are shown in Table 2 below.

[0134] Matrix resin PE3 Under the conditions given in Table 2 below, PE2 was subjected to multi-stage polymerization as described above. The properties of the resulting matrix resin PE3 are also shown in the table.

[0135] Table 2

[0136] The free radical initiator used was dihexadecyl peroxide dicarbonate (Perkadox® 24L, hereinafter referred to as "Perkadox"), which is commercially available from Nouryon Functional Chemical BV of Herkenbosch, Netherlands.

[0137] The diene used is 1,7-octadiene (hereinafter referred to as "octadiene"), which is commercially available from Evonik Industries AG in Essen, Germany.

[0138] The blending and extrusion of the polymer mixtures are carried out under the following process conditions: Extrusion equipment: Coperion ZSK18 co-rotating twin-screw extruder Melt temperature: 215℃ to 220℃ Screw speed: 300 RPM Extruder output: 5 kg / hour Extruder motor torque: 75% The matrix resin was purged with nitrogen (approximately 50 kg / h), stabilized with commercial additives, and then extruded under the conditions described above. The composition and properties of the composition are given in the table below.

[0139] Table 3 Process parameters and polymer properties of CE1, IE1 and IE2

[0140] Table 3 clearly shows that, compared to CE1, the viscosities (η) of IE1 and IE2 prepared by thermal and shear-induced blending in low-density polyethylene resin, using dihexyl peroxide dicarbonate (Perkadox 24L) as an initiator and in the presence of octadiene, are significantly lower than those of CE1. 747 The shear thinning index (SHI) showed a significant increase. Similarly, the shear thinning index (SHI) also showed a significant increase. 5 / 300 The melt strength and overall strength also increased. Meanwhile, both Tm and Tc increased. It was observed that octadiene, as an auxiliary agent (C), also acted as a nucleating agent.

[0141] Table 4 Process parameters and polymer properties of CE2 and IE3

[0142] Table 4 clearly shows that, compared to CE2, the viscosity (η) of IE3, prepared by thermal and shear-induced blending in polyethylene resin with dihexadecyl peroxide dicarbonate (Perkadox 24L) as the initiator and in the presence of octadiene, is significantly lower. 747 The shear thinning index (SHI) showed a significant increase. Similarly, the shear thinning index (SHI) also showed a significant increase. 5 / 300 The concentration of MFR5 increased as MFR5 decreased. Simultaneously, both Tm and Tc increased. It was observed that octadiene, as an adjuvant (C), also acted as a nucleating agent.

[0143] Table 5 Process parameters and polymer properties of CE3, IE4 and IE5

[0144] nm = Untested Table 5 clearly shows that, compared to CE3, the viscosities (η) of IE4 and IE5 prepared by thermal and shear-induced blending with dihexadecyl peroxide dicarbonate (Perkadox 24L) as initiator in medium-density polyethylene resin are significantly lower. 747 The initiator concentration showed a high increase. MFR5 decreased with increasing initiator concentration. The decrease in MFR5 was not significant due to changes in comonomer composition and type (here: the 1-butene content of PE3 was 4.2 wt.-%). On the other hand, both IE4 and IE5 achieved high η. 747 The value reflects the improved rheological properties.

[0145] Typically, as entanglement in the polymer network increases, the stiffness of the polymer also increases, but IE5 is observed to exhibit a fairly moderate tensile modulus, thus the composition is quite flexible. Therefore, compositions of IE5 are useful for applications such as flexible piping.

[0146] The above data convincingly demonstrate that the polyethylene composition according to the present invention has the following effects and advantages: The polyethylene resin obtained using the mixture of free radical initiators (B) showed a decrease in MFR5 (increased molecular weight). This indicates that the viscosity of the polymer resin in the inventive examples is increased compared to the corresponding comparative examples. This is likely because the initiator-induced LCB / partial crosslinking mechanism ideally leads to a potential chain extension effect, which tends to increase chain length and thus increase molecular weight.

[0147] Traditionally, reducing the melt flow rate (MFR) is typically achieved by adjusting the hydrogen concentration ratio in the gas-phase reactor and optimizing the properties of the polymerization catalyst. This imposes some limiting constraints on process parameters, particularly with hydrogen feed. Therefore, hydrogen, as a chain transfer agent, has a significant activating effect on supported catalysts, reaching an order of magnitude, and eventually plateaus above which the polymerization rate is no longer affected. In current process designs, this variation in MFR is limited, and hydrogen cannot effectively reduce the MFR or increase the molecular weight.

[0148] The formulation of this invention surprisingly achieves a reduction in the melt flow rate of the material at this processing stage. This alleviates process limitations while simultaneously improving rheological properties. Tables 3 and 4 illustrate this advantageous performance, while also achieving a higher viscosity η. 747 .

[0149] The compositions of the present invention exhibit improved flow rate ratio (FRR) and shear thinning index (SHI). Both of these parameters reflect the molecular weight distribution of the polymer. Since improvements in both FRR and SHI have been observed, the compositions of the present invention are expected to broaden the molecular weight distribution in terms of rheological properties.

[0150] The compositions of the present invention exhibit viscosity (η) 747 A significant increase in η. 747 Indicators of the anti-sagging properties of polymer melts during processing are provided, and these properties are known to be a function of molecular weight. The initiator according to the invention induces chain elongation via LCB and / or through partial crosslinking with the polymer backbone, resulting in greater chain entanglement and network formation. As shown in Tables 3 and 4, this η is expected to... 747 The addition of [amount] will improve the sag resistance of the composite material.

[0151] As shown by the melting temperature (Tm) and crystallization temperature (Tc), and their respective melting and crystallization enthalpies ΔHm and ΔHc, the thermal properties of the polyethylene compositions of the present invention are not negatively affected.< / gp> < / gp> < / gp>

Claims

1. A polyethylene composition having an MFR5 (5.0 kg, 190 °C, ISO 1133) of 0.1 g / 10 min to 4.0 g / 10 min, and a viscosity η at a constant shear stress of 747 Pa. 747 As measured in this article, equal to or greater than 130 kPa s, the polyethylene composition can be obtained by a method comprising the following steps or by a method comprising the following steps: a) Provides a polyethylene matrix resin (A) having an MFR5 (5.0 kg, 190°C, ISO 1133) of 0.1 g / 10 min to 3.0 g / 10 min, and optionally comprising one or more C3 to C4 compounds in an amount of 1 wt.-% to 10 wt.-% based on the total weight of said polyethylene matrix resin (A). 12 α-olefin comonomer, preferably further melted in an extruder in the polyethylene matrix resin (A); b) Mix the polyethylene matrix resin (A) in an amount of 73.5 wt.-% to 99.99 wt.-% based on the total weight of the resulting mixture with a free radical initiator (B) in an amount of 0.01 wt.-% to 1.5 wt.-% selected from peroxides of formulas (I) to (III) below and any mixture thereof. (I)， (II), and (III), R1 and R2 are each independently selected from alkyl groups having 4 to 30 carbon atoms, and the alkyl groups can be cyclic, linear, branched, or unbranched. R1 and R2 can be the same or different. Preferably, the polyethylene matrix resin (A) and the free radical initiator (B) are melt-mixed in a melt-mixing apparatus, such as an extruder. c) The polyethylene matrix resin (A) is reacted with the free radical initiator (B) in a temperature range of 150°C to 300°C, preferably 160°C to 280°C, more preferably 180°C to 260°C, to obtain the polyethylene composition.

2. The polyethylene composition according to claim 1, wherein the polyethylene matrix resin (A) is an ethylene homopolymer or an ethylene copolymer, and / or The polyethylene matrix resin (A) wherein C3 to C 12 The α-olefin comonomer is selected from 1-butene, 1-hexene, 1-octene and mixtures thereof.

3. The polyethylene composition according to claim 1 or 2, wherein the free radical initiator (B) is selected from di(2-ethylhexyl) peroxide dicarbonate, di(4-tert-butylcyclohexyl) peroxide dicarbonate, dihexadecyl peroxide dicarbonate, ditetradecyl peroxide dicarbonate, and mixtures thereof.

4. The polyethylene composition according to any one of the preceding claims, wherein in step b), the amount of the free radical initiator added is from 0.5 wt.% to 1.5 wt.%, preferably from 0.5 wt.% to 1.2 wt.%, based on the total weight of the resulting mixture.

5. The polyethylene composition according to any one of the preceding claims, wherein in step b), at least one conjugated or non-conjugated, linear or branched diene, preferably 1,3-butadiene, 2,4-octadiene or 1,7-octadiene or any mixture thereof, is further mixed with the polyethylene matrix resin (A) and a free radical initiator (B), wherein the amount of the diene is preferably from 0.1 wt.-% to 5 wt.-% relative to the ethylene content in the resulting mixture, and / or The additive (D) is further mixed with the polyethylene matrix resin (A) and the free radical initiator (B), and the amount of the additive (D) is from 0.1 wt.-% to 10 wt.-% based on the total weight of the resulting mixture, wherein the additive is preferably an antioxidant.

6. The polyethylene composition according to any one of the preceding claims, having a melt temperature Tm of 122°C to 135°C as determined by differential scanning calorimetry (DSC) as described herein.

7. The polyethylene composition according to any one of the preceding claims, having a density of not less than 915 kg / m³ as determined according to ISO 1183-1:2012. 3 Preferably 915 kg / m 3 Up to 965 kg / m 3 .

8. The polyethylene composition according to any one of the preceding claims, having a shear thinning index SHI 5 / 300 The SHI is equal to or greater than 50 and equal to or less than 160. 5 / 300 According to ISO 6721-1 and 6721-10 and as determined herein, and / or Its flow rate is higher than that of FRR 21 / 5 It is equal to or greater than 20 and equal to or less than 36.

9. A method for producing a polyethylene composition, comprising the following steps: a) Provides a polyethylene matrix resin (A) having an MFR5 (5.0 kg, 190°C, ISO 1133) of 0.1 g / 10 min to 3.0 g / 10 min, and optionally comprising one or more C3 to C4 compounds in an amount of 1 wt.-% to 10 wt.-% based on the total weight of said polyethylene matrix resin (A). 12 α-olefin comonomer; b) Mix the polyethylene matrix resin (A) in an amount of 73.5 wt.-% to 99.99 wt.-% based on the total weight of the resulting mixture with a free radical initiator (B) in an amount of 0.01 wt.-% to 1.5 wt.-% selected from peroxides of formulas (I) to (III) below and any mixture thereof. (I)， (II), and (III), R1 and R2 are each independently selected from alkyl groups having 4 to 30 carbon atoms, and the alkyl groups can be cyclic, linear, branched or unbranched, wherein R1 and R2 can be the same or different, preferably in a melt mixing apparatus, such as an extruder, the polyethylene matrix resin (A) and the free radical initiator (B) are melt-mixed. and c) The polyethylene matrix resin (A) is reacted with the free radical initiator (B) at a temperature range of 150°C to 300°C, preferably 160°C to 280°C, and more preferably 180°C to 260°C, to obtain the polyethylene composition; the polyethylene composition has an MFR5 (5.0 kg, 190°C, ISO 1133) of 0.1 g / 10 min to 4.0 g / 10 min, and a viscosity η at a constant shear stress of 747 Pa. 747 As measured in this article, equal to or greater than 130 kPa s.

10. The method according to claim 9, wherein in step b), at least one conjugated or non-conjugated, linear or branched diene, preferably 1,3-butadiene, 2,4-octadiene or 1,7-octadiene or any mixture thereof, is further mixed with the polyethylene matrix resin (A) and the free radical initiator (B), wherein the amount of the diene is preferably from 0.1 wt.-% to 5 wt.-% relative to the ethylene content in the resulting mixture.

11. The method according to claim 9 or 10, wherein in step c), the polyethylene matrix resin (A) and the free radical initiator (B) are melt-mixed in a melt-mixing apparatus, such as an extruder, preferably at a barrel temperature in the range of 160°C to 280°C.

12. The method according to any one of claims 9 to 11, wherein in step b), the amount of the free radical initiator (B) added is 0.1 wt.-% to 1.5 wt.-%, preferably 0.5 wt.-% to 1.5 wt.-%, more preferably 0.5 wt.-% to 1.2 wt.-%, each amount added is based on the total weight of the resulting mixture.

13. An article comprising a polyethylene composition according to any one of claims 1 to 8, preferably comprising at least 90 wt.- based on the total weight of the article.

14. The article of claim 13, which is a pipe or auxiliary pipe article, preferably having hydrostatic resistance with a failure time of at least 150 hours measured according to ISO 1167-1:2006 at 12.0 MPa stress and 20°C, and / or According to ISO 1167-1:2006, the article has hydrostatic resistance with a failure time of at least 100 h under stress of 5.4 MPa and at 80°C.

15. Use of the polyethylene composition according to any one of claims 1 to 8 for manufacturing articles, preferably for manufacturing pipes or auxiliary pipe articles.

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