Polyethylene composition with high expansion ratio

Abstract

The present invention relates to a polyethylene composition having a high expansion ratio. A polyethylene composition, particularly suitable for the production of blow-molded hollow articles, has the following features: 1) a density of 0.940 to 0.955 g / cm3, determined according to ISO 1183 at 23 DEG C; 2) the ratio of MIF / MIP is 12 to 30; 3) Mz is in the range of 2,000,000 to 4,500,000 g / mol; 4) Eta 0.02 is in the range of from 160,000 to 300,000 Pa.s, and Eta 0.02 is in the range And 5) a long chain branching index, LCBI, equal to or greater than 0.75.

Description

[0001] This application is a divisional application of the parent application with the application number 202080037771.1. The filing date of the parent application is June 12, 2020; the invention title is "Polyethylene composition with high expansion ratio". Technical Field

[0002] The present invention relates to a polyethylene composition suitable for preparing various types of shaped articles. In particular, due to its enhanced processability, high die swell, high surface quality of the final product, high dimensional stability, high environmental stress cracking resistance (FNCT), and high impact resistance, the composition of the present invention is suitable for manufacturing extrusion blow - molded hollow articles such as drums, containers, and oil storage tanks. Background Art

[0003] Compared with polyethylene compositions for the same use (especially as disclosed in US6201078 and WO2014064062), the polyethylene composition of the present invention provides an unparalleled balance between mechanical properties and processability. Summary of the Invention

[0004] Therefore, the present invention provides a polyethylene composition having the following characteristics:

[0005] 1) A density of 0.940 to 0.955 g / cm 3 , preferably 0.940 to 0.951 g / cm 3 , especially 0.945 to 0.952 g / cm 3 , or 0.946 to 0.952 g / cm 3 , or 0.945 to 0.951 g / cm 3 , or 0.946 to 0.951 g / cm 3 , measured at 23 °C according to ISO 1183;

[0006] 2) The MIF / MIP ratio is 12 to 30, especially 15 to 28 or 17 to 27, where MIF is the melt flow index at a load of 21.60 kg at 190 °C, and MIP is the melt flow index at a load of 5 kg at 190 °C, both measured according to ISO 1133;

[0007] 3) Mz is 2,000,000 to 4,500,000 g / mol, preferably 2,500,000 to 4,200,000 g / mol, especially 2,500,000 to 3,500,000 g / mol, where Mz is the z - average molecular weight, measured by GPC;

[0008] 4) η 0.02is from 160,000 to 300,000 Pa·s, or from 170,000 to 300,000 Pa·s, or from 180,000 to 300,000 Pa·s, preferably from 160,000 to 250,000 Pa·s, or from 170,000 to 250,000 Pa·s, or from 180,000 to 250,000 Pa·s, where η 0.02 is the complex shear viscosity at an angular frequency of 0.02 rad / s, measured using dynamic oscillatory shear in a plate - plate rotational rheometer at a temperature of 190 °C;

[0009] 5) The long - chain branching index LCBI is equal to or greater than 0.75, preferably equal to or greater than 0.80, where LCBI is the ratio of the radius of gyration squared R g to the radius of gyration squared of a linear PE having the same molecular weight; BRIEF DESCRIPTION OF THE DRAWINGS

[0010] These and other features, aspects, and advantages of the present invention will be better understood with reference to the following description, the appended claims, and the drawings, in which:

[0011] The drawings are illustrative embodiments of a simplified process flow diagram of two gas - phase reactors connected in series, the two gas - phase reactors connected in series being suitable for various embodiments of the ethylene polymerization process disclosed herein to produce various embodiments of the polyethylene compositions disclosed herein.

[0012] It should be understood that the various embodiments are not limited to the arrangements and apparatus shown in the drawings. DETAILED DESCRIPTION

[0013] The expression "polyethylene composition" is intended to include, alternatively, a single ethylene polymer and ethylene polymer compositions, particularly compositions of two or more ethylene polymer components, preferably compositions of two or more ethylene polymer components having different molecular weights, such compositions also being referred to in the relevant art as "bimodal" or "multimodal" polymers.

[0014] Generally, the polyethylene compositions of the present invention consist of or comprise one or more ethylene copolymers.

[0015] All features defined herein (including the previously defined features 1) to 5)) relate to the ethylene polymer or ethylene polymer composition. The addition of other components, such as additives commonly used in the art, can modify one or more of the said features.

[0016] The MIF / MIP ratio provides a rheological measure of the molecular weight distribution.

[0017] Another measure of the molecular weight distribution is given by the M w / M n ratio, where M w is the weight-average molecular weight and M n is the number-average molecular weight, measured by GPC (gel permeation chromatography) as described in the examples.

[0018] The preferred M w / M n value of the polyethylene composition of the present invention is from 12 to 35, particularly from 14 to 30.

[0019] The M w value is preferably from 300,000 g / mol to 550,000 g / mol, particularly from 350,000 g / mol to 450,000 g / mol.

[0020] The preferred range of the LCBI value is:

[0021] -0.75 to 0.95; or

[0022] -0.75 to 0.93; or

[0023] -0.75 to 0.90; or

[0024] -0.80 to 0.95; or

[0025] -0.80 to 0.93; or

[0026] -0.80 to 0.90.

[0027] In addition, the polyethylene composition of the present invention preferably has at least one of the following additional features.

[0028] - The MIF is 4 to 15 g / 10 min., particularly 5 to 12 g / 10 min.;

[0029] - The (η 0.02 / 1000) / LCBI ratio, which is between η 0.02 divided by 1000 and LCBI, is equal to or greater than 150, or greater than 190, particularly 150 to 300, or 190 to 300, or 190 to 250;

[0030] - The comonomer content is equal to or less than 2% by weight, particularly 0.5 to 2% by weight, based on the total weight of the composition;

[0031] - The HMWcopo index is 1 to 15, particularly 1 to 10 or 1 to 8.

[0032] The HMWcopo index is determined according to the following formula:

[0033] HMWcopo = (η 0.02 x t maxDSC ) / (10^5)

[0034] where η 0.02 is the complex shear viscosity of the melt in Pa·s measured at a temperature of 190 °C and an angular frequency of 0.02 rad / s in a parallel plate (or so-called plate - plate) rheometer in dynamic oscillatory shear mode as described previously; t maxDSC is the time (time to reach maximum crystallization rate, equivalent to the t1 / 2 half - crystallization time) in minutes required to reach the maximum value of the heat flow (in mW) of crystallization at a temperature of 124 °C under static conditions, measured in isothermal mode in a differential scanning calorimeter DSC; LCBI is the ratio of the mean square radius of gyration R g to that of a linear PE of the same molecular weight with a molar mass of 1,000,000 g / mol, measured by GPC - MALLS.

[0035] The comonomer or comonomers present in the ethylene copolymer are generally selected from olefins having the formula CH 2 =CHR, where R is a straight - chain or branched - chain alkyl group having 1 to 10 carbon atoms.

[0036] Specific examples are propylene, 1 - butene, pentene - 1, 4 - methylpentene - 1, 1 - hexene, 1 - octene, and 1 - decene. A particularly preferred comonomer is 1 - hexene.

[0037] In particular, in a preferred embodiment, the composition of the present invention comprises:

[0038] A) 30 - 70 wt%, preferably 40 - 60 wt% of an ethylene homopolymer or copolymer (preferably a homopolymer) having a density equal to or greater than 0.960 g / cm 3 and a melt flow index MIE of 2 g / 10 min or higher, preferably 5 g / 10 min or higher, at a load of 2.16 kg at 190 °C according to ISO 1133;

[0039] B) 30 - 70 wt%, preferably 40 - 60 wt% of an ethylene copolymer having an MIE value lower than that of A), preferably lower than 0.5 g / 10 min.

[0040] The above percentages are given relative to the total weight of A) + B).

[0041] The specific MIE range of component A) is:

[0042] -2 to 20 g / 10 min; or

[0043] -3 to 20 g / 10 min; or

[0044] -2 to 15 g / 10 min; or

[0045] -3 to 15 g / 10 min.

[0046] As mentioned above, the polyethylene composition of the present invention can be advantageously used for the production of blow molded articles.

[0047] In fact, it preferably has the following properties.

[0048] - The environmental stress cracking resistance measured by FNCT at 4 MPa / 80 °C is higher than 150 h, particularly higher than 250 h;

[0049] - The swelling ratio is higher than 185%;

[0050] - The Charpy aCN impact (T = 0 °C) is 10 kJ / m 2 or higher;

[0051] - There are substantially no gels with a gel diameter higher than 700 μm.

[0052] Details of the test methods are given in the examples.

[0053] The blow molding method is generally carried out by first plasticizing the polyethylene composition in an extruder at a temperature of 180 to 250 °C and then extruding it through a die into a blow molding die (where the polyethylene composition is cooled).

[0054] Although in principle there are no necessary restrictions on the polymerization method and the type of catalyst used, it has been found that the polyethylene composition of the present invention can be prepared by a gas phase polymerization method in the presence of a Ziegler-Natta catalyst.

[0055] The Ziegler-Natta catalyst comprises the product of the reaction of an organometallic compound of Group 1, 2 or 13 of the Periodic Table with a transition metal compound of Groups 4-10 of the Periodic Table (new notation). In particular, the transition metal compound can be selected from compounds of Ti, V, Zr, Cr and Hf, and is preferably supported on MgCl 2 on.

[0056] Particularly preferred catalysts comprise the reaction product of the organometallic compound of Group 1, 2 or 13 of the Periodic Table with a solid catalyst component comprising a Ti compound supported on MgCl 2 on.

[0057] The preferred organometallic compound is an organoaluminum compound.

[0058] Thus, in a preferred embodiment, the polyethylene composition of the present invention can be obtained by using a Ziegler-Natta polymerization catalyst, more preferably a Ziegler-Natta catalyst supported on MgCl 2 and even more preferably a Ziegler-Natta catalyst comprising the product of the following reaction:

[0059] a) A solid catalyst component comprising a Ti compound and an electron donor compound ED supported on MgCl 2 ;

[0060] b) An organoaluminum compound; and optionally

[0061] c) An external electron donor compound ED ext .

[0062] Preferably, in component a), the ED / Ti molar ratio is from 1.5 to 3.5 and the Mg / Ti molar ratio is higher than 5.5, especially from 6 to 80.

[0063] Suitable titanium compounds are tetrahalides or compounds of the formula TiX n (OR 1 ) 4-n where 0 ≤ n ≤ 3, X is a halogen, preferably chlorine, and R 1 is a C 1 -C 10 hydrocarbyl group. A preferred compound is titanium tetrachloride.

[0064] ED compounds are generally selected from alcohols, ketones, amines, amides, nitriles, alkoxysilanes, aliphatic ethers and aliphatic carboxylic acid esters.

[0065] Preferably, the ED compound is selected from amides, esters and alkoxysilanes.

[0066] Excellent results have been obtained using esters, so esters are particularly preferred as ED compounds. Specific examples of esters are alkyl esters of C 1 -C 20 aliphatic carboxylic acids, especially C 1 -C 8 alkyl esters of aliphatic monocarboxylic acids, such as ethyl acetate, methyl formate, ethyl formate, methyl acetate, propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate. In addition, aliphatic ethers are also preferred, especially C 2 -C 20 aliphatic ethers such as tetrahydrofuran (THF) or dioxane.

[0067] In the solid catalyst component, MgCl 2 is a basic carrier, even though a small amount of additional carrier can be used. MgCl 2Can be used as such or obtained from a Mg compound used as a precursor, which precursor can be converted into MgCl by reaction with a halogenated compound 2 . It is particularly preferred to use the active form of MgCl 2 , which is well known as a support for Ziegler-Natta catalysts in the patent literature. Patents USP 4,298,718 and USP 4,495,338 first described the use of these compounds in Ziegler-Natta catalysis. It is known from these patents that the active form of magnesium dihalide used as a support or co-support in catalyst components for olefin polymerization is characterized by an X-ray spectrum in which the intensity of the strongest diffraction line appearing in the ASTM card reference of the non-active halide spectrum is attenuated and broadened. In the X-ray spectrum of the preferred active form of magnesium dihalide, the intensity of the strongest line is attenuated and replaced by a halo, and the maximum intensity of the halo is shifted to a lower angle relative to the strongest line.

[0068] Particularly suitable for preparing the polyethylene composition of the present invention is a catalyst in which the solid catalyst component a) is prepared by first contacting a titanium compound with MgCl 2 or a Mg compound precursor, optionally in the presence of an inert medium, to prepare an intermediate product a') containing a titanium compound supported on MgCl 2 , and then contacting the intermediate product a') with an ED compound, which is added to the reaction mixture alone or as a mixture with other compounds (where the ED compound represents the main component), optionally in the presence of an inert medium.

[0069] For the term "main component", we wish that the ED compound must be the main component in molar amounts relative to other possible compounds (excluding inert solvents or diluents used to treat the contact mixture). The ED-treated product can then be washed with a suitable solvent to recover the final product. If desired, the treatment with the required ED compound can be repeated one or more times.

[0070] As previously mentioned, the precursor of MgCl 2 can be used as the starting Mg compound required. This can be selected, for example, from Mg compounds of the formula MgR' 2 , where the R' groups can independently be optionally substituted C 1 -C 20 hydrocarbyl groups, OR groups, OCOR groups, chlorine, where R is an optionally substituted C 1 -C 20 hydrocarbyl group, with the obvious condition that the R' groups are not simultaneously chlorine. Also suitable as a precursor is the Lewis adduct between MgCl 2 and a suitable Lewis base. A particularly preferred class is that formed by MgCl 2 (R”OH)m an adduct composition, wherein the R” group is C 1 -C 20 hydrocarbyl, preferably C 1 -C 10 alkyl, m is from 0.1 - 6, preferably from 0.5 - 3, more preferably from 0.5 - 2. Such adducts can generally be obtained by mixing an alcohol and MgCl 2 in the presence of an inert hydrocarbon immiscible with the adduct, operating under stirring conditions at the melting temperature of the adduct (100 - 130 °C). Then, the emulsion is rapidly quenched so that the adduct solidifies in the form of spherical particles. Representative methods for preparing these spherical adducts are reported, for example, in USP 4,469,648, USP 4,399,054 and WO98 / 44009. Another available method for spheronization is spray cooling as described, for example, in USP 5,100,849 and 4,829,034.

[0071] Of particular interest is the MgCl 2 ·(EtOH) m adduct, wherein m is from 0.15 - 1.7, obtained by subjecting an adduct with a higher alcohol content to a thermal dealcoholization process at a temperature of 50 - 150 °C in a nitrogen stream until the alcohol content is reduced to the above value. A method of this type is described in EP 395083.

[0072] Dealcoholization can also be carried out chemically by contacting the adduct with a compound capable of reacting with the alcohol groups.

[0073] These dealcoholized adducts are generally also characterized by their porosity (measured by the mercury method), which is due to pores with pore diameters up to 0.1 μm in the range of 0.15 - 2.5 cm 3 / g, preferably 0.25 - 1.5 cm 3 / g.

[0074] These adducts react with the above TiX n (OR 1 ) 4-n compounds (or possible mixtures thereof), preferably titanium tetrachloride. The reaction with the Ti compound can be carried out by suspending the adduct in TiCl 4It is carried out in a mixture (usually cold). The mixture is heated to a temperature of 80 - 130 °C and maintained at this temperature for 0.5 - 2 hours. Treatment with a titanium compound can be carried out one or more times. It is preferably repeated twice. It can also be carried out in the presence of an electron donor compound as described above. At the end of the process, the solid is recovered by separating the suspension by conventional methods (such as sedimentation and removal of the liquid, filtration, centrifugation), and can be washed with a solvent. Although the washing is usually carried out with an inert hydrocarbon liquid, more polar solvents (such as those with a higher dielectric constant, for example) can also be used, such as halogenated hydrocarbons.

[0075] As described above, the intermediate product is then contacted with the ED compound under conditions that enable an effective amount of the donor to be fixed on the solid. Due to the high generality of this method, the amount of donor used can vary within a wide range. For example, relative to the Ti content in the intermediate product, it can be used in a molar ratio of 0.5 - 20, preferably 1 - 10. Although not strictly required, the contact is usually carried out in a liquid medium such as a liquid hydrocarbon. The temperature at which the contact occurs can vary depending on the nature of the reagents. Generally, the range is from -10 °C to 150 °C, preferably 0 °C to 120 °C. Even if they fall within the generally suitable range, temperatures that cause decomposition or degradation of any particular reagent should be avoided. The treatment time can also vary depending on other conditions, such as the nature of the reagents, temperature, concentration, etc. As a general indication, this contact step can last from 10 minutes to 10 hours, more frequently 0.5 to 5 hours. If necessary, to further increase the final donor content, this step can be repeated one or more times. At the end of the process, the solid is recovered by separating the suspension by conventional methods (such as sedimentation and removal of the liquid, filtration, centrifugation), and can be washed with a solvent. Although the washing is usually carried out with an inert hydrocarbon liquid, more polar solvents (such as those with a higher dielectric constant, for example) can also be used, such as halogenated hydrocarbons or oxidized hydrocarbons.

[0076] As described above, according to known methods, the solid catalyst component is converted into a catalyst for olefin polymerization by reacting it with an organometallic compound of Group 1, 2, or 13 of the Periodic Table of the Elements, in particular with an Al-alkyl compound.

[0077] The alkylaluminum compound is preferably selected from trialkylaluminum compounds, such as triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. Alkylaluminum halides, alkylaluminum hydrides, or alkylaluminum sesquichlorides can also be used, such as AlEt 2 Cl and A1 2 Et 3 Cl 3 , optionally mixed with the trialkylaluminum compound.

[0078] Optionally, an external electron donor compound ED for preparing the Ziegler - Natta catalystext It can be the same as or different from the ED used in the solid catalyst component a). Preferably, it is selected from the group consisting of ethers, esters, amines, ketones, nitriles, silanes, and mixtures thereof. In particular, it can advantageously be selected from C 2 -C 20 aliphatic ethers, particularly preferably cyclic ethers having 3 to 5 carbon atoms, such as tetrahydrofuran and dioxane.

[0079] The catalyst can be prepolymerized by producing a reduced amount of polyolefin, preferably polypropylene or polyethylene, according to known techniques. The prepolymerization can be carried out before the addition of the electron donor compound ED and thus through the prepolymer intermediate a'). Alternatively, the solid catalyst component a) can be prepolymerized.

[0080] The amount of the prepolymer prepared can be up to 500 g / g of the intermediate a') or component a). Preferably, it is 0.5 - 20 g / g of the intermediate a').

[0081] The prepolymerization is carried out using a suitable cocatalyst such as an organoaluminum compound, which can also be used in combination with the external electron donor compound as described above.

[0082] It can be carried out in the liquid phase or the gas phase at a temperature of 0 - 80°C, preferably 5 - 70°C.

[0083] Particularly preferred is the catalyst in which the prepolymer intermediate a') as described above is prepolymerized.

[0084] It has been found that by using the above polymerization catalyst, the polyethylene composition of the present invention can be prepared in any mutual order according to the following steps:

[0085] a) Polymerize ethylene, optionally together with one or more comonomers, in a gas-phase reactor in the presence of hydrogen;

[0086] b) Copolymerize ethylene with one or more comonomers in another gas-phase reactor in the presence of an amount of hydrogen less than that in step a);

[0087] Wherein in at least one of the gas-phase reactors, the growing polymer particles flow upward through a first polymerization zone (riser) under fast fluidization or transport conditions, leave the riser and enter a second polymerization zone (downcomer), and they flow downward through the second polymerization zone under the action of gravity, leave the downcomer and are reintroduced into the riser, thereby establishing a polymer circulation between the two polymerization zones.

[0088] In the first polymerization zone (riser), fast fluidization conditions are established by feeding a gas mixture comprising one or more olefins (ethylene and comonomer) at a velocity higher than the conveying velocity of the polymer particles. The velocity of the gas mixture is preferably from 0.5 to 15 m / s, more preferably from 0.8 to 5 m / s. The terms "conveying velocity" and "fast fluidization conditions" are well known in the art; for their definitions, see, for example, "D. Geldart, Gas Fluidisation Technology, page 155 et seq., J. Wiley & Sons Ltd., 1986".

[0089] In the second polymerization zone (downcomer), the polymer particles flow in a dense form under the action of gravity, thereby achieving a high solid density value close to the polymer bulk density (polymer mass per reactor volume).

[0090] In other words, the polymer flows vertically downward through the downcomer in a plug flow (packed flow pattern), such that only a small amount of gas is entrained between the polymer particles.

[0091] This method results in an ethylene polymer obtained from step a) having a lower molecular weight than the ethylene copolymer obtained from step b).

[0092] Preferably, the copolymerization of ethylene to produce a relatively low molecular weight ethylene copolymer (step a) is carried out upstream of the ethylene copolymerization to produce a relatively high molecular weight ethylene copolymer (step b). For this purpose, in step a), a gaseous mixture comprising ethylene, hydrogen, comonomer and inert gas is fed to a first gas phase reactor, preferably a gas phase fluidized bed reactor. Polymerization is carried out in the presence of the aforementioned Ziegler-Natta catalyst.

[0093] The feed amount of hydrogen depends on the specific catalyst used and, in any case, is suitable for obtaining an ethylene polymer having a melt flow index MIE of 5 g / 10 min or higher in step a). To obtain the above MIE range, in step a), the hydrogen / ethylene molar ratio is indicated as 0.8 - 3, based on the total volume of the gas present in the polymerization reactor, and the amount of ethylene monomer is 2 - 20% by volume, preferably 5 - 15% by volume. If any, the remainder of the feed mixture is represented by inert gas and one or more comonomers. The inert gas necessary for dissipating the heat generated by the polymerization reaction is conveniently selected from nitrogen or saturated hydrocarbons, most preferably propane.

[0094] The operating temperature in the reactor of step a) is selected from 50 - 120 °C, preferably 65 - 100 °C, while the operating pressure is 0.5 - 10 MPa, preferably 2.0 - 3.5 MPa.

[0095] In a preferred embodiment, the ethylene polymer obtained in step a) accounts for 30 - 70% by weight of the total ethylene polymer produced in the whole process (i.e., in the first and second series reactors).

[0096] Then the ethylene polymer from step a) and the entrained gas are passed through a solid / gas separation step to prevent the gas mixture from the first polymerization reactor from entering the reactor in step b) (the second gas-phase polymerization reactor). The gaseous mixture can be recycled back to the first polymerization reactor, while the separated ethylene polymer is fed into the reactor in step b). A suitable point for feeding the polymer into the second reactor is on the connecting part between the downcomer and the riser, where the solid concentration is particularly low, so the flow conditions are not negatively affected.

[0097] The operating temperature in step b) is in the range of 65 - 95 °C, and the pressure is in the range of 1.5 - 4.0 MPa. The second gas-phase reactor is designed to produce a relatively high molecular weight ethylene copolymer by copolymerizing ethylene with one or more comonomers. In addition, in order to broaden the molecular weight distribution of the final ethylene polymer, the reactor in step b) can be conveniently operated by establishing different monomer and hydrogen concentration conditions in the riser and the downcomer.

[0098] For this purpose, in step b), it is possible to partially or completely prevent the gas mixture entraining polymer particles and coming from the riser from entering the downcomer, thereby obtaining two different gas composition regions. This can be achieved by feeding a gas and / or liquid mixture into the downcomer through a pipeline placed at a suitable point in the downcomer, preferably at its upper part. The gas and / or liquid mixture should have a suitable composition, different from the composition of the gas mixture present in the riser. The flow of the gas and / or liquid mixture can be adjusted to generate an upward gas flow countercurrent to the polymer particle flow, especially at the top of the polymer particles, as a barrier to the gas mixture entrained in the polymer particles coming from the riser. In particular, it is advantageous to feed a mixture with a low hydrogen content to produce a higher molecular weight polymer fraction in the downcomer. One or more comonomers can be optionally added to the downcomer in step b) together with ethylene, propane, or other inert gases.

[0099] The hydrogen / ethylene molar ratio in the downcomer of step b) is 0.005 - 0.2, based on the total amount of gas present in the downcomer, the ethylene concentration is 0.5 - 15 vol%, preferably 0.5 - 10 vol%, and the comonomer concentration is 0.1 - 1.5 vol%. The rest is propane or a similar inert gas. Since there is a very low molar concentration of hydrogen in the downcomer, by carrying out the method of the present invention, a relatively high content of comonomer can be incorporated into the high molecular weight polyethylene fraction.

[0100] Reintroduce the polymer particles from the downcomer into the riser of step b).

[0101] Since the polymer particles remain reactive and no more comonomer is fed into the riser, the concentration of the comonomer drops to 0.1 - 1.2% by volume based on the total volume of the gas present in the riser. In practice, the comonomer content is controlled to obtain the desired density of the final polyethylene. In the riser of step b), the molar ratio of hydrogen / ethylene is 0.01 - 0.5, and the ethylene concentration is 5 - 20% by volume based on the total volume of the gas present in the riser. The remainder is propane or other inert gases.

[0102] More details on the above polymerization method are provided in WO2005019280.

[0103] Examples

[0104] The practice and advantages of the various embodiments, compositions, and methods provided herein are disclosed in the following examples. These examples are illustrative only and are not intended to limit the scope of the appended claims in any way.

[0105] The following analytical methods are used to characterize the polymer compositions.

[0106] Density

[0107] Determined according to ISO 1183 at 23 °C.

[0108] Complex shear viscosity η 0.02 (eta(0.02))

[0109] Measured as follows at an angular frequency of 0.02 rad / s and 190 °C.

[0110] The specimen is melt-pressed at 200 °C and 200 bar for 4 minutes to form a 1 mm thick plate. A disk specimen with a diameter of 25 mm is punched and inserted into a rheometer that is preheated at 190 °C. The measurement can be carried out using any commercially available rotational rheometer. Here, an Anton Paar MCR300 with a plate-plate geometry is used. At T = 190 °C, under the condition of a constant strain amplitude of 5%, a so-called frequency sweep is carried out (after annealing the specimen at the measurement temperature for 4 minutes), and the stress response of the material in the range of excitation frequencies ω from 628 to 0.02 rad / s is measured and analyzed. Standardized basic software is used to calculate the rheological properties, namely the storage modulus, G', the loss modulus, G", the phase lag δ (= arctan(G" / G')), and the complex viscosity, η*, as a function of the applied frequency, i.e., η*(ω) = [G’(ω) 2 +G”(ω) 2 1 / 2 ​ / ω. The value of the latter is η at an applied frequency ω of 0.02 rad / s 0.02 .

[0111] HMWcopo Index

[0112] To quantify the crystallinity and processability of the polymer, the HMWcopo (high molecular weight copolymer) index is used, which is defined by the following formula:

[0113] HMWcopo = (η 0.02 x t maxDSC ) / (10^5)

[0114] As the processability of the polymer (low melt viscosity) and the possibility of rapid crystallization increase, it is decreasing. It is also a description and quantification of the amount of the high molecular weight part, related to the melt complex shear viscosity η at a frequency of 0.02 rad / s measured as described above 0.02 , as well as the amount of comonomer incorporated that delays crystallization (quantified by the maximum heat flow time t maxDSC of static crystallization).

[0115] t is determined using a differential scanning calorimeter TA Instruments Q2000 under isothermal conditions at a constant temperature of 124 °C maxDSC . Weigh 5 - 6 mg of the sample and place it in an aluminum DSC pan. Heat the sample to 200 °C at 20 K / min and also cool it to the test temperature at 20 K / min to eliminate the thermal history. Immediately start the isothermal test afterwards and record the time until crystallization occurs. Use the vendor software (TA Instruments) to determine the time interval until the maximum crystallization heat flow (peak) t maxDSC . Repeat the measurement 3 times, and then calculate the average value (in minutes). If no crystallization is observed within 120 minutes under these conditions, the value of t maxDSC = 120 minutes is used for further calculation of the HMWcopo index.

[0116] Multiply the melt viscosity η 0.02 value by the t maxDSC value, and normalize the product by the factor 100000 (10^5).

[0117] Molecular Weight Distribution Measurement

[0118] The determination of the molar mass distribution and the average values of Mn, Mw, Mz and Mw / Mn thus obtained were carried out by high-temperature gel permeation chromatography using the methods described in ISO 16014-1, -2, -4 published in 2003. The specific details according to the mentioned ISO standard are as follows: Solvent 1,2,4-trichlorobenzene (TCB), temperature of the equipment and solution 135 °C, and PolymerChar (Valencia, Paterna 46980, Spain) IR-4 infrared detector used as a concentration detector, which can be used together with TCB. WATERS Alliance 2000 was used, which was equipped with the following pre-columns SHODEX UT-G and separation columns SHODEX UT 806M(3x) and SHODEX UT 807 (Showa Denko Europe GmbH, Konrad-Zuse-Platz 4, 81829 München, Germany) connected in series.

[0119] The solvent was vacuum distilled under nitrogen and stabilized with 0.025 wt% 2,6-di-tert-butyl-4-methylphenol. The flow rate used was 1 ml / min, 500 μl was injected, and the polymer concentration was 0.01% < concentration < 0.05% (concentration in w / w). Molecular weight calibration was carried out using monodisperse polystyrene (PS) standards in the range of 580 g / mol to 11,600,000 g / mol from Polymer Laboratories (now Agilent Technologies, Herrenberger Str. 130, 71034 Böblingen, Germany) and additionally hexadecane.

[0120] Then the calibration curve was applied to polyethylene (PE) by the universal calibration method (Benoit H., Rempp P. and Grubisic Z., & in J. Polymer Sci., Phys. Ed., 5, 753 (1967)). The Mark-Houwink parameters used for PS are: k PS = 0.000121 dl / g, α PS = 0.706 and for PE k PE = 0.000406 dl / g, α PE = 0.725, which are valid in TCB at 135 °C. Data recording, calibration and calculation were carried out using NTGPC_Control_V6.02.03 and NTGPC_V6.4.24 (hs GmbH, Hauptstraße 36, D-55437 Ober-Hilbersheim, Germany).

[0121] Melt Flow Index

[0122] Determined at 190 °C with a specified load according to ISO 1133.

[0123] Long Chain Branching Index (LCBI)

[0124] The LCB index measured for a molecular weight of 106 g / mol corresponds to the branching factor g'. The branching factor g' is measured by gel permeation chromatography (GPC) combined with multi-angle laser light scattering (MALLS), which allows the determination of long-chain branching at high Mw. The radius of gyration of each fraction eluted from the GPC is measured by analyzing the light scattering at different angles using MALLS (detector Wyatt Dawn EOS, Wyatt Technology, Santa Barbara, Calif.) (as described above, but with a flow rate of 0.6 ml / min and a column packed with 30-μm particles). A laser source of 120 mW at a wavelength of 658 nm is used. The specific refractive index increment is taken as 0.104 ml / g. Data evaluation is performed using Wyatt ASTRA 4.7.3 and CORONA 1.4 software. The LCB index is determined as described below.

[0125] The parameter g' is the ratio of the measured mean-square radius of gyration to that of a linear polymer of the same molecular weight. Linear molecules show g' = 1, while values less than 1 indicate the presence of LCB. The value of g' as a function of the mol weight M is calculated by the following formula:

[0126] g'(M) = <Rg 2 > 试样，M / <Rg 2 > 线性参考，M

[0127] where <Rg 2 > is the root-mean-square radius of gyration of the fraction with the molar weight M.

[0128] The radius of gyration of each fraction eluted from the GPC is measured by analyzing the light scattering at different angles (as described above, as described above, but with a flow rate of 0.6 ml / min and a column packed with 30-μm particles). Thus, the molar weight M and <Rg 2 > 试样，M can be determined from this MALLS setup, and g' is defined at the measured M = 106 g / mol. <Rg 2 > 线性参考，M is calculated from the relationship between the radius of gyration and the molecular weight established for linear polymers in solution (Zimm and Stockmayer WH 1949) and confirmed by measuring a linear PE reference using the same apparatus and method as described.

[0129] The same procedures are described in the following documents.

[0130] Zimm BH, Stockmayer WH(1949) The dimensions of chain molecules containing branches and rings. J Chem Phys 17

[0131] Rubinstein M., Colby RH.(2003), Polymer Physics, Oxford University Press

[0132] Comonomer Content

[0133] Using a Tensor 27 FT-IR spectrometer from Bruker, calibrated with a chemometric model, the comonomer content was determined by IR according to ASTM D624898. For butene or hexene as comonomers respectively, it was used to determine the ethyl- or butyl-side chains in PE. The results were compared with the estimated comonomer content obtained from the mass balance of the polymerization process and found to be consistent.

[0134] Swelling Ratio

[0135] The swell ratio of the polymers studied was measured using a capillary rheometer Rheotester2000 and Rheograph25 at T = 190 °C. The capillary rheometer Rheotester2000 and Rheograph25 were equipped with a commercial 30 / 2 / 2 / 20 die (total length 30 mm, effective length = 2 mm, diameter = 2 mm, L / D = 2 / 2 and 20° angle of incidence) and an optical device for measuring the thickness of the extruded strand (laser from ). The sample was melted in the capillary at 190 °C for 6 minutes and extruded at a piston speed corresponding to a shear rate of 1440 s-1 at the die.

[0136] When the piston reached a position 96 mm from the die inlet, the extrudate (automatic cutting device from ) was cut at a distance of 150 mm from the die outlet. The diameter of the extrudate was measured using a laser at a distance of 78 mm from the die outlet as a function of time. The maximum value corresponded to D 挤出物 . The swell ratio was calculated and determined by the following formula:

[0137] SR=(D 挤出物 - D 模具)100% / D 模具

[0138] where D 模具 is the corresponding diameter at the die outlet, measured using a laser.

[0139] Notched Tensile Impact Test AZK

[0140] According to Method A, the tensile impact strength is determined using ISO 8256:2004 and Type 1 double-notch specimens. Specimens (4×10×80 mm) are cut from a compression mold plate prepared according to the requirements of ISO 1872-2 (average cooling rate of 15 K / min and high pressure during the cooling phase). The specimens have notches on both sides, with 45° V-shaped notches. The depth is 2 ± 0.1 mm, and the radius of curvature of the notch inclination is 1.0 ± 0.05 mm.

[0141] The free length between the clamps is 30 ± 2 mm. Before measurement, all specimens are conditioned at a constant temperature of -30 °C for 2 to 3 hours. The measurement procedure for the tensile impact strength including the energy correction of Method A is described in ISO 8256.

[0142] ESCR Belltest

[0143] The environmental stress cracking resistance (ESCR Bell Telephone Test) is measured according to ASTM D1693:2013 (Method B) and DIN EN ISO 22088-3:2006. Ten rectangular specimens (38×13×2 mm) are cut from a compression mold plate prepared according to the requirements of ISO 1872-2 (average cooling rate of 15 K / min and high pressure during the cooling phase). They are cut with a razor to a depth of 0.4 mm centered on one of the wide faces parallel to the longitudinal axis. Then, they are bent into a U-shape using a special bending device with the notch side facing up. Within 10 minutes after bending, the U-shaped specimens are placed in a glass tube and filled with an aqueous solution of 10 vol% 4-nonylphenyl-polyethylene glycol (Arkopal N100) at 50 °C and sealed with a rubber stopper. The specimens are visually inspected for cracks every hour on the first day, then daily, and once a week (every 168 hours) after 7 days. The final value obtained is the 50% failure point (F 50 ) of the 10 specimens in the glass tube.

[0144] Environmental Stress Cracking Resistance According to Full Notch Creep Test (FNCT)

[0145] The environmental stress cracking resistance of polymer specimens was determined in an aqueous surfactant solution according to the international standard ISO 16770 (FNCT). Sheets with a thickness of 10 mm were prepared from the polymer specimens by compression molding. A notch was cut into rods with a square cross-section (10 x 10 x 100 mm) on four sides perpendicular to the stress direction using a razor blade. The notching device described by M. Fleissner in Kunststoffe 77 (1987), pp. 45 was used for sharp notches with a depth of 1.6 mm.

[0146] The applied load was calculated by dividing the tensile force by the initial ligament area. The ligament area is the remaining area = the total cross-sectional area of the specimen minus the notch area. For FNCT specimens: 10 x 10 mm 2 - 4 times the trapezoidal notch area = 46.24 mm 2 (remaining cross-section of the failure process / crack propagation). The specimens were loaded under the standard conditions recommended by ISO 16770 at a constant load of 4 MPa at 80 °C in an aqueous solution of 2 wt% non-ionic surfactant ARKOPAL N100. The time until specimen rupture was detected.

[0147] Charpya CN

[0148] The fracture toughness of test rods with dimensions 10 × 10 × 80 mm was determined by an in-house method. These test rods were sawn from compression-molded sheets with a thickness of 10 mm. Six of these test rods were notched in the center using a razor blade in the notching device mentioned above for FNCT. The notch depth was 1.6 mm. The measurement was carried out essentially according to the Charpy measurement method in ISO 179-1, using modified specimens and modified impact geometry (distance between supports).

[0149] All specimens were conditioned at a measurement temperature of -30 °C for 2 to 3 hours. Then the specimens were placed without delay on the supports of a pendulum impact tester according to ISO 179-1. The distance between the supports was 60 mm. The drop of the 2 J hammer was triggered, the drop angle was set to 160°, the pendulum length was 225 mm, and the impact speed was 2.93 m / s. The fracture toughness values are expressed in kJ / m 2 and are given by the quotient of the impact energy consumed and the initial cross-sectional area aCN at the notch. Only the values for complete fracture and hinge fracture can be used here as a basis for common sense (see the recommendations of ISO 179-1).

[0150] Cast Film Measurement

[0151] The film recording measurements were carried out on an OCS extruder model ME202008-V3 with a screw diameter of 20 mm, a screw length of 25D, and a slot die width of 150 mm. The casting line was equipped with a cooling roll and a winder (model OCS CR-9). The optical equipment included an OSC film surface analyzer camera, model FTA-100 (flash camera system), with a resolution of 26 μm x 26 μm. After purging the resin for 1 hour to stabilize the extrusion conditions, inspection and value recording were then carried out for 30 minutes. The resin was extruded at 220 °C, and the take-off speed was approximately 2.7 m / min to produce a film with a thickness of 50 μm. The temperature of the cooling roll was 70 °C.

[0152] The inspection carried out with the surface analyzer camera provided the total gel content and the gel content with a diameter greater than 700 μm, as shown in Table 1.

[0153] - Process Settings

[0154] The polymerization process was carried out under continuous conditions in an apparatus comprising two gas-phase reactors connected in series, as Figure 1 shown.

[0155] The polymerization catalyst was prepared as follows.

[0156] Procedure for Preparing Catalyst Components

[0157] A magnesium chloride and alcohol adduct containing approximately 3 moles of alcohol was prepared according to the method described in Example 2 of USP 4,399,054, but operating at 2000 RPM instead of 10000 RPM. Under a nitrogen stream, the adduct was heat-treated in the temperature range of 50 - 150 °C until an alcohol weight content of 25% was reached.

[0158] In a nitrogen-purged 2 L four-necked round-bottom flask, 1 L of TiCl 4 was added at 0 °C. Then, at the same temperature, 70 g of spherical MgCl 2 / EtOH adduct containing 25 wt% ethanol and prepared as described above was added with stirring. The temperature was raised to 140 °C within 2 hours and maintained for 120 minutes. Then, stirring was stopped, the solid product was allowed to settle, and the supernatant was siphoned off. The solid residue was then washed once with heptane at 80 °C and five times with hexane at 25 °C and dried in vacuo at 30 °C.

[0159] In a 260 cm 3 glass reactor equipped with a stirrer, 351.5 cm 3 of hexane at 20 °C was added at 20 °C, and 7 g of the catalyst component prepared as described above was added with stirring while maintaining the internal temperature constant. 5.6 cm 3A hexane solution of tri-n-octylaluminum (TNOA) (about 370 g / l) and a certain amount of cyclohexylmethyl-dimethoxysilane (CMMS) such that the molar ratio of TNOA / CMMS is 50 were slowly added to the reactor, and the temperature was raised to 10 °C. After stirring for 10 minutes, 10 g of propylene was carefully added to the reactor at the same temperature over a period of 4 hours. The consumption of propylene in the reactor was monitored, and the polymerization was stopped when the theoretical conversion of 1 g of polymer per g of catalyst was considered to have been reached. Then, the entire content was filtered and washed three times with hexane at 30 °C (50 g / l). After drying, the resulting prepolymerized catalyst was analyzed and found to contain 1.05 g of polypropylene, 2.7% Ti, 8.94% Mg, and 0.1% Al per gram of the initial catalyst.

[0160] Loading of Internal Electron Donor on Prepolymerization Catalyst

[0161] Approximately 42 g of the solid prepolymerized catalyst prepared as described above was charged into a glass reactor purged with nitrogen and slurried with 8 L of hexane at 50 °C.

[0162] Then, ethyl acetate was carefully added dropwise (within 10 minutes) in an amount such that the molar ratio of Mg of the prepolymerized catalyst to the organic Lewis base was 1.7.

[0163] The slurry was maintained for 2 hours with an internal temperature of 50 °C under stirring.

[0164] After that, stirring was stopped and the solid was allowed to settle. A single hexane wash was carried out at room temperature, and then the final catalyst was recovered and dried.

[0165] Example 1

[0166] Polymerization

[0167] 8.9 g / h of the solid catalyst prepared as described above with a molar feed ratio of electron donor / Ti of 8 was added to the first stirred pre-contact vessel using 5 kg / h of liquid propane, and triisobutylaluminum (TIBA), diethylaluminum chloride (DEAC), and the electron donor tetrahydrofuran (THF) were also metered into it. The weight ratio of triisobutylaluminum to diethylaluminum chloride is 7:1. The ratio of alkylaluminum (TIBA + DEAC) to the solid catalyst is 5:1. The weight ratio of alkyl to THF is 70. The first pre-contact vessel was maintained at 50 °C with an average residence time of 30 minutes. The catalyst suspension in the first pre-contact vessel was continuously transferred to the second stirred pre-contact vessel, which was operated with an average residence time of 30 minutes and also maintained at 50 °C. Then, the catalyst suspension was continuously transferred to a fluidized bed reactor (FBR) (1) through line (10).

[0168] In the first reactor, ethylene is polymerized using H 2 as a molecular weight regulator and in the presence of propane as an inert diluent. 42 kg / h of ethylene and 100 g / h of hydrogen are fed into the first reactor through line 9. No comonomer is fed into the first reactor.

[0169] The polymerization is carried out at a temperature of 80 °C and a pressure of 2.9 MPa. The polymer obtained in the first reactor is discharged discontinuously through line 11, separated from the gas, enters the gas / solid separator 12, and is reintroduced into the second gas-phase reactor through line 14.

[0170] The melt index MIE of the polymer produced in the first reactor is approximately 12 g / 10 min and the density is 0.965 g / cm 3 .

[0171] The second reactor is operated under polymerization conditions of approximately 80 °C and a pressure of 2.5 MPa. The inner diameter of the riser is 200 mm and the length is 19 m. The total length of the downcomer is 18 m; the upper part is 5 m with an inner diameter of 300 mm; the lower part is 13 m with an inner diameter of 150 mm. To broaden the molecular weight distribution of the final ethylene polymer, the second reactor is operated by establishing different conditions of monomer and hydrogen concentration in the riser 32 and the downcomer 33. This is achieved by feeding a liquid stream (liquid barrier) of 330 kg / h into the upper part of the downcomer 33 via line 52. The composition of the liquid stream is different from the composition of the gas mixture present in the riser. The different concentrations of monomer and hydrogen in the riser and downcomer of the second reactor and the composition of the liquid barrier are shown in Table 1. The liquid stream of line 52 comes from the bottom of the distillation column 62, where a part of the recycle stream is separated into a liquid part and a gas part. As shown, a pump is placed downstream of the distillation column 62. Monomer is fed into the downcomer at 3 locations (line 46). At feed point 1, which is directly below the barrier, 12 kg / h of ethylene and 1.15 kg / h of 1-hexene are added. At feed point 2, which is 2.3 m below feed point 1, 3 kg / h of ethylene is added. At feed point 3, which is 4 m below feed point 2, 3 kg / h of ethylene is added. In each of the 3 feed points, the liquid withdrawn from the stream 52 is additionally fed in a ratio of 1:1 with ethylene. 5 kg / h of propane, 22.3 kg / h of ethylene and 30 g / h of hydrogen are fed into the recycle system through line 45.

[0172] The final polymer is discharged discontinuously through line 54.

[0173] The polymerization process in the second reactor produces a relatively high molecular weight polyethylene fraction. In Table 1, the properties of the final product are illustrated. It can be seen that compared with the ethylene resin produced in the first reactor, the melt index of the final product decreases, indicating that a high molecular weight fraction is formed in the second reactor.

[0174] The first reactor produces approximately 50 wt% (split wt%) of the total final polyethylene resin produced by the first and second reactors.

[0175] The amount of comonomer (1-hexene) is approximately 1.2 wt%.

[0176] Comparative Example 1

[0177] The polymer of this comparative example is a polyethylene composition produced in the gas phase using a chromium-containing catalyst, which is sold by LyondellBasell under the trademark Lupolen 4261AG UV 60005.

[0178] Table 1

[0179] Example 1 Comparative Example 1 First Reactor Operating Conditions <![CDATA[H 2 / C 2 H 4 Molar ratio]]> 1.2 - <![CDATA[C 2 H 4 %]]> 10.5 - <![CDATA[The density of (A) (g / cm 3 )]]> 0.967 MIE[2.16 kg](g / 10 min) of A 12 Split (wt%) 50 - Second Reactor Operating Conditions <![CDATA[H 2 / C 2 H 4 Mole ratio riser]]> 0.25 - <![CDATA[C 2 H 4 % riser]]> 12.2 - <![CDATA[C 6 H 12 % riser]]> 0.57 - <![CDATA[H 2 / C 2 H 4 Mole ratio downcomer]]> 0.010 - <![CDATA[C 2 H 4 % downcomer]]> 8.6 - <![CDATA[C 6 H 12 % downcomer]]> 0.84 - <![CDATA[H 2 / C 2 H 4 Molar ratio barrier]]> 0.009 - <![CDATA[C 2 H 4 % barrier]]> 7.8 - <![CDATA[C 6 H 12 % barrier]]> 0.89 - Final Polymer Properties MIP[5 kg](g / 10 min) 0.29 0.30 MIF[21.6 kg](g / 10 min) 7.5 6.1 MIF / MIP 25.8 20.1 <![CDATA[Density (g / cm 3 )]]> 0.9485 0.9452 Swelling Ratio (%) 200 202 Mw (g / mol) 408,109 358,112 Mz (g / mol) 3,028,050 3,911,139 Mw / Mn 26.3 21.1 LCBI 0.87 0.90 Comonomer Content IR (wt%) 1.2 <![CDATA[1(C 6 H 12 )]]> <![CDATA[η 0.02 > 191,887 156,083 <![CDATA[(eta 0.02 / 1000) / LCBI]]> 220 173.425 <![CDATA[AZK - 30 °C (kJ / m 2 )]]> 153 152 <![CDATA[CharpyaCN, T = -30 °C (kJ / m 2 )]]> 15.8 Belltest at 50 °C (hours) >6000 850 FNCT * 4 MPa / 80 °C (hours) 250 30.4 <![CDATA[Total gel / m 2 >700μm]]> 0 0 <![CDATA[Total gel / m 2 Total]]> 277 1261 HMWCOPO Index 29.5

[0180] Note: C 2 H 4 = ethylene; C 6 H 12 = hexene; *2% aqueous solution of Arkopal N100.

Claims

1. A polyethylene composition, having the following characteristics: 1) A density of 0.940 to 0.955 g / cm 3 , preferably 0.940 to 0.951 g / cm 3 , measured according to ISO 1183 at 23 °C; 2) The MIF / MIP ratio is from 12 to 30, in particular from 15 to 28 or from 17 to 27, where MIF is the melt flow index at a load of 21.60 kg at 190 °C and MIP is the melt flow index at a load of 5 kg at 190 °C, both determined according to ISO 1133; 3) Mz is from 2,000,000 to 4,500,000 g / mol, preferably from 2,500,000 to 4,200,000 g / mol, in particular from 2,500,000 to 3,500,000 g / mol, where Mz is the z - average molecular weight, measured by GPC; 4) η 0.02 is 160,000 to 300,000 Pa·s, or 170,000 to 300,000 Pa·s, or 180,000 to 300,000 Pa·s, preferably 160,000 to 250,000 Pa·s, or 170,000 to 250,000 Pa·s, or 180,000 to 250,000 Pa·s, where η 0.02 is the complex shear viscosity at an angular frequency of 0.02 rad / s, measured using dynamic oscillatory shear in a plate-plate rotational rheometer at a temperature of 190 °C; 5) The long - chain branching index LCBI is equal to or greater than 0.75, preferably equal to or greater than 0.80, where LCBI is the ratio of the radius of gyration squared Rg measured by GPC - MALLS to the radius of gyration squared of linear PE with the same molecular weight; 6) Mw is from 350,000 to 450,000 g / mol (measured by GPC); 7) MIF is from 5 to 12 g / 10 min (determined according to ISO 1133); 8) The swelling ratio is greater than 185%; wherein, the polyethylene composition further has the following characteristics: 1) FNCT is at least 200 hours (determined in a 2% ARKOPAL solution at 80 °C and 4 MPa according to ISO 16770); 2) ESCR is at least 6000 hours (determined according to ASTM D1693:2013 (Method B) and DIN EN ISO 22088 - 3:2006).

2. The polyethylene composition according to claim 1, which consists of or contains one or more ethylene copolymers.

3. The polyethylene composition according to claim 1 or 2, obtained by using a Ziegler - Natta polymerization catalyst.

4. The polyethylene composition according to claim 3, wherein the Ziegler - Natta polymerization catalyst comprises the product of the following reactions: a) a solid catalyst component containing a Ti compound supported on MgCl 2 obtained by contacting a titanium compound with MgCl 2 or a precursor Mg compound, optionally in the presence of an inert medium, to obtain an intermediate product a'), and then a') Pre - polymerization is carried out and contacted with an electron donor compound; b) An organoaluminum compound; and optionally c) An external electron donor compound.

5. The polyethylene composition of claim 1, having an (η 0.02 / 1000) / LCBI ratio that is between η 0.02 divided by 1000 and LCBI, and equal to or greater than 150; where η 0.02 is the complex shear viscosity of the melt (in Pa·s) measured at an applied angular frequency of 0.02 rad / s in a dynamic oscillatory shear mode in a parallel plate (or so-called plate-plate) rheometer at a temperature of 190 °C; LCBI is the ratio of the measured mean-square radius of gyration Rg measured by GPC-MALLS to the mean-square radius of gyration of linear PE with the same molecular weight (molecular weight of 1,000,000 g / mol).

6. The polyethylene composition according to claim 1 or 5, having an HMWcopo index of from 1 to 15; where the HMWcopo index is determined according to the following formula: HMWcopo = (η 0.02 × tmaxDSC) / (10^5) where η 0.02 is the complex shear viscosity of the melt in Pa·s measured at a temperature of 190 °C and an angular frequency of 0.02 rad / s in a parallel plate (or so-called plate-plate) rheometer in a dynamic oscillatory shear mode; the tmaxDSC is the time required to reach the maximum value of the heat flow (in mW) of crystallization at a temperature of 124 °C under static conditions (the time to reach the maximum crystallization rate, equivalent to the t1 / 2 half-crystallization time), in minutes, measured in an isothermal mode in a differential scanning calorimeter DSC; the LCBI is the ratio of the radius of gyration squared Rg measured by GPC-MALLS to the radius of gyration squared of linear PE of the same molecular weight with a molar amount of 1,000,000 g / mol.

7. The polyethylene composition according to claim 1, comprising: A) 30 - 70% by weight, preferably 40 - 60% by weight of a homopolymer or copolymer of ethylene (preferably a homopolymer), having a density equal to or greater than 0.960 g / cm 3 and having a melt flow index MIE of 2 g / 10 min or higher, preferably 5 g / 10 min or higher, at a load of 2.16 kg at 190 °C according to ISO 1133; B) 30 - 70 wt%, preferably 40 - 60 wt% of an ethylene copolymer, the MIE value of which is lower than the MIE value of A), preferably lower than 0.5 g / 10 min.

8. An article comprising the polyethylene composition according to claim 1.

9. The article according to claim 8, which is in the form of a blow - molded hollow article.

10. A process for preparing the polyethylene composition according to claim 1, wherein all polymerization steps are carried out in the presence of a Ziegler-Natta polymerization catalyst supported on MgCl 2 2.

11. The method according to claim 10, comprising the following steps in any mutual order: a) In the presence of hydrogen, polymerizing ethylene, optionally together with one or more comonomers, in a gas - phase reactor; b) copolymerize ethylene with one or more comonomers in another gas-phase reactor in the presence of an amount of hydrogen less than that in step a); wherein in at least one of said gas-phase reactors, the growing polymer particles flow upward through a first polymerization zone under fast fluidization or transport conditions, leave said riser and enter a second polymerization zone, where they flow downward under the action of gravity, leave said second polymerization zone and are reintroduced into said first polymerization zone, thereby establishing a circulation of the polymer between said two polymerization zones.

12. A process for preparing a polyethylene composition having the following characteristics: 1) With a density of 0.940 to 0.955 g / cm 3 , preferably 0.940 to 0.951 g / cm 3 , determined according to ISO 1183 at 23 °C; 2) The MIF / MIP ratio is from 12 to 30, especially from 15 to 28 or from 17 to 27, where MIF is the melt flow index at a load of 21.60 kg at 190 °C and MIP is the melt flow index at a load of 5 kg at 190 °C, both determined according to ISO 1133; 3) Mz is from 2,000,000 to 4,500,000 g / mol, preferably from 2,500,000 to 4,200,000 g / mol, especially from 2,500,000 to 3,500,000 g / mol, where Mz is the z-average molecular weight, measured by GPC; 4) η 0.02 is 160,000 to 300,000 Pa·s, or 170,000 to 300,000 Pa·s, or 180,000 to 300,000 Pa·s, preferably 160,000 to 250,000 Pa·s, or 170,000 to 250,000 Pa·s, or 180,000 to 250,000 Pa·s, where η 0.02 is the complex shear viscosity at an angular frequency of 0.02 rad / s, measured using dynamic oscillatory shear in a plate-plate rotational rheometer at a temperature of 190 °C; 5) The long-chain branching index LCBI is equal to or greater than 0.75, preferably equal to or greater than 0.80, where LCBI is the ratio of the radius of gyration squared Rg measured by GPC-MALLS to the radius of gyration squared of linear PE having the same molecular weight; All of the polymerization steps are carried out in the presence of a Ziegler-Natta polymerization catalyst supported on MgCl 2 wherein the Ziegler-Natta polymerization catalyst comprises the product of the following reaction: a) a solid catalyst component containing a Ti compound supported on MgCl 2 obtained by contacting a titanium compound with MgCl 2 or a precursor Mg compound, optionally in the presence of an inert medium, to obtain an intermediate product a'), and then a') perform prepolymerization and contact with an electron donor compound, where the amount of the prepolymer is from 0.5 to 20 g / g of intermediate a'); b) an organoaluminum compound; and optionally c) an external electron donor compound.

Images