High-density polyethylene composition for molding and film applications

Abstract

A polyethylene composition comprising a base resin which comprises a first ethylene homopolymer fraction, and a second ethylene-hexene-1 copolymer fraction, wherein fraction (A) has a lower molecular weight than fraction (B), wherein the base resin comprises fraction (A) in an amount of at least 43.0 wt.% based on the total weight of the base resin, wherein the base resin comprises fraction (B) in an amount of equal to or lower than 57.0 wt.% based on the total weight of the base resin, wherein the base resin has a loss tangent (tan δ) at 300 rad / s measured according to ISO 6721 of lower than 0.500, wherein the polyethylene composition has a density determined according to ISO 1183-1:2022 - method A in the range of from 950 to 956 kg / m3, wherein the polyethylene composition has a melt flow rate MFR5 determined according to ISO 1133 at 190 °C and at a loading of 5 kg in the range of from 0.15 to 0.6 g / 10 min, wherein the polyethylene composition has a flow rate ratio FRR21 / 5 in the range of from 17 to 36, wherein the polyethylene composition has a molecular weight distribution MWD determined by Gel Permeation Chromatography (GPC) according to ISO 16014-1:2003 of equal to or more than 27.

Description

[0001] High-Density Polyethylene Composition for Molding and Film Applications

[0002] Technical Field of the Invention

[0003] The present invention relates to a high-density polyethylene composition for molding and film applications. In particular, the present invention relates to a high-density polyethylene composition having an exceptional balance of stiffness, impact, and environmental stress crack resistance. Moreover, the present invention relates to an article made from this high-density polyethylene composition, preferably a film or a molded article.

[0004] Background of the Invention

[0005] Blow molding may be used to make a wide variety of articles including articles having relatively complex shapes and a range of sizes. In extrusion blow molding processes, polymer material is extruded in a parison, preferably a tube-shaped parison, which is inserted into a mold. The mold preferably has a shape in that the assembled mold closes the tube-shaped parison at one end and allows for inserting pressurized gas into the parison allowing for inflating the parison onto an inner surface of the mold. In injection blow molding processes, a preform is formed by injection molding on a hollow core pin in a first step. Subsequently the preform and the core pin are added into a mold, the preform is heated and inflated by pressurized air through the hollow core pin allowing for inflating the preform onto an inner surface of the mold.

[0006] Polymer films are also widely used in packaging. These films must obviously protect the contents of the package from damage and the environment.

[0007] Sustainability is becoming more and more important in the production of molded articles and films. Hence, it is a general ambition to reduce the amount of material needed to provide an article or film with the same properties. Reduced amounts of material used result in less energy consumption in production and transport as well as generally less waste material per article or film. Furthermore, reducing the amount of material per article or film has also the effect of reducing costs. Generally, this can be achieved by producing articles and films with lower thickness.

[0008] However, this usually has the drawback that certain physical properties are sacrificed. Strength is the ability of a material to stay together when stretched or compressed. Stiffness is how well a material resists deformation. Toughness is the ability of a material to absorb energy before failure. Environmental stress crack resistance (ESCR) is the ability of a material of resisting slow growth in cracks or environmental stress cracking.

[0009] Environmental stress cracking can cause the polymer material of an article or film to become weaker and more brittle, making it more susceptible to breaking or shattering. Environmental stress cracking can even lead to the formation of voids or holes in the polymer material. This can compromise the structural integrity of the article or film and make it more likely to fail under stress.

[0010] Hence, to produce an article or film, which uses less polyethylene composition material, an improved balance of these properties is needed. Hence the balance of impact properties, stiffness, and ESCR of said polyethylene composition needs to be improved.

[0011] To add to the challenge, however, these improvements must not be at the expense of processability of the polymer or the appearance of any article or film formed. Processability must be maintained or even improved to meet customer needs. For example, injection molded articles are produced rapidly and any reduction in processability can increase cycle times and hence reduce process efficiency.

[0012] In order to improve the ESCR, typically the density of the high-density polyethylene is reduced, which in turns negatively effects the stiffness. This, however, prevents downgauging of molded products and incorporation of post-consumer recycled (PCR).

[0013] WO 2009 / 085922 A1 discloses a composition comprising a blend, which blend comprises a high molecular weight ethylene-based polymer, and a low molecular weight ethylene-based polymer, and wherein the high molecular weight ethylene-based polymer has a density less than, or equal to, 0.955 g / cm3, and wherein the blend has a high load melt index (I21) greater than, or equal to, 15 g / 10 min, and wherein the blend has a molecular weight distribution (Mw / Mn) greater than, or equal to, 15. However, the composition of WO 2009 / 085922 A1 shows bad tensile properties and the ESCR can still be improved.

[0014] WO 2010 / 063445 A1 discloses a polyethylene suitable for the production of intermediate bulk containers. In particular, the polyethylene disclosed in WO 2010 / 063445 A1 is ethylene polymer according to the present invention is a high- density polyethylene having a high-load melt index (HLMI) larger than or equal to 3 g / 10 min and smaller than or equal to 10 g / 10 min, a molecular weight distribution (Mw / Mn) larger than or equal to 14 and smaller than or equal to 25, a density of larger than or equal to 945 kg / m3and smaller than or equal to 955 kg / m3, and an Izod impact strength (-30 °C) of larger than or equal to 10 kJ / m2and smaller than or equal to 50 kJ / m2. However, the polyethylene of WO 2010 / 063445 A1 shows inferior impact properties. Summary of the Invention

[0015] Hence, the prior art still lacks a high-density polyethylene for molded articles and films, which has an improved balance in impact, stiffness, and ESCR at maintained processability. Thus, there is still the object of achieving such a polyethylene composition. It is further an object to achieve an article, preferably molded article or film, more preferably blow molded article or blown film, comprising such a composition.

[0016] It has now surprisingly been found that these objects are achieved by a polyethylene composition comprising a base resin which comprises a first ethylene homopolymer fraction, and a second ethylene-hexene-1 copolymer fraction, wherein fraction (A) has a lower molecular weight than fraction (B), wherein the base resin comprises fraction (A) in an amount of at least 43.0 wt.% based on the total weight of the base resin, wherein the base resin comprises fraction (B) in an amount of equal to or lower than 57.0 wt.% based on the total weight of the base resin, wherein the base resin has a loss tangent (tan 5) at 300 rad / s measured according to ISO 6721 of lower than 0.500, wherein the polyethylene composition has a density determined according to ISO 1183- 1 :2022 - method A in the range of from 950 to 956 kg / m3, wherein the polyethylene composition has a melt flow rate MFRs determined according to ISO 1133 at 190 °C and at a loading of 5 kg in the range of from 0.15 to 0.6 g / 10 min, wherein the polyethylene composition has a flow rate ratio FRR21 / 5 in the range of from 17 to 36, wherein the polyethylene composition has a molecular weight distribution MWD determined by Gel Permeation Chromatography (GPC) according to ISO 16014-1 :2003 of equal to or more than 27.

[0017] Moreover, it has been surprisingly found that above-mentioned objects are achieved by a process for producing a polyethylene composition according to the present invention comprising the steps of pre-polymerizing in a first polymerizing step in the presence of catalyst / cocatalyst, ethylene and comonomer butene-1. Further transferring the prepolymerized contents to a second polymerization reactor for producing a first intermediate material comprising fraction (A) of the base resin; transferring the second intermediate material into a third polymerization reactor; polymerizing in a third polymerizing step ethylene and hexene-1 in the presence of the first intermediate material for producing a base resin comprising fraction (A) and fraction (B); compounding the base resin to obtain the polyethylene composition.

[0018] It has further surprisingly been found that these objects are achieved by an article comprising the polyethylene composition according to the present invention. Finally, it has been surprisingly found that these objects are achieved by the use of the polyethylene composition according to the present invention for the production of a film or a molded article.

[0019] The present invention has the advantage that articles and films can be prepared, which have lower material usage, i.e. by having thinner walls, while maintaining processability, impact and stiffness properties, while even enhancing the environmental stress cracking resistance. This allows for the production of articles and films having higher sustainability, i.e. lower impact on the environment, and having improved durability.

[0020] Detailed Description of the Invention

[0021] In the following, the present invention is described in detail, in particular, the polyethylene composition, the process for preparing the polyethylene composition and the article made from the ethylene composition.

[0022] Preparation Process of the Polyethylene Composition

[0023] The present invention furthermore relates to a process for producing a polyethylene composition in any one of the above-described embodiments wherein the base resin is produced in a multistage polymerization process in the presence of a Ziegler-Natta catalyst.

[0024] Generally, the process for producing a polyethylene composition according to the present invention comprises the steps of: pre-polymerizing in a first polymerizing step in the presence of catalyst / cocatalyst, ethylene and comonomer butene-1. Further transferring the pre-polymerized contents to a second polymerization reactor for producing a first intermediate material comprising fraction (A) of the base resin; transferring the second intermediate material into a third polymerization reactor; polymerizing in a third polymerizing step ethylene and hexene-1 in the presence of the first intermediate material for producing a base resin comprising fraction (A) and fraction (B); compounding the base resin to obtain the polyethylene composition.

[0025] Hence, the process of the present invention which makes use of at least two reactors, one for producing a lower molecular weight component and a second for producing a higher molecular weight component. These reactors may be employed in parallel, in which case the components must be mixed after production. More commonly, the reactors are employed in series, such that the products of the first reactor are used as the starting material in the second reactor, e.g. one component is formed in the first reactor and the second is formed in the second reactor in the presence of the first component. In this way, the two components are more intimately mixed, since one is formed in the presence of the other.

[0026] The polymerization reactions used in each stage may involve conventional ethylene homopolymerization (second reactor) or ethylene hexene-1 copolymerization reactions (third reactor), e.g. gas phase, slurry phase, liquid phase polymerizations, using conventional reactors, e.g. loop reactors, gas phase reactors, batch reactors, etc.

[0027] The polymerization may be carried out continuously or batchwise, preferably the polymerization is carried out continuously.

[0028] The multi-stage process can be any combination of liquid phase, slurry phase and gas phase processes.

[0029] In the preferred multistage process, the lower molecular weight fraction (A) and the higher molecular weight fraction (B) are produced in different polymerization steps.

[0030] The lower molecular weight fraction (A) can be prepared in the first polymerization step and the higher molecular weight fraction (B) in the second polymerization step. This can be referred to as the normal mode and is preferred.

[0031] If a fraction is produced in the first polymerization step, the melt flow rate of said fraction can be directly measured as described herein. If said fraction is produced in the second polymerization step, the melt flow rate of the said fraction can be calculated on the basis of the weight ratio of said fraction and the fraction taken from the preceding polymerization step and the molecular weight of the total polyethylene composition.

[0032] In addition, subtracting GPC curves, when fractions of each polymer are known, is also possible for determining melt flow rate of the polymer produced in the second or third stage of a multi-stage polymerization process.

[0033] Preferably, the multistage process of the present invention is a slurry phase-slurry phase-gas phase process.

[0034] The slurry and gas phase stages may be carried out using any conventional reactors known in the art. A slurry phase polymerization may, for example, be carried out in a continuously stirred tank reactor; a batch-wise operating stirred tank reactor or a loop reactor. Preferably, slurry phase polymerization is carried out in a loop reactor. In such reactors, the slurry is circulated with a high velocity along a closed pipe by using a circulation pump. Loop reactors are generally known in the art and examples are given, for instance, in US 4,582,816 A, US 3,405,109 A, US 3,324,093 A, EP 479 186 A and US 5,391 ,654 A. The term gas phase reactor encompasses any mechanically mixed, fluidized bed reactor, fast fluidized bed reactor or settled bed reactor or gas phase reactors having two separate zones, for instance one fluidized bed combined with one settled bed zone. Preferably, the gas phase reactor for the third polymerization step is a fluidized bed reactor.

[0035] In a preferred embodiment of the invention the fraction (A) is produced first and the fraction (B).

[0036] The resulting end product consists of an intimate mixture of the polymer fractions from the reactors, the different molecular-weight-distribution curves of these polymers together forming a molecular-weight-distribution curve having a broad maximum or several maxima, i.e. the end product is a multimodal polymer mixture.

[0037] It is preferred that the multimodal base resin of the polyethylene composition according to the invention is a bimodal polyethylene mixture consisting of polymer fractions (A) and (B), optionally further comprising a small pre-polymerization fraction. It is also preferred that this bimodal polymer mixture has been produced by polymerization as described above under different polymerization conditions in two or more polymerization reactors connected in series. Owing to the flexibility with respect to reaction conditions thus obtained, it is most preferred that the polymerization is carried out in a loop reactor / gas-phase reactor combination.

[0038] According to a preferred embodiment of the invention, the process comprises a slurryphase polymerization stage and a gas-phase polymerization stage. One suitable reactor configuration comprises one slurry reactor, preferably loop reactor, and one gas-phase reactor.

[0039] The catalyst may be transferred into the polymerization zone by any means known in the art. It is thus possible to suspend the catalyst in a diluent and maintain it as homogeneous slurry. Especially preferred it is to use oil having a viscosity from 20 to 1500 mPa-s as diluent, as disclosed in WO 2006 / 063771 A1.

[0040] The polymerization in slurry usually takes place in an inert diluent, typically a hydrocarbon diluent such as methane, ethane, propane, n-butane, isobutane, pentanes, hexanes, heptanes, octanes etc., or their mixtures. Preferably, the diluent is a low- boiling hydrocarbon having from 1 to 4 carbon atoms or a mixture of such hydrocarbons. An especially preferred diluent is propane, possibly containing minor amount of methane, ethane and / or butane.

[0041] The temperature in the slurry polymerization is typically from 40 to 115 °C, preferably from 60 to 110 °C, more preferably from 70 to 100 °C, and most preferably from 93 to 98 °C. The pressure is from 1 to 150 bar, preferably from 10 to 100 bar, and most preferably from 60 to 70 bar.

[0042] The slurry polymerization may be conducted in any known reactor used for slurry polymerization. Such reactors include a continuous stirred tank reactor and a loop reactor. It is especially preferred to conduct the polymerization in loop reactor. Hydrogen is fed, optionally, into the reactor to control the molecular weight of the polymer as known in the art.

[0043] Furthermore, one or more a-olefin comonomers may be added into the reactor to control the density and morphology of the polymer product. The actual amount of such hydrogen and comonomer feeds depends on the desired melt index (or molecular weight) and density (or comonomer content) of the resulting polymer.

[0044] The polymerization in gas-phase may be conducted in a fluidized bed reactor, in a fast- fluidized bed reactor or in a settled bed reactor or in any combination of these.

[0045] Typically, the fluidized bed or settled bed polymerization reactor is operated at a temperature within the range of from 50 to 100 °C, preferably from 65 to 90 °C. The pressure is suitably from 10 to 40 bar, preferably from 15 to 25 bar.

[0046] Hexene-1 is fed in a comonomer / monomer ratio (i.e. hexene-1 / ethylene ratio) in the gas phase reactor to maintain the hexene-1 concentration in the range of from 20 to 40 mol / kmol, preferably 25 to 40 mol / kmol, and most preferably 27 to 38 mol / kmol.

[0047] In addition, antistatic agent(s) may be introduced into the slurry and / or gas-phase reactor if needed.

[0048] The process may further comprise pre- and post-reactors.

[0049] The polymerization steps may be preceded by a pre-polymerization step. The prepolymerization step may be conducted in slurry or in gas phase. Preferably, prepolymerization is conducted in slurry, and especially in a loop reactor. The temperature in the pre-polymerization step is typically from 0 to 90 °C, preferably from 20 to 80 °C and more preferably from 30 to 70 °C.

[0050] The pressure is not critical and is typically from 1 to 150 bar, preferably from 10 to 100 bar, and most preferably from 60 to 70 bar.

[0051] The polymerization may be carried out continuously or batch wise, preferably the polymerization is carried out continuously.

[0052] In an example of the present process, polymerizing ethylene optionally with comonomers as herein discussed is accomplished in a multi-stage polymerization process comprising two slurry reactors and one gas-phase reactor. A chain-transfer agent, preferably hydrogen, can be added as required to the reactors. Preferably, 500 to 1500 mol of H2 per one kmol of ethylene are added to the reactor, more preferably 700 to 1300 mol of H2 per one kmol of ethylene, when the fraction (A) is produced in this reactor. Furthermore, preferably 30 to 70 mol of H2 per one kmol of ethylene are added to the reactor, more preferably 30 to 60 moles of H2 per one kmol of ethylene, when the fraction (B) is produced in this reactor.

[0053] The polymerization is conducted in the presence of an olefin polymerization catalyst. The catalyst preferably may be any Ziegler-Natta catalyst suitable for ethylene polymerization.

[0054] A Ziegler-Natta type catalyst typically used for ethylene polymerization and / or copolymerization will be a stereospecific, solid, high yield Ziegler-Natta catalyst component comprising as main components Mg, Ti and Cl. In addition to the solid catalyst component, a cocatalyst(s) as well as external donor(s) will generally be used in the polymerization process.

[0055] The components of the catalyst may be supported on a particulate support, such as inorganic oxide, like silica or alumina, or, usually, a magnesium halide may form the solid support. It is also possible that the catalyst components are not supported on an external support, but the catalyst is prepared by an emulsion-solidification method or by a precipitation method, as is well-known by the man skilled in the art of catalyst preparation.

[0056] The solid catalyst usually also comprises at least one electron donor (internal electron donor) and optionally aluminium.

[0057] Suitable external electron donors used in the polymerization are well known in the art and include ethers, ketones, amines, alcohols, phenols, phosphines and silanes.

[0058] Examples of suitable Ziegler-Natta catalysts and components in the catalysts are described among others in WO 87 / 07620, WO 92 / 21705, WO 93 / 11165, WO 93 / 11166, WO 93 / 19100, WO 97 / 36939, WO 98 / 12234, WO 99 / 33842, WO 03 / 000756, WO 03 / 000757, WO 03 / 000754, WO 03 / 000755, WO 2004 / 029112, EP2610271 , WO 2012 / 007430, WO 92 / 19659, WO 92 / 19653, WO 92 / 19658, US 4382019, US 4435550, US 4465782, US 4473660, US 4560671 , US 5539067, US 5618771 ,

[0059] EP45975, EP45976, EP45977, WO 95 / 32994, US 4107414, US 4186107, US 4226963, US 4347160, US 4472524, US 4522930, US 4530912, US 4532313, US 4657882, US 4581342, US 4657882.

[0060] The catalyst may be commercially available or be produced in accordance or analogously to the literature. For the preparation of the preferable catalyst usable in the invention, reference is made to WO 2004 / 055068 A1 , WO 2004 / 055069 A1 of Borealis AG and WO 2015 / 078924 of Abu Dhabi Polymers Co., Ltd. (Borouge) / Borealis AG and EP 0 810 235 A1. The content of these documents in its entirety is incorporated herein by reference, in particular concerning the general and all preferred embodiments of the catalysts described therein as well as the methods for the production of the catalysts. Particularly preferred Ziegler-Natta catalysts are described in EP 0 810 235 A1.

[0061] The composition of the invention preferably is produced in a process comprising a compounding step, wherein the composition, i.e. the blend, which is typically obtained as a polyolefin base resin powder from the reactor, and optional additives, is extruded in an extruder and then pelletized to polymer pellets in a manner known in the art. The extruder may be e.g. any conventionally used extruder. As an example of an extruder for the present compounding step may be those supplied by Japan Steel works, Kobe Steel or Farrel-Pomini, e.g. JSW 460P, JSW CIM90P or LCM80H.

[0062] In certain embodiments, in said extrusion step the SEI (specific energy input) of the extruder may be 150 kWh / ton to 400 kWh / ton, more preferably 200 kWh / ton to 300 kWh / ton.

[0063] The melt temperature in said extrusion step is preferably 180 °C to 300 °C, more preferably 200 °C to 270 °C.

[0064] It is believed that utilizing the various processing windows as mentioned above, the polyethylene composition having the mentioned property balance is achieved. Without wishing to be bound by theory it is believed that the choice of 1-hexene as comonomer in the gas phase reactor for the high molecular weight fraction, and the low molecular weight loop reactor fraction being a homopolymer achieves a broad molecular weight distribution. The low molecular weight fraction (A) is believed to improve the stiffness of the composition while a broad MWD achieved with the copolymer fraction with 1- hexene comonomer is believed to improve the impact and ESCR properties.

[0065] Polyethylene Composition

[0066] It has been found that the polyethylene composition according to the present invention provides an improved material for articles, such as blown articles or films, which exhibit an improved balance of mechanical properties e.g. stiffness and toughness, stiffness, environmental stress crack resistance, and processability.

[0067] The polyethylene composition according to the present invention comprises a base resin comprising

[0068] (A) a first ethylene homopolymer fraction, and (B) a second ethylene-hexene-1 copolymer fraction, wherein fraction (A) has a lower molecular weight than fraction (B), wherein the base resin comprises fraction (A) in an amount of at least 43.0 wt.% based on the total weight of the base resin, wherein the base resin comprises fraction (B) in an amount of equal to or lower than 57.0 wt.% based on the total weight of the base resin, wherein the base resin has a loss tangent (tan 5) at 300 rad / s measured according to ISO 6721 of lower than 0.500, wherein the polyethylene composition has a density determined according to ISO 1183- 1 :2022 - method A in the range of from 950 to 956 kg / m3, wherein the polyethylene composition has a melt flow rate MFRs determined according to ISO 1133 at 190 °C and at a loading of 5 kg in the range of from 0.15 to 0.6 g / 10 min, wherein the polyethylene composition has a flow rate ratio FRR21 / 5 in the range of from 17 to 36, wherein the polyethylene composition has a molecular weight distribution MWD determined by Gel Permeation Chromatography (GPC) according to ISO 16014-1 :2003 of equal to or more than 27.

[0069] By ethylene homopolymer is meant a polymer having mainly ethylene monomer units. Such polymer may contain up to 1 mol-% comonomer units, due to the fact that during polymerization some impurities may be present. Preferably, the homopolymer contains no comonomer units.

[0070] By ethylene hexene-1 copolymer is meant a polymer the majority by weight of which derives from ethylene monomer units, i.e. at least 50 wt.-% ethylene relative to the total weight of the copolymer. The hexene-1 comonomer contribution preferably is up to 10 mol-%, more preferably up to 5 mol-%. Ideally however there are very low levels of hexene-1 present in the polymers of the present invention such as maximum of 2.0 mol- %. The ethylene hexene-1 copolymer might comprise another comonomer, which preferably is a C3-12, especially C3-10, alpha olefin comonomer, particularly singly or multiply ethylenically unsaturated comonomer, in particular Cs- -alpha olefin such as propene, 1-butene, 1-octene and 4-methyl-pent-1-ene. The use of 1-octene and 1- butene is particularly preferred, especially 1-butene. Ideally, however, there is only one comonomer, i.e. hexene-1 , present in the polyethylene composition.

[0071] The polyethylene composition according to present invention is multimodal, comprising at least two fractions. Usually, a polyethylene composition comprising at least two polyethylene fractions, which have been produced under different polymerization conditions resulting in different (weight average) molecular weights and molecular weight distributions for the fractions, is referred to as “multimodal" . The prefix “multi" relates to the number of different polymer fractions the composition is consisting of.

[0072] The form of the molecular weight distribution curve, i.e. the appearance of the graph of the polymer weight fraction as a function of its molecular weight, of such a multimodal polyethylene will show two or more maxima or at least be distinctly broadened in comparison with the curves for the individual fractions. It should be understood that the present invention is not limited to a bimodal polyethylene composition but can also have three or even more differing fractions.

[0073] Preferably, however, the polyethylene composition is a bimodal polyethylene composition.

[0074] The tensile modulus determined according to ISO 527-1 of the polyethylene composition is preferably more than 1000 MPa, more preferably more than 1050 MPa, and most preferably of more than 1100 MPa. Preferably, the tensile modulus of the base resin is not higher than 1330 MPa, more preferably not higher than 1300 MPa, even more preferably not higher than 1280 MPa and most preferably not higher than 1250 MPa.

[0075] The tensile stress at yield determined according to ISO 527-1 of the polyethylene composition is preferably more than 4 MPa, more preferably more than 6 MPa, and most preferably more than 7 MPa. Preferably, the tensile stress at yield of the base resin not higher than 11 MPa, preferably not higher than 10 MPa.

[0076] The polyethylene composition preferably has a flexural modulus determined according to ISO 178 of at least 1100 MPa to 1350 MPa, preferably of at least 1200 MPa, and more preferably of at least 1275 MPa. If during transportation and / or warehousing the stiffness of the polyethylene compositions is lower than these ranges, problems under product stacking may occur.

[0077] The polyethylene composition further preferably has a Charpy Notched Impact Strength (NIS) at +23 °C measured according to ISO 179-1A of higher than 20 kJ / m2, more preferably higher than 23 kJ / m2, and most preferably higher than 24 kJ / m2. Typically, the Charpy Notched Impact Strength (NIS) of the base resin is not higher than 100 kJ / m2. Preferably not higher than 30 kJ / m2, and most preferably not higher than 27 kJ / m2. If the Charpy Notched Impact Strength (NIS) level is lower than these ranges, the toughness is impaired. The polyethylene composition preferably has an environmental stress crack resistance determined according to ASTM D1693 condition B of more than 1000 h, more preferably more than 1500 h, even more preferably more than 2000 h, and most preferably more than 3000 h.

[0078] Usually, packaging systems comprising the polyethylene composition of the invention, such as containers of films, carry a chemical or a detergent, what requires a certain performance in view of environmental stress conditions. If the polyethylene composition has an ESCR lower than 1000 h, high corrosive chemicals cannot be held by such container.

[0079] The polyethylene composition preferably has an oxygen induction time (OIT) determined according to ISO 11357-6 at a temperature of 210 °C of at least 30 min, preferably of at least 35 min, more preferably of at least 40 min, and most preferably of at least 44 min.

[0080] The polyethylene composition may consist of the base resin. However, in a preferred embodiment of the invention, the polyethylene composition comprises further additives in amount of 3 wt.-% or less based on the total amount of the polyethylene composition, more preferred of 2.5 wt.-% or less, and most preferred of 2 wt.-% or less. Usually, the amount of additives in the polyethylene composition is not lower than 0.01 wt.-% or less.

[0081] Such additives might be selected from as pigments (e.g. carbon black), stabilizers (e.g. antioxidant agents), antiacids and / or anti-UVs, antistatic agents, and utilization agents (such as processing aid agents).

[0082] The UV stabilizer may be a hindered amine light-stabilizer (HALS), selected from Chimassorb® 944, Tinuvin® 622, Tinuvin® 770 and mixtures thereof. Above that, any of the UV stabilizers, preferably HALS compounds recited in EP 3 622 541 A1 may be used. Two or more UV stabilizers may be combined. Any of the above-mentioned UV stabilizers may also be combined with one or more UV absorbers, such as benzotriazoles, benzophenones, triazines, or phenolic compounds. Any of the UV absorbers recited in EP 19 191 837.4 may be used. The UV stabilizer may preferably be contained in an amount of from 0.1 to 2 wt.-%, more preferably 0.2 to 1 .5 wt.-%, and most preferably 0.3 to 1 wt.-%, based on the total weight of the polyethylene composition.

[0083] An antioxidant may be selected e.g. from sterically hindered phenols (e.g. Irganox 1010 (CAS no 128-37-0), Irganox 1076 (CAS no 2082-79-3), Irganox 1035 (Cas no 41484- 359), sulfur-containing antioxidants (e.g. Irganox PS 802 (Cas no 693-36-7), Irganox PS 800 (Cas no 2500-88-1), phosphites / phosphonites (e.g. Irgafos 168 (Cas no 31570- 04-4), Irgafos P-EPQ (Cas no 38613-77-3), nitrogen-containing antioxidants (e.g. Naugard 445 (Cas 10081-67-1), Vulcanox HS / LG (cas no 26780-96-1). A combination of two or more may be used. The antioxidant may preferably be contained in an amount of from 0.1 to 2 wt.-%, more preferably 0.2 to 1 wt.-%, and most preferably 0.3 to 0.5 wt.-%, based on the total weight of the polyethylene composition.

[0084] Base Resin

[0085] The density measured according to ISO 1183-1 :2022 - method A of the base resin is preferably in the range of 951 to 956.5 kg / m3, more preferably of 952 to 955 kg / m3. Hence, preferably, the base resin is a high-density base resin. If the density is lower than this range, the physical properties as needed for the articles and films will be impaired, i.e. the film becomes too soft. If the density is higher than this range, the articles may become too heavy.

[0086] The base resin has an MFRs determined according to ISO 1133 in the range of from 0.15 to 0.6 g / 10 min or less. Preferably, the base resin has an MFRs determined according to ISO 1133 in of 0.5 g / 10 min or less, and most preferably of 0.4 g / 10 min or less. The base resin preferably has a minimum MFRs determined according to ISO 1133 of 0.24 g / 10 min, and most preferably at least 0.25 g / 10 min. Thus, particularly suitable values of MFRs determined according to ISO 1133 for base resin are from 0.24 to 0.5 g / 10 min, such as 0.25 to 0.4 g / 10 min.

[0087] Preferably, the base resin preferably has an MFR21 determined according to ISO 1133 of 16 g / 10 min or less, more preferably 13 g / 10 min or less, and most preferably 11 g / 10 min or less. The base resin preferably has a minimum MFR21 determined according to ISO 1133 of 4 g / 10 min, more preferably at least 5 g / 10 min, and most preferably at least 7 g / 10 min. Thus, particularly suitable values of MFR21 determined according to ISO 1133 for base resin are from 4 to 16 g / 10 min, preferably from 5 to 13 g / 10 min, and more preferably from 7 to 11 g / 10 min.

[0088] Preferably, the base resin preferably has an FRR21 / 5 of 32 or less, more preferably 30 or less, and most preferably 28 or less. The base resin preferably has a minimum FRR21 / 5 of 25, more preferably at least 26, and most preferably at least 27. Thus, particularly suitable values of FRR21 / 5 for base resin are from 25 to 32, such as 26 to 30. If the values for the FRR21 / 5 are below these ranges, the processability of the composition is impaired too much. On the other hand, if the values for the FRR21 / 5 are above these ranges, the miscibility of the fractions can be reduced.

[0089] In a preferred embodiment of the invention, the difference between the density of fraction (A) and the density of fraction (B) is between 25 and 40 kg / m3, more preferably between 30 and 38 kg / m3, and most preferably between 33 and 36 kg / m3. Density differences above these upper ranges can lead to compatibility problems between the fractions.

[0090] The base resin preferably has a z-average molecular weight Mz determined by gel permeation chromatography according to ISO 16014-1 :2003 of 1 ,500,000 to 2,000,000 g / mol, more preferably of 1 ,600,000 to 1 ,900,000 g / mol, and most preferably of 1 ,650,000 to 1 ,850,000 g / mol. Likewise, the base resin preferably has a weight average molecular weight Mw determined by gel permeation chromatography according to ISO 16014-1 :2003 of 250,000 to 320,000 g / mol, more preferably of 260,000 to 310,000 g / mol, even more preferably of 270,000 to 300,000 g / mol, and most preferably of 275,000 to 290,000 g / mol. Moreover, the base resin preferably has a number average molecular weight Mn determined by gel permeation chromatography according to ISO 16014-1 :2003 of not more than 11 ,000 g / mol, more preferably of not more than 10,000 g / mol, and most preferably of not more than 8500 g / mol. The base resin preferably has a molecular weight distribution Mw / Mn of from 27 to 40, preferably from 30 to 38, and most preferably from 33 to 36.

[0091] The base resin of the polyethylene composition according to the present invention preferably has a complex viscosity at 0.05 rad / s, eta o.os rad / s, of 100,000 Pa s to 150,000 Pa s, more preferably 110,000 Pa s to 130,000 Pa s, and most preferably 120,000 Pa s to 130,000 Pa s.

[0092] The base resin of the polyethylene composition according to the present invention preferably has a complex viscosity at 300 rad / s, eta 300 rad / s, of 1000 Pa s to 1275 Pa s, more preferably 1075 Pa s to 1250 Pa s, and most preferably 1150 Pa s to 1200 Pa s.

[0093] The base resin of the polyethylene composition preferably has a shear thinning index SHI2.7 / 210 of 10 to 90, more preferably a shear thinning index SHI2.7 / 210 of 30 to 150, even more preferably a shear thinning index SH I 2.7 / 210 of 35 to 120 and most preferably a shear thinning index SH I 2.7 / 210 of 36 to 100.

[0094] The shear thinning index SHI2.7 / 210 can be modified for a given catalyst system by varying the relative amounts of low and high molecular weight material (via split of the reactors) and by varying the molecular weights of the respective low and high molecular weight materials, for example by variation of the chain transfer agent feed. Moreover, different catalyst systems result in a specific intrinsic shear thinning index.

[0095] The base resin of the polyethylene composition according to the present invention preferably has an extrapolated shear thinning index SH I 5 / 200 of 25 to 80, more preferably of 25 to 50, even more preferably of 25 to 45, and most preferably of 26 to 38. The shear thinning index SHI5 / 200 can be modified as explained above for the SHI2.7 / 210 shear thinning index. Moreover, the shear thinning index SHI5 / 200 is particularly sensitive to the molecular weight distribution provided intrinsically by a catalyst system.

[0096] The base resin of the polyethylene composition according to the present invention has a loss tangent (tan 5) measured at 300 rad / s according to ISO 6721 of lower than 0.500. Preferably, the base resin of the polyethylene composition according to the present invention has a loss tangent (tan 5) measured at 300 rad / s according to ISO 6721 of lower than 0.470, more preferably lower than 0.450.

[0097] Preferably, in the base resin the comonomer content determined by NMR spectroscopy is in the range of from 0.01 to 1.0 mol-%, more preferably in the range of from 0.1 to 0.8 mol-%, and most preferably in the range of from 0.15 to 0.3 mol-% with respect of the molecular weight of the base resin.

[0098] Likewise, preferably, in the base resin the comonomer content determined by NMR spectroscopy is in the range of from 0.05 to 3.0 wt.-%, more preferably in the range of from 0.3 to 2.0 wt.-%, and most preferably in the range of from 0.5 to 0.9 wt.-% with respect of the weight of the base resin.

[0099] The base resin of the polyethylene composition comprises, preferably consists of, two fractions (A) and (B).

[0100] Fraction (A)

[0101] Fraction (A) is a polyethylene homopolymer. Fraction (A) preferably has a density, which is higher than the density fraction (B).

[0102] The density of fraction (A) measured according to ISO 1183-1 :2022 - method A is in the range of 965 to 975 kg / m3, preferably of 967 to 975 kg / m3, and most preferably of 970 to 974 kg / m3.

[0103] Fraction (A) preferably has a melt flow rate MFR2 determined according to ISO 1133 of 150 to 500 g / 10 min. More preferably, fraction (A) has an MFR2 determined according to ISO 1133 of 480 g / 10 min or less, and most preferably 430 g / 10 min or less. Fraction (A) preferably has a minimum MFR2 determined according to ISO 1133 of 150 g / 10 min, more preferably at least 200 g / 10 min, and most preferably at least 300 g / 10 min. Thus, particularly suitable values of MFR2 determined according to ISO 1133 for fraction (A) are from 200 to 480 g / 10 min, such as 300 to 430 g / 10 min.

[0104] The fraction (A) is present in the base resin in an amount at least 43.0 wt.-%, preferably of at least 44.0 wt.%, based on the total weight of the base resin. Usually, fraction (A) is present in the base resin in an amount of not higher than 47.0 wt.-%. Fraction (B)

[0105] Fraction (B) is an ethylene hexene-1 copolymer.

[0106] Fraction (B) preferably has a density, which is lower than the density of fraction (A).

[0107] The density of fraction (B) is preferably in the range of from 930 to 946 kg / m3, more preferably in the range of from 932 to 944 kg / m3, and most preferably in the range of from 933 to 940 kg / m3.

[0108] The fraction (B) is preferably present in the base resin in an amount of equal to or lower than 56.0 wt.%, more preferably equal to or lower than 55.0 wt.%, based on the total weight of the base resin. Usually, fraction (B) is present in the base resin in an amount of not lower than 53.0 wt.-%.

[0109] Article

[0110] The present invention furthermore relates to an article, preferably a molded article or a film, more preferably a blow-molded article or blown film, comprising, or consisting of, the polyethylene composition in any one of the embodiments as herein described.

[0111] If the article is a molded article, it is preferably a blow-molded article. Preferably the blow-molded article is a bottle or a container, preferably a bottle or container for household or industrial chemicals, for cosmetics, for pharmaceutical packaging or for food and drinks

[0112] If the article is a film, the film is preferably a blown or a cast film or at least one layer of a multi-layered film. Furthermore, if the article is a film, the invention further relates to an article comprising said film, wherein preferred articles comprising said film are packaging articles such as pouches, like stand-up pouches, sacks, bag, sachets, lamitubes etc.

[0113] The film according to the present invention preferably has a tensile modulus in machine direction (TM-MD) measured according to ASTM D 882 of at least 700 MPa, more preferably at least 750 MPa. Usually, the tensile modulus in machine direction (TM-MD) of the film according to the present invention is not higher than 1000 MPa.

[0114] The film according to the present invention preferably has a tensile modulus in transverse direction (TM-TD) measured according to ASTM D 882 of at least 800 MPa, more preferably at least 1000 MPa. Usually, the tensile modulus in machine direction (TM-TD) of the film according to the present invention is not higher than 1100 MPa.

[0115] The film according to the present invention preferably has an elongation at break in machine direction (EB-MD) measured according to ISO 527-3 of at least 470%, more preferably at least 500%, and most preferably at least 530%. Usually, the film according to the present invention has an elongation at break in machine direction (EB-MD) of not higher than 600%.

[0116] The film according to the present invention preferably has an Elmendorf tear strength in transverse direction (ETS-TD) measured according to ASTM D 1922 of at least 4.5 N, preferably at least 5.0 N, and most preferably at least 5.5 N. Preferably, the film according to the present invention preferably has an Elmendorf tear strength in transverse direction (ETS-TD) of not more than 7 N, more preferably of not more than 8 N.

[0117] The film according to the present invention preferably has an Elmendorf tear strength in machine direction (ETS-MD) measured according to ASTM D 1922 of at least 0.4 N, preferably at least 0.5 N, and most preferably at least 0.6 N. Preferably, the film according to the present invention preferably has an Elmendorf tear strength in machine direction (ETS-MD) of not more than 1.0 N, more preferably of not more than 0.9 N.

[0118] The film according to the present invention preferably has a gel content having a size of 100-300 pm diameter of not more than 30 pcs / m2, more preferably of not more than 20 pcs / m2.. Usually, the film according to the present invention preferably has a gel content having a size of 100-300 pm diameter of more than 1.0 pcs / m2, more preferably of more than 3.0 pcs / m2, and most preferably of more than 15pcs / m2.

[0119] The film according to the present invention preferably has a gel content having a size of 301-600 pm diameter of not more than 5 pcs / m2, preferably of not more than 4 pcs / m2, and most preferably of not more than 2 pcs / m2. The film according to the present invention can have a gel content having a size of 301-600 pm diameter of more than 0.1 pcs / m2, of more than 0.5 pcs / m2, or of more than 0.7 pcs / m2.

[0120] The film according to the present invention preferably has a dart drop impact (DDI) strength measured according to ASTM D1709, method A, of more than 300 g, preferably more than 330 g, and most preferably more than 350 g.

[0121] Preferably, the film according to the present invention has at least one, preferably all, of the following properties: a tensile modulus in machine direction (TM-MD) measured according to ASTM D 882 of at least 700 MPa, preferably at least 750 MPa; a tensile modulus in transverse direction (TM-TD) measured according to ASTM D 882 of at least 800 MPa, preferably at least 1000 MPa; an elongation at break in machine direction (EB-MD) measured according to ISO 527-3 of at least 470%, preferably at least 500%, and most preferably at least 530%; an Elmendorf tear strength in transverse direction (ETS-TD) measured according to ASTM D 1922 of at least 4.5 N, preferably at least 5.0 N, and most preferably at least 5.5 N; an Elmendorf tear strength in machine direction (ETS-MD) measured according to ASTM D 1922 of at least 0.4 N, preferably of at least 0.5 N, and most preferably of at least 0.6 N; a gel content having a size of 100-300 pm diameter of not more than 30 pcs / m2, more preferably of not more than 20 pcs / m2; a gel content having a size of 301-600 pm diameter of not more than 5 pcs / m2, preferably of not more than 4 pcs / m2, and most preferably of not more than 2 pcs / m2; a dart drop impact (DDI) strength measured according to ASTM D 1709, method A, of more than 300 g, preferably more than 330 g, and most preferably more than 350 g.

[0122] More preferably, the film according to the present invention has a gel content having a size of 301-600 pm diameter of not more than 2 pcs / m2and / or a gel content having a size of 100-300 pm diameter of not more than 20 pcs / m2.

[0123] Preparation of the Film

[0124] The film of the present invention may be produced by any conventional method for producing films, such as blown films or cast films. The polyethylene composition according to the invention may be extruded preferably at a temperature of from 180 to 230 °C, more preferably from 200 to 220 °C. Conventional film extrusion techniques used in this regard are known in the art. Preferably, the film layer is extruded at a temperature in the range of from 200 to 215 °C in the extruder zones and passed through the annular die at the temperatures of from 195 to 220 °C and then cooled by blowing air at a temperature of from 14 to 16 °C, to provide a frost line height of from 0.5 to 3 times the diameter of the die. The blow-up ratio can be in the range of from 1 : 1.5 to 1 :3.5, preferably from 1 : 1.8 to 1 :3.3, more preferably from 1 :2.0 to 1 :3.2.

[0125] One production method is described in detail in the Example section herein. Blown film extrusion and stretching techniques used for the examples are done on Reifenhauser MDO line well known in the art, as described in EP 2 849 929 A1.

[0126] Preferably primary film with a thickness range of from 25 to 100 pm, more preferably from 25 to 70 pm and most preferably from 40 to 60 pm are thus prepared. It is preferred, that the primary film is a blown film that is stretched majorly in one direction, referred to as uniaxially oriented film or monoaxially oriented film. Most preferably, the primary film is stretched in the machine direction (MD). Stretching may be carried out by any conventional technique using any conventional stretching devices which are well known in the art.

[0127] The film may be stretched at least 3 times, such as from 3 to 20 times to its original length in the machine direction. Moreover, the film may be stretched in a draw ratio of from 1 :4 to 1 :8. The obtained thickness of the oriented film is preferably in the range of up to 100 pm, such as in the range of from 25 to 100 pm, more preferably from 25 to 70 pm, and most preferably from 40 to 60 pm.

[0128] Use

[0129] The invention also relates to the use of a polyethylene composition in any one of the embodiments as herein described for producing an article, preferably a molded article or a film as described above.

[0130] Experimental Part

[0131] Unless explicitly described otherwise, the description of the present invention is to be understood so that one or more of any of the above-described preferred embodiments of the invention can be combined with the invention described in its most general features.

[0132] In the following, the measurement and determination methods for the parameters as used herein are given and the present invention is further illustrated by way of example and comparative example.

[0133] Measurement methods

[0134] The following definitions of terms and determination methods apply for the above general description of the invention including the claims as well as to the below examples unless otherwise defined. a) Melt Flow Rate

[0135] The melt flow rate (MFR) was determined according to ISO 1133 and is indicated in g / 10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR2 of polypropylene was determined at a temperature of 190 °C and a load of 2.16 kg. The MFR5 of polypropylene was determined at a temperature of 190 °C and a load of 5.0 kg. The MFR21 of polypropylene was determined at a temperature of 190 °C and a load of 21 .6 kg. b) Calculation of Melt Flow Rate of Polymer Fractions wherein wi is the weight fraction [wt.-%] of a polymer fraction 1 ,

[0136] W2 is the weight fraction [wt.-%] of a polymer fraction 2,

[0137] MFRi is the melt flow rate MFR2 (230°C) [g / 10 min] of the polymer fraction 1 ,

[0138] M FRI+2 is the melt flow rate MFR2 (230°C) [g / 10 min] of the combined fractions 1 and 2,

[0139] MFR2 is the calculated melt flow rate MFR2 (230 °C) [g / 10 min] of the polymer fraction 2. c) Density

[0140] The density was measured according to ISO 1183-1 :2022 - method A. Sample preparation was done by compression molding in accordance With ISO 1872-2:2007. d) Calculation of Density of Polymer Fractions

[0141] , . 1 - w2

[0142] (.Pl+2 Pl) 1 QQ p2=

[0143] W2wherein

[0144] W2 is the weight fraction [wt.-%] of a polymer fraction 2, pi is the density [kg / m3] of the polymer fraction 1 , p -1 +2 is the density [kg / m3] of the combined fractions 1 and 2,

[0145] P2 is the calculated density [kg / m3] of the polymer fraction 2. e) Quantification of microstructure by NMR spectroscopy

[0146] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers.

[0147] Quantitative13C{1H} NMR spectra recorded in the molten state using a Bruker Avance III 500 NMR spectrometer operating at 500.13 and 125.76 MHz for1H and13C respectively. All spectra were recorded using a13C optimized 7 mm magic-angle spinning (MAS) probe head at 150 °C using nitrogen gas for all pneumatics. Approximately 200 mg of material was packed into a 7 mm outer diameter zirconia MAS rotor and spun at 4 kHz. This setup was chosen primarily for the high sensitivity needed for rapid identification and accurate quantification (Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2006, 207:382; Parkinson, M., Klimke, K., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2007. 208:2128; Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50, 2009, 2373). Standard single-pulse excitation was employed utilizing the transient NOE at short recycle delays of 3s (Pollard, M., Klimke, K., Graf, R., Spiess, H.W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004, 37:813; Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2006, 207:382) and the RS-HEPT decoupling scheme (Filip, X., Tripon, C., Filip, C., J. Mag. Resn. 2005, 176, 239; Griffin, J.M., Tripon, C., Samoson, A., Filip, C., and Brown, S.P., Mag. Res. in Chem. 2007, 45, S1 , S198). A total of 16348 (16k) transients were acquired per spectrum. This setup was chosen due its high sensitivity towards sometimes low comonomer contents.

[0148] Quantitative13C{1H} NMR spectra were processed, integrated and quantitative properties determined using custom spectral analysis automation programs. All chemical shifts are internally referenced to the bulk methylene signal (5+) at 30.00 ppm (J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201).

[0149] Characteristic signals corresponding to the incorporation of 1 -hexene were observed (J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201.) and all contents calculated with respect to all other monomers present in the polymer.

[0150] Characteristic signals resulting from isolated 1-hexene incorporation i.e. EEHEE comonomer sequences, were observed. Isolated 1-hexene incorporation was quantified using the integral of the signal at 38.2 ppm assigned to the *B4 sites, accounting for the number of reporting sites per comonomer:

[0151] H = l*B4

[0152] When characteristic signals resulting from consecutive 1-hexene incorporation, i.e. EHHE comonomer sequences were observed, such consecutive 1-hexene incorporation was quantified using the integral of the signal at 40.4 ppm assigned to the aaB4B4 sites accounting for the number of reporting sites per comonomer:

[0153] HH=2 laaB4B4

[0154] When characteristic signals resulting from non-consecutive 1-hexene incorporation, i.e. EHEHE comonomer sequences were observed, such non-consecutive 1-hexene incorporation was quantified using the integral of the signal at 24.6 ppm assigned to the PPB4B4 sites accounting for the number of reporting sites per comonomer:

[0155] HEH = 2 * l B4B4 Due to the overlap of the signals from the *B4 and *pB4B4 sites from isolated (EEHEE) and non-consecutively incorporated (EHEHE) 1 -hexene respectively the total amount of isolated 1 -hexene incorporation is corrected based on the amount of non-consecutive 1 -hexene present:

[0156] H = l*B4 - 2 * l B4B4

[0157] With no other signals indicative of other comonomer sequences, i.e. 1-hexene chain initiation, observed the total 1-hexene comonomer content was calculated based solely on the amount of isolated (EEHEE), consecutive (EHHE) and non-consecutive (EHEHE) 1-hexene comonomer containing sequences:

[0158] Htotai = H + HH + HEH

[0159] Characteristic signals resulting from saturated end-groups were observed. The content of such saturated end-groups was quantified using the average of the integral of the signals at 22.8 and 32.2 ppm assigned to the 2s and 3s sites respectively:

[0160] S =(1 / 2)*( l2S+ l3s )

[0161] The relative content of ethylene was quantified using the integral of the bulk methylene (5+) signals at 30.00 ppm:

[0162] E =(1 / 2)*ls+

[0163] The total ethylene content was calculated based the bulk methylene signals and accounting for ethylene units present in other observed comonomer sequences or end- groups:

[0164] Etotai = E + (2 / 2)*H + (1 / 4)*HH + (3 / 4)*HEH + (3 / 2) *S

[0165] The total mole fraction of 1-hexene in the polymer was then calculated as: fH=Htotai / ( Etotal + Htotai )

[0166] The total comonomer incorporation of 1-hexene in mole percent was calculated from the mole fraction in the usual manner:

[0167] H [mol%] = 100 * fH

[0168] The total comonomer incorporation of 1-hexene in weight percent was calculated from the mole fraction in the standard manner:

[0169] H [wt%] = 100 * ( fH * 84. 16) / ( (fH * 84. 16) + ((1-fH) * 28.05) )

[0170] The comonomer incorporation of 1-hexene in mole percent in high Mw fraction was calculated from the total comonomer incorporation in the usual manner:

[0171] H in HMW [mol%] = 100 % * H [mol%] / Split of HMW fraction % Note, that amount of HDPE or LDPE color master batch carrier resin is not taken into account. f) Gel Permeation Chromatography (GPC)

[0172] GPC conventional method

[0173] Molecular weight averages (Mz, Mwand Mn), molecular weight distribution (MWD) and its broadness, described by polydispersity index, PDI= Mw / Mn(wherein Mnis the number average molecular weight and Mwis the weight average molecular weight) were generally determined by Gel Permeation Chromatography (GPC) according to ISO 16014-1 :2003 and ASTM D 6474-12 using the following formulas:

[0174] For a constant elution volume interval AVj, where Aj, and Mj are the chromatographic peak slice area and polyolefin molecular weight (MW), respectively associated with the elution volume, Vi, where N is equal to the number of data points obtained from the chromatogram between the integration limits.

[0175] A high temperature GPC instrument, equipped with either infrared (IR) detector (IR4 or IR5 from PolymerChar (Valencia, Spain)) or differential refractometer ((Rl) from Agilent Technologies, equipped with 3x Agilent-PLgel Olexis and 1x Agilent-PLgel Olexis Guard columns) was used. As mobile phase 1 ,2,4-trichlorobenzene (TCB) stabilized with 250 mg / L 2,6-Di tert-butyl-4-methyl-phenol) was used. The chromatographic system was operated at column temperature of 160 °C and detector at 160 °C and at a constant flow rate of 1 mL / min. 200 pL of sample solution was injected per analysis. Data collection was performed using either Agilent Cirrus software version 3.3 or PolymerChar GPC-IR control software.

[0176] The column set was calibrated using 19 narrow MWD polystyrene (PS) standards in the range of from 0.5 kg / mol to 11500 kg / mol. The PS standards were dissolved at room temperature over several hours. The conversion of the polystyrene peak molecular weight to polyolefin molecular weights is accomplished by using the Mark-Houwink equation and the following Mark-Houwink constants:

[0177] KPS = 19 x 10~3mL / g, aPS= 0.655

[0178] KPE= 39 x 10-3mL / g, aPE= 0.725 A third order polynomial fit was used to fit the calibration data.

[0179] All samples were prepared in the concentration range of around 1 mg / ml and dissolved at 160 °C for 3 (three) hours for PE in fresh distilled TCB stabilized with 250 ppm Irgafos168 under continuous gentle shaking. g) Dynamic Rheology

[0180] The characterization of polymer melts by dynamic shear measurements complies with ISO standards 6721-1 and 6721-10. The measurements were performed on an Anton Paar MCR301 stress controlled rotational rheometer, equipped with a 25 mm parallel plate geometry. Measurements were undertaken on compression moulded plates using nitrogen atmosphere and setting a strain within the linear viscoelastic regime. The oscillatory shear tests were done at 190 °C applying a frequency range between 0.015 and 500 rad / s and setting a gap of 1.2 mm.

[0181] In a dynamic shear experiment the probe is subjected to a homogeneous deformation at a sinusoidal varying shear strain or shear stress (strain and stress-controlled mode, respectively). On a controlled strain experiment, the probe is subjected to a sinusoidal strain that can be expressed by y(t) = Yo sin(wt) (1)

[0182] If the applied strain is within the linear viscoelastic regime, the resulting sinusoidal stress response can be given by o(t) = oO sin(cot +5) (2) where Oo, and Yo are the stress and strain amplitudes, respectively; co is the angular frequency; 5 is the phase shift (loss angle between applied strain and stress response); t is the time.

[0183] Dynamic test results are typically expressed by means of several different rheological functions, namely the shear storage modulus, G’, the shear loss modulus, G”, the complex shear modulus, G*, the complex shear viscosity, q*, the dynamic shear viscosity, q' , the out-of-phase component of the complex shear viscosity, q" and the loss tangent, tan q, which can be expressed as follows:

[0184] G' = — cosb [Pa] (3)

[0185] Yo

[0186] G" = — sin6 [Pa] (4)

[0187] Yo

[0188] G* = G‘ + iG“ [Pa] (5) q* = q' - iq" [Pa s] (6)

[0189] The determination of so-called Shear Thinning Index, which correlates with MWD and is independent of Mw, is done as described in equation 9.

[0190] Ql_l l > Eta* for (G* = x kPa) ,Q. bH I(x / y) - Eta* for (G* = y kPa)(9)

[0191] For example, the SHI(2.7 / 2io> is defined by the value of the complex viscosity, in Pa s, determined for a value of G* equal to 2.7 kPa, divided by the value of the complex viscosity, in Pa s, determined for a value of G* equal to 210 kPa and the SHI(5 / 2oo) is defined by the value of the complex viscosity, in Pa s, determined for a value of G* equal to 5 kPa, divided by the value of the complex viscosity, in Pa s, determined for a value of G* equal to 200 kPa.

[0192] The values of storage modulus (G1), loss modulus (G"), complex modulus (G*) and complex viscosity (q*) were obtained as a function of frequency (co).

[0193] Thereby, e.g. n*3oorad / s (eta*3oorad / s) is used as abbreviation for the complex viscosity at the frequency of 300 rad / s and n*o.osrad / s (eta*o.osrad / s) is used as abbreviation for the complex viscosity at the frequency of 0.05 rad / s, and n*orad / s(eta*orad / s) is used as abbreviation for the complex viscosity at the frequency of 0 rad / s or zero shear viscosity.

[0194] The loss tangent tan (delta) is measured in accordance with ISO 6721 and is defined as the ratio of the loss modulus (G") and the storage modulus (G1) at a given frequency. Thereby, e.g. tano.os is used as abbreviation for the ratio of the loss modulus (G") and the storage modulus (G1) at 0.05 rad / s and tansoo is used as abbreviation for the ratio of the loss modulus (G") and the storage modulus (G1) at 300 rad / s.

[0195] The elasticity balance tano.os / tansoo is defined as the ratio of the loss tangent tano.os and the loss tangent tansoo.

[0196] Besides the above-mentioned rheological functions one can also determine other rheological parameters such as the so-called elasticity index El(x). The elasticity index Ei(x) is the value of the storage modulus, G’ determined for a value of the loss modulus, G” of x kPa and can be described by equation 10.

[0197] EI(x) = G' for (G" = x kPa) [Pa] (10)

[0198] For example, the El(5 kPa) is the defined by the value of the storage modulus G’, determined for a value of G” equal to 5 kPa. The polydispersity index, PI, is defined by equation 11. where COCOP is the cross-over angular frequency, determined as the angular frequency for which the storage modulus, G', equals the loss modulus, G".

[0199] The values are determined by means of a single point interpolation procedure, as defined by Rheocompass software. In situations for which a given G* value is not experimentally reached, the value is determined by means of an extrapolation, using the same procedure as before. In both cases (interpolation or extrapolation), the option from Rheocompass ‘Interpolate y-values to x-values from parameter’ and the ‘logarithmic interpolation type’ were applied.

[0200] References:

[0201] [1] ‘Rheological characterization of polyethylene fractions’, Heino, E.L., Lehtinen. A., Tanner J., Seppala, J., Neste Oy, Porvoo, Finland, Theor. Appl. Rheol., Proc. Int. Congr. Rheol, 11th (1992), 1 , 360-362.

[0202] [2] ‘The influence of molecular structure on some rheological properties of polyethylene’, Heino, E.L., Borealis Polymers Oy, Porvoo, Finland, Annual Transactions of the Nordic Rheology Society, 1995.

[0203] [3] ‘Definition of terms relating to the non-ultimate mechanical properties of polymers’, Pure & Appl. Chem., Vol. 70, No. 3, pp. 701-754, 1998. h) Oxidation induction temperature

[0204] A differential thermal analysis (DTA) instrument of the type DSC 4000 (PerkinElmer, USA) was utilized to characterize the oxidation induction temperature (dynamic OIT) according to ISO 11357-6 (Plastics - Differential scanning calorimetry (DSC) - Part 6: Determination of oxidation induction time (isothermal OIT) and oxidation induction temperature (dynamic OIT)). Samples were cut from shoulders of injection molded MPS and encapsuled in perforated aluminum pans. The average sample weight was around 5 mg. A single heating step between 23 °C and 300 °C was performed with a heating rate of 10 K / min with synthetic air as purge gas and a flow rate of 20 ml / min. The point of intersect of the slope before oxidation and during oxidation gives the onset of oxidation or the oxidation induction temperature in °C. For each material, five samples, each cut from an individual MPS, were used for the calculation of average values and standard deviations. i) Tensile Modulus and Tensile Properties

[0205] Tensile properties are measured at 23 °C according to ISO 527-1 with a specimen Type 1A, at cross head speed 1 mm / min. Test specimens were notched out of the sheets as per Type 1A dimensions and compression molded sheets of thickness 4.0 mm was prepared according to ISO 1872-2 at molding temperature of 180 °C. Material was preheated by applying light contact pressure for 5 min. Then full pressure was applied for 5 min, after which material was cooled with a cooling rate of 15°C / min and demolding temperature was 40 °C. j) Flexural Modulus

[0206] The flexural modulus is determined according to ISO 178. The test specimens having a dimension of 80 x 10 x 4.0 mm3(length x width x thickness) and was cut from ISO 527-1 Type 1A prepared by compression molding according to EN ISO 1872-2. The specimens are conditioned at 23 °C and 50% relative humidity. The length of the span between the supports is 64 mm and the test speed is 2 mm / min. k) Charpy impact test

[0207] The Charpy notched impact strength (NIS) was measured according to ISO 179-1 eA at +23 °C and -20 °C, using injection-molded bar test specimens of 80 x 10 x 4 mm3prepared in accordance with ISO 1873-2:2007 l) Environmental Stress Crack Resistance (ESCR)

[0208] ESCR was conducted according to ASTM D 1693 (50 °C, 10% Igepal CO630). Test specimens according to ASTM D 1693 condition B were prepared through compression molding of sheets of thickness 1.90 ± 0.06 mm. Compression molding was done according to ISO 1872-2 at molding temperature of 180 °C. Material was pre-heated by applying light contact pressure for 5 in. Then full pressure was applied for 5 min, after which material was cooled with a cooling rate of 15 °C / min. Demolding temperature was 40 °C. The specimens (38.0 ± 2.5 mm x 13 ± 0.8 mm) were cut out of the sheets, and notched according to ASTM D 1693, condition B. m) Tensile Properties of Films

[0209] Film tensile properties were measured at 23 °C according to ISO 527-3 on films with a thickness of 40 pm produced as described in the experimental part herein. Tensile modulus in machine direction (TM-MD) and Tensile modulus in transverse direction (TM-TD) were measured as 1 % secant modulus with 5 mm / min test speed and 50 mm gauge length according to ASTM D882. Tensile strength at break (TSB-MD and TSB-TD), Tensile strength at yield (TSY-MD and TSY-TD), Elongation at break (EB-MD), Elongation at yield (EY-MD and EY-TD) were measured according to ISO 527-3 specimen Type 2 with 50 mm gauge length and 500 mm / min test speed. n) Dart-drop impact strength (DDI)

[0210] DDI was measured using ASTM D1709, method A (Alternative Testing Technique) from the film samples. A dart with a 38 mm diameter hemispherical head was dropped from a height of 0.66 m onto a film clamped over a hole. Successive sets of twenty specimens are tested. One weight was used for each set and the weight is increased (or decreased) from set to set by uniform increments. The weight resulting in failure of 50% of the specimens is calculated and reported. o) Tear resistance (determined as Elmendorf tear (N))

[0211] Tear resistance was measured according to according to ASTM D 1922 on films with a thickness of 40 pm produced as described in the experimental part herein p) Gel content

[0212] The gel content was measured via gel count with a gel counting apparatus consisting of a measuring extruder, ME 25 I 5200 V1 , 25*25D, with five temperature conditioning zones adjusted to a temperature profile of 170 / 180 / 190 / 190 / 190 °C, an adapter and a slit die (with an opening of 0.5 * 150 mm). Attached to this were a chill roll unit (with a diameter of 13 cm with a temperature set of 50 °C), a line camera (CCD 4096 pixel for dynamic digital processing of grey tone images) and a winding unit.

[0213] For the gel count measurements, the materials were extruded at a screw speed of 30 rounds per minute, a drawing speed of 3-3.5 m / min and a chill roll temperature of 50 °C to make thin cast films with a thickness of 70 pm and a width of approximately 110 mm.

[0214] The resolution of the camera is 25 pm x 25 pm on the film. The camera works in transmission mode with a constant grey value (auto. set. margin level = 170). The system is able to decide between 256 grey values from black = 0 to white = 256. For detecting gels, a sensitivity level dark of 25% is used. For each material the average number of gel dots on a film surface area of 10 m2was inspected by the line camera. The line camera was set to differentiate the gel dot size according to the following:

[0215] Gel size (the size of the longest dimension of a gel)

[0216] Size class 1 : 100 pm to 300 pm

[0217] Size class 2: 301 pm to 500 pm Size class 3: 601 m to 1000 pm

[0218] The gel counts for the gels of the different size classes were measured and are given as counts per m2. They represent the gel content of the respective size classes. The total gel content is the sum of these gel contents. q) Full Notch Creep Test (FNCT)

[0219] The full notch creep test has been carried out according to ISO 16770:2019.

[0220] Sample Preparation: Plaques with a dimension of 210 x 210 x 6 mm were compression moulded according ISO 16770:2019 (chapter 6.3.2, table 2 - conditions for compression moulding of the test specimen) with a Collin 400P / M laboratory press. After compression moulding the plaques were annealed for 3 h in an air oven at a temperature of 100 °C and then slowly cooled down to room temperature. A set of specimens with a dimension of 90 x 6 x 6 mm were milled from the plaque with a G- Tech milling machine and notched with a razor blade at room temperature to a notch depth of 1 mm, which results in a final specimen ligament of 4 x 4 mm (ligament 16 mm2).

[0221] Surfactant solution: Stirred solution (deionised water with a concentration equivalent to 6.67% mass Dehyton PL). Full notch creep tests (FNCT) have been executed according to ISO 16770 on an OCS FNCT device at 50 °C and a stress level of 6 MPa. The notched specimens were conditioned for 24 h without load at 50 °C in a stirred surfactant solution (deionised water with a concentration equivalent to 6.67% mass Dehyton PL). After conditioning the load of 6 MPa was applied to the specimen. At the same time, the timing device was started and the time to failure was measured.

[0222] Examples

[0223] The polyethylene base resins and compositions according to the invention (IE1 and IE2) were produced using a Ziegler-Natta catalyst A which was prepared as described in Example 1 of WO-A-99 / 51646.

[0224] For comparison, a comparative resin and composition (CE1) was produced using the same a Ziegler-Natta catalyst A.

[0225] The inventive and comparative resin were produced in a Borstar plant with a 2-reactor set-up (loop - GPR) and a pre-polymerization loop reactor according to the conditions as given in Table 1 .

[0226] Into the pre-polymerization reactor propane, ethylene, butene-1 and hydrogen were introduced for conducting a pre-polymerization step. In addition, the Ziegler-Natta catalyst A was introduced into the reactor together with triethylaluminium cocatalyst so that the ratio of aluminium to titanium was 3 mol / mol (for catalyst A).

[0227] The slurry was withdrawn intermittently from the pre-polymerization reactor and directed to the loop reactor. Additionally, propane, ethylene, triethylaluminium and hydrogen were fed to the loop reactor whereby the ethylene concentration and the hydrogen to ethylene ratio for the inventive and reference example were adjusted so that ethylene homopolymers were produced having the MFR2 and production split indicated in Table 1 .

[0228] Table 1: Process conditions for IE 1, IE2 and CE1 The slurry was intermittently withdrawn from the loop reactor by using settling legs and directed to the gas phase reactor. Additional ethylene, 1-hexene (IE1 and IE2) or 1- butene (CE1) comonomer, and hydrogen were fed, whereby the comonomer to ethylene ratio, the MFR5 as well as the production split and the density of the polymers withdrawn from the gas phase reactor are listed in Table 1. Inventive resins IE1 and IE2 were produced with catalyst A and with 1-hexene comonomer. Comparative resin CE2 was also produced with catalyst A, but the comonomer used was 1-butene.

[0229] Pellets of the resulting compositions with the components shown at the bottom of table 1 have been produced and compared in their melt flow behavior, comonomer content, and mechanical properties. Respective results can be retrieved from Table 2.

[0230] For additional comparison, CE2, CE3, and CE4 have also been measured, wherein

[0231] CE2 is EMDA-6147 commercially available from Equate,

[0232] CE3 is HDPE BM1052J commercially available from Sabie,

[0233] CE4 is HDPE HPA 020HDZ commercially available from ExxonMobil.

[0234] The above properties indicate that the inventive examples IE1 and IE2 exhibit superior properties than the comparative examples. These balanced properties are achieved by adjustment of the process design parameters to influence the homogeneity of the polyethylene thereby reducing the gels in the polymers and improving the mechanical properties performance for blow molding applications. Furthermore, the combination of broader MWD with 1-hexene as comonomer leads to higher environmental stress crack resistance and improved impact properties.

[0235] The blow-molded articles such as drums, jerrycans, or IBC products, produced from inventive examples IE1 and IE2 have higher mechanical performance in terms of rigidity, top load, and drop test. This rigidity combines with drop test resistance to allow for further down gauging, so that these articles can be produced about 10-20% lighter than articles known from the prior art.

[0236] The test films consisting of a single layer of 40 pm thickness were prepared using a large-scale single layer blown film line (Reifenhauser Machinery). The die diameter was 150 mm, die gap was 1 .2 mm, the total film thickness of film was 40 pm. The high neckheight and blow-up ratio (BUR) was 4.0. The extrusion conditions and film properties are listed in Table 3. orouge / Borealis - 32 - A19270EP

[0237] Table 2: Melt flow behavior, comonomer content, and mechanical properties of tested compositions (pellets) n.m. = not measured

[0238] Table 3: Extrusion conditions for the test film production

[0239] All samples were easy to process and exhibited good bubble stability. The film produced from the inventive example IE1 has a higher tensile modulus maintaining the toughness of the film (cf. Table 4). The film has a very low number of gels due to the unique design of the product (cf. Table 5). The tear strength and dart drop impact strength of the film is better than the tear strength of the comparative example CE2 (cf. Table 4).

[0240] Table 4: Mechanical properties of 40 micron blown film of IE1 and CE1 samples

[0241] Table 5: OCS gel analysis on 70 micron film samples of IE1, IE2 and CE1

Claims

Claims1. A polyethylene composition comprising a base resin which comprises(A) a first ethylene homopolymer fraction, and(B) a second ethylene-hexene-1 copolymer fraction, wherein fraction (A) has a lower molecular weight than fraction (B), wherein the base resin comprises fraction (A) in an amount of at least 43.0 wt.% based on the total weight of the base resin, wherein the base resin comprises fraction (B) in an amount of equal to or lower than 57.0 wt.% based on the total weight of the base resin, wherein the base resin has a loss tangent (tan 5) at 300 rad / s measured according to ISO 6721 of lower than 0.500, wherein the polyethylene composition has a density determined according to ISO 1183-1 :2022 - method A in the range of from 950 to 956 kg / m3, wherein the polyethylene composition has a melt flow rate MFRs determined according to ISO 1133 at 190 °C and at a loading of 5 kg in the range of from 0.15 to 0.6 g / 10 min, wherein the polyethylene composition has a flow rate ratio FRR21 / 5 in the range of from 17 to 36, wherein the polyethylene composition has a molecular weight distribution MWD determined by Gel Permeation Chromatography (GPC) according to ISO 16014- 1 :2003 of equal to or more than 27.

2. The polyethylene composition according to claim 1 , wherein the base resin comprises fraction (A) in an amount of least 44.0 wt.%, based on the total weight of the base resin.

3. The polyethylene composition according to claims 1 or 2, wherein the base resin comprises fraction (B) in an amount equal to or lower than 56.0 wt.%, preferably equal to or lower than 55.0 wt.%, based on the total weight of the base resin.

4. The polyethylene composition according to any of the preceding claims 1 to 3, wherein the fraction (A) has a density determined according to ISO 1183-1 :2022- method A in the range of from 965 to 975 kg / m3, preferably in the range of from 967 to 975 kg / m3, and most preferably in the range of from 970 to 974 kg / m3.

5. The polyethylene composition according to any of the preceding claims 1 to 4, wherein the fraction (A) has a MFR2 determined according to ISO 1133 at 190 °C and at a loading of 2.16 kg in the range of from 150 to 500 g / 10 min.

6. The polyethylene composition according to any of the preceding claims 1 to 5, wherein the fraction (B) has a density calculated as disclosed in the description in the range of from 930 to 946 kg / m3, preferably in the range of from 932 to 944 kg / m3, and most preferably in the range of from 935 to 942 kg / m3.

7. The polyethylene composition according to any of the preceding claims 1 to 6, wherein the fraction (B) has a MFR5 calculated as disclosed in the description in the range of from 0.25 to 0.50 g / 10 min.

8. The polyethylene composition according to any of the preceding claims 1 to 7, wherein the base resin of the polyethylene composition has a melt flow rate MFR21 determined according to ISO 1133 at 190 °C and at a loading of 21.6 kg of 4 to 16 g / 10 min, preferably of 5 to 13 g / 10 min, and more preferably of 7 to 11 g / 10 min.

9. The polyethylene composition according to any of the preceding claims 1 to 8, wherein the polyethylene composition has an oxygen induction time (OIT) determined according to ISO 11357-6 at a temperature of 210 °C of at least 30 min, preferably of at least 35 min, more preferably of at least 40 min, and most preferably of at least 44 min.

10. The polyethylene composition according to any of the preceding claims 1 to 9, wherein the polyethylene composition has an environmental stress crack resistance determined according to ASTM D1693 condition B of more than 1000 h, preferably more than 1500 h, and most preferably more than 3000 h.

11. A process for producing a polyethylene composition according to any one of the preceding claims 1 to 10 comprising the steps of: pre-polymerizing in a first polymerizing step in the presence of catalyst / cocatalyst, ethylene and comonomer butene-1. Further transferring the pre-polymerized contents to a second polymerization reactor for producing a first intermediate material comprising fraction (A) of the base resin; transferring the second intermediate material into a third polymerization reactor;polymerizing in a third polymerizing step ethylene and hexene-1 in the presence of the first intermediate material for producing a base resin comprising fraction (A) and fraction (B); compounding the base resin to obtain the polyethylene composition.

12. An article comprising the polyethylene composition according to any of the preceding claims 1 to 10, wherein the article preferably is a film or a molded article.

13. The article according to claim 12, wherein the film has at least one of the following properties: a tensile modulus in machine direction (TM-MD) measured according to ASTM D 882 of at least 700 MPa, preferably at least 750 MPa; a tensile modulus in transverse direction (TM-TD) measured according to ASTM D 882 of at least 800 MPa, preferably at least 1000 MPa; an elongation at break in machine direction (EB-MD) measured according to ISO 527-3 of at least 470%, preferably at least 500%, and most preferably at least 530%; an Elmendorf tear strength in transverse direction (ETS-TD) measured according to ASTM D 1922 of at least 4.5 N, preferably at least 5.0 N, and most preferably at least 5.5 N; an Elmendorf tear strength in machine direction (ETS-MD) measured according to ASTM D 1922 of at least 0.4 N, preferably of at least 0.5 N, and most preferably of at least 0.6 N; a gel content having a size of 100-300 pm diameter of not more than 30 pcs / m2, more preferably of not more than20 pcs / m2; a gel content having a size of 301-600 pm diameter of not more than 5 pcs / m2, preferably of not more than 4 pcs / m2, and most preferably of not more than 2 pcs / m2; a dart drop impact (DDI) strength measured according to ASTM D1709, method A, of more than 300 g, preferably more than 330 g, and most preferably more than 350 g.

14. The use of a polyethylene composition according to any one of claims 1 to 10 for the production of an article, preferably a film or a molded article.

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