WO2021028159A1

WO2021028159A1 - Multimodal polyethylene

Info

Publication number: WO2021028159A1
Application number: PCT/EP2020/070484
Authority: WO
Inventors: Thomas LANGSTRAAT; Shaneesh VADAKE KULANGARA; Matthijs Van Kessel
Original assignee: Sabic Global Technologies B.V.
Priority date: 2019-08-12
Filing date: 2020-07-20
Publication date: 2021-02-18
Also published as: EP4013799A1; CN114222767A

Abstract

The invention relates to a multimodal ethylene polymer which has a density of 0.955 to 0.960 g/cm3 at 23 °C, a melt flow index as measured according to ISO1133-1:2011 at 190 ºC and 5 kg of 0.9 to 1.7 dg/min and a ratio of Mz/Mw of at least 7.0, and which comprises 40 to 53 wt% of a low-molecular-mass ethylene polymer component A, 25 to 40 wt% of a high-molecular-mass ethylene polymer component B and 15 to 28 wt% of an ultrahigh-molecular-mass ethylene polymer component C, wherein all values are based on the total weight of the multimodal ethylene polymer, wherein the multimodal ethylene polymer is prepared by polymerizing the component A, subsequently polymerizing the component B in the presence of the component A and subsequently polymerizing the component C in the presence of the components A and B and the ethylene polymer component A has a viscosity number VN1 of 90 to 110 cm3/g, for example 95 to 105 cm3/g, the mixture of the ethylene polymer component A and the ethylene polymer component B has a viscosity number VN2 of 175 to 225 cm3/g, for example 180 to 220 cm3/g, and the mixture of the ethylene polymer component A, the ethylene polymer component B and the ethylene polymer component C has a viscosity number VN3 of 240 to 320 cm3/g, for example 250 to 300 cm3/g, wherein VN1, VN2 and VN3 are measured according to ISO/R 1191 in decalin at 135 ºC.

Description

MULTIMODAL POLYETHYLENE

The present invention relates to a multimodal, preferably trimodal, polyethylene and use of such polyethylene in blow moulding applications.

Compositions comprising an ethylene copolymer are used in many application fields for example in blow-molding applications. Blow molding is a molding process commonly used to produce for example household and industrial containers. In a blow molding process the polyethylene is melted and extruded into a mold and compressed air is used to inflate and shape the polymer into the desired form. Important properties of the polymer to be molded are its mechanical properties which, in turn, determine the properties of the final molded article. The key properties for blow moulding application are good processability, as characterized by good die swell and high shear thinning index. This in combination with good environmental stress cracking resistance (ESCR) properties as indicated by high strain hardening modulus will enable optimum wall thickness control for the production of hollow articles and facilitates excellent weld line formation whilst offering potential for down gauging.

EP1576047B1 discloses a polyethylene composition with multimodal molecular mass distribution, which has a density in the range from 0.955 to 0.960 g/cm³ at 23 °C and an MF1190/5 in the range from 0.8 to 1 .6 dg/min, and which comprises from 45 to 55 % by weight of a low-molecular-mass ethylene homopolymer A, from 20 to 35 % by weight of a high-molecular-mass copolymer B made from ethylene and from another 1- olefin having from 4 to 8 carbon atoms, and from 20 to 30 % by weight of an ultrahigh- molecular-mass ethylene copolymer C. According to EP1576047B1 , the polyethylene composition is suitable for blow molding.

WO2018/046711 discloses a process for producing a multimodal polyethylene composition by polymerization in three reactors. A hydrogen removal unit is arranged between the first reactor and the second reactor. There is an ongoing need to provide an ethylene polymer suitable for use in blow molding which has a combination of good processability and good ESCR. It is an object of the invention to provide an ethylene polymer in which above- mentioned and/or other problems are solved.

Accordingly, the present invention provides a multimodal ethylene polymer which has a density of 0.955 to 0.960 g/cm³ at 23 °C, a melt flow index as measured according to IS01133-1 :2011 at 190 ^SC and 5 kg of 0.9 to 1.7 dg/min and a ratio of Mz/Mw of at least 7.0, and which comprises

40 to 53 wt% of a low-molecular-mass ethylene polymer component A,

25 to 40 wt% of a high-molecular-mass ethylene polymer component B and 15 to 28 wt% of an ultrahigh-molecular-mass ethylene polymer component C, wherein all values are based on the total weight of the multimodal ethylene polymer.

The present invention provides a multimodal ethylene polymer which has a density of 0.955 to 0.960 g/cm³ at 23 °C, a melt flow index as measured according to IS01133- 1 :2011 at 190 ^SC and 5 kg of 0.9 to 1 .7 dg/min and a ratio of Mz/Mw of at least 7.0, and which comprises

40 to 53 wt% of a low-molecular-mass ethylene polymer component A,

25 to 40 wt% of a high-molecular-mass ethylene polymer component B and 15 to 28 wt% of an ultrahigh-molecular-mass ethylene polymer component C, wherein all values are based on the total weight of the multimodal ethylene polymer, wherein the multimodal ethylene polymer is prepared by polymerizing the component A, subsequently polymerizing the component B in the presence of the component A and subsequently polymerizing the component C in the presence of the components A and B and the ethylene polymer component A has a viscosity number VNi of 90 to 110 cm³/g, for example 95 to 105 cm³/g, the mixture of the ethylene polymer component A and the ethylene polymer component B has a viscosity number VN₂ of 175 to 225 cm³/g, for example 180 to 220 cm³/g, and the mixture of the ethylene polymer component A, the ethylene polymer component B and the ethylene polymer component C has a viscosity number VN₃ of 240 to 320 cm³/g, for example 250 to 300 cm³/g, wherein VNi, VN₂ and VN₃ are measured according to ISO/R 1191 in decalin at 135 ^SC

It was surprisingly found that the multimodal ethylene polymer according to the invention has a combination of good processability and good ESCR. Multimodal ethylene polymer

By ethylene polymer is meant a polymer the majority by weight of which derives from ethylene monomer units. The ethylene polymer may be an ethylene homopolymer or a copolymer of ethylene and a C3-C20 comonomer. The C3-C20 comonomer is preferably selected from the group consisting of C3-10 a-olefins such as propylene, 1 - butene, 1 -hexene and 1-octene. Preferably, the ethylene polymer is an ethylene-1 - butene copolymer.

The ethylene polymer according to the invention has a density of 955 to 960 g/cm³, preferably 956 to 959 g/cm³.

The ethylene polymer according to the invention has a melt flow index as measured according to IS01133-1 :2011 at 190 ^SC and 5 kg (MF1190_/5) of 0.9 to 1 .7 dg/min, preferably 1 .0 to 1 .5 dg/min.

Preferably, the ethylene polymer according to the invention has a melt flow index as measured according to IS01133-1 :2011 at 190 ^SC and 21 .6 kg (MFI 190/21.6) of 10 to 40 dg/min, preferably 20 to 30 dg/min. The melt flow index and the density of the multimodal ethylene polymer according to the invention are measured for a pelletized ethylene polymer.

The ethylene polymer according to the invention has a ratio of Mz/Mw of at least 7.0, for example 7.0 to 10.0, 7.1 to 9.0, 7.2 to 8.0. Mz/Mw is determined according to size exclusion chromatography as described in the experimental section. Such high Mz/Mw ratio was surprisingly found to result in the combination of good processability and good ESCR.

Preferably, the ethylene polymer according to the invention has a ratio of Mw/Mn of at least 22.0, preferably 23.0 to 33.0, more preferably 25.0 to 30.0. Mw/Mn is determined according to size exclusion chromatography as described in the experimental section. The advantage of such high Mw/Mn ratio is a good processability.

Preferably, the ethylene polymer according to the invention has a Flow Rate Ratio (FRR) calculated as M F 1190/21.e/M F 1190/5 of 10 to 30, preferably 15 to 25. FRR is indicative for the rheological broadness of the material. The ethylene polymer according to the invention has a relatively high Shear thinning index (SHI), which is a ratio of the viscosity of the polymer at a lower shear rate (e.g.

0.1 rad/s or 0.01 rad/s) to the viscosity of the polymer at a higher shear rate (e.g. 100 rad/s). High values of SHI are beneficial in that it means the viscosity is low at high shear rates where processability is important and the viscosity is high at low shear rates where dimension stability is important.

The viscosity values are calculated according to the method as described in the experimental section. hioo is the viscosity value in Pa.s at 190 ^SC and a shear rate of 100 rad/s.

Ho i is the viscosity value in Pa.s at 190 ^SC and a shear rate of 0.1 rad/s.

Ho.01 is the viscosity value in Pa.s at 190 ^SC and a shear rate of 0.01 rad/s.

Preferably, the ethylene polymer according to the invention has a shear thinning index SHI (ho.i / hioo) of at least 15, more preferably at least 17, for example 17 to 20.

Preferably, the ethylene polymer according to the invention has a shear thinning index SHI (ho.oi/ P100) of at least 25, more preferably at least 30, for example 30 to 35.

Preferably, the ethylene polymer according to the invention has a die swell of at least 1.40, more preferably at least 1 .50 to 1 .80, as determined according to IS011443:2014 at 200/s.

Preferably, the ethylene polymer according to the invention has a die swell of at least 1.70, more preferably at least 1 .80 to 2.10, as determined according to IS011443:2014 at 400/s.

Preferably, the ethylene polymer according to the invention has a die swell of at least 2.10, more preferably at least 2.20 to 2.50, as determined according to IS011443:2014 at 800/s.

Preferably, the ethylene polymer according to the invention has a die swell of at least 2.60, more preferably at least 2.80 to 3.00, as determined according to IS011443:2014 at 1600/s. Advantageously, the ethylene polymer according to the invention results in a smooth extrudate free from melt fracture or shark skin in the measurement of the die swell. Preferably, the ethylene polymer according to the invention has a strain hardening modulus determined according to ISO 18488:2014 of at least 15 MPa, preferably at least 17 MPa.

Ethylene polymer components A, B and C

The ethylene polymer according to the invention comprises ethylene polymer component A, ethylene polymer component B and ethylene polymer component C. The ethylene polymer according to the invention may comprise polymer components other than polymer components A, B and C. Preferably however, the ethylene polymer according to the invention does not comprise polymer components other than polymer components A, B and C. Preferably, the total of polymers A, B and C is at least 80 wt%, preferably at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% of the ethylene polymer according to the invention.

The amount of the ethylene polymer component A in the ethylene polymer according to the invention is 40 to 53 wt%, for example 43 to 50 wt%.

The amount of the ethylene polymer component B in the ethylene polymer according to the invention is 25 to 40 wt%, for example 28 to 35 wt%.

The amount of the ethylene polymer component C in the ethylene polymer according to the invention is 15 to 28 wt%, for example 18 to 25 wt%. When the ethylene polymer according to the invention is produced with a multi-step polymerisation process using cascaded reactors, the amount of the ethylene fed in each of the polymerization steps may herein be used as the amount of each of the ethylene polymer components in the ethylene polymer according to the invention. The ethylene polymer component A may be an ethylene homopolymer or a copolymer of ethylene and a C3-C20 comonomer. The C3-C20 comonomer is preferably selected from the group consisting of C3-10 a-olefins such as propylene, 1 -butene, 1 -hexene and 1-octene. If the ethylene polymer component A is a copolymer, the ethylene polymer component A is preferably a copolymer of ethylene and 1 -butene. If the ethylene polymer component A is a copolymer, the amount of the comonomer units in the ethylene polymer component A is preferably 0.001 to 1 .5 mol%, for example 0.01 to 0.1 mol%. Preferably, however, the ethylene polymer component A is an ethylene homopolymer.

The ethylene polymer component B may be an ethylene homopolymer or a copolymer of ethylene and a C3-C20 comonomer. The C3-C20 comonomer is preferably selected from the group consisting of C3-10 a-olefins such as propylene, 1 -butene, 1 -hexene and 1-octene. Preferably, the ethylene polymer component B is a copolymer of ethylene and a C3-C20 comonomer, most preferably a copolymer of ethylene and 1- butene. Preferably, the amount of the comonomer units in the ethylene polymer component B is 0.1 to 0.8 mol%, for example 0.2 to 0.5 mol%. The ethylene polymer component B has a higher molar amount of comonomer units than that of the ethylene polymer component A. The ethylene polymer component B has a density lower than that of the ethylene polymer component A. The ethylene polymer component B has a melt flow index lower than that of the ethylene polymer component A.

The ethylene polymer component C may be an ethylene homopolymer or a copolymer of ethylene and a C3-C20 comonomer. The C3-C20 comonomer is preferably selected from the group consisting of C3-10 a-olefins such as propylene, 1 -butene, 1 -hexene and 1-octene. Preferably, the ethylene polymer component C is a copolymer of ethylene and a C3-C20 comonomer, most preferably a copolymer of ethylene and 1- butene. Preferably, the amount of the comonomer units in the ethylene polymer component C is 0.3 to 1 .5 mol%, for example 0.4 to 1 .0 mol%. Typically, the ethylene polymer component C has a higher molar amount of comonomer units than that of the ethylene polymer component B, although it is possible that the ethylene polymer component C has an equal or lower molar amount of comonomer units than that of the ethylene polymer component B. Typically, the ethylene polymer component C has a density lower than that of the ethylene polymer component B, although it is possible that the ethylene polymer component C has an equal or lower molar amount of comonomer units than that of the ethylene polymer component B. The ethylene polymer component C has a melt flow index lower than that of the ethylene polymer component B.

The amount of the comonomer units in each of the ethylene polymer components may be determined by the method as described in the experimental section. The ethylene polymer according to the invention is multimodal, i.e. has a multimodal molecular mass distribution. Preferably, the ethylene polymer according to the invention is trimodal, i.e. has a trimodal molecular mass distribution.

The trimodality is a measure of the position of the centers of gravity of the three individual molecular mass distributions, and can be described with the aid of the viscosity number VN to ISO/R 1191 of the polymers formed in the successive polymerization stages. The relevant band widths for the polymers formed in each of the stages of the reaction are therefore as follows:

The viscosity number VNi measured on the polymer after the first polymerization stage is identical with the viscosity number VN_A of the low-molecular-mass polyethylene A and according to the invention is preferably in the range of from 90 to 110 cm³/g, for example 95 to 105 cm³/g.

The viscosity number VN₂ measured on the polymer after the second polymerization stage is not equal to VN_B of the high-molecular-mass polyethylene B formed in the second polymerization stage, which can only be determined by calculation, but rather represents the viscosity number of the mixture of polymer A and polymer B. According to the invention, VN₂ is preferably in the range of from 175 to 225 cm³/g, for example 180 to 220 cm³/g.

The viscosity number VN₃ measured on the polymer after the third polymerization stage is not equal to VN_C of the ultra-high-molecular-mass copolymer C formed in the third polymerization stage, which can only be determined by calculation, but rather represents the viscosity number of the mixture of polymer A, polymer B and polymer C. According to the invention, VN₃ is preferably in the range of from 240 to 320 cm³/g, for example 250 to 300 cm³/g.

Preferably, the ethylene polymer component A has a density of at least 968 g/cm³, preferably 969 to 971 g/cm³.

Preferably, the ethylene polymer component A has a melt flow index as measured according to IS01133-1 :2011 at 190 ^SC and 1 .2 kg of 10 to 60 dg/min, preferably 15 to 35 dg/min. Preferably, the mixture of ethylene polymer component A and ethylene polymer component B has a density of 960 to 965 g/cm³.

Preferably, the mixture of ethylene polymer component A and ethylene polymer component B has a melt flow index as measured according to IS01133-1 :2011 at 190 ^SC and 5 kg of 5 to 15 dg/min, preferably 7 to 12 dg/min.

Preferably, the mixture of ethylene polymer component A, ethylene polymer component B and ethylene polymer component C has a density of 955 to 960 g/cm³.

Preferably, the mixture of ethylene polymer component A, ethylene polymer component B and ethylene polymer component C has a melt flow index as measured according to IS01133-1 :2011 at 190 ^SC and 5 kg of 0.5 to 2.0 dg/min.

The density and melt flow index of A, mixture of A and B and mixture of A, B and C are typically measured for the powder obtained after each of the polymerization steps.

Process for preparation of ethylene polymer

Preferably, the ethylene polymer according to the invention is produced with a multi- step slurry polymerisation process using cascaded reactors in the presence of a Ziegler Natta catalyst system.

The ethylene polymer according to the invention may be prepared by a process comprising producing the component A, the component B and the component C as a trimodal ethylene polymer made by polymerizing the component A, subsequently polymerizing the component B in the presence of the component A and subsequently polymerizing the component C in the presence of the components A and B.

Accordingly, the invention provides a process for the preparation of the ethylene polymer according to the invention, wherein the process comprises a sequential polymerization process comprising at least three reactors connected in series, wherein said process comprises the steps of

- preparing the component A in a first reactor under a first set of conditions,

- transferring the component A and unreacted monomers of the first reactor to a second reactor,

- feeding monomers to the second reactor,

- preparing the component B in the second reactor in the presence of the component A under a second set of conditions, - transferring the component A, the component B and unreacted monomers of the second reactor to a third reactor,

- feeding monomers to the third reactor,

- preparing the component C in the third reactor in the presence of the component A and the component B under a third set of conditions, wherein the first set of conditions, the second set of conditions and the third set of conditions are different from each other.

The order of the preparation of components A, B and C may be different from the one described above. Thus, all possible orders are considered to be disclosed herein: component A in reactor 1 , component B in reactor 2, component C in reactor 3 (embodiment described above); component A in reactor 1 , component C in reactor 2, component B in reactor 3; component B in reactor 1 , component A in reactor 2, component C in reactor 3; component B in reactor 1 , component C in reactor 2, component C in reactor 3; component C in reactor 1 , component A in reactor 2, component B in reactor 3; component C in reactor 1 , component B in reactor 2, component A in reactor 3;

The polymerization process may be performed in suspension at temperatures of e.g.

70 to 100 °C, preferably 75 to 90 °C and a pressure of e.g. 0.15 to 10 bar. The molecular mass of each of components A, B and C may be regulated by a molar mass regulator, preferably by hydrogen.

The multi-step slurry polymerisation process using cascaded reactors is per se well- known and details thereof are further described e.g. in W02007022908, p.5, 1.32- p.8, 1.1 , incorporated herein by reference.

Preferably, the ethylene polymer according to the invention is produced with a multi- step slurry polymerisation process of ethylene using cascaded reactors in the presence of a catalyst system comprising (I) the solid reaction product obtained by reaction of: a) a hydrocarbon solution containing

1) an organic oxygen containing magnesium compound or a halogen containing magnesium compound and

2) an organic oxygen containing titanium compound and b) an aluminium halogenide having the formula AIR_n X₃-n in which R is a hydrocarbon moiety containing 1 - 10 carbon atoms , X is halogen and 0 < n < 3 and

(II) an aluminium compound having the formula AIR3 in which R is a hydrocarbon moiety containing 1 - 10 carbon atoms.

During the reaction of the hydrocarbon solution comprising the organic oxygen containing magnesium compound and the organic oxygen containing titanium compound with component (I b) a solid catalyst precursor precipitates and after the precipitation reaction the resulting mixture is heated to finish the reaction.

The aluminium compound (II) is dosed prior to or during the polymerization and may be referred to as a cocatalyst.

The multi-step slurry polymerisation process may be a three-step slurry polymerisation process.

Preferably, the diluent in the slurry polymerisation process is a diluent consisting of aliphatic hydrocarbon compounds that displays an atmospheric boiling temperature of at least 35°C, more preferred above 55°C. Suitable diluent is hexane and heptane. The preferred diluent is hexane.

Suitable organic oxygen containing magnesium compounds include for example magnesium alkoxides such as magnesium methylate, magnesium ethylate and magnesium isopropylate and alkylalkoxides such as magnesium ethylethylate and so called carbonized magnesiumalkoxide such as magnesium ethyl carbonate. Preferably, the organic oxygen containing magnesium compound is a magnesium alkoxide. Preferably the magnesium alkoxide is magnesium ethoxide Mg(OC2H )2 .

Suitable halogen containing magnesium compounds include for example magnesium dihalides and magnesium dihalide complexes wherein the halide is preferably chlorine.

Preferably the hydrocarbon solution comprises an organic oxygen containing magnesium compound as (I) (a) (1). Suitable organic oxygen containing titanium compound may be represented by the general formula [TiO_x (OR)4-2x]n in which R represents an organic moiety, x ranges between 0 and 1 and n ranges between 1 and 6.

Suitable examples of organic oxygen containing titanium compounds include alkoxides, phenoxides, oxyalkoxides, condensed alkoxides, carboxylates and enolates. Preferably the organic oxygen containing titanium compounds is a titanium alkoxide. Suitable alkoxides include for example Ti (CX^Hs Ti (OC3H₇)4, TiOC₄H₉)₄ and Ti(OC8Hi₇)4. Preferably the organic oxygen containing titanium compound is Ti ((C HQH

Preferably the aluminium halogenide is a compound having the formula AIR_n X3-_n in which R is a hydrocarbon moiety containing 1 - 10 carbon atoms , X is halogen and 0.5 < n < 2. Suitable examples of the aluminium halogenide in (I) b having the formula AIR_nX3-_n include ethyl aluminium dibromide, ethyl aluminium dichloride, propyl aluminium dichloride, n- butyl aluminium dichloride, iso butyl aluminium dichloride, diethyl aluminium chloride, diisobutyl aluminium chloride,. Preferably X is Cl. Preferably the organo aluminium halogenide in (I) b) is an organo aluminium chloride, more preferably the organo aluminium halogenide in (I) b) is chosen from ethyl aluminium dichloride, diethyl aluminium dichloride, isobutyl aluminium dichloride, diisobutyl aluminium chloride or mixtures thereof.

Generally the molar ratio of Al from I b): Ti from I a) 2 ranges between 3:1 and 16:1. According to a preferred embodiment of the invention the molar ratio of Al from I b): Ti from I a) 2 ranges between 6:1 and 10:1.

Suitable examplesl of the cocatalyst of the formula AIR₃ include tri ethyl aluminium, tri isobutyl aluminium, tri-n-hexyl aluminium and tri octyl aluminium. Preferably the aluminium compound in (II) of the formula AIR₃ is tri ethyl aluminium or tri isobutyl aluminium.

The hydrocarbon solution of organic oxygen containing magnesium compound and organic oxygen containing titanium compound can be prepared according to procedures as disclosed for example in US 4178300 and EP0876318. The solutions are in general clear liquids. In case there are any solid particles, these can be removed via filtration prior to the use of the solution in the catalyst synthesis. Generally the molar ratio of magnesium: titanium is lower than 3:1 and preferably the molar ratio magnesium: titanium ranges between 0, 2:1 and 3:1. Generally the molar ratio of aluminium from (II): titanium from (a) ranges between 1 :1 and 300:1 and preferably the molar ratio of aluminium from (II): titanium from (a) ranges between 3:1 and 100:1.

The catalyst may be obtained by a first reaction between a magnesium alkoxide and a titanium alkoxide, followed by dilution with a hydrocarbon solvent, resulting in a soluble complex consisting of a magnesium alkoxide and a titanium alkoxide and thereafter a reaction between a hydrocarbon solution of said complex and the organo aluminium halogenide having the formula AIR_nX3-_n Optionally an electron donor can be added either during the preparation of the solid catalytic complex (at the same time as the subsequent step or in an additional step) or at the polymerization stage. The addition of an electron donor is for example disclosed in WO2013087167. Generally, the aluminium halogenide having the formula AIR_nX3-_n is used as a solution in a hydrocarbon. Any hydrocarbon that does not react with the organo aluminium halogenide is suitable to be applied as the hydrocarbon.

The sequence of the addition can be either adding the hydrocarbon solution containing the organic oxygen containing magnesium compound and organic oxygen containing titanium compound to the compound having the formula AIR_nX3-_n or the reversed.

The temperature for this reaction can be any temperature below the boiling point of the used hydrocarbon. Generally the duration of the addition is preferably shorter than 1 hour.

In the reaction of the hydrocarbon solution of the organic oxygen containing magnesium compound and the organic oxygen containing titanium compound with the organo aluminium halogenide of formula AIR_nX3-_n, the solid catalyst precursor precipitates. After the precipitation reaction the resulting mixture is heated for a certain period of time to finish the reaction. After the reaction the precipitate is filtered and washed with a hydrocarbon. Other means of separation of the solids from the diluents and subsequent washings can also be applied, like for example multiple decantation steps. All steps should be performed in an inert atmosphere of nitrogen or another suitable inert gas.

Further aspects

The present invention further relates to a composition comprising the ethylene polymer according to the invention. The composition may consist of the ethylene polymer according to the invention and additives such as pigments, nucleating agents, antistatic agents, fillers, antioxidants etc. The amount of the additives in the composition is generally up to 10% by weight, preferably up to 5% by weight of the composition.

The present invention further relates to an article comprising the ethylene polymer according to the invention or the composition according to the invention. Preferably, the article is a blow molded article.

It is noted that the invention relates to all possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the composition according to the invention; all combinations of features relating to the process according to the invention and all combinations of features relating to the composition according to the invention and features relating to the process according to the invention are described herein. It is further noted that the term ‘comprising’ does not exclude the presence of other elements. However, it is also to be understood that a description on a product/composition comprising certain components also discloses a product/composition consisting of these components. The product/composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product/composition. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps. The process consisting of these steps may be advantageous in that it offers a simpler, more economical process. When values are mentioned for a lower limit and an upper limit for a parameter, ranges made by the combinations of the values of the lower limit and the values of the upper limit are also understood to be disclosed. The invention is now elucidated by way of the following examples, without however being limited thereto. Catalyst preparation Experiment I

Preparation of a hydrocarbon solution comprising the organic oxygen containing magnesium compound and the organic oxygen containing titanium compound

100 grams of granular Mg(OC H and 150 millilitres of Ti(OC H were brought in a 2 litre round bottomed flask equipped with a reflux condensor and stirrer. While gently stirring, the mixture was heated to 180°C and subsequently stirred for 1.5 hours. During this, a clear liquid was obtained. The mixture was cooled down to 120°C and subsequently diluted with 1480 ml of hexane. Upon addition of the hexane, the mixture cooled further down to 67°C. The mixture was kept at this temperature for 2 hours and subsequently cooled down to room temperature. The resulting clear solution was stored under nitrogen atmosphere and was used as obtained. Analyses on the solution showed a titanium concentration of 0.25 mol/l.

Experiment II Preparation of the catalyst

In a 0.8 liters glass reactor, equipped with baffles, reflux condenser and stirrer, 424 ml hexane and 160 ml of the complex from Experiment I were dosed. The stirrer was set at 1200 RPM. In a separate flask, 100 ml of 50% ethyl aluminum dichloride (EADC) solution was added to 55 ml. of hexane. The resulting EADC solution was dosed into the reactor in 15 minutes using a peristaltic pump. Subsequently, the mixture was refluxed for 2 hours. After cooling down to ambient temperature, the obtained red/brown suspension was transferred to a glass P4 filter and the solids were separated. The solids were washed 3 times using 500 ml of hexane. The solids were taken up in 0.5 L of hexane and the resulting slurry was stored under nitrogen. The solid content was 64 g ml^-1 Catalyst analysis results:

Ti 10.8 wt%; Mg 11 .2 wt%; Al 5.0 wt%; Cl 65 wt%; OEt 3.2 wt% and OBu 2.6 wt%. Polymerization A copolymer of ethylene and 1 -butene was prepared in three reactors R1 , R2, R3 connected in series, separated by two flash vessel. All the three reactors are identical in size (20L) and during normal production the level in each reactor is controlled at 75% by the discharge frequency. Hexane was used as a diluent. The hydrogen and comonomer (1 -butene) feeds to each reactor were controlled separately. The hydrogen was used to control the molecular weight and the 1 -butene was used to control the density. The composition of the gas cap in each reactor was analyzed by gas chromatography (GC). The temperature in R1 , R2 and R3 was 84 ^SC.

The catalyst prepared by Experiment II and a cocatalyst (tri isobutyl aluminium) were dosed to the first reactor R1 . The Al concentration in the first reactor was 21 .3 ppm.

The ethylene pressure in R1 was controlled by the amount of catalyst dosed to the reactor. Hydrogen was dosed to R1 to control the MFI of the polymer. A low molecular weight homopolymer A was produced in R1 . The gas cap in the reactor was analyzed by GC. In the first reactor ~10 - 15% of nitrogen was analyzed.

The reason for the presence of nitrogen in R1 is because the vessel of the diluent was kept under 15 bar nitrogen. The diluent was added to the reactors by the difference in pressure (no pump). Typical residence time in the first reactor was ~3.6 hours.

The slurry was continuously discharged from the first reactor into the first flash vessel. In the first flash vessel, the unreacted hydrogen and ethylene gasses were removed as much as possible before the slurry was pumped into the second reactor. Typical pressure in the flash vessel was 0.1 bar and temperatures were between 32 - 45°C. The pressure in the flash vessel was controlled at 0.1 bar.

In the second reactor R2 fresh hexane was added together with ethylene, hydrogen and 1 -butene. The level in R2 was controlled at 75% by the discharge to the second flash vessel. The gas cap in the second reactor was analyzed by GC. Hydrogen was used to steer the MFI within the specification of MFI 8-12 and 1 -butene was used to steer the density of the polymer within the specification of 960-964 g/cm³. A high molecular weight copolymer B was produced in R2. After an average residence time of ~2 hour the polymer slurry was discharged to the second flash vessel.

In the second flash vessel, the unreacted hydrogen, ethylene and 1 -butene gasses were removed as much as possible before the slurry was pumped into the third reactor.

In the third reactor R3 fresh hexane was added together with ethylene, hydrogen and 1 -butene. The level in R3 was controlled at 75% by the discharge to the decanter. The composition in the third reactor was analyzed by GC. To prevent clogging of the discharge lines, the pressure in the third reactor was increased with nitrogen to ~5 bars. Hydrogen was used to steer the MFI within the specification of 1.4-1.8 and 1 - butene was used to control the density of the final polymer within the specification of 955-959 g/cm³. An ultrahigh molecular weight copolymer C was produced in R1 . After residence time of 1 .3 hour the polymer slurry was discharged. The catalyst yield was 25.2 kg/g.

The weight ratio of ethylene fed to the reactors was 47:32:21 . Various conditions of the polymerization process are summarized in Table 1 . MFI, VN, density and the amount of 1 -butene of the polymer obtained from each of the reactors are also summarized in Table 1 .

Table 1

The obtained ethylene copolymer was pelletized and various properties were measured as shown in Table 2, along with the same properties of typical commercial products used for blow molding. Table 2

Critical - extrudate shows a rough surface as characterised by melt fracture / shark skin.

It can be understood that the polyethylene according to the invention has a combination of a good processability as shown by a high SHI and a high die swell and a good ESCR as shown by high SH modulus.

Upon measurement of the die swell at the highest shear rate (1600/s), CEx 1 and CEx 3 showed some melt fracture so the diameter of the strand could not be accurately measured. The polyethylene according to the invention having desirable processing properties did not show such behavior.

Further, the die swell at 72/s was measured for Ex 1 to be in the range of 1.17-1 .29. Further, tan delta at 600 rad/s was measured for Ex 1 to be 0.57.

Melt flow index MFI

MFI was measured according to ISO 1133-1 :2011 under a load of 1 .2kg, 5 kg and 21 .6 kg at 190°C. Measurements were made on samples wherein standard stabilizers have been added.

Viscosity number VN

VN was measured according to ISO/R 1191 in decalin at 135 ^SC. Density

Densities in table 1 were determined as follows:

Polymer powders from the reactor were compression moulded at 160°C followed by cooling at a rate of 40°C/min. Density of the moulded plaques was measured directly after moulding according to ISO 1183-1 :2012 at 23 ^SC. The measured density was converted to an annealed density (indicated in Table 1) using the formula:

Calculated annealed density (kg/m³) = Measured density (kg/m³) + 2.7 kg/m³

Densities in table 2 were determined as follows: Polymer granules were compression moulded according to ISO 1872-2. Density of the moulded plaques was measured according to ISO 1183-1 :2012 at 23 ^SC. Prior to the density measurement the moulded plaques were conditioned for > 16h at 23 ^SC, 50%RH. 1 -butene content

1 H-NMR measurements were performed for samples taken from each reactor, which may be a mixture of polymers A and B (second reactor) or a mixture of polymers A, B and C (third reactor). The comonomer contents in polymers B and C were calculated based on the proportions of polymers A, B and C in the samples.

Approximately 15mg of sample were dissolved at ~135°C in ~0.5ml of 1 ,1 ,2,2- tetrachloroethane-d2 (TCE-d2) / BHT stock solution using a 5mm NMR tube. The stock solution was made by dissolving ~2mg on BHT in 25ml of TCE-d2. Oxygen concentration in the tube was reduced by flushing the tube for ~1min with nitrogen before dissolution. The sample was periodically checked for homogeneity and manually mixed as necessary.

All NMR experiments were carried out on a Bruker 500 Avance III HD spectrometer equipped with a 10mm cryogenically cooled probe head operating at 125°C. The 1 H NMR measurements were performed using a spectral width of 20 ppm, an acquisition time of ~3.3s, a 30° excitation pulse and a relaxation delay of 10s between each of the 512 transients. The spectra were calibrated by setting the signal of TCE at 5.91 ppm.

Mz/Mw and Mw/Mn Mw, Mn and Mz were measured in accordance with ASTM D6474-12 (Standard Test Method for determining molecular weight distribution (MWD) and molecular weight Averages of Polyolefins by High Temperature Gel Permeation Chromatography). Mw stands for the weight average molecular weight and Mn stands for the number average weight. Mz stands for the z-average molecular weight. A high-temperature chromatograph Polymer Char GPC-IR system equipped with IR5 MCT detector and Polymer Char viscometer (Polymer Char S.A., Spain) was used at 160°C to determine the MWD and SCB as function of molecular weight. Three columns of Polymer Laboratories 13pm PLgel Olexis, 300 x 7.5mm, were used in series for GPC separation. 1 ,2,4-trichlorobenzene stabilized with 1 g/L butylhydroxytoluene (also known as 2,6-di-tert-butyl-4-methylphenol or BHT) was used as eluent at a flow rate of 1mL/min. Sample concentration was around 0.7mg/mL and injection volume was 300pL. The molar mass was determined based on the Universal GPC-principle using a calibration made with PE narrow and broad standards (in the range of 0.5-2800kg/mol, Mw/Mn - 4 to 15) in combination with known Mark Houwink constants of PE-calibrant (alfa = 0.725 and log K = -3.721 ).

Shear thinning index SHI

The viscosity value is calculated by fitting flow curves generated by oscillatory rheometer according to ISO6721-10 with a modified Carreau-Yasuda model, which is represented by the following equation:

where h is the viscosity in Pa.s

Ho is the zero shear viscosity (Pa.s) a is the rheological breadth parameter n is the power law constant, set to 0 in the present case (defines the slope of the high shear rate region)

Y is the shear rate (1/s) l is the relaxation time (s) hioo is the viscosity value in Pa.s at 190 ^SC and a shear rate of 100 rad/s. ho.i is the viscosity value in Pa.s at 190 ^SC and a shear rate of 0.1 rad/s.

Ho.01 is the viscosity value in Pa.s at 190 ^SC and a shear rate of 0.01 rad/s. To facilitate model fitting, the power law constant is held at a constant value, in this case zero. Details of the significance and interpretation of the Carreau-Yasuda model and derived parameters may be found in: C.A. Hieber and H.H. Chiang, Rheol Acta,

28, 321 (1989); C.A. Hieber and H.H. Chiang, Polym. Eng. Sci., 32, 931 (1992); and R.B. Bird, R.C. Armstrong and O. Hasseger, Dynamics of Polymeric Liquids, Volume 1 , Fluid Mechanics, 2^nd Edition, John Wiley & Sons (1987), each of which is incorporated by reference herein in its entirety.

Die swell

Die swell was measured at different shear rates according to IS011443:2014 on a Gottfert capillary rheometer equipped with a die of 1mm diameter and a length of 10mm with an 30° entrance angle. Measurements were performed at 190°C. Die swell was calculated from the diameter of the extrudate after crystallization measured with a caliper using the formula:

Die swell = (extudate diameter / die diameter)² - 1

Strain hardening modulus

The strain hardening modulus in the context of the present invention is used as an indicator for resistance to slow crack growth. Resistance to slow crack growth is related to the lifetime of ethylene polymers. The strain hardening modulus may be considered as a measure for the disentanglement capability of tie molecules in ethylene polymers. Tie molecules are those molecules that via physical entanglement form intermolecular interactions that for example contribute to the mechanical strength of an ethylene polymer. The strain hardening modulus is determined according to the method described in ISO DIS 18488 (2014), using test specimens of 0.30 mm thickness. The strain hardening modulus is determined as the slope of the Neo-Hookean constitutive model between a true strain of 8 and 12.

Tan delta

Tan delta is the parameter that represents the elasticity of the molten polymer, which strongly influences on the swelling ratio of the polymer. The Tan delta is determined by using controlled stress rheometer model DHR3 from TA instrument. The geometry is Plate-Plate 25mm diameter at the measurement gap Imm. The dynamic oscillatory shear performed under nitrogen atmosphere at 90°C. Tan (delta) 600 is calculated ratio of Loss modulus (G") and storage modulus (G') at angular frequency 600 rad/s.

Claims

1. A multimodal ethylene polymer which has a density of 0.955 to 0.960 g/cm³ at 23 °C, a melt flow index as measured according to IS01133-1 :2011 at 190 ^SC and 5 kg of 0.9 to 1 .7 dg/min and a ratio of Mz/Mw of at least 7.0, and which comprises 40 to 53 wt% of a low-molecular-mass ethylene polymer component A,

25 to 40 wt% of a high-molecular-mass ethylene polymer component B and 15 to 28 wt% of an ultrahigh-molecular-mass ethylene polymer component C, wherein all values are based on the total weight of the multimodal ethylene polymer, wherein the multimodal ethylene polymer is prepared by polymerizing the component A, subsequently polymerizing the component B in the presence of the component A and subsequently polymerizing the component C in the presence of the components A and B and the ethylene polymer component A has a viscosity number VNi of 90 to 110 cm³/g, for example 95 to 105 cm³/g, the mixture of the ethylene polymer component A and the ethylene polymer component B has a viscosity number VN₂ of 175 to 225 cm³/g, for example 180 to 220 cm³/g, and the mixture of the ethylene polymer component A, the ethylene polymer component B and the ethylene polymer component C has a viscosity number VN₃ of 240 to 320 cm³/g, for example 250 to 300 cm³/g, wherein VNi, VN₂ and VN₃ are measured according to ISO/R 1191 in decalin at 135 ^SC.

2. The ethylene polymer according to claim 1 , wherein the ethylene polymer has a density of 0.956 to 0.959 g/cm³ at 23 °C, a melt flow index as measured according to IS01133-1 :2011 at 190 ^SC and 5 kg of 1 .0 to 1 .5 dg/min, a melt flow index as measured according to IS01133-1 :2011 at 190 ^SC and 21 .6 kg of 10 to 40 dg/min, preferably 20 to 30 dg/min, and/or a ratio of Mz/Mw of 7.0 to 10.0, preferably 7.1 to 9.0 or 7.2 to 8.0.

3. The ethylene polymer according to any one of the preceding claims, wherein the amount of the ethylene polymer component A in the ethylene polymer is 43 to 50 wt%, the amount of the ethylene polymer component B in the ethylene polymer is 28 to 35 wt% and/or the amount of the ethylene polymer component C in the ethylene polymer is 18 to 25 wt%. 4. The ethylene polymer according to any one of the preceding claims, wherein the ethylene polymer component A is an ethylene homopolymer, the ethylene polymer component B is a copolymer of ethylene and a C3-10 a-olefin copolymer, preferably a copolymer of ethylene and 1 -butene, and wherein the amount of the comonomer units in the ethylene polymer component B is 0.1 to 0.8 mol%, for example 0.2 to 0.5 mol% and the ethylene polymer component C is a copolymer of ethylene and a C3-10 a-olefin copolymer, preferably a copolymer of ethylene and 1 -butene, and wherein the amount of the comonomer units in the ethylene polymer component C is 0.3 to 1 .5 mol%, for example 0.

4 to 1 .0 mol%.

5. The ethylene polymer according to any one of the preceding claims, wherein the total of the ethylene polymer components A, B and C is at least 80 wt%, at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% of the ethylene polymer.

6. The ethylene polymer according to any one of the preceding claims, wherein the ethylene polymer has a Flow Rate Ratio (FRR) calculated as MFI190_/21.6/MFI190/5 of 10 to 30, preferably 15 to 25.

7. The ethylene polymer according to any one of the preceding claims, wherein the ethylene polymer has a shear thinning index SHI (ho_.i/hioo) of at least 15, more preferably at least 17, for example 17 to 20, and/or a shear thinning index SHI (ho.oi/G|ioo) of at least 25, more preferably at least 30, for example 30 to 35, wherein hioo is the viscosity value in Pa.s at 190 ^SC and a shear rate of 100 rad/s.

Ho i is the viscosity value in Pa.s at 190 ^SC and a shear rate of 0.1 rad/s. ho.01 is the viscosity value in Pa.s at 190 ^SC and a shear rate of 0.01 rad/s, wherein P0.01 , P0.1 , Hioo are calculated by fitting flow curves generated by oscillatory rheometer according to IS06721 -10 with a modified Carreau-Yasuda model, which is represented by the following equation:

where h is the viscosity in Pa.s go is the zero shear viscosity (Pa.s) a is the rheological breadth parameter n is the power law constant, set to 0 Y is the shear rate (1/s) l is the relaxation time (s).

8. The ethylene polymer according to any one of the preceding claims, wherein the ethylene polymer has a die swell as determined according to IS011443:2014 of at least 1 .40, preferably at least 1.50 to 1.80, at 200/s, and/or at least 1 .70, preferably at least 1.80 to 2.10, at 400/s, and/or at least 2.10, preferably at least 2.20 to 2.50, at 800/s, and/or at least 2.60, preferably at least 2.80 to 3.00, at 1600/s.

9. The ethylene polymer according to any one of the preceding claims, wherein the ethylene polymer has a strain hardening modulus determined according to ISO 18488:2014 of at least 15 MPa, preferably at least 17 MPa.

10. The ethylene polymer according to any one of the preceding claims, wherein the ethylene polymer has a ratio of Mw/Mn of at least 22.0, preferably 23.0 to 33.0, more preferably 25.0 to 30.0.

11 . A process for the preparation of the ethylene polymer according to any one of the preceding claims which is a multi-step slurry polymerisation process using cascaded reactors in the presence of a Ziegler Natta catalyst system.

12. The process according to claim 11 , wherein the catalyst system comprises (I) the solid reaction product obtained by reaction of: a) a hydrocarbon solution containing

13. A composition consisting of the ethylene polymer according to any one of claims 1 - 10 and additives.

14. An article comprising the ethylene polymer according to any one of claims 1 -10 or the composition according to claim 13.

15. The article according to claim 14, wherein the article is a blow moulded article.