Multimodal ethylene copolymer compositions and films comprising same

Abstract

The present invention relates to a multimodal ethylene copolymer composition comprising: 5 to 25% by weight, relative to the total weight of the multimodal ethylene copolymer composition, of a first ethylene copolymer (A1) comprising a copolymer of ethylene and at least a first alpha-olefin comonomer having a density, determined according to ISO 1183-187, in the range of 920 to 960 kg / m3; 15 to 35% by weight, relative to the total weight of the multimodal ethylene copolymer composition, of a second ethylene copolymer (A2) comprising a copolymer of ethylene and at least a first alpha-olefin comonomer having a density, determined according to ISO 1183-187, in the range of 920 to 960 kg / m3; 40 to 80% by weight, relative to the total weight of the multimodal ethylene copolymer composition, of a third ethylene copolymer (B) comprising a copolymer of ethylene with at least the first and second alpha-olefin comonomers; wherein the third ethylene copolymer (B) has a higher weight average molecular weight (Mw) than the first ethylene copolymer (A1) and the second ethylene copolymer (A2); wherein the composition has a density in the range of from 915 to 930 kg / m3, as determined according to ISO 1183-187; an MFR5 in the range of from 0.5 to 5.0 g / 10 min, as determined according to ISO 1133; wherein the content of the second alpha-olefin comonomer in the third ethylene copolymer (B) is in the range of 15 to 85% based on the total comonomer content in the third ethylene copolymer (B) on a mole basis. Methods of making the compositions and films comprising the compositions are also disclosed.

Description

Technical Field

[0001] The present invention relates to a multimodal ethylene copolymer composition, a process for producing the multimodal ethylene copolymer composition and a film comprising the multimodal ethylene copolymer composition and / or obtainable by the process. In particular, the present invention relates to a multimodal ethylene copolymer composition and a film comprising the multimodal ethylene copolymer having an excellent balance of properties between impact resistance, tensile modulus and optical properties. Background Art

[0002] Linear low density polyethylene polymers (LLDPE) are used for a variety of applications. In particular, films for packaging are a highly relevant market for LLDPE. In order to protect the contents of the package, it is desirable that the film has good or even excellent mechanical properties, such as a high tensile modulus and / or high impact resistance. Excellent mechanical properties also allow the production of thinner films, thereby reducing the amount of polymer used to obtain the film.

[0003] Furthermore, it is known that films produced from LLDPE grades with high haze values ​​have a very particular appearance, which is popular in specific market segments.

[0004] Therefore, there is a need to develop LLDPE polymers having higher impact resistance while maintaining the tensile modulus and / or haze value of films made from such LLDPE polymers at a high level.

[0005] In particular, it is known to produce ethylene copolymers suitable for the production of films by copolymerizing ethylene in two polymerization stages, for example from EP-A-691367 which discloses bimodal ethylene copolymers produced in two fluidized bed reactors.

[0006] Furthermore, WO-A-20040009 discloses bimodal low density PE resins. This document does not disclose multimodal ethylene polymer compositions produced in three polymerisation stages.

[0007] EP-A-2067799 discloses multimodal LLDPE resins prepared in two polymerization stages in a loop and a gas phase reactor in the presence of a ligand modified catalyst. The document does not disclose a third polymerization stage.

[0008] EP-A-2246369 discloses LLDPE prepared in the presence of a Ziegler-Natta catalyst with a specific aluminum halide alkyl compound as a cocatalyst. Although the document briefly mentions a two-stage polymerization, its examples are one-stage polymerization runs. The document does not disclose any three-stage polymerization.

[0009] WO2015 / 086812 (EP2883887) describes a process for preparing a multimodal ethylene copolymer, wherein the process comprises polymerizing ethylene and a comonomer in three polymerization stages and further using the copolymer to prepare a film. The density of the ethylene copolymer produced according to the process is 906 to 925 kg / m 3 , MFR5 (190°C, 5.0kg load, 1501133) is 0.5 to 5.0g / 10min. The density of the copolymer produced in the first polymerization stage and the first copolymer mixture (a mixture of the first polymer and the polymer produced in the second stage) is 945 to 955kg / m 3 WO2020 / 136166A1 relates to a method for producing a multimodal ethylene polymer film composition, focusing on the impact properties of a film comprising the composition.

[0010] WO2020 / 136164A1 relates to multilayer films comprising ethylene copolymers and / or terpolymers. The document also emphasizes the importance of mechanical properties, more specifically impact properties.

[0011] It is therefore apparent that there remains a need to provide ethylene copolymer compositions suitable for film forming and / or packaging applications, the films having excellent mechanical properties, such as dart impact strength and tensile modulus.

[0012] Furthermore, it has been found that the market needs ethylene copolymer compositions which not only have excellent mechanical properties (which would allow a reduction in film thickness) but which at the same time meet specific requirements with regard to optical properties (haze, gloss, transparency).

[0013] The purpose of the present invention is to meet the above needs. Summary of the invention

[0014] In one aspect, the present invention provides a multimodal ethylene copolymer composition comprising:

[0015] - 5 to 25 wt.-% of a first ethylene copolymer (A1 ), relative to the total weight of the multimodal ethylene copolymer composition,

[0016] It comprises a copolymer of ethylene and at least a first alpha-olefin comonomer having a density in the range of 920 to 960 kg / m 3 ;

[0017] - 15 to 35 wt.-% of a second ethylene copolymer (A2), relative to the total weight of the multimodal ethylene copolymer composition, comprising a copolymer of ethylene and at least a first α-olefin comonomer, having a density in the range of 920 to 960 kg / m 3 ;

[0018] - 40 to 80 wt.-% of a third ethylene copolymer (B), relative to the total weight of the multimodal ethylene copolymer composition,

[0019] It comprises a copolymer of ethylene and at least a first and a second alpha-olefin comonomer;

[0020] wherein the third ethylene copolymer (B) has a higher weight average molecular weight (M) than the first ethylene copolymer (A1) and the second ethylene copolymer (A2). W ); wherein the density of the composition is between 915 and 930 kg / m 3 in the range of 0.5 to 5.0 g / 10 min according to ISO 1133; and wherein, according to the quantitative 13 C-NMR spectral analysis determines that the content of the second α-olefin comonomer in the third ethylene polymer (B) is in the range of 15 to 85%, based on the total comonomer content on a mole basis in the third ethylene copolymer (B).

[0021] In another aspect, the present invention provides a process for producing a multimodal ethylene copolymer composition comprising the steps of:

[0022] (a) polymerizing ethylene and at least one first α-olefin comonomer in a first polymerization step to produce a first ethylene copolymer (A1);

[0023] (b) polymerizing ethylene and at least a first α-olefin comonomer in the presence of said first ethylene copolymer (A1) in a second polymerization step to produce a first ethylene copolymer mixture (PEM1) comprising said first ethylene copolymer (A1) and a second ethylene copolymer (A2), and

[0024] (c) polymerizing ethylene, the first α-olefin comonomer and a second α-olefin comonomer in the presence of the first ethylene copolymer mixture (PEM1) in a third polymerization step to produce a second ethylene copolymer mixture (PEM2) comprising the first ethylene copolymer mixture (PEM1) and a third ethylene copolymer (B),

[0025] (d) extruding said second ethylene copolymer mixture (PEM2) to obtain said multimodal ethylene copolymer composition.

[0026] In another aspect, the present invention provides a film comprising the multimodal ethylene copolymer composition and / or the multimodal ethylene copolymer composition obtainable by the process.

[0027] Surprisingly, it was found that the multimodal ethylene copolymer compositions described herein are suitable for the production of films showing improved impact properties as evidenced by the higher DDI values ​​measured on films made from the inventive ethylene polymer compositions and also showing desirable tensile and optical properties comparable to those of films obtainable from currently commercially available multimodal LLDPE polymers. DETAILED DESCRIPTION

[0028] The present invention relates to a multimodal ethylene copolymer composition, a process for its preparation and articles, especially films, comprising the multimodal ethylene copolymer composition and / or the multimodal ethylene copolymer composition obtainable by said process.

[0029] Multimodal ethylene copolymer composition

[0030] The multimodal ethylene copolymer composition of the present invention comprises: 5 to 25 wt. % of a first ethylene copolymer (A1), relative to the total weight of the multimodal ethylene copolymer composition, comprising a copolymer of ethylene and at least one first α-olefin comonomer, having a density in the range of 920 to 960 kg / m 3 15 to 35 wt. % of a second ethylene copolymer (A2), relative to the total weight of the multimodal ethylene copolymer composition, comprising a copolymer of ethylene and at least one first α-olefin comonomer, having a density in the range of 920 to 960 kg / m 3 % of a third ethylene copolymer (B), relative to the total weight of the multimodal ethylene copolymer composition, comprising a copolymer of ethylene and at least a first and a second α-olefin comonomer, wherein the third ethylene copolymer (B) has a higher weight average molecular weight (M) than the first ethylene copolymer (A1) and the second ethylene copolymer (A2). W ); wherein the density of the composition is between 915 and 930 kg / m 3 in the range of 0.5 to 5.0 g / 10 min according to ISO 1133; and wherein, according to the quantitative 13 C-NMR spectral analysis determines that the content of the second α-olefin comonomer in the third ethylene copolymer (B) is in the range of 15 to 85%, based on the total comonomer content on a mole basis in the third ethylene polymer (B).

[0031] Preferably, the multimodal ethylene copolymer composition has an MFR2 determined according to ISO 1133 in the range of 0.01 to 0.5 g / 10 min, preferably 0.1 to 0.4 g / 10 min, more preferably 0.15 to 0.30 g / 10 min.

[0032] Preferably, the multimodal ethylene copolymer composition has an MFR5 determined according to ISO 1133 in the range of 0.5 to 3.0 g / 10 min, more preferably 0.6 to 2.0 g / 10 min, even more preferably 0.7 to 1.5 g / 10 min.

[0033] Preferably, the multimodal ethylene copolymer composition has an MFR determined according to ISO 1133. 21 In the range of 5 to 40 g / 10 min, more preferably 10 to 30 g / 10 min, even more preferably 15 to 28 g / 10 min.

[0034] Preferably, the multimodal ethylene copolymer composition has a 3 density.

[0035] The above MFR2, MFR5, MFR 21 The and density ranges relate to the multimodal ethylene copolymer composition after extrusion into pellets.

[0036] Preferably, the multimodal ethylene copolymer composition has a number average molecular weight (Mn) of 8 to 14 kg / mol; a weight average molecular weight (Mw) of 150 to 200 kg / mol; and a z average molecular weight (Mz) of 750 to 1000 kg / mol; as determined by GPC.

[0037] Furthermore, preferably, the M of the multimodal ethylene copolymer composition is W / M n Ratio of 10 to 25 and / or M Z / M W More preferably, the M of the multimodal ethylene copolymer composition is 4 to 10 (calculated based on GPC measurements as described in the experimental part below). W / M n ratio in the range of 10 to 20, and / or M Z / M W The ratio is in the range of 4 to 8.

[0038] Preferably, the polydispersity index (PI) of the multimodal ethylene copolymer composition is between 2.0 and 3.0 Pa -1 , more preferably 2.25 to 2.50 Pa -1 and / or a shear thinning index (SHI 2,7 / 210) in the range of 25 to 40, more preferably in the range of 30 to 35; PI and SHI are determined by rheological measurements as detailed in the experimental part.

[0039] Preferably, as detailed in the experimental section, according to quantitative 13The total comonomer content of the multimodal ethylene copolymer composition is in the range of 1.5 to 5.0 mol%, more preferably in the range of 2.5 to 3.9 mol%, as determined by C-NMR spectroscopy.

[0040] According to a particularly preferred embodiment, the multimodal ethylene copolymer composition comprises 13 0.5 to 4.5 mole percent of a first alpha-olefin comonomer, more preferably 1-butene, as determined by C-NMR spectroscopy; and / or 13 0.5 to 4.5 mole percent of a second alpha-olefin comonomer as determined by C-NMR spectroscopy, more preferably 1-hexene.

[0041] Unless otherwise specified, the expression "properties of the composition" is understood to relate to the properties of the final polymer composition, ie in the form of polymer pellets after compounding.

[0042] First ethylene copolymer (A1)

[0043] The first ethylene copolymer (A1) is a copolymer of ethylene and at least one first α-olefin comonomer. Relative to the total weight of the multimodal ethylene copolymer composition, it constitutes 5 to 25% by weight, preferably 10 to 20% by weight of the multimodal ethylene copolymer composition. The first α-olefin comonomer is preferably selected from α-olefin comonomers having 3 to 10 carbon atoms. More preferably, the first α-olefin comonomer is selected from 1-butene, 1-hexene and 1-octene; even more preferably, the first α-olefin comonomer is 1-butene. According to a particularly preferred embodiment of the present invention, the first ethylene copolymer (A1) is a copolymer of ethylene and 1-butene.

[0044] The first ethylene copolymer (A1 ) preferably has an MFR2 determined according to ISO 1133 in the range of 50 to 600 g / 10 min, preferably 100 to 400 g / 10 min.

[0045] The density of the first ethylene copolymer (A1) is in the range of 920 to 960 kg / m 3 , more preferably 940 to 955 kg / m 3 .

[0046] Second ethylene copolymer (A2)

[0047] The second ethylene copolymer (A2) is a copolymer of ethylene and at least a first α-olefin comonomer. Relative to the total weight of the multimodal ethylene copolymer composition, it accounts for 15 to 35% by weight, preferably 20 to 30% by weight of the multimodal ethylene copolymer composition. The first α-olefin comonomer is the same as that in the first ethylene copolymer (A1), and is preferably selected from α-olefin comonomers having 3 to 10 carbon atoms. More preferably, the first α-olefin comonomer is selected from 1-butene, 1-hexene and 1-octene; even more preferably, the first α-olefin comonomer is 1-butene. According to a particularly preferred embodiment of the present invention, the second ethylene copolymer (A2) is a copolymer of ethylene and 1-butene.

[0048] The second ethylene copolymer (A2) preferably has an MFR2 determined according to ISO 1133 in the range of 50 to 600 g / 10 min, preferably 100 to 400 g / 10 min.

[0049] The density of the second ethylene copolymer (A2) is in the range of 920 to 960 kg / m 3 , more preferably 940 to 955 kg / m 3 .

[0050] The first ethylene copolymer (A1 ) and the second ethylene copolymer (A2) and optionally further polymer fractions from an optional prepolymerisation step are comprised in the first ethylene copolymer mixture (PEM1 ).

[0051] The total comonomer content of the first ethylene copolymer mixture (PEM1) is preferably in the range of 0.5 to 3.0 mol%.

[0052] The third ethylene copolymer (B)

[0053] The third ethylene copolymer (B) comprises a copolymer of ethylene and a first and a second α-olefin comonomer. Relative to the total weight of the multimodal ethylene copolymer composition, it accounts for 40 to 80% by weight, preferably 50 to 70% by weight of the multimodal ethylene copolymer composition. The first α-olefin comonomer is the same as that in the above-mentioned first ethylene copolymer (A1) and the second ethylene copolymer (A2). On the other hand, the second α-olefin comonomer is preferably selected from α-olefin comonomers having 3 to 10 carbon atoms. More preferably, the second α-olefin comonomer is selected from 1-butene, 1-hexene and 1-octene. More preferably, the third ethylene copolymer (B) comprises 1-butene as the first α-olefin comonomer and / or 1-hexene as the second α-olefin comonomer. Even more preferably, the third ethylene copolymer (B) is a terpolymer of ethylene, 1-butene and 1-hexene. In this embodiment, the multimodal ethylene copolymer composition comprises according to quantitative 13 0.5 to 5.0 mol % of 1-butene as determined by CNMR spectral analysis and / or13 0.5 to 4.0 mol % 1-hexene as determined by C NMR spectral analysis.

[0054] According to quantitative 13 The total comonomer content in the third ethylene copolymer (B) is preferably 1 to 10 mol%, more preferably 2 to 8 mol%, even more preferably 3 to 7 mol%, as determined by C-NMR spectroscopy.

[0055] According to quantitative 13 C-NMR spectral analysis determines that, based on the total comonomer content in the third ethylene copolymer (B) by mole, the second α-olefin comonomer is preferably contained in the third ethylene copolymer (B) in an amount of 15 to 85%, preferably in an amount of 20 to 83%, more preferably in an amount of 5 to 80%.

[0056] According to a particularly preferred embodiment, the third ethylene copolymer (B) is a terpolymer of ethylene, 1-butene and 1-hexene, wherein, based on the quantitative 13 The total comonomer content in moles of the third ethylene copolymer (B) determined by C-NMR spectroscopy analysis is 25 to 80% by weight of 1-hexene, and wherein, according to the quantitative 13 The total comonomer content in the third ethylene copolymer (B) determined by C-NMR spectroscopy is between 3 and 7%.

[0057] The third ethylene copolymer (B) has a higher weight average molecular weight (M) than the first ethylene copolymer (A1) and the second ethylene copolymer (A2). W ).

[0058] The first ethylene copolymer mixture (PEM1) and the third ethylene copolymer (B) are comprised in the second ethylene copolymer mixture (PEM2). Preferably, the first ethylene copolymer mixture (PEM1) and the third ethylene copolymer (B) constitute the second ethylene copolymer mixture (PEM2).

[0059] Preferably, the second ethylene copolymer mixture (PEM2) has an MFR2 determined according to ISO 1133 in the range of 0.01 to 0.5 g / 10 min, more preferably 0.1 to 0.4 g / 10 min, even more preferably 0.15 to 0.30 g / 10 min.

[0060] Preferably, the second ethylene copolymer mixture (PEM2) has an MFR5 determined according to ISO 1133 in the range of 0.1 to 2.0 g / 10 min, more preferably 0.5 to 1.5 g / 10 min, even more preferably 0.7 to 1.2 g / 10 min.

[0061] Preferably, the second ethylene copolymer mixture (PEM2) has an MFR of 21 In the range of 5 to 40 g / 10 min, more preferably 10 to 30 g / 10 min, even more preferably 15 to 27 g / 10 min.

[0062] Preferably, the density of the second ethylene copolymer mixture (PEM2) is between 900 and 940 kg / m 3 , more preferably 910 to 930 kg / m 3 , even more preferably between 915 and 925 kg / m 3 within the range.

[0063] Aggregation methods

[0064] As described herein, the present invention process for producing a multimodal ethylene copolymer composition comprises the following steps:

[0065] (a) polymerizing ethylene and at least one first α-olefin comonomer in a first polymerization step to produce a first ethylene copolymer (A1);

[0066] (b) polymerizing ethylene and at least a first α-olefin comonomer in the presence of said first ethylene copolymer (A1) in a second polymerization step to produce a first ethylene copolymer mixture (PEM1) comprising said first ethylene copolymer (A1) and a second ethylene copolymer (A2), and

[0067] (c) polymerizing ethylene, a first α-olefin comonomer and a second α-olefin comonomer in the presence of said first ethylene copolymer mixture (PEM1) in a third polymerization step to produce a second ethylene copolymer mixture (PEM2) comprising the first ethylene copolymer mixture (PEM1) and a third ethylene copolymer (B),

[0068] (d) extruding said second ethylene copolymer mixture (PEM2) to obtain said multimodal ethylene copolymer composition.

[0069] Preferably, steps (a), (b) and (c) of the process are carried out in the presence of a Ziegler-Natta polymerisation catalyst.

[0070] The first and second α-olefin comonomers used in steps (a), (b) and (c) can be independently selected from α-olefins having 3 to 10 carbon atoms and mixtures thereof. Particularly suitable α-olefins are α-olefins having 4 to 8 carbon atoms, including mixtures thereof. In particular, 1-butene, 1-hexene and 1-octene and mixtures thereof are preferred α-olefins. The first α-olefin comonomer used in steps (a), (b) and (c) is the same, while the second α-olefin comonomer is different from the first α-olefin comonomer. The polymerization steps can be connected in any order, i.e. the first polymerization step can precede the second polymerization step, or the second polymerization step can precede the first polymerization step, or the polymerization steps can be connected in parallel.

[0071] However, it is preferred to run the polymerisation step in cascade mode.

[0072] catalyst

[0073] As mentioned above, the polymerisation steps (a), (b) and (c) of the process for producing a multimodal ethylene copolymer composition described herein are preferably carried out in the presence of a Ziegler-Natta polymerisation catalyst.

[0074] Ziegler-Natta catalysts are useful because they can produce polymers over a wide range of molecular weights and other desirable properties at high productivity. The Ziegler-Natta catalyst used in the present invention is preferably supported on an external support.

[0075] Suitable Ziegler-Natta catalysts preferably comprise a magnesium compound, an aluminum compound and a titanium compound supported on a particulate support.

[0076] The particle supports commonly used in Ziegler-Natta catalysts include inorganic oxide supports, such as supports based on silica, alumina, titania, silica-alumina and silica-titania or MgCl. The catalyst used in the present invention is supported on an inorganic oxide support. Most preferably, the Ziegler-Natta catalyst used in the present invention is supported on silica.

[0077] The average particle size of the silica support is generally in the range of 10 to 100 μm. However, it has been shown that particular advantages can be obtained if the average particle size of the support is in the range of 15 to 30 μm, preferably 18 to 25 μm. Alternatively, the average particle size of the support may be in the range of 30 to 80 μm, preferably 30 to 50 μm. Suitable examples of support materials are, for example, ES747JR produced and sold by Ineos Silicas (formerly Crossfield) and SP9-491 produced and sold by Grace.

[0078] The magnesium compound is the reaction product of a dialkylmagnesium and an alcohol. The alcohol is a linear or branched aliphatic monohydric alcohol. Preferably, the alcohol has 6 to 16 carbon atoms. Branched alcohols are particularly preferred, 2-ethyl-1-hexanol being an example of a preferred alcohol. The dialkylmagnesium can be any compound of magnesium bonded to two alkyl groups, which can be the same or different. Butyl-octylmagnesium is an example of a preferred dialkylmagnesium.

[0079] The aluminum compound is a chlorine-containing aluminum alkyl. Particularly preferred compounds are alkyl aluminum dichlorides, dialkyl aluminum chlorides and alkyl aluminum sesquichlorides.

[0080] The transition metal is preferably titanium. The titanium compound is a halogen-containing titanium compound, preferably a chlorine-containing titanium compound. A particularly preferred titanium compound is titanium tetrachloride.

[0081] The catalyst can be prepared by contacting the support with the above compounds in sequence, as described in EP-A-688794 or WO-A-99 / 51646. Alternatively, it can be prepared by first preparing a solution from the components and then contacting the solution with the support, as described in WO-A-01 / 55230.

[0082] Ziegler-Natta catalysts are used together with an activator, which is also referred to as a co-catalyst. Suitable activators are metal alkyl compounds, typically Group 13 metal alkyl compounds, especially alkyl aluminum compounds. They include trialkyl aluminum compounds, such as trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, trihexyl aluminum and tri-n-octylaluminum. Alkyl aluminum compounds can also include alkyl aluminum halides, such as ethyl aluminum dichloride, diethyl aluminum chloride, ethyl aluminum sesquichloride, dimethyl aluminum chloride, etc. and alkyl aluminum oxide compounds, such as methyl aluminum oxane, hexaisobutyl aluminum oxane and tetraisobutyl aluminum oxane, and other alkyl aluminum compounds, such as isoprenyl aluminum. Particularly preferred co-catalysts are trialkyl aluminums, with triethyl aluminum, trimethyl aluminum and triisobutyl aluminum being particularly preferred.

[0083] The amount of activator depends on the specific catalyst and activator. Typically, the amount of triethylaluminum is such that the molar ratio of aluminum to transition metal (such as Al / Ti) is, for example, 1 to 1000, preferably 3 to 100, particularly about 5 to about 30 mol / mol.

[0084] Prepolymerization

[0085] In addition to the actual polymerization steps (a), (b) and (c), i.e. in addition to the at least three polymerization steps, the process may also comprise a prepolymerization step prior to the actual polymerization step. The purpose of the prepolymerization is to polymerize a small amount of polymer onto the catalyst at low temperature and / or low monomer concentration. The properties of the catalyst can be improved by prepolymerization. The prepolymerization step is carried out in slurry.

[0086] Thus, the prepolymerization step can be carried out in a loop reactor. The prepolymerization is then preferably carried out in an inert diluent, typically a hydrocarbon diluent such as methane, ethane, propane, n-butane, isobutane, pentane, hexane, heptane, octane, etc., or a mixture thereof. The diluent is preferably a low boiling hydrocarbon having 1 to 4 carbon atoms or a mixture of such hydrocarbons.

[0087] The temperature in the prepolymerization step is generally from 0 to 90° C., preferably from 20 to 80° C., more preferably from 55 to 75° C. The pressure is not critical and is generally from 1 to 150 bar, preferably from 40 to 80 bar.

[0088] The amount of monomer is usually such that about 0.1 to 1000g of monomer is polymerized per gram of solid catalyst component in the prepolymerization step. As known to those skilled in the art, the catalyst particles recovered from the continuous prepolymerization reactor do not all contain the same amount of prepolymer. On the contrary, each particle has its own characteristic amount, which depends on the residence time of the particle in the prepolymerization reactor. Since some particles stay in the reactor for a relatively long time, while some particles stay for a relatively short time, the amount of prepolymer on different particles is also different, and some individual particles may contain an amount of prepolymer that exceeds the above-mentioned limit. However, the average amount of prepolymer on the catalyst is usually within the above-mentioned limit.

[0089] The molecular weight of the prepolymer can be controlled by hydrogen, as is well known in the art. In addition, antistatic additives can be used to prevent the particles from adhering to each other or to the reactor walls, as disclosed in WO-A-96 / 19503 and WO-A-96 / 32420.

[0090] If a prepolymerization step is used, it is preferred that the prepolymer is an ethylene copolymer. Any prepolymer component is considered to be part of the first ethylene copolymer (A1). Therefore, when determining the split, MFR, density, etc. of the first polymer, the prepolymer is considered to be part of the first ethylene copolymer (A1).

[0091] When there is a prepolymerization step, the catalyst components are preferably all introduced into the prepolymerization step (separately or together). However, when the solid catalyst component and the cocatalyst can be fed separately, only a portion of the cocatalyst can be introduced into the prepolymerization stage, and the remaining portion can be introduced into the subsequent polymerization stage. Again, in this case, it is necessary to introduce the cocatalyst into the prepolymerization stage in order to obtain a sufficient polymerization reaction therein.

[0092] Typically, the amount of hydrogen and comonomer is adjusted so that the presence of the prepolymer does not affect the properties of the final multimodal polymer. In particular, it is preferred that the melt flow rate of the prepolymer is greater than the melt flow rate of the final polymer, but less than the melt flow rate of the polymer produced in the first polymerization stage, i.e. the first ethylene copolymer (A1). It is further preferred that the density of the prepolymer is greater than the density of the final polymer. Suitably, the density is approximately equal to or greater than the density of the polymer produced in the first polymerization stage, i.e. the first ethylene copolymer (A1). Furthermore, typically the amount of prepolymer does not exceed about 5% by weight of the multimodal ethylene copolymer composition, more preferably the amount of prepolymer does not exceed 2% by weight of the multimodal ethylene copolymer composition.

[0093] Step (a) of producing the first ethylene copolymer (A1)

[0094] Step (a) of the process comprises polymerizing ethylene and a first α-olefin comonomer in a first polymerization reactor to produce a first ethylene copolymer (A1).

[0095] In step (a), a first ethylene copolymer (A1) is produced. The density of the first ethylene copolymer (A1) is in the range of 920 to 960 kg / m 3 , and preferably, the melt flow rate MFR2 measured according to ISO1133 is 50 to 600 g / 10 min.

[0096] The catalyst can be transferred to the first polymerization step by any method known in the art. The catalyst can thus be suspended in a diluent and maintained as a homogeneous slurry. Particularly preferred is the use of a diluent having a viscosity of 20 to 1500 mPa. . The catalyst may also be mixed with a viscous mixture of grease and oil and the resulting paste may be fed to the first polymerization step. Furthermore, it is also possible to allow the catalyst to settle and to introduce part of the catalyst slurry thus obtained into the first polymerization step, for example in the manner disclosed in EP-A-428054. The first polymerization step may also be preceded by a prepolymerization step as described above, in which case the mixture removed from the prepolymerization step is conducted to the first polymerization step (a).

[0097] In the first polymerization step (a), ethylene, a first α-olefin, an optional inert diluent and optionally hydrogen are introduced in such amounts that the melt flow rate MFR2 and the density of the first ethylene copolymer (A1) reach the desired values.

[0098] Preferably, the first α-olefin is as defined above, having 3 to 10 carbon atoms. In particular, 1-butene, 1-hexene and 1-octene are preferred α-olefins. It is particularly preferred that the first α-olefin comonomer is 1-butene.

[0099] The polymerization of the first polymerization step (a) can be carried out in a slurry. The polymer particles formed in the polymerization are then suspended in a fluid hydrocarbon together with the catalyst broken up and dispersed within the particles. The slurry is stirred to transfer the reactants from the fluid to the particles.

[0100] The polymerization is usually carried out in an inert diluent, usually a hydrocarbon diluent, such as methane, ethane, propane, n-butane, isobutane, pentane, hexane, heptane, octane, etc., or a mixture thereof. Preferably, the diluent is a low boiling hydrocarbon having 1 to 4 carbon atoms or a mixture of such hydrocarbons. A particularly preferred diluent is propane, which may contain small amounts of methane, ethane and / or butane.

[0101] The ethylene content in the slurry fluid phase may be 1 to about 50 mol%, preferably about 1.5 to about 20 mol%, and particularly about 2 to about 15 mol%. The benefit of high ethylene concentration is increased catalyst productivity, but the disadvantage is that more ethylene needs to be recovered compared to lower concentrations.

[0102] Slurry polymerization can be carried out in any known reactor for slurry polymerization. Such reactors include continuous stirred tank reactors and loop reactors. Particularly preferably, the polymerization of step (a) is carried out in a loop reactor. In such reactors, a circulating pump is used to circulate the slurry along a closed pipe at high speed. Loop reactors are well known in the art, and examples are given, for example, in US-A-4582816, US-A-3405109, US-A-3324093, EP-A-479186 and US-A-5391654.

[0103] If the first ethylene copolymer (A1) is produced under the condition that the ratio of the first α-olefin to ethylene is no more than about 400 mol / kmol (e.g. no more than 300 mol / kmol), it is usually advantageous to carry out slurry polymerization above the critical temperature and pressure of the fluid mixture. This operation is described in US-A-5391654.

[0104] When the first polymerization step (a) is carried out as a slurry polymerization, it is carried out at a temperature in the range of 50 to 115° C., preferably in the range of 70 to 110° C., especially in the range of 80 to 105° C. While the pressure in the first polymerization step (a) is 1 to 300 bar, preferably 40 to 100 bar, more preferably 50 to 80 bar.

[0105] The amount of hydrogen is adjusted based on the desired melt flow rate of the first ethylene copolymer (A1), and depends on the specific catalyst used. For many commonly used Ziegler-Natta catalysts, the molar ratio of hydrogen to ethylene is from 10 to 2000 mol / kmol, preferably from 100 to 1000 mol / kmol, especially from 150 to 800 mol / kmol.

[0106] The amount of the first α-olefin is adjusted based on the desired density of the first ethylene copolymer (A1) and also depends on the specific catalyst used. For many commonly used Ziegler-Natta catalysts, the molar ratio of the first α-olefin to ethylene is 100 to 1000 mol / kmol, preferably 150 to 600 mol / kmol.

[0107] The polymerization of step (a) can also be carried out in the gas phase. A preferred embodiment of a gas phase polymerization reactor is a fluidized bed reactor. In which, the polymer particles formed in the polymerization are suspended in the gas moving upward. The gas is introduced into the bottom of the reactor. The gas moving upward passes through the fluidized bed, wherein a portion of the gas reacts in the presence of a catalyst, and the unreacted gas is extracted from the top of the reactor. The gas is then compressed and cooled to remove the heat of polymerization. In order to increase the cooling capacity, it is sometimes necessary to cool the circulating gas to a temperature at which a portion of the gas condenses. After cooling, the circulating gas is reintroduced into the bottom of the reactor. Fluidized bed polymerization reactors are disclosed in US-A-4994534, US-A-4588790, EP-A-699213, EP-A-628343, FI-A-921632, FI-A-935856, US-A-4877587, FI-A-933073 and EP-A-75049, etc.

[0108] According to a preferred embodiment of the present invention, the polymerization of the first polymerization step (a) is carried out in slurry.

[0109] Furthermore, the polymerization is suitably carried out at a temperature exceeding the critical temperature of the fluid mixture and at a pressure exceeding the critical pressure of the fluid mixture.

[0110] According to the present invention, at least one first α-olefin comonomer is present in the first polymerization step (a), wherein the polymer produced in the first step is a first ethylene copolymer (A1). The polymerization is preferably carried out in a liquid diluent in the form of a slurry polymerization, at a temperature of 50°C to 115°C, such as 70 to 115°C, and a pressure of 1 bar to 300 bar, such as 40 to 100 bar, such as 50 to 80 bar. The molar ratio of the first α-olefin to ethylene is 100 to 1000 mol / kmol, preferably 150 to 600 mol / kmol, and most preferably 180 to 400 mol / kmol. The molar ratio of hydrogen to ethylene is suitably 10 to 2000 mol / kmol, preferably 100 to 1000 mol / kmol, and more preferably 150 to 800 mol / kmol. The MFR2 of the first ethylene copolymer (A1) produced in the first polymerization step (a) is preferably in the range of 50 to 600 g / 10min, as determined according to ISO1133.

[0111] The polymerisation rate in the first polymerisation step (a) is suitably controlled to achieve the desired amount of the first ethylene copolymer (A1 ) in the multimodal ethylene copolymer composition.The polymerisation rate is suitably controlled by adjusting the ethylene concentration in the first polymerisation step (a).

[0112] When the first polymerisation step is carried out as a slurry polymerisation in a loop reactor, the mole fraction of ethylene in the reaction mixture is suitably from 2 to 10 mol %, preferably from 3 to 8 mol %.

[0113] Step (b) of producing the second ethylene copolymer (A2)

[0114] The second ethylene copolymer (A2) is produced in the second polymerization step (b) in the presence of the first ethylene copolymer (A1 ).

[0115] The polymerization can be carried out in slurry, gas phase or solution. In the second polymerization step (b), the second ethylene copolymer (A2) is produced in the presence of the first ethylene copolymer (A1). Therefore, the polymer produced in the second polymerization step (b) is a mixture of the first (A1) and the second (A2) ethylene copolymers, i.e. the first ethylene copolymer mixture (PEM1).

[0116] The density of the second ethylene copolymer (A2) is in the range of 920 to 960 kg / m 3 , and preferably, the melt flow rate MFR2 measured according to ISO1133 is 50 to 600 g / 10 min.

[0117] The first ethylene copolymer (A1) is transferred from the first polymerization step (a) to the second polymerization step (b) using any method known to a person skilled in the art. If the first polymerization step (a) is carried out as a slurry polymerization in a loop reactor, it is advantageous to utilize the pressure difference between the first polymerization step (a) and the second polymerization step (b) to transfer the slurry from the first polymerization step (a) to the second polymerization step (b).

[0118] In the second polymerization step (b), ethylene, the first α-olefin comonomer, an optional inert diluent and optionally hydrogen are introduced. The amount of hydrogen and α-olefin introduced should be such that the density and melt flow rate MFR2 of the second ethylene copolymer (A2) are preferably within the desired value range.

[0119] The first α-olefin comonomer used in the second polymerization step (b) for producing the second ethylene copolymer (A2) is the same as the first α-olefin comonomer used in the first polymerization step (a) for producing the first ethylene copolymer (A1).

[0120] The polymerization of the second polymerization step (b) may be carried out in slurry in the same manner as discussed above for the first polymerization step (a).

[0121] The polymerisation of the second polymerisation step (b) may also be carried out in gas phase in the same manner as discussed above for the first polymerisation step (a). Preferably, the second polymerisation step (b) is carried out in slurry phase as described above.

[0122] When the second polymerization step (b) is carried out as a slurry polymerization, it is carried out, as in the first polymerization step (a), at a temperature in the range of 50 to 115° C., preferably 70 to 110° C., in particular 80 to 105° C. The pressure in the first polymerization step (a) is 1 to 300 bar, preferably 40 to 100 bar, more preferably 50 to 80 bar.

[0123] The molar ratio of hydrogen to ethylene in the second polymerisation step (b) is suitably from 10 to 2000 mol / kmol, preferably from 100 to 1000 mol / kmol, especially from 150 to 800 mol / kmol.

[0124] Furthermore, the polymerization is suitably carried out at a temperature exceeding the critical temperature of the fluid mixture and at a pressure exceeding the critical pressure of the fluid mixture.

[0125] The density of the second ethylene copolymer (A2) is controlled by the molar ratio of the first α-olefin to ethylene in the second polymerization step (b). In the second polymerization step (b), the molar ratio of α-olefin to ethylene is 50 to 1000 mol / kmol, preferably 200 to 900 mol / kmol, most preferably 400 to 800 mol / kmol.

[0126] The polymerisation rate in the second polymerisation step (b) may be suitably controlled to achieve a desired amount of the second ethylene copolymer (A2) in the multimodal ethylene copolymer composition.

[0127] The polymerization rate can be suitably controlled by adjusting the ethylene concentration in the second polymerization step (b).When the second polymerization step is carried out as a slurry polymerization in a loop reactor, the mole fraction of ethylene in the reaction mixture is suitably 1 to 10 mol%, preferably 2 to 6 mol%.

[0128] As stated above, the melt flow rate MFR2 of the second ethylene copolymer (A2) measured according to ISO 1133 is preferably in the range of 50 to 600 g / 10 min.

[0129] Step (c) of producing the third ethylene copolymer (B)

[0130] The third ethylene copolymer (B) is produced in the third polymerization step (c) in the presence of the first ethylene copolymer mixture (PEM1). Thus, the polymer obtained in the third polymerization step is the second ethylene copolymer mixture (PEM2).

[0131] In addition to the first ethylene copolymer mixture (PEM1) ethylene, at least a first α-olefin comonomer, a second α-olefin comonomer, hydrogen and optionally an inert diluent are introduced into the third polymerization step (c).

[0132] The polymerization in the third polymerization step (c) is preferably carried out at a temperature in the range of 50 to 100° C., preferably 60 to 100° C., in particular 70 to 95° C. The pressure in the third polymerization step (c) is, for example, 1 to 300 bar, preferably 5 to 100 bar.

[0133] The polymerization in the third polymerization step (c) may be carried out in slurry. The polymerization may then be carried out in the same manner as in the first and second polymerization steps described above.

[0134] The amount of hydrogen in the third polymerization step (c) is adjusted to achieve the desired melt flow rate of the third ethylene copolymer (B). The molar ratio of hydrogen to ethylene depends on the specific catalyst used. For many commonly used Ziegler-Natta catalysts, the molar ratio of hydrogen to ethylene is, for example, 0 to 50 mol / kmol, preferably 3 to 35 mol / kmol.

[0135] In addition, the amount of the alpha-olefin comonomer preferably having 3 to 10 carbon atoms is adjusted to reach the target density. The ratio of alpha-olefin (the sum of alpha-olefins) to ethylene depends on the type of catalyst and the type of alpha-olefin. This ratio is usually, for example, 100 to 1000 mol / kmol, preferably 150 to 800 mol / kmol. Due to the use of more than one alpha-olefin, the ratio of alpha-olefin to ethylene is the ratio of the sum of all alpha-olefins to ethylene.

[0136] The α-olefin comonomer is preferably selected from α-olefins having 3 to 10 carbon atoms or mixtures thereof. In particular, 1-butene, 1-hexene and 1-octene and mixtures thereof are preferred α-olefins, with 1-butene and 1-hexene being particularly preferred.

[0137] The content of the second α-olefin comonomer in the third ethylene copolymer (B) is in the range of 15 to 85%, based on the total comonomer content in moles in the third ethylene copolymer (B).

[0138] As mentioned above, the third ethylene copolymer (B) preferably comprises at least two comonomers, ideally only two comonomers. It is particularly preferred that these comonomers are 1-butene and 1-hexene. That is, it is even more particularly preferred that the first α-olefin comonomer is 1-butene and the second α-olefin comonomer is 1-hexene.

[0139] The polymerization in the third polymerization step (c) can and is preferably carried out in gas phase. In the gas phase polymerization using Ziegler-Natta catalyst, hydrogen is usually added in an amount such that the ratio of hydrogen to ethylene is 3 to 100 mol / kmol, preferably 4 to 50 mol / kmol, to obtain the desired melt index of the third ethylene copolymer (B). The amount of the alpha-olefin with 3 to 10 carbon atoms is regulated to reach the target density of the third ethylene copolymer (B). The ratio of alpha-olefin to ethylene is generally 100 to 1000 mol / kmol, preferably 150 to 800 mol / kmol, more preferably 200 to 500 mol / kmol. Due to the use of more than one alpha-olefin, the ratio of alpha-olefin to ethylene is the ratio of the sum of all alpha-olefins to ethylene.

[0140] The gas phase reactor is preferably a vertical fluidized bed reactor. In which the polymer particles formed in the polymerization are suspended in the gas moving upward. The gas is introduced into the bottom of the reactor. The gas moving upward passes through the fluidized bed, where a portion of the gas reacts in the presence of a catalyst, and the unreacted gas is extracted from the top of the reactor. The gas is then compressed and cooled to remove the heat of polymerization. In order to increase the cooling capacity, it is sometimes necessary to cool the circulating gas to a temperature at which a portion of the gas condenses. After cooling, the circulating gas is reintroduced into the bottom of the reactor. Fluidized bed polymerization reactors are disclosed in US-A-4994534, US-A-4588790, EP-A-699213, EP-A-628343, FI-A-921632, FI-A-935856, US-A-4877587, FI-A-933073 and EP-A-75049, etc.

[0141] When the first (a) or second (b) polymerisation step is carried out in slurry and the third polymerisation step (c) is carried out in gas phase, the polymer is suitably transferred from the first (a) or second (b) polymerisation step to the third polymerisation step (c) as described in EP-A-1415999. The procedure described in paragraphs

[0037] to

[0048] of EP-A-1415999 provides a cost-effective method of product transfer.

[0142] The conditions in the third polymerization step (c) are adjusted so that the third ethylene copolymer (B) has MFR2, MFR5, MFR 21 and density.

[0143] The polymerization rate in the third polymerization step (c) is suitably controlled to achieve the desired amount of the third ethylene copolymer (B) in the second ethylene copolymer mixture (PEM2) and the multimodal ethylene copolymer composition, respectively. Preferably, the final multimodal ethylene copolymer composition contains 40 to 80% by weight, more preferably 50 to 70% by weight of the third ethylene copolymer (B). The polymerization rate is suitably controlled by adjusting the ethylene concentration in the third polymerization step (c). When the third polymerization step (c) is carried out in the gas phase, the mole fraction of ethylene in the reactor gas is suitably 3 to 50% by mole, and preferably 5 to 25% by mole.

[0144] In addition to ethylene, comonomers and hydrogen, the gas also comprises an inert gas. The inert gas can be any gas that is inert under the reaction conditions, for example a saturated hydrocarbon having 1 to 5 carbon atoms, nitrogen or a mixture of the above compounds. Suitable hydrocarbons having 1 to 5 carbon atoms are methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane and mixtures thereof.

[0145] Reactor post-treatment

[0146] After the second ethylene copolymer mixture (PEM2) is removed from the polymerization reactor, it is subjected to a process step for removing residual hydrocarbons from the polymer. Such processes are well known in the art and may include a decompression step, a washing step, a stripping step, an extraction step, etc. Different steps may also be combined.

[0147] According to a preferred method, a portion of the hydrocarbons is removed from the polymer powder by reducing the pressure. The powder is then contacted with steam at a temperature of 90 to 110° C. for a period of 10 minutes to 3 hours. Thereafter, the powder is purged with an inert gas, such as nitrogen, at a temperature of 20 to 80° C. for a period of 1 to 60 minutes.

[0148] According to another preferred method, the polymer powder is subjected to decompression as described above. Thereafter, it is purged with an inert gas (e.g. nitrogen) at a temperature of 50 to 90° C. for a period of 20 minutes to 5 hours. The inert gas may contain 0.0001 to 5% by weight, preferably 0.001 to 1% by weight, of a component (e.g. steam) for deactivating the catalyst contained in the polymer.

[0149] The purge step is preferably carried out continuously in a settling moving bed. The polymer moves downward in plug flow while the purge gas introduced into the bottom of the bed flows upward.

[0150] Suitable processes for removing hydrocarbons from polymers are disclosed in WO-A-02 / 088194, EP-A-683176, EP-A-372239, EP-A-47077 and GB-A-1272778.

[0151] After removal of residual hydrocarbons, the polymer is preferably mixed with additives, as is well known in the art, to form a polymer composition. Such additives include antioxidants, process stabilizers, neutralizers, lubricants, nucleating agents, pigments, and the like.

[0152] As is well known in the art, the polymer particles are mixed with additives and extruded into pellets. The extrusion step preferably uses a counter-rotating twin-screw extruder. Such extruders are manufactured, for example, by Kobe and Japan Steel. Suitable examples of such extruders are disclosed in EP-A-1600276. The specific energy input (SEI) during extrusion is generally between 100 and 230 kWh / ton. The melt temperature is generally between 220 and 290°C.

[0153] film

[0154] The film according to the invention comprises the multimodal ethylene copolymer composition, preferably in an amount of at least 90 wt. %, more preferably at least 95 wt. % of the film, most preferably the film consists of the multimodal copolymer composition. In addition to the multimodal ethylene copolymer composition, the film may comprise antioxidants, process stabilizers, slip agents, pigments, UV stabilizers and other additives known in the art.

[0155] Examples of stabilizers are hindered phenols, hindered amines, phosphates, phosphites and phosphites. Examples of pigments are carbon black, ultramarine blue and titanium dioxide. Examples of other additives are, for example, clay, talc, calcium carbonate, calcium stearate, zinc stearate and antistatic additives, etc. As is known in the art, additives can be added as individual components or as part of a masterbatch.

[0156] Suitable antioxidants and stabilizers include, for example, 2,6-di-tert-butyl-p-cresol, tetrakis-[methylene-3-(3',5-di-tert-butyl-4'hydroxyphenyl)propionate]methane, octadecyl-3-3(3'5'-di-tert-butyl-4'-hydroxyphenyl)propionate, dilauryl thiodipropionate, and dilauryl thiodipropionate. thiodipropionate), distearylthiodipropionate, tris-(nonylphenyl)phosphate, distearyl-pentaerythritol-diphosphite, and tetrakis(2,4-di-tertbutylphenyl)-4,4'-biphenylene-diphosphonite.

[0157] Some hindered phenols are sold under the trade names Irganox 1076 and Irganox 1010, or commercially available mixtures thereof, such as Irganox B561. Commercially available mixtures of antioxidants and process stabilizers may also be used, such as Irganox B225 sold by Ciba-Geigy.

[0158] Suitable acid scavengers are, for example, metal stearates, such as calcium stearate and zinc stearate. The amounts used are generally known in the art, typically 300 ppm to 10000 ppm, preferably 400 to 5000 ppm.

[0159] The polymer composition of the present invention may be provided in the form of powder or pellets, preferably pellets.

[0160] Pellets are obtained by conventional extrusion, pelletizing or grinding techniques and are an ideal form of the polymers of the present invention because they can be added directly to the conversion machinery. Pellets are different from polymer powders having a particle size of less than 1 mm. The use of granules ensures that the composition of the present invention can be converted into a film, such as a monolayer film, by simply adding the granules in-line to the conversion machinery.

[0161] The multimodal ethylene copolymer composition of the present invention allows the formation of films showing a good balance of mechanical and optical properties. The composition can be extruded into films according to any method known in the art. The film preparation process steps of the present invention are known and can be carried out in a film production line in a manner known in the art, such as flat film extrusion or blown film extrusion. Well-known film production lines are commercially available, for example from & Reifenhauser, Hosokawa Alpine, etc.

[0162] Importantly, the ethylene polymer composition of the present invention has excellent processing properties. The multimodal, particularly trimodal, nature of the polyethylene film composition of the present invention makes it very suitable for the manufacture of films. The advantages can be seen in the excellent extrudability, especially the significantly higher output of film making machinery compared to corresponding film materials with the same density and MFR level. High output is not achieved at the expense of good mechanical properties.

[0163] The film of the present invention may be a monolayer film, or the polymer composition of the present invention is used to form one layer of a multilayer film. Films comprising the ethylene polymer composition of the present invention and being multilayer films are preferred.

[0164] The thickness of any film of the invention may be 3 to 1000 μm, preferably 5 to 500 μm, more preferably 10 to 250 μm, more preferably 10 to 150 μm, for example 10 to 100 μm, or even 10 to 60 μm. The thickness chosen depends on the requirements of the desired end application.

[0165] The composition produced according to the process of the present invention is suitable for the manufacture of blown films. The film of the present invention can be manufactured by simply adding the polymer pellets in-line to the extruder. For the formation of films using polymer mixtures, it is important to thoroughly mix the different polymer components before extrusion and blowing the film, otherwise inhomogeneities such as gels may occur in the film.

[0166] Therefore, it is particularly preferred to thoroughly mix the components prior to extrusion and film blowing, for example using a twin-screw extruder, preferably a counter-rotating extruder.

[0167] Sufficient uniformity can also be obtained by selecting the screw design of the film extruder so that it is designed for good mixing and homogenization. The film of the present invention is a blown film. Blown films are usually extruded through an annular die and blown into a tubular film by forming bubbles, which collapse between pressure rollers after production solidification. The film can then be cut, trimmed or converted (e.g., gusseted) as required. Conventional film production techniques can be used in this regard. Typically, the composition will be extruded at a temperature of 160°C to 240°C and cooled at a temperature of 10 to 50°C by blowing (usually air) to provide a frost line height of 1 or 2 to 8 times the diameter of the die. The blow-up ratio (BUR) should generally be in the range of 1.5 to 4, such as 2 to 4, preferably 2.5 to 3.

[0168] The films of the present invention exhibit high dart drop impact strength and tear strength, especially in the machine direction. In the following paragraphs, certain parameters are given based on a specific film thickness. This is because changes in film thickness will result in changes in the magnitude of the parameter in question, so in order to obtain quantitative values, specific film thicknesses are quoted. This does not mean that other film thicknesses are not covered by the present invention, but it means that when formulated at a given thickness, the film should have a given parameter value.

[0169] Thus, for a 40 μm blown film produced as described below, at maximum output, the dart drop impact strength (DDI) of the film can be measured according to ISO7765-1 "Method A" and is in the range of 300 g to 900 g, preferably 350 g to 700 g. In addition, the film preferably has a longitudinal (MD) tensile modulus of 150 MPa to 500 MPa, more preferably 200 to 350 MPa, and / or a transverse (TD) tensile modulus of 250 to 500 MPa, more preferably 270 to 400 MPa (ISO 527-3).

[0170] In addition to excellent mechanical properties, films comprising the multimodal ethylene copolymer composition of the present invention also have beneficial optical properties.

[0171] Specifically, preferably, the haze of the film is in the range of 50 to 95%, more preferably 60 to 90%, and most preferably 70 to 80%, as measured on a 40 μm blown film prepared as shown below according to ASTM D1003. In addition, it is also preferred that the transparency of the film is in the range of 5 to 20%, more preferably 10 to 18%, as measured on a 40 μm blown film prepared as shown below according to ASTM D1003.

[0172] Similarly, measured at an angle of 45° on a 40 μm blown film according to ASTM D 2457, preferably, the film has a longitudinal (MD) gloss value in the range of 5.0 to 15.0 GU (gloss unit), preferably in the range of 5.5 to 10.0 GU (gloss unit); and a transverse (TD) gloss value in the range of 5.5 to 15.0 GU (gloss unit), preferably 5.8 to 10.0 GU (gloss unit).

[0173] In summary, it has surprisingly been found that the multimodal ethylene copolymer composition according to the present invention allows the production of films having desirable optical and tensile properties and also showing significantly improved impact properties.

[0174] Example

[0175] method

[0176] The following methods were used to measure the properties generally defined above and in the examples below. Unless otherwise stated, film samples used for measurements and definitions were prepared as described under the heading "Film Sample Preparation".

[0177] MFR

[0178] MFR is measured at 190°C according to ISO 1133. The load is indicated as a subscript, i.e. MFR2 means measured under a load of 2.16 kg, MFR5 means measured under a load of 5 kg, and MFR 21 Indicates that the measurement was performed under a load of 21.6 kg.

[0179] The MFR value can be determined on a sample as described above or calculated, e.g. in a manner known in the art, from the MFR value determined on a sample as described above, in particular, for example, the MFR value of the third ethylene copolymer (B) can be calculated based on the measured MFR value of the first ethylene copolymer mixture (PEM1), the measured MFR value of the second ethylene copolymer mixture (PEM2) and the respective amounts of PEM1 and the third (B) ethylene copolymer.

[0180] The MFR value of the third ethylene copolymer (B) can for example be calculated based on the logarithmic mixing rule, for example given by:

[0181] log MFRPEM2 =w PEM1 ×log MFR PEM1 +w B ×log MFR B

[0182] density

[0183] Density was measured according to ISO 1183-187. Sample preparation was done by compression molding according to ISO 1872-2:2007. If the density of a specific fraction could not be measured directly, it was calculated assuming a linear mixing rule and knowledge of the split between the individual fractions.

[0184] Molecular weight and molecular weight distribution

[0185] The average molecular weight (Mn, Mw and Mz) as well as the Mw / Mn ratio (PDI) and molecular weight distribution were determined by GPC.

[0186] The molecular weight averages (Mz, Mw and Mn), molecular weight distribution (MWD) and their width are determined by gel permeation chromatography (GPC) and described by the polydispersity index, PDI = Mw / Mn (where Mn is the number average molecular weight and Mw is the weight average molecular weight), as follows:

[0187]

[0188] For a constant elution volume interval ΔV i , where A i and M i and the elution volume V i The associated chromatographic peak slice area and the polyolefin molecular weight (MW), where N equals the number of data points obtained from the chromatogram between the integration limits.

[0189] A high temperature GPC instrument equipped with an infrared (IR) detector (IR4 or IR5 from PolymerChar (Valencia, Spain)) was used, equipped with 3x Agilent-PLgel Olexis and 1x Agilent-PLgel Olexis Guard columns. 1,2,4-Trichlorobenzene (TCB) stabilized with 250 mg / L 2,6-di-tert-butyl-4-methylphenol was used as solvent and mobile phase. The chromatographic system was operated at 160°C with a constant flow rate of 1 mL / min. 200 μL of sample solution was injected for each analysis. Data collection was performed using Agilent Cirrus software version 3.3 or PolymerChar GPC-IR control software.

[0190] The column set was calibrated using universal calibration (according to ISO 16014-2:2003) with 19 narrow MWD polystyrene (PS) standards ranging from 0.5 kg / mol to 11500 kg / mol. The PS standards were dissolved at room temperature for several hours. The polystyrene peak molecular weight was converted to polyolefin molecular weight using the Mark Houwink equation and the following Mark Houwink constants:

[0191] K PS =19x 10 -3 mL / g,α PS =0.655

[0192] K PE =39x 10 -3 mL / g,α PE =0.725

[0193] K PP =19x 10 -3 mL / g,α PP =0.725

[0194] A third-order polynomial fit was used to fit the calibration data.

[0195] All samples had a concentration range of 0.5-1 mg / ml and were dissolved at 160°C for 3 hours with constant gentle shaking.

[0196] Comonomer content - quantitative 13 C-NMR spectroscopy analysis

[0197] Quantification of microstructure by NMR spectroscopy

[0198] Quantitative nuclear magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers.

[0199] Quantitative 13C{1H}NMR spectra were recorded in the molten state using a Bruker Avance III 500 NMR spectrometer, operating at 500.13 and 125.76 MHz for 1H and 13C spectra, respectively. All spectra were recorded at 150 °C using a 13C-optimized 7 mm magic angle spinning (MAS) probe head, with nitrogen used for all pneumatics. Approximately 200 mg of material was loaded into a 7 mm outer diameter zirconium oxide MAS rotor, which was spun at 4 kHz. This setup was chosen primarily because it has the high sensitivity required for rapid identification and accurate quantification {klimke06,parkinson07,castignolles09}. Standard single pulse excitation was used, utilizing the NOE {pollard04,klimke06} with a short recycle delay of 3 s and the RS-HEPT decoupling scheme {fillip05,griffin07}. A total of 1024 (1k) transients were acquired for each spectrum.

[0200] Quantitative 13C{1H}NMR spectra were processed, integrated, and the relevant quantitative features determined from the integration. All chemical shifts were internally referenced to the bulk methylene signal (δ+) at 30.00 ppm and matched according to {randall89}.

[0201] The amount of ethylene is quantified using the integral of the methylene (δ+) sites at 30.00 ppm over the number of reported sites per monomer:

[0202] E=Iδ+ / 2

[0203] Characteristic signals arising from saturated end groups are observed. The amount of such saturated end groups is quantified using the average of the integrals of the 22.8 [I2S] and 32.2 ppm [I3S] signals matching the 2s and 3s sites, respectively:

[0204] S=(1 / 2)*(I2S+I3S)

[0205] The presence of comonomer units is corrected for the number of comonomer units and saturated end groups present:

[0206] Total E=E+(3 / 2)*B+(3 / 2)*BB+(5 / 2)*BEB+(2 / 2)*H+(3 / 2)*S

[0207] B and H are defined as the respective comonomers. If there is continuous and discontinuous comonomer incorporation, correction is made in a similar manner.

[0208] Characteristic signals corresponding to the incorporation of 1-butene were observed, and the comonomer fraction was calculated as the fraction of 1-butene in the polymer relative to all monomers in the polymer.

[0209] The amount of isolated 1-butene incorporated into the EEBEE sequence was quantified using the integral of the *B2 site at 39.9 ppm over the number of reported sites per comonomer:

[0210] B=I*B2

[0211] If present, the amount of 1-butene continuously incorporated into the EEBBEE sequence is quantified using the integral of the ααB2B2 site at 39.4 ppm over the number of reported sites per comonomer:

[0212] BB=2*IααB2B2

[0213] If present, the amount of non-continuously incorporated 1-butene in the EEBEBEE sequence was quantified using the integral of the ββB2B2 sites at 24.8 ppm over the number of reported sites per comonomer:

[0214] BEB=2*IββB2B2

[0215] Since the *B2 and *βB2B2 sites of isolated (EEBEE) and discontinuously incorporated (EEBEBEE) 1-butene overlap, the total amount of isolated 1-butene incorporation was corrected for the amount of discontinuous 1-butene present:

[0216] B=I*B2-2*IββB2B2

[0217] No BBB sequence was observed. The total 1-butene content was calculated from the sum of isolated, continuously and discontinuously incorporated 1-butene:

[0218] Total B=B+BB+BEB

[0219] The total mole fraction of 1-butene in the polymer is then calculated:

[0220] fB=B total / (E total+B total+H total)

[0221] Characteristic signals corresponding to 1-hexene incorporation were observed, and the comonomer fraction was calculated as the fraction of 1-hexene in the polymer relative to all monomers in the polymer.

[0222] The amount of isolated 1-hexene incorporated into the EEHEE sequence is quantified by the integration of the *B4 site at 38.3 ppm over the number of reported sites per comonomer:

[0223] H=I*B4

[0224] The total 1-hexene content is calculated from the separated incorporated 1-hexene only:

[0225] Htotal=H

[0226] Then calculate the mole fraction of 1-hexene in the polymer:

[0227] fH=H total / (E total+B total+H total)

[0228] The mole percentage of comonomer incorporation is calculated from the following mole fractions:

[0229] B [mol %] = 100 * fB

[0230] H [mol %] = 100 * fH

[0231] The weight percent comonomer incorporation was calculated from the following mole fractions:

[0232] B [weight %] = 100 * (fB * 56.11) / ((fB * 56.11) + (fH * 84.16) + ((1 - (fB + fH)) * 28.05))

[0233] H [weight %] = 100 * (fH * 84.16) / ((fB * 56.11) + (fH * 84.16) + ((1 - (fB + fH)) * 28.05))

[0234] For more details on this method see: J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201; Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, HW, Wilhelm, M., Macromol. Chem. Phys. 2006; 207: 382; Parkinson, M., Klimke, K., Spiess, HW, Wilhelm, M., Macromol. Chem. Phys. 2007; 208: 2128; Pollard, M., Klimke, K., Graf, R., Spiess, HW, Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004;37:813;Filip,X.,Tripon,C.,Filip,C.,J.Mag.Resn.2005,176,239;Griffin,JM,Tripon,C.,Samoson,A.,Filip,C.,and Brown, SP, Mag. Res. in Chem. 200745, S1, S198; Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373.

[0235] Dynamic shear measurement (frequency sweep measurement)

[0236] Elasticity Index (EI) and Shear Thinning Index (SHI)

[0237] 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 MCR501 stress-controlled rotational rheometer equipped with 25 mm parallel plate geometry. The measurements were performed as follows: on compression molded plaques, using a nitrogen atmosphere and setting strains in the linear viscoelastic range. Oscillatory shear tests were performed at 190 °C, applying a frequency range between 0.01 and 600 rad / s and setting a gap of 1.3 mm.

[0238] In dynamic shear experiments, the probe is subjected to uniform deformation under sinusoidally varying shear strain or shear stress (strain and stress controlled modes, respectively). In controlled strain experiments, the probe is subjected to a sinusoidal strain, which can be expressed as

[0239] γ(t)=γ0sin(ωt) (1)

[0240] If the applied strain is within the linear viscoelastic range, the resulting sinusoidal stress response can be expressed as

[0241] σ(t)=σ0sin(ωt+δ) (2)

[0242] in

[0243] σ0 and γ0 are stress and strain amplitudes, respectively;

[0244] ω is the angular frequency;

[0245] δ is the phase shift (loss angle between applied strain and stress response);

[0246] t is the time.

[0247] Dynamic test results are usually expressed by several different rheological functions, namely shear storage modulus G', shear loss modulus G", complex shear modulus G * , complex shear viscosity η * , dynamic shear viscosity, η', the out-of-phase component of complex shear viscosity, η", and the loss tangent tanδ can be expressed as follows:

[0248]

[0249] G * =G′+iG"[Pa] (5)

[0250] η * =η′-η"[Pa.s] (6)

[0251]

[0252] In addition to the above rheological functions, other rheological parameters can also be determined, such as the so-called elastic index EI(x). The elastic index EI(x) is the value of the storage modulus G', which is determined from the loss modulus G" in x kPa and can be described by Equation 9.

[0253] EI(χ)=G′(G″=χkPα)[Pa] (9)

[0254] For example, EI(5 kPa) is defined by the value of the storage modulus G', determined by G" being equal to 5 kPa.

[0255] The so-called shear thinning index is determined as shown in formula 10.

[0256]

[0257] For example, SHI(2,7 / 210) is defined as G* The complex viscosity value (in Pa.s) measured when it is equal to 2.7 kPa, divided by G * The complex viscosity value measured when the pressure is equal to 210 kPa (in Pa.s).

[0258] These values ​​were determined using a single-point interpolation procedure defined in the Rheoplus software. * In the case of a value, the value was determined by extrapolation using the same procedure as before. In both cases (interpolation or extrapolation), the options of Rheoplus - "Interpolate y values ​​into x values ​​according to parameter" and "Logarithmic interpolation type" were applied.

[0259] Polydispersity index PI, PI = 10 5 / GC, is calculated based on the intersection of G'(ω) and G"(ω), where G'(ω)=G"(ω)=GC holds.

[0260] For more details on this method, see “Rheological characterization ofpolyethylene fractions” Heino,EL,Lehtinen,A.,Tanner J., J., Neste Oy, Porvoo, Finland, Theor.Appl.Rheol., Proc.Int.Congr.Rheol, 11th (1992), 1, 360-362; "The influence of molecular structure on some rheological properties ofpolyethylene", Heino, EL, Borealis Polymers Oy, Porvoo, Finland, Annual Transactions of the Nordic Rheology Society, 1995; and "Definition of terms relating to the non-ultimate mechanical properties of polymers", Pure & Appl. Chem., Vol. 70, No. 3, pp. 701-754, 1998.

[0261] Tensile modulus

[0262] Tensile modulus was measured in machine direction (MD) and transverse direction (TD) according to ISO 527-3, blown film samples were prepared as described below under "Film Sample Preparation" with a film thickness of 40 μm and a crosshead speed of 1 mm / min for modulus.

[0263] Drop Dart Impact (DDI)

[0264] The dart drop impact (DDI) was measured using the ISO 7765-1 method on blown film samples having a thickness of 40 μm.

[0265] Haze and transparency

[0266] Haze and clarity were measured according to ASTM D1003-00 on blown films having a thickness of 40 μm as shown below.

[0267] Glossiness

[0268] Gloss was measured according to ASTM D 2457 on blown films with a thickness of 40 μm.

[0269] Invention Example 1 (IE1)

[0270] Volume: 50dm 3 The loop reactor was operated at a temperature of 70° C. and a pressure of 57 bar. Ethylene, propane diluent and hydrogen were fed to the reactor so that the feed rate of ethylene was 2.0 kg / h, the feed rate of 1-butene was 109 g / h and the feed rate of hydrogen was 5 g / h. In addition, a solid polymerization catalyst component as described above and prepared in Example 1 of EP1378528 was introduced into the reactor together with a triethylaluminum cocatalyst so that the molar ratio of Al / Ti was about 15. The production split was estimated to be about 1.5% by weight.

[0271] The slurry flow is continuously drawn out and directed to a volume of 150 dm 3 The reactor was further fed with additional ethylene, 1-butene comonomer, propane diluent and hydrogen so that the ethylene concentration in the fluid mixture was 4.3 mol%, the ratio of hydrogen to ethylene was 400 mol / kmol, the ratio of 1-butene to ethylene was 280 mol / kmol and the fresh propane (diluent) feed was 72.4 kg / h. The production split was estimated to be 15 wt%. The MFR2 of the resulting copolymer was 320 g / 10 min and the density was 953 kg / m 3 .

[0272] The slurry stream was intermittently withdrawn from the reactor and introduced into a 350 dm 3The reactor was operated at a temperature of 85°C and a pressure of 53 bar. Fresh propane, ethylene, 1-butene comonomer and hydrogen were further added to the reactor so that the ethylene concentration in the reaction mixture was 2.7 mol-%, the molar ratio of hydrogen to ethylene was 421 mol / kmol, and the molar ratio of 1-butene to ethylene was 745 mol / kmol. The MFR2 of the ethylene copolymer withdrawn from the reactor was 480 g / 10 min and the density was 950 kg / m 3 The estimated production split was 23.5 wt%.

[0273] The slurry was intermittently withdrawn from the loop reactor and directed to a flash tank operated at a temperature of 50° C. and a pressure of 3 bar. From there the polymer was directed to a fluidized bed gas phase reactor operated at a pressure of 20 bar and a temperature of 80° C. Additional ethylene, 1-butene comonomer, 1-hexene comonomer, nitrogen as an inert gas, and hydrogen were added so that the ethylene content in the reaction mixture was 14.5 mol-%, the ratio of hydrogen to ethylene was 7,49 mol / kmol, the molar ratio of 1-butene to ethylene was 345 mol / kmol, and the molar ratio of 1-hexene to ethylene was 65 mol / kmol. The polymer production split in the gas phase reactor was 60 wt.-%.

[0274] The polymer powder was mixed with 1200 ppm Irganox B561 and 400 ppm calcium stearate under nitrogen atmosphere, and then compounded and extruded into pellets using a JSW CIMP90 twin screw extruder under nitrogen atmosphere.

[0275] Tables 1 and 2 provide more details on the polymerization conditions and polymer properties.

[0276] IE2, CE1, and CE2

[0277] The procedure of IE1 was repeated by changing the reactor conditions as described in Table 1.

[0278] Tables 1 and 2 summarize the polymerization conditions and material properties of the present invention and comparative examples.

[0279] Table 1

[0280]

[0281]

[0282]

[0283] To calculate the properties of fraction B, the PEM1 fraction is collected after the second loop reactor and analyzed (except for the Mw and C4 content of CE2; in this case, the average of CE1, IE1 and IE2 is taken for the calculation, since the process parameters are intended to remain the same or not differ significantly after the second loop. See Table 2 below for details). This allows the calculation of the properties of the third ethylene copolymer B, more specifically the contents of the two comonomers and their relative ratios.

[0284] Table 2

[0285]

[0286]

[0287] *Not directly measured. Calculated using the average of CE1, IE1 and IE2.

[0288] **Values ​​calculated based on PEM1 and composition measurements.

[0289] Thin film preparation method

[0290] The film samples were produced on a small laboratory blown film line from COLLIN Lab&Pilot Solutions GmbH.

[0291] The production line consists of an extruder with a screw diameter of The L / D ratio was 30. The extruder temperature was set at 200°C and the melt temperature was 202°C and recorded after 45 minutes of process stabilization. The extruder was followed by a blow head equipped with a 60 mm diameter annular die and a die gap of 1.5 mm. The line was run at a constant line speed of 7.5 m / min. The blow-up ratio (BUR) of the film bubble was 2.5:1 and the frost line height was 120 mm. The film thickness produced was 40 μm.

[0292] Thin film sample preparation

[0293] The blown film was wound into reels and the film was cut to size for further mechanical testing.

[0294] According to the above film preparation method, blown films were produced using the compositions of CE, CE2, IE1 and IE2.

[0295] The film properties are shown in Table 3.

[0296] Table 3

[0297]

[0298]

[0299] The above experimental results prove that the ethylene copolymer composition of the present invention can produce films with significantly improved dart impact performance. Importantly, the optical properties (such as haze, gloss and transparency) of the film can be maintained at the desired level. In addition, the film obtained by the ethylene copolymer composition of the present invention exhibits the same or even better mechanical properties (tensile modulus) than traditional ethylene polymer compositions. Therefore, the present invention provides materials with a unique balance of properties, which are particularly suitable for packaging applications.

[0300] In particular, by comparing the results of Table 2 and Table 3, the effect of the second comonomer content in the third copolymer portion B on the dart impact performance can be clearly seen. CE1 has no second comonomer in portion B and has a moderate DDI value of 238 g. CE2, although containing 8.4% of the second α-olefin comonomer (relatively speaking), still has a moderate DDI value of 250 g. However, once the relative proportion of the second comonomer increases to 29.9 or even 76% for IE1 and IE2, respectively, the DDI increases significantly to 408 and 480 g, respectively. At the same time, the mechanical and optical properties are essentially unchanged.

Claims

1. A multimodal ethylene copolymer composition comprising: - 5 to 25 wt.-%, relative to the total weight of the multimodal ethylene copolymer composition, of a first ethylene copolymer (A1) comprising a copolymer of ethylene and at least a first α-olefin comonomer having a density of from 920 to 960 kg / m 3 within the scope of - 15 to 35 wt.-%, relative to the total weight of the multimodal ethylene copolymer composition, of a second ethylene copolymer (A2) comprising a copolymer of ethylene and at least the first α-olefin comonomer having a density of from 920 to 960 kg / m 3 within the scope of - 40 to 80 wt.-%, relative to the total weight of said multimodal ethylene copolymer composition, of a third ethylene copolymer (B) comprising a copolymer of ethylene with at least said first and second α-olefin comonomers; wherein the third ethylene copolymer (B) has a higher weight average molecular weight (M) than the first ethylene copolymer (A1) and the second ethylene copolymer (A2). W ); wherein the composition has: - 915 to 930 kg / m2 measured according to ISO 1183-187 3 Density within range; - an MFR5 in the range of 0.5 to 5.0 g / 10 min, measured according to ISO 1133; and Among them, according to the quantitative 13 C-NMR spectral analysis determines that the content of the second α-olefin comonomer in the third ethylene polymer (B) is in the range of 15 to 85%, based on the total comonomer content on a mole basis in the third ethylene copolymer (B).

2. The multimodal ethylene copolymer composition according to claim 1, wherein According to quantitative 13 The total comonomer content in the multimodal ethylene copolymer composition is in the range of 1.5 to 5 mol %, as determined by C-NMR spectroscopy.

3. The multimodal ethylene copolymer composition according to any one of the preceding claims, in, The first α-olefin comonomer is selected from α-olefins having 3 to 10 carbon atoms, preferably 1-butene; and / or The second α-olefin comonomer is selected from α-olefins having 3 to 10 carbon atoms, preferably 1-hexene.

4. The multimodal ethylene copolymer composition according to claim 3, in, The multimodal ethylene copolymer composition has the first α-olefin comonomer as 1-butene, according to the quantitative 13 C-NMR spectral analysis determined that its content is 0.5 to 4.5 mol%, and / or The multimodal ethylene copolymer composition has the second α-olefin comonomer as 1-hexene, according to the quantitative 13 The content thereof is 0.5 to 4.5 mol %, as determined by C-NMR spectral analysis.

5. The multimodal ethylene copolymer composition according to any one of the preceding claims, in, According to quantitative 13 The total comonomer content in the third ethylene copolymer (B) is 1 to 10 mol % as determined by C-NMR spectral analysis.

6. A multimodal ethylene copolymer composition according to any one of the preceding claims, in, The multimodal copolymer composition has an MFR2, determined according to ISO 1133, in the range of 0.01 to 0.5 g / 10 min.

7. A multimodal ethylene copolymer composition according to any one of the preceding claims, in, The composition M W / M n ratio in the range of 10 to 25 and / or M Z / M W The ratio is in the range of 4 to 10.

8. A process for producing a multimodal ethylene copolymer composition according to any one of the preceding claims, comprising the steps of: (a) polymerizing ethylene and at least one first α-olefin comonomer in a first polymerization step to produce a first ethylene copolymer (A1); (b) polymerizing ethylene and at least a first α-olefin comonomer in the presence of said first ethylene copolymer (A1) in a second polymerization step to produce a first ethylene copolymer mixture (PEM1) comprising said first ethylene copolymer (A1) and a second ethylene copolymer (A2), and (c) polymerizing ethylene, the first α-olefin comonomer and a second α-olefin comonomer in the presence of the first ethylene copolymer mixture (PEM1) in a third polymerization step to produce a second ethylene copolymer mixture (PEM2) comprising the first ethylene copolymer mixture (PEM1) and a third ethylene copolymer (B), (d) extruding said second ethylene copolymer mixture (PEM2) to obtain said multimodal ethylene copolymer composition.

9. The method according to claim 8, wherein: Steps (a), (b) and (c) are carried out in the presence of a Ziegler-Natta polymerisation catalyst.

10. A film comprising a multimodal ethylene copolymer composition according to any one of claims 1 to 7 and / or obtainable by the process of claim 8 or 9.

11. The film according to claim 10, having a haze in the range of 50 to 95%, preferably 60 to 90%, more preferably 70 to 80%, measured on a 40 μm blown film according to ASTM D1003.

12. The film according to any one of claims 10 or 11, having a dart drop impact strength (DDI) in the range of 300 g to 900 g, preferably in the range of 350 g to 700 g, measured according to ISO 7765-1 "Method A" on a 40 μm blown film.

13. The film according to any one of claims 10 to 12, A tensile modulus in the machine direction (MD) in the range of 150 to 500 MPa, measured on a 40 μm blown film according to ISO 527-3, and / or The tensile modulus in the transverse direction (TD) is in the range of 250 to 500 MPa, measured according to ISO 527-3 on 40 μm blown films.

14. The film according to any one of claims 10 to 13, The transparency is in the range of 5 to 20%, preferably 10 to 18%, measured on a 40 μm blown film according to ASTM D1003.

15. The film according to any one of claims 10 to 14, which is a single-layer or multi-layer film.

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