Process for preparing a polypropylene composition

Abstract

The present invention relates to a process for preparing a polypropylene composition by sequential polymerization which is improved in terms of a balanced combination of high flow, high stiffness and impact resistance, and high optical properties.

Description

[0001] This application is a divisional application of a patent application with application number 201880003734.1 filed on June 27, 2018 and invention name “Method for Preparing Polypropylene Composition”. Technical Field

[0002] The present invention relates to a process for preparing a polypropylene composition by sequential polymerization. More specifically, the present invention relates to the preparation of a polypropylene composition comprising propylene and one or more selected from ethylene and C4-C 10 The present invention relates to a method for producing a polypropylene composition having a comonomer of an α-olefin, and relates to a polypropylene composition obtained by the method. The present invention also relates to an article comprising the polypropylene composition.

[0003] BACKGROUND OF THE INVENTION Propylene homopolymers and copolymers are suitable for use in many applications, such as packaging, textiles, automotive and pipes. One important field of application of propylene homopolymers and copolymers is the packaging industry, in particular in film and molding applications.

[0004] In the field of packaging, polypropylene compositions with good flowability and good mechanical properties (i.e. high tensile modulus and good impact strength) are very important. Good flowability is required in order to achieve good processability in a variety of product manufacturing processes (e.g., in injection molding processes), thereby allowing the higher production speeds typically required in the mass production market. In this type of application, especially in the field of containers where it is necessary to accommodate contents (e.g., food or fluids contained therein), mechanical properties are also important. In addition, for containers to be stacked, it is necessary to have sufficient rigidity.

[0005] Additionally, the polypropylene composition should also be able to withstand mechanical compression damage which may occur from time to time, for example by throwing the article.

[0006] In addition, the haze should also be acceptable. Specifically, there needs to be a good balance between stiffness and haze.

[0007] However, at least some of these properties can only be achieved at the expense of other properties in these properties. For example, as the melt flow rate increases, the stiffness can be improved, but the impact properties decrease significantly. Therefore, the impact strength and melt flow rate of the polypropylene composition are manifested in a contradictory manner.

[0008] Furthermore, the high crystallinity of the polypropylene composition makes it very stiff, but this also increases its haze. Therefore, the balance of stiffness and haze in the polypropylene composition is very important.

[0009] Therefore, there is a need for a process for preparing polypropylene compositions having a balanced combination of high flow, high stiffness and high impact resistance as well as high optical properties (low haze values).

[0010] EP2539398 discloses a method for preparing a random propylene copolymer by a sequential polymerization process, wherein the method comprises the following steps:

[0011] a) in a first reactor (R1) propylene and at least one ethylene and / or C4 to C 20 α-olefins are polymerized to obtain a polypropylene (PP1) which is a random propylene copolymer (R-PP1), the polypropylene (PP1) having a melt flow rate MFR measured according to ISO 1133 of not more than 1.5 g / 10 min 10 (230℃),

[0012] b) transferring the first polypropylene (PP1) into a second reactor (R2),

[0013] c) in a second reactor (R2), propylene and optionally at least one ethylene and / or C4 to C 20 a first propylene homopolymer (H-PP1) or a second random propylene copolymer (R-PP2),

[0014] d) transferring the mixture of the first polypropylene (PP1) and the second polypropylene (PP2) into a third reactor (R3), and

[0015] e) in a third reactor (R3), propylene and optionally at least one ethylene and / or C4 to C6 polypropylene are reacted in the presence of a mixture of the first polypropylene (PP1) and the second polypropylene (PP2); 20 The α-olefin is polymerized to obtain a third polypropylene (PP3), which is the second propylene homopolymer (H-PP2) or the third random propylene copolymer (R-PP3), and the first polypropylene (PP1), the second polypropylene (PP2) and the third polypropylene (PP3) form a (compact) mixture.

[0016] However, the invention in EP2539398 relates to pipes, and thus the obtained random propylene copolymer has an MFR2 between 0.5 and 10.0 g / 10 min and may contain, inter alia, a β-nucleating agent. Furthermore, EP2539398 does not disclose the haze properties of the obtained random propylene copolymer. Summary of the invention

[0017] The present invention is based on the finding that the above discussed need for a balanced combination of high flowability, high stiffness and impact resistance and high optical properties (low haze values) can be achieved by a process for preparing a specific polypropylene composition. Accordingly, the present invention provides a process for preparing a polypropylene composition by sequential polymerization, the process comprising the following steps:

[0018] a) reacting a monomer comprising propylene and optionally one or more monomers selected from ethylene and C4-C 10 a-olefin comonomer is polymerized to obtain a first propylene polymer fraction having a comonomer content in the range of 0.0 to 1.0 wt%,

[0019] b) in a second reactor (preferably a first gas phase reactor), in the presence of a first propylene polymer fraction, reacting a monomer comprising propylene and one or more monomers selected from ethylene and C4-C 10 a-olefin comonomer to obtain a second propylene polymer fraction having a comonomer content in the range of 0.3 to 2.0 wt%,

[0020] c) in a third reactor (preferably a second gas phase reactor), reacting a monomer comprising propylene and one or more monomers selected from ethylene and C4-C 10 a-olefin comonomer to obtain a third propylene polymer fraction having a comonomer content in the range of 1.5 to 5.0 wt%,

[0021] d) extruding a third propylene polymer fraction in the presence of at least one alpha nucleating agent,

[0022] Therein the polypropylene composition has an MFR2 in the range of 12.0 to 60.0 g / 10 min, measured according to ISO 1133 at 230°C and 2.16 kg load.

[0023] According to the present invention, the first propylene polymer fraction, the second propylene polymer fraction and the third propylene polymer fraction are produced in a sequential polymerization process. In the present application, the term "sequential polymerization process" refers to producing propylene polymer fractions in a process comprising at least three reactors connected in series. In a preferred embodiment, in the present application, the term "sequential polymerization process" refers to conveying (preferably directly conveying) the reaction mixture of the first reactor (that is, the first propylene polymer fraction containing unreacted monomers) to the second reactor where the second propylene polymer fraction is obtained. The reaction mixture of the second reactor (that is, the second propylene polymer fraction containing unreacted monomers) is conveyed (preferably directly conveyed) to the third reactor where the third propylene polymer fraction is obtained.

[0024] Therefore, in the method according to the invention:

[0025] i- the first propylene polymer fraction obtained from the first reactor typically comprises the first propylene polymer produced in said first reactor,

[0026] ii- The second propylene polymer fraction obtained from the second reactor typically comprises the second propylene polymer produced in said second reactor.

[0027] iii- The third propylene polymer fraction obtained from the third reactor typically comprises the third propylene polymer produced in said third reactor.

[0028] Therefore, the present method comprises at least a first reactor, a second reactor and a third reactor. The method may include at least one additional polymerization reactor after the third reactor. In a specific embodiment, the method according to the present invention consists of three polymerization reactors (i.e., a first reactor, a second reactor and a third reactor). The term "polymerization reactor" should refer to where the main polymerization reaction occurs. Therefore, in the case where the method consists of three or more polymerization reactors, this definition does not exclude the selection of a prepolymerization step, such as in a prepolymerization reactor, for the entire method. The term "consisting of..." is only a closed form considering the case of the main polymerization reactor.

[0029] In case the overall process according to the present invention comprises a prepolymerization reactor, the term "first propylene polymer fraction" refers to the sum of the (co)polymer produced in the prepolymerization reactor and the (co)polymer produced in the first reactor.

[0030] The reactor is typically selected from a slurry reactor and a gas phase reactor.

[0031] The first reactor is preferably a slurry reactor and can be any continuous or simply stirred batch reactor or loop reactor operating in bulk polymerization or slurry polymerization. "Bulk polymerization" refers to a method of polymerization in liquid monomers substantially absent of an inert diluent. However, as known to those skilled in the art, monomers used for commercial production are never pure and always contain aliphatic hydrocarbons as impurities. For example, propylene monomers may contain up to 5% propane as an impurity. Therefore, "bulk polymerization" preferably refers to polymerization carried out in a reaction medium comprising at least 60% (wt / wt) monomer. According to the present invention, the first reactor is more preferably a loop reactor.

[0032] The second reactor is preferably a first gas phase reactor. The first gas phase reactor may be any mechanically mixed or fluidized bed reactor or a settled bed reactor. Preferably, the first gas phase reactor comprises a mechanically stirred fluidized bed reactor having a gas velocity of at least 0.2 m / s. The first gas phase reactor of the fluidized bed reactor may also comprise a mechanical agitator to facilitate mixing in the fluidized bed.

[0033] The third reactor is preferably a second gas phase reactor. The second gas phase reactor may be any mechanically mixed reactor or a fluidized bed reactor or a settled bed reactor. Preferably, the second gas phase reactor comprises a mechanically stirred fluidized bed reactor having a gas velocity of at least 0.2 m / s. The second gas phase reactor of the fluidized bed reactor may also comprise a mechanical agitator to facilitate mixing in the fluidized bed.

[0034] The potential subsequent polymerization reactor or reactors are preferably gas phase reactors.

[0035] The preferred polymerization process is a "loop-gas phase" process, such as that developed by Borealis and known as BORSTAR TM The "loop-gas phase" process of the WO 92 / 12182 technology. Examples of such polymerization processes are described in EP0887379, WO92 / 12182, WO2004 / 000899, WO2004 / 111095, WO99 / 24478, WO99 / 24479 and WO00 / 68315.

[0036] When the overall process according to the invention comprises a prepolymerization reactor, the prepolymerization step is carried out before the polymerization carried out in the first reactor. The prepolymerization step is carried out in a prepolymerization reactor in which the pre(co)polymerization of propylene is carried out. The prepolymerization reactor is smaller in size compared to the first reactor, the second reactor, the third reactor and the subsequent one or more polymerization reactors according to the invention, respectively. The reaction volume of the prepolymerization reactor can be, for example, between 0.001% and 10% of the reaction volume of the first reactor (such as a loop reactor). In the prepolymerization reactor, the pre(co)polymerization of propylene is carried out in a bulk or slurry manner to produce a propylene (co)polymer.

[0037] The operating temperature in the prepolymerization reactor is in the range of 0 to 60°C, preferably in the range of 15 to 50°C, more preferably in the range of 18 to 35°C.

[0038] The pressure in the prepolymerization reactor is not critical, but the pressure needs to be high enough to keep the reaction mixture in liquid phase. Therefore, the pressure in the prepolymerization reactor may be in the range of 20 to 100 bar, preferably in the range of 30 to 70 bar.

[0039] Hydrogen may be added to the prepolymerization reactor in order to control the molecular weight and thus the melt flow rate MFR2 of the propylene (co)polymer produced in the prepolymerization reactor.

[0040] In the first reactor of the process according to the invention, a mixture containing propylene and optionally one or more hydrocarbons selected from ethylene and C4-C 10 A monomer feed of a comonomer of an α-olefin is fed. In case a prepolymerization step is present in the process, the propylene (co)polymer produced in the prepolymerization reactor is also fed to the first reactor. In this first reactor, a first propylene polymer fraction is obtained.

[0041] The first propylene polymer fraction is selected from ethylene and C4-C 10 The comonomer content of the α-olefin is typically in the range of 0.0 to 1.0 wt%, preferably in the range of 0.0 to 0.8 wt%, more preferably in the range of 0.0 to 0.7 wt%, relative to the total amount of monomers present in the first propylene polymer fraction.

[0042] Typically, the melt flow rate (MFR2) of the first propylene polymer fraction is in the range of 11 to 60 g / 10 min, preferably in the range of 15 to 40 g / 10 min, more preferably in the range of 17 to 35 g / 10 min. MFR2 is determined according to ISO 1133 at a temperature of 230°C and a load of 2.16 kg.

[0043] The operating temperature in the first reactor is generally in the range of 62 to 85°C, preferably in the range of 65 to 82°C, more preferably in the range of 67 to 80°C.

[0044] Typically, the pressure in the first reactor is in the range of 20 to 80 bar, preferably in the range of 30 to 70 bar, more preferably in the range of 35 to 65 bar.

[0045] Hydrogen may be added to the first reactor in order to control the molecular weight and thus the melt flow rate MFR2 of the first propylene polymer fraction obtained in said first reactor.

[0046] Typically, the hydrogen / propylene (H2 / C3) ratio in the first reactor is in the range of 1.5 to 6.0 mol / kmol, preferably in the range of 1.6 to 5.5 mol / kmol, more preferably in the range of 1.7 to 5.0 mol / kmol.

[0047] Typically, the one or more comonomers (selected from ethylene and C4-C 10The ratio of C1-α-olefins to C3 is lower than 10.0 mol / kmol, preferably in the range of 0.0 to 8.0 mol / kmol, more preferably in the range of 0.0 to 7.5 mol / kmol.

[0048] Typically, the reaction mixture of the first reactor is transferred (preferably directly transferred) to the second reactor. "Direct transfer" refers to a method in which the reaction mixture of the first reactor is directly fed to the next polymerization step (i.e., the second reactor). The monomers comprising propylene and one or more selected from ethylene and C4-C 10 The comonomer of α-olefin is fed into the second reactor. In the second reactor, a second propylene polymer fraction is obtained.

[0049] The amount of monomers selected from the group consisting of ethylene and C4-C 10 The comonomer content of the α-olefin is generally in the range of 0.3 to 2.0 wt%, preferably in the range of 0.5 to 1.7 wt%, more preferably in the range of 0.6 to 1.5 wt%.

[0050] Typically the melt flow rate (MFR2) of the second propylene polymer fraction is in the range of 11 to 60 g / 10 min, preferably in the range of 15 to 40 g / 10 min, more preferably in the range of 17 to 35 g / 10 min. MFR2 is determined according to ISO 1133 at a temperature of 230°C and a load of 2.16 kg.

[0051] The operating temperature in the second reactor is generally in the range of 70 to 95°C, preferably in the range of 75 to 90°C, more preferably in the range of 78 to 88°C.

[0052] Typically, the pressure in the second reactor is in the range of 5 to 50 bar, preferably in the range of 15 to 40 bar.

[0053] Hydrogen may be added to the second reactor in order to control the molecular weight and thus the melt flow rate MFR2 of the second propylene polymer fraction obtained from said second reactor.

[0054] Typically, the ratio of hydrogen / propylene (H2 / C3) in the second reactor is in the range of 12.0 to 70.0 mol / kmol, preferably in the range of 15.0 to 60.0 mol / kmol, more preferably in the range of 16.0 to 50.0 mol / kmol.

[0055] Typically, the one or more comonomers (selected from ethylene and C4-C 10The ratio of C1-α-olefins to C3 is in the range of 4.5 to 20.0 mol / kmol, preferably in the range of 5.0 to 18.0 mol / kmol, and more preferably in the range of 5.5 to 17.0 mol / kmol.

[0056] Typically, the reaction mixture of the second reactor is transferred (preferably directly transferred) to the third reactor. "Direct transfer" refers to a method in which the reaction mixture of the second reactor is directly fed to the next polymerization step (i.e., the third reactor). Include Propylene monomer and one or more selected from ethylene and C4-C 10 The comonomer of α-olefin is fed into the third reactor. In the third reactor, a third propylene polymer fraction is obtained.

[0057] The third propylene copolymer fraction contains ethylene and C4-C 10 The comonomer content of the α-olefin is generally in the range of 1.5 to 5.0 wt%, preferably in the range of 1.6 to 4.0 wt%, more preferably in the range of 1.7 to 3.5 wt%.

[0058] Typically, the melt flow rate (MFR2) of the third propylene polymer fraction is in the range of 12 to 60 g / 10 min, preferably in the range of 15 to 40 g / 10 min, more preferably in the range of 17 to 35 g / 10 min. MFR2 is determined according to ISO 1133 at a temperature of 230°C and a load of 2.16 kg.

[0059] The operating temperature in the third reactor is generally in the range of 70 to 95°C, preferably in the range of 75 to 90°C, more preferably in the range of 78 to 88°C.

[0060] Typically, the pressure in the third reactor is in the range of 5 to 50 bar, preferably in the range of 15 to 40 bar.

[0061] Hydrogen may be added to the third reactor in order to control the molecular weight and thus the melt flow rate MFR2 of the third propylene polymer fraction obtained from said third reactor.

[0062] Typically, the ratio of hydrogen / propylene (H2 / C3) in the third reactor is in the range of 15.0 to 80.0 mol / kmol, preferably in the range of 17.0 to 70.0 mol / kmol, and more preferably in the range of 19.0 to 60.0 mol / kmol.

[0063] Typically, the one or more comonomers (selected from ethylene and C4-C 10The ratio of C1-α-olefins to C3 is in the range of 45.0 to 200.0 mol / kmol, preferably in the range of 50.0 to 180.0 mol / kmol, and more preferably in the range of 55.0 to 170.0 mol / kmol.

[0064] In the process according to the present invention, the production amount of the propylene polymer produced in the first reactor (i.e. the first propylene polymer) is generally in the range of 8 to 55 wt%, preferably in the range of 9 to 52 wt%, more preferably in the range of 10 to 50 wt%.

[0065] In the process according to the present invention, the production amount of the propylene polymer produced in the second reactor (i.e., the second propylene polymer) is generally in the range of 30 to 86 wt%, preferably in the range of 35 to 80 wt%, more preferably in the range of 38 to 78 wt%. In the process according to the present invention, the production amount of the propylene polymer produced in the third reactor (i.e., the third propylene polymer) is generally in the range of 6 to 30 wt%, preferably in the range of 7 to 28 wt%, more preferably in the range of 8 to 27 wt%. The amount of the first propylene polymer, the second propylene polymer and the third propylene polymer is relative to the sum of the first propylene polymer, the second propylene polymer and the third propylene polymer contained in the third propylene polymer fraction.

[0066] In a preferred embodiment, one or more selected from ethylene and C4-C 10 A comonomer of an α-olefin is incorporated into the reactor of the process of the present invention at different levels to obtain a third propylene polymer fraction containing a trimodal comonomer distribution regarding the comonomer content of each propylene polymer contained in the third propylene polymer fraction, i.e. the first propylene polymer, the second propylene polymer and the third propylene polymer.

[0067] In the process according to the invention, throughout the present invention, the one or more comonomers are selected from ethylene and C4-C 10 The α-olefin is preferably selected from ethylene and C4-C8 α-olefins, more preferably selected from ethylene and C4-C6 α-olefins, even more preferably selected from one or more comonomers comprising ethylene, even more preferably still, the comonomer is selected only from ethylene.

[0068] After the polymerization in the third reactor step, the third propylene polymer fraction obtained in the third reactor is recovered by conventional methods known to those skilled in the art. The recovered third propylene polymer fraction according to the present invention is typically in the form of particles.

[0069] Typically, a polymerization catalyst is present in the process according to the invention. The polymerization catalyst is preferably a Ziegler-Natta catalyst. Typically, the Ziegler-Natta polymerization catalyst comprises one or more compounds of transition metals (TM) of groups 4 to 6 as defined by IUPAC (2013 edition) (such as titanium), and also comprises a metal compound of group 2 (such as a magnesium compound) and an internal donor (ID).

[0070] The catalyst components can be supported on a particulate support, for example an inorganic oxide, such as silicon dioxide or aluminum oxide. Alternatively, the magnesium halide can form a solid support. The catalyst components can also not be supported on an external support, but the catalyst is prepared by an emulsion-solidification method or by a precipitation method (as known to those skilled in the art of catalyst preparation).

[0071] Preferably, a specific type of Ziegler-Natta catalyst is present in the method according to the invention. In this specific type of Ziegler-Natta catalyst, the internal donor needs to be a non-phthalic acid compound. Preferably, in the preparation of the entire specific type of Ziegler-Natta catalyst, no phthalate compound is used, so that the final specific type of Ziegler-Natta catalyst does not contain any phthalic acid compound. Therefore, the specific type of Ziegler-Natta catalyst does not contain phthalic acid compounds. Therefore, the third propylene polymer fraction obtained in the third reactor of the method according to the invention does not contain phthalic acid compounds.

[0072] Typically, the specific type of Ziegler-Natta catalyst comprises an internal donor (ID) selected as a non-phthalic acid compound, in such a way that the specific type of Ziegler-Natta catalyst is completely free of phthalic acid compounds. In addition, the specific type of Ziegler-Natta catalyst may be a solid catalyst, which preferably does not contain any external support material (such as silica or MgCl2), so that the solid catalyst is self-supported.

[0073] The solid catalyst can be obtained by the following conventional steps:

[0074] a) Provide the following solution:

[0075] a1) a solution of at least a Group 2 metal alkoxide (Ax) which is the reaction product of a Group 2 metal compound and an alcohol (A) which comprises, in addition to hydroxyl moieties, at least one ether moiety, optionally in an organic liquid reaction medium; or

[0076] a2) at least one Group 2 metal alkoxide (A X '), the Group 2 metal alkoxide (A X') is the reaction product of a Group 2 metal compound with an alcohol mixture of an alcohol (A) and a monohydric alcohol (B) of the formula ROH, optionally in an organic liquid reaction medium; or

[0077] a3) A solution of a mixture of a Group 2 metal alkoxide (A X ) and a Group 2 metal alkoxide (B X ), wherein the Group 2 metal alkoxide (B X ) is the reaction product of a Group 2 metal compound with a monohydric alcohol (B), optionally in an organic liquid reaction medium; or

[0078] a4) A solution of a mixture of a Group 2 metal alkoxide or Group 2 alcoholate of the formula M(OR1) n (OR2) m X 2-n-m and M(OR2) n’ X 2-n’ and M(OR2) m’ X 2-m’ wherein M is a Group 2 metal, X is a halogen, R1 and R2 are different alkyl groups having 2 to 16 carbon atoms, and 0 ≤ n < 2, 0 ≤ m < 2 and n + m+(2 - n - m)=2, provided that n and m are not both 0, 0 < n' ≤ 2 and 0 < m' ≤ 2; and

[0079] b) Adding the solution from step a) to a compound of at least one transition metal of Groups 4 to 6, and

[0080] c) Obtaining solid catalyst component particles,

[0081] and adding a non-phthalic internal electron donor (ID) in at least one step before step c).

[0082] Preferably, the internal donor (ID) or its precursor is added to the solution of step a) or to the transition metal compound before adding the solution of step a).

[0083] According to the above steps, a solid catalyst can be obtained via a precipitation method or via an emulsion-curing method, depending on the physical conditions, especially the temperature used in steps b) and c). An emulsion is also referred to as a liquid-liquid two-phase system. In both methods (precipitation or emulsion-curing), the chemical properties of the catalyst are the same.

[0084] In the precipitation method, the solution of step a) is mixed with at least one transition metal compound in step b), and the entire reaction mixture is maintained at a temperature of at least 50 °C, more preferably in the temperature range of 55 to 110 °C, more preferably in the range of 70 to 100 °C, to ensure complete precipitation of the catalyst components in the form of solid catalyst component particles (step c).

[0085] In the emulsion-solidification process, in step b), the solution of step a) is added to at least one transition metal compound, usually at a relatively low temperature (such as from -10 to below 50°C, preferably from -5 to 30°C). During the stirring of the emulsion, the temperature is usually maintained at -10 to below 40°C, preferably from -5 to 30°C. The droplets of the dispersed phase of the emulsion form an active catalyst composition. The droplets are suitably solidified (step c) by heating the emulsion to a temperature of 70 to 150°C (preferably 80 to 110°C). The catalyst prepared by the emulsion-solidification process is preferably used in the present invention.

[0086] In step a), preferably a solution of a2) or a3) is used, ie a solution of (Ax') or a solution of a mixture of (Ax) and (Bx).

[0087] Preferably, the Group 2 metal is magnesium. The alkoxymagnesium compounds (Ax), (Ax'), (Bx) can be prepared in situ in the first step (step a)) of the catalyst preparation process by reacting a magnesium compound with an alcohol as described above. Another option is to prepare the various alkoxymagnesium compounds separately, or they can even be commercially available as already prepared alkoxymagnesium compounds, and to use the alkoxymagnesium compounds thus obtained in the catalyst preparation process of the present invention.

[0088] Illustrative examples of alcohol (A) are glycol monoethers. Preferred alcohols (A) are C2 to C4 glycol monoethers, wherein the ether moiety contains 2 to 18 carbon atoms, preferably 4 to 12 carbon atoms. Preferred examples are 2-(2-ethylhexyloxy)ethanol, 2-butoxyethanol, 2-hexyloxyethanol and 1,3-propylene glycol-monobutyl ether, 3-butoxy-2-propanol, wherein 2-(2-ethylhexyloxy)ethanol and 1,3-propylene glycol-monobutyl ether and 3-butoxy-2-propanol are particularly preferred.

[0089] An exemplary monohydric alcohol (B) is represented by the structural formula ROH, wherein R is a linear or branched C2-C 16 Alkyl residues, preferably C4 to C 10 The most preferred monohydric alcohol is 2-ethyl-1-hexanol or octanol.

[0090] Preferably, a mixture of alkoxymagnesium compounds (Ax) and (Bx) or a mixture of alcohols (A) and (B) is used, respectively, and the molar ratio of Bx:Ax or B:A used is 10:1 to 1:10, more preferably 6:1 to 1:6, still more preferably 5:1 to 1:3, most preferably 5:1 to 3:1.

[0091] The alkoxymagnesium compound may be the reaction product of an alcohol (class) as defined above and a magnesium compound selected from the group consisting of dialkylmagnesium, alkylmagnesium alkoxides, dialkoxymagnesium, alkoxymagnesium halides and alkylmagnesium halides. In addition, dialkoxymagnesium, diaryloxymagnesium, aryloxymagnesium halides, aryloxymagnesium and alkylaryloxymagnesium may be used. The alkyl groups in the magnesium compound may be similar or different C1-C 20 Alkyl group, preferably C2-C 10 Alkyl group. When an alkyl-alkoxy magnesium compound is used, typical alkyl-alkoxy magnesium compounds are ethyl butoxy magnesium, butyl pentoxy magnesium, octyl butoxy magnesium and octyl octoxy magnesium. Preferably, a dialkyl magnesium is used. Most preferably, the dialkyl magnesium is butyl octyl magnesium or butyl ethyl magnesium.

[0092] The magnesium compound may also react with an alcohol of the formula R" (OH) other than the alcohol (A) and the alcohol (B). m If a polyol is used, the preferred polyol is a C2 to C3 polyol wherein R" is a linear, cyclic or branched 10 A hydrocarbon residue and m is an alcohol having an integer of 2 to 6.

[0093] Thus, the alkoxymagnesium compound of step a) is selected from the group consisting of dialkoxymagnesium, diaryloxymagnesium, alkoxymagnesium halide, aryloxymagnesium halide, alkylmagnesium alkoxide, arylalkoxymagnesium and alkylaryloxymagnesium or a mixture of dihalide and dialkoxymagnesium.

[0094] The solvent used for preparing the catalyst of the present invention can be selected from aromatic and aliphatic straight chain, branched and cyclic hydrocarbons or mixtures thereof having 5 to 20 carbon atoms (more preferably 5 to 12 carbon atoms). Suitable solvents include benzene, toluene, cumene, xylene, pentane, hexane, heptane, octane and nonane. Hexane and pentane are particularly preferred.

[0095] The reaction for preparing the alkoxymagnesium compound can be carried out at a temperature of 40 to 70° C. A person skilled in the art knows how to select the most suitable temperature depending on the magnesium compound and alcohol used.

[0096] The Group 4 to 6 transition metal (TM) compound as defined by IUPAC (2013 edition) is preferably a titanium compound, most preferably a titanium halide, such as TiCl4.

[0097] The non-phthalic internal donor (ID) used in the preparation of the specific type of Ziegler-Natta catalyst used in the present invention is preferably selected from (di)esters of non-phthalic carboxylic (di)acids, 1,3-diethers, derivatives and mixtures thereof. Particularly preferred donors are diesters of monounsaturated non-phthalic dicarboxylic acids, in particular esters belonging to the group comprising malonates, maleates, succinates, citraconates, glutarates, cyclohexene-1,2-dicarboxylates and benzoates and derivatives and / or mixtures thereof. Preferred examples are, for example, substituted maleates and citraconates, most preferably citraconates.

[0098] Here and hereinafter the term derivative includes substituted compounds.

[0099] In the emulsion-curing process, a liquid-liquid two-phase system can be formed by simple stirring in a manner known in the art and optionally adding (other) solvents and / or additives, such as turbulence minimizing agents (TMAs) and / or emulsifiers and / or emulsion stabilizers (such as surfactants). These solvents and / or additives are used to promote emulsion formation and / or stabilize the emulsion. Preferably, the surfactant is an acrylic polymer or a methacrylic polymer. Particularly preferred are unbranched C 12 To C 20 (Meth)acrylates, such as poly(hexadecyl)methacrylate and poly(octadecyl)methacrylate and mixtures thereof. Turbulence minimizing agents (TMA), if used, are preferably selected from polymers of alpha-olefin monomers having 6 to 20 carbon atoms, such as polyoctenes, polynonenes, polydecenes, polyundecenes or polydodecenes or mixtures thereof. Most preferred is polydecene.

[0100] The solid particle product obtained by the precipitation method or the emulsion-solidification method can be washed at least once, preferably washed at least twice, and most preferably washed at least three times. Aromatic and / or aliphatic hydrocarbons can be used for washing, preferably toluene, heptane or pentane can be used for washing. TiCl4 optionally combined with aromatic and / or aliphatic hydrocarbons can also be used for washing. The washing liquid can also contain donors and / or Group 13 compounds, such as trialkylaluminum, haloalkylaluminum compounds or alkoxyaluminum compounds. Aluminum compounds can also be added during the catalyst synthesis process. The catalyst can be further dried, for example by evaporation or flushing with nitrogen, or it can be slurried into an oily liquid without any drying step.

[0101] The Ziegler-Natta catalyst of the particular type finally obtained is desirably obtained in the form of particles having a typical average particle size in the range of 5 to 200 μm, preferably 10 to 100 μm. The particles are typically compact, low in porosity, and typically have a particle size of less than 20 g / m 2, more preferably less than 10g / m 2 Typically, the amount of Ti present in the catalyst is in the range of 1 to 6 wt%, the Mg content is in the range of 10 to 20 wt%, and the amount of the internal donor present in the catalyst is in the range of 10 to 40 wt% of the catalyst composition. WO2012 / 007430, EP2610271 and EP2610272 disclose detailed descriptions of the preparation of the catalyst used in the present invention, which are incorporated herein by reference.

[0102] The external donor (ED) is preferably present as an additional component in the polymerization process according to the invention. Suitable external donors (ED) include certain silanes, ethers, esters, amines, ketones, heterocyclic compounds and blends thereof. Particular preference is given to using silanes. Most preferably, silanes of the general formula (I) are used:

[0103] R a p R b q Si(OR c ) (4-p-q) (I)

[0104] Where R a , R b and R c represents a hydrocarbon group, in particular an alkyl or cycloalkyl group, and wherein p and q are numbers ranging from 0 to 3, the sum of which (p+q) is equal to or less than 3. R a , R b and R c Can be selected independently of each other and can be the same or different. Specific examples of silanes according to formula (I) are (tert-butyl) 2 Si (OCH 3 ) 2, (cyclohexyl) (methyl) Si (OCH 3 ) 2, (phenyl) 2 Si (OCH 3 ) 2 and (cyclopentyl) 2 Si (OCH 3 ) 2. Another most preferred silane is a silane according to general formula (II):

[0105] Si(OCH2CH3)3(NR 3 R 4 )(II),

[0106] Where R 3 and R 4 may be the same or different and represent a linear, branched or cyclic hydrocarbon group having 1 to 12 carbon atoms. 3 and R 4Independently selected from the group consisting of: methyl, ethyl, n-propyl, n-butyl, octyl, decyl, isopropyl, isobutyl, isopentyl (iso-pentyl), tert-butyl, tert-amyl (tert-amyl), neopentyl, cyclopentyl, cyclohexyl, methylcyclopentyl and cycloheptyl. Most preferably, ethyl is used.

[0107] Typically, in addition to the Ziegler-Natta catalyst or a specific type of Ziegler-Natta catalyst and an optional external donor (ED), a cocatalyst (Co) may also be present in the polymerization process according to the present invention. The cocatalyst is preferably a compound of Group 13 of the Periodic Table of Elements (IUPAC, 2013 edition), such as an aluminum compound, such as an organoaluminum compound or an aluminum halide compound. Examples of suitable organoaluminum compounds are alkylaluminum compounds or alkylaluminum halide compounds. Therefore, in a specific embodiment, the cocatalyst (Co) is a trialkylaluminum, such as triethylaluminum (TEAL), dialkylaluminum chloride or alkylaluminum dichloride or a mixture thereof. In a specific embodiment, the cocatalyst (Co) is triethylaluminum (TEAL).

[0108] Typically, for each process, the molar ratio between the co-catalyst (Co) and the external donor (ED) [Co / ED] and / or the molar ratio between the co-catalyst (Co) and the transition metal (TM) [Co / TM] is carefully selected. The molar ratio between the co-catalyst (Co) and the external donor (ED) [Co / ED] may suitably be in the range of 2.5 to 50.0 mol / mol, preferably in the range of 4.0 to 35.0 mol / mol, more preferably in the range of 5.0 to 30.0 mol / mol. A suitable lower limit may be 2.5 mol / mol, preferably 4.0 mol / mol, more preferably 5.0 mol / mol. A suitable upper limit may be 50.0 mol / mol, preferably 35.0 mol / mol, more preferably 30.0 mol / mol. The lower and upper limits of this range are included.

[0109] The molar ratio [Co / TM] between the co-catalyst (Co) and the transition metal (TM) may be suitably in the range of 20.0 to 500.0 mol / mol, preferably in the range of 50.0 to 400.0 mol / mol, more preferably in the range of 100.0 to 300.0 mol / mol. A suitable lower limit may be 20.0 mol / mol, preferably 50.0 mol / mol, more preferably 100.0 mol / mol. A suitable upper limit may be 500.0 mol / mol, preferably 400.0 mol / mol, more preferably 300.0 mol / mol. The lower and upper limits of the range are included.

[0110] According to the present invention the third propylene polymer fraction recovered from the polymerization process is extruded in the presence of at least one alpha nucleating agent in order to prepare the inventive polypropylene composition.

[0111] The extruder for carrying out the extrusion step may be any extruder known in the art. Thus, the extruder may be a single screw extruder; a twin screw extruder, such as a co-rotating twin screw extruder or a counter-rotating twin screw extruder; or a multi-screw extruder, such as an annular extruder. Preferably, the extruder is a single screw extruder or a twin screw extruder. A particularly preferred extruder is a co-rotating twin screw extruder.

[0112] An extruder generally comprises a feed zone, a melting zone, a mixing zone, and optionally a die zone.

[0113] The extruder length to diameter ratio (L / D) is typically up to 60:1, preferably up to 40:1.

[0114] The extruder may also have one or more feed ports for introducing other components (such as additives) into the extruder. The location of such additional feed ports depends on the type of material added through the feed port.

[0115] Examples of additives include, but are not limited to, stabilizers such as antioxidants (e.g., sterically hindered phenols, phosphites / phosphonites, sulfur-containing antioxidants, alkyl scavengers, aromatic amines, hindered amine stabilizers, or blends thereof), metal deactivators (e.g., ) or UV stabilizers (e.g. hindered amine light stabilizers). Other typical additives are modifiers, such as antistatic agents or antifogging agents (e.g. ethoxylated amines and amides or glycerides), acid scavengers (e.g. calcium stearate), blowing agents, adhesives (e.g. polyisobutylene), lubricants and resins (e.g. ionomer waxes, polyethylene waxes and ethylene copolymer waxes, Fischer Tropsch waxes, lignite-based waxes, fluorine-based compounds or paraffin waxes) as well as slip agents and anti-caking agents (e.g. erucamide, oleamide, talc, natural and synthetic silica or zeolites) and mixtures thereof.

[0116] Typically, the total amount of additives introduced into the extruder during the process according to the present invention is not more than 5.0 wt%, preferably not more than 2.0 wt%, more preferably not more than 1.5 wt%. The amount of additives is relative to the total amount of polypropylene composition introduced into the extruder.

[0117] In the process according to the invention, the third propylene polymer fraction is extruded at a temperature higher than the melting temperature of the third propylene polymer fraction but lower than the decomposition temperature of the third propylene polymer fraction. Suitably, the third propylene polymer fraction is extruded at a temperature at least 30°C higher than the melting temperature of the third propylene polymer fraction, preferably at a temperature at least 40°C higher than the melting temperature of the third propylene polymer fraction, more preferably at a temperature at least 50°C higher than the melting temperature of the third propylene polymer fraction but lower than the decomposition temperature of the third propylene polymer fraction (i.e., 300°C lower).

[0118] In the process according to the present invention the third propylene polymer fraction is extruded in the presence of an amount of at least one alpha nucleating agent in the range of 0.01 to 1.0 wt%, preferably in the range of 0.03 to 0.9 wt%, more preferably in the range of 0.05 to 0.8 wt%. The amount of the at least one alpha nucleating agent is relative to the total amount of the polypropylene composition according to the present invention.

[0119] The α-nucleating agent is typically selected from the group consisting of:

[0120] (i) salts of mono- and polycarboxylic acids, for example sodium benzoate or aluminium tert-butylbenzoate,

[0121] (ii) dibenzylidene sorbitol (e.g. 1,3:2,4-dibenzylidene sorbitol) and C1-C8 alkyl-substituted dibenzylidene sorbitol derivatives (e.g. methyldibenzylidene sorbitol, ethyldibenzylidene sorbitol or dimethyldibenzylidene sorbitol (e.g. 1,3:2,4-di(methylbenzylidene) sorbitol)) or substituted nonol derivatives (e.g. 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonol),

[0122] (iii) salts of phosphoric acid diesters, for example sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl)phosphate or hydroxy-bis[2,2'-methylene-bis(4,6-di-tert-butylphenyl)phosphate]aluminum,

[0123] (iv) vinylcycloalkane polymers and vinylalkane polymers, and

[0124] (v) mixtures thereof.

[0125] Preferably, the α-nucleating agent is dibenzylidene sorbitol (e.g. 1,3:2,4-dibenzylidene sorbitol) or a C1-C8-alkyl-substituted dibenzylidene sorbitol derivative (e.g. methyldibenzylidene sorbitol, ethyldibenzylidene sorbitol or dimethyldibenzylidene sorbitol (e.g. 1,3:2,4-di(methylbenzylidene)sorbitol)) or a substituted nonol derivative (e.g. 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonol).

[0126] The at least one alpha nucleating agent is typically fed into the extruder via a feed zone. However, the at least one alpha nucleating agent may be fed into the extruder via one or more feed ports comprised in the extruder, for example via a side feeder.

[0127] At the end of the extruder, a polypropylene composition melt is obtained. The polypropylene composition melt of the present invention can then be made to flow out of a die in an optional die zone of the extruder. When the polypropylene composition melt of the present invention flows out of the die, it is usually further cooled and pelletized.

[0128] The die section usually consists of a die plate, which is usually a thick metal disk with a plurality of holes. The holes are parallel to the screw axis.

[0129] The pelletizer is usually a strand pelletizer (also called a strand pelletizer) or an underwater pelletizer.

[0130] The present invention also provides a polypropylene composition obtainable (preferably obtained) by the process according to the present invention.

[0131] The polypropylene composition obtainable (preferably obtained) by the process according to the present invention typically has one or more comonomers selected from ethylene and C4-C 10 The α-olefin is preferably selected from ethylene and C4-C8 α-olefins, more preferably selected from ethylene and C4-C6 α-olefins, even more preferably selected from one or more comonomers comprising ethylene, even more preferably still, the comonomer is selected only from ethylene.

[0132] The polypropylene composition obtainable (preferably obtained) by the process according to the present invention typically has a comonomer content in the range of 1.5 to 5.0 wt%, preferably in the range of 1.6 to 4.0 wt%, more preferably in the range of 1.7 to 3.5 mol%. The comonomer content is relative to the total amount of monomers present in the polypropylene composition.

[0133] Typically, the melt flow rate (MFR2) of the polypropylene composition obtainable (preferably obtained) by the process according to the present invention is in the range of 12 to 60 g / 10 min, preferably in the range of 15 to 40 g / 10 min, more preferably in the range of 17 to 35 g / 10 min. The MFR2 is determined according to ISO 1133 at a temperature of 230°C and a load of 2.16 kg.

[0134] Typically, the polypropylene composition obtainable (preferably obtained) by the process according to the present invention has a haze value <20%, preferably between 2% and 18%, more preferably between 3% and 17%. The haze value is determined according to ASTM D1003 on 1 mm thick injection molded plaques prepared as described in EN ISO 1873-2.

[0135] Typically, the polypropylene composition obtainable (preferably obtained) by the process according to the present invention has a melting temperature > 152 °C, preferably in the range of 153 to 163 °C, more preferably in the range of 154 to 162 °C. The melting temperature (Tm) is determined by DSC according to ISO 11357 / 3.

[0136] Typically, the polypropylene composition obtainable (preferably obtained) by the process according to the present invention has a crystallization temperature > 120° C., preferably in the range of 122 to 132° C., more preferably in the range of 123 to 130° C. The melting temperature (Tc) is determined by DSC according to ISO 11357 / 3.

[0137] Typically, the polypropylene composition obtainable (preferably obtained) by the process according to the present invention has a xylene soluble content (XCS) in the range of 5.5 to 18.0 wt-%, preferably in the range of 6.0 to 16.0 wt-%, more preferably in the range of 6.2 to 15.0 wt-%. The xylene soluble content is determined according to ISO 16152 at 25°C.

[0138] Typically, the tensile modulus of the polypropylene composition obtainable (preferably obtained) by the process according to the present invention is > 950 MPa, preferably in the range of 951 to 1600 MPa, more preferably in the range of 1000 to 1600 MPa, even more preferably in the range of 1050 to 1550 MPa. The tensile modulus is determined according to ISO 527-1:2012 / ISO 527-2:2012 at 23 °C on injection molded specimens.

[0139] Typically, the polypropylene composition obtainable (preferably obtained) by the process according to the present invention has a Charpy notched impact strength of > 4.8 kJ / m 2 , preferably between 4.9 and 20.0 kJ / m 2In the range of 5.0 to 15.0 kJ / m 2 In the range of 5.0 to 13.0 kJ / m 2 In the range of 7.0 to 13 kJ / m 2 The Charpy notched impact strength was determined in accordance with ISO 179 / 1eA at 23° C. on injection-molded test specimens as described in EN ISO 1873-2.

[0140] The present invention also provides an article comprising the polypropylene composition obtainable (preferably obtained) by the process according to the present invention. Suitable articles are films, such as cast films and injection molded articles. Preferred articles are closures, screw caps or closure systems for food or fluid packaging.

[0141] Finally, the present invention relates to the use of a polypropylene composition obtainable (preferably obtained) by the process according to the present invention for the preparation of cast films or injection moulded articles, preferably closures, screw caps or closure systems for food or fluid packaging. A fluid is generally defined as a substance that continuously deforms (flows) under applied shear stress. DETAILED DESCRIPTION

[0142] Example

[0143] I. Determination Method

[0144] a) Melt flow rate

[0145] The melt flow rate (MFR) is determined according to ISO 1133 and is expressed in g / 10 min. The MFR indicates the fluidity and thus the processability of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR2 of polypropylene is determined at a temperature of 230°C and a load of 2.16 kg.

[0146] b) DSC analysis

[0147] Melting and crystallization temperatures were determined with a TA Instrument Q2000 differential scanning calorimeter (DSC) according to ISO 11357 / 3 with 5 to 10 mg sample under a 50 mL / min nitrogen atmosphere. Crystallization and melting temperatures were obtained via a heating / cooling / heating cycle at a scan rate of 10°C / min between 30°C and 225°C. The crystallization temperature was taken as the exothermic peak in the cooling step, and the melting temperature as the endothermic peak in the second heating step.

[0148] c) Xylene soluble content (XCS, wt%)

[0149] The xylene-soluble polymer content is determined according to ISO 16152 (5th edition, 2005-07-01) at 25.0°C.

[0150] d) Tensile modulus

[0151] The tensile modulus was determined according to ISO 527-1:2012 / ISO527-2:2012 at 23°C and crosshead speed = 50 mm / min using injection molded specimens as described in EN ISO 1873-2 (dog bone shape, 4 mm thick).

[0152] e) Simply supported beam notched impact strength

[0153] Injection molded test specimens (80×10×4 mm2) were prepared according to ISO 179 / 1eA at 23°C as described in EN ISO 1873-2. 3 ) Determine the notched impact strength of a simply supported beam.

[0154] f) Haze

[0155] Injection molded plaques (1 mm thick, 60×60 mm in area) were prepared according to ASTM D1003 as described in EN ISO 1873-2. 2 ) to measure the haze.

[0156] g) Comonomer content

[0157] Determination of the ethylene content of poly(propylene-co-ethylene) by infrared spectroscopy

[0158] Quantitative infrared (IR) spectroscopy was used to quantify the ethylene content of poly(ethylene-co-propylene) copolymers by calibration to the primary method.

[0159] By using a set of known ethylene contents (quantitatively 13 Calibration was facilitated by using in-house non-commercial calibration standards (determined by C solution state nuclear magnetic resonance (NMR) spectroscopy). The calibration procedure was performed in a conventional manner well documented in the literature. The calibration set consisted of 38 calibration standards with ethylene contents ranging from 0.2 to 75.0 wt% produced at pilot or full scale under various conditions. The calibration set was selected to reflect typical copolymer species encountered by the final quantitative IR spectroscopy method.

[0160] Quantitative IR spectra were recorded in the solid state using a Bruker Vertex 70 FTIR spectrometer. Square films (300 μm thick, 25×25 mm2) prepared by compression molding at 180-210° C. and 4-6 mPa were prepared. 2 ) were used. For samples with very high ethylene content (>50 mol%), 100 μm thick films were used. -1 spectral range, 6mm aperture, 2cm-1 Standard transmission FTIR spectroscopy was used with a spectral resolution of 100 nm, 16 background scans, 16 spectral scans, an interferogram zero filling factor of 64 and Blackmann-Harris 3-term apodisation.

[0161] Using the corresponding (CH2) >2 Structural units at 730 and 720 cm -1 The total area of ​​CH2 rocking deformation at Q ) for quantitative analysis (integral method G, limits 762 and 694 cm -1 The quantitative band was normalized to the band corresponding to the CH structural unit at 4323 cm -1 The CH band area (A R )(Integral method G, limits are 4650, 4007cm -1 Then, a secondary calibration curve was used to normalize the absorbance (A Q / A R ) predicts the ethylene content in weight percent. A calibration curve has been previously constructed by ordinary least squares regression (OLS) of the normalized absorbance and the initial comonomer content determined from the calibration set.

[0162] use 13 C NMR spectroscopy calibration of ethylene content in poly(propylene-co-ethylene)

[0163] Adopt 1 H and 13 Quantitative measurements were recorded in solution on a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz, respectively. 13 C{ 1 H} NMR spectroscopy. Nitrogen was used for all pneumatics at 125 °C, using 13All spectra were recorded with a 10 mm extended temperature probe optimized for C. About 200 mg of material was dissolved in 3 ml of 1,2-tetrachloroethane-d2 (TCE-d2) along with chromium (III) acetylacetonate (Cr(acac)3) to give a 65 mM solution of the relaxant in the solvent (Singh, G., Kothari, A., Gupta, V., Polymer Testing 28 5 (2009), 475). To ensure a homogeneous solution, the NMR tube was further heated in a rotating oven for at least 1 hour after the initial sample preparation in a heating block. After insertion of the magnet, the tube was rotated at 10 Hz. This setup was chosen primarily for high resolution and since accurate quantification of ethylene content is quantitatively required. Standard single pulse excitation (Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225, Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128) was performed without NOE. A total of 6144 (6k) transients were obtained for each spectrum. For quantitative 13 C{ 1 H} NMR spectra are processed, integrated, and the relevant quantitative properties are determined from the integrals. All chemical shifts are indirectly referenced to the central methylene of the ethylene block (EEE) using the chemical shift of the solvent at 30.00 ppm. This method allows a similar reference even without this structural unit. Characteristic signals corresponding to ethylene incorporation are observed (Cheng, HN, Macromolecules 17 (1984), 1950) and the comonomer content is calculated as the fraction of ethylene in the polymer relative to all monomers in the polymer: fE = (E / (P+E)). By 13 C{ 1The integration of multiple signals over the entire spectral region in the H} spectrum was used to quantify the comonomer fraction using the method of Wang et al. (Wang, WJ., Zhu, S., Macromolecules 33 (2000), 1157). This method was chosen because of its robust nature and the ability to account for the presence of regional defects when necessary. The integration region was slightly adjusted to improve applicability over the entire range of comonomer content encountered. For systems with very low ethylene content where only isolated ethylene in the PPEPP sequence was observed, the method of Wang et al. was modified to reduce the impact of the integration of sites that no longer exist. This method reduces the overestimation of the ethylene content of such systems, and it is achieved by reducing the number of sites used to determine the absolute ethylene content to E = 0.5 (Sββ + Sβγ + Sβδ + 0.5 (Sαβ + Sαγ)). By adopting this set of sites, the corresponding integral equation is changed to E = 0.5 (I H +I G +0.5(I C +I D ))(Wang, WJ., Zhu, S., Macromolecules 33 (2000), 1157). Unmodified equation for absolute propylene content. The mole percent of comonomer incorporation was calculated from the mole fraction (E[mol%]=100*fE). The weight percent of comonomer incorporation was calculated from the mole fraction (E[wt%]=100*(fE*28.06) / ((fE*28.06)+((1-fE)*42.08)).

[0164] II. Examples of the present invention and comparative examples

[0165] a) Catalyst preparation

[0166] To prepare the catalyst, 3.4 liters of 2-ethylhexanol and 810 ml of propylene glycol butyl monoether (molar ratio of 4 / 1) were added to a 20 liter reactor. Then 7.8 liters of a 20% toluene solution of BEM (butylethylmagnesium) supplied by Crompton GmbH was slowly added to the well-stirred alcohol mixture. During the addition, the temperature was maintained at 10.0°C. After the addition, the temperature of the reaction mixture was raised to 60°C and mixing was continued at this temperature for 30 minutes. After finally cooling to room temperature, the resulting magnesium alkoxide was transferred to a storage container.

[0167] 21.2 g of the magnesium alkoxide prepared above was mixed with 4.0 ml of bis(2-ethylhexyl) citraconic acid for 5 minutes. After mixing, the obtained Mg complex was immediately used to prepare the catalyst component.

[0168] 19.5 ml of titanium tetrachloride were placed in a 300 ml reactor equipped with a mechanical stirrer at 25°C. The mixing speed was adjusted to 170 rpm. 26.0 g of the Mg-complex prepared above were added over 30 minutes, keeping the temperature at 25.0°C. 3.0 ml of 1-254 and 1.0ml contains 2mg Necadd 447 TM 24.0 ml of toluene solution was then added to form an emulsion. Mixing was continued at 25°C for 30 minutes, and then the reactor temperature was raised to 90°C over 30 minutes. The reaction mixture was stirred for another 30 minutes at 90°C. Stirring was then stopped and the reaction mixture was allowed to settle at 90°C for 15 minutes. The solid material was washed 5 times: at 80°C for 30 minutes with stirring at 170 rpm. After stopping stirring, the reaction mixture was allowed to settle for 20-30 minutes and then siphoned.

[0169] 1st wash: Wash with a mixture of 100 ml toluene and 1 ml donor

[0170] Second washing: washing with a mixture of 30 ml TiCl4 and 1 ml donor.

[0171] The third wash: wash with 100 ml of toluene.

[0172] 4th wash: Wash with 60 ml of heptane.

[0173] Fifth wash: Wash with 60 ml of heptane and stir for 10 minutes.

[0174] Then the stirring was stopped and the reaction mixture was allowed to settle for 10 minutes while the temperature was lowered to 70°C, followed by siphoning and then N2 bubbling for 20 minutes to obtain an air-sensitive powder.

[0175] b) Embodiments of the present invention (IE1 and IE2)

[0176] The third propylene polymer fraction related to inventive example (IE) was prepared in a pilot plant with a prepolymerization reactor, a slurry loop reactor and two gas phase reactors. The above solid catalyst component was used in the process of the invention together with triethylaluminium (TEAL) as cocatalyst and dicyclopentyldimethoxysilane (D-donor) as external donor.

[0177] Table 1 describes the polymerization process conditions and the properties of the propylene polymer fractions.

[0178] The inventive polypropylene composition was prepared by extruding the corresponding third propylene polymer fraction with a nucleating agent in a co-rotating twin screw extruder type Coperion ZSK 40 with a screw diameter of 40 mm and an L / D ratio of 38. The temperature in the extruder ranged from 190 to 230°C. In each example of the present invention, 0.05 wt% of Irganox 1010 (pentaerythritol tetrakis (3- (3', 5'-di-tert-butyl-4-hydroxyphenyl) -propionate, CAS No. 6683-19-8, commercially available from BASF AG, Germany), 0.05 wt% of Irgafos 168 (tris (2,4-di-tert-butylphenyl) phosphite, CAS No. 31570-04-4, commercially available from BASF AG, Germany), 0.10 wt% of calcium stearate (CAS. No. 1592-23-0, commercially available from Baerlocher GmbH, Germany under the trade name Ceasit FI) and 0.06 wt% of glyceryl monostearate (CAS No. 97593-29-8, commercially available from Danisco, Denmark under the trade name Grindsted PS 426) were added. A / S, purity 90%) was added into the extruder as an additive.

[0179] After the extrusion step and after solidification of the strands in a water bath the obtained polypropylene composition is pelletized in a strand pelletizer.

[0180] Table 2 describes the properties of the polypropylene compositions.

[0181] c) Comparative Examples (CE1 and CE2)

[0182] CE-1 is a C2 propylene random copolymer with MFR2 of 13.0 g / 10 min produced in a one reactor process and distributed by Borealis (trade name RE420MO).

[0183] CE-2 is a C2 propylene random copolymer with MFR2 of 20.0 g / 10 min produced in a one reactor process and distributed by Borealis (trade name RF365MO).

[0184] Table 1. Polymerization process conditions and properties of propylene polymer fractions

[0185]

[0186] *Split represents the amount of propylene polymer produced in each specific reactor.

[0187] Table 2. Extrusion process conditions and polypropylene composition properties

[0188]

[0189] *Measured on pellets obtained after the extrusion process.

[0190] From Table 2 it can be deduced that the polypropylene compositions (inventive examples) show an improvement in a balanced combination of high flowability, high stiffness and impact resistance and high optical properties (low haze values) compared to the comparative examples.

Claims

1. A method for preparing a polypropylene composition by sequential polymerization, comprising the following steps: a) polymerizing in a first reactor a monomer comprising propylene and optionally ethylene comonomer to obtain a first propylene polymer fraction having a comonomer content in the range of 0.0 to 1.0 wt% and an MFR2 measured according to ISO 1133 at 230°C under a load of 2.16 kg in the range of 11 to 60 g / 10 min, b) polymerizing monomers comprising propylene and ethylene comonomers in the presence of said first propylene polymer fraction in a second reactor to obtain a second propylene polymer fraction having a comonomer content in the range of 0.3 to 2.0 wt%, c) polymerizing monomers comprising propylene and ethylene comonomers in the presence of said second propylene polymer fraction in a third reactor to obtain a third propylene polymer fraction having a comonomer content in the range of 1.5 to 5.0 wt%, d) extruding the third propylene polymer fraction in the presence of at least one alpha nucleating agent, wherein the polypropylene composition has an MFR2 in the range of 12.0 to 60.0 g / 10 min, measured according to ISO 1133 at 230° C. and 2.16 kg load; wherein the process is operated in the presence of a Ziegler-Natta catalyst having a transition metal from Groups 4 to 6 of the Periodic Table of Elements and comprising an internal donor, an optional cocatalyst and an optional external donor, wherein the internal donor is a non-phthalic acid internal donor; and wherein the non-phthalic internal donor is selected from esters of non-phthalic carboxylic acids, wherein the esters of non-phthalic carboxylic acids belong to the group comprising malonates, maleates, succinates, citraconates, glutarates, cyclohexene-1,2-dicarboxylates and benzoates and derivatives thereof or mixtures thereof.

2. The method according to claim 1, wherein: a) the hydrogen / propylene (H2 / C3) ratio in the first reactor is in the range of 1.5 to 6.0 mol / kmol, b) the hydrogen / propylene (H2 / C3) ratio in the second reactor is in the range of 12.0 to 70.0 mol / kmol, and c) the hydrogen / propylene (H2 / C3) ratio in the third reactor is in the range of 15.0 to 80.0 mol / kmol.

3. The process according to claim 1, wherein the third propylene polymer fraction is extruded in the presence of at least one alpha nucleating agent in an amount ranging from 0.01 to 1.0 wt.-% relative to the total amount of the polypropylene composition.

4. The process according to claim 1, wherein the polypropylene composition has a haze value of < 20% measured according to ASTM D1003 on 1 mm thick injection molded plaques prepared as described in EN ISO 1873-2.

5. The process of claim 1, wherein the first reactor is a slurry reactor.

6. The process of claim 1, wherein the second reactor is a first gas phase reactor.

7. The process of claim 1, wherein the third reactor is a second gas phase reactor.

8. The method of claim 1, wherein the Ziegler-Natta catalyst does not contain phthalic acid compounds.

9. The method of claim 1, wherein the esters of non-phthalic carboxylic acids are diesters of non-phthalic dicarboxylic acids.

10. A polypropylene composition obtainable by a sequential polymerization process, the sequential polymerization process comprising the steps of: a) polymerizing in a first reactor a monomer comprising propylene and optionally ethylene comonomer to obtain a first propylene polymer fraction having a comonomer content in the range of 0.0 to 1.0 wt% and an MFR2 measured according to ISO 1133 at 230°C under a load of 2.16 kg in the range of 11 to 60 g / 10 min, b) polymerizing monomers comprising propylene and ethylene comonomers in the presence of said first propylene polymer fraction in a second reactor to obtain a second propylene polymer fraction having a comonomer content in the range of 0.3 to 2.0 wt%, c) polymerizing monomers comprising propylene and ethylene comonomers in the presence of said second propylene polymer fraction in a third reactor to obtain a third propylene polymer fraction having a comonomer content in the range of 1.5 to 5.0 wt%, d) extruding the third propylene polymer fraction in the presence of at least one alpha nucleating agent, wherein the polypropylene composition has an MFR2 in the range of 12.0 to 60.0 g / 10 min, measured according to ISO 1133 at 230° C. and 2.16 kg load, wherein said ethylene comonomer is incorporated into said reactor at different levels such that said third propylene polymer fraction has a trimodal comonomer distribution with respect to the comonomer content of each propylene polymer contained in said third propylene polymer fraction; wherein the polypropylene composition has a xylene soluble content (XCS) in the range of 6.0 to 18.0 wt% measured at 25 °C according to ISO 16152; wherein the polypropylene composition has a haze value of <20% measured according to ASTM D1003 on 1 mm thick injection molded plaques prepared as described in EN ISO 1873-2; wherein the sequential polymerization process is operated in the presence of a Ziegler-Natta catalyst having a transition metal from Groups 4 to 6 of the Periodic Table of Elements and comprising an internal donor, an optional cocatalyst and an optional external donor, wherein the internal donor is a non-phthalic internal donor; and wherein the non-phthalic internal donor is selected from esters of non-phthalic carboxylic acids, wherein the esters of non-phthalic carboxylic acids belong to the group comprising malonates, maleates, succinates, citraconates, glutarates, cyclohexene-1,2-dicarboxylates and benzoates and derivatives thereof or mixtures thereof.

11. The polypropylene composition according to claim 10, wherein the polypropylene composition has a melting temperature > 152°C and a crystallization temperature > 120°C as determined by DSC according to ISO 11357 / 3.

12. The polypropylene composition according to claim 10, wherein the polypropylene composition has a tensile modulus > 950 MPa measured according to ISO 527-1:2012 / ISO 527-2:2012 at 23°C on injection molded specimens.

13. The polypropylene composition according to claim 10, wherein the polypropylene composition has a thermal conductivity of >4.8 kJ / m<40>, measured at 23°C on injection molded specimens according to ISO 179 / 1eA. 2 The simply supported beam notched impact strength.

14. The polypropylene composition of claim 10, wherein the first reactor is a slurry reactor.

15. The polypropylene composition of claim 10, wherein the second reactor is a first gas phase reactor.

16. The polypropylene composition of claim 10, wherein the third reactor is a second gas phase reactor.

17. The polypropylene composition of claim 10, wherein the esters of non-phthalic carboxylic acids are diesters of non-phthalic dicarboxylic acids.

18. An article comprising the polypropylene composition according to any one of claims 10 to 17.

19. The article of claim 18, wherein the article is a cast film, an injection molded article, a closure, a screw cap, or a closure system for food or fluid packaging.

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