BR112022000700B1 - POLYPROPYLENE FILM WITH IMPROVED SLIDING PERFORMANCE - Google Patents

Abstract

POLYPROPYLENE FILM WITH IMPROVED SLIDING PERFORMANCE. The invention relates to a film comprising a polypropylene composition that exhibits improved coefficient of friction as well as improved optical properties.

Description

[0001] The invention relates to a film comprising a polypropylene composition with a small dynamic coefficient of friction (CoF). The invention further relates to a process for producing said film.

[0002] Polypropylene is widely used in the packaging sector, including flexible packaging. Polypropylene cast film has the disadvantage of a very slow migration of the slip agent compared to, for example, polyethylene. Especially cast films produced from vis-reduced polypropylenes with a thickness below 50 μm do not exhibit a sufficiently small CoF after production, which is necessary for good winding quality and also for the following converting steps. For good winding quality and further manufacturing steps, a small CoF is technically necessary and therefore a market requirement.

[0003] In order to meet this requirement, it is prior art to add one or more slip agents (in combination with one or more anti-blocking agents) to polypropylene cast film grades. The slip agent migrates to the surface of the film, thereby creating a slip film that reduces the CoF dramatically. Since the migration to the surface of the slip agent in polypropylene is very slow, an excessive amount of slip agent is added in order to overcome this problem and obtain the CoF required immediately after film production for good winding quality. If less slip agent is added, the CoF immediately after film production is too high and the film must be stored for a long period (about 14 days) to obtain a sufficiently small CoF.

[0004] The disadvantages of this solution are - high cost due to excessive amount of slip agent. - deterioration of the optical properties of the film after a long period of time because too much slip agent migrates to the film surface. - slip agent deposits on the cast film production line when films with a thickness of about 70 μm are produced.

[0005] Another known approach is the production of polypropylene with specific catalyst technology to obtain lower CoF in the presence of the same amount, or even reduced amount of slip agent.

[0006] EP 1747239 discloses a process for producing a polypropylene film with a small dynamic friction coefficient, in which a specific catalyst composition comprising a catalyst component in the form of particles with a defined size range is used for the polymerization of propylene.

[0007] Document KR 2001045571 discloses a process for preparing a film with good sliding properties. This process comprises the steps of a) dispersing magnesium ethoxide as a raw material of a magnesium-based carrier in a mixed solvent of organic alcohol, a hydrocarbon solvent and an organic phosphorus compound, b) adding anhydrous phthalic acid and c) dripping a titanium tetrachloride solution into the magnesium compound solution and d) collecting a solid component by filtration and adding titanium tetrachloride to the solid component.

[0008] US 9701801 also discloses a process comprising (1) combining a metallocene-catalyzed polypropylene with a nucleator and a slip agent to form a composition, wherein the amount of nucleator combined with the metallocene-catalyzed polypropylene is adjusted to achieve a coefficient of friction (CoF) of less than 0.5; and (2) forming a cast film from the composition, wherein the cast film has a coefficient of friction at least 90% lower than an identical cast film in which the nucleator is not present, wherein the coefficient of friction is measured in accordance with ASTM D1894.

[0009] However, in addition to the coefficient of friction (CoF), also satisfactory optical properties, especially low opacity and high clarity of the cast film, are usually required in the flexible packaging area. Therefore, it is the aim of the present invention to provide a cast or blown polypropylene film with a small dynamic coefficient of friction and satisfactory optical properties, especially low opacity and high clarity, at the same time.

[0010] The above problem was surprisingly solved by providing a film prepared with a polypropylene homopolymer with a low fraction of cold soluble in xylene (XCS) polymerized in the presence of a special metallocene catalyst.

[0011] Accordingly, the present invention is directed to a film comprising a polypropylene composition comprising (a) 95.0-99.9 wt. % of a propylene homopolymer (HPP) polymerized in the presence of a metallocene catalyst, wherein the propylene homopolymer (HPP) has a melting temperature (Tm) measured by differential scanning calorimetry (DSC) in the range of 152 to 162 °C, a xylene cold soluble (XCS) fraction determined at 23 °C according to ISO 16152 equal to or less than 1.5 wt. % and has a 2,1-erythro regiodefect content as determined from 13C NMR spectroscopy in the range of 0.01 to 1.00 mol. %, (b) 0.1-0.4 wt. % of one or more slip agents, and (c) 0.0-0.5% by weight of one or more anti-blocking agents.

[0012] With the invention it is surprisingly possible to use the same amount of slip agent to achieve reduced CoF after 7 days after production due to accelerated migration of the slip agent. Furthermore, improved optical properties of the film such as lower haze value are observed.

[0013] The film is preferably a non-oriented blown or cast film, more preferably a non-oriented cast film.

[0014] In a further aspect, the present invention is directed to the process for preparing a film, comprising the steps of: i) polymerizing the propylene homopolymer (HPP) according to the present invention in a multistage process, in which a loop reactor is followed by a gas phase reactor, in the presence of a metallocene catalyst system, and ii) forming the propylene homopolymer (HPP) obtained in step (i) into a film together with 0.1-0.4 wt. % of one or more slip agents and 0.0-0.5 wt. % of one or more anti-blocking agents using a casting or film blowing process. Detailed Description of the Invention

[0015] In the following, the film comprising the polypropylene composition as well as the production process are defined in greater detail. Propylene homopolymer (HPP)

[0016] According to the present invention, the polypropylene composition comprises 95.0-99.9% by weight, preferably 96.0-99.9% by weight, more preferably 96.5 to 99.5% by weight of a propylene homopolymer (HPP).

[0017] The term “propylene homopolymer (HPP)” as used in the present invention refers to a polypropylene consisting substantially, i.e., of more than 98.0 wt.%, preferably more than 99.0 wt.%, even more preferably more than 99.5 wt.%, even more preferably at least 99.8 wt.%, of propylene units. In a preferred embodiment, only propylene units in the propylene homopolymer (HPP) are detectable.

[0018] It is essential that the propylene homopolymer (HPP) has been polymerized in the presence of a metallocene catalyst.

[0019] Additionally, it is necessary that the propylene homopolymer (HPP) has a relatively high melting temperature Tm. More precisely, it is essential that the propylene homopolymer (HPP) has a melting temperature Tm measured by differential scanning calorimetry (DSC) according to ISO 11357 in the range of 152 to 162 °C. For example, the polypropylene homopolymer (HPP) has a melting temperature Tm measured by differential scanning calorimetry (DSC) according to ISO 11357 in the range of 152 to 158 °C, preferably in the range of 152 to 156 °C.

[0020] It is also important that the propylene homopolymer (HPP) has a xylene cold soluble (XCS) content equal to or below 1.5 wt. %, based on the total weight of the propylene homopolymer (HPP). For example, the propylene homopolymer (HPP) has a xylene cold soluble (XCS) content in the range of 0.1 to 1.5 wt. %, preferably in the range of 0.3 to 1.2 wt. %, more preferably in the range of 0.3 to 1.0 wt. %, based on the total weight of the propylene homopolymer (HPP).

[0021] It is preferred that the polypropylene homopolymer (HPP) has a melt flow rate MFR2 (230 °C, 2.16 kg) measured in accordance with ISO 1133 in the range of 4.0 to 20.0 g/10 min, preferably in the range of 5.0 to 18.0 g/10 min, more preferably in the range of 5.5 to 16.0 g/10 min.

[0022] The relatively high melting temperature Tm indicates that the propylene homopolymer (HPP) has a rather low regiodefect content. Therefore, the propylene homopolymer (HPP) has a regiodefect content of 2.1 erythro as determined from 13C-NMR spectroscopy in the range of 0.01 to 1.00 mol%. More preferably, the propylene homopolymer (HPP) has regiodefects of 2.1 erythro in the range of 0.20 to 0.80 mol% and most preferably in the range of 0.30 to 0.80 mol% as determined by 13C-NMR spectroscopy.

[0023] Additionally or alternatively, the propylene homopolymer (HPP) has an isotactic triad fraction (mm) determined from 13C-NMR spectroscopy of at least 97.5%. For example, the propylene homopolymer (HPP) has an isotactic triad fraction (mm) determined from 13C-NMR spectroscopy of at least 98.5%, more preferably at least 99.0%, such as in the range of 99.0 to 99.9%.

[0024] Additionally, it is preferred that the propylene homopolymer (HPP) has a weight average molecular weight (Mw) in the range of 80 to 500 kg/mol, preferably in the range of 100 to 400 kg/mol, more preferably in the range of 120 to 350 kg/mol, and/or a number average molecular weight (Mn) of 20 to 200 kg/mol, more preferably 50 to 150 kg/mol, determined by GPC according to ISO 16014.

[0025] It is preferred that the propylene homopolymer (HPP) has a molecular weight distribution (MWD) measured according to ISO 16014 of <4.0, preferably in the range 1.5 to 4.0, more preferably in the range 2.0 to 4.0, and most preferably in the range 2.5 to 4.0. Said MWD is achieved by polymerization using the specified metallocene catalyst, and not by visbreaking with peroxides or other radical generators.

[0026] It is preferred that the propylene homopolymer (HPP) is polymerized in the presence of a metallocene catalyst complex of formula (I) Formula (I) where Mt is Hf or Zr; each X is a sigma ligand, each R1 is independently the same or may be different and is a CH2-R7 group, where R7 is H or a linear or branched C1-6-alkyl group, a C3-8 cycloalkyl group, a C6-10 aryl group, each R2 is independently a -CH=, -CY=, —CH2-, -CHY-, or -CY2- group, where Y is a C1-10 hydrocarbyl group and where n is 2-6, each R3 and R4 are independently the same or may be different and are each hydrogen, a linear or branched C1-C6-alkyl group, an OY group, or a C7-20 arylalkyl, C7-20 alkylaryl group, or C6-20 aryl group, wherein at least one R3 per phenyl group and at least one R4 is not hydrogen, and optionally two adjacent R3 or R4 groups may be part of a ring including the phenyl carbons to which they are attached, R5 is a linear or branched C1-C6 alkyl group, C7-20 arylalkyl group and C7-20 alkylaryl group or C6-C20 aryl group, R6 is a C(R8)3 group, wherein R8 is a linear or branched C1-C6 alkyl group, each R is independently a C1-C20 hydrocarbyl, C6-C20 aryl, C7-C20 arylalkyl or C7-C20 alkylaryl.

[0027] The catalyst of the invention can be used in unsupported form or in solid form. The catalyst of the invention can be used as a homogeneous catalyst or heterogeneous catalyst.

[0028] The catalyst of the invention in solid form, preferably in solid particulate form, may be supported on an external carrier material such as silica or alumina, or, in a particularly preferred embodiment, is free of an external carrier but is still in solid form. For example, the solid catalyst is obtainable by a process in which (a) a liquid/liquid emulsion system is formed, said liquid/liquid emulsion system comprising a solution of catalyst components (i) and (ii) dispersed in a solvent for the purpose of forming dispersed droplets; and (b) solid particles are formed by solidification of said dispersed droplets.

[0029] Details about the catalyst used in the present invention are described below.

Definitions

[0030] Throughout the description, the following definitions are employed.

[0031] “Free of an external carrier” means that the catalyst does not contain an external support, such as an inorganic support, e.g., silica or alumina, or an organic polymeric support material.

[0032] The term “C1-20 hydrocarbyl group” includes C1-20 alkyl, C2-20 alkenyl, C2-20 alkynyl, C3-20 cycloalkyl, C3-20 cycloalkenyl, C6-20 aryl, C7-20 alkylaryl groups or C7-20 arylalkyl groups or, of course, mixtures of these groups, such as alkyl-substituted cycloalkyl. Linear or branched hydrocarbyl groups may not contain cyclic units. Aliphatic hydrocarbyl groups may not contain aryl rings.

[0033] Unless otherwise stated, preferred C1-20hydrocarbyl groups are C1-20alkyl, C4-20cycloalkyl, C5-20cycloalkyl-alkyl groups, C7-20alkylaryl groups, C7-20arylalkyl groups or C6-20aryl groups, especially C1-10alkyl groups, C6-10aryl groups or C7-12arylalkyl groups, for example C1-8alkyl groups. Particularly more preferred hydrocarbyl groups are methyl, ethyl, propyl, isopropyl, tert-butyl, isobutyl, C5-6-cycloalkyl, cyclohexylmethyl, phenyl or benzyl.

[0034] The term halo includes fluorine, chlorine, bromine and iodine groups, especially chlorine or fluoro groups, when referring to the definition of the complex.

[0035] The oxidation state of the metal ion is governed by the nature of the metal ion in question and the stability of the individual oxidation states of the metal ion.

[0036] It will be appreciated that in the complexes of the invention the metal ion M is coordinated by ligands X for the purpose of satisfying the valency of the metal ion and filling its available coordination sites. The nature of these o-ligands may vary greatly.

[0037] The terms "C4 phenyl ring" and "C4' phenyl ring" refer to the substituted phenyl rings attached to the 4 and 4' positions of the indenyl and indacenyl rings, respectively. The numbering of these rings will be apparent from the structures shown herein.

[0038] Catalyst activity is defined in the present application as the amount of catalyst/h produced/g polymer. Catalyst metal activity is defined herein as the amount of polymer produced/g metal/h. The term productivity is sometimes used to indicate catalyst activity, although in the present document it indicates the amount of polymer produced per unit weight of catalyst.

[0039] The term "molecular weight" is used herein to refer to the weight-average molecular weight Mw, unless otherwise indicated.

Detailed Catalyst Description

[0040] The metallocene catalyst complexes of the present invention are C1-symmetric, chiral, racemic, bisindenyl-linked metallocenes in their anti-configuration activity. Although the complexes of the invention are formally C1-symmetric, the complexes ideally retain a pseudo-C2-symmetry since they maintain C2-symmetry in close proximity to the metal center although not at the ligand periphery. By the nature of their chemistry, both anti and syn enantiomer pairs (in the case of C1-symmetric complexes) are formed during the synthesis of the complexes. For the purposes of this invention, racemic-anti means that the two indenyl ligands are oriented in opposite directions with respect to the cyclopentadienyl-metal-cyclopentadienyl plane, while racemic-syn means that the two indenyl ligands are oriented in the same direction with respect to the cyclopentadienyl-metal-cyclopentadienyl plane, as shown in the Figure below.

Racemic Anti Racemic Syn

[0041] Formula (I), and any subformulas, are intended to encompass both syn and anti configurations. Preferred metallocene catalyst complexes are in the anti configuration.

[0042] The metallocene catalyst complexes of the invention are employed as the racemic-anti isomers. Therefore, ideally at least 95 mol %, such as at least 98 mol %, especially at least 99 mol % of the metallocene catalyst complex is in the racemic-anti isomeric form.

[0043] The following preferences apply to the metallocene catalyst complexes of the invention. The metallocene catalyst complexes according to the invention are of the formula (I): Formula (I)

[0044] In a complex of formula (I), it is preferred that Mt is Zr or Hf, preferably Zr;

[0045] Each X is a sigma ligand. Most preferably, each X is independently a hydrogen atom, a halogen atom, a C1-6alkoxy group or an R' group, where R' is a C1-6 alkyl, phenyl or benzyl group. Most preferably, X is chlorine, benzyl or a methyl group. Preferably, both X groups are the same. Most preferred options are two chlorides, two methyl groups or two benzyl groups, especially two chlorides.

[0046] In the formula -SÍR2-, each R is independently a C1-C20 hydrocarbyl, C6-C20 aryl, C7-C20 arylalkyl or C7-C20 alkylaryl. The term C1-20 hydrocarbyl group therefore includes C1-20 alkyl, C2-20 alkenyl, C2-20 alkynyl, C3-20 cycloalkyl, C3-20 cycloalkenyl, C6-20 aryl, C7-20 alkylaryl groups or C7-20 arylalkyl groups or, of course, mixtures of these groups, such as alkyl-substituted cycloalkyl. Unless otherwise indicated, preferred C1-20 hydrocarbyl groups are C1-20 alkyl, C4-20 cycloalkyl, C5-20 cycloalkyl-alkyl, C7-20 alkylaryl, C7-20 arylalkyl groups or C6-20 aryl groups.

[0047] Preferably, both R groups are the same. It is preferred that R is a C1-C10 hydrocarbyl or C6C10 aryl group, such as methyl, ethyl, propyl, isopropyl, tert-butyl, isobutyl, C5-6 cycloalkyl, cyclohexylmethyl, phenyl or benzyl, more preferably both R are a C1-C6 alkyl, C3-8 cycloalkyl or C6 aryl group, such as a C1-C4 alkyl, C5-6 cycloalkyl or C6 aryl group, and most preferably both R are methyl or one is methyl and the other is cyclohexyl. Most preferably, the bridge is -Si(CH3)2-.

[0048] Each R1 is independently the same or may be different and is a CH2-R7 group, with R7 being H or linear or branched C1-6-alkyl group such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl and tert-butyl or C3-8 cycloalkyl group (e.g. cyclohexyl), C6-10 aryl group (pref. phenyl);

[0049] Preferably, both R1 are the same and are a CH2-R7 group, with R7 being H or a linear or branched C1-C4 alkyl group, more preferably, both R1 are the same and consist of the CH2-R7 group, with R7 being H or a linear or branched C1-C3 alkyl group. Most preferably, both R1 are methyl.

[0050] Each R2 is independently a -CH=, -CY=, -CH2-, -CHY- or -CY2 - group, wherein Y is a C1-10 hydrocarbyl group, preferably a C1-4 hydrocarbyl group, and wherein n is 2-6, preferably 3-4.

[0051] Each substituent R3 and R4 is independently the same or may be different and is hydrogen, a linear or branched C1-C6 alkyl group, an OY group or a C7-20 arylalkyl, C7-20 alkylaryl group or C6-20 aryl group, preferably hydrogen, a linear or branched C1-C6 alkyl group or C6-20 aryl group, and optionally two adjacent R3 or R4 groups may be part of a ring including the phenyl carbons to which they are attached. More preferably, R3 and R4 are hydrogen or a linear or branched C1-C4 alkyl group or an OY group, wherein Y is a C1-4 hydrocarbyl group. Even more preferably, each R3 and R4 is independently hydrogen, methyl, ethyl, isopropyl, tert-butyl or methoxy, especially hydrogen, methyl or tert-butyl, wherein at least one R3 per phenyl group and at least one R4 is not hydrogen.

[0052] Thus, preferably one or two R3 per phenyl group are not hydrogen, more preferably in both phenyl groups the R3 are the same, such as 3',5'-dimethyl or 4'-tert-butyl for both phenyl groups.

[0053] For the indenyl moiety, preferably one or two R4 in the phenyl group are not hydrogen, more preferably two R4 are not hydrogen, and most preferably these two R4 are the same as 3',5'-dimethyl or 3',5'-di-tert-butyl.

[0054] R5 is a linear or branched C1-C6 alkyl group such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl and tert-butyl, C7-20 arylalkyl, C7 group -20 alkylaryl or C6-C20 aryl.

[0055] R5 is preferably a linear or branched C1-C6 alkyl group or C6-20 aryl group, more preferably a linear C1-C4 alkyl group, even more preferably a C1-C2 alkyl group and most preferably methyl.

[0056] R6 is a C(R8)3 group, where R8 is a linear or branched C1-C6 alkyl group.

[0057] Each R is independently a C1-C20 hydrocarbyl, C6-C20 aryl, C7-C20 arylalkyl or C7-C20 alkylaryl. Preferably, each R8 is the same or different with R8 being a linear or branched C1-C4 alkyl group, more preferably with R8 being the same and being a C1-C2 alkyl group. Most preferably, all R8 groups are methyl.

[0058] In a preferred embodiment, the invention provides a metallocene catalyst complex of formula (Ia) wherein each R3 and R4 are independently the same or may be different and are either hydrogen or a linear or branched C1-C6 alkyl group, whereby at least one R3 per phenyl group and at least one R4 is not hydrogen.

[0059] Specific metallocene catalyst complexes of the invention include: rac-anti-dimethylsilanedi-yl[2-methyl-4,8-bis-(4'-tert-butylphenyl)-1,5,6,7 dichloride -tetrahydro-s-indacen-1-yl][2-methyl-4-(3',5'-dimethyl-phenyl)-5-methoxy-6-tert-butylinden-1-yl] zirconium rac dichloride -anti-dimethylsilanedi-yl[2-methyl-4,8-bis(3',5'-dimethylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl] [2-methyl -4-(3',5'-dimethylphenyl)-5-methoxy-6-tert-butylinden-1-yl] zirconium dichloride rac-anti-dimethylsilanedi-yl[2-methyl-4,8-bis-(3',5'-dimethylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2 -methyl-4-(3',5'-ditert-butyl-phenyl)-5-methoxy-6-tert-butylinden-1-yl] zirconium or its corresponding dimethyl zirconium analogues.

[0060] Throughout the above disclosure, when a more limited definition of a substituent is presented, that more limited definition is considered to be disclosed in combination with all broader and more limited definitions of other substituents in the application. Summary

[0061] The ligands required to form the catalysts of the invention may be synthesized by any process and the skilled organic chemist would be able to devise various synthetic protocols for the manufacture of the necessary ligand materials. WO2007/116034 discloses the necessary chemistry and is incorporated herein by reference. Synthetic protocols can also generally be found in WO2002/02576, WO2011/135004, WO2012/084961, WO2012/001052, WO2011/076780 and WO2015/158790. The examples section also provides the skilled person with sufficient direction.

[0062] Process for producing the metallocene catalyst complex ligand of formula (I or Ia) comprising the two substituents of the (R3)3-phenyl group. Synthesis of the metallocene catalyst complex ligand of formula (I or Ia) comprising the two substituents of the (R3)--phenyl group preferably the synthesis of indacenyl ligand.

[0063] The metallocene ligand, as disclosed in PCT/EP2017/084273, includes two different indenes, a methoxyindene and an indacene. The synthesis of methoxyindene is straightforward and in high yield, while the synthesis of indacene requires several steps, as shown in Scheme 1 for the case of 4-(4-tert-butylphenyl)indacene: Br Scheme 1

[0064] The ligand of the metallocene catalyst complex of formula (I or Ia) comprising the two substituents of the (R3)3-phenyl group, preferably the indacene ligand used in the synthesis of the inventive metallocene catalyst complexes, which is the structural analogue of the above structure, is obtained with one less step, as shown in scheme 2: Scheme 2

[0065] Thus, the innovative metallocene catalyst complexes of the present invention can be prepared in a simpler way and as shown in the experimental part in a more efficient way as well.

[0066] The present invention therefore also relates to a process for producing the metallocene catalyst complex ligand of formula (I or Ia) comprising the two substituents of the (R3)3-phenyl group, preferably the indacene ligand.

[0067] This process analogous to Scheme 2 comprises the steps 1. Electrophilic dibromination of the starting ketone compound, e.g., R1-3,5,6,7-tetrahydro-s-indecen-1(2H)-one 2. Reduction of the corresponding dibromo compound, e.g., 4,8-dibromo-R1-3,5,6,7-tetrahydro-s-indecen-1(2H)-one, followed by methylation to produce the corresponding OMe compound 3. Kumada coupling with (R3)3-phenylmagnesium bromide and 4. Demethoxylation

[0068] Step 1 is preferably carried out with aluminium chloride in dichloromethane at low temperature, such as 2 to 10 °C, for example around +5 °C.

[0069] The reduction in step 2 is preferably done by sodium borohydride in THF-MeOH medium at low temperature, such as 2 to 10 °C, for example about +5 °C.

[0070] Methylation is preferably performed at room temperature with MeI/KOH/DMSO.

[0071] Step 3 is preferably carried out in the presence of NiCl2(PPh3)IPr catalyst at reflux temperature and step 4 is preferably carried out with a catalytic amount of TsOH in toluene at reflux temperature.

Cocatalyst

[0072] In order to form an active catalytic species, it is typically necessary to employ a cocatalyst as is well known in the art.

[0073] According to the present invention, a cocatalyst system comprising a boron-containing cocatalyst and/or an aluminoxane cocatalyst is used in combination with the metallocene catalyst complex defined above.

[0074] The aluminoxane cocatalyst may be one of the formula (X): where n is usually from 6 to 20 and R has the meaning below.

[0075] Aluminoxanes are formed on partial hydrolysis of organoaluminium compounds, for example those of the formula AlR3, AlR2Y and Al2R3Y3 wherein R may be, for example, C1-C10 alkyl, preferably C1-C5 alkyl or C3-C10-cycloalkyl, C7-C12 arylalkyl or alkylaryl and/or phenyl or naphthyl, and wherein Y may be hydrogen, halogen, preferably chlorine or bromine, or C1-C10 alkoxy, preferably methoxy or ethoxy. The resulting oxygen-containing aluminoxanes are in general not pure compounds but mixtures of oligomers of the formula (X).

[0076] The preferred aluminoxane is methylaluminoxane (MAO). Since the aluminoxanes used according to the invention as cocatalysts are not pure compounds due to their method of preparation, the molarity of aluminoxane solutions hereinafter is based on their aluminum content.

[0077] According to the present invention, also a boron-containing cocatalyst can be used instead of the aluminoxane cocatalyst or the aluminoxane cocatalyst can be used in combination with a boron-containing cocatalyst.

[0078] It will be understood by the skilled person that when boron-based cocatalysts are employed, it is usual to pre-alkylate the complex by reacting it with an alkyl aluminium compound such as TIBA. This procedure is well known and any suitable alkyl aluminium, e.g. Al(C1-6-alkyl)3 may be used. Preferred alkyl aluminium compounds are triethylaluminium, triisobutylaluminium, triisohexylaluminium, tri-n-octylaluminium and triisooctylaluminium.

[0079] Alternatively, when a borate cocatalyst is used, the metallocene catalyst complex is in its alkylated version, which is, for example, a dimethyl or dibenzyl metallocene catalyst complex.

[0080] Boron-based cocatalysts of interest include those of the formula (Z)BY3(Z) where Y is the same or different and is a hydrogen atom, an alkyl group of 1 to about 20 carbon atoms, an aryl group of 6 to about 15 carbon atoms, alkylaryl, arylalkyl, haloalkyl or haloaryl, each having from 1 to 10 carbon atoms in the alkyl radical and from 6-20 carbon atoms in the aryl radical or fluorine, chlorine, bromine or iodine. Preferred examples for Y are methyl, propyl, isopropyl, isobutyl or trifluoromethyl, unsaturated groups such as aryl or haloaryl such as phenyl, tolyl, benzyl groups, p-fluorophenyl, 3,5-difluorophenyl, pentachlorophenyl, pentafluorophenyl, 3,4,5-trifluorophenyl and 3,5-di(trifluoromethyl)phenyl. Preferred options are trifluoroborane, triphenylborane, tris(4-fluorophenyl)borane, tris(3,5-difluorophenyl)borane, tris(4-fluoromethylphenyl)borane, tris(2,4,6-trifluorophenyl)borane, tris(pentafluorophenyl)borane, tris(tolyl)borane, tris(3,5-dimethylphenyl)borane, tris(3,5-difluorophenyl)borane, and/or tris(3,4,5-trifluorophenyl)borane.

[0081] Particular preference is given to tris(pentafluorophenyl)borane.

[0082] However, it is preferred that borates, i.e. compounds containing a borate ion 3+, are used. Such ionic cocatalysts preferably contain a non-coordinating anion, such as tetrakis(pentafluorophenyl)borate and tetraphenylborate. Suitable counterions are protonated amine and aniline derivatives, such as methylammonium, anilinium, dimethylammonium, diethylammonium, N-methylanilinium, diphenylammonium, N,N-dimethylanilinium, trimethylammonium, tri-n-butylammonium, methyldiphenylammonium, pyridinium, p-bromo-N,N-dimethylanilinium or p-nitro-N,N-dimethylanilinium.

[0083] Preferred ionic compounds that may be used in accordance with the present invention include: triethylammoniumtetra(phenyl)borate, tributylammoniumtetra(phenyl)borate, trimethylammoniumtetra(tolyl)borate, tributylammoniumtetra(tolyl)borate, tributylammoniumtetra(pentafluorophenyl)borate, tripropylammoniumtetra(dimethylphenyl)borate, tributylammoniumtetra(trifluoromethylphenyl)borate, tributylammoniumtetra(4-fluorophenyl)borate, N,N-dimethylcyclohexylammoniumtetrakis(pentafluorophenyl)borate, N,N-dimethylbenzylammoniumtetrakis(pentafluorophenyl)borate, N,N-dimethylaniliniumtetra(phenyl)borate, N,N-diethylaniliniumtetra(phenyl)borate, N,N-dimethylaniliniumtetrakis(pentafluorophenyl)borate, N,N-di(propyl)ammoniumtetrakis(pentafluorophenyl)borate, di(cyclohexyl)ammoniumtetrakis(pentafluorophenyl)borate, triphenylphosphoniumtetrakis(phenyl)borate, triethylphosphoniumtetrakis(phenyl)borate, diphenylphosphoniumtetrakis(phenyl)borate, tri(methylphenyl)phosphoniumtetrakis(phenyl)borate, tri(dimethylphenyl)phosphoniumtetrakis(phenyl)borate, triphenylcarbeniumtetrakis(pentafluorophenyl)borate, or ferroceniumtetrakis(pentafluorophenyl)borate.

[0084] Preference is given to triphenylcarbeniumtetrakis(pentafluorophenyl)borate, N,N-dimethylcyclohexylammoniumtetrakis(pentafluorophenyl)borate or N,N-dimethylbenzylammoniumtetrakis(pentafluorophenyl)borate.

[0085] It has surprisingly been found that certain boron cocatalysts are especially preferred. Preferred borates for use in the invention therefore comprise trityl ion. Thus, the use of N,N-dimethylammonium-tetrakispentafluorophenylborate and Ph3CB(PhF5)4 and the like are therefore especially favored.

[0086] According to the present invention, the preferred cocatalysts are alumoxanes, more preferably methylalumoxanes, combinations of alumoxanes with Al-alkyls, boron or borate cocatalysts and combination of alumoxanes with boron-based cocatalysts.

[0087] Suitable amounts of cocatalyst will be well known to those skilled in the art.

[0088] The molar ratio of boron to the metallocene metal ion may be in the range of 0.5:1 to 10:1 mol/mol, preferably 1:1 to 10:1, especially 1:1 to 5:1 mol/mol.

[0089] The molar ratio between Al in the aluminoxane and the metal ion of the metallocene may be in the range of 1:1 to 2000:1 mol/mol, preferably 10:1 to 1000:1, and most preferably 50:1 to 500:1 mol/mol. Catalyst Manufacturing

[0090] The metallocene catalyst complex of the present invention can be used in combination with a suitable cocatalyst as a catalyst for the polymerization of propylene, for example in a solvent such as toluene or an aliphatic hydrocarbon, (i.e. for solution polymerization), as is well known in the art. Preferably, the polymerization of propylene occurs in the condensed phase or in the gas phase.

[0091] The catalyst of the invention can be used in supported or unsupported form. The particulate support material used is preferably an organic or inorganic material such as silica, alumina or zirconia or a mixed oxide such as silica-alumina, in particular silica, alumina or silica-alumina. The use of a silica support is preferred. The skilled person is aware of the procedures required to support a metallocene catalyst.

[0092] Particularly preferably, the support is a porous material so that the complex can be loaded into the pores of the support, for example using a process analogous to those described in WO94/14856, WO95/12622 and WO2006/097497. The particle size is not crucial, but is preferably in the range 5 to 200 μm, more preferably 20 to 80 μm. The use of such supports is common in the art.

[0093] In an alternative embodiment, no support is used. Such a catalyst may be prepared in solution, e.g., in an aromatic solvent such as toluene, by contacting the metallocene (as a solid or as a solution) with the cocatalyst, e.g., methylaluminoxane or a borate or borate salt previously dissolved in an aromatic solvent, or it may be prepared by sequentially adding the dissolved catalyst components to the polymerization medium.

[0094] In one embodiment, no external carrier is used, but the catalyst is still present in solid particulate form. Thus, no external support material, such as an inert organic or inorganic carrier, e.g., silica as described above, is employed.

[0095] In order to provide the catalyst of the invention in solid form, but without using an external carrier, it is preferred that a liquid/liquid emulsion system is used. The process involves forming the dispersant catalyst components (i) and (ii) in a solvent, and solidifying said dispersed droplets to form solid particles.

[0096] In particular, the method involves preparing a solution of one or more catalyst components; dispersing said solution in a solvent to form an emulsion in which said one or more catalyst components are present in the droplets of the dispersed phase; immobilizing the catalyst components in the dispersed droplets, in the absence of an external particulate porous support, in order to form solid particles comprising said catalyst, and optionally recovering said particles.

[0097] This process enables the manufacture of active catalyst particles with improved morphology, e.g. with a predetermined spherical shape, surface properties and particle size, and without using any added external porous support material such as inorganic oxide, e.g. silica. By the term "preparing a solution of one or more catalyst components" it is meant that the catalyst-forming compounds may be combined in a solution which is dispersed in the immiscible solvent or, alternatively, at least two separate catalyst solutions for each part of the catalyst-forming compounds may be prepared, which are then successively dispersed in the solvent.

[0098] The full disclosure of the required process can be found in WO03/051934 which is also incorporated herein by reference.

[0099] The invention is also industrially advantageous since it enables the preparation of the solid particles to be carried out as a one-pot procedure. Continuous or semi-continuous processes are also possible for producing the catalyst. Off-line prepolymerization of catalyst

[0100] The use of heterogeneous catalysts, in which no external support material is used, (also called “self-supported” catalysts) may have, as a disadvantage, a tendency to dissolve to some extent in the polymerization medium, i.e. some active catalyst components may leach out of the catalyst particles during slurry polymerization, thus the original good morphology of the catalyst may be lost. These leached catalyst components are very active, possibly causing problems during polymerization. Therefore, the amount of leached components can be minimized, i.e. all catalyst components should be kept in heterogeneous form.

[0101] Additionally, self-supporting catalysts generate, due to the high amount of catalytically active species in the catalyst system, high temperatures at the beginning of polymerization, which can cause melting of the product material. Both effects, i.e. partial dissolution of the catalyst system and heat generation, can cause fouling, lamination and deterioration of the morphology of the polymeric material.

[0102] In order to minimize potential problems associated with high activity and leaching, it is possible to "off-line pre-polymerize" the catalyst before using it in the polymerization process.

[0103] It should be noted that the offline prepolymerization in question is part of the catalyst preparation process, being a step performed after a solid catalyst is formed. The offline catalyst prepolymerization step is not part of the actual polymerization process configuration comprising a prepolymerization step. After the offline catalyst prepolymerization step, the solid catalyst can be used in the polymerization.

[0104] The "off-line prepolymerization" of the catalyst occurs after the solidification step of the liquid-liquid emulsion process. The prepolymerization can occur by known methods described in the art, such as that method described in WO 2010/052263, WO 2010/052260 or WO 2010/052264. Preferred embodiments of this aspect of the invention are described herein.

[0105] As monomers in the catalyst off-line prepolymerization step, preferably alpha-olefins are used. Preferred C2-C10 olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, styrene and vinylcyclohexene are used. The most preferred alpha-olefins are ethylene and propylene, especially propylene.

[0106] Off-line prepolymerization of catalyst may be carried out in the gas phase or in an inert diluent, typically oil or fluorinated hydrocarbon, preferably in fluorinated hydrocarbons or a mixture of fluorinated hydrocarbons. Preferably, perfluorinated hydrocarbons are used. The melting point of such (per)fluorinated hydrocarbons is typically in the range of 0 to 140 °C, preferably 30 to 120 °C, such as 50 to 110 °C.

[0107] When off-line prepolymerization of the catalyst is carried out on fluorinated hydrocarbons, the temperature for the prepolymerization step is below 70 °C, for example in the range of -30 to 70 °C, preferably 0-65 °C and most preferably in the range of 20 to 55 °C. The pressure within the reaction vessel is preferably higher than atmospheric pressure to minimize eventual leaching of air and/or moisture into the catalyst vessel. Preferably, the pressure is in the range of at least 0.1 to 1.5 MPa (1 to 15 bar), preferably 0.2 to 1 MPa (2 to 10 bar). The reaction vessel is preferably maintained in an inert atmosphere such as under nitrogen or argon or under a similar atmosphere.

[0108] Off-line prepolymerization is continued until the desired degree of prepolymerization, defined as weight of polymer matrix/weight of solid catalyst prior to the prepolymerization step, is reached. The degree is less than 25, preferably 0.5 to 10.0, more preferably 1.0 to 8.0, most preferably 2.0 to 6.0.

[0109] The use of the off-line catalyst prepolymerization step offers the advantage of minimizing leaching of catalyst components and thus local overheating.

[0110] After offline prepolymerization, the catalyst can be isolated and stored.

Polymerization

[0111] The propylene homopolymer (HPP) is preferably produced by a single-stage or multi-stage process polymerization of propylene, such as bulk polymerization, gas phase polymerization, slurry polymerization, solution polymerization, or combinations thereof. Preferably, the propylene homopolymer (HPP) can be produced in a combination of a loop and gas phase reactor. Those processes are well known to one skilled in the art.

[0112] A preferred multi-stage process is a “cycled gas phase” process as developed by Borealis (known as BORSTAR® technology) described, for example, in the patent literature. In the patent literature, such as EP 0 887 379, WO 92/12182, WO 2004/000899, WO 2004/111095, WO 99/24478, WO 99/24479 or WO 00/68315.

[0113] An additional gas phase-slurry process is the Basell Spheripol® process.

[0114] Preferably, in the present process for producing the C2C3 random copolymer composition as defined above, the conditions for the first reactor (R-1), i.e. the slurry reactor (SR) as a loop reactor (LR), of step (a) may be as follows: - the temperature is within the range of 40 °C to 110 °C, preferably between 60 °C and 100 °C, more preferably between 65 and 95 °C, - the pressure is within the range of 2 MPa (20 bar) to 8 MPa (80 bar), preferably between 4 MPa (40 bar) to 7 MPa (70 bar), - hydrogen may be added to control the molar mass in a manner known per se.

[0115] Subsequently, the reaction mixture from the first reactor (R-1) is transferred to the second reactor (R-2), i.e. gas phase reactor (GPR-1), wherein the conditions are preferably as follows: - the temperature is within the range of 50 °C to 130 °C, preferably between 60 °C and 100 °C, - the pressure is within the range of 0.5 MPa (5 bar) to 5 MPa (50 bar), preferably between 1.5 MPa (15 bar) to 3.5 MPa (35 bar), - hydrogen may be added to control the molar mass in a manner known per se. Polypropylene composition

[0116] The polypropylene composition according to the present invention comprises 0.1-0.4% by weight, preferably 0.1 to 0.35% by weight, more preferably 0.1 to 0.3% by weight of one or more slip agents and 0.0-0.5% by weight, preferably 0.1 to 0.4% by weight, more preferably 0.1 to 0.3% by weight of one or more anti-blocking agents.

[0117] Slip agents are also commonly known in the art. Slip agents migrate to the surface and act as polymer-to-polymer and polymer-to-metal roller lubricants, generating reduced coefficient of friction (CoF) as a result. Examples are fatty acid amides such as erucamide (CAS No. 112-84-305), oleamide (CAS No. 301-02-0), stearamide (CAS No. 124-26-5) or combinations thereof. A comprehensive list of suitable slip agents can be found in Chapter 8 “Slip Additives” of the book “Plastic Additives Handbook” edited by H. Zweifel, R.D. Maier and M. Schiller, 6th edition, Hanser Publishers 2009, pages 629-636.

[0118] Common anti-blocking agents are natural silica such as diatomaceous earth (such as CAS No. 60676-86-0 (SuperfFloss™), CAS No. 60676-86-0 (SuperFloss E™), or CAS No. 60676-86-0 (Celite 499™)), synthetic silica (such as CAS No. 7631-86-9 or CAS No. 112926-00-8), silicates (such as aluminum silicate (kaolin) CAS No. 1318-74-7, sodium aluminum silicate CAS No. 1344-00-9, calcined kaolin CAS No. 92704-411, aluminum silicate CAS No. 1327-36-2, or calcium silicate CAS No. 1344-95-2), synthetic zeolites (such as calcium sodium aluminosilicate hydrate CAS No. 134401-0). A comprehensive list of suitable anti-blocking agents can be found in Chapter 7 “Anti-blocking Additives” of the book “Plastic Additives Handbook” edited by H. Zweifel, R.D. Maier and M. Schiller, 6th edition, Hanser Publishers 2009, pages 613-628.

[0119] In a preferred embodiment, the polypropylene composition may additionally comprise one or more additives in a total amount of 0.1 to 5.0% by weight, based on the composition, selected from the group comprising UV stabilizers, antistatic agents, alpha-nucleating agents and antioxidants.

[0120] These additives are commonly known to one skilled in the art.

[0121] Examples of antioxidants that are commonly used in the art are sterically hindered phenols (such as CAS No. 6683-19-8, also sold as Irganox 1010 FF™ by BASF), phosphorus-based antioxidants (such as CAS No. 31570-04-4, also sold as Hostanox PAR 24 (FF)™ by Clariant, or Irgafos 168 (FF)TM by BASF), sulfur-based antioxidants (such as CAS No. 693-36-7, sold as Irganox PS-802 FL™ by BASF), nitrogen-based antioxidants (such as 4,4'-bis(1,1'-dimethylbenzyl)diphenylamine) or antioxidant blends.

[0122] Acid sequestrants are also commonly known in the art. Examples are calcium stearate, sodium stearates, zinc stearates, magnesium and zinc oxides, synthetic hydrotalcite (e.g., SHT, CAS No. 11097-59-9), lactates and lactylates, as well as calcium stearate (CAS No. 1592-23-0) and zinc stearate (CAS No. 557-05-1).

[0123] Suitable UV stabilizers are, for example, Bis-(2,2,6,6-tetramethyl-4-piperidyl)-sebacate (CAS No. 52829-07-9, Tinuvin 770); 2-Hydroxy-4-n-octoxy-benzophenone (CAS No. 1843-05-6, Chimassorb 81).

[0124] Alpha-nucleating agents such as sodium benzoate (CAS no. 532-32-1); a mixture of aluminium-hydroxy-bis[2,2'-methylene-bis(4,6-di-t-butylphenyl)phosphate] and lithium myristate (commercially available as Adekastab NA-21 from Adeka Palmarole, France) or 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (CAS no. 135861-56-2, commercially available as Millad 3988 from Milliken, USA) may be added.

[0125] Suitable antistatic agents are, for example, glycerol esters (CAS No. 97593-29-8) or ethoxylated amines (CAS No. 71786-60-2 or 61791-31-9) or ethoxylated amides (CAS No. 204-393-1).

[0126] Typically, these additives are added in amounts of 100-1,000 ppm for each single component. Preferably, at least one antioxidant is added.

[0127] The polypropylene composition according to the invention may be compounded and pelletized using any of a variety of compounding and blending machines and methods well known and commonly used in the resin compounding art. For blending the individual components of the present polypropylene composition, a conventional compounding or blending apparatus, for example a Banbury mixer, a 2-roll rubber mill, a Buss co-kneader or a twin screw extruder may be used. Preferably, a co-rotating twin screw extruder is used. The polypropylene compositions recovered from the extruder/blender are usually in the form of pellets. These pellets are then processed and formed into a film according to the present invention.

Film

[0128] The polypropylene composition described above is suitable for the production of blown films as well as cast films. Description of film production by blown film technology

[0129] The composition described above is capable of being manufactured into water-quenched or air-quenched blown films, preferably air-quenched blown films, on typical polyethylene blown film production equipment.

[0130] In principle, the process comprises the steps of (i) blowing a tube of molten material with air perpendicularly upwards from a side-feed blown film die; (ii) cooling the same with a water contact cooling ring or air quenching; (iii) bending and guiding the same over the deflector rollers to the winder Blown film technology with water contact cooling ring

[0131] In this polymer film production technology, the molten blend is extruded through a tubular die fed by an extruder (usually single screw) and expanded into a tube. The film tube is in contact on the outside with a water cooling ring and is rapidly cooled. The already solidified film tube is then flattened by take-up rollers and fed to a winder.

[0132] For a more detailed description, see “Polypropylene Handbook,” edited by Edward P. Moore, Jr., Hanser Publishers, 1996. Air-Quenched Blown Film Technology

[0133] In this manufacturing step for air-tempered blown films, the film is produced using at least a blow-up ratio of 1.5, preferably at least a blow-up ratio of 2.0, more preferably at least a blow-up ratio of 2.5.

[0134] The air-quenched blown film extrusion technique is well known for the production of thin plastic films. In one advantageous process, the blends described above are extruded through a circular die to form a film. Air is introduced through the center of the die to hold the film in the form of a bubble which increases the diameter of the film by about 1.5 to 6 times, after which the bubble is collapsed onto the rollers. There are several variations of this process within the art. Most references to polyolefin film blowing disclose processes used for polyethylene, but these are applicable to the blends described above with few modifications within the art without undue experimentation.

[0135] For example, cooling is often advantageously modified because the technique recognizes that polypropylene cools and crystallizes at a different rate than polyethylene.

[0136] Therefore, adjustments to the cooling parameters generally produce a more stable bubble at the desired output rates.

[0137] In blown film forming, the molten mixture (molten material) enters a ring-shaped die through the bottom or from the side. The molten material is forced through spiral grooves around the surface of a mandrel within the die and extruded through the die opening as a thick-walled tube. The tube is expanded into a bubble of the desired diameter and correspondingly reduced in thickness as previously described. Description of film production by cast film technology

[0138] In this simplest technology for producing polymer films, the molten blend is extruded through a slot die fed by an extruder (usually single-screw) onto a first chilled roll, the so-called chill-roll. From this roll, the already solidified film is withdrawn by a second roll (pinch roll or take-up roll) and transported to a winding device after trimming the edges. Only a very limited amount of orientation is created in the film, which is determined by the ratio of the die thickness to the film thickness or the extrusion speed to the winding speed, respectively. Due to its technical simplicity, cast film technology is a very economical and easy-to-handle process. The films resulting from this technology are characterized by good transparency and rather isotropic mechanical properties (limited stiffness, high toughness).

[0139] In summary, the process comprises the steps of i) pouring or spreading a solution, hot melt or dispersion of a material onto a temporary carrier, ii) hardening the material, and iii) removing the hardened film from the surface of the carrier.

[0140] Monolayer films having a thickness of 5 to 300 μm, preferably 10 to 200 μm, more preferably 20 to 150 μm are suitable according to the present invention.

[0141] The films according to the present invention may be unoriented, mono-axially or bi-axially oriented.

[0142] It is preferable that films are not oriented.

[0143] Especially preferred are, however, cast films, especially preferred are non-oriented cast films.

[0144] In a particularly preferred embodiment, the polypropylene composition has a coefficient of friction (CoF) determined in accordance with ISO 8295 fulfilling the equation (I) CoF < 0.658 days-0.189 (I) when cast into a film with a thickness of 50 micrometers.

[0145] In another embodiment, the polypropylene composition has an opacity of no more than 2.5%, preferably no more than 2.3%, more preferably no more than 2.1%, determined in accordance with ASTM D 1003, when cast into a film having a thickness of 50 micrometers.

[0146] In the following, the present invention is further illustrated by means of examples.

EXAMPLES 1. Measurement methods

[0147] The following definitions of terms and methods of determination apply to the above general description of the invention as well as to the examples below, unless otherwise defined.

[0148] MFR2 (230 °C) is measured according to ISO 1133 (230 °C, 2.16 kg load). Microstructure quantification by NMR spectroscopy

[0149] Quantitative nuclear magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers. Quantitative 13C{1H}NMR spectra were recorded in the solution state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for 1H and 13C, respectively. All spectra were recorded using an optimized 10 mm extension 13C temperature probe head at 125 °C using nitrogen gas for all tires. Approximately 200 mg of material was dissolved in 3 ml of 1,2-tetrachloroethane-d2 (TCE-d2) together with chromium(III)-acetylacetonate (Cr(acac)3) resulting in a 65 mM solution of relaxing agent in solvent (Singh, G., Kothari, A., Gupta, V., Polymer Testing 28 5 (2009), 475). To ensure a homogeneous solution, after initial sample preparation on a hot block, the NMR tube was further heated in a rotating furnace for at least 1 h. Upon insertion into the magnet, the tube was rotated at 10 Hz. This configuration was chosen primarily because of the high resolution and quantitative accuracy required for accurate quantification of ethylene content. Standard single-pulse excitation was employed without NOE, using an optimized tip angle, 1 s recycle delay, and a WALTZ16 bilevel decoupling scheme (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). A total of 6144 (6k) variables were acquired per spectra.

[0150] Quantitative 13C{1H}NMR spectra were processed, integrated, and relevant quantitative properties determined from the integrals using proprietary computer programs. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm using the solvent chemical shift. This approach allowed comparable referencing even when this structural unit was not present. Characteristic signals corresponding to ethylene incorporation were observed in Cheng, H. N., Macromolecules 17 (1984), 1950).

[0151] With characteristic signals corresponding to 2,1-erythro regiodefects observed (as described in L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 2000, 100 (4), 1253, in Cheng, H. N., Macromolecules 1984, 17, 1950, and in W-J. Wang and S. Zhu, Macromolecules 2000, 33 1157) correction for the influence of regiodefects on certain properties was necessary. Characteristic signals corresponding to other types of regiodefects were not observed.

[0152] The comonomer fraction was quantified using the method of Wang et. al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157) by integrating multiple signals across the spectral region in the 13C{1H} spectra. This method was chosen for its robust nature and ability to account for the presence of region defects when necessary. The integral regions were slightly adjusted to increase applicability across the range of comonomer content encountered.

[0153] For systems in which only isolated ethylene in PPEPP sequences was observed, the method of Wang et al. was modified to reduce the influence of non-zero integrals from sites that are known not to be present. This approach reduced the overestimation of ethylene content for such systems and was achieved by reducing the number of sites used to determine absolute ethylene content to: E = 0.5(Sββ + Sβy + Sβδ + 0.5(Sαβ + Say ))

[0154] By using this set of sites, the corresponding integral equation becomes: E = 0.5(IH +IG + 0.5(IC + ID)) using the same notation as used in the paper by Wang et. al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157). The equations used for absolute propylene content were not modified.

[0155] Comonomer incorporation in mole percent was calculated from the mole fraction: E [mol%] = 100 * fE

[0156] Comonomer incorporation in weight percent was calculated from the mole fraction: E [wt%] = 100 * (fE * 28.06) / ((fE * 28.06) + ((1-fE) * 42.08))

[0157] Comonomer sequence distribution at the triad level was determined using the analysis method of Kakugo et al. (Kakugo, M., Naito, Y., Mizunuma, K., Miyatake, T. Macromolecules 15 (1982) 1150). This method was chosen for its robust nature and slightly adjusted integration regions to increase applicability to a wide range of comonomer content.

[0158] Xylene solubles (XCS, % by weight): The content of cold solubles in xylene (XCS) is determined at 25 °C according to ISO 16152; first edition; 01/07/2005 Number-average molecular weight (Mn), weight-average molecular weight (Mw) and polydispersity (Mw/Mn)

[0159] are determined by Gel Permeation Chromatography (GPC) according to the following method:

[0160] The weight-average molecular weight Mw and polydispersity (Mw/Mn, where Mn is the number-average molecular weight, and Mw is the weight-average molecular weight) are measured by a method based on ISO 16014-1:2003 and ISO 16014-4:2003. A Waters Alliance GPCV 2000 instrument equipped with a refractive index detector and an online viscometer was used with TosoHaas 3xTSK (GMHXL-HT) gel columns and 1,2,4-trichlorobenzene (TCB, stabilized with 200 mg/L 2,6-di-tert-butyl-4-methyl-phenol) as solvent at 145 °C and a constant flow rate of 1 ml/min. 216.5 μL of sample solution was injected per analysis. The column set was calibrated using relative calibration with 19 narrow MWD polystyrene (PS) standards in the range of 0.5 kg/mol to 11,500 kg/mol and a set of well-characterized broad polypropylene standards. All samples were prepared by dissolving 5–10 mg of polymer in 10 mL (at 160 °C) of stabilized TCB (the same as the mobile phase) and holding for 3 h with continuous stirring prior to sampling on the GPC instrument.

[0161] DSC analysis, melting temperature (Tm) and heat of fusion (Hf), crystallization temperature (Tc) and heat of crystallization (Hc): measured with a TA Instrument Q2000 differential scanning calorimetry (DSC) on 5 to 7 mg samples. DSC is performed according to ISO 11357/part 3/method C2 in a heating/cooling/heating cycle with a scan rate of 10 °C/min in the temperature range -30 to +225 °C. The crystallization temperature and heat of crystallization (Hc) are determined from the cooling step, while the melting temperature and heat of fusion (Hf) are determined from the second heating step.

[0162] The glass transition temperature Tg is determined by dynamic mechanical analysis according to ISO 6721-7. Measurements are made in torsion mode on compression molded samples (40x10x1 mm3) between -100 °C and +150 °C with a heating rate of 2 °C/min and a frequency of 1 Hz. Transparency, opacity, clarity

[0163] Transparency, opacity and clarity were determined on cast films with a thickness of 50 μm according to ASTM D 1003.

[0164] Retortability performance in terms of transparency, opacity and clarity was determined according to ASTM D 1003 by measuring these optical parameters after steam sterilization at 121 °C for 30 min on cast films with a thickness of 50 μm for propylene homopolymers. Coefficient of Friction (CoF)

[0165] The dynamic coefficient of friction (CoF) as a measure of the friction behavior of the film was determined according to ISO 8295 on film samples with a thickness of 50 μm. Immediately after film production, the film was stored at 23 °C and 50 % relative humidity for different times: 1 day, 3 days, 7 days and 21 days. The CoF measurement was then carried out at 23 °C inside the film roll (inside/inside - friction).

2. Examples

[0166] The catalyst used in the polymerization process for the polypropylene homopolymer (HPP) of the inventive examples (IE1, 2, 3) was produced as follows: Preparation of MAO silica support

[0167] A steel reactor equipped with a mechanical stirrer and a filter mesh was purged with nitrogen and the reactor temperature was set to 20 °C. Next, silica grade DM-L-303 from AGC Si-Tech Co, pre-calcined at 600 °C (5.0 kg), was added from a feed drum followed by careful pressurization and depressurization with nitrogen using hand valves. Then, toluene (22 kg) was added. The mixture was stirred for 15 min. Next, 30 wt % MAO solution in toluene (9.0 kg) from Lanxess was added via the feed line at the top of the reactor within 70 min. The reaction mixture was then heated to 90 °C and stirred at 90 °C for an additional two hours. The slurry was allowed to settle and the mother liquor was removed by filtration. The catalyst was washed twice with toluene (22 kg) at 90 °C, followed by sedimentation and filtration. The reactor was cooled to 60 °C and the solid was washed with heptane (22.2 kg). Finally, MAO-treated SiO2 was dried at 60 °C under nitrogen flow for 2 h and then for 5 h under vacuum (-0.5 barg) with stirring. The MAO-treated support was collected as a free-flowing white powder found to contain 12.2 wt % Al.

Catalyst Synthesis

[0168] The metallocene complex C2 was produced as described in WO2019/179959 for MC-2

[0169] 30 wt % MAO in toluene (0.7 kg) was added into a nitrogen-sparse steel reactor via a burette at 20 °C. Toluene (5.4 kg) was then added under stirring. Metallocene C2 (93 g) was added from a metal cylinder followed by purging with 1 kg of toluene. The mixture was stirred for 60 min at 20 °C. Trityltetrakis(pentafluorophenyl)borate (91 g) was then added from a metal cylinder followed by purging with 1 kg of toluene. The mixture was stirred for 1 h at room temperature. The resulting solution was added to a stirred cake of MAO silica support prepared as described above for 1 h. The cake was allowed to stand for 12 h, followed by drying under N2 flow at 60 °C for 2 h and additionally for 5 h under vacuum (-0.5 barg) with stirring.

[0170] The dried catalyst was sampled as a free-flowing pink powder containing 13.9 wt% Al and 0.11 wt% Zr.

Polymerization

[0171] The HPP polymerization conditions used as inventive examples in IE1 to IE3 are indicated in Table 1. The polymerizations were carried out in a Borstar pilot plant, with prepolymerizer, cycle reactor and first gas phase reactor connected sequentially, in the presence of the catalyst described above. The resulting polymer powder was compounded with 0.1 wt.% Irganox B215, 0.05 wt.% calcium stearate in the TSE 16 twin screw extruder, with a yield of 7 kg/h and a melting temperature of 210 °C. The properties measured on these products (indicated as Final) are also shown in Table 1.

[0172] The HPP in CE1 is a commercially available HD234CF polypropylene homopolymer from Borealis AG produced in the presence of Zigler-Natta catalyst having a melting temperature of 164 °C and an MFR2 (230 °C) of 8.0 g/10 min. Table 1: Preparation of examples

[0173] The IEs are produced with the HPP base powder sample as shown in Table 1, and the difference amount of slip agent and anti-blocking agent are added in the compounding step. The recipe is shown in Table 2. The compounding was produced in a ZSK 32 twin-screw extruder, with a flow rate of 200 kg/h and a melting temperature of 210 °C.

[0174] Cast films were produced in a single screw extruder with a barrel diameter of 30 mm and a 200 x 0.5 mm slot die in combination with a chilled and take-up roll. The melt temperature was 260 °C at the die. The chilled roll and take-up roll were maintained at 15 °C. The film thickness was 50 μm and is adjusted by varying the ratio of extruder output to withdrawal speed. Additives:

[0175] Calcium stearate is Ceasit FI (CAS No. 216 472-8), produced by Baerlocher.

[0176] Erucic acid amide is Finawax-E (CAS No. 11284-5), commercially available from Fine Organics.

[0177] The synthetic silica is Slobloc 45B (CAS No. 7631-869), commercially available from Grace.

[0178] The results are shown in Table 2 for films produced from polypropylene homopolymers (IE1-3 and CE1) Table 2: Properties of films produced from propylene homopolymers

[0179] It is clearly shown in Table 2 that the cast films of the present invention have a lower CoF already 3 days after film production, and an even lower value 7 days after film production, compared to the comparative examples. At the same time, the optical properties such as opacity and clarity of the films are clearly improved.

Claims (14)

1. A film comprising a polypropylene composition comprising (a) 95.0-99.9 wt. % of a propylene homopolymer (HPP) polymerized in the presence of a metallocene catalyst, wherein the propylene homopolymer (HPP) has a melting temperature (Tm) measured by differential scanning calorimetry (DSC) according to ISO 11357 in the range of 152 to 162 °C, a xylene cold soluble (XCS) fraction determined at 25 °C according to ISO 16152 equal to or less than 1.5 wt. % and has a 2,1-erythro regiodefect content as determined from 13C-NMR spectroscopy in the range of 0.01 to 1.00 mol. %, (b) 0.1-0.4 wt. % of one or more glidants, and (c) 0.0-0.5% by weight of one or more antiblocking agents. 2. The film of claim 1, the film being a non-oriented blown or cast film, preferably a non-oriented cast film. 3. Film according to claim 1 or 2, characterized in that the propylene homopolymer (H-PP) has a melt flow rate MFR2 (230 °C, 2.16 kg) determined according to ISO 1133 in the range 4.0-20.0 g/10 min. 4. Film according to any one of the preceding claims, characterized in that the propylene homopolymer (H-PP) has a molecular weight distribution (MWD) equal to or less than 4.0. 5. Film according to any one of the preceding claims, characterized in that the propylene homopolymer (H-PP) has 2,1-erythro regiodefects in the range of 0.20 to 0.80 mol% and, more preferably, in the range of 0.30 to 0.80 mol%, determined by 13C-NMR spectroscopy. 6. Film according to any one of the preceding claims, characterized in that the propylene homopolymer (H-PP) has an isotactic triad fraction (mm) determined from 13C-NMR spectroscopy of at least 97.5%. 7. Film according to any one of the preceding claims, characterized in that the polypropylene composition has a coefficient of friction (CoF) determined in accordance with ISO 829 fulfilling the equation (I) CoF < 0.658 days-0.189 (I) when cast into a film with a thickness of 50 micrometers. 8. Film according to any one of the preceding claims, characterized in that the polypropylene composition has an opacity of not more than 2.5%, determined in accordance with ASTM D 1003, when cast into a film with a thickness of 50 micrometers. 9. Film according to any one of the preceding claims, characterized in that the propylene homopolymer (HPP) is polymerized in the presence of a metallocene catalyst complex of formula (I): Formula (I) where Mt is Hf or Zr; each X is a sigma ligand, each R1 is independently the same or may be different and is a CH2-R7 group, where R7 is H or a linear or branched C1-6-alkyl group, a C3-8 cycloalkyl group, a C6-10 aryl group, each R2 is independently a -CH=, —CY=, -CH2-, —CHY-, or -CY2- group, where Y is a C1-10 hydrocarbyl group and where n is 2-6, each R3 and R4 are independently the same or may be different and are each hydrogen, a linear or branched C1-C6-alkyl group, an OY group, or a C7-20 arylalkyl, C7-20 alkylaryl group, or C6-20 aryl group, wherein at least one R3 per phenyl group and at least one R4 is not hydrogen, and optionally two adjacent R3 or R4 groups may be part of a ring including the phenyl carbons to which they are attached, R5 is a linear or branched C1-C6 alkyl group, C7-20 arylalkyl group and C7-20 alkylaryl group or C6-C20 aryl group, R6 is a C(R8)3 group, wherein R8 is a linear or branched C1-C6 alkyl group, each R is independently a C1-C20 hydrocarbyl, C6-C20 aryl, C7-C20 arylalkyl or C7-C20 alkylaryl. 10. The film of claim 9, wherein the propylene homopolymer (HPP) is polymerized in the presence of a metallocene catalyst complex, wherein Mt is Zr, each X is independently a hydrogen atom, a halogen atom, C1-6alkoxy group or an R' group, wherein R' is a C1-6 alkyl, phenyl or benzyl group, each R is independently a C1-C20 hydrocarbyl, C6-C20 aryl, C7-C20 arylalkyl or C7-C20 alkylaryl, each R1 is independently the same or may be different and is a CH2-R7 group, wherein R7 is H or a linear or branched C1-6 alkyl group, C6-10 aryl group, each R2 is independently a -CH=, -CY=, -CH2-, -CHY- or -CY2- group, wherein Y is a C1-4 hydrocarbyl group and wherein n is 3-4, each R3 and R4 are independently the same or may be different and are hydrogen, a linear or branched C1-C6 alkyl group or C6-20 aryl groups wherein at least one R3 per phenyl group and at least one R4 is not hydrogen, R5 is a linear or branched C1-C6 alkyl group or C620 aryl group, and R6 is a C(R8)3 group wherein R8 is a linear or branched C1-C4 alkyl group. 11. The film of claim 9 or 10, wherein the propylene homopolymer (HPP) is polymerized in the presence of a metallocene catalyst complex, wherein Mt is Zr, each X is independently a chlorine, benzyl or a methyl group, each R is independently a C1-C10 hydrocarbyl or C6-C10 aryl group, both R1 are the same and are a CH2-R7 group, wherein R7 is H or a linear or branched C1-C3 alkyl group, each R2 is independently a -CH=, —CY=, -CH2-, —CHY- or -CY2- group, wherein Y is a C1-4 hydrocarbyl group and wherein n is 3-4, each R3 and R4 are independently the same or may be different and are hydrogen, a linear or branched C1-C6 alkyl group or C6-20 aryl groups, wherein at least one R3 per phenyl group and at least one R4 is not hydrogen, R5 is a linear or branched C1-C6 alkyl group or C620 aryl group and R6 is a C(R8)3 group, wherein R8 is the same and is a C1-C2 alkyl group. 12. The film of any one of claims 1-8, wherein the propylene homopolymer (HPP) is polymerized in the presence of a metallocene catalyst system comprising (i) a complex as defined in any one of claims 9-11; (ii) a cocatalyst comprising a compound of a group 13 metal. 13. Film, according to claim 12, characterized in that the catalyst system comprises as cocatalyst (ii) alumoxane, combinations of alumoxane with Al-alkyls, boron or borate cocatalysts and combination of alumoxanes with boron-based cocatalysts. 14. Process for preparing a film characterized by comprising the steps of: i) the propylene homopolymer (HPP) as defined in any one of the previous claims 1-8 is polymerized in a multistage process, in which a cycle reactor is followed by a gas phase reactor, in the presence of a catalyst system as defined in claim 12 or 13, ii) the propylene homopolymer (HPP) obtained in step i is formed into a film together with 0.1-0.4% by weight of a slip agent and 0.0-0.5% by weight of an anti-blocking agent.