Polypropylene-based film

Abstract

The present invention relates to a film comprising a polypropylene composition, preferably an unoriented film, a method for producing such a film, and the use of such a polypropylene composition for producing a film having a balanced performance of improved tensile modulus and impact resistance against protrusions, the polypropylene composition comprising a random copolymer of propylene monomer units and ethylene comonomer units, wherein the random copolymer has an ethylene comonomer unit content of 0.5 to 4.0% by weight based on the total weight of the monomer units in the random copolymer, and the polypropylene composition has a melt flow rate MFR measured according to ISO 1133 at a temperature of 230 °C and a load of 2.16 kg of 0.5 to 20.0 g / 10 min 2 , and when measured on a 50 μm single-layer cast film according to ISO 527-3, the film has a tensile modulus TM-MD in the longitudinal direction in the range of 450 to 850 MPa.

Description

Technical Field

[0001] The present application relates to a film comprising a polypropylene composition having a high tensile modulus in the longitudinal direction, a method for producing the film, and the use of the polypropylene composition for producing a film having a good balance of tensile modulus and protrusion impact resistance, the polypropylene composition comprising a random copolymer of propylene monomer units and ethylene comonomer units. Background Art

[0002] Propylene copolymers are well-known and are often used in the field of film manufacturing. In this technical field, polymers that combine high transparency, high mechanical strength, and high impact strength are required. It is also generally desirable for the polymers used to have high flowability to reduce process costs. Since the improvement of one property comes at the expense of the loss of another property, there is an urgent need to propose a polymer that meets all the requirements.

[0003] WO 2014 / 187686 A1 of Borealis AG discloses a polypropylene composition comprising a propylene random copolymer for non-oriented film applications having good optical and mechanical properties. The blown films in the example section show good mechanical and impact properties, but the optical properties still need to be improved.

[0004] WO 2015 / 169653 A1 of Basell Poliolefine Italia SRL discloses a random propylene-ethylene copolymer for film applications having good optical properties, but the mechanical and impact properties remain open.

[0005] Therefore, there is a need in the art for polypropylene-based films that exhibit a good balance of good mechanical properties, good impact properties, and good optical properties.

[0006] Surprisingly, it has been found that films showing such a good balance of properties can be prepared from a polypropylene composition comprising a random copolymer of propylene monomer units and ethylene comonomer units, the film having a rather low ethylene comonomer unit content of 0.5 to 4.0% by weight based on the total amount of monomer units in the random copolymer. Summary of the Invention

[0007] The present invention relates to a film, preferably a non-oriented film, comprising a polypropylene composition comprising a random copolymer of propylene monomer units and ethylene comonomer units, wherein

[0008] the random copolymer has an ethylene comonomer unit content of 0.5 to 4.0% by weight based on the total weight of the monomer units in the random copolymer,

[0009] The polypropylene composition has a melt flow rate MFR measured according to ISO 1133 at a temperature of 230 °C and a load of 2.16 kg of from 0.5 to 20.0 g / 10 min 2 , and

[0010] When measured on a 50 μm monolayer cast film according to ISO 527-3, the film has a tensile modulus TM-MD in the longitudinal direction in the range of 450 to 850 MPa.

[0011] On the other hand, the present invention relates to a method for producing a film as described above or below, preferably an unoriented film, comprising the following steps

[0012] a) polymerizing a random copolymer of propylene monomer units and ethylene comonomer units in the presence of a single-site catalyst system;

[0013] b) preparing a polypropylene composition; and

[0014] c) preparing a film.

[0015] On the other hand, the present invention relates to the use of a polypropylene composition comprising a random copolymer of propylene monomer units and ethylene comonomer units for producing a film, preferably an unoriented film, having a balanced property of improved tensile modulus and impact resistance to protrusion, wherein the random copolymer has an ethylene comonomer unit content of from 0.5 to 4.0% by weight based on the total weight of the monomer units in the random copolymer, and the polypropylene composition has a melt flow rate MFR measured according to ISO 1133 at a temperature of 230 °C and a load of 2.16 kg of from 0.5 to 20.0 g / 10 min 2 .

[0016] Definition

[0017] An atactic polypropylene copolymer is a copolymer of propylene monomer units and comonomer units (in this case ethylene comonomer units), wherein the comonomer units are randomly distributed on the polypropylene chain. Thus, based on the total amount of the atactic polypropylene copolymer, the atactic polypropylene copolymer comprises at least 70% by weight, more preferably at least 80% by weight, still more preferably at least 85% by weight, and most preferably at least 88% by weight of an amount of a fraction insoluble in xylene, the xylene cold insoluble matter (XCI) fraction. Accordingly, the atactic polypropylene copolymer does not contain an elastomeric polymer phase dispersed therein.

[0018] An isotactic polypropylene homopolymer is a polymer consisting essentially of propylene monomer units. Due to impurities, especially in commercial polymerization processes, the isotactic polypropylene homopolymer may contain up to 0.1 mol% of comonomer units, preferably up to 0.05 mol% of comonomer units and most preferably up to 0.01 mol% of comonomer units.

[0019] Visbreaking is a post-reactor chemical process for modifying semi-crystalline polymers such as propylene polymers. During the visbreaking process, the propylene polymer backbone is degraded via beta scission by a peroxide such as an organic peroxide. The degradation is typically used to increase the melt flow rate and narrow the molecular weight distribution.

[0020] Hereinafter, unless otherwise specified, amounts are given in weight percentages (wt%). Detailed Description

[0021] The present invention relates to a film comprising a polypropylene composition comprising a random copolymer of propylene monomer units and ethylene comonomer units, wherein

[0022] based on the total weight of the monomer units in the random copolymer, the random copolymer has an ethylene comonomer unit content of 0.5 to 4.0 wt%,

[0023] the polypropylene composition has a melt flow rate MFR measured according to ISO 1133 at a temperature of 230 °C and a load of 2.16 kg of 0.5 to 20.0 g / 10 min 2 , and

[0024] when measured on a 50 μm single-layer cast film according to ISO 527-3, the film has a tensile modulus TM-MD in the machine direction of 450 to 850 MPa.

[0025] The film of the present invention is preferably an unoriented film.

[0026] Random copolymer

[0027] The random copolymer is a random copolymer having a majority of moles of propylene monomer units and a minority of moles of ethylene comonomer units.

[0028] In one embodiment, the random copolymer may comprise other comonomer units selected from alpha-olefins having 4 to 12 carbon atoms. However, it is preferred that the random copolymer consists of propylene monomer units and ethylene comonomer units.

[0029] Based on the total weight of the monomer units in the random copolymer, the random copolymer has an ethylene comonomer unit content of 0.5 to 4.0 wt%, preferably 0.7 to 3.5 wt%, more preferably 1.0 to 3.0 wt% and most preferably 1.3 to 2.8 wt%.

[0030] Furthermore, the random copolymer preferably has a melt flow rate MFR measured according to ISO 1133 at a temperature of 230 °C and a load of 2.16 kg of 0.5 to 20.0 g / 10 min, more preferably 1.0 to 15.0 g / 10 min and most preferably 1.5 to 12.5 g / 10 min. 2 .

[0031] Based on the total weight content of the random copolymer, the random copolymer preferably has a xylene cold soluble (XCS) content of 0.05 to 5.00 wt%, more preferably 0.10 to 3.50 wt% and most preferably 0.20 to 2.50 wt%.

[0032] Furthermore, the random copolymer preferably has a melting temperature Tm of 122 °C to 150 °C, more preferably 123 °C to 148 °C, still more preferably 125 °C to 144 °C.

[0033] Preferably, the random copolymer has been produced in the presence of a single-site catalyst system, which preferably comprises a metallocene catalyst. The catalyst particularly affects the microstructure of the polymer. In particular, compared to polypropylene prepared by using a Ziegler-Natta (ZN) catalyst, polypropylene prepared by using a metallocene catalyst provides a different microstructure. The most significant difference is the presence of regio-defects in metallocene-made polypropylene. These regio-defects can be of three different types, namely 2,1-erythro (2,1e), 2,1-threo (2,1t) and 3,1 defects. A detailed description of the structure and mechanism of the formation of regio-defects in polypropylene can be found in Chemical Reviews 2000, 100(4), pages 1316 - 1327. By introducing defects such as comonomers, stereochemical errors or regio-defects into the polymer chain, the physical properties of polypropylene can be modified. In particular, by increasing the amount of chain defects, the crystallinity and melting point of polypropylene can be reduced.

[0034] The term "2,1 regio-defect" used in the present invention defines the sum of 2,1-erythro regio-defects and 2,1-threo regio-defects.

[0035] Thus, it is preferred that the propylene copolymer (R-PP) according to the present invention has at least 0.10 mol%, such as 0.10 to 1.40 mol%, more preferably in the range of 0.20 to 1.20 mol%, still more preferably in the range of 0.30 to 1.10 mol% and most preferably 0.35 to 1.00 mol% of the sum of 2,1- and 3,1-regio-defects determined by 13 C-NMR spectroscopy.

[0036] The random copolymer is preferably produced by a sequential polymerization process in the presence of a single-site catalyst system as defined below.

[0037] The term "sequential polymerization process" means that the random copolymer is produced in at least two reactors, preferably in two reactors connected in series. Thus, the process of the present invention comprises at least a first reactor (R1) and a second reactor (R2). The term "polymerization reactor" shall indicate where the main polymerization occurs. Thus, in the case where the process consists of two polymerization reactors, this definition does not exclude the option that the whole process includes, for example, a pre-polymerization step in a pre-polymerization reactor. The term "consisting of" is a closed expression only in respect of the main polymerization reactors.

[0038] The first reactor (R1) is preferably a slurry reactor (SR) and can be any continuous or simple batch stirred tank reactor or loop reactor operating in bulk or in slurry. Bulk means polymerization in a reaction medium containing at least 60% by weight of monomers. According to the present invention, the slurry reactor (SR) is preferably a (bulk) loop reactor (LR).

[0039] The second reactor (R2) is preferably a gas-phase reactor (GPR). Such a gas-phase reactor (GPR) can be any mechanically mixed or fluidized bed reactor. For example, the gas-phase reactor (GPR) can be a mechanically stirred fluidized bed reactor with an air flow rate of at least 0.2 m / s. Thus, it should be understood that the gas-phase reactor is a fluidized bed type reactor optionally having a mechanical stirrer.

[0040] Thus, in a preferred embodiment, the first reactor (R1) is a slurry reactor (SR), such as a loop reactor (LR), while the second reactor (R2) is a gas-phase reactor (GPR). Thus, for the process of the present invention, the two polymerization reactors, namely the slurry reactor (SR) such as the loop reactor (LR) and the gas-phase reactor (GPR), are connected in series. If desired, a pre-polymerization reactor is placed before the slurry reactor (SR).

[0041] Preferably, a first random copolymer fraction of the random copolymer is produced in the first reactor (R1), while a second random copolymer fraction is produced in the second reactor (R2).

[0042] In one embodiment, the two random copolymer fractions can differ in their ethylene comonomer content or their molecular weight or in both aspects. In this embodiment, the random copolymer is multimodal, preferably a bimodal random copolymer.

[0043] In another embodiment, the atactic copolymer fraction does not differ significantly in terms of its ethylene comonomer content and its molecular weight. In this embodiment, the atactic copolymer is a unimodal atactic copolymer.

[0044] A preferred multistage process is the "loop-gas phase" process, such as the process developed by Borealis A / S of Denmark (referred to as technology), as described, for example, in patent documents 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.

[0045] Another suitable slurry-gas phase process is the process of Basell, as described, for example, in Figure 20 of the paper by Galli and Vecello in Prog. Polym. Sci. 26 (2001) 1287-1336.

[0046] Preferably, in the process of the present invention for producing the atactic copolymer as defined above, the conditions for the first reactor (R1), i.e., the slurry reactor (SR), such as the loop reactor (LR), in step (a) may be the following conditions:

[0047] - The temperature is in the range of 40 °C to 110 °C, preferably between 60 °C and 100 °C, such as 68 °C to 95 °C,

[0048] - The pressure is in the range of 20 bar to 80 bar, preferably between 40 bar and 70 bar,

[0049] - Hydrogen can be added to control the molar mass in a manner known per se.

[0050] The feed ratio of ethylene to propylene (C 2 / C 3 ) is preferably in the range of 10 to 50 mol / kmol. The feed ratio of hydrogen to propylene (H 2 / C 3 ) is adjusted to achieve the desired molecular weight or melt flow rate.

[0051] Subsequently, the reaction mixture from step (a) (preferably containing the first atactic copolymer fraction) is transferred to the second reactor (R2), i.e., the gas phase reactor (GPR), where the conditions are preferably the following conditions:

[0052] - The temperature is in the range of 50 °C to 130 °C, preferably between 60 °C and 100 °C,

[0053] - The pressure is in the range of 5 bar to 50 bar, preferably between 15 bar and 35 bar.

[0054] - Hydrogen can be added to control the molar mass in a manner known per se.

[0055] The feed ratio of ethylene to propylene (C 2 / C 3 ) is preferably in the range of 50 to 120 mol / kmol. The feed ratio of hydrogen to propylene (H 2 / C 3 ) is adjusted to achieve the desired molecular weight or melt flow rate.

[0056] The residence times in the two reaction zones can be different.

[0057] In one embodiment of the process for producing the random copolymer, the residence time in the first reactor (R1), i.e., the slurry reactor (SR), such as a loop reactor (LR), is in the range of 0.2 to 4.0 hours, such as 0.3 to 1.5 hours, while the residence time in the gas phase reactor (GPR) is typically 0.4 to 6.0 hours, such as 0.5 to 4.0 hours.

[0058] If desired, the polymerization can be carried out in the first reactor (R1), i.e., the slurry reactor (SR), such as in a loop reactor (LR), under supercritical conditions in a known manner, and / or in the gas phase reactor (GPR) in a condensation mode.

[0059] The prepolymerization reaction is generally carried out at a temperature of 0 to 50 °C, preferably 10 to 45 °C, and more preferably 15 to 40 °C. The prepolymerization time is generally 0.1 to 1.0 hours, such as 0.2 to 0.8 hours.

[0060] The random copolymer is preferably polymerized in the presence of a single-site catalyst system, more preferably a metallocene catalyst complex and a cocatalyst.

[0061] Preferred complexes of the metallocene catalyst include:

[0062] rac-dimethylsilylbis[2-methyl-4-(3’,5’-dimethylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride,

[0063] rac-trans-dimethylsilyl[2-methyl-4-(4′-tert-butylphenyl)-inden-1-yl][2-methyl-4-(4′-tert-butylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride,

[0064] rac-anti-dimethylsilanediyl[2-methyl-4-(4′-tert-butylphenyl)-inden-1-yl][2-methyl-4-phenyl-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride,

[0065] rac-anti-dimethylsilanediyl[2-methyl-4-(3′,5′-tert-butylphenyl)-1,5,6,7-tetrahydro-sindacen-1-yl][2-methyl-4-(3’,5’-dimethyl-phenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride,

[0066] rac-anti-dimethylsilanediyl[2-methyl-4,8-bis-(4′-tert-butylphenyl)-1,5,6,7-tetrahydro-sindacen-1-yl][2-methyl-4-(3’,5’-dimethylphenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride,

[0067] rac-anti-dimethylsilanediyl[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,

[0068] rac-anti-dimethylsilanediyl[2-methyl-4,8-bis-(3’,5’-dimethylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3’,5’-5di-tert-butylphenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride.

[0069] Particularly preferred is rac-anti-dimethylsilanediyl[2-methyl-4,8-bis-(3’,5’-dimethylphenyl)-1,5,6,7-tetrahydro-sindacen-1-yl][2-methyl-4-(3’,5’-dimethylphenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride.

[0070] As is well known in the art, a cocatalyst is generally required to form the active catalyst species.

[0071] Preferably, a cocatalyst system comprising a boron-containing cocatalyst and an aluminoxane cocatalyst is used in combination with the metallocene catalyst complex defined above.

[0072] The aluminoxane cocatalyst can be one of the formulas (I):

[0073]

[0074] where n is from 6 to 20 and R has the following meanings.

[0075] The aluminoxane is formed upon partial hydrolysis of an organoaluminum compound, such as an organoaluminum compound having the formula AlR 3 、AlR 2 Y and Al 2 R 3 Y 3 compounds, where R can be, for example, a C1-C10-alkyl group, preferably a C1-C5-alkyl group, or a C3-C10-cycloalkyl group, a C7-C12-arylalkyl group or a C7-C12-alkaryl group and / or a phenyl or naphthyl group, and where Y can be hydrogen, a halogen, preferably chlorine or bromine, or a C1-C10-alkoxy group, preferably a methoxy or ethoxy group. The resulting oxyaluminoxane is usually not a pure compound but a mixture of oligomers of the formula (I).

[0076] The preferred aluminoxane is methylaluminoxane (MAO). Since the aluminoxane used as a cocatalyst according to the present invention is not a pure compound due to its preparation method, the molar concentration of the aluminoxane solution is based on their aluminum content hereinafter.

[0077] The boron-containing cocatalyst can also be used in combination with the aluminoxane cocatalyst.

[0078] The catalyst complex desirably contains a cocatalyst, and certain boron-containing cocatalysts are preferred. Thus, particularly preferred borates for use in the present invention contain a trityl ion, i.e., a triphenylcarbenium ion. Thus, the use of Ph 3 CB(PhF 5 ) 4 and its analogues is particularly preferred.

[0079] The catalyst system of the present invention is used in a supported form. The particulate support material used is silica or a mixed oxide, such as silica-alumina, especially silica. A silica support is preferably used. Those skilled in the art know the procedures required for supporting metallocene catalysts.

[0080] In a preferred embodiment, the catalyst system corresponds to ICS3 of PCT / EP2020 / 064194.

[0081] Polypropylene composition

[0082] The polypropylene composition comprises the random copolymer as described above or below.

[0083] Preferably, the random copolymer is present in the polypropylene composition in an amount of at least 90.00% by weight, such as from 90.00% to 100% by weight, more preferably from 92.50% to 99.99% by weight and most preferably from 95.0% to 99.90% by weight.

[0084] In addition to the random copolymer, the polypropylene composition may further comprise one or more other polymers, such as propylene-based polymers, such as propylene homopolymers or propylene random copolymers. If present, the amount of the one or more other polymers is preferably less than 10.0% by weight, preferably not exceeding 5.0% by weight.

[0085] However, it is preferred that the random copolymer is the only polymer in the polypropylene composition.

[0086] The polypropylene composition generally comprises additives suitable for film applications. Suitable additives are, for example, antioxidants, slip agents and anti-caking agents. Preferably, based on the total weight content of the polypropylene composition, the additive content is from 0.01 to 5.00% by weight, more preferably from 0.10 to 1.00% by weight.

[0087] In one specific embodiment, the polypropylene composition may comprise an α-nucleating agent.

[0088] The α-nucleating agent is preferably selected from the group consisting of

[0089] (i) salts of monocarboxylic and polycarboxylic acids, such as sodium benzoate or aluminum tert-butylbenzoate, and

[0090] (ii) dibenzylidene sorbitol (e.g., 1,3:2,4-dibenzylidene sorbitol) and C 1 -C 8 -alkyl-substituted dibenzylidene sorbitol derivatives, such as methyl dibenzylidene sorbitol, ethyl dibenzylidene sorbitol or dimethyl dibenzylidene sorbitol (e.g., 1,3:2,4-bis(methylbenzylidene) sorbitol), or substituted nonitol derivatives, such as 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol, and

[0091] (iii) salts of diesters of phosphoric acid, such as sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl) phosphate or aluminum bis[2,2'-methylene-bis(4,6-di-tert-butylphenyl) phosphate] hydroxide, and

[0092] (iv) vinyl cycloalkane polymers and vinyl alkane polymers (discussed in more detail below), and

[0093] (v) their mixtures.

[0094] Preferably, the polypropylene composition comprises from 0.00001 to 5.00% by weight, more preferably from 0.0001 to 2.50% by weight of an α-nucleating agent.

[0095] The amount of pure α-nucleating agent in the polypropylene composition (excluding the optional carrier polymer of the masterbatch) is preferably in the range of 0.01 to 2000 ppm, more preferably 0.1 to 1000 ppm.

[0096] The α-nucleating agent is preferably selected from the group consisting of dibenzylidene sorbitol (such as 1,3:2,4-dibenzylidene sorbitol), dibenzylidene sorbitol derivatives, preferably dimethyldibenzylidene sorbitol (such as 1,3:2,4-bis(methylbenzylidene) sorbitol), or substituted nonitol derivatives such as 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol, vinyl cycloalkane polymers, vinyl alkane polymers, and mixtures thereof.

[0097] Particularly preferred are vinyl cycloalkane polymers such as, for example, vinyl cyclohexane (VCH) polymers. Such polymers can be added, for example, using Borealis Nucleation Technology (BNT).

[0098] The additives and the α-nucleating agent can be added to the polypropylene composition as separate raw materials or as a mixture with a carrier polymer, i.e., in the form of a so-called masterbatch. Thereby, the amount of the carrier polymer of the masterbatch is calculated as the amount of the additive or the α-nucleating agent.

[0099] The additives and the α-nucleating agent are generally commercially available and are described, for example, in Hans Zweifel's "Plastic Additives Handbook", 6th Edition 2009 (pages 967 - 983).

[0100] The polypropylene composition has a melt flow rate determined according to ISO 1133 at a temperature of 230 °C and a load of 2.16 kg of from 0.5 to 20.0 g / 10 min, more preferably from 1.0 to 15.0 g / 10 min and most preferably from 1.5 to 12.5 g / 10 min.

[0101] The melt flow rate of the polypropylene composition mainly depends on the melt flow rate of the random copolymer. In some embodiments, the random copolymer has a relatively low melt flow rate of less than 5.0 g / 10 min or even less than 3.5 g / 10 min. In these embodiments, the melt flow rate of the polypropylene composition can be increased by visbreaking in the presence of a peroxide such as an organic peroxide, preferably during the compounding step of adding optional additives and an α-nucleating agent to the polypropylene composition.

[0102] The peroxide is then usually selected according to the compounding conditions. Suitable peroxides are commercially available and the optimum visbreaking conditions such as temperature, pressure, operating time and dosage are disclosed in their technical data sheets.

[0103] After visbreaking, the polypropylene composition usually has a melt flow rate determined according to ISO 1133 at a temperature of 230 °C and a load of 2.16 kg of 5.5 to 20.0 g / 10 min, preferably 6.0 to 17.5 g / 10 min, more preferably 6.5 to 15.0 g / 10 min and most preferably 7.0 to 13.0 g / 10 min.

[0104] The polypropylene composition preferably has a melting temperature Tm of 122 °C to 150 °C, more preferably 123 °C to 148 °C, still more preferably 125 °C to 144 °C.

[0105] In addition, the polypropylene composition preferably has a crystallization temperature Tc of 90 °C to 115 °C, more preferably 95 °C to 113 °C, still more preferably 98 °C to 110 °C.

[0106] Film

[0107] The present invention relates to a film, preferably an unoriented film, which comprises the polypropylene composition as described above or below.

[0108] Hereinafter, the term "film" preferably relates to an unoriented film.

[0109] The film preferably comprises at least 70% by weight, preferably at least 80% by weight, more preferably at least 90% by weight, still more preferably at least 95% by weight, yet more preferably at least 99% by weight of the polypropylene composition of the present invention.

[0110] Preferably, the film consists of the polypropylene composition of the present invention.

[0111] Preferably, the film is a cast film, a wound film or a blown film, such as an air-cooled blown film. More preferably, the film is a cast film or a wound film. Even more preferably, the film is a cast film.

[0112] It is possible to distinguish between non-oriented films and oriented films (see, for example, the Polypropylene Handbook, Nello Pasquini, 2nd Edition, Hanser). Oriented films are usually biaxially oriented films, while non-oriented films are cast or blown films, such as air-cooled blown films, and wound films are considered a specific category of thicker cast films. Accordingly, non-oriented films are not strongly stretched in the longitudinal and transverse directions like oriented films. Thus, the film according to the invention is preferably not a biaxially oriented film. Preferably, the film according to the invention is a cast film or a blown film.

[0113] Preferably, the film has a thickness of 5 to 2000 μm, preferably 10 to 1000 μm, more preferably 15 to 700 μm, such as 20 to 500 μm.

[0114] Surprisingly, the film according to the invention has a good balance with respect to mechanical properties, impact properties, optical properties and other film properties. Thus, it has been found that by adding an α-nucleating agent, some properties of the film, such as the coefficient of friction (CoF) and the hot tack, can be further improved when needed without sacrificing other properties.

[0115] When measured on a 50 μm single-layer cast film according to ISO 527-3, the film has a tensile modulus TM-MD in the longitudinal direction in the range of 450 to 850 MPa, preferably in the range of 470 to 800 MPa and most preferably in the range of 500 to 750 MPa.

[0116] When measured on a 50 μm single-layer cast film according to ISO 527-3, the film further preferably has a tensile modulus TM-TD in the transverse direction in the range of 450 to 850 MPa, preferably in the range of 470 to 800 MPa and most preferably in the range of 500 to 750 MPa.

[0117] Furthermore, when measured on a 50 μm single-layer cast film according to ASTM D5748, the film preferably has an impact resistance to protrusion of 30.0 to 125.0 N, more preferably 32.5 to 110.0 N and most preferably 35.0 to 100.0 N.

[0118] When measured on a 50 μm single-layer cast film according to ASTM D 1003, the film preferably has a haze of 0 to 2.5%, more preferably 0 to 2.4% and most preferably 0 to 2.3%.

[0119] In addition, when measured on a 50 μm single-layer cast film, the film has a seal initiation temperature SIT of 105 to 120 °C, more preferably 107 to 118 °C and most preferably 109 to 116 °C.

[0120] When measured on a 50 μm single-layer cast film according to DIN 53 375, the film preferably has a coefficient of friction CoF@7 days of 0.01 to 0.30, more preferably 0.02 to 0.27, and most preferably 0.03 to 0.25.

[0121] Furthermore, when measured on a 50 μm single-layer cast film according to ASTM F 1921–98(2004), Method B, the film preferably has a hot tack force HTF of 1.5 to 5.0 N, more preferably 2.0 to 4.0 N, and most preferably 2.5 to 3.5 N.

[0122] For films comprising an α-nucleated polypropylene composition, the coefficient of friction and the hot tack force are preferably at the upper end of the ranges described above.

[0123] Method

[0124] On the other hand, the present invention relates to a method for producing a film as described above or below, comprising the following steps

[0125] a) polymerizing a random copolymer of propylene monomer units and ethylene comonomer units in the presence of a single-site catalyst system;

[0126] b) preparing a polypropylene composition; and

[0127] c) preparing a film.

[0128] The film is preferably an unoriented film prepared by cast film or blown film extrusion.

[0129] The film (preferably an unoriented film), the polypropylene composition, and the random copolymer are preferably defined as in any of the embodiments described above or below.

[0130] The random copolymer is preferably polymerized as described above or below.

[0131] The polypropylene composition is preferably prepared in a compounding step, optionally by adding additives, α-nucleating agents, and additional polymers as described above or below during the compounding step, preferably optionally adding additives and α-nucleating agents.

[0132] In one embodiment, only additives are added.

[0133] In another embodiment, additives and α-nucleating agents are added.

[0134] In some embodiments, as described above or below, the polypropylene composition is subjected to a devolatilization step, preferably during the compounding step of the present invention after polymerization.

[0135] Compounding can be carried out in any suitable extruder using conventional compounding conditions. Usually, a co-rotating twin-screw extruder is used, including a special mixing section operating in the temperature range of 180 to 280 °C.

[0136] The film is preferably prepared by introducing the polypropylene composition into a suitable film production line.

[0137] In the case of producing a film by the cast film technique, the polypropylene composition is extruded through a slit die onto a cooling roll to cool the polymer into a solid film. Typically, the polypropylene composition is first compressed and liquefied in an extruder, and any additives can have been added to the polymer or introduced via a masterbatch at this stage. Then, the melt is forced through a flat film die (slit die), and the extruded film is taken up on one or more take-up rolls, during which the film cools and solidifies. It has proven particularly advantageous to maintain the extruded film at a temperature of 10 to 50 °C, preferably 15 to 40 °C, on one or more take-up rolls through which it cools and solidifies.

[0138] In the blown film process, the melt of the polypropylene composition is extruded through an annular die and blown into a tubular film by forming a bubble, which bursts between rolls after solidification. The blown extrusion can preferably be carried out in the temperature range of 160 to 240 °C and cooled by water or preferably by blowing air (usually air) at a temperature of 10 to 50 °C to provide a frost line height of 0.5 to 8 times the die diameter. The blow-up ratio should generally be in the range of 1.5 to 4, such as 2 to 4, preferably 2.5 to 3.5.

[0139] The resulting film preferably exhibits all the properties described above or below.

[0140] Use

[0141] In another aspect, the present invention relates to the use of a polypropylene composition comprising an atactic copolymer of propylene monomer units and ethylene comonomer units for producing a film (preferably an unoriented film) having a balanced property of improved tensile modulus and impact resistance to protrusion, wherein the atactic copolymer has an ethylene comonomer unit content of 0.5 to 4.0% by weight based on the total weight of the monomer units in the atactic copolymer, and the polypropylene composition has a melt flow rate MFR measured according to ISO 1133 at a temperature of 230 °C and a load of 2.16 kg of 0.5 to 20.0 g / 10 min 2 。

[0142] Preferably, the film (preferably an unoriented film), the polypropylene composition, and the atactic copolymer are defined as in any of the above or below embodiments.

[0143] The obtained film preferably exhibits all the properties described above or below.

[0144] Examples

[0145] 1. Measurement methods

[0146] MFR 2 (230 °C) is measured according to ISO 1133 (230 °C, 2.16 kg load). The MFR of the polypropylene composition 2 is determined on the granules of the material, while the MFR of the meltblown web 2 is determined on slices of the compression-molded plate prepared from the web in a hot press at a temperature not exceeding 200 °C, the slices having dimensions comparable to the granule size.

[0147] Xylene solubles content at room temperature (xylene cold solubles XCS, wt%): The amount of polymer soluble in xylene is determined at 25 °C according to ISO 16152; 5th edition; 2005-07-01.

[0148] Microstructure quantification by NMR spectroscopy

[0149] Quantitative nuclear magnetic resonance (NMR) spectroscopy is used to quantify the comonomer and regiodefect content of the polymer.

[0150] Using for 1 H and 13 C, a Bruker Avance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz respectively records quantitative 13 C{ 1 H} NMR spectra in the solution state. All spectra are recorded at 125 °C using a 13 C-optimized 10 mm extended temperature probe, and nitrogen is used for all pneumatic devices. Approximately 200 mg of the material together with chromium(III) acetylacetonate (Cr(acac) 3 ) is dissolved in approximately 3 ml of 1,2-tetrachloroethane-d 2 (TCE-d 2 ) to obtain a 65 mM solution of the relaxant in the solvent {singh09}. To ensure the homogeneity of the solution, after the preparation of the initial sample in the heating block, the NMR tube is further heated in a rotary oven for at least 1 hour. After insertion into the magnet, the tube is rotated at 10 Hz. This setting is chosen mainly for high resolution and because accurate quantification of the ethylene content is required quantitatively. Standard single-pulse excitation without NOE is used, with an optimized tip angle, 1 s recycle delay, and a two-stage WALTZ16 decoupling scheme {zhou07, busico07}. A total of 6144 (6k) transient signals are acquired for each spectrum.

[0151] The quantitative 13 C{ 1 H} NMR spectra are processed, integrated, and relevant quantitative properties are determined from the integrals. Using the chemical shift of the solvent, all chemical shifts are indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm. Even if this structural unit is absent, this method allows for comparable referencing.

[0152] Characteristic signals corresponding to ethylene incorporation are observed {wang00, cheng84, randall89}.

[0153] Using the method of Wang et al. {wang00}, the comonomer fraction is quantified by integrating multiple signals over the entire spectral region in the 13 C{ 1 H} spectrum. This method is chosen for its robustness and the ability to account for the presence of regio-defects when needed. Minor adjustments are made to the integration regions to improve applicability over the entire range of comonomer contents encountered.

[0154] For systems where only isolated ethylene is observed in the PPEPP sequence, the method of Wang et al. is modified to reduce the effect of non-zero integrals at sites known to be absent. This method reduces the overestimation of ethylene content in such systems and is achieved by reducing the number of sites used to determine the absolute ethylene content to the following. By using this set of sites, the corresponding integration equations become:

[0155] p S = I A +(0.5 * I B )

[0156] p T = I D + I F + I D

[0157] p = (p S + p T ) / 2

[0158] e = 0.5 * (I H +(0.5 * I B ))

[0159] fE = e / (e + p)

[0160] The same symbols used in the article by Wang et al. {wang00} are used.

[0161] The mole percent of comonomer incorporation is calculated from the mole fraction:

[0162] E [mol%] = 100 * fE

[0163] Calculate the weight percentage of comonomer incorporation from the mole fraction:

[0164] E [wt%] = 100 * (fE * 28.06) / ((fE * 28.06) + ((1 - fE) * 42.08))

[0165] Characteristic signals {resconi00, wang00} corresponding to regio defects were observed. The presence of two methyl sites at 17.7 and 17.2 ppm indicates the presence of isolated 2,1-erythro regio defects, which are confirmed by other characteristic sites. The presence of 2,1 regio defects adjacent to ethylene units is indicated by two non-equivalent Sαβ signals at 34.9 ppm and 34.7 ppm and a Tγγ signal at 34.1 ppm, respectively.

[0166] Using the average integrals of two characteristic methyl sites at 17.7 (I e8 ) and 17.4 (I e6 ) ppm to quantify the amount (P 21e孤立 ) of isolated 2,1-erythro regio defects:

[0167] P 21e孤立 = (I e6 + I e8 ) / 2

[0168] Using the methine site at 34.1 ppm (I Tγγ ) to quantify the amount (P E21 ) of 2,1 regio defects adjacent to ethylene:

[0169] P E21 = I Tγγ

[0170] Quantify the total amount of propylene (P CH3 ) based on the methyl region between 23.0 and 19.9 ppm (I 总 ), and correct for sites in this region that are not related to propylene insertion. The methyl P γγ generated by 2,1 regio defects adjacent to ethylene is already present in I CH3 :

[0171] P 总 = I CH3 + 2 * P 21e孤立

[0172] The isolated 2,1-erythro regio defects (P 21e孤立) Multiply by 2 to account for the two (2) propylene units in the 2,1-erythro regiodefect.

[0173] Quantify the mole percentage of isolated 2,1-erythro regiodefects relative to all propylene:

[0174] [21e] mole % = 100 * P 21e孤立 / P 总

[0175] Quantify the mole percentage of 2,1 regiodefects adjacent to ethylene relative to all propylene:

[0176] [E21] mole % = 100 * P E21 / P 总

[0177] The total amount of 2,1 defects is quantified as follows:

[0178]

[21] mole % = [21e] + [E21]

[0179] No characteristic signals corresponding to other types of regiodefects (2,1-threo, 3,1 insertion) were observed {resconi00}.

[0180] zhou07 Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225

[0181] busico07 Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128

[0182] resconi00 Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253

[0183] wang00 Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157

[0184] cheng84 Cheng, H.N., Macromolecules 17 (1984), 1950

[0185] singh09 Singh,G.,Kothari,A.,Gupta,V.,Polymer Testing 28 5(2009),475

[0186] randall89 Randall,J.Macromol.Sci.,Rev.Macromol.Chem.Phys.1989,C29,201。

[0187] The tensile modulus (in the longitudinal and transverse directions) was determined at 23 °C on a single-layer cast film with a thickness of 50 μm according to ISO 527-3. The single-layer cast film was produced as described below. The test was carried out at a crosshead speed of 1 mm / min.

[0188] The puncture impact resistance was determined on a single-layer cast film with a thickness of 50 μm according to ASTM D5748. The single-layer cast film was produced as described below.

[0189] The transparency, haze and clarity were determined on a single-layer cast film with a thickness of 50 μm according to ASTM D1003-00. The single-layer cast film was produced as described below.

[0190] Sealing initiation temperature (SIT); (sealing termination temperature (SET), sealing range):

[0191] This method determines the sealing temperature range (sealing range) of polypropylene films, especially blown films or cast films. The sealing temperature range is the temperature range within which the film can be sealed according to the given conditions below. The lower limit (heat seal initiation temperature (SIT)) is the sealing temperature at which a sealing strength of ≥3 N is obtained. The upper limit (sealing termination temperature (SET)) is reached when the film adheres to the sealing device. The sealing range was determined on a single-layer cast film with a thickness of 50 μm produced as described below on a J&B 3000 type universal sealing machine according to the following further parameters:

[0192] Specimen width: 25.4 mm Sealing pressure: <![CDATA[0.1N / mm 2 > Sealing time: 0.1 second Cooling time: 99 seconds Peeling speed: 10 mm / second Initial temperature: 80℃ Final temperature: 150℃ Increment: 10℃

[0193] At each sealbar temperature, specimens A to A were sealed and the sealing strength (force) was measured at each step. The temperature at which the sealing strength reached 3 N was measured.

[0194] Hot tack:

[0195] The hot tack was determined on a single-layer cast film with a thickness of 50 μm on a J&B hot tack tester according to ASTM F1921-12 – Method B. The single-layer cast film was produced as described below.

[0196] All film test specimens were prepared in a standard atmosphere for conditioning and testing at 23 °C (±2 °C) and 50% (±10%) relative humidity.

[0197] Before starting the test, the minimum conditioning time of the test specimens in the standard atmosphere was at least 16 h. The minimum storage time between extrusion of the film samples and starting the test was at least 88 h.

[0198] Thermal tack measurement determines the strength of the heat seal formed in the film immediately after sealing is completed and before it cools to ambient temperature. Thermal tack measurements were carried out under the following conditions.

[0199] Width of film specimen: 25.4 mm.

[0200] Length of seal strip: 50 mm.

[0201] Width of seal strip: 5 mm.

[0202] Shape of seal strip: flat.

[0203] Sealing pressure: 0.3 N / mm 2 。

[0204] Sealing time: 0.5 s.

[0205] Cooling time: 99 s.

[0206] Peeling speed: 200 mm / s.

[0207] Initial temperature: 90 °C; final temperature: 140 °C; increment: 10 °C.

[0208] Thermal tack force was measured as a function of temperature in the above temperature range and with the above temperature increment. At each temperature, the number of test specimens was at least 3 specimens. The output of the method was a thermal tack curve; a curve of force vs. temperature.

[0209] The thermal tack force (HTF) was evaluated from the curve as the maximum force (maximum peak) under the failure mode "peel".

[0210] The coefficient of friction (CoF) (including static CoF and dynamic CoF), as a measure of the frictional properties of the film, was determined using the methods according to ISO 8295:1995 and ASTM D1894:2008 on a single-layer cast film with a thickness of 50 μm, which was produced as described below.

[0211] 2. Catalyst

[0212] A single-site catalyst system for the polymerization of random copolymers RC1, RC2, RC3, and RC4 (according to the present invention) was prepared as follows:

[0213] Catalyst synthesis

[0214] The catalyst used is trans-dimethylsilylene[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-butylindene-1-yl]zirconium dichloride as disclosed in ICS3 in PCT / EP2020 / 064194.

[0215] Preparation of MAO-silica support

[0216] Flush a steel reactor equipped with a mechanical stirrer and a filter net with nitrogen and set the reactor temperature to 20 °C. Then add silica (5.0 kg) of grade DM-L-303 from AGC Si-Tech pre-calcined at 600 °C from the feed drum, and then carefully pressurize and depressurize with nitrogen using a manual valve. Then add toluene (22 kg). Stir the mixture for 15 min. Then add a 30 wt% solution of MAO in toluene (9.0 kg) from Lanxess through the feed line at the top of the reactor within 70 min. Then heat the reaction mixture to 90 °C and stir for another two hours at 90 °C. Allow the slurry to settle and filter off the mother liquor. Wash the catalyst twice with toluene (22 kg) at 90 °C, then carry out sedimentation and filtration. Cool the reactor to 60 °C and wash the solid with heptane (22.2 kg). Finally, the MAO-treated SiO 2 Dry under a nitrogen stream at 60 °C for 2 hours, then stir and dry under vacuum (-0.5 bar, gauge pressure) for 5 hours. The MAO-treated support is collected as a free-flowing white powder, which is found to contain 12.2% aluminum (by weight).

[0217] Catalyst preparation

[0218] At 20 °C, add 30 wt% MAO in toluene (0.7 kg) to a steel reactor under nitrogen protection through a burette. Then add toluene (5.4 kg) with stirring. Add the above catalyst (93 g) from a metal cylinder, and then rinse with 1 kg of toluene. Stir the mixture at 20 °C for 60 minutes. Then add triphenylmethyltetrakis(pentafluorophenyl)borate (91 g) from a metal cylinder, and then rinse with 1 kg of toluene. Stir the mixture at room temperature for 1 h. Add the resulting solution to the stirred cake of the MAO-silica support prepared as above over a period of more than 1 hour. Let the cake stand for 12 hours, then at 60 °C in N 2It was dried by flowing down for 2 hours and further dried under vacuum (-0.5 bar, gauge pressure) with stirring for 5 hours. The dried catalyst was sampled as a pink free-flowing powder, which contained 13.9% Al and 0.11% Zr.

[0219] For the polymerization of the random copolymer RC5 (comparative), a phthalate-free Ziegler-Natta catalyst prepared as described in the example section of WO 2020 / 064673 A1 was used as the "reference catalyst".

[0220] 3. Polymerization of random copolymers RC1 - RC4 and RC5

[0221] The polymerization of random copolymers RC1, RC2, RC3, and RC4 (all according to the present invention) and a random copolymer (comparative) of propylene and ethylene comonomer units was carried out in a Borstar pilot plant, which had a 2-reactor setup (loop-gas phase reactor (GPR 1)) before the prepolymerization reactor.

[0222] RC1 to RC4 were polymerized in the presence of the single-site catalyst (SSC) system as described above, while RC5 was polymerized in the presence of the phthalate-free Ziegler-Natta (ZN) catalyst as described above.

[0223] The polymerization conditions and properties for RC1, RC2, RC3, and RC4 are given in Table 1.

[0224] Table 1: Polymerization conditions of random copolymers RC1 to RC5

[0225] RC1 RC2 RC3 RC4 RC5 Catalyst SSC SSC SSC SSC ZN <![CDATA Prepolymerization: > Temperature [°C] 20 20 20 20 20 <![CDATA[TEAL[g / t C 3 > --- --- --- --- 170 <![CDATA[Donor [g / t C 3 > --- --- --- --- 40 Donor type --- --- --- --- D Residence time [h] 0.4 0.4 0.4 0.4 0.2 Loop reactor: Temperature [°C] 70 70 70 70 70 Pressure [bar] 5258 5258 5258 5258 5258 <![CDATA[Feed ratio H 2 / C 3 [mol / kmol]]]> 0.10 0.16 0.09 0.30 0.40 <![CDATA[Feed ratio C 2 / C 3 [mol / kmol]]]> 30.1 15.9 17.3 30.3 8.5 Split ratio (split) [wt%] 57 54 46 53 36 Residence time [h] 0.5 0.5 0.4 0.5 0.4 <![CDATA[C 2 Content [wt%]]]> 2.1 0.6 1.2 2.2 3.6 <![CDATA[MFR 2 [g / 10min]]]> 1.3 1.3 2.2 11.5 2.0 <![CDATA GPR1: > Temperature [°C] 80 80 80 80 80 Pressure [bar] 2500 2500 2500 2500 2500 <![CDATA[Feed H 2 / C 3 [mol / kmol]]]> 1.6 1.0 1.6 2.9 7.7 <![CDATA[Feed C 2 / C 3 [mol / kmol]]]> 88.1 65.5 69.0 86.6 33.8 Split ratio [wt%] 43 46 54 47 64 Residence time [h] 2.0 2.0 2.0 2.0 1.8 <![CDATA[C 2 Content [wt%]]]> 2.5 1.4 1.7 2.5 4.3 Resulting base resin <![CDATA[C 2 Content [wt%]]]> 2.3 1.5 1.7 2.5 4.3 2,1 and 3,1e regio defects [mol%] 0.62 0.7 0.48 0.75 0 Tm [°C] 134 143 142 134 140 XCS [wt%] 0.6 0.6 0.3 1.5 7.9 <![CDATA[MFR 2 [g / 10min]]]> 1.9 1.8 2.1 11.0 1.8

[0226] 4. Preparation of compositions and films of Examples IE1 - IE4 and CE1 - CE2

[0227] After polymerization, the melt flow rate of random copolymers RC1 - RC3 and RC5 was modified by visbreaking during the compounding step in a twin-screw extruder. During the compounding step, the additives described below were added.

[0228] The random copolymer RC1 was visbroken to a final melt flow rate MFR of 8.0 g / 10 min 2 to obtain the polypropylene composition of Example IE1 of the present invention.

[0229] The random copolymer RC2 was visbroken to a final melt flow rate MFR of 12.0 g / 10 min 2 to obtain the polypropylene composition of Example IE2 of the present invention.

[0230] The random copolymer RC2 was also visbroken to a final melt flow rate MFR of 7.5 g / 10 min 2 to obtain the polypropylene composition of Example IE3 of the present invention.

[0231] The random copolymer RC3 was visbroken to a final melt flow rate MFR of 12.0 g / 10 min 2 to obtain the polypropylene composition of Example IE4 of the present invention.

[0232] The random copolymer RC5 was visbroken to a final melt flow rate MFR of 8.0 g / 10 min 2 to obtain the polypropylene composition of Comparative Example CE1.

[0233] The random copolymer RC5 was also visbroken alone to a final melt flow rate MFR of 11.0 g / 10 min 2 to obtain the polypropylene composition of Comparative Example CE2.

[0234] For example, IE1, IE2, IE3 and CE1 were added with 1000 ppm of Irganox B 215 (a 1:2 mixture of pentaerythritol tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate CAS-no. 6683-19-8 and tris(2,4-di-tert-butylphenyl)phosphite CAS-no. 31570-04-4, commercially available from BASF SE, Germany) and 150 ppm of magnesium oxide (CAS-no. 1309-48-4) as an acid scavenger during the compounding step.

[0235] The polypropylene composition was extruded into a single-layer cast film with a thickness of 50 μm using a cast film coextrusion production line.

[0236] The properties of the compositions and films are listed in Table 2 below.

[0237] Table 2: Properties of the compositions and cast films of IE1-IE3 and CE1

[0238] IE1 IE2 IE3 CE1 Random copolymer RC1 RC2 RC2 RC5 <![CDATA Composition: > <![CDATA[MFR 2 [g / 10min]]]> 8.3 12.0 7.5 8.0 Tc [°C] 100 107 106 98 Tm [°C] 135 142 143 140 50 μm single-layer cast film: Tensile modulus MD [MPa] 529 649 646 449 Tensile modulus TD [MPa] 530 649 651 454 Impact resistance to protrusion [N] 82.66 83.91 92.73 75.43 Haze [%] 0.42 0.05 0.05 0.26

[0239] When compared with Comparative Example CE1, Examples IE1 to IE3 of the present invention all showed improved mechanical properties (in terms of tensile modulus) and improved impact properties (in terms of dart impact resistance) under comparable optical properties (in terms of haze).

[0240] For example, IE4 and CE2, 2000 ppm of Crodamide OR (oleic acid amide, CAS number 301-02-0, commercially available from Croda Polymer Additives Ltd., UK), 2000 ppm of Gasil AB 725 (silica, CAS number 7631-86-9, commercially available from PQ Corporation, UK), 1000 ppm of calcium stearate (CAS number 1592-23-0) and 2000 ppm of Irganox B215 (a 1:2 mixture of pentaerythrityl tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate, CAS number 6683-19-8 and tris(2,4-di-tert-butylphenyl) phosphite, CAS number 31570-04-4), commercially available from BASF SE, Germany) are added during the compounding step.

[0241] The polypropylene composition is extruded into a single-layer cast film with a thickness of 50 μm using a Collin pilot-scale cast film production line.

[0242] The properties of the composition and the film are listed in Table 3 below.

[0243] Table 3: Properties of the compositions and cast films of IE4 and CE2

[0244] IE4 CE2 Random copolymer RC3 RC5 <![CDATA Composition: > <![CDATA[MFR 2 [g / 10min]]]> 11.0 11.0 Tc [°C] 104 98 Tm [°C] 140 141 <![CDATA 50 μm single-layer cast film: > Tensile modulus MD [MPa] 587 425 Tensile modulus TD [MPa] 575 440 Impact resistance to protrusion [N] 60 46 Haze [%] 2.0 2.0 SIT [°C] 115 117 CoF after 7 days 0.20 0.20

[0245] When compared with Comparative Example CE1, Example IE4 of the present invention also shows improved mechanical properties (in terms of tensile modulus) and improved impact properties (in terms of dart impact resistance) at comparable optical properties (in terms of haze). In addition, IE1 shows improved sealing properties at a lower SIT.

[0246] 5. Preparation of the compositions and films of Examples IE5 and IE6

[0247] After polymerization, the random copolymer RC4 is compounded in a twin-screw extruder. Due to its high MFR 2 , visbreaking is unnecessary. During the compounding step, the additives described below are added.

[0248] For example, in IE5, 600 ppm of Irganox 1010 (pentaerythritol tetrakis(3-(3’,5’-di-tert-butyl-4-hydroxyphenyl)propionate, CAS No. 6683-19-8) and 600 ppm of Irgafos 168 (tris(2,4-di-tert-butylphenyl) phosphite, CAS No. 31570-04-4), both commercially available from BASF SE, Germany), 2000 ppm of Crodamide OR (oleic acid amide, CAS No. 301-02-0, commercially available from Croda Polymer Additives), 2000 ppm of Gasil AB 725 (silica, CAS No. 7631-86-9, commercially available from PQ Corporation, UK) and 1000 ppm of calcium stearate are added during the compounding step.

[0249] For example, in IE6, an additional 2.0 wt% of HF995MO (a highly crystalline propylene homopolymer produced by Borealis Nucleation Technology (BNT)) (commercially available from Borealis AG) is added as an α-nucleating masterbatch, containing poly(vinyl cyclohexane), and 0.7 wt% of talc to produce an α-nucleated polypropylene composition.

[0250] The polypropylene composition is extruded into a single-layer cast film with a thickness of 50 μm using a cast film coextrusion production line.

[0251] The properties of the composition and the film are listed in Table 4 below.

[0252] Table 4: Properties of the compositions and cast films of IE4 and CE2

[0253] IE5 IE6 Random copolymer RC4 RC4 Nucleating agent None HF995MO <![CDATA Composition: > <![CDATA[MFR 2 [g / 10min]]]> 10.7 10.7 Tc [°C] 99 108 Tm [°C] 134 128 Hm [J / g] 83 90 XCS [wt%] 1.53 1.53 <![CDATA 50 μm single-layer cast film: > Tensile modulus MD [MPa] 548 546 Tensile modulus TD [MPa] 567 557 Impact resistance to protrusion [N] 38.9 38.7 Haze [%] 2.11 1.78 SIT [°C] 112 112 Thermal adhesion force [N] 2.82 3.19 CoF after 1 day 0.14 0.14 CoF after 3 days 0.10 0.09 CoF after 7 days 0.09 0.07 CoF after 14 days 0.08 0.07

[0254] When comparing the α-nucleated polypropylene composition IE6 and the single-layer cast film made from said composition with the non-nucleated polypropylene composition IE5 and the single-layer cast film made from said composition, it can be seen that α-nucleation has no effect on the mechanical properties, impact properties and SIT of the film, but improves the optical properties, hot tack and faster migration of slip. In addition, the hot tack HTF is improved.

Claims

1. A film comprising a polypropylene composition, said polypropylene composition comprising a random copolymer of propylene monomer units and ethylene comonomer units, wherein based on the total weight of the monomer units in the random copolymer, the random copolymer has an ethylene comonomer unit content of 0.5 to 4.0 wt%, The polypropylene composition has a melt flow rate MFR measured according to ISO 1133 at a temperature of 230 °C and a load of 2.16 kg of from 0.5 to 20.0 g / 10 min 2 , the polypropylene composition has a xylene cold soluble (XCS) content of 0.05 to 5.00 wt%, The random copolymer has a total of 2,1- and 3,1-regio defects of 0.10 to 1.40 mol% determined by 13 13C-NMR spectroscopy, and when measured on a 50 μm single-layer cast film according to ISO 527-3, the film has a tensile modulus TM-MD in the longitudinal direction in the range of 450 to 850 MPa, wherein, the random copolymer is produced in the presence of a single-site catalyst system.

2. The film according to claim 1, wherein the film is an unoriented film and / or the random copolymer has a total of 2,1- and 3,1-regio defects in the range of 0.20 to 1.20 mol% as determined by 13 13C-NMR spectroscopy.

3. The film according to claim 1, wherein the polypropylene composition has a melting temperature Tm of 122 to 150 °C, and / or has a crystallization temperature Tc of 90 to less than 115 °C.

4. The film according to claim 1, wherein the polypropylene composition comprises an α-nucleating agent.

5. The film according to claim 1, wherein the polypropylene composition comprises a polymeric α-nucleating agent.

6. The film according to claim 1, when measured on a 50 μm single-layer cast film according to ISO 527-3, the film has a tensile modulus TM-TD in the transverse direction of 450 to 850 MPa.

7. The film according to claim 1, when measured on a 50 μm single-layer cast film according to ASTM D 1003, the film has a haze of 0 to 2.5%.

8. The film according to claim 1, when measured on a 50 μm single-layer cast film, the film has a seal initiation temperature SIT of 105 to 120 °C.

9. The film according to claim 1, when measured on a 50 μm single-layer cast film according to DIN 53 375, the film has a coefficient of friction CoF@7 days of 0.01 to 0.

30.

10. The film according to claim 1, when measured on a 50 μm single-layer cast film according to ASTM F 1921–98(2004), method B, the film has a hot tack force HTF of 1.5 to 5.0 N.

11. The film according to claim 1, when measured on a 50 μm single-layer cast film according to ASTM D5748, the film has a puncture resistance of 30.0 to 125.0 N.

12. The film according to any one of claims 1 to 11, which is a cast film, a wound film or a blown film.

13. The film according to any one of claims 1 to 11, wherein the single-site catalyst system comprises (i) a metallocene catalyst selected from rac-dimethylsilylenebis[2-methyl-4-(3’,5’-dimethylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4-(4′-tert-butylphenyl)-inden-1-yl][2-methyl-4-(4′-tert-butylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4-(4′-tert-butylphenyl)-inden-1-yl][2-methyl-4-phenyl-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4-(3′,5′-tert-butylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3’,5’-dimethylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4,8-bis-(4′-tert-butylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3’,5’-dimethylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[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-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4,8-bis-(3’,5’-dimethylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3’,5’-di-tert-butylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, and (ii) a cocatalyst system comprising a boron-containing cocatalyst and an aluminoxane cocatalyst.

14. A method for producing a film according to any one of claims 1 to 13, comprising the following steps a) polymerizing a random copolymer of propylene monomer units and ethylene comonomer units in the presence of a single-site catalyst system; b) preparing a polypropylene composition; and c) preparing the film.

15. The method according to claim 14, wherein the film is a non-oriented film and is prepared by cast film or blown film extrusion.

16. The method according to claim 14, wherein the single-site catalyst system comprises (i) a metallocene catalyst selected from rac-dimethylsilylenebis[2-methyl-4-(3’,5’-dimethylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4-(4′-tert-butylphenyl)-inden-1-yl][2-methyl-4-(4′-tert-butylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4-(4′-tert-butylphenyl)-inden-1-yl][2-methyl-4-phenyl-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4-(3’,5′-tert-butylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3’,5’-dimethylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4,8-bis-(4′-tert-butylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3’,5’-dimethylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[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-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4,8-bis-(3’,5’-dimethylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3’,5’-di-tert-butylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, and (ii) a cocatalyst system comprising a boron-containing cocatalyst and an aluminoxane cocatalyst.

17. The method according to any one of claims 14 to 16, wherein the random copolymer is polymerized to have a melt flow rate MFR determined according to ISO 1133 at a temperature of 230 °C and a load of 2.16 kg of from 0.5 to 3.5 g / 10 min 2 , and then visbroken to a melt flow rate MFR determined according to ISO 1133 at a temperature of 230 °C and a load of 2.16 kg of from 5.5 to 20.0 g / 10 min 2 .

18. Use of a polypropylene composition comprising an atactic copolymer comprising propylene monomer units and ethylene comonomer units for producing a film having a balanced property of improved tensile modulus and resistance to impact extrusion, wherein based on the total weight of the monomer units in the atactic copolymer, the atactic copolymer has an ethylene comonomer unit content of 0.5 to 4.0% by weight and a total of 2,1- and 3,1-regio defects of 0.10 to 1.40 mol% determined by 13 13C-NMR spectroscopy, and the polypropylene composition has a melt flow rate MFR of 0.5 to 20.0 g / 10 min determined according to ISO 1133 at a temperature of 230 °C and a load of 2.16 kg 2 and a xylene cold soluble (XCS) content of 0.05 to 5.00% by weight, wherein the atactic copolymer is produced in the presence of a single-site catalyst system.

19. The use according to claim 18, wherein the single-site catalyst system comprises (i) A metallocene catalyst selected from rac-dimethylsilylenebis[2-methyl-4-(3’,5’-dimethylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4-(4′-tert-butylphenyl)-inden-1-yl][2-methyl-4-(4′-tert-butylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4-(4′-tert-butylphenyl)-inden-1-yl][2-methyl-4-phenyl-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4-(3′,5′-tert-butylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3’,5’-dimethylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4,8-bis-(4′-tert-butylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3’,5’-dimethylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[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-butylindene-1-yl]zirconium dichloride, rac-trans-dimethylsilylene[2-methyl-4,8-bis-(3’,5’-dimethylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3’,5’-di-tert-butylphenyl)-5-methoxy-6-tert-butylindene-1-yl]zirconium dichloride, and (ii) A cocatalyst system comprising a boron-containing cocatalyst and an aluminoxane cocatalyst.

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