Polypropylene composition for heat sealable films

Abstract

The present disclosure relates to a polypropylene composition (I) comprising: (a) 20 to 45 wt.% of a propylene-hexene copolymer; (b) from 25 to 45 wt.% of a propylene-hexene-ethylene terpolymer; and (c) 20 to 45 wt.% of a propylene-ethylene copolymer, wherein the amounts of (a), (b) and (c) are based on the total weight of (a) + (b) + (c).

Description

Technical Field

[0001] The present disclosure relates to polyolefin compositions having good sealing properties suitable for film applications, particularly BOPP or cast films. Background Art

[0002] Polypropylene heat-sealable films are used in many common packaging applications, such as cigarettes, candy, snacks, and food wraps. Polypropylene is also used in shrink wrap, hygiene products, and aseptic packaging for medical applications.

[0003] In the packaging field, polypropylene films are usually closed by heat sealing. Propylene homopolymers do not have good sealing properties, so it is known in the art to improve the sealing properties of polypropylene by using blends of propylene copolymers.

[0004] In particular, blends of propylene-hexene copolymers and copolymers of propylene and ethylene are suitable for preparing films with low sealing initiation temperature and low haze, in particular biaxially oriented polypropylene films (BOPP) and cast films, see, for example, WO2017 / 097579, WO2018 / 202396 and WO2020 / 249388. The crystallization temperature of the blends of copolymers of the prior art is generally low.

[0005] Polypropylene compositions comprising blends of propylene-ethylene random copolymers, propylene-hexene random copolymers and propylene-hexene-ethylene terpolymers are also known from EP 3 670 547 A1, said compositions having a SIT above 108° C., beneficial optical properties and low overall migration.

[0006] In this framework, there remains a need to provide polypropylene materials with good thermal and optical properties, which are suitable for producing films with good sealing properties. Summary of the invention

[0007] The present disclosure provides a polypropylene composition (I), comprising:

[0008] (a) 20 wt.% to 45 wt.% of a propylene-hexene copolymer comprising 3.5 wt.% to less than 7.0 wt.% of units derived from hexene, based on the weight of (a);

[0009] (b) 25 wt.% to 45 wt.% of a propylene-hexene-ethylene terpolymer comprising 6.0 wt.% to 12.0 wt.% of units derived from hexene and 0.5 wt.% to 3.5 wt.% of units derived from ethylene, based on the weight of (b); and

[0010] (c) 20 wt.% to 45 wt.% of a propylene-ethylene copolymer comprising 0.5 wt.% to 5.0 wt.% of units derived from ethylene, based on the weight of (c),

[0011] The amounts of (a), (b) and (c) are based on the total weight of (a)+(b)+(c), the total weight being 100.

[0012] The polypropylene composition (I) of the present disclosure is endowed with good thermal properties (such as high melting and crystallization temperatures) and good optical properties (such as low haze).

[0013] The polypropylene composition (I) disclosed herein is suitable for preparing films having good sealing properties such as low seal initiation temperature (SIT), high seal strength and high hot tack.

[0014] Therefore, another object of the present disclosure is a film comprising the polypropylene composition (I), preferably in at least one skin layer.

[0015] Although multiple embodiments are disclosed, other embodiments will become apparent to those skilled in the art from the detailed description below. As will be apparent, certain embodiments as disclosed herein are capable of modification in various obvious aspects without departing from the spirit and scope of the claims presented herein. Therefore, the following detailed description is to be construed as illustrative in nature and not restrictive. DETAILED DESCRIPTION

[0016] In the context of this disclosure;

[0017] - Percentages are expressed by weight unless otherwise stated;

[0018] - (polypropylene) the total weight of the composition adds up to 100%, unless otherwise indicated;

[0019] - the term "comprising" in relation to a polymer, plastic material, polymer composition, mixture or blend shall be interpreted as meaning "comprising or consisting essentially of";

[0020] - The term "consisting essentially of" means that in addition to the mandatory ones, other components may also be present in the material, provided that the basic characteristics of the material are not substantially affected by their presence. Examples of components that do not substantially affect the properties of the polymer or polyolefin composition, mixture or blend when present in conventional amounts are catalyst residues and processing aids;

[0021] - the term "copolymer" refers to a polymer derived from the intentional polymerization of two different comonomers, i.e. the term "copolymer" does not include terpolymers;

[0022] - The term "terpolymer" means a polymer derived from the intentional polymerization of three different comonomers;

[0023] - the term "hexene" refers to hexene-1 and the term "butene" refers to butene-1;

[0024] - The term "skin layer" refers to the outermost layer of a multilayer film;

[0025] - The term "base layer" refers to the innermost layer of a multilayer film, to which at least one skin layer is preferably adhered.

[0026] The present disclosure provides a polypropylene composition (I), comprising:

[0027] (a) 20 wt.% to 45 wt.%, preferably 27 wt.% to 37 wt.% of a propylene-hexene copolymer comprising 3.5 wt.% to less than 7.0 wt.% of units derived from hexene, based on the weight of (a);

[0028] (b) 25 wt.% to 45 wt.%, preferably 30 wt.% to 40 wt.% of a propylene-hexene-ethylene terpolymer comprising 6.0 wt.% to 12.0 wt.% of units derived from hexene and 0.5 wt.% to 3.5 wt.% of units derived from ethylene, based on the weight of (b); and

[0029] (c) 20 wt.% to 45 wt.%, preferably 27 wt.% to 37 wt.% of a propylene-ethylene copolymer, based on the weight of (c), comprising 0.5 wt.% to 5.0 wt.% of units derived from ethylene,

[0030] The amounts of (a), (b) and (c) are based on the total weight of (a)+(b)+(c), the total weight being 100.

[0031] In the following, the individual components of the polyolefin composition (I) are defined in more detail.The individual components may be comprised in the polyolefin composition (I) in any combination.

[0032] Preferably, the propylene-hexene copolymer (a) comprises 4.0 to 6.5 wt.%, more preferably 4.5 to 6.0 wt.%, of units derived from hexene, based on the weight of (a).

[0033] More preferably, the propylene-hexene copolymer (a) has at least one, preferably all, of the following properties:

[0034] - comprising a xylene soluble fraction XS(a) at 25°C in the range of 9.0 wt.% to 20.0 wt.%, preferably 10.0 wt.% to 17.0 wt.%, based on the weight of (a); and / or

[0035] - a melting temperature Tm(a) measured by DSC of from 125°C to 143°C, preferably from 130°C to 140°C, more preferably from 132°C to 138°C; and / or

[0036] - a melt flow rate MFR(a), measured according to method ISO 1133-1:2011 (230°C / 2.16kg) of 3.5 to 8.5 g / 10 min.

[0037] Preferably, the propylene-hexene-ethylene terpolymer (b) comprises 6.7 wt.% to 11.0 wt.%, more preferably 7.0 wt.% to 10.0 wt.% of units derived from hexene and 0.5 wt.% to 2.8 wt.%, more preferably 1.5 wt.% to 2.5 wt.%, still more preferably 1.7 wt.% to 2.5 wt.% of units derived from ethylene, wherein the amounts of units derived from hexene and derived from ethylene are based on the weight of (b).

[0038] Preferably, the propylene-ethylene copolymer (c) comprises 0.5 to less than 3.5 wt.%, more preferably 1.0 to 3.0 wt.%, still more preferably 1.0 to 2.8 wt.% of units derived from ethylene, based on the weight of (c).

[0039] In one embodiment, the polypropylene composition (I) further comprises up to and including 5.0 wt.%, more preferably 0.01 wt.% to 5.0 wt.% of at least one additive (d) selected from nucleating agents, antistatic agents, antioxidants, light stabilizers, slip agents, antacids, melt stabilizers and combinations thereof, the amount of the additive being based on the total weight of the polypropylene composition (I) including the additive, the total weight being 100.

[0040] In one embodiment the polypropylene composition (I) consists of components (a), (b) (c) and (d) as described above.

[0041] Preferably, the polypropylene composition (I) has at least one, preferably all, of the following properties:

[0042] - comprising 12.0 to 20.0 wt.%, preferably 14.0 to 17.0 wt.% of a xylene soluble fraction XS (I) at 25°C, based on the weight of the polypropylene composition (I); and / or

[0043] - a melting temperature Tm(I) measured by DSC of from 125°C to 143°C, preferably from 135°C to 140°C; and / or

[0044] - a crystallization temperature Tc(I) measured by DSC of from 85°C to 100°C, more preferably from 89°C to 95°C; and / or

[0045] - a melt flow rate MFR(I) measured according to method ISO 1133-1:2011 (230°C / 2.16 kg) of 2.0 to 12.0 g / 10 min, more preferably of 4.0 to 10.0 g / 10 min, more preferably of 4.5 to 8.0 g / 10 min.

[0046] Preferably, the polypropylene composition (I) further has a haze value up to and including 1.00 %, preferably from 0.20 to 1.00 %, measured according to method ASTM D1003 on BOPP film.

[0047] In a preferred embodiment, the total amount of hexene included in the polypropylene composition (I) is 3.0 wt.% to 7.0 wt.%, preferably 3.5 wt.% to 6.0 wt.%, and the total amount of ethylene is 0.5 wt.% to 3.0 wt.%, preferably 1.0 wt.% to 2.5 wt.%, wherein the total amount of hexene and ethylene is based on the weight of the polypropylene composition (I), and the weight is 100.

[0048] The polypropylene composition (I) is obtainable by melt blending components (a), (b), (c) and optionally (d) or, preferably, the polypropylene composition (I) is a reactor blend of components (a), (b) and (c), optionally with component (d), wherein the reactor blend is obtained by polymerizing the relevant monomers in gas phase in at least three polymerization stages, wherein the second and each subsequent polymerization stage is carried out in the presence of the produced polymer and the catalyst system used in the immediately preceding polymerization stage.

[0049] In a preferred embodiment the polypropylene composition (I) is obtained by polymerizing the relevant monomers in the presence of a highly stereospecific Ziegler-Natta catalyst system comprising:

[0050] (1) A solid catalyst component comprising a magnesium halide support and a stereoregular internal donor, on which a Ti compound having at least one Ti-halogen bond is present;

[0051] (2) optionally, but preferably, an aluminum-containing promoter; and

[0052] (3) Optionally, but preferably, additional electron donor compounds (external donors).

[0053] The solid catalyst component (1) preferably comprises TiCl4 in an amount ensuring the presence of 0.5 to 10 wt.% Ti relative to the total weight of the solid catalyst component (1).

[0054] The solid catalyst component (1) comprises at least one stereoregular internal electron donor compound selected from mono- or bidentate organic Lewis bases, preferably selected from esters, ketones, amines, amides, carbamates, carbonates, ethers, nitriles, alkoxysilanes and combinations thereof.

[0055] Suitable donors are esters of phthalic acid, for example those described in EP 45977 A2 and EP 395083 A2, in particular diisobutyl phthalate, di-n-butyl phthalate, di-n-octyl phthalate, diphenyl phthalate, benzyl butyl phthalate and combinations thereof.

[0056] The esters of aliphatic acids may also be selected from esters of malonic acid, such as those described in WO98 / 056830, WO98 / 056833, WO98 / 056834, esters of glutaric acid, such as those disclosed in WO00 / 55215, and esters of succinic acid, such as those disclosed in WO00 / 63261.

[0057] A specific type of diesters are those derived from the esterification of aliphatic or aromatic diols, such as those described in WO 2010 / 078494 and USP 7,388,061.

[0058] In a preferred embodiment, the internal donor is selected from 1,3-diethers, such as those described in EP361493, EP728769 and WO02 / 100904.

[0059] Internal donors, in particular specific mixtures of aliphatic or aromatic mono- or dicarboxylic acid esters and 1,3-diethers as disclosed in WO 07 / 57160 and WO 2011 / 061134, can be used as internal donors.

[0060] The preferred magnesium halide support is magnesium dihalide.

[0061] The amount of the internal donor to be held fixed on the solid catalyst component (1) is 5 to 20 mol% relative to the magnesium dihalide.

[0062] The preparation of catalyst components according to general methods is described, for example, in European patent applications US 4,399,054, US 4,469,648, WO 98 / 44009 A1 and EP 395 083 A2.

[0063] The catalyst system preferably comprises an Al-containing cocatalyst (2) selected from Al-trialkyl, preferably selected from Al-triethyl, Al-triisobutyl and Al-tri-n-butyl. The Al / Ti weight ratio in the catalyst system is 1-1000, preferably 20-800.

[0064] In a preferred embodiment, the catalyst system comprises a further electron donor compound (3) (external electron donor) selected from silicon compounds, ethers, esters, amines, heterocyclic compounds (especially 2,2,6,6-tetramethylpiperidine) and ketones.

[0065] Preferred silicon compounds are selected from methylcyclohexyldimethoxysilane (C-donor), dicyclopentyldimethoxysilane (D-donor) and mixtures thereof.

[0066] The polymerization temperature is preferably comprised within the range from 20°C to 100°C and the polymerization pressure is preferably from 3.3 to 4.3 MPa for a process in liquid phase and from 0.5 to 3.0 MPa for a process in gas phase.

[0067] The molecular weight of the polymer is regulated by feeding a molecular weight regulator such as hydrogen into the polymerization reactor.

[0068] Preferably, the propylene-hexene copolymer (a) is obtained in a first gas phase reactor, the propylene-hexene-ethylene terpolymer (b) is obtained in a second gas phase reactor in the presence of the prepared polymer and the catalyst system used in the first gas phase reactor; the propylene-ethylene copolymer (c) is obtained in a third gas phase reactor in the presence of the formed polymer and the catalyst used in the preceding polymerization step. Gas phase reactors are of a type known in the art.

[0069] When the polypropylene composition (I) is a reactor blend prepared by sequential polymerization the amounts of components (a), (b) and (c) correspond to the separation between reactors.

[0070] The polypropylene composition (I) is suitable for preparing films, in particular heat-sealable films with a low heat-seal initiation temperature (SIT). The polypropylene composition (I) also has a relatively high melting temperature Tm(I) and crystallization temperature Tc(I).

[0071] Advantageously, the ΔTm-SIT (the difference between Tm(I) and SIT of the polypropylene composition (I) measured on a BOPP film) is broad, thereby allowing good processability of the film.

[0072] In one embodiment, the ΔTm-SIT value is in the range of 30°C to 45°C, preferably 30°C to 40°C, wherein Tm(I) and SIT are measured as shown below.

[0073] In another aspect the present disclosure is directed to a film comprising or consisting of the polypropylene composition (I) as described above.

[0074] In one embodiment the film is a multilayer film comprising a base layer and at least one skin layer, wherein the skin layer comprises or consists of the polypropylene composition (I) as described above.

[0075] The base layer preferably comprises a polyolefin, more preferably a polypropylene selected from the group consisting of a propylene homopolymer, a propylene copolymer, and combinations thereof.

[0076] In one embodiment, the film of the present disclosure is an unoriented film, preferably a cast film or a blown film.

[0077] In one embodiment, the film of the present disclosure is an oriented film, preferably a biaxially oriented polypropylene (BOPP) film.

[0078] In one embodiment, the films of the present disclosure have a total film thickness of 10 to 70 microns, preferably 15 to 30 microns, more preferably 18 to 22 microns.

[0079] The membranes of the present disclosure are obtained according to known methods.

[0080] In a preferred embodiment, the membrane of the present disclosure has at least one, preferably all, of the following properties:

[0081] - a seal initiation temperature (SIT) below 105°C, preferably ranging from 90°C to 105°C, more preferably from 95°C to 103°C, even more preferably from 97°C to 102°C; and / or

[0082] - a seal strength in the range of 3.0 to 4.5 N at 130°C; and / or

[0083] - a hot tack of 400-600 N, preferably 460-560 N at 110°C; and / or

[0084] - Gloss on BOPP film of 83 to 95, preferably 85 to 90.

[0085] The features describing the subject matter of the present disclosure are not indefinitely linked to each other. Thus, a preferred range for one feature can be combined with a more or less preferred range for a different feature, regardless of their level of preference.

[0086] Example

[0087] The following examples are illustrative only, and are not intended to limit the scope of the present disclosure in any way.

[0088] Characterization Methods: The following methods were used to determine the properties indicated in the specification, claims and examples.

[0089] Melt flow rate: determined according to method ISO 1133-1:2011 (230°C / 2.16kg for propylene polymer and 190°C / 2.16kg for butene-1 copolymer).

[0090] Solubility of propylene polymer in xylene at 25°C: 2.5 g of polymer sample and 250 ml of xylene were introduced into a glass flask equipped with a refrigerator and a magnetic stirrer. The temperature was raised to 135°C in 30 minutes. The resulting clear solution was kept under reflux and stirred for another 30 minutes. The solution was cooled in two stages. In the first stage, the temperature was reduced to 100°C in air under stirring for 10 to 15 minutes. In the second stage, the flask was transferred to a thermostatically controlled water bath at 25°C for 30 minutes. The temperature was reduced to 25°C without stirring during the first 20 minutes, and maintained at 25°C in the last 10 minutes under stirring. The solid formed was filtered on a fast filter paper (e.g. Whatman filter paper grade 4 or 541). 100 ml of the filtrate (S1) was poured into a pre-weighed aluminum container and heated to 140°C on a heating plate under a nitrogen stream to remove the solvent by evaporation. The container was then kept in an oven at 80°C under vacuum until constant weight was reached. The amount of polymer soluble in xylene at 25°C is then calculated. XS(I) and XS A The value is determined experimentally. The fraction of component (B) soluble in xylene at 25°C (XS B ) can be calculated by the following formula:

[0091] XS=W(A)×(XS A )+W(B)×(XS B )

[0092] Wherein W(A) and W(B) are the relative amounts of components (A) and (B), respectively, and W(A)+W(B)=1.

[0093] Comonomer content of polypropylene composition: Determined by IR using Fourier transform infrared spectrometer (FTIR). Spectra of polymer pressed films are recorded as absorbance versus wave number (cm-1). The following measured values ​​are used to calculate ethylene and hexene-1 content:

[0094] - the area (At) of the combined absorption band at 4482 and 3950 cm-1, which is used as a spectroscopic standard for film thickness;

[0095] - Subtract the linear baseline in the range 790-660 cm-1 and eliminate the remaining constant offset;

[0096] -The contents of ethylene and hexene-1 were obtained by applying partial least squares (PLS1) multiple regression in the range of 762-688 cm-1.

[0097] The method was calibrated by using polymer standards based on 13C NMR analysis.

[0098] Sample preparation: Using a hydraulic press, a thick sheet is obtained by pressing about 1 g of sample between two aluminum foils. The pressing temperature is 180 ± 10 ° C (356 ° F), the pressure is about 10 kg / cm2, and the duration is about 1 minute (minimum two pressing operations for each sample). A small portion is cut from the sheet to mold a film. The recommended film thickness range is 0.02-0.05 cm.

[0099] Comonomer content of butene-ethylene copolymers: obtained on a Bruker AV-600 spectrometer equipped with a cryoprobe 13 C NMR spectra, operated in Fourier transform mode at 120°C. Samples were dissolved in 1,1,2,2-tetrachloroethane-d2 at 8% wt / v at 120°C. Each spectrum was acquired with a 90° pulse with a 15 s delay between pulse and CPD to remove 1H-13C coupling. The spectrometer was operated at 160.91 MHz. S δδ The peak of carbon (according to the nomenclature of "Monomer sequence distribution in ethylene-propylene rubber measured by 13C NMR. 3. Use of reaction probability models," CJ Carman, RA Harrington and CE Wilkes, Macromolecules, 1977, 10, 536) was used as an internal reference. 512 transients were stored in 32K data points using a spectral window of 9000 Hz.

[0100] Spectral assignment, triplet distribution and composition evaluation were performed according to Kakugo [M. Kakugo, Y. Naito, K. Mizunuma and T. Miyatake, Macromolecules, 16, 4, 1160 (1982)] and Randall [JC Randall, Macromol. Chem Phys., C30, 211 (1989)] using the following:

[0101] BBB=100T ββ / S BBE=100T βδ / S EBE=100P δδ / S

[0102] BEB=100S ββ / S BEE=100S αδ / S EEE=100(0.25S γδ +0.5S δδ ) / S

[0103] S=T ββ +Tβδ +P δδ +S ββ +S αδ+ 0.25S γδ +0.5S δδ

[0104] The total amount of 1-butene and ethylene (in mole percent) was calculated from the triad using the following relationship:

[0105] [E]=EEE+BEE+BEB

[0106] [B]=BBB+BBE+EBE

[0107] The weight percent of ethylene content (E wt. %) was calculated using the following equation:

[0108]

[0109] in

[0110] [B]mol = molar percentage of 1-butene content;

[0111] MWE = molecular weight of ethylene

[0112] MWB = molecular weight of 1-butene.

[0113] Molecular weight distribution Mw / Mn: The determination of the average Mn and Mw and the Mw / Mn derived therefrom was performed using a Waters GPCV 2000 apparatus equipped with four PLgel Olexis mixed gel column sets (Polymer Laboratories) and an IR4 infrared detector (Polymer Char). The dimensions of the columns were 300×7.5 mm and their particle size was 13 μm. The mobile phase used was 1-2-4-trichlorobenzene (TCB) at a flow rate maintained at 1.0 ml / min. All measurements were performed at 150°C. The solution concentration in TCB was 0.1 g / dl, and 0.1 g / l of 2,6-diterbuthyl-p-chresole was added to prevent degradation. For GPC calculations, a universal calibration curve was obtained using 10 polystyrene (PS) standard samples (peak molecular weights of 580 to 8,500,000) provided by Polymer Laboratories. The experimental data were interpolated using a cubic polynomial fit to obtain the corresponding calibration curve. Data acquisition and processing were performed using Empower (Waters). The molecular weight distribution and the related average molecular weight were determined using the Mark-Houwink relationship: the K values ​​for PS and PB were KPS = 1.21 × 10-4 dL / g and KPB = 1.78 × 10-4 dL / g, respectively, and the Mark-Houwink exponents for PS and PB were α = 0.706 and α = 0.725, respectively. For butene-1 / ethylene copolymers, for data evaluation, the composition was assumed to be constant over the entire range of molecular weights, and the K value of the Mark-Houwink relationship was calculated using the linear combination reported below:

[0114] K EB =x E K PE +x P K PB

[0115] Where K EB is the constant of the copolymer, K PE (4.06×10 -4 ,dL / g) and K PB (1.78×10 -4 dl / g) are constants for polyethylene and polybutene, xE and xB are the wt.% contents of ethylene and butene-1. The Mark-Houwink index α=0.725 is applied independently to the compositions of all butene-1 / ethylene copolymers.

[0116] Melting Temperature: Measured according to method ISO 11357-3:2018. Polypropylene and polypropylene compositions:Samples weighing 5-7 mg were cooled and heated at a scan rate of 20°C / min under a nitrogen stream. Indium was used for instrument calibration. Polybutene: To determine the melting temperature (Tm(I)) of the polybutene crystalline form I, the sample was melted, held at 200° C. for 5 minutes, and then cooled to 20° C. at a cooling rate of 10° C. / min. The sample was then stored at room temperature for 10 days. After 10 days, the sample was subjected to DSC, which was cooled to −20° C. and then heated at 200° C. at a scanning rate corresponding to 10° C. / min. In this heating run, the first peak temperature from the lower temperature side in the thermogram was taken as the melting temperature Tm(I).

[0117] Flexural modulus: determined according to method ISO 178:2010 on injection-moulded test specimens (80×10×4 mm) for propylene polymers or compression-moulded test specimens for butene polymers obtained according to method ISO 1873-2:2007. Prior to testing, the test specimens of butene copolymers were conditioned at 23° C. for 10 days.

[0118] Preparation of BOPP film specimens. Films with a thickness of 50 μm were prepared by extruding each test composition in a single screw Collin extruder (screw length / diameter ratio of 1:25) at a film drawing speed of 7 m / min and a melt temperature of 210-250°C. Each film was superimposed on a 1000 μm thick film of a propylene homopolymer having a xylene insoluble fraction of 97 wt.% and an MFR of 2.0 g / 10 min (ISO 1133-1:2011, 230°C / 2.16 kg). The superimposed films were pressed in a flat press at 200°C under 35 kg x cm 2 The laminate was stretched 7 times in both longitudinal and transverse directions (ie, biaxially) at 160° C. using a Karo 4 Brueckener film stretcher, thereby obtaining a 20 μm thick BOPP film (18 μm homopolymer + 2 μm test composition).

[0119] Seal strength and seal initiation temperature (SIT): Cut a 6x35cm film strip from the center of the BOPP test specimen and superimpose two film strips. The strips are covered with foil and sealed with an RDM heat sealer: flat metal sealing bars, both bars are heated; sealing time 0.5 seconds; sealing pressure 0.14 MPa (20 psi). After a conditioning time of at least 10 minutes at 23°C and 50% RH, six test specimens, 15 mm wide and long enough to be claimed in the tensile tester fixture, are cut from each sealed strip. The seal strength at a given temperature is tested with a dynamometer at a load cell capacity of 100 N, a lateral speed of 100 mm / min and a clamping distance of 50 mm. The seal strength value is the average of 6 measurements on the same film sample. The test is repeated by increasing or decreasing the temperature by 1°C or 2°C. The lowest temperature at which a seal strength equal to or greater than 1.5 N is reached is defined as the seal initiation temperature SIT.

[0120] Determination of hot tack. Hot tack is measured after sealing the BOPP test specimens for 5 seconds at a pressure of 0.12 MPa (18 psi) with a Brugger HSG heat sealer (with hot tack kit). The films are cut in a minimum length of 15×200 mm, superimposed and sealed at different temperatures, starting from 80° C. and increasing the sealing temperature by 5° C. Immediately after sealing, the test specimens are pulled onto a mandrel by a pulley to separate the heat-sealed seam. For each sealing temperature, the force required to separate the still hot sealed seam at half its length (hot tack) is determined using different falling weights generated by impacting the test specimens.

[0121] Haze: Measured on 50 μm cast film on ASTM D1003.

[0122] Gloss: ASTM D2457 (angle 45°) on 50 μm cast film and BOPP film.

[0123] raw material:

[0124] ADSYL 5C30F LyondellBasell®: A polyolefin sold by LyondellBasell designed for use as a sealant layer in coextruded film applications.

[0125] Irganox 1010: Pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), sold by BASF.

[0126] Irgafos168: Tris(2,4-di-tert-butylphenyl)phosphite, sold by BASF.

[0127] Examples E1-E4 and Comparative Examples CE5-CE6

[0128] Preparation of catalyst system : For the preparation of the polypropylene composition, a Ziegler-Natta catalyst system is used, which comprises:

[0129] - a titanium-containing solid catalyst component prepared by the procedure described in EP728769, Example 1, according to which 9,9-bis(methoxymethyl)fluorene was used as internal electron donor compound;

[0130] - triethylaluminium (TEAL) as co-catalyst;

[0131] - Dicyclopentyldimethoxysilane (DCPMS) as external electron donor.

[0132] Under the conditions reported in Table 1, the solid catalyst component was contacted with TEAL and DCPMS in a precontact vessel.

[0133] polymerization: Before the catalyst system is introduced into the first polymerization reactor, the catalyst system is prepolymerized by keeping a suspension of the catalyst system in liquid propylene at 20° C. for 20 minutes. In the first gas phase polymerization reactor, the propylene-hexene copolymer (a) is prepared by supplying a continuous and constant flow of the prepolymerized catalyst system, hydrogen as a molecular weight regulator, gaseous propylene and hexene. The propylene-hexene copolymer prepared in the first gas phase reactor is continuously discharged and introduced into the second gas phase polymerization reactor together with a quantitative constant flow of gaseous hydrogen, propylene, hexene and ethylene, wherein a propylene-hexene-ethylene terpolymer is prepared. The polymer produced in the second gas phase reactor is discharged in a continuous flow and, after purging the unreacted monomers, is introduced into the third gas phase polymerization reactor in a continuous flow together with a quantitative constant flow of gaseous hydrogen, ethylene and propylene. The polymerization conditions are reported in Table 1.

[0134] Table 1

[0135]

[0136] The polymer obtained from the polymerization run was added with 0.05 wt.% Irganox 1010, 0.1 wt.% Irgafos 168, 0.05% calcium stearate, wherein the amount of additives is based on the total weight of the polymer including additives, and pelletized. Table 2 shows the characterization characteristics of the polypropylene composition.

[0137] In comparative example CE6, Adsyl 5C30F was used.

[0138] Table 2

[0139]

Claims

1. A polypropylene composition (I), comprising: (a) 20 wt.% to 45 wt.%, preferably 27 wt.% to 37 wt.% of a propylene-hexene copolymer comprising 3.5 wt.% to less than 7.0 wt.% of units derived from hexene, based on the weight of (a); (b) 25 wt.% to 45 wt.%, preferably 30 wt.% to 40 wt.% of a propylene-hexene-ethylene terpolymer comprising 6.0 wt.% to 12.0 wt.% of units derived from hexene and 0.5 wt.% to 3.5 wt.% of units derived from ethylene, based on the weight of (b); and (c) 20 wt.% to 45 wt.%, 27 wt.% to 37 wt.% of a propylene-ethylene copolymer comprising 0.5 wt.% to 5.0 wt.% of units derived from ethylene, based on the weight of (c), The amounts of (a), (b) and (c) are based on the total weight of (a)+(b)+(c).

2. The polypropylene composition (I) according to claim 1, wherein the propylene-hexene copolymer (a) comprises 4.0 to 6.5 wt.%, more preferably 4.5 to 6.0 wt.%, of units derived from hexene, based on the weight of (a).

3. The polypropylene composition (I) according to claim 1 or 2, wherein the propylene-hexene-ethylene terpolymer (b) comprises 6.7 wt.% to 11.0 wt.%, preferably 7.0 wt.% to 10.0 wt.% of units derived from hexene and 0.5 wt.% to 2.8 wt.%, preferably 1.5 wt.% to 2.5 wt.%, more preferably 1.7 wt.% to 2.5 wt.% of units derived from ethylene, based on the weight of (b).

4. The polypropylene composition (I) according to any one of claims 1 to 3, wherein the propylene-ethylene copolymer (c) comprises from 0.5 wt.% to less than 3.5 wt.%, preferably from 1.0 wt.% to 3.0 wt.%, more preferably from 1.0 wt.% to 2.8 wt.%, based on the weight of (c), of units derived from ethylene.

5. The polypropylene composition (I) according to any one of claims 1 to 4, wherein the polypropylene composition (I) comprises 12.0 to 20.0 wt.-%, preferably 14.0 to 17.0 wt.-%, based on the weight of the polypropylene composition (I), of a xylene soluble fraction XS (I) at 25 °C.

6. The polypropylene composition (I) according to anyone of claims 1-5, wherein the polypropylene composition (I) has a melting temperature Tm(I) measured by DSC of 125 to 143°C, preferably 135 to 140°C.

7. The polypropylene composition (I) according to any one of claims 1-6, wherein the polypropylene composition (I) has a crystallization temperature Tc(I) measured by DSC of 85 to 100°C, more preferably of 89 to 95°C.

8. The polypropylene composition (I) according to any one of claims 1 to 7, wherein the polypropylene composition (I) has a melt flow rate, MFR(I), measured according to method ISO 1133-1:2011 (230°C / 2.16kg), of 2.0 to 12.0 g / 10min, more preferably of 4.0 to 10.0 g / 10min, more preferably of 4.5 to 8.0 g / 10min.

9. A film comprising the polypropylene composition (I) according to any one of claims 1 to 8.

10. The film according to claim 9, wherein the film is a multilayer film comprising a base layer and at least one skin layer, wherein the skin layer comprises the polypropylene composition (I) according to any one of claims 1 to 8.

11. The film according to claim 9 or 10, wherein the film is unoriented, preferably a cast or blown film.

12. The film according to claim 9 or 10, wherein the film is an oriented film, preferably a biaxially oriented polypropylene (BOPP) film.

13. The film according to any one of claims 9-12, wherein the total film thickness is in the range of 10 to 70 microns, preferably 15 to 30 microns, more preferably 18 to 22 microns.

14. The multilayer film according to any one of claims 10 to 13, having at least one, preferably all, of the following characteristics: - a seal initiation temperature (SIT) equal to or lower than 105°C, preferably ranging from 90°C to 105°C, more preferably from 95°C to 103°C, even more preferably from 97°C to 102°C; and / or - a seal strength in the range of 3.0 to 4.5 N at 130°C; and / or - Hot tack at 110°C 400-600N, preferably 460-560N.

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