Polypropylene composition for heat-sealing film

Abstract

The present disclosure relates to a polypropylene composition (I), the composition comprising: (a) 20% to 45% by weight of a propylene-hexene copolymer; (b) 25% to 45% by weight of a propylene-hexene-ethylene terpolymer; and (c) 20% to 45% by weight 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 invention relates to a polyolefin composition having good sealing properties suitable for use in film applications, particularly BOPP or cast films.

Background Art

[0002] Heat-sealable films of polypropylene are used in many common packaging applications such as tobacco, candy, snacks, food wraps, etc. Polypropylene can also be used for shrink packaging, sanitary products, and sterilization wraps for medical applications.

[0003] In the packaging field, polypropylene films are generally closed by heat sealing. Since a propylene homopolymer does not have good sealability, it is known in the art to use a blend of propylene copolymers to improve the sealability of polypropylene.

[0004] In particular, blends of propylene-hexene copolymers and copolymers of propylene and ethylene are suitable for the production of films with low seal start temperature and low haze, particularly biaxially oriented polypropylene films (BOPP) and cast films (see, for example, International Patent No. 2017 / 097579, International Patent No. 2018 / 202396, and International Patent No. 2020 / 249388). The crystallization temperature of blends of prior art copolymers is generally low.

[0005] Polypropylene compositions containing blends of propylene-ethylene random copolymers, propylene-hexene random copolymers, and propylene-hexene-ethylene terpolymers are also known from European Patent No. 3670547A1, and these compositions have a SIT above 108°C, beneficial optical properties, and low overall migration.

[0006] In this framework, there is still a need to provide a polypropylene material having good thermal and optical properties suitable for manufacturing a film with good sealing properties.

Summary of the Invention

[0007] The present invention relates to (a) A propylene-hexene copolymer that is 20% to 45% by weight and contains 3.5% to less than 7.0% by weight of units derived from hexene based on the weight of (a), and (b) A propylene-hexene-ethylene terpolymer that is 25% to 45% by weight and contains 6.0% to 12.0% by weight of units derived from hexene and 0.5% to 3.5% by weight of units derived from ethylene based on the weight of (b), and (c) A propylene-ethylene copolymer that is 20% to 45% by weight and contains 0.5% to 5.0% by weight of units derived from ethylene based on the weight of (c), and The amounts of (a), (b), and (c) are based on the total weight of (a)+(b)+(c), and the total weight is 100, to provide a polypropylene composition (I).

[0008] The polypropylene composition (I) of the present invention has good thermal properties such as a high melting point and crystallization temperature, and good optical properties such as a low haze.

[0009] The polypropylene composition (I) of the present invention is suitable for manufacturing a film with good sealing properties such as a low seal start temperature (SIT), high seal strength, and high hot tack.

[0010] Therefore, a further object of the present disclosure is a film preferably containing the polypropylene composition (I) in at least one skin layer.

[0011] Although multiple embodiments are disclosed, other embodiments will become apparent to those skilled in the art from the following detailed description. As will be apparent, the specific embodiments disclosed herein can be modified in various obvious aspects without departing from the spirit and scope of the claims presented herein. Accordingly, the following detailed description is to be considered illustrative in nature and not restrictive.

Best Mode for Carrying Out the Invention

[0012] In the context of the present disclosure, - Percentages are expressed by weight unless otherwise specified.

[0013] - Unless otherwise specified, the total weight of the (polypropylene) composition is 100%.

[0014] - The term "comprising" when referring to a polymer, plastic material, polymer composition, mixture or blend should be construed to mean "consisting essentially of or composed of".

[0015] - The term "consisting essentially of" means that in addition to the essential components, other components may be present in the material as long as the essential properties of the material are not substantially affected by their presence. Examples of components that, when present in normal amounts, do not substantially affect the properties of a polymer or polyolefin composition, mixture or blend include catalyst residues and processing aids.

[0016] - The term "copolymer" refers to a polymer obtained from the intentional polymerization of two different comonomers, i.e., the term "copolymer" does not include terpolymers.

[0017] - The term "terpolymer" refers to a polymer obtained from the intentional polymerization of three different comonomers.

[0018] - The term "hexene" refers to hexene-1 and the term "butene" refers to butene-1.

[0019] - The term "skin layer" refers to the outermost layer of the multilayer film.

[0020] - The term "base layer" refers to the innermost layer of the multilayer film, and it is preferable that at least one skin layer is adhered thereon.

[0021] The present invention provides (a) A propylene - hexene copolymer of 20% by weight to 45% by weight, preferably 27% by weight to 37% by weight, containing units derived from hexene of less than 3.5% by weight to 7.0% by weight based on the weight of (a), a propylene - hexene copolymer; and (b) A propylene - hexene - ethylene terpolymer of 25% by weight to 45% by weight, preferably 30% by weight to 40% by weight, containing units derived from hexene of 6.0% by weight to 12.0% and units derived from ethylene of 0.5% by weight to 3.5% based on the weight of (b), a propylene - hexene - ethylene terpolymer; and (c) A propylene - ethylene copolymer of 20% by weight to 45% by weight, preferably 27% by weight to 37% by weight, containing units derived from ethylene of 0.5% by weight to 5.0% based on the weight of (c), a propylene - ethylene copolymer, and provides a polypropylene composition (I) wherein the amounts of (a), (b) and (c) are based on the total weight of (a)+(b)+(c), and the total weight is 100.

[0022] Hereinafter, the individual components of the polyolefin composition (I) will be defined in more detail. The individual components can be included in the polyolefin composition (I) in any combination.

[0023] Preferably, the propylene - hexene copolymer (a) contains units derived from hexene of 4.0% by weight to 6.5% by weight, more preferably 4.5% by weight to 6.0% by weight based on the weight of (a).

[0024] More preferably, the propylene-hexene copolymer (a) has at least one, preferably all, of the following characteristics.

[0025] - Based on the weight of the propylene copolymer (a), the xylene-soluble fraction XS(a) at 25°C is in the range of 12 to 20% by weight, preferably 14 to 18% by weight. - The melting point Tm(a) measured by DSC is in the range of 125°C to 143°C, preferably 130°C to 140°C, more preferably 132°C to 138°C, and / or - The melt flow rate MFR(a) measured according to the ISO 1133-1:2011 method (230°C / 2.16 kg) is in the range of 3.5 to 8.5 g / 10 min.

[0026] Preferably, the propylene-hexene-ethylene terpolymer (b) contains 6.7 to 11.0% by weight, more preferably 7.0 to 10.0% by weight, of units derived from hexene, and 0.5 to 2.8% by weight, more preferably 1.5 to 2.5% by weight, even more preferably 1.7 to 2.5% by weight, of units derived from ethylene, where the amounts of the units derived from hexene and ethylene are based on the weight of (b).

[0027] Preferably, the propylene-ethylene copolymer (c) contains 0.5 to less than 3.5% by weight, more preferably 1.0 to 3.0% by weight, even more preferably 1.0 to 2.8% by weight, of units derived from ethylene, based on the weight of (c).

[0028] In one embodiment, the polypropylene composition (I) further contains at least one additive (d) selected from the group consisting of a nucleating agent, an antistatic agent, an antioxidant, a light stabilizer, a lubricant, an antacid, a melt stabilizer, and combinations thereof, in an amount of 5.0% by weight or less, more preferably 0.01 to 5.0% by weight, and the amount of the additive is based on the total weight (total weight 100) of the polypropylene composition (I) containing the additive.

[0029] In one embodiment, the polypropylene composition (I) consists of the above components (a), (b), (c) and (d).

[0030] Preferably, the polypropylene composition (I) has at least one, preferably all, of the following properties.

[0031] - Based on the weight of the polypropylene composition (I), the xylene-soluble fraction XS(I) at 25 °C is in the range of 12.0 wt% to 20.0 wt%, preferably 14.0 wt% to 17.0 wt%, and / or - The melting point Tm(I) measured by DSC is in the range of 125 °C to 143 °C, preferably 135 °C to 140 °C, and / or - The crystallization temperature Tc(I) measured by DSC is in the range of 85 °C to 100 °C, more preferably 89 °C to 95 °C, and / or - The melt flow rate MFR(I) measured according to the ISO 1133-1:2011 method (230 °C / 2.16 kg) is in the range of 2.0 to 12.0 g / 10 min, more preferably 4.0 to 10.0 g / 10 min, even more preferably 4.5 to 8.0 g / 10 min

[0032] Preferably, the polypropylene composition (I) has a haze value measured according to ASTM D1003 method for BOPP film of 1.00% or less, preferably in the range of 0.20 wt% to 1.00%.

[0033] In a preferred embodiment, the total amount of hexene contained in the polypropylene composition (I) is in the range of 3.0 wt% to 7.0 wt%, preferably 3.5 wt% to 6.0 wt%, and the total amount of ethylene is in the range of 0.5 wt% to 3.0 wt%, preferably 1.0 wt% to 2.5 wt%, and the total amount of hexene and ethylene is based on the weight when the weight of the polypropylene composition (I) is 100.

[0034] The polypropylene composition (I) is obtained by melt blending components (a), (b), (c) and optionally component (d), or preferably, the polypropylene composition (I) is a reactor blend obtained by melt blending components (a), (b) and (c) and optionally component (d), and the reactor blend is obtained by polymerizing monomers related in the gas phase in at least three polymerization stages, and the second and each subsequent polymerization stage are carried out in the presence of the polymer produced and the catalyst system used in the immediately preceding polymerization stage.

[0035] In a preferred embodiment, the polypropylene composition (I)

[0036] (1) a solid catalyst component comprising a magnesium halide carrier in which a Ti compound having at least a Ti-halogen bond is present, and a stereoregulating internal donor; (2) optionally, but preferably, an Al-containing cocatalyst, and (3) optionally, but preferably, obtained by polymerizing the relevant monomers in the presence of a highly stereospecific Ziegler-Natta catalyst system comprising a further electron-donating compound (external donor).

[0037] The solid catalyst component (1) preferably contains TiCl4 in an amount that ensures that 0.5 to 10% by weight of Ti is present based on the total weight of the solid catalyst component (1).

[0038] The solid catalyst component (1) contains at least one stereoregulating internal electron-donating compound selected from monodentate or bidentate organic Lewis bases, preferably selected from esters, ketones, amines, amides, carbamates, carbonates, ethers, nitriles, alkoxysilanes and combinations thereof.

[0039] Suitable donors are phthalic esters such as those described in European Patent No. 45977A2 and European Patent No. 395083A2, especially diisobutyl phthalate, di-n-butyl phthalate, di-n-octyl phthalate, diphenyl phthalate, benzyl butyl phthalate, and combinations thereof.

[0040] The fatty acid ester can also be selected from malonic esters as described in International Patent No. 98 / 056830, International Patent No. 98 / 056833, International Patent No. 98 / 056834, glutaric esters as disclosed in International Patent No. 00 / 55215, and succinic esters as disclosed in International Patent No. 00 / 63261.

[0041] A specific type of diester is obtained from the esterification of aliphatic or aromatic diols as described in International Patent No. 2010 / 078494 and US Patent No. P7,388,061.

[0042] In a preferred embodiment, the internal donor is selected from 1,3 - diethers such as those described in European Patent No. 361493, European Patent No. 728769, and International Patent No. 02 / 100904.

[0043] An internal donor, in particular a specific mixture of aliphatic or aromatic mono - or dicarboxylic acid esters and 1,3 - diethers as disclosed in International Patent No. 07 / 57160 and International Patent 2011 / 061134, can be used as the internal donor.

[0044] A preferred magnesium halide carrier is magnesium dihalide.

[0045] The amount of the internal donor remaining fixed on the solid catalyst component (1) is 5 - 20 mol% with respect to the magnesium dihalide.

[0046] The preparation of the catalyst component by a general method is described, for example, in US Patent No. 4,399,054, US Patent No.,469,648, International Patent No. 98 / 44009A1, and European Patent No. 395083A2.

[0047] The catalyst system preferably includes an Al-containing cocatalyst (2) selected from Al-trialkyls, preferably selected from the group consisting of Al-triethyl, Al-triisobutyl, and Al-tri-n-butyl. The Al / Ti weight ratio in the catalyst system is 1 to 1000, preferably 20 to 800.

[0048] In a preferred embodiment, the catalyst system includes a further electron donor compound (3) (external electron donor) selected from silicon compounds, ethers, esters, amines, heterocyclic compounds, particularly 2,2,6,6-tetramethylpiperidine, and ketones.

[0049] Preferred silicon compounds are selected from methylcyclohexyldimethoxysilane (C-donor), dicyclopentyldimethoxysilane (D-donor), and mixtures thereof.

[0050] The polymerization temperature is preferably in the range of 20°C to 100°C, and the polymerization pressure is preferably 3.3 to 4.3 MPa in the case of a liquid-phase process and 0.5 to 3.0 MPa in the case of a gas-phase process.

[0051] The molecular weight of the polymer is adjusted by supplying a molecular weight regulator such as hydrogen to the polymerization reactor.

[0052] Preferably, the propylene-hexene copolymer (a) is obtained in the first gas-phase reactor, the propylene-hexene-ethylene terpolymer (b) is obtained in the second gas-phase reactor in the presence of the prepared polymer and the catalyst system used in the first gas-phase reactor, and the propylene-ethylene copolymer (c) is obtained in the third gas-phase reactor in the presence of the formed polymer and the catalyst used in the preceding polymerization step. The gas-phase reactors are of the types known in the art.

[0053] When the polypropylene composition (I) is a reactor blend produced by sequential polymerization, the amounts of components (a), (b), and (c) correspond to the split between the reactors.

[0054] The polypropylene composition (I) is suitable for the production of films, particularly heat-sealable films with a low heat-sealing start temperature (SIT). The polypropylene composition (I) also has a relatively high melting point Tm(I) and crystallization temperature Tc(I).

[0055] Advantageously, △Tm - SIT (the difference between Tm(I) and SIT of the polypropylene composition (I) measured on a BOPP film) is wide, thereby enabling good processability of the film.

[0056] In one embodiment, the △Tm - SIT value ranges from 30°C to 45°C, preferably from 30°C to 40°C, and Tm(I) and SIT are measured as shown below.

[0057] In a further aspect, the present invention relates to a film comprising or consisting of the polypropylene composition (I) as described above.

[0058] In one embodiment, the film is a multilayer film comprising a base layer and at least one skin layer, and the skin layer comprises or consists of the above polypropylene composition (I).

[0059] The base layer preferably comprises polypropylene selected from polyolefins, more preferably homopolymer of propylene, propylene copolymer, and combinations thereof.

[0060] In one embodiment, the film of the present disclosure is an unoriented film, preferably a cast film or an inflation film.

[0061] In one embodiment, the film of the present disclosure is an oriented film, preferably a biaxially oriented polypropylene (BOPP) film.

[0062] In one embodiment, the film of the present disclosure has a total film thickness in the range of 10 to 70 microns, preferably 15 to 30 microns, more preferably 18 to 22 microns.

[0063] The film of the present disclosure is obtained according to known methods.

[0064] In a preferred embodiment, the film of the present disclosure has at least one, preferably all, of the following characteristics.

[0065] - The seal initiation temperature (SIT) is less than 105 °C, preferably in the range of 90 °C to 105 °C, more preferably in the range of 95 °C to 103 °C, and even more preferably in the range of 97 °C to 102 °C, and / or - The seal strength at 130 °C is in the range of 3.0 to 4.5 N, - The hot tack at 110 °C is in the range of 400 to 600 N, preferably in the range of 460 to 560 N, and / or - The gloss of the BOPP film is in the range of 83 to 95, preferably in the range of 85 to 90

[0066] The features that describe the subject matter of the present disclosure are not necessarily closely related to each other. Therefore, a preferred range of one function can be combined with a more preferred or less preferred range of another function, regardless of the level of preference.

[0067]

Example

[0068] The following examples are for illustrative purposes only and are not intended to limit the scope of the disclosure in any way.

[0069] Characteristic evaluation method: The following method is used to determine the characteristics shown in the description, claims, and examples.

[0070] Melt flow rate: Measured according to the DISO 1133-1:2011 method (230 °C / 2.16 kg for propylene polymers, 190 °C / 2.16 kg for butene-1 copolymers).

[0071] Solubility of Propylene Polymer in Xylene at 25°C: Place 2.5 g of the polymer sample and 250 ml of xylene in a glass flask equipped with a refrigerator and a magnetic stirrer. Raise the temperature to 135°C within 30 minutes. Stir the resulting transparent solution for an additional 30 minutes while refluxing. Cool the solution in two steps. In the first step, lower the temperature to 100°C in air with stirring for 10 - 15 minutes. In the second step, transfer the flask to a 25°C thermostatically controlled water bath for 30 minutes. Lower the temperature to 25°C without stirring for the first 20 minutes and maintain at 25°C with stirring for the last 10 minutes. Filter the formed solid through a fast-drying filter paper (e.g., Whatman filter paper grade 4 or 541), pour 100 ml of the filtered solution (S1) into a pre-weighed aluminum container, heat to 140°C on a heating plate under a nitrogen stream to evaporate and remove the solvent. Next, store the container in an 80°C oven under vacuum until a constant weight is reached. Next, calculate the amount of polymer dissolved in xylene at 25°C. The XS(I) and XS A values are determined experimentally. The proportion (XS B ) of component (B) dissolved in xylene at 25°C is calculated by the following formula. XS = W(A)×(XS A ) + W(B)×(XS B ) Here, W(A) and W(B) are the relative amounts of component (A) and (B) respectively, and W(A) + W(B) = 1.

[0072] Comonomer Content in Polypropylene Composition: Measured by IR using a Fourier Transform Infrared Spectrometer (FTIR). The spectrum of the compressed film of the polymer is recorded as absorbance vs. wavenumber (cm-1). To calculate the ethylene and hexene-1 contents, the following measured values are used. - Area (At) of the composite absorption band between 4482 - 3950 cm-1 used for spectroscopic measurement normalization of film thickness - Subtract the linear baseline in the range of 790 - 660 cm-1 and remove the remaining constant offset. - The contents of ethylene and hexene-1 are obtained by applying partial least squares (PLS1) multivariate regression in the range of 762 - 688 cm-1. This method is calibrated using polymer standards based on 13C NMR analysis. Sample Preparation: Using a hydraulic press, sandwich approximately 1 g of the sample between two sheets of aluminum foil to create a thick sheet. The press temperature is 180 ± 10 °C (356 °F), the pressure is approximately 10 kg / cm2 for about 1 minute (at least two press operations per specimen). Cut small pieces from this sheet to form films. The recommended film thickness ranges from 0.02 to 0.05 cm.

[0073] Comonomer Content of Butene-Ethylene Copolymer: 13 The 13C NMR spectra are acquired on a Bruker AV-600 spectrometer equipped with a cryoprobe and operated in Fourier transform mode at 120 °C. The sample is dissolved in 1,1,2,2-tetrachloroethane-d2 at 120 °C to a concentration of 8% wt / v. Each spectrum is acquired with a 90° pulse and a 15-second delay is provided between the pulse and CPD to remove 1H-13C coupling. The spectrometer operates at 160.91 MHz. The peak of Sδδ carbon (Monomer Sequence Distribution in Ethylene-Propylene Rubber Measured by 13C NMR. 3. Use of Reaction Probability Mode” C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 1977, 10, 536) is used as an internal reference at 29.9 ppm. 512 transients are stored at 32K data points using a spectral window of 9000 Hz.

[0074] The spectrum assignment, the evaluation of the triad distribution, and the composition are carried out as follows according to Kakugo [M. Kakugo, Y. Naito, K. Mizunuma, and T. Miyatake, Macromolecules, 16, 4, 1160 (1982)] and Randall [J. C. Randall, Macromol. Chem Phys., C30, 211 (1989)]. BBB = 100T ββ / S BBE = 100T βδ / S EBE = 100P δδ / S BEB = 100S ββ / S BEE = 100S αδ / S EEE = 100(0.25S γδ +0.5S δδ ) / S S = T ββ +T βδ +P δδ +S ββ +S αδ +0.25S γδ +0.5S δδ

[0075] The total amount (mole percent) of 1-butene and ethylene is calculated from the triad using the following relational expressions. [E] = EEE + BEE + BEB [B] = BBB + BBE + EBE

[0076] The weight percentage (E%wt) of the ethylene content is calculated using the following equation.

[0077] [Number] Here [B]mol = mole percentage of 1-butene content MWE = molecular weight of ethylene MWB = molecular weight of 1-butene

[0078] Molecular weight distribution Mw / Mn: The determination of the average values of Mn and Mw, and the resulting Mw / Mn is carried out using a Waters GPCV 2000 device equipped with a column set of four PLgel Olexis mixed gels (Polymer Laboratories) and an IR4 infrared detector (Polymer Char). The column dimensions are 300×7.5 mm and the particle size is 13 μm. 1-2-4-Trichlorobenzene (TCB) is used as the mobile phase, and the flow rate is maintained at 1.0 ml / min. All measurements are carried out at 150 °C. The solution concentration is 0.1 g / dl in TCB, and 0.1 g / l of 2,6-di-tert-butyl-p-cresol is added to prevent decomposition. In GPC calculations, a universal calibration curve is obtained using 10 polystyrene (PS) standard samples (peak molecular weight range 580 - 8500000) provided by Polymer Laboratories. The experimental data is interpolated and a cubic polynomial approximation is used to obtain the relevant calibration curve. Data acquisition and processing are performed using Empower (Waters). The Mark-Houwink relationship is used to determine the average molecular weights related to the molecular weight distribution. The K values are KPS = 1.21×10-4 dL / g and KPB = 1.78×10-4 dL / g for PS and PB respectively, and the Mark-Houwink exponents are α = 0.706 for PS and α = 0.725 for PB. For the butene-1 / ethylene copolymer, regarding data evaluation, it is assumed that the composition is constant over the entire range of molecular weights, and the K value of the Mark-Houwink relationship is calculated using a linear combination as shown below. K EB =x E K PE +x p K PE Here, K EB is the copolymer constant, K PE (4.06×10 -4 ,dL / g) and K PB (1.78×10 -4(dl / g) are constants for polyethylene and polybutene, and xE and xB are the contents by weight % of ethylene and butene-1. The Mark-Houwink exponent α = 0.725 is used for all butene-1 / ethylene copolymers regardless of composition.

[0079] Melting point: Measured according to the method of ISO 11357-3:2018. Polypropylene and polypropylene compositions : Under a nitrogen stream, sample weight 5 - 7 mg, scan rate during cooling and heating 20 °C / min. The calibration of the instrument is performed using indium. Under a nitrogen stream, sample weight 5 - 7 mg, scanning rate during cooling and heating 20 °C / min After 10 days, the sample is subjected to DSC, cooled to -20 °C, and then heated to 200 °C at a scan rate of 10 °C / min. In this heating run, the first peak temperature from the low-temperature side of the thermogram is adopted as the melting point Tm(I).

[0080] Flexural modulus: For propylene polymers, it is measured according to ISO 178:2010 on injection-molded test specimens (80×10×4 mm, obtained according to ISO 1873-2:2007). For butene polymers, it is measured on compression-molded test specimens. The test specimens of butene copolymers are conditioned at 23 °C for 10 days before the test.

[0081] Polybutene: To measure the melting point (Tm(I)) of polybutene crystalline form I, the sample is melted, held at 200 °C for 5 minutes, and then cooled to 20 °C at a cooling rate of 10 °C / min. Then, the sample is stored at room temperature for 10 days. Each film has a xylene-insoluble fraction of 97 wt% and an MFR (ISO 1133-1:2011, 230 °C / 2.16 kg) of 2.0 g / 10 min and is overlaid on a 1000-μm-thick film of a propylene homopolymer. The overlaid films are adhered to each other by a flat-plate press at 35 kg×cm 2 of load at 200 °C and maintained in this state for 5 minutes. The laminate obtained with a coefficient of 7 in both the longitudinal and transverse directions, i.e., biaxially, at 160 °C using a Karo 4 Brueckener film stretching machine is stretched to obtain a 20-μm-thick BOPP film (18-μm homopolymer + 2-μm test composition).

[0082] Seal Strength and Seal Initiation Temperature (SIT): Cut a 6 × 35 cm film strip from the center of a BOPP test piece and overlap two film strips. The strip is covered with a 50-micron Teflon® foil and sealed with an RDM heat sealer under the following conditions: a smooth metal sealing bar, both bars heated, sealing time 0.5 seconds, and sealing pressure 0.14 MPa (20 psi). After an adjustment time of at least 10 minutes at 23°C and 50% R.H., cut six 15-mm-wide test pieces of a length that fits into the grips of a tensile testing machine from each sealed strip. The seal strength at a given temperature is tested with a dynamometer having a load cell capacity of 100 N, a crosshead speed of 100 mm / min, and a grip distance of 50 mm. The value of the seal strength is the average of six measurements of the same film sample. Repeat the test by raising or lowering the temperature by 1°C or 2°C. Define the lowest temperature at which a seal strength of 1.5 N or more is achieved as the seal initiation temperature SIT.

[0083] Determination of Hot Tack Hot tack is measured after sealing a BOPP test piece with a Brugger HSG heat sealer (equipped with a hot tack kit) at a pressure of 0.12 MPa (18 psi) for 5 seconds. Cut the film into a minimum length of 15 × 200 mm and seal by overlapping at various temperatures starting from 80°C and increasing the seal temperature by 5°C each time. Immediately after sealing, pull the test piece over a mandrel by a pulley to split the hot seal seam. At each seal temperature, the force (hot tack) required to split the still-hot sealed seam at half its length is determined using different drop weights designed to impact the test piece.

[0084] Haze: Measured according to ASTM D1003 for a 50-μm cast film.

[0085] Gloss: ASTM D2457 (angle 45°) on a 50-μm cast film and a BOPP film.

[0086] Raw Materials:

[0087] Adsyl5C30F : A polyolefin sold by Lyondell Basell, designed to be used as a sealing layer for coextruded film applications.

[0088] Irganox 1010: Pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) sold by BASF.

[0089] Irgafos 168: Tris(2,4-di-tert-butylphenyl) phosphite sold by BASF.

[0090] Examples E1 - E4 and Comparative Examples CE5 - CE6

[0091] Preparation of the catalyst system : For the preparation of the polypropylene composition, a Ziegler - Natta catalyst system containing the following is used.

[0092] - A titanium - containing solid catalyst component produced by the procedure described in Example 1 of European Patent No. 728769, using 9,9 - bis(methoxymethyl)fluorene as an internal electron donor compound.

[0093] - Triethylaluminum (TEAL) as a co - catalyst

[0094] - Dicyclopentyldimethoxysilane (DCPMS) as an external electron donor.

[0095] The solid catalyst component is contacted with TEAL and DCPMS in a pre - contact vessel under the conditions shown in Table 1.

[0096] Polymerization:Before introducing the catalyst system into the first polymerization reactor, the catalyst system is prepolymerized by maintaining it at 20 °C for 20 minutes in a suspended state in liquid propylene. In the first gas-phase polymerization reactor, a propylene-hexene copolymer (a) is produced by continuously supplying a fixed amount of a prepolymerized catalyst system, hydrogen as a molecular weight regulator, gaseous propylene, and hexene. The propylene-hexene copolymer produced in the first gas-phase reactor is continuously discharged and introduced into the second gas-phase polymerization reactor together with a quantitatively constant flow of gaseous hydrogen, propylene, hexene, and ethylene, where a propylene-hexene-ethylene terpolymer is produced. The polymer produced in the second gas-phase reactor is discharged as a continuous flow, and after purging unreacted monomers, it is introduced into the third gas-phase polymerization reactor as a continuous flow together with a quantitatively constant flow of gaseous hydrogen, ethylene, and propylene. The polymerization conditions are shown in Table 1.

Table 1

Table 1-1

[0097] To the polymer obtained from the polymerization experiment, 0.05 wt% of Irganox 1010, 0.1 wt% of Irgafos 168, and 0.05% of calcium stearate are added. The amounts of the additives are based on the total weight of the polymer containing the additives, and pelletization is carried out. Table 2 shows the characteristic properties of the polypropylene composition.

[0098] In Comparative Example CE6, Adsyl5C30F is used.

Table 2

Table 2-1

Table 2-2

Claims

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

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

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

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

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

6. The polypropylene composition (I) according to any one of claims 1 to 5, wherein the melting point Tm(I) measured by DSC is in the range of 125 °C to 143 °C, preferably 135 °C to 140 °C.

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

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

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

10. The film according to claim 9, which is a multilayer film comprising a base layer and at least one skin layer, and 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, which is non-oriented, preferably a cast film or an inflation film.

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

13. The film according to any one of claims 9 to 12, wherein the thickness of the entire film 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. - The seal start temperature (SIT) is in the range of 105 °C or lower, preferably 90 °C to 105 °C, more preferably 95 °C to 103 °C, still more preferably 97 °C to 102 °C, and / or - The seal strength at 130 °C is in the range of 3.0 to 4.5 N - The hot tack at 110 °C is in the range of 400 to 600 N, preferably 460 to 560 N

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