TITLE POLYPROPYLENE COMPOSITION FOR HEAT SEALABLE FILMS FIELD OF THE INVENTION [0001] The present disclosure relates to a polyolefin composition suitable for use in film applications, particularly in BOPP or cast films, having good sealing properties. BACKGROUND OF THE INVENTION [0002] Polypropylene heat sealable films are used in many common packaging applications, such as cigarette, candy, snack and food wraps. Polypropylene can also be used for shrink packaging, hygiene items and sterile wrap used in medical applications. [0003] In the packaging field, the polypropylene films are generally closed by heat sealing. Propylene homopolymers do not have good sealing properties, it is therefore 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 of copolymers of propylene and ethylene are suited for preparing films, in particular biaxially oriented polypropylene films (BOPP) and cast films, having low seal initiation temperature and low haze, see for instance WO2017/097579, WO2018/202396 and WO2020/249388. The crystallization temperature of the blends of the copolymers of the prior art is generally low. [0005] Polypropylene compositions comprising a blend of propylene-ethylene random copolymers, propylene-hexene random copolymers and propylene-hexene-ethylene terpolymers are also known from EP3670547A1, said compositions having SIT higher than 108°C, beneficial optical properties and low overall migration. [0006] In this frame, there is still the need to provide a polypropylene material having good thermal and optical properties, which is suitable for producing films having good sealing properties. SUMMARY OF THE INVENTION [0007] The present disclosure provides a polypropylene composition (I) comprising: FE7446-WO-01 [0008] (a) from 20% to 45% by weight of a propylene-hexene copolymer comprising from 3.5% to less than 7.0% by weight, based on the weight of (a), of units deriving from hexene; [0009] (b) from 25% to 45% by weight of a propylene-hexene-ethylene terpolymer comprising from 6.0% to 12.0% by weight of units deriving from hexene and from 0.5% to 3.5% by weight of units deriving from ethylene, based on the weight of (b); and [0010] (c) from 20% to 45% by weight of a propylene-ethylene copolymer comprising from 0.5% to 5.0% by weight, based on the weight of (c), of units derived from ethylene, [0011] wherein 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, like high melting and crystallization temperature, and good optical properties, like low haze. [0013] The polypropylene composition (I) of the present disclosure is suitable for producing films having good sealing properties, like low seal initiation temperature (SIT), high seal strength and high hot tack. [0014] A further object of the present disclosure is therefore a film comprising the polypropylene composition (I), preferably in at least one skin layer. [0015] While multiple embodiments are disclosed, still other embodiments will become apparent to those skilled in the art from the following detailed description. As will be apparent, certain embodiments, as disclosed herein, are capable of modifications in various obvious aspects, all without departing from the spirit and scope of the claims as presented herein. Accordingly, the following detailed description is to be regarded as illustrative in nature and not restrictive. DETAILED DESCRIPTION OF THE INVENTION [0016] In the context of the present disclosure; [0017] - the percentages are expressed by weight, unless otherwise specified; [0018] - the total weight of a (polypropylene) composition sums up to 100%, unless otherwise specified; [0019] - the term “comprising” referred to a polymer, a plastic material, a polymer composition, mixture or blend, should be construed to mean “comprising or consisting essentially of”; FE7446-WO-01 [0020] - the term “consisting essentially of” means that, in addition to those components which are mandatory, other components may also be present in the material, provided that the essential characteristics of the material are not materially affected by their presence. Examples of components that, when present in customary amounts, do not materially affect the characteristics of a polymer or of a polyolefin composition, mixture or blend are catalyst residues and processing aids; [0021] - the term “copolymer” is referred to a polymer deriving from the intentional polymerization of two different comonomers, i.e. the term “copolymer” does not include terpolymers; [0022] - the term “terpolymer” is referred to a polymer deriving 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” is referred to an outermost layer of a multilayer film; [0025] - the term “base layer” is referred to the innermost layer of a multilayer film, onto which at least one skin layer is preferably adhered. [0026] The present disclosure provides a polypropylene composition (I) comprising: [0027] (a) from 20% to 45% by weight, preferably from 27% to 37% by weight, of a propylene-hexene copolymer comprising from 3.5% to less than 7.0% by weight, based on the weight of (a), of units deriving from hexene; [0028] (b) from 25% to 45% by weight, preferably from 30% to 40% by weight, of a propylene-hexene-ethylene terpolymer comprising from 6.0% to 12.0% by weight of units deriving from hexene and from 0.5% to 3.5% by weight of units deriving from ethylene, based on the weight of (b); and [0029] (c) from 20% to 45% by weight, preferably from 27% to 37% by weight, of a propylene-ethylene copolymer comprising from 0.5% to 5.0% by weight, based on the weight of (c), of units derived from ethylene, [0030] wherein 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. FE7446-WO-01 [0032] Preferably, the propylene-hexene copolymer (a) comprises from 4.0% to 6.5% by weight, more preferably from 4.5% to 6.0% by weight, based on the weight of (a), of units deriving from hexene. [0033] More preferably, the propylene-hexene copolymer (a) has at least one of, preferably all, the following properties: [0034] - comprises a xylene soluble fraction at 25°C XS(a) ranging from 9.0% to 20.0% by weight, preferably from 10.0% to 17.0% by weight, based on the weight of (a); and/or [0035] - has melting temperature Tm(a) measured by DSC ranging from 125°C to 143°C, preferably from 130°C to 140°C, more preferably from 132°C to 138°C; and/or [0036] - has melt flow rate MFR(a) measured according to the method ISO 1133-1:2011 (230°C/2.16kg) ranging from 3.5 to 8.5 g/10min. [0037] Preferably, the propylene-hexene-ethylene terpolymer (b) comprises from 6.7% to 11.0% by weight, more preferably from 7.0% to 10.0% by weight, of units deriving from hexene and from 0.5% to 2.8% by weight, more preferably from 1.5% to 2.5% by weight, still more preferably from 1.7% to 2.5% by weight, of units deriving from ethylene, wherein the amounts of units deriving from hexene and from ethylene are based on the weight of (b). [0038] Preferably, the propylene-ethylene copolymer (c) comprises from 0.5 to less than 3.5% by weight, more preferably from 1.0% to 3.0% by weight, still more preferably from 1.0% to 2.8% by weight, of units deriving from ethylene, based on the weight of (c). [0039] In one embodiment, the polypropylene composition (I) further comprises up to and including 5.0% by weight, more preferably from 0.01% to 5.0% by weight, of at least one additive (d) selected from the group consisting of nucleating agents, antistatic agents, anti-oxidants, light stabilizers, slipping agents, antiacids, melt stabilizers, and combinations thereof, the amount of additive being based on the total weight of the polypropylene composition (I) comprising 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 of, preferably all, the following properties: FE7446-WO-01 [0042] - comprises a xylene soluble fraction at 25°C XS(I) ranging from 12.0% to 20.0% by weight, preferably from 14.0% to 17.0% by weight, based on the weight of the polypropylene composition (I); and/or [0043] - a melting temperature Tm(I) measured by DSC ranging from 125°C to 143°C, preferably from 135°C to 140°C; and/or [0044] - a crystallization temperature Tc(I) measured by DSC ranging from 85°C to 100°C, more preferably from 89°C to 95°C; and/or [0045] - melt flow rate MFR(I) measured according to the method ISO 1133-1:2011 (230°C/2.16kg) ranging from 2.0 to 12.0 g/10min, more preferably from 4.0 to 10.0 g/10 min, more preferably from 4.5 to 8.0 g/10 min. [0046] Preferably, the polypropylene composition (I) also has haze value, measured according to the method ASTM D1003 on BOPP films, of up to and including 1.00%, preferably ranging from 0.20% to 1.00%. [0047] In a preferred embodiment, the total amount of hexene comprised in the polypropylene composition (I) ranges from 3.0% to 7.0% by weight, preferably from 3.5% to 6.0% by weight and the total amount of ethylene ranges from 0.5% to 3.0% by weight, preferably from 1.0% to 2.5% by weight, wherein the total amounts of hexene and ethylene are based on the weight of the polypropylene composition (I), the weight being 100. [0048] The polypropylene composition (I) is obtainable melt blending the components (a), (b), (c) and optionally (d) or, preferably, the polypropylene composition (I) is a reactor blend of the components (a), (b) and (c) optionally melt blended with component (d), wherein the reactor blend is obtained by polymerizing the relevant monomers in the gas-phase in at least three polymerization stages, wherein the second and each subsequent polymerization stage is carried out in the presence of the polymer produced 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 systems comprising: [0050] (1) a solid catalyst component comprising a magnesium halide support on which a Ti compound having at least a Ti-halogen bond is present, and a stereoregulating internal donor; [0051] (2) optionally, but preferably, an Al-containing cocatalyst; and FE7446-WO-01 [0052] (3) optionally, but preferably, a further electron-donor compound (external donor). [0053] The solid catalyst component (1) preferably comprises TiCl ₄ in an amount securing the presence of from 0.5 to 10% by weight of Ti with respect to the total weight of the solid catalyst component (1). [0054] The solid catalyst component (1) comprises at least one stereoregulating 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 the esters of phthalic acids such as those described in EP45977A2 and EP395083A2, in particular di-isobutyl phthalate, di-n-butyl phthalate, di-n-octyl phthalate, diphenyl phthalate, benzylbutyl phthalate and combinations thereof. [0056] Esters of aliphatic acids can also be selected from esters of malonic acids such as those described in WO98/056830, WO98/056833, WO98/056834, esters of glutaric acids such as those disclosed in WO00/55215, and esters of succinic acids such as those disclosed WO00/63261. [0057] Particular type of diesters are those deriving from esterification of aliphatic or aromatic diols such as those described in WO2010/078494 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] Specific mixtures of internal donors, in particular of aliphatic or aromatic mono or dicarboxylic acid esters and 1,3-diethers as disclosed in WO07/57160 and WO2011/061134 can be used as internal donor. [0060] Preferred magnesium halide support is magnesium dihalide. [0061] The amount of internal donor that remains fixed on the solid catalyst component (1) is 5 to 20% by moles, with respect to the magnesium dihalide. [0062] The preparation of catalyst components according to a general method is described for example in European Patent Applications US4,399,054, US4,469,648, WO98/44009A1 and EP395083A2. [0063] The catalyst system preferably comprises 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 from 1 to 1000, preferably from 20 to 800. FE7446-WO-01 [0064] In preferred embodiments, the catalyst system comprises a further electron donor compound (3) (external electron donor) selected among silicon compounds, ethers, esters, amines, heterocyclic compounds, particularly 2,2,6,6-tetramethylpiperidine, and ketones. [0065] Preferred silicon compounds are selected among methylcyclohexyldimethoxysilane (C-donor), dicyclopentyldimethoxysilane (D-donor) and mixtures thereof. [0066] The polymerization temperature is preferably comprised in 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 the gas phase. [0067] The molecular weight of the polymers is regulated by feeding a molecular weight regulator, like hydrogen, into a 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 polymer prepared 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 polymer formed and the catalyst used in the preceding polymerizations steps. Gas-phase reactors are of the type known in the art. [0069] 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. [0070] The polypropylene composition (I) is suitable for producing films, in particular heat sealable films having low heat sealing initiation temperature (SIT). The polypropylene composition (I) also has relatively high melting temperature Tm(I) and crystallization temperature Tc(I). [0071] Advantageously, the ΔTm-SIT (difference between the Tm(I) and the SIT of the polypropylene composition (I) measured on a BOPP film) is broad, thereby allowing good processability of the films. [0072] In one embodiment, the ΔTm-SIT value ranges from 30° to 45°C, preferably from 30° to 40°C, wherein the Tm(I) and the SIT are measured as illustrated below. [0073] In a further aspect, the present disclosure refers to a film comprising or consisting of the polypropylene composition (I) as described above. FE7446-WO-01 [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 propylene homopolymers, propylene copolymers 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 film of the present disclosure has total film thickness ranging from 10 to 70 microns, preferably from 15 to 30 microns, more preferably from 18 to 22 microns. [0079] The film of the present disclosure is obtained according to known processes. [0080] In a preferred embodiment, the film of the present disclosure has at least one of, preferably all, the following properties: [0081] - seal initiation temperature (SIT) lower than 105°C, preferably ranging from 90° to 105°C, more preferably from 95° to 103°C, even more preferably from 97° to 102°C; and/or [0082] - seal strength at 130°C ranging from 3.0 to 4.5 N; and/or [0083] - hot tack at 110°C ranging from 400 to 600 N, preferably from 460 to 560 N; and/or [0084] - gloss on BOPP film ranging from 83 to 95, preferably from 85 to 90. [0085] The features describing the subject matter of the present disclosure are not inextricably linked to each other. Hence, preferred ranges of one feature may be combined with more or less preferred ranges of a different feature, independently from their level of preference. [0086] EXAMPLES [0087] The following examples are illustrative only, and are not intended to limit the scope of the disclosure in any manner whatsoever. [0088] CHARACTERIZATION METHODS: the following methods are used to determine the properties indicated in the description, claims and examples. [0089] Melt Flow Rate: Determined according to the method ISO 1133-1:2011 (230°C/2.16 kg for the propylene polymers and 190°C/2.16kg for the butene-1 copolymer). [0090] Solubility in xylene at 25°C for propylene polymers: 2.5 g of polymer sample and 250 ml of xylene are introduced in a glass flask equipped with a refrigerator and a magnetic stirrer. FE7446-WO-01 The temperature is raised in 30 minutes up to 135°C. The obtained clear solution is kept under reflux and stirring for further 30 minutes. The solution is cooled in two stages. In the first stage, the temperature is lowered to 100°C in air for 10 to 15 minute under stirring. In the second stage, the flask is transferred to a thermostatically controlled water bath at 25°C for 30 minutes. The temperature is lowered to 25°C without stirring during the first 20 minutes and maintained at 25°C with stirring for the last 10 minutes. The formed solid is filtered on quick filtering paper (eg. Whatman filtering paper grade 4 or 541). 100 ml of the filtered solution (S1) is poured in a previously weighed aluminum container, which is heated to 140°C on a heating plate under nitrogen flow, to remove the solvent by evaporation. The container is then kept on an oven at 80°C under vacuum until constant weight is reached. The amount of polymer soluble in xylene at 25°C is then calculated. XS(I) and XSA values are experimentally determined. The fraction of component (B) soluble in xylene at 25°C (XSB) can be calculated from the formula: XS = W(A)×(XSA) + W(B)×(XSB) wherein W(A) and W(B) are the relative amounts of components (A) and (B), respectively, and W(A)+ W(B)=1. [0091] Comonomer content of the polypropylene composition: determined by IR using Fourier Transform Infrared Spectrometer (FTIR). The spectrum of a pressed film of the polymer is recorded in absorbance vs. wavenumbers (cm-1). The following measurements are used to calculate ethylene and hexene-1 content: - Area (At) of the combination absorption bands between 4482 and 3950 cm-1 which is used for spectrometric normalization of film thickness; - a linear baseline is subtracted in the range 790 – 660 cm-1 and the remaining constant offset is eliminated; - the content of ethylene and hexene-1 are obtained by applying a Partial Least Square (PLS1) multivariate regression to the 762 – 688 cm-1 range. The method is calibrated by using polymer standards based on 13C NMR analyses. Sample preparation: Using a hydraulic press, a thick sheet is obtained by pressing about 1g of sample between two aluminum foils. Pressing temperature is 180±10°C (356°F) and about 10 kg/cm2 pressure for about one minute (minimum two pressing operations for each specimen). A small portion is cut from this sheet to mold a film. Recommended film thickness ranges between 0.02-0.05 cm. FE7446-WO-01 [0092] Comonomer content of butene-ethylene copolymers: ¹³ C NMR spectra are acquired on a Bruker AV-600 spectrometer equipped with cryoprobe, operating in the Fourier transform mode at 120°C. The samples are dissolved in 1,1,2,2-tetrachloroethane-d2 at 120°C with a 8 % wt/v concentration. Each spectrum is acquired with a 90° pulse, and 15 seconds of delay between pulses and CPD to remove 1H-13C coupling. The spectrometer is operated at 160.91 MHz. The peak of the Sδδ carbon (nomenclature according to “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 in 32K data points using a spectral window of 9000 Hz. [0093] The assignments of the spectra, the evaluation of triad distribution and the composition were made 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)] using the following: BBB = 100 Tββ/S BBE = 100 Tβδ/S EBE = 100 Pδδ/S BEB = 100 Sββ/S BEE = 100 S _{^ ^} /S EEE = 100(0.25 Sγδ + 0.5 Sδδ)/S S = T _ββ + T _βδ + P _δδ + S _ββ + S _{^ ^} + 0.25 S _γδ + 0.5 S _δδ [0094] The total amount of 1-butene and ethylene as molar percent is calculated from triad using the following relations: [E] = EEE+BEE+BEB [B] = BBB+BBE+EBE [0095] The weight percentage of ethylene content (E% wt) is calculated using the following equation: wherein [B] mol = the molar percentage of 1-butene content; MWE = molecular weights of ethylene MWB = molecular weight of 1-butene. [0096] Molecular weight distribution Mw/Mn: The determination of the means Mn and Mw, and Mw/Mn derived therefrom was carried out using a Waters GPCV 2000 apparatus, which was equipped with a column set of four PLgel Olexis mixed-gel (Polymer Laboratories) and an FE7446-WO-01 IR4 infrared detector (PolymerChar). The dimensions of the columns were 300 ^ 7.5 mm and their particle size 13 µm. The mobile phase used was 1-2-4-trichlorobenzene (TCB) and its flow rate was kept at 1.0 ml/min. All the measurements were carried out at 150°C. Solution concentrations were 0.1 g/dl in TCB and 0.1 g/l of 2,6-diterbuthyl-p-chresole were added to prevent degradation. For GPC calculation, a universal calibration curve was obtained using 10 polystyrene (PS) standard samples supplied by Polymer Laboratories (peak molecular weights ranging from 580 to 8500000). A third order polynomial fit was used for interpolating the experimental data and obtaining the relevant calibration curve. Data acquisition and processing was done using Empower (Waters). The Mark-Houwink relationship was used to determine the molecular weight distribution and the relevant average molecular weights: the K values were KPS = 1.21 ^ 10-4 dL/g and KPB = 1.78 ^ 10-4 dL/g for PS and PB respectively, while the Mark-Houwink exponents ^ = 0.706 for PS and ^ = 0.725 for PB were used. For butene-1/ethylene copolymers, as far as the data evaluation is concerned, it is assumed that the composition is constant in the whole range of molecular weights and the K value of the Mark-Houwink relationship is calculated using a linear combination as reported below: where KEB is the constant of the copolymer, KPE (4.06 ^ 10 ^{^4} , dL/g) and KPB (1.78 ^ 10 ^{^4} dl/g) are the constants of polyethylene and polybutene and xE and xB are the ethylene and the butene-1 weight% content. The Mark-Houwink exponent ^ = 0.725 is used for all the butene-1/ethylene copolymers independently of their composition. [0097] Melting temperature: measured according to the method ISO 11357-3:2018. Polypropylene and polypropylene compositions: scanning rate of 20°C/min in cooling and heating, on a sample weighting 5-7 mg, under nitrogen flow. Instrument calibration made with Indium. Polybutene: to determine the melting temperature of the polybutene crystalline form I (Tm(I)), the sample was melted, kept at 200°C for 5 minutes and then cooled down to 20°C with a cooling rate of 10°C/min. The sample was then stored for 10 days at room temperature. After 10 days the sample was subjected to DSC, it was cooled to -20°C, and then it was heated at 200°C with a scanning speed corresponding to 10°C/min. In this heating run, the first peak temperature coming from the lower temperature side in the thermogram was taken as the melting temperature Tm(I). [0098] Flexural Modulus: determined according to the method ISO 178:2010 on injection molded test specimens (80 x 10 x 4 mm) obtained according to the method ISO 1873-2:2007 for FE7446-WO-01 propylene polymers or on compression molded specimens for butene polymers. Specimens of butene copolymers were conditioned for 10 days at 23°C before testing. [0099] Preparation of BOPP film test specimens. Films with thickness of 50 μm are prepared by extruding each test composition in a single screw Collin extruder (length/diameter ratio of screw 1:25) at a film drawing speed of 7 m/min and a melt temperature of 210-250°C. Each film is superimposed on a 1000μm thick film of a propylene homopolymer having a xylene insoluble fraction of 97 wt% and a MFR (ISO1133-1:2011, 230°C/2.16kg) of 2.0 g/10 min. The superimposed films are bonded to each other in a plat press at 200°C under a 35 kg x cm ² load, which is maintained for 5 minutes. The resulting laminates are simultaneously stretched longitudinally and transversally, i.e. biaxially, by a factor 7 with a Karo 4 Brueckener film stretcher at 160°C, thus obtaining a 20μm thick BOPP film (18μm homopolymer + 2μm test composition). [0100] Seal strength and seal initiation temperature (SIT): Film strips, 6x35cm are cut from the center of the BOPP test specimens and two film strips are superimposed. The strips are covered with 50 micron Teflon® foil and sealed by a RDM Heat Sealer, in the following conditions: smooth metallic sealing bars, both bars heated; sealing time 0.5 sec.; sealing pressure of 0.14 MPa (20 psi). After at least 10 minutes of conditioning time at 23°C and 50 %R.H. six test specimens are cut from each sealed strip, 15 mm wide, long enough to be claimed in the tensile tester grips. The seal strength at a given temperature is tested with a dynamometer at load cell capacity 100 N, cross speed 100 mm/min and grip distance 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 of 1° or 2°C. The lowest temperature at which a seal strength equal to or greater than 1.5N is achieved is defined as the sealing initiation temperature SIT. [0101] Determination of the hot tack. Hot tack is measured after sealing the BOPP test specimens with a Brugger HSG Heat-Sealer (with Hot Tack kit) at a pressure of 0.12 MPa (18 psi) for 5 sec. Films are cut at a minimum length of 15x200mm, superimposed and sealed at different temperatures, starting at 80°C and increasing the sealing temperature by 5°C. Immediately after sealing, the test specimen are pulled onto a mandrel by means of a pulley to split the hot seal seam. For each sealing temperature, the force necessary to split the still hot sealed seam at half of its length (hot tack) is determined using different drop weights made to impact the test specimens. [0102] Haze: measured on ASTM D1003 on 50μm cast films. [0103] Gloss: ASTM D2457 (angle 45°) on 50μm cast films and on BOPP films. FE7446-WO-01 [0104] RAW MATERIALS: [0105] Adsyl 5C30F: a polyolefin marketed by LyondellBasell, designed for use as sealing layer in coextruded film applications. [0106] Irganox 1010: Pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate) marketed by BASF. [0107] Irgafos 168: tris(2,4-di-tert.-butylphenyl) phosphite marketed by BASF. [0108] Examples E1-E4 and comparative examples CE5-CE6 [0109] Preparation of the catalyst system: for the preparation of the polypropylene compositions a Ziegler-Natta catalyst system was used comprising: [0110] - a titanium-containing solid catalyst component prepared with the procedure described in EP728769, Example 1, according to which 9,9-bis(methoxymethyl)fluorene is used as internal electron donor compound; [0111] - triethylaluminium (TEAL) as co-catalyst; [0112] - dicyclopentyl dimethoxy silane (DCPMS) as external electron donor. [0113] The solid catalyst component was contacted with TEAL and DCPMS in a pre- contacting vessel, in the conditions reported in table 1. [0114] Polymerization: before entering the catalyst system into the first polymerization reactor, the catalyst system is prepolymerized by maintaining the catalyst system in suspension in liquid propylene at 20°C for 20 minutes. In the first gas phase polymerization reactor the propylene-hexene copolymer (a) is produced by feeding a continuous and constant flow of the prepolymerized catalyst system, hydrogen as molecular weight regulator, propylene and hexene in gas state. The propylene-hexene copolymer produced in the first gas phase reactor is continuously discharged and is introduced, together with a quantitatively constant flow of hydrogen, propylene, hexene and ethylene in the gas state into the second gas phase polymerization reactor, where the propylene-hexene-ethylene terpolymer is produced. The polymer produced in the second gas phase reactor is discharged in a continuous flow and, after purging of unreacted monomers, is introduced, in a continuous flow, into the third gas phase polymerization reactor, together with quantitatively constant flows of hydrogen, ethylene and propylene in the gas state. The polymerization conditions are reported in table 1. FE7446-WO-01 Table 1 [0115] The polymers obtained from the polymerization runs were additivated with 0.05 wt.% of Irganox 1010, 0.1 wt.% of Irgafos 168, 0.05% of calcium stearate, wherein the amounts of the FE7446-WO-01 additives are based on the total weight of the polymers including the additives, and pelletized. Table 2 illustrates the characterizing features of the polypropylene compositions. [0116] In comparative example CE6 Adsyl 5C30F was used. Table 2 FE7446-WO-01 FE7446-WO-01