Propylene polymer composition

Abstract

A propylene polymer composition comprising: A) from 30 to 50 wt% of a propylene homopolymer having a melting point of from 152 to 162°C as measured by DSC; B) from 35 to 55 wt% of a copolymer of propylene with ethylene containing from 2.5 to 5.8 wt% of ethylene derived units; C) from 5 to 24 wt% of a copolymer of propylene with ethylene containing from 6.0 to 8.0 wt% of ethylene derived units; the sum of the amounts of A, B and C being 100 wt%.

Description

TECHNICAL FIELD

[0001] The present invention relates to a propylene polymer composition having excellent optical properties and good mechanical properties after sterilization. BACKGROUND

[0002] The excellent combination of properties conferred to isotactic polypropylene makes it suitable for a very large number of uses.

[0003] To improve the properties of isotactic polypropylene, the crystallinity of the propylene homopolymer is reduced by copolymerization of propylene with small amounts of ethylene and / or a-olefins such as 1-butene, 1-pentene and 1-hexene. In this way so-called atactic crystalline propylene copolymers are obtained, which are characterized, when compared to homopolymers, essentially by better flexibility and transparency.

[0004] However, although propylene atactic copolymers have good transparency, they cannot provide impact resistance sufficiently better than homopolymers which can be satisfactorily used for the above-mentioned applications, especially at low temperatures.

[0005] It has long been known that the impact resistance of polypropylene can be improved by adding to the homopolymer, by mechanical blending or sequential polymerization, a sufficient amount of an elastomeric propylene-ethylene copolymer. However, this improvement is obtained at the expense of the transparency of the material, especially after the sterilization process.

[0006] WO2013 / 135654 relates to a propylene polymer composition comprising:

[0007] A) 70 to 95 wt% of a random copolymer of propylene with ethylene containing 3.5 to 8.5 wt% of ethylene derived units, having a fraction soluble in xylene at 25°C of 7.1 to 15.2 wt% and a melting point higher than 142.0°C;

[0008] B) 5 to 35 wt% of a copolymer of propylene with ethylene containing 8.5 to 17.0 wt% of ethylene derived units;

[0009] The sum of A+B is 100;

[0010] wherein the melt flow rate MFR (ISO 1133 (230°C, 2.16 kg)) is 0.6 to 20.2 g / 10 min.

[0011] The composition shows a limited increase in haze of the film after the sterilization process. However, the haze after sterilization can be improved. SUMMARY

[0012] The Applicant has found a propylene polymer composition which can be used to obtain a sterilization film having a specific balance of properties.

[0013] It is therefore an object of the present disclosure a propylene polymer composition comprising:

[0014] A) from 30 to 50 wt% of a propylene homopolymer or a copolymer of propylene with ethylene containing up to 1.0 wt% of ethylene derived units, measured by NMR; having a melting point, measured by DSC, from 152 to 162 °C;

[0015] B) from 35 to 55 wt% of a copolymer of propylene with ethylene containing from 2.5 to 5.8 wt% of ethylene derived units, measured by NMR;

[0016] C) from 5 to 24 wt% of a copolymer of propylene with ethylene containing from 6.0 to 8.0 wt% of ethylene derived units, measured by NMR;

[0017] The sum of the amounts of A, B and C is 100 wt%;

[0018] wherein in the propylene polymer composition:

[0019] - the melt flow rate (ISO 1133 (230 °C, 2.16 kg) ranges from 0.5 to 15.2 g / 10 min; preferably from 1.0 to 15.2 g / 10 min;

[0020] - the fraction soluble in xylene, measured at 25 °C, ranges from 3.0 to 8.0 wt%;

[0021] - the total content of ethylene derived units, measured by NMR; ranges from 2.0 to 4.5 wt%;

[0022] - the content of ethylene derived units, measured by NMR; ranges from 18.2 to 23.4 wt% in the fraction soluble in xylene at 25 °C;

[0023] - the melting point, measured by DSC, ranges from 145 to 160 °C. DETAILED DESCRIPTION

[0024] The Applicant has found a propylene polymer composition which can be used to obtain sterilization films having a specific balance of properties.

[0025] It is therefore an object of the present disclosure a propylene polymer composition comprising:

[0026] A) from 30 wt% to 50 wt%; preferably 35 wt% to 45 wt%; more preferably 37 wt% to 43 wt% of a propylene homopolymer or a copolymer of propylene with ethylene comprising up to 1.0 wt%, preferably up to 0.8 wt%; more preferably up to 0.6 wt% of ethylene derived units, measured by NMR; a melting point measured by DSC in the range of 152 °C to 162 °C; preferably comprised between 155 °C and 161 °C; more preferably comprised between 156 °C and 160 °C;

[0027] B) 35 wt% to 55 wt%, preferably 40 wt% to 50 wt%; more preferably 40 wt% to 47 wt% of a copolymer of propylene with ethylene containing 2.5 wt% to 5.8 wt%, preferably containing 3.5 wt% to 5.3 wt%, more preferably containing 3.9 wt% to 4.9 wt% of ethylene derived units, measured by NMR;

[0028] C) 5 wt% to 24 wt%, preferably 8 wt% to 18 wt%, more preferably 12 wt% to 16 wt% of a copolymer of propylene with ethylene containing 6.0 wt% to 8.0 wt%, preferably containing 6.3 wt% to 7.8 wt% of ethylene derived units; more preferably comprised between 6.5 wt% and 7.3 wt%,

[0029] The sum of the amounts of A, B and C is 100 wt%;

[0030] wherein in the propylene polymer composition:

[0031] - a melt flow rate, (ISO 1133 (230 °C, 2.16 kg) in the range of 0.5 g / 10 min to 15.2 g / 10 min, preferably 1.0 g / 10 min to 15.2 g / 10 min; more preferably 4.2 g / 10 min to 11.2 g / 10 min; even more preferably 5.3 g / 10 min to 8.4 g / 10 min;

[0032] - a fraction of xylene solubles measured at 25 °C in the range of 3.0 wt% to 8.0 wt%; preferably 3.5 wt% to 7.5 wt%; more preferably 4.2 wt% to 6.3 wt%;

[0033] - a total content of ethylene derived units, measured by NMR; in the range of 2.0 wt% to 4.5 wt%; preferably in the range of 2.5 wt% to 4.2 wt%; in the range of 2.7 wt% to 3.7 wt%;

[0034] - content of ethylene-derived units, measured by NMR; in the fraction soluble in xylene at 25°C ranging from 18.2 wt% to 23.4 wt%; preferably ranging from 19.2 wt% to 22.4 wt%; more preferably ranging from 19.8 wt% to 21.4 wt%;

[0035] - melting point ranging from 145°C to 160°C; preferably ranging from 147°C to 159°C; more preferably ranging from 148°C to 158°C, measured by DSC.

[0036] The term "copolymer" means a polymer containing only propylene and ethylene.

[0037] The present application preferably has one or more of the following characteristics:

[0038] The tensile modulus of the composition is higher than 700 MPa;

[0039] The haze of the composition measured on a 70 pm film after sterilization is lower than 12.0%, preferably lower than 11.0%, more preferably lower than 10.5%;

[0040] The difference between the melting point and the seal initiation temperature (SIT) measured on a 70 pm is higher than 15°C; preferably higher than 16°C;

[0041] - hexane soluble fraction ranging from 0.5 wt% to 2.2 wt%; preferably ranging from 0.7 wt% to 1.9 wt%; more preferably ranging from 0.9 wt% to 1.6 wt%, measured on a film having a thickness of 100 pm.

[0042] Component A) of the composition of the present application can be obtained by polymerizing propylene and optionally ethylene according to known techniques, for example slurry polymerization using an inert hydrocarbon solvent as diluent, or bulk polymerization using a liquid monomer (e.g. propylene) as reaction medium. Furthermore, the polymerization process can be carried out in gas phase, operated in one or more fluidized bed or mechanically agitated bed reactors.

[0043] Components B) and C) of the composition of the present application can be obtained by polymerizing propylene and ethylene according to known techniques, for example slurry polymerization using an inert hydrocarbon solvent as diluent, or bulk polymerization using a liquid monomer (e.g. propylene) as reaction medium. Furthermore, the polymerization process can be carried out in gas phase, operated in one or more fluidized bed or mechanically agitated bed reactors.

[0044] The polymerization to obtain components A), B) and C) is generally carried out at a temperature ranging from 20 to 120°C, preferably from 40 to 80°C. When the polymerization is carried out in gas phase, the operating pressure is generally from 0.5 to 5 MPa, preferably from 1 to 4 MPa. In bulk polymerization, the operating pressure is generally from 1 to 8 MPa, preferably from 1.5 to 5 MPa. Hydrogen is generally used as molecular weight regulator.

[0045] Components A), B) and C) can be prepared according to methods well known in the art and blended together, otherwise they can be prepared in series. For example, component A) can be prepared in bulk in a loop reactor using propylene as reaction medium, the product prepared in the first loop can be fed in a second loop to polymerize in bulk component B) by using propylene as reaction medium, and the reaction product can be fed to a gas phase reactor to obtain component C) and the final composition.

[0046] Such polymerization can be carried out in the presence of a Ziegler-Natta catalyst. The basic components of said catalyst are a solid catalyst component comprising a titanium compound having at least one titanium-halogen bond and an electron donor compound, both supported on magnesium halide in active form. Another essential component (cocatalyst) is an organoaluminum compound, for example an alkylaluminum compound.

[0047] An external donor is optionally added.

[0048] The catalysts normally used in the process of the present application are able to produce polypropylene homopolymers having a xylene insoluble value greater than 90%, preferably greater than 95%, at ambient temperature.

[0049] Catalysts having the above characteristics are well known in the patent literature; particularly advantageous are the catalysts described in U.S. Patent 4,399,054 and European Patent 45977. Other examples can be found in U.S. Patent 4,472,524.

[0050] The solid catalyst component for said catalysts comprises, as electron donor (internal donor), a compound selected from ethers, ketones, lactones, compounds containing N, P and / or S atoms and esters of monocarboxylic and dicarboxylic acids.

[0051] Particularly suitable electron donor compounds are esters of phthalic acid and 1,3-diethers of formula:

[0052]

[0053] wherein R I and R II are the same or different and are C1-C 18 alkyl, C3-C 18 cycloalkyl or C7-C 18 aryl; R III and R IVidentical or different and are C1-C4 alkyl; or are 1,3-diethers, wherein the carbon atom in position 2 belongs to a cyclic or polycyclic structure consisting of 5, 6 or 7 carbon atoms or 5-n or 6-n' carbon atoms and n nitrogen atoms and n' heteroatoms selected from N, O, S and Si, respectively, wherein n is 1 or 2 and n' is 1, 2 or 3, which structure contains two or three unsaturations (cyclopolyene structure) and is optionally condensed with other cyclic structures, or is substituted by one or more substituents selected from linear or branched alkyl; cycloalkyl, aryl, aralkyl, alkaryl and halogen, or is fused with other cyclic structures and is substituted by one or more of the above-mentioned substituents, which can also be bound to the fused cyclic structure; a fused ring structure of one or more of the above-mentioned alkyl, cycloalkyl, aryl, aralkyl or alkaryl groups and optionally containing one or more heteroatoms as carbon or hydrogen atoms or both.

[0054] Ethers of this type are described in published European patent applications 361493 and 728769.

[0055] Representative examples of said diethers are 2-methyl-2-isopropyl-1,3-dimethoxypropane, 2,2-diisobutyl-1,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane, 2-isopropyl-2-isopentyl-1,3-dimethoxypropane, 9,9-bis(methoxymethyl)fluorene.

[0056] Other suitable electron donor compounds are phthalic acid esters, such as diisobutyl phthalate, dioctyl phthalate, diphenyl phthalate and benzyl butyl phthalate.

[0057] Alkylaluminum compounds used as cocatalysts include trialkylaluminums, such as triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, and linear or cyclic alkylaluminum compounds containing two or more Al atoms bound to each other via O or N atoms or SO4 or SO3 groups.

[0058] The alkylaluminum compounds are generally used in such an amount that the Al / Ti ratio is from 1 to 1000.

[0059] Electron donor compounds which can be used as external donors include aromatic acid esters, such as alkyl benzoates, in particular silicon compounds containing at least one Si-OR bond, wherein R is a hydrocarbon group.

[0060] Examples of silicon compounds are (tert-butyl)2Si(OCH3)2, (cyclohexyl)(methyl)Si(OCH3)2, (cyclopentyl)2Si(OCH3)2and (phenyl)2Si(OCH3)2and (1,1,2-trimethylpropyl)Si(OCH3)3.

[0061] 1,3-diethers having the above general formula can also be advantageously used. If the internal donor is one of these diethers, the external donor can be omitted.

[0062] In particular, even if many other combinations of the aforementioned catalyst components can allow to obtain propylene polymer compositions according to the present application, the terpolymers are preferably prepared by using a catalyst containing phthalate as internal donor and (cyclopentyl)2Si(OCH3)2as external donor, or said 1,3-diether as internal donor.

[0063] Preferably, said polypropylene composition is obtainable by a polymerization process carried out in the presence of a catalyst system comprising the product obtained by contacting (a) a solid catalyst component, preferably having a mean particle size of 15-80 μm, comprising a magnesium halide, a titanium compound having at least one Ti-halogen bond and at least two electron donor compounds, one of which is present in an amount of 40-90 mol% with respect to the total amount of donors and is selected from succinates, and the other is selected from 1,3-diethers, (b) a hydrocarbyl aluminium compound and optionally (c) an external electron donor compound.

[0064] The regulation of the molecular weight is carried out by using known regulators, in particular hydrogen.

[0065] The aforementioned MFR and [η] values are obtained by suitably metering the concentration of the molecular weight regulator in the relevant step.

[0066] The catalyst can be precontacted (prepolymerized) with small amounts of olefins.

[0067] The composition of the present application can also be obtained by preparing said components A), B) and C) separately, by operating with the same catalyst and substantially under the same polymerization conditions as the aforementioned ones (except that a completely continuous polymerization process is not carried out, but said components and fractions are prepared in separate polymerization steps), then mechanically blending said components and fractions in the molten or softened state. Conventional mixing devices can be used, such as screw extruders, in particular twin-screw extruders.

[0068] The composition of the present application can also contain additives commonly used in the art, such as antioxidants, light stabilizers, heat stabilizers, nucleating agents, colorants and fillers.

[0069] In particular, the addition of nucleating agents leads to a significant improvement in important physical-mechanical properties such as flexural modulus, heat deflection temperature (HDT), tensile strength at yield and transparency.

[0070] Typical examples of nucleating agents are p-tert-butyl benzoate and 1,3- and 2,4- dibenzylidene sorbitol.

[0071] The nucleating agent is preferably added to the composition of the present application in an amount of 0.05 to 2 wt%, more preferably 0.1 to 1 wt% relative to the total weight.

[0072] The addition of inorganic fillers such as talc, calcium carbonate and mineral fillers also brings some improvement in mechanical properties such as flexural modulus and HDT. Talc can also have a nucleating effect.

[0073] The melt flow rate of the composition can be adjusted by visbreaking the composition with methods known in the art such as peroxides.

[0074] The composition of the present application is particularly suitable for the production of films such as BOPP films, blown films or monolayer and multilayer cast films. Cast films are particularly preferred. The films obtained with the composition of the present disclosure can be easily sterilized with limited deterioration of optical properties such as haze and gloss. The films obtained with the composition of the present disclosure have a low SIT.

[0075] The composition of the present disclosure is particularly suitable for the production of retortable pouches. Retortable pouches are multi-material laminated packages that are sterilized to preserve their food content after sealing. The melting point and SIT of the composition of the present disclosure allow the preparation of fully recyclable single material packages, while in the art the outer layer is usually made of PET.

[0076] Therefore, another object of the present disclosure is a film prepared with the propylene polymer composition described above. Preferably, a cast film is prepared with the propylene polymer composition described above. More preferably, a multilayer film comprising the propylene polymer composition described above. Even more preferably, the propylene polymer composition described above is suitable for the preparation of multilayer sterilizable films.

[0077] Sterilization can be performed with methods known in the art, for example heating the polymer at a temperature higher than 120°C but lower than the melting point of the polymer.

[0078] Details are given in the following examples, which serve to illustrate and not to limit the present application.

[0079] Example

[0080] Melt flow rate

[0081] Determined according to ISO 1133 (230°C, 2.16 kg).

[0082] Propylene / ethylene copolymer 13 C NMR

[0083] 13 C NMR spectra were obtained on a Bruker Av-600 spectrometer equipped with a cryoprobe, operating in Fourier transform mode at 160.91 MHz at 120°C.

[0084] S at 29.9 ppmββ The peaks of carbon (nomenclature according to "Monomer sequence distribution in ethylene-propylene rubbers measured by13C NMR. 3. Use of reaction probability models" C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 1977, 10, 536) were used as internal references. The samples were dissolved at 120°C at 8 wt / v% concentration in 1,1,2,2-tetrachloroethane-d2. Each spectrum was obtained with a 90° pulse, a delay of 15 seconds between pulse and CPD to remove1H-13C couplings. 512 transients were stored in 32K data points using a spectral window of 9000 Hz.

[0085] The evaluation of the spectrum assignment, the triad distribution, the composition was made according to Kakugo ("Carbon-13 NMR determination of monomer sequence distribution in ethylene-propylene copolymers prepared with δ-titanium trichloride-diethylaluminum chloride" M. Kakugo, Y. Naito, K. Mizunuma and T. Miyatake, Macromolecules, 1982, 15, 1150) using the following equations:

[0086] PPP = 100T ββ / S PPE = 100T βδ / S EPE = 100T δδ / S

[0087] PEP = 100S ββ / S PEE = 100S βδ / S EEE = 100 (0.25S γδ + 0.5S δδ / S

[0088] S = T ββ + T βδ + T δδ + S ββ + S βδ + 0.25S γδ + 0.5S δδ

[0089] The molar percentage of ethylene content was evaluated using the following equation:

[0090] E% mol = 100 * [PEP + PEE + EEE] weight percent of ethylene content is evaluated using the following equation:

[0091]

[0092] where P mol% is the mole percent of propylene content, and MW E and MW P are the molecular weights of ethylene and propylene, respectively.

[0093] According to Carman (C. J. Carman, R. A. Harrington, and C. E. Wilkes, Macromolecules 1977; 10, 536), the product of the reaction ratios r1r2is calculated as:

[0094]

[0095] The tacticity of the propylene sequences is calculated as mm content from the ratio of the PPP mm T ββ (28.90-29.65 ppm) and the total T ββ (29.80-28.37 ppm).

[0096] The amount of ethylene derived units of components B) and C) is calculated by using the following formula

[0097] C 2总 = C 2A *A + C 2B *B + C 2c *C

[0098] for each stage of the polymerization process.

[0099] where C 2总 is the amount of ethylene derived units in the composition; C2 A is the amount of ethylene derived units in component A); C 2B is the amount of ethylene derived units in component B); C 2c is the amount of ethylene derived units in component C), and A, B and C are the amounts of components A), B) and C), where A + B + C = 1.

[0100] Seal initiation temperature (SIT)

[0101] Preparation of film samples

[0102] Cast films were prepared by extruding each test composition in a single screw Dr. Collin cast film extruder equipped with a three-layer co-extrusion cast film line (main extruder screw diameter 45 mm, L / D 30; two side extruder screw diameter 30 mm, L / D 30) at a melt temperature of 190-250 °C.

[0103] The produced cast films had a nominal thickness of 70 pm, which is the final sample thickness. Some films with a nominal thickness of 50 pm were also prepared in the same way.

[0104] Some films with a thickness of 50 pm were prepared by extruding each test composition in a single screw Collin extruder (screw length / diameter ratio 1 :25) at a film stretching speed of 7 m / min and a melt temperature of 210-250 °C. Each resulting film was laminated on a 1000 pm thick propylene homopolymer film having a 97 wt% xylene insoluble fraction and a MFR L of 2 g / 10 min. The laminated films were bonded to each other in a Carver press at 200 °C under a 9000 kg load for 5 minutes. The resulting laminates were stretched 6 times in machine direction and in transverse direction (i.e. biaxially) at 150 °C using a TOM Long film stretcher, thereby obtaining 20 pm thick films (18 pm homopolymer + 2 pm test). Test specimens of 2 x 5 cm were cut from the films.

[0105] Determination of SIT

[0106] Seal strength was measured according to ASTM F2029-16 and ASTM F88-15. By plotting the seal strength against the sealing temperature, a seal curve was generated. Then, the SIT on the cast film was determined as the temperature at the half height of the plateau of the seal curve (plateau defined as D F < 3 N).

[0107] Tensile modulus was measured on injection molded samples according to ISO 527-2 and ISO 1873-2.

[0108] Flexural modulus was measured according to ISO 178, complemented with conditions measured on injection molded samples according to ISO 1873-2.

[0109] Haze

[0110] Preparation of film test specimens

[0111] Films with a given thickness were prepared by extruding the polymer in a single screw Collin extruder (screw length / diameter ratio: 25) at a film stretching speed of 7 m / min and a melt temperature of 210-250 °C.

[0112] Determined on a cast film of the composition under test. The measurements were performed on 50 x 50 mm portions cut from the central area of the film.

[0113] The instrument used for the test was a Gardner photometer with a haze meter UX-10, equipped with a G.E. 1209 lamp and filter C. The instrument calibration was performed by making a measurement without sample (0% haze) and with the beam intercepted (100% haze).

[0114] Melting temperature, melting enthalpy and crystallization temperature

[0115] Determined by differential scanning calorimetry (DSC). The sample, having a weight of 6 ± 1 mg, was heated at a rate of 20 °C / min to 200 ± 1 °C and kept at 220 ± 1 °C for 2 minutes in a nitrogen stream, then cooled at a rate of 20 °C / min to 40 ± 2 °C, so as to keep the sample crystallized at this temperature for 2 minutes. Then, the sample was again melted to 220 ± 1 °C at a temperature increase rate of 20 °C / min. The melting scan was recorded, the thermogram was obtained and from this the melting temperature was read.

[0116] Solubility in xylene at 25 °C

[0117] The xylene solubles were measured according to ISO 16 152-2005; the solution volume was 250 ml, precipitated at 25 °C for 20 minutes, with 10 minutes stirring (magnetic stirrer) with the solution, dried at 70 °C.

[0118] Hexane extractables on 100 pm film

[0119] According to FDA 177,1520, the determination was made by suspending a sample of the composition in an excess of hexane. A film was prepared by extrusion. The suspension was placed in an autoclave at 50 °C for 2 hours, then the hexane was removed by evaporation and the dried residue was weighed.

[0120] Example 1

[0121] Preparation of solid intermediate components

[0122] The catalyst system was prepared according to Example 1 of EP728769. Dicyclopentyl dimethoxysilane (Donor-D) has been used as external donor.

[0123] Polymerization

[0124] The polymerization was run in a continuous mode in a series of three reactors equipped with means for transferring the product from one reactor to the one next to it. The first and second reactors were liquid phase loop reactors and the third reactor was a fluidized bed gas phase reactor. Components A) and B) were produced in the loop reactors and component C) was produced in the gas phase reactor. Hydrogen was used as molecular weight regulator. The gas phase (propylene, ethylene and hydrogen) was continuously analyzed by gas chromatography. At the end of the run the powder was discharged and dried under a stream of nitrogen.

[0125] The main polymerization conditions and analytical data related to the polymers produced in the three reactors are reported in Table 1. The properties of the polymers are reported in Table 4.

[0126] Table 1

[0127] Process conditions Example 1 Precontacting Temperature °C 12 Residence time (min) 15 Teal / donor ratio 3 Prepolymerization Temperature °C 20 Residence time (min) 8 Loop first reactor in liquid phase - component A) Temperature, °C 67 Pressure, bar 40 Residence time, min 50 H2feed, mol ppm 340 Split, wt% 40 Loop second reactor in liquid phase - component B) Temperature, °C 67 Pressure, bar 40 Residence time, min 45 H2feed, mol ppm 550 C2feed, kg / h 10 Split, wt% 45 Gas phase reactor - component C) Temperature, °C 80 Pressure, bar 18 Residence time, min 30 H2 / C3, mol / mol 0.005 H2 / C2, mol / mol 0.103 C2 / C2+C3, mol / mol 0.05 Split, wt% 15

[0128] Table 2

[0129] Component A) Example 1 C2content, * wt% <0.5 Split - 41％ T m DSC]]> ℃ 158.7 Component B) Split stage - 45％ C2component B) wt% 4.5 Component C) MFR dg / min 0.95 Split stage ％ 14％ C2component C) wt% 6.9

[0130] * = even if no ethylene was added to the reactor, a small amount of ethylene entered the first reactor from the second reactor.

[0131] ** calculated C2 = ethylene derived units

[0132] The polymer of Example 1 has been added with the additives reported in Table 3 and visbrooken.

[0133] Table 3

[0134] Irganox 1010 wt% 0.05 Irgafos 168 wt% 0.10 Calcium stearate wt% 0.05 Peroxan wt% 0.03

[0135] The properties of the polymers obtained after visbreaking are reported in Table 4.

[0136] Table 4

[0137] MFR dg / min 6.7 Xylene solubles wt% 5.8 C2content, NMR wt% 3.1 C2-XS content, NMR wt% 20.9 [CAT m DSC ℃ 150.4 T C DSC]]> ℃ 105.6 Hexane extractables (100 mm film) wt% 1.3 Tensile modulus MPa 910 Yield stress MPa 25.3 Yield elongation ％ 13.6 Break stress MPa 28.2 Break elongation ％ 590 Charpy @ +23 °C kJ / m2 8.1 Charpy @ 0 °C kJ / m2 2.3

[0138] The products of Table 4 have been used to produce cast films having a thickness of 50 μιη and 70 μιη, the properties of the films have been reported in Table 5.

[0139]

[0140] The haze of the films of Example 1 is compared in Table 6 with the haze reported for the 50 mm films of the polymer of Example 1 of WO2013 / 135654 (Comparative Example 3).

[0141] Example 1 (50 pm) 1 (70 pm) Comparative example 3 (50 pm) Haze % 0.24 1.16 2.4 Haze, after sterilization % Example 1 (50 pm) 1 (70 pm) Comparative example 3 (50 pm) Haze % 0.2 0.2 0.2 Haze, after sterilization % 0.2 0.2 0.2 - 9.1 15.5

[0142] The haze of the 50 mm film of Example 1 was significantly lower than the haze of the 50 mm film of Comparative Example 3. Furthermore, the haze of the 70 mm film of Example 1 was lower than the 50 mm of Comparative Example 3. The difference in haze before and after sterilization was significantly lower for the 70 mm of Example 1 compared to the 50 mm of Comparative Example 3 (7.94 vs. 13.1).

[0143] Sterilization procedure

[0144] The samples were placed in a steam sterilization autoclave Systec DX-65 set at 121 °C and 2.1 bar of internal pressure of nitrogen. After 20 minutes of treatment in the autoclave, the items were cooled to room temperature and conditioned at room temperature for 48 hours before testing.

Claims

1. A propylene polymer composition comprising: A) from 30 to 50 wt% of a propylene homopolymer or a copolymer of propylene with ethylene containing up to 1.0 wt% of ethylene derived units, measured by NMR; having a melting point, measured by DSC, from 152 to 162 °C; B) from 35 to 55 wt% of a copolymer of propylene with ethylene containing from 2.5 to 5.8 wt% of ethylene derived units, measured by NMR; C) from 5 to 24 wt% of a copolymer of propylene with ethylene containing from 6.0 to 8.0 wt% of ethylene derived units; the sum of the amounts of A), B) and C) being 100 wt%; wherein in the propylene polymer composition: - the melt flow rate, ISO 1133, 230 °C, 2.16 kg, is from 0.5 to 15.2 g / 10 min; - the fraction soluble in xylene, measured at 25 °C, ranges from 3.0 to 8.0 wt%; - the total content of ethylene derived units, measured by NMR; ranges from 2.0 to 4.5 wt%; - the content of ethylene derived units, measured by NMR; in the fraction soluble in xylene at 25 °C ranges from 18.2 to 23.4 wt%; - the melting point, measured by DSC, ranges from 145 to 160 °C.

2. The propylene polymer composition according to claim 1, wherein: component A) is from 35 to 45 wt%; component B) is from 40 to 50 wt%; component C) is from 8 to 18 wt%.

3. The propylene polymer composition according to claim 1, wherein component B) contains from 3.5 to 5.3 wt% of ethylene derived units.

4. The propylene polymer composition according to claim 1, wherein component C) contains from 6.3 to 7.8 wt% of ethylene derived units.

5. The propylene polymer composition according to claim 1, wherein the fraction soluble in xylene, measured at 25 °C, ranges from 3.5 to 7.5 wt%.

6. The propylene polymer composition according to claim 1, wherein the total content of ethylene derived units, measured by NMR, is from 2.5 to 4.2 wt%.

7. The propylene polymer composition according to claim 1, wherein the content of ethylene derived units, measured by NMR; in the fraction soluble in xylene at 25 °C is from 19.2 to 22.4 wt%.

8. The propylene polymer composition according to claim 1, wherein the melting point, measured by DSC, is from 147 to 159 °C.

9. The propylene polymer composition according to claim 1, wherein the fraction soluble in hexane, measured on a film having a thickness of 100 pm, is from 0.7 to 1.9 wt%.

10. The propylene polymer composition according to claim 1, wherein the melt flow rate, ISO 1133, 230 °C, 2.16 kg, is from 4.2 to 11.2 g / 10 min.

11. The propylene polymer composition according to claim 1, wherein the hexane soluble fraction measured on a film having a thickness of 100 pm is from 0.5 wt% to 2.2 wt%.

12. The propylene polymer composition according to claim 1, wherein the hexane soluble fraction measured on a film having a thickness of 100 pm is from 0.9 wt% to 1.6 wt%.

13. A film comprising the propylene polymer composition according to claim 1.

14. A cast film comprising the propylene polymer composition according to claim 1.

15. A sterilized cast film comprising the propylene polymer composition according to claim 1.

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