MXPA00008257A - Bottle closures made of polyolefins - Google Patents

Abstract

A bottle closure comprising an olefin polymer composition (A) which comprises:1) 90-100%by weight of a crystalline propylene homopolymer or propylene/C2-C10&agr;-olefin random copolymer;said polymers containing at least 94%by weight a fraction insoluble in xylene at room temperature;and 2) 0-10%by weight of an ethylene/C3-C10&agr;-olefin elastomeric copolymer;provided that when the amount of Polymer (2) is 0%by weight, Polymer (1) is selected from the above said random copolymers. Said composition (A) having a flexural elastic modulus value at 23°C at least of 1620 MPa;a value of the strength at yield at 23°C at least of 33 MPa;and an IZOD impact resistance value at 0°C at least of 2.5 kJ/m2.

Description

CLOSURES FOR BOTTLES MADE OF POLIOLEPHINS The present invention relates to closures for bottles made from olefin polymer resins. In particular, it refers to screw caps for bottles. The use of thermoplastic olefin polymer resins for the production of bottle closures is known per se. In particular, the use of a propylene and high density polyethylene homopolymer is already known. Closures for bottles made from such polymers are widely used, for example, in beverage industries throughout the world. However, their use is limited due to the fact that bottles with said closures can not be subjected to heat treatments at high temperatures, such as severe pasteurization cycles at 80-90 ° C. Polyolefin closures that can be pasteurized are described in the patent specification of GB 1, 387,556. According to the description of said GB patent specification, the bottle closures are capable of withstanding temperatures up to 75 ° C. Currently, the need to pasteurize beverages in bottles at higher temperatures is felt. Examples of beverages that could be pasteurized are non-alcoholic beverages, in particular cider, fruit juices and some carbonated beverages. It is now advisable to carry out the pasteurization cycles at a temperature above 75 ° C, generally around 77 to 88 ° C. The pasteurization time is normally 10 to 50 minutes, more typically 10-30 minutes. Due to the low mechanical properties, in particular in terms of heat resistance and slippage, of the olefin polymers hitherto employed, such closures do not withstand the high pressure of the contents within the bottle during the pasteurization cycle. As a result, gas and liquid tend to escape during the pasteurization cycle and the closures can even fly out of the bottles. Surprisingly, it has now been found that closures for bottles made of particular polypropylenes can be subjected to heat treatments at high temperatures, in particular pasteurization cycles. Accordingly, the closures for bottles of the present invention are capable of withstanding heat treatments, in particular pasteurization, at said high temperature without deficiencies. In particular, the problem of fragility is solved. Therefore, it is now possible to pasteurize bottles with the propylene polymer closures of the present invention at temperatures above 75 ° C and for a relatively long time (for example 10-75 minutes) without the problems encountered with polypropylene closures. used so far. In addition to the above, the closures for bottles of the present invention do not undergo any deformation at high temperatures.

Also, the types of polymers selected to produce the closures for bottles of the present invention are suitable for use in contact with food and beverages. Therefore, an object of the present invention is a bottle closure comprising or substantially made of an olefin polymer composition (A) comprising: 1) 90-100% by weight, preferably 92-98, very preferably 94-98, of a crystalline propylene homopolymer or random copolymer thereof with a comonomer selected from ethylene and an α-olefin of C -C?; said polymers contain at least 94% by weight, preferably at least 96% of a fraction insoluble in xylene at room temperature (Polymer (i)); and 2) 0-10% by weight, preferably 2-8%, most preferably 2-6%, of an elastomeric copolymer of ethylene with propylene or an α-olefin of C -C- or mixtures thereof and, optionally, from 0.5 to 10% by weight of a diene, said elastomeric copolymer contains from 40% to 85% by moles of ethylene (Polymer (2)); provided that when the amount of the Polymer (2) is 0% by weight, the Polymer (1) is selected from the aforementioned random copolymers. The polymer composition (A) typically has an elastic modulus of flexure (FM) value at 23 ° C at least 1620 MPa, preferably 1650-2500 MPa; a resistance value during deformation at 23 ° C at least 33 MPa, preferably up to 45 MPa; an impact resistance value IZOD at 0 ° C at least 2.5 kJ / m2, preferably up to 20 kJ / m2. Said polymer composition (A) has approximately a VICAT value of at least 150 ° C, preferably 155 ° C, up to 160 ° C. The methods for measuring the above properties and insoluble fraction in xylene are described below. Preferably Polymer (1) is a propylene homopolymer. When the copolymers are used as Polymer (1), copolymers of propylene with a comonomer selected from ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene and 1-octene are preferred. The most preferred comonomers are ethylene and butene-1. The comonomer content normally varies from 0.5 to 6% by weight, preferably 2 to 5%. The MFRL value of the polymer composition (A) is typically 0.3 to 100 g / 10 min, preferably 0.7-30 g / 10 min, most preferably 1-1 5 g / 10 min. A suitable example of Polymer (1) above is a crystalline propylene polymer with a broad molecular weight distribution (hereinafter referred to as Polymer (I)) in terms of the PM / NM ratio. Propylene homopolymer is preferred. Typically Polymer (I) has PM / NM values of 50 to 60, preferably 5 to 30. The intrinsic viscosity values [α] of Polymer (I) determined in tetrahydronaphthalene at 135 ° C may vary from 1.2 to 7 dl / g, for example.

Suitable examples of Polymer (I) are those containing 10-65% by weight of a high molecular weight fraction (fraction (i)) and 35-60% by weight of a low molecular weight fraction (fraction (ii)) as described in European patent application 573862. The polymer (2) is preferably selected from ethylene / propylene copolymers, ethylene / butene-1 copolymers, ethylene / propylene / C4-C10 α-olefin copolymers containing from 5 to 15 mol% of the α-olefin. Preferably, the Polymer (2) comprises from 0 to 40% by weight of a fraction insoluble in xylene at room temperature. The Polymer (2) can be added in the pure state or as a mixture with crystalline polyolefins. Said mixture can replace Polymer (2) totally or partially. Suitable examples of said mixtures are thermoplastic elastomeric olefin polymer compositions. Accordingly, an object of the present invention is also a bottle closure comprising a mixture of said Polymer (I) and a thermoplastic elastomeric olefin polymer composition comprising the following components (weight percentage): a) 70-97 %, preferably 78-97%, of a propylene homopolymer containing more than 90%, preferably more than 94%, of a fraction insoluble in xylene at room temperature, or a copolymer of crystalline propylene with ethylene or a olefin of C4-C10 or a mixture thereof, which contains more than 85% by weight of propylene; the copolymer contains at least 85% by weight of a fraction insoluble in xylene at room temperature; b) 0-10%, preferably 1-10%, of a crystalline copolymer containing ethylene, insoluble in xylene at room temperature; and c) 3-20%, preferably 3-12%, of an amorphous ethylene copolymer with propylene and / or a C4-C10 1-olefin and, optionally, from 1 to 10% of a diene, soluble in xylene to ambient temperature, and containing 20 to 75% ethylene. In this case, the aforementioned Polymer (2) is constituted by the sum of components (b) and (c). Preferably said mixture comprises 30-80% by weight of the Polymer (I) and 20-70% by weight of the thermoplastic elastomeric olefin polymer composition with respect to the blend, most preferably 40-60% by weight of the polymer (I) and 60-40% by weight of the composition of thermoplastic elastomeric olefin polymer. In the preferred embodiment, both Polymer (I) and component (a) of the thermoplastic elastomeric olefin polymer composition are propylene homopolymers and the total ethylene content is 4% by weight or less. In the present application, the ambient temperature means a temperature of approximately 25 ° C.

Typically the thermoplastic elastomeric olefin polymer composition used in the present invention has a flexural modulus value at 23 ° C of 1300 to 1600 MPa. Examples of dienes useful in the preparation of component (c) are 1,4-hexadiene, 1,5-hexadiene, dicyclopentadiene, ethylidene norbornene, 1,6-octadiene and vinylnormen. Ethylidene norbornene is preferred. Examples of C4-C10 α-olefins useful in the preparation of the different components of the thermoplastic elastomeric olefin polymer compositions are the same as mentioned above. Component (c) is preferably an amorphous ethylene / propylene copolymer, ethylene / propylene / diene copolymer or ethylene / propylene / butene-1 copolymer. When component (c) is a terpolymer, the α-olefin employed as a thermonomer is preferably present in an amount of about 3 to about 10% by weight. The polymer composition (A) can be obtained by separately preparing the Polymer (1) and the polymer (2) and then mixing them in the molten state or they can be prepared directly in synthesis by adding an additional polymerization step after the polymerization step to produce the Polymer (1). The Polymer (I) and said thermoplastic elastomeric olefin polymer composition can be prepared by mixing the separated polymers or, preferably, directly in polymerization by a sequential polymerization process in a series of two or more reactors and in the presence of particular Ziegler-Natta catalysts. Generally, the Polymer (1) is formed in the first polymerization step, while in the following steps the relevant monomers are polymerized to form the Polymer (2) or the thermoplastic elastomeric olefin polymer composition. In the case of Polymer (I) said fraction (i) is prepared before fraction (ii). The polymerization process can be carried out in an inert atmosphere in an uninterrupted or batchwise manner, according to known techniques and operating in liquid phase, in the presence or absence of an inert diluent, or in gas phase or in mixed phases of liquid-gas. It is preferred to operate in gas phase. The preferred method for preparing said thermoplastic elastomeric olefin polymer composition is a two-caps polymerization process comprising the preparation of component (a) in a liquid monomer and, subsequently, the preparation of components (b) and (c) in gas phase. Hydrogen can be added as well as other known molecular regulators as needed as a chain transfer agent for molecular weight control. By suitably measuring the concentration of the molecular weight regulator in the different stages, it is possible to obtain the intrinsic viscosity and MFRL values described above. The times and temperatures of reaction are not decisive; however, the temperatures of preference vary from 20 to 100 ° C. For example, the typical reaction temperature used in the preparation of component (a) and in the preparation of components (b) and (c) may be the same or different. Generally, the reaction temperature used for the preparation of component (a) is from about 40 to about 90 ° C, preferably from about 50 to about 80 ° C. Components (b) and (c) are typically prepared at a temperature of from about 50 to about 80 ° C, preferably about 65 to 80 ° C. The reactions can be carried out at a pressure from about atmospheric to about 7 MPa, preferably from about 1 MPa to 4 MPa in liquid phase polymerization and from 0.1 to 3 Mpa, preferably from 0.5 to 3 MPa, in phase polymerization soda. Typical residence times are from about 30 minutes to about 8 hours. Suitable inert hydrocarbon diluents include saturated hydrocarbons such as propane, butane, hexane and heptane. The catalysts used to prepare the above polymers can be previously contacted with small amounts of olefin (prepolymerization). The prepolymerization improves both the catalyst activity and the morphology of the polymers. The prepolymerization is carried out by keeping the catalyst in suspension in a hydrocarbon solvent (hexane or heptane, for example) and operating between room temperature and 60 ° C for a period that is sufficient to produce an amount of polymer ranging from 0.5 to 3 times the weight of the solid component. It can also be carried out in liquid propylene under the aforementioned temperature conditions and producing amounts of polymer which can reach 1000 g per gram of catalyst component. The catalyst used to prepare the Polymer (I) is preferably characterized in that it is capable of producing propylene polymers having an insoluble fraction xylene at 25 ° C greater than or equal to 90% by weight, preferably greater than or equal to 94%. In addition, it has a sensitivity to molecular weight regulators high enough to produce propylene homopolymers having a high molecular weight fraction and a low molecular weight fraction. For example, in the aforementioned European patent application 573 862, methods are described for preparing the polypropylene (I) of broad molecular weight distribution. The catalysts used in the process for preparing the Polymer (I) and said thermoplastic elastomeric olefin polymer composition are obtained by contacting: (a) a solid catalyst component comprising a titanium compound having at least one titanium- halogen, and an electron donor compound, both supported on an active magnesium halide; (b) an Al-alkyl compound; and, optionally, (c) an external electron donor compound. The solid catalyst components (a) having the aforementioned characteristics as well as the catalysts are well known in the patent literature. The catalysts described in the U.S.A. 4,399,054 and European patents 45977 and 395083 are particularly favorable. In general, the solid catalyst components used in said catalyst comprise, as electron donor components, compounds selected from ethers, ketones, lactones, compounds containing N, P and / or S atoms and esters of mono- and dicarboxylic acids. Particularly suitable electron donor compounds are phthalic acid esters, such as diisobutyl, dioctyl, diphenyl and benzylbutyl phthalate. Other particularly suitable electron donors are 1,3-diethers of the formula: (R ') (R ") C (CH 2 OR 1) (CH 2 OR 1) wherein R 1 and R" are the same or different and are C 1 -C 18 alkyl, cycloalkyl of C3-C18 or aryl radicals of C7-C? 8; Rm and R v are the same or different and are C 1 -C 4 alkyl radicals; or are the 1,3-diethers in which the carbon atom in position 2 belongs to a cyclic or polycyclic structure formed of 5, 6 or 7 carbon atoms and contains two or three unsaturations. Ethers of this type are described in published European patent applications 361493 and 728769. 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-isoamyl-1,3-dimethoxypropane and 9,9-bis (methoxymethyl) fluorene. The polymers and polymer compositions mentioned above can be mixed with the usual additives for polymers, such as stabilizers, pigments, nucleating agents, such as p-tert-butyl benzoate, 1,3- and 2,4-dibenzylidene sorbitol , sodium benzoate, talc, and customary additives for bottle closures, such as antistatic and slip additives. Any suitable apparatus available in the art, for example extruders, may be used to prepare the blends. As already mentioned, typically the MFRL values of the polymer composition (A) vary from 0.3 to 100 g / 10 min. Said MFR values can be obtained directly in the polymerization process or successively by chemical degradation (viscosity reduction) of the polymers or polymer compositions as prepared in the polymerization process. The reduction in viscosity can be obtained by free radical initiators such as organic peroxides. Examples of organic peroxides are (2,5-dimethyl-2,5-diter-butylperoxy) hexane and dumumyl peroxide. The reduction in viscosity is carried out using suitable amounts of free radical initiators and under an inert atmosphere such as nitrogen. Said process can be carried out according to the known techniques, methods and operating conditions. The bottle closures of the present invention can be prepared by a compression molding process of the above α-olefin polymer composition which preferably has an MFRL value of 0.8 to 6 g / 10 min. However, an injection molding process can also be used when using compositions with MFRL values of at least 2 g / 10 min, preferably from 3 to 20. Such molding processes are carried out according to known techniques. The closures for bottles according to the present invention may have the standard size and weight of closures that are commonly employed in the art for pasteurization. In particular, they may have the standard size and weight of the closures, such as screw caps for bottles, which are not for pasteurization. Generally the bottle caps have an internal diameter that varies from 12 to 48 mm and a weight of 0.5 to 10 grams. Typically, the non-alcoholic beverage caps have an inner diameter of approximately 28 mm, a height of approximately 20 mm, a wall thickness ranging from 0.8 to 1.8 mm and weight of 2.5 to 4 grams. The bottle closures of the present invention may also include a band for evidence of tampering. In addition, the bottle closures of the present invention may comprise a hermetic plug, which ensures the tightness of the gas and liquid or a separate rubbery hermetic coating. In general, the closures for bottles of the present invention can be used when the bottles have to be subjected to high temperatures, thanks to their good mechanical properties at high temperatures. For example, the bottle closures of the present invention are particularly suitable for being subjected to pasteurization cycles as stated above as well as for closing bottles that are to be stored at high temperatures for a prolonged time. The following analytical methods 3 are used to characterize the polymers and compositions obtained therefrom. Melt Flow Rate (MFRL): ASTM-D 1238, condition L Intrinsic viscosity f? 1: determined in tetrahydronaphthalene at 135 ° C Ethylene content: I.R spectroscopy.

Soluble and insoluble fractions in xylene at 25 ° C 2.5 g of polymer are dissolved in 250 ml of xylene at 135 ° C under agitation. After 20 minutes the solution is allowed to cool to 25 ° C, still under stirring, and then left to stand for 30 minutes. The precipitate is filtered with filter paper, the solution is evaporated under nitrogen flow, and the residue is dried under vacuum at 80 ° C until a constant weight is reached. Accordingly, the weight percent of the polymer soluble and insoluble in xylene at room temperature is calculated. PM / NM: measured by Gel Permeation Chromatography Polydispersity index (Pl) Measurement of molecular weight distribution in the polymer. To determine the Pl value, the module to low module value separation, for example 500 Pa, is determined at a temperature of 200 ° C using a RMS-800 parallel plate rheometer model marketed by Rheometrics (USA), operating at an oscillation frequency that increases from 0.01 rad / second to 100 rad / second. From the module separation value, Pl can be derived using the following equation: Pl = 54.6x (module separation) "1 76 where the module separation (MS) is defined as: MS = (frequency a G) '= 500 Pa) / (frequency at G "= 500 Pa) Where G'es the storage module and G" is the low module.

Elastic Bending Module (FM): ISO 178 Lengthening during deformation: ISO / R 527 Resistance during breaking and resistance during deformation: ISO 527 Impact test IZOD recorded: ISO 180/1 A Temperature of distortion with heat (HDT ): ISO 75 VICAT: ISO 306. The following examples are presented to illustrate but not limit the present invention.

Polymer compositions used in the examples - The composition (A) is a propylene polymer composition having an MFRL value of 1.9 g / 10 min and is obtained by chemical degradation of a precursor composition by suitable amounts of organic peroxides. The composition subjected to viscosity reduction has an MFRL value of 1.2 g / 10 min, a xylene-soluble fraction of 6.5% by weight, an intrinsic viscosity value [?] Of the xylene-soluble fraction (without oils) of dl / g and shows the following composition: 95.2% by weight of a propylene homopolymer having a xylene-soluble fraction content of 2.5% by weight, a Pl value of 4.7 and a PM / NM value of 7.6; and - 4.8% by weight of an ethylene / propylene copolymer having an ethylene content of 48% by weight. The xylene-soluble fraction of the copolymer is 86% by weight and contains 28.2% by weight of ethylene. The precursor composition is produced uninterruptedly in a series of three connected reactors, wherein the propylene homopolymer is produced in the first two reactors and the ethylene / propylene copolymer is produced in the third. The polymerization is carried out in the presence of a catalyst obtained by contacting a solid catalyst component comprising TiCU and diisobutylphthalate, both supported on MgCl2 in active form, triethylaluminum and dicyclopentyldimethoxysilane as an electron donor compound. - Polymer (B) is a propylene homopolymer having an MFRL value of 3.5 g / 10 min. a xylene-soluble fraction of 1.8% by weight, Pl value of 6 and PM / NM value of 9.3; the homopolymer was converted to a core with 1800 ppm of 3,4-dimethylbenzylidylsorbitol. It is produced in the same way as the composition (A), except that the third stage of polymerization is not carried out. The results of the polymerization runs to produce composition (A) and polymer (B) are shown in table 1.

TABLE 1 The composition (C) is a propylene polymer composition having an MFRL value of 4.6 g / 10 min and is obtained by chemical degradation of a precursor composition by suitable amounts of organic peroxides. The composition subjected to degradation has an MFRL value of 3.0 g / 10 min, a xylene-soluble fraction (without oils) of 8.4% by weight, an intrinsic viscosity value [?] Of the xylene-soluble fraction (without oils) of 2.3 dl / g and shows the following composition: - 93% by weight of a propylene homopolymer having an MFRL value of 3.1 g / 10 min; The fraction soluble in xylene is approximately 2. 5% by weight, Pl value of 4.2 and MW / NM value of 6.9, and - 7% by weight of an amorphous ethylene / propylene copolymer containing 48% ethylene. The xylene-soluble fraction of the copolymer is 86% and contains 32% by weight of ethylene.

The composition (D) is a thermoplastic elastomeric olefin polymer composition with an MFRL value of 6.0 g / 10 min. and is obtained by chemical degradation of a precursor composition by suitable amounts of organic peroxides. The composition subjected to viscosity reduction has an MFRL value of 4.0 g / 10 min, an intrinsic viscosity value [?] Of the fraction soluble in xylene (without oils) of 2.3 dl / g and has the following composition: - 91.5% of a crystalline propylene homopolymer containing about 2.5% xylene-soluble fraction; and - 8.5% of an ethylene / propylene copolymer containing 60% by weight of ethylene. The xylene-soluble fraction of the copolymer is 72% by weight and contains 40% by weight of ethylene. The compositions (C) and (D) are obtained by sequential polymerization in the presence of a high yield stereospecific Ziegler-Natta catalyst supported on MgCl2.

EXAMPLE 1 Polymer pellets (A) containing 5500 ppm of erucamide, 3000 ppm of glycerol monostearate and 1 100 ppm of sodium benzoate are prepared by extrusion in a Werner ZSK 280 (L / D is 16 and the diameter is 280 mm) It operates at a temperature that varies from 235-240 ° C.

The models are prepared by injection molding with pellets of the polymer obtained by extrusion. The models are prepared according to the ISO 1873-2 method.

EXAMPLE 2 Example 1 is repeated. The only difference is that the composition (C) is used instead of the composition (A).

EXAMPLE 3 Example 1 is repeated, except that a mixture of the polymer (B) and the composition (D) is used instead of the composition (A). The polymer (B) / composition (D) ratio is 1/1.

COMPARATIVE EXAMPLE 1c Example 1 is repeated, except that composition (D) is used instead of composition (A). Table 2 shows the mechanical properties determined using the test models prepared in Examples 1-3 and Comparative Example 1c.

EXAMPLE 4 The pellets as extruded in example 3 are transformed into standard screw caps by injection molding. Said screw caps are for non-alcoholic beverages, have an internal diameter of approximately 3 g and are equipped with a rubbery hermetic coating and band for evidence handling. The processing conditions for a 32 cavity injection moulder are: Barrel temperatures: 210-230 ° C; Hot slide temperature: 221-260 ° C; Molding water temperature: 15 ° C; Injection time: 0.33 second; Subsequent pressure time: 0.90 seconds; Power time: 3.14 seconds. The injection molding used is a Netstall Synergy 240 produced by Netstal. Then the bottles with the screw caps thus obtained are filled with lemonade having a C02 content of 5.0 g / l. Then the bottles are subjected to a pasteurization cycle carried out at 77 ° C and for a time of 50 minutes. The standard torsional force for the closure is 1.15 kg cm.

. It is noted that the screw caps do not fly out of the bottles and the liquid does not escape from the bottles during or after the pasteurization cycle. The gas content in the bottles is 4.13 g / l after the pasteurization cycle (3.5 g / l being the minimum required CO2 content).

EXAMPLE 5 Example 4 is repeated except that a mixture of 25% by weight of the polymer (B) and 75% by weight of the composition (D) is used. It is noted that the screw caps do not fly out of the bottles and the liquid does not escape from the bottles during or after the pasteurization cycle. The gas content in the bottles is 4.06 g / l after the pasteurization cycle.

COMPARATIVE EXAMPLE 2c Example 5 is repeated except that composition (D) is used in place of the mixture. It is noted that a number of screw caps are flying out of the bottles and a number of screw caps are slightly unthreaded so that a certain amount of gas and, sometimes, liquid has escaped from the bottles during or after the pasteurization cycle.

TABLE 2

Claims (12)

NOVELTY OF THE INVENTION CLAIMS

1. - A bottle closure comprising an olefin polymer composition (A) comprising: 1) 90-100% by weight, preferably 92-98, most preferably 94-98, of a crystalline propylene homopolymer or random copolymer of the same with a selected comonomer of ethylene and a C4-C10 α-olefin; said polymers contain at least 94% by weight, preferably at least 96% by weight of a fraction insoluble in xylene at room temperature (Polymer (1)); and 2) 0-10% by weight, preferably 2-8% by weight, most preferably 2-6%, of an elastomeric copolymer of ethylene with propylene or a C4-C10 α-olefin or mixtures thereof, and optionally, from 0.5 to 10% by weight of a diene, said elastomeric copolymer contains from 40% to 85% by moles of ethylene (Polymer (2)); provided that when the amount of the Polymer (2) is 0% by weight, the Polymer (1) is selected from the aforementioned random copolymers; said composition (A) has a value of elastic modulus of flexure at 23 ° C at least 1620 MPa, preferably 1650 to 2500 MPa; a resistance value during deformation at 23 ° C at least 33 MPa; an IZOD impact resistance value at 0 ° C at least 2.5 kJ / m2.

2. The bottle closure according to claim 1, further characterized in that the olefin polymer composition (A) has an MFR value (according to ASTM D 1238, condition L), in the range of 0.3 to 100 g. /10 minutes.

3. The bottle closure according to claim 2, further characterized in that the olefin polymer composition (A) has been subjected to chemical degradation.

4. The bottle closure according to claims 1, 2 or 3, further characterized in that the Polymer (1) is a crystalline propylene polymer having a PM / NM ratio in the range of 5 to 60.

5 .- The closure for bottle in accordance with the claims 1 to 4, further characterized in that the Polymer (1) is a propylene homopolymer.

6. The bottle closure according to claim 1, further characterized in that the olefin polymer composition (A) is a mixture of polymer comprising (percentage by weight): A) 30-80% of a propylene polymer crystalline according to claim 4; and B) 20-70% of a thermoplastic elastomeric olefin polymer composition comprising: a) 70-97%, preferably 78-97%, of a propylene homopolymer containing more than 90%, preferably more than 945 , of a fraction insoluble in xylene at room temperature, or a copolymer of crystalline propylene with ethylene or a C4-C10 α-olefin or a mixture thereof, containing more than 85% by weight of propylene; the copolymer contains at least 85% by weight of a fraction insoluble in xylene at room temperature; b) 0-10%, preferably 1-10%, of a crystalline copolymer containing ethylene, insoluble in xylene at room temperature; and c) 3-20%, preferably 3-12% of an amorphous copolymer of ethylene with propylene and / or a C4-C10 1-olefin and, optionally, from 1 to 10% of a diene, soluble in xylene at temperature environment, and containing 20 to 75% ethylene; provided that the total content of fractions b) and c) of B) is up to 10% by weight with respect to the polymer mixture.

7. The bottle closure according to claim 6, further characterized in that Polymer (1) and component (a) are propylene homopolymers and the total ethylene content is 4% by weight with respect to the mixture.

8. The bottle closure according to claims 6 to 7, further characterized in that the thermoplastic elastomeric olefin polymer composition has a flexural modulus value at 23 ° C of 1300 to 1600 MPa.

9. The bottle closure according to any of claims 1 to 8, in the form of a screw cap for bottle.

10. Bottles closed with the bottle closure according to claims 1 to 9.

11. A process for producing a bottle closure according to any of claims 1 to 8 by compression molding the polymer composition of the bottle. olefin (A).

12. - A process for producing a bottle closure according to any of claims 1 to 8 by injection molding the olefin polymer composition (A).