Multilayer film

Abstract

A multilayer film comprising a skin layer (A) and a core layer (B) wherein:-the skin layer (A) comprises a polyolefin composition (I) comprising: (a) 70% to 95% by weight of a propylene copolymer containing up to and comprising 10.0% by weight of units derived from alpha-olefins and having a fraction soluble in xylene at 25 DEG C of 10% to 20% by weight; and (b) from 5% to 30% by weight of a butene-1 polymer, wherein the amounts of (a) and (b) are based on the total weight of (a) + (b); and-the core layer (B) comprises a copolymer of propylene and up to and comprising 25 wt.% of an alpha-olefin.

Description

Technical Field

[0001] The present invention relates to a heat-sealable multilayer film, preferably a blown multilayer film or a cast multilayer film, having good sealing and optical properties. Background Art

[0002] Polypropylene heat sealable films are used in many common packaging applications, such as cigarette, candy, snack and food packaging. Polypropylene can also be used for shrink wrap, hygiene products and sterile packaging for medical applications.

[0003] Typically, the heat sealing properties of polypropylene are not sufficient for rapid packaging systems. It is known in the art to add polybutene-1 to polypropylene to improve its heat sealing properties. Therefore, multilayer films containing a blend of polypropylene and polybutene-1 in the outer sealing layer are known in the art.

[0004] Patent application WO 2004 / 048424 discloses a multilayer film with a low sealing initiation temperature, wherein the sealing layer comprises a combination of polybutene-1 containing 2.1 mol.% of ethylene and a propylene-butene-ethylene terpolymer.

[0005] Patent application WO 2011 / 064131 discloses the use of polybutene-1 having a low flexural modulus in combination with a heterophasic propylene polymer to provide a sealing layer having a low sealing initiation temperature.

[0006] Patent application WO 2012 / 031953 discloses the use of butene-1 homopolymer or copolymer to reduce the seal initiation temperature of a seal layer containing a copolymer of propylene and hexene- 1. The film also has a reduced number of fisheyes.

[0007] Patent application WO2018 / 211107 discloses the use of polybutene-1 having a Mw of 100,000 to 300,000 and a MWD of less than 6.0 to reduce the seal initiation temperature and hot tack of propylene random copolymers having a comonomer content of 1.0-10 wt%. The optical properties of multilayer films containing a blend of polypropylene and polybutene-1 are not significantly affected by the presence of polybutene-1.

[0008] In this framework, there is still a need to provide propylene polymer compositions having improved heat sealing and optical properties and a good balance of mechanical properties. Summary of the invention

[0009] The present invention provides a multilayer film comprising a surface layer (A) and a core layer (B), wherein:

[0010] - the surface layer (A) comprises a polyolefin composition (I) comprising:

[0011] (a) from 70% to 95% by weight of a copolymer of propylene and at least one α-olefin of the formula CH2=CHR, wherein R is hydrogen or a linear or branched C2-C8 alkyl group, comprising up to and including 10.0% by weight, based on the weight of component (a), of units derived from α-olefins, the propylene copolymer having from 10% to 20% by weight of a fraction soluble in xylene at 25°C; and

[0012] (b) 5 to 30 wt. % of a butene-1 polymer selected from butene-1 homopolymers, copolymers of butene-1 with up to and including 5.0 wt. %, based on the weight of component (b), of units derived from ethylene and / or propylene, and mixtures thereof,

[0013] wherein the amounts of (a) and (b) are based on the total weight of (a) + (b);

[0014] - The core layer (B) comprises a copolymer (c) of propylene and up to and including 25 wt. %, based on the weight of the copolymer, of at least one α-olefin of formula CH2=CHR, wherein R is hydrogen or a linear or branched C2-C8 alkyl group.

[0015] The multilayer film of the present invention has good sealing properties, namely low seal initiation temperature (SIT) and high hot tack. In particular, if compared with a multilayer film in which the skin layer does not include component (b), the SIT is low and the hot tack is high.

[0016] The good sealing properties are combined with improved optical properties, in particular higher gloss and lower haze, if compared to multilayer films in which the skin layers do not comprise component (b).

[0017] Furthermore, the mechanical properties of the multilayer films of the invention are suitable for the production of cast and blown films.

[0018] Although multiple embodiments are disclosed, other embodiments will become apparent to those skilled in the art from the following detailed description. Obviously, certain embodiments as disclosed herein can be modified in various obvious aspects without departing from the spirit and scope of the claims presented herein. Therefore, the following detailed description should be regarded as illustrative rather than restrictive in nature. DETAILED DESCRIPTION

[0019] In the context of the present invention;

[0020] - Unless otherwise stated, percentages are expressed by weight;

[0021] - unless otherwise stated, the total weight of the compositions adds up to 100%;

[0022] - the term "comprising" in relation to a polymer, plastic material, polymer composition, mixture or blend shall be interpreted as meaning "comprising or consisting essentially of";

[0023] - The term "consisting essentially of" means that in addition to the mandatory ones, other components may also be present in the material, provided that the basic properties of the material are not substantially affected by their presence. Examples of components that do not substantially affect the properties of the polymer or polyolefin composition, mixture or blend when present in conventional amounts are catalyst residues, antistatic agents, processing aids, melt stabilizers, light stabilizers, antioxidants and antacids;

[0024] - the term "copolymer" refers to a polymer derived from the polymerization of at least two comonomers, i.e. the term "copolymer" includes binary copolymers and ternary copolymers;

[0025] - The term "skin layer" refers to the outermost layer of a multilayer film;

[0026] - The term "core layer" refers to the innermost layer of a multilayer film.

[0027] The polyolefin composition (I) of the surface layer (A) preferably comprises 75 to 90 wt% of the propylene copolymer (a) and 10 to 25 wt% of the butene-1 polymer (b), wherein the amounts of (a) and (b) are based on the total weight of (a) + (b).

[0028] In the following, the individual components of the polyolefin composition (I) included in the skin layer (A) and the propylene copolymer included in the core layer (B) are defined in more detail. The individual components may be included in the layers in any combination.

[0029] The polyolefin composition (I) preferably comprises a propylene copolymer (a) comprising from 0.5 to 10.0 wt.-%, based on the weight of component (a), of units derived from α-olefins, preferably ethylene, and a butene-1 copolymer (b) comprising from 0.5 to 5.0 wt.-%, based on the weight of component (b), of units derived from ethylene and / or propylene, preferably ethylene.

[0030] In a preferred embodiment the propylene copolymer (a) comprised in the polypropylene composition (I) is a propylene-ethylene copolymer, i.e. a copolymer consisting of repeating units derived from propylene and ethylene, having at least one, preferably all, of the following properties:

[0031] - comprises 2.0 to 10.0 wt.-%, preferably 2.2 to 9.8 wt.-%, more preferably 3.0 to 8.0 wt.-%, still more preferably 4.5 to 7.2 wt.-% of units derived from ethylene, based on the weight of the propylene copolymer (a); and / or

[0032] - a melt flow rate MFR(a) measured according to ISO 1133-1:2011 (230°C / 2.16kg) of 0.1 to 10.0 g / 10 min, preferably 0.3 to 7.0 g / 10 min, more preferably 0.5 to 3.0 g / 10 min; and / or

[0033] - comprising 12 to 20 wt.-%, preferably 14 to 18 wt.-%, based on the weight of the propylene copolymer (a), of a xylene soluble fraction XS (a) at 25 °C measured according to the method reported in the experimental part.

[0034] In addition to one or more of the above mentioned properties, the propylene-ethylene copolymer (a) preferably has a melting temperature of 130 to 142°C, more preferably 131 to 140°C, still more preferably 132 to 137°C, measured by DSC according to method ISO 11357-3:2018.

[0035] In one embodiment, the propylene copolymer (a) comprises up to and including 5.0 wt%, more preferably 0.01 wt% to 5.0 wt%, of at least one additive selected from nucleating agents, antistatic agents, antioxidants, light stabilizers, slip agents, antacids, melt stabilizers and combinations thereof, the amount of the additive being based on the total weight of the copolymer (a) including the additive, the total weight being 100%.

[0036] The propylene copolymer (a) is obtainable by polymerizing the relevant monomers in the presence of a highly stereospecific Ziegler-Natta catalyst system comprising:

[0037] (1) A solid catalyst component comprising a magnesium halide support and a stereoregular internal donor, on which a Ti compound having at least one Ti-halogen bond is present;

[0038] (2) optionally, but preferably, an Al promoter; and

[0039] (3) Optionally, but preferably, additional electron donor compounds (external donors).

[0040] The solid catalyst component (1) preferably comprises TiCl4 in an amount ensuring the presence of 0.5 to 10 wt% Ti relative to the total weight of the solid catalyst component (1).

[0041] The solid catalyst component (1) comprises at least one stereoregular internal electron donor compound selected from monodentate or bidentate organic Lewis bases, preferably selected from esters, ketones, amines, amides, carbamates, carbonates, ethers, nitriles, alkoxysilanes and combinations thereof.

[0042] Preferred donors are esters of phthalic acid, such as those described in EP 45977 A2 and EP 395083 A2, in particular diisobutyl phthalate, di-n-butyl phthalate, di-n-octyl phthalate, diphenyl phthalate, benzyl butyl phthalate and combinations thereof.

[0043] The esters of aliphatic acids may also be selected from esters of malonic acid, such as those described in WO98 / 056830, WO98 / 056833, WO98 / 056834; esters of glutaric acid, such as those disclosed in WO00 / 55215; and esters of succinic acid, such as those disclosed in WO00 / 63261.

[0044] A specific type of diesters are those derived from the esterification of aliphatic or aromatic diols, such as those described in WO 2010 / 078494 and USP 7,388,061.

[0045] In some embodiments, the internal donor is selected from 1,3-diethers such as those described in EP361493, EP728769, and WO02 / 100904.

[0046] Internal donors, in particular specific mixtures of aliphatic or aromatic mono- or dicarboxylic acid esters and 1,3-diethers as disclosed in WO 07 / 57160 and WO 2011 / 061134, can be used as internal donors.

[0047] The preferred magnesium halide support is magnesium dihalide.

[0048] The amount of the internal donor to be held fixed on the solid catalyst component (1) is 5 mol% to 20 mol% relative to the magnesium dihalide.

[0049] A preferred process for preparing the solid catalyst component (1) is described in EP 395 083 A2.

[0050] The preparation of catalyst components according to general methods is described, for example, in European patent applications US 4,399,054, US 4,469,648, WO 98 / 44009 A1 and EP 395 083 A2.

[0051] The catalyst system preferably comprises an Al-containing cocatalyst (2) selected from Al-trialkyl, preferably selected from Al-triethyl, Al-triisobutyl and Al-tri-n-butyl. The Al / Ti weight ratio in the catalyst system is 1 to 1000, preferably 20 to 800.

[0052] In a preferred embodiment, the catalyst system comprises a further electron donor compound (3) (external electron donor) selected from silicon compounds, ethers, esters, amines, heterocyclic compounds (especially 2,2,6,6-tetramethylpiperidine) and ketones.

[0053] Preferred silicon compounds are selected from methylcyclohexyldimethoxysilane (C-donor), dicyclopentyldimethoxysilane (D-donor) and mixtures thereof.

[0054] The polymerization process to obtain the propylene copolymer (a) can be carried out continuously or batchwise in liquid or gas phase.

[0055] Liquid phase polymerisation can be in slurry, solution or bulk (liquid monomer). The latter technique is most preferred and can be carried out in various types of reactors such as continuous stirred tank reactors, loop reactors or plug flow reactors.

[0056] The gas phase polymerization can be carried out in a fluidized bed or stirred fixed bed reactor or preferably in a multizone circulation reactor (MZCR), as described in EP 1 012 195 B1.

[0057] The polymerization process described in detail in EP1012195B1 discloses that it is particularly useful for preparing wide molecular weight olefin polymers, particularly multimodal olefin polymers in a single reactor, wherein the term multimodal refers to the mode of molecular weight distribution. As used in the art and as used herein, multimodal should include bimodal. Such polymers can be obtained by polymerizing olefins under different reaction conditions in a cascade of two or more polymerization reactors or in different zones of an MZCR reactor. Therefore, "mode" indicates how many different polymerization conditions are used to prepare polymers, independently indicating whether the mode of the molecular weight distribution can be considered as the maximum value separated in a gel permeation chromatography (GPC) curve. In addition to molecular weight distribution, olefin polymers can also be multimodal, i.e. bimodal, in comonomer distribution. In one embodiment, the average comonomer content of polymer chains with higher molecular weight is higher than the average comonomer content of polymer chains with lower molecular weight. However, the same or very similar reaction conditions can also be adopted in all polymerization reactors of a reaction cascade, thereby preparing narrow molecular weight or unimodal olefin polymers.

[0058] The polymerization temperature is preferably comprised in the range of 40 to 90° C., and the polymerization pressure is preferably from 3.3 to 4.3 MPa for a liquid phase process and from 0.5 to 3.0 MPa for a gas phase process.

[0059] Propylene copolymers (a) are also commercially available, for example from LyondellBasell under the trade names Adstif, Clyrell, Moplen and Purell.

[0060] Preferably, the butene-1 polymer (b) comprised in the polyolefin composition (I) is a copolymer of butene-1 and ethylene having at least one, preferably all, of the following properties:

[0061] - a content of units derived from ethylene of from 1.0% to 4.5% by weight, preferably from 1.5% to 4.5% by weight, more preferably from 2.0% to 4.0% by weight, still more preferably from 2.5% to 3.5% by weight, based on the weight of (b); and / or

[0062] - the melting temperature Tm(I) of form I measured by DSC according to method ISO 11357-3:2018 is below 100°C, preferably from 80°C to below 100°C, more preferably from 90°C to 97°C; and / or

[0063] - a melt flow rate measured according to ISO 1133-1:2011 (190°C / 2.16kg) of 1.0 to 6.0 g / 10 min, preferably 2.0 to 5.0 g / 10 min, still more preferably 3.0 to 4.5 g / 10 min; and / or

[0064] The flexural modulus measured according to ISO 178:2010 is equal to or higher than 80 MPa, preferably from 80 to 250 MPa, more preferably from 100 to 210 MPa.

[0065] In a preferred embodiment, in addition to one or more of the above properties, the butene-1 copolymer (b) also has a molecular weight distribution Mw / Mn of 4.0 to 9.0, preferably 4.0 to 8.0, more preferably 4.0 to 7.0, and more preferably greater than 4.5 to less than 6.0.

[0066] In one embodiment, the butene-1 polymer (b) includes up to and including 5.0 wt %, more preferably 0.01 wt % to 5.0 wt %, of at least one additive selected from nucleating agents, antistatic agents, antioxidants, light stabilizers, slip agents, antacids, melt stabilizers, and combinations thereof, the amount of the additive being based on the total weight of the butene-1 polymer (b) including the additive, the total weight being 100%.

[0067] In some embodiments, the butene-1 polymer (b) is obtained using a metallocene-based catalyst system.

[0068] The butene-1 polymer (b) is preferably obtainable by polymerizing the relevant monomers in the presence of a Ziegler-Natta catalyst system as described above.

[0069] The polymerization process can be carried out according to known techniques, such as slurry polymerization using a liquid inert hydrocarbon as diluent, or solution polymerization using, for example, liquid butene-1 as reaction medium. In addition, the polymerization process can also be carried out in the gas phase, operating in one or more fluidized or mechanically stirred bed reactors. It is highly preferred to carry out the polymerization in liquid butene-1 as reaction medium.

[0070] The polymerization is generally carried out at a temperature of 20° C. to 120° C., preferably 40° C. to 80° C. The polymerization can be carried out in one or more reactors, which can operate under the same or different reaction conditions such as concentration of molecular weight regulator, comonomer concentration, temperature, pressure, etc.

[0071] Suitable catalyst systems and polymerization processes for obtaining butene-1 polymers (b) are disclosed in patent application WO 2004 / 048424 A1.

[0072] Butene-1 polymers (b) are also commercially available, for example sold under the trade name Toppyl by LyondellBasell.

[0073] In one embodiment, the polyolefin composition (I) consists of component (a) and component (b) as described above, optionally containing additives.

[0074] In one embodiment, the skin layer (A) consists of the polyolefin composition (I) as described above.

[0075] The core layer (B) comprises a copolymer (c) of propylene and up to and including 25 wt%, preferably 10 wt% to 25 wt% of at least one α-olefin of formula CH2=CHR, wherein R is hydrogen or a linear or branched C2-C8 alkyl. In a preferred embodiment, the α-olefin is ethylene.

[0076] The propylene copolymer (c) comprised in the core layer (B) is preferably selected from the group consisting of propylene random copolymers, heterophasic propylene polymers, recycled propylene polymers and combinations thereof, particularly preferably heterophasic propylene polymers.

[0077] In a preferred embodiment the propylene copolymer (c) comprised in the core layer (B) is a heterophasic propylene polymer comprising:

[0078] 20 to 40 wt.-% of polymer fraction (i), comprising propylene polymers selected from propylene homopolymers, copolymers of propylene with up to and comprising 6.0 wt.-%, preferably 0.1 to 6.0 wt.-%, based on the weight of fraction (i), of at least one α-olefin of formula CH2=CHR, wherein R is hydrogen or a linear or branched C2-C8 alkyl group, and combinations thereof; and

[0079] - 60 to 80% by weight of a polymer fraction (ii) comprising a copolymer of propylene and at least one α-olefin of formula CH2=CHR, in which R is hydrogen or a linear or branched C2-C8 alkyl group, the copolymer comprising up to and including 35.0% by weight, based on the weight of fraction (ii), preferably from 20 to 35.0% by weight, of units derived from α-olefins, and having a solubility in xylene at 25° C. of from 45.0 to 75.0% by weight, based on the weight of fraction (ii),

[0080] The amounts of (i) and (ii) are based on the total weight of (i) + (ii).

[0081] In a further preferred embodiment, the heterophasic propylene polymer comprises:

[0082] 20 to 40 wt.-%, preferably 25 to 35 wt.-%, of a polymer fraction (i) comprising a propylene-ethylene copolymer comprising up to and including 6.0 wt.-%, preferably 0.1 to 6.0 wt.-%, more preferably 1.5 to 4.5 wt.-%, based on the weight of fraction (i), of units derived from ethylene; and

[0083] 60 to 80 wt.-%, preferably 65 to 75 wt.-%, of fraction (ii), which fraction (ii) comprises a propylene-ethylene copolymer comprising up to and including 35.0 wt.-%, preferably 20.0 to 35.0 wt.-%, more preferably 23.0 to 30.0 wt.-%, based on the weight of fraction (ii), of units derived from ethylene and having a solubility in xylene at 25° C. of 55.0 to 75.0 wt.-%, preferably 60.0 to 70.0 wt.-%, based on the weight of fraction (ii),

[0084] The amounts of (i) and (ii) are based on the total weight of (i) + (ii).

[0085] The heterophasic propylene polymer preferably has at least one, more preferably all, of the following properties:

[0086] - a melt flow rate measured according to method ISO 1133-1:2011 (230°C / 2.16kg) of 0.1 to 5 g / 10 min, preferably 0.2 to 3.0 g / 10 min, more preferably 0.3 to 1.2 g / 10 min, more preferably 0.3 to 0.8 g / 10 min; and / or

[0087] - a melting temperature of 135°C to 148°C as measured by DSC according to method ISO 11357-3; and / or

[0088] - Flexural modulus measured according to method ISO 178:2010 is equal to or lower than 250 MPa, preferably equal to or lower than 150 MPa, the lower limit of each upper limit being preferably 50 MPa.

[0089] In one embodiment, the propylene copolymer (c) comprises conventional amounts, preferably up to and including 5.0 wt.-%, more preferably from 0.01 wt.-% to 5.0 wt.-%, based on the total weight of copolymer (c), of at least one additive selected from nucleating agents, antistatic agents, antioxidants, light stabilizers, slip agents, antacids, melt stabilizers and combinations thereof, the total weight being 100%.

[0090] The propylene copolymer (c) is preferably obtained by polymerizing the relevant comonomers in the presence of a highly stereospecific Ziegler-Natta catalyst system and using a polymerization process as described above.

[0091] The heterophasic propylene polymer is obtained by melt blending fractions (i) and (ii) or preferably by polymerizing the relevant monomers in the gas phase in at least two polymerization stages, wherein the second and each subsequent polymerization stage is carried out in the presence of the produced polymer and the catalyst used in the previous polymerization stage, or in a multi-zone circulation reactor as disclosed in WO2011 / 144489 and WO2018 / 177701. The polymerization temperature and pressure are as described above.

[0092] When the heterophasic propylene polymer is a reactor blend produced by sequential polymerization, the amount of fractions (i) and (ii) corresponds to the split between reactors; when the heterophasic propylene polymer is produced in a multizone circulation reactor, the amount of fractions (i) and (ii) corresponds to the split between riser and downcomer.

[0093] Propylene copolymers (c) are also commercially available, for example sold under the trade names Adflex and Hiflex by LyondellBasell.

[0094] In one embodiment the core layer (B) consists of a propylene copolymer (c) as described above.

[0095] The multilayer films of the present invention preferably have a total film thickness of from 10 to 200 micrometers, preferably from 20 to 140 micrometers.

[0096] In a preferred embodiment, in the multilayer film, the ratio of the thickness of the skin layer (A) to the thickness of the core layer (B) is from 1:1 to 1:12, preferably from 1:2 to 1:6.

[0097] According to a preferred embodiment, the multilayer film comprises a second skin layer (C) comprising a polyolefin composition (I) as described above. Optionally, at least one intermediate layer D may be inserted between skin layer A and / or skin layer C and core layer B.

[0098] In a more preferred embodiment, skin layer (A) and skin layer (C) comprise the same polyolefin composition (I). More preferably, skin layer (A) and skin layer (C) are identical and the multilayer film has an A / B / A structure.

[0099] In a most preferred embodiment, the multilayer film of the present invention has the structure A / B / A, wherein:

[0100] - The surface layer (A) and the second surface layer (C) comprise or consist of a polyolefin composition (I), the polyolefin composition (I) comprising or consisting of:

[0101] (a) 70 to 95 wt%, preferably 75 to 90 wt% of a propylene-ethylene copolymer comprising:

[0102] - up to and comprising 10.0 wt.-%, preferably 2.0 to 10.0 wt.-%, more preferably 2.2 to 9.8 wt.-%, more preferably 3.0 to 8.0 wt.-%, still more preferably 4.5 to 7.2 wt.-% of ethylene based on the weight of the propylene copolymer (a);

[0103] 10 to 20 wt.-%, preferably 12 to 20 wt.-%, more preferably 14 to 18 wt.-%, based on the weight of the propylene copolymer (a), of the fraction soluble in xylene at 25°C, and

[0104] - a melt flow rate measured according to ISO 1133-1:2011 (230°C / 2.16kg) of 0.1 to 10.0 g / 10 min, preferably 0.3 to 7.0 g / 10 min, more preferably 0.5 to 3.0 g / 10 min;

[0105] as well as

[0106] (b) 5 to 30% by weight, preferably 10 to 25% by weight, of a copolymer of butene-1 and ethylene

[0107] - comprises up to and including 5.0 wt%, preferably 1.0 to 4.5 wt%, preferably 1.5 to 4.5 wt%, more preferably 2.0 to 4.0 wt%, still more preferably 2.5 to 3.5 wt%, of units derived from ethylene, based on the weight of (b); and / or

[0108] - a melting temperature Tm(I) measured according to method ISO 11357-3:2018 of less than 100°C, preferably from 80°C to less than 100°C, more preferably from 90°C to 97°C; and / or

[0109] - a melt flow rate measured according to ISO 1133-1:2011 (190°C / 2.16kg) of 1.0 to 6.0 g / 10 min, preferably 2.0 to 5.0 g / 10 min, still more preferably 2.5 to 4.5 g / 10 min,

[0110] Flexural modulus measured according to ISO 178:2010 equal to or higher than 80 MPa, preferably from 80 to 250 MPa, more preferably from 100 to 210 MPa,

[0111] wherein the amounts of (a) and (b) are based on the total weight of (a) + (b);

[0112] and

[0113] - the core layer (B) comprises or consists of a heterophasic propylene polymer comprising:

[0114] 20 to 40 wt.-%, preferably 25 to 35 wt.-%, of a polymer fraction (i) comprising a propylene-ethylene copolymer comprising up to and including 6.0 wt.-%, preferably 0.1 to 6.0 wt.-%, more preferably 1.5 to 4.5 wt.-%, based on the weight of fraction (i), of units derived from ethylene; and

[0115] 60 to 80 wt.-%, preferably 65 to 75 wt.-%, of fraction (ii), which fraction (ii) comprises a propylene-ethylene copolymer comprising up to and including 35.0 wt.-%, preferably 20.0 to 35.0 wt.-%, more preferably 23.0 to 30.0 wt.-%, based on the weight of fraction (ii), of units derived from ethylene and having a solubility in xylene at 25° C. of 55.0 to 75.0 wt.-%, preferably 60.0 to 70.0 wt.-%, based on the weight of fraction (ii),

[0116] Therein the heterophasic propylene polymer has a total ethylene content up to and including 25 wt-% based on the weight of the heterophasic propylene composition and the amounts of (i) and (ii) are based on the total weight of (i) + (ii).

[0117] The multilayer film of the present invention optionally comprises additional layers, which when present are interposed between the core layer (B) and the skin layer (A) and / or the optional skin layer (C).

[0118] The multilayer films of the invention are obtained according to known processes, for example by coextrusion or lamination, wherein in coextrusion a plurality of extruders are fed with the components comprised in the different layers.

[0119] In a preferred embodiment, the multilayer film of the present invention is a non-oriented film, more preferably a cast film or a blown film.

[0120] In one embodiment, the multilayer film of the present invention, preferably a multilayer cast film or blown film, has at least one, preferably all, of the following properties:

[0121] - a seal initiation temperature (SIT) equal to or lower than 125°C, preferably from 90°C to 125°C, more preferably from 100°C to 125°C, even more preferably from 110°C to 120°C; and / or

[0122] The hot tack at -110°C is 1.0 to 6.0N, preferably 1.5 to 4.0N.

[0123] The features describing the subject matter of the invention are not inseparably linked to one another. Thus, a preferred range for one feature may be combined with a more preferred range or a less preferred range for a different feature, regardless of their order of preference.

[0124] Examples

[0125] The following examples are illustrative only and are not intended to limit the scope of the present invention in any way.

[0126] Characterization Methods: The following methods were used to determine the properties indicated in the specification, claims, and examples.

[0127] Melt flow rate: Determined according to method ISO 1133-1:2011 (230°C / 2.16 kg for propylene polymers and 190°C / 2.16 kg for butene-1 copolymers).

[0128] Solubility of propylene polymer in xylene at 25°C: 2.5g of polymer sample and 250ml of xylene are introduced into a glass flask equipped with a cooler and a magnetic stirrer. The temperature is raised to 135°C in 30 minutes. The clear solution obtained is kept under reflux and stirred for another 30 minutes. The solution is cooled in two stages. In the first stage, the temperature is reduced to 100°C in air under stirring for 10 to 15 minutes. In the second stage, the flask is transferred to a thermostatically controlled water bath at 25°C for 30 minutes. The temperature is reduced to 25°C without stirring during the first 20 minutes, and maintained at 25°C for the last 10 minutes under stirring. The solid formed is filtered on a fast filter paper (e.g., Whatman filter paper grade 4 or 541). 100ml of the filtered solution (S1) is poured into a pre-weighed aluminum container, which is heated to 140°C on a heating plate under a nitrogen stream to remove the solvent by evaporation. The container is then kept in 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. A The fraction of component (B) soluble in xylene at 25°C (XS B ) can be calculated by the following formula:

[0129] XS=W(A)×(XS A )+W(B)×(XS B )

[0130] Wherein W(A) and W(B) are the relative amounts of components (A) and (B), respectively, and W(A)+W(B)=1.

[0131] Comonomer content: 13C NMR spectra were acquired on a Bruker AV-600 spectrometer equipped with a cryoprobe, operating at 120°C in Fourier transform mode. The sample was dissolved in 1,1,2,2-tetrachloroethane-d2 at 8% weight / volume concentration at 120°C. Each spectrum was acquired with a 90° pulse, and 1H-13C coupling was removed with a 15 second delay between pulses and CPD. The spectrometer was operated at 160.91 MHz. The peak of Sδδ carbon at 29.9 ppm (according to "Monomer Sequence Distribution in Ethylene-Propylene Rubber Measured by 13C NMR. 3. Use of Reaction Probability Mode" CJ Carman, RA Harrington and CE Wilkes, "Macromolecules", 1977, 10, 536) was used as an internal reference. 512 transients were stored in 32K data points using a spectral window of 9000 Hz.

[0132] Propylene copolymer Spectral assignment, triad distribution and composition evaluation were performed 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 equation:

[0133] PPP=100T ββ / S PPE=100T βδ / S EPE=100T δδ / S

[0134] PEP=100s ββ / S PEE=100S βδ / S EEE=100(0.25S γδ +0.5S δδ ) / S

[0135] S=T ββ +T βδ +T δδ +S ββ +S βδ +0.25S γδ +0.5S δδ

[0136] The molar contents of ethylene and propylene were calculated from the triad using the following equations:

[0137] [E]mol=EEE+PEE+PEP

[0138] [P]mol=PPP+PPE+EPE

[0139] The weight percent of ethylene content (E wt %) was calculated using the following equation:

[0140]

[0141] in

[0142] [P]mol = molar percentage of propylene content;

[0143] MWE = molecular weight of ethylene

[0144] MWP = molecular weight of propylene.

[0145] The total ethylene content C2(tot) and the ethylene content C2(A) of component (A) were measured; the ethylene content C2(B) of component (B) was calculated using the following formula:

[0146] C2(tot)=W(A)×C2(A)+W(B)×C2(B)

[0147] Wherein W(A) and W(B) are the relative amounts of components (A) and (B) (W(A)+W(B)=1).

[0148] Butene-1 copolymer: The assignment of spectra, triad distribution and evaluation of composition were performed according to Kakugo [M. Kakugo, Y. Naito, K. Mizunuma and T. Miyatake, Macromolecules, 16, 4, 1160 (1982)] and Randall [JC Randall, Macromol. Chem Phys., C30, 211 (1989)] using the following equations:

[0149] BBB=100T ββ / S BBE=100T βδ / S EBE=100P δδ / S

[0150] BEB=100S ββ / S BEE=100S αδ / S EEE=100(0.25S γδ +0.5S δδ ) / S

[0151] S=T ββ +T βδ +P δδ +S ββ +S αδ +0.25S γδ +0.5S δδ

[0152] The total amount of 1-butene and ethylene was calculated as a mole percent from the triad using the following relationship:

[0153] [E]=EEE+BEE+BEB

[0154] [B]=BBB+BBE+EBE

[0155] The weight percent of ethylene content (E wt %) was calculated using the following equation:

[0156]

[0157] in

[0158] [B]mol = molar percentage of 1-butene content;

[0159] MWE = molecular weight of ethylene

[0160] MWB = molecular weight of 1-butene.

[0161] Molecular weight distribution Mw / Mn: The average Mn and Mw and the Mw / Mn derived therefrom were determined using a Waters GPCV 2000 device equipped with a column set of 4 PLgel Olexis mixed gels (Polymer Laboratories) and an IR4 infrared detector (PolymerChar). The dimensions of the column were 300×7.5 mm, and the particle size was 13 μm. The mobile phase used was 1-2-4-trichlorobenzene (TCB), and its flow rate was maintained at 1.0 ml / min. All measurements were performed at 150°C. The solution concentration in TCB was 0.1 g / dl, and 0.1 g / l of 2,6-di-tert-butyl-p-cresol was added to prevent degradation. For GPC calculations, a universal calibration curve was obtained using 10 polystyrene (PS) standard samples (peak molecular weights of 580 to 8500000) supplied by Polymer Laboratories. The experimental data were interpolated using a third-order polynomial fit and the associated calibration curve was obtained. Empower (Waters) was used for data acquisition and processing. The molecular weight distribution and the related average molecular weight were determined using the Mark-Houwink relationship: the K values ​​for PS and PB were KPS=1.21×10-4dL / g and KPB=1.78×10-4dL / g, respectively, while the Mark-Houwink index α=0.706 was used for PS and the Mark-Houwink index α=0.725 was used for PB. For butene-1 / ethylene copolymers, for data evaluation, the composition was assumed to be constant over the entire range of molecular weights, and the K value of the Mark-Houwink relationship was calculated using the linear combination reported below:

[0162] K EB =x E K PE +x P K PB

[0163] Where K EB is the constant of the copolymer, K PE (4.06×10 -4 , dL / g) and K PB (1.78×10 -4 dl / g) are constants for polyethylene and polybutene, and xE and xB are the weight % contents of ethylene and butene-1. The Mark-Houwink index α=0.725 is used for all butene-1 / ethylene copolymers, regardless of their composition.

[0164] Melting temperature: measured according to method ISO 11357-3:2018. To determine the melting temperature (Tm(I)) of polybutene-1 form I, the sample was melted, kept at 200°C for 5 minutes and then cooled to 20°C at a cooling rate of 10°C / min. The sample was then stored at room temperature for 10 days. After 10 days, the sample was subjected to DSC, cooled to -20°C and then heated at 200°C at a scanning rate corresponding to 10°C / min. In this heating run, the first peak temperature from the lower temperature side of the thermogram was regarded as the melting temperature Tm(I).

[0165] Flexural modulus: Determined according to method ISO 178:2010 on injection molded test specimens (80x10x4 mm) of propylene polymers or compression molded specimens of butene-1 polymers obtained according to method ISO 1873-2:2007. Prior to testing, specimens of butene-1 copolymers were conditioned at 23°C for 10 days.

[0166] Seal initiation temperature (SIT). Film strips of 6×35 cm were cut from the cast film and two film strips were superimposed. The strips were sealed using a Brugger Feinmechanik sealer model HSG-ETK 745 under the following conditions: Teflon coated TM Smooth metal sealing bars, both bars are heated; sealing time 5 seconds; sealing pressure 0.14MPa (20psi); initial sealing temperature is 90°C. Six 15mm wide test specimens are cut from each sealing strip, and their length is sufficient to be protected in the tensile testing machine fixture. The seal strength at a given temperature is tested at a load cell capacity of 100N, a lateral speed of 100mm / min and a clamping distance of 50mm. The seal strength value is the average of 6 measurements on the same specimen. The temperature is increased by 5°C and the test is repeated. When the seal strength differs by less than 3N for the three temperatures, a plateau is reached and the average plateau strength is calculated. The seal initiation temperature (SIT) is calculated on the sealing diagram (force / temperature) as the temperature corresponding to half of the plateau seal strength.

[0167] Determination of hot tack. The hot tack is measured after sealing the test specimen for 5 seconds at a pressure of 0.12 MPa (18 psi) with a Brugger HSG heat sealer (with a hot tack test kit). The films are cut with a minimum length of 15x200 mm, superimposed, and sealed at different temperatures, i.e. the sealing temperature is increased by 5°C starting from 80°C. Immediately after sealing, the test specimen is pulled onto a mandrel by a pulley to separate the heat-sealed seam. For each sealing temperature, a different drop weight is used to impact the test specimen, and the force required to separate the still hot sealed seam at half its length (hot tack) is determined.

[0168] Haze: ASTM D1003

[0169] Gloss: ASTM D2457 (angle 45°)

[0170] Raw materials:

[0171] PP(a) : a propylene-ethylene copolymer obtained by a gas phase polymerization process as described in Example 44 of EP1012195B1, containing 6.0 wt% of ethylene-derived units, based on the weight of PP(a), having a solubility in xylene at 25°C of 16.0 wt% and an MFR(a) of 0.8 g / 10 min (230°C / 2.16 kg),

[0172] PB1(b): A copolymer of butene-1 and ethylene containing 3.6% by weight of ethylene and having a Tm(I) of 94°C, a molecular weight distribution Mw / Mn of 5.6, a melt flow rate of 3.5 g / 10 min (190°C / 2.16 kg) and a flexural modulus of 120 MPa. The butene-1 copolymer was obtained by sequential polymerization in two reactors under the following polymerization conditions in the first reactor, using butene-1 as liquid medium and a Ziegler-Natta catalyst system according to Example 11 of patent WO2004 / 048424: temperature of 75°C and a hydrogen / butene feed ratio of 1000 ppmV. After 2.5 hours, the polymer content of the first reactor was transferred to the second reactor, where the copolymerization was continued under the same conditions, the only difference being that the ethylene feed was interrupted. The polymerization was stopped after 2 hours.

[0173] PP(c): A heterophasic propylene copolymer comprising 32 wt% of a propylene-ethylene copolymer (i) containing 3.2 wt% of ethylene-derived units, based on the weight of (i), and 68 wt% of a propylene ethylene copolymer (ii), the propylene-ethylene copolymer (i) containing 27.0 wt% of units derived from ethylene, based on the weight of (ii), and having a solubility in xylene of 64 wt% at 25°C, wherein the amounts of (i) and (ii) are based on the total weight of (i) + (ii). The heterophasic propylene polymer has a melt flow rate of 0.6 g / 10 min (230°C / 2.16 kg), a melting temperature of 142°C as measured by DSC, and a flexural modulus of 100 MPa. The heterophasic propylene polymer is prepared by a gas phase polymerization process (H2 / C3 GPR1: 0.03 mol; C2 / C3 GPR2: 0.17 mol) carried out in at least two reactors connected in series in the presence of a Ziegler-Natta catalyst system as described in Example 4 of WO 2012 / 139897. The amounts of (i) and (ii) correspond to the split between the reactors.

[0174] PP45NP : A premix containing as carrier resin 10% by weight of the silica Sylobloc 45H sold by Grace and 90% by weight of Moplen RP310M sold by LyondellBasell, a slightly modified propylene-ethylene copolymer with a melt flow rate of 8.5 g / 10 min (230° C. / 2.16 kg).

[0175] Examples E1-E2 and Comparative Example CE3

[0176] A blown film with structure A / B / A and a total film thickness of 100 microns (layer distribution A=20% / B=60% / A=20%) was produced on a Collin coex blown film line, wherein the diameter of the extruder for layer A was 30 mm and the diameter of the extruder for core layer B was 45 mm. The ABA stream was fed into an annular die with a diameter of 80 mm and a die gap (die lip opening) of 1.2 mm. Total output: 12 Kg / h. The annular melt stream was then blown up to a diameter of 200 mm with air, resulting in a blow-up ratio of 2.5:1 (BUR=blown film diameter / annular die diameter), followed by cooling with cold air at the outlet of a distribution ring located outside and coaxial with the annular die. The cooled tubular film was then collapsed with a nip roll and collected into a reel by a winding unit.

[0177] The components included in the monolayers are reported in Table 1. The mechanical, thermal and optical properties of the blown films are reported in Table 2.

[0178] Table 1

[0179]

[0180] Table 2

[0181] E1 E2 CE3 Haze 16.7 20.1 24.4 Gloss at 45° 40.3 35.4 29.3 SIT ℃ 115 118 127 Hot tack at 110°C N 2.5 2.0 0.2

Claims

1. A multilayer film comprising a surface layer (A) and a core layer (B), wherein: - the surface layer (A) comprises a polyolefin composition (I), the polyolefin composition (I) comprising: (a) a copolymer of 70 to 95 wt.% of propylene and at least one α-olefin of the formula CH2=CHR, wherein R is hydrogen or a linear or branched C2-C8 alkyl group, comprising up to and including 10.0 wt.% of units derived from said α-olefin, based on the weight of (a), said propylene copolymer having from 10 to 20 wt.% of a fraction soluble in xylene at 25°C; and (b) 5 to 30 wt. % of a butene-1 polymer selected from butene-1 homopolymers, copolymers of butene-1 with up to and including 5.0 wt. %, based on the weight of (b), of units derived from ethylene and / or propylene, and mixtures thereof, wherein the amounts of (a) and (b) are based on the total weight of (a) + (b); - the core layer (B) comprises a copolymer (c) of propylene and up to and including 25 wt. %, based on the weight of the copolymer, of at least one α-olefin of formula CH2=CHR, wherein R is hydrogen or a linear or branched C2-C8 alkyl group.

2. The multilayer film according to claim 1, wherein the polyolefin composition (I) comprises 75 to 90 wt% of the propylene copolymer (a) and 10 to 25 wt% of the butene-1 polymer (b), wherein the amounts of (a) and (b) are based on the total weight of (a) + (b).

3. The multilayer film according to claim 1 or 2, wherein the polyolefin composition (I) comprises a propylene copolymer (a) comprising from 0.5 to 10.0 wt.-%, based on the weight of (a), of units derived from the α-olefin, preferably ethylene, and a butene-1 copolymer (b) comprising from 0.5 to 5.0 wt.-%, based on the weight of (b), of units derived from ethylene and / or propylene, preferably ethylene.

4. The multilayer film according to any one of claims 1 to 3, wherein the propylene copolymer (a) is a propylene-ethylene copolymer having at least one of the following properties: - comprises 2.0 to 10.0 wt.-%, preferably 2.2 to 9.8 wt.-%, more preferably 3.0 to 8.0 wt.-%, still more preferably 4.5 to 7.2 wt.-% of units derived from ethylene, based on the weight of the propylene copolymer (a); and / or - a melt flow rate measured according to 1133-1:2011 (230°C / 2.16Kg) of 0.1 to 10.0 g / 10 min, preferably 0.3 to 7.0 g / 10 min, more preferably 0.5 to 3.0 g / 10 min; and / or - having from 12 to 20 wt.-%, preferably from 14 to 18 wt.-%, based on the weight of the propylene copolymer (a), of a fraction XS (a) soluble in xylene at 25°C.

5. The multilayer film according to any one of claims 1 to 4, wherein the butene-1 polymer (b) is a copolymer of butene-1 and ethylene having at least one of the following properties: - a content of units derived from ethylene of from 1.0% to 4.5% by weight, preferably from 1.5% to 4.5% by weight, more preferably from 2.0% to 4.0% by weight, still more preferably from 2.5% to 3.5% by weight, based on the weight of (b); and / or - a melting temperature Tm(I) measured by DSC according to method ISO 11357-3:2018 of less than 100°C, preferably from 80°C to less than 100°C, more preferably from 90°C to 97°C; and / or - a melt flow rate measured according to ISO 1133-1:2011 (190°C / 2.16kg) of 1.0 to 6.0 g / 10 min, preferably 2.0 to 5.0 g / 10 min, still more preferably 3.0 to 4.5 g / 10 min; and / or - Flexural modulus measured according to ISO 178:2010 equal to or higher than 80 MPa, preferably from 80 to 250 MPa, more preferably from 100 to 210 MPa.

6. The multilayer film according to any one of claims 1 to 5, wherein the propylene copolymer (c) is a heterophasic propylene polymer comprising: - 20 to 40 wt.-% of a polymer fraction (i), said polymer fraction (i) comprising a propylene polymer chosen from propylene homopolymers, propylene copolymers having up to and comprising 6.0 wt.-%, preferably 0.1 to 6.0 wt.-%, based on the weight of said fraction (i), of at least one α-olefin of formula CH2=CHR, wherein R is hydrogen or a linear or branched C2-C8 alkyl group, and combinations thereof; and 60 to 80% by weight of a polymer fraction (ii) comprising a copolymer of propylene and up to and including 35.0% by weight, preferably 20 to 35.0% by weight, based on the weight of fraction (ii), of at least one alpha-olefin of formula CH2=CHR, in which R is hydrogen or a linear or branched C2-C8 alkyl group, and having a solubility in xylene at 25°C of 45.0 to 75.0% by weight, based on the weight of fraction (ii), The amounts of (i) and (ii) are based on the total weight of (i) + (ii).

7. The multilayer film according to claim 6, wherein the propylene copolymer (c) is a heterophasic propylene polymer comprising: 20 to 40 wt.-%, preferably 25 to 35 wt.-%, of a polymer fraction (i) comprising a propylene-ethylene copolymer comprising up to and including 6.0 wt.-%, preferably 0.1 to 6.0 wt.-%, more preferably 1.5 to 4.5 wt.-%, based on the weight of fraction (i), of units derived from ethylene; as well as 60 to 80 wt.-%, preferably 65 to 75 wt.-%, of fraction (ii), said fraction (ii) comprising a propylene-ethylene copolymer comprising up to and including 35.0 wt.-%, preferably 20.0 to 35.0 wt.-%, more preferably 23.0 to 30.0 wt.-%, based on the weight of fraction (ii), of units derived from ethylene and having a solubility in xylene at 25° C. of 55.0 to 75.0 wt.-%, preferably 60.0 to 70.0 wt.-%, based on the weight of fraction (ii), The amounts of (i) and (ii) are based on the total weight of (i) + (ii).

8. The multilayer film according to any one of claims 1 to 7, wherein the total film thickness is from 10 to 200 microns, preferably from 20 to 140 microns.

9. The multilayer film according to any one of claims 1 to 8, wherein the ratio of the thickness of the skin layer (A) to the thickness of the core layer (B) is from 1:1 to 1:12, preferably from 1:2 to 1:

6.

10. The multilayer film according to any one of claims 1 to 9, comprising a second skin layer (C), said second skin layer (C) comprising the polyolefin composition according to any one of claims 1 to 5.

11. The multilayer film according to claim 10, wherein the skin layer (A) and the second skin layer (C) comprise the same polyolefin composition (I).

12. The multilayer film according to claim 10 or 11, wherein the skin layer (A) and the second skin layer (C) are identical, and the multilayer film has an A / B / A structure.

13. The multilayer film of any one of claims 1-12, wherein the film is a non-oriented film.

14. The multilayer film of claim 13, wherein the film is a cast film or a blown film.

15. The multilayer film according to claim 13 or 14, having at least one of the following properties: - a seal initiation temperature (SIT) equal to or lower than 125°C, preferably from 90°C to 125°C, more preferably from 100°C to 125°C, even more preferably from 110°C to 120°C; and / or The hot tack at -110°C is 1.0 to 6.0N, preferably 1.5 to 4.0N.

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