BOPP film with increased water vapour permeability

Abstract

The present invention relates to a new biaxially oriented polypropylene (BOPP) film, a process for the preparation of such film as well as the use of a beta-nucleated polypropylene homopolymer for the preparation of such film and an article comprising such film.

Description

[0001] BOPP FILM WITH INCREASED WATER VAPOUR PERMEABILITY

[0002] Field of the invention

[0003] The present invention relates to a new biaxially oriented polypropylene (BOPP) film, a process for the preparation of such film as well as the use of a beta-nucleated polypropylene homopolymer for the preparation of such film and an article comprising such film.

[0004] Background

[0005] Breathable films have microporous morphology (i.e. , microvoids) to provide a water vapor transmission rate (“WVTR”) that assists in allowing the passage of moisture vapor and eliminating water droplet condensation. Breathability or WVTR is an important property of many breathable films because films can act as a liquid barrier while permitting the transmission of water vapor to provide benefits such as protection or comfort. Sreathable films are typically made by incorporating filler (e.g., CaCOs) into polyolefin resins, such as polyethylene or polypropylene, making a cast or blown film, and stretching or orienting the cast or blown film via machine direction orientation rolls via tentering, or via intermeshing gears whereby the film is ringrolled or incrementally stretched in one or both the machine direction or transverse direction below the melting point of the polyolefin resins.

[0006] Microvoids are created, in part, because of the addition of the filler into polyolefins of the film. The post extrusion process, such as machine direction orientation or use of interdigitating, also contributes to creating microvoids in the film by creating cavitation around the filler particles at the filler and polyolefin interface.

[0007] Controlled vapour permeability is a key property for several high- and low-end applications. A well know high-end example is Gore-Tex®, which is used in performance fabrics, medical implants, filter media, etc. Gore-Tex® membranes are made of polytetrafluoroethylene (PTFE) film that has been stretched creating tiny cracks (crazes) in the material allowing gaseous water to pass whereas liquid water cannot pass, rendering the material “breathable”. PTFE is associated high costs, as well as it renders applications made thereafter not “halogen-free”.

[0008] Examples of low-end applications are non-wovens used e.g. in diapers, coveralls, housewrap, etc..

[0009] EP1375584 describes breathable films prepared from linear low-density polyethylene compositions. The composition comprises 20 to 50 wt.-%; based on the weight of the total composition, of a bimodal polyethylene composition, 40 to 70 wt.-%, based on the weight of the total composition, of a particulate filler, and optionally 0 to 30 wt.-%, based on the weight of the total composition of an olefin-based polymer, like polypropylene. It is described that when the composition is extruded to a film and the film is stretched, micropores are formed adjacent to the filler particles. These micropores allow the passage of gases and vapours through the film. On the other hand, the micropores are small enough to prevent the passage of liquids through the film.

[0010] The films described herein are blown films, which are stretched only in machine direction. The use of such high amounts of fillers is disadvantageous, i.a. in view of recyclability.

[0011] US3920785 describes a process for increasing the porosity of open-celled microporous films. The process comprises contacting the film with at least one liquid organic compound having up to 8 carbon atoms and a boiling point less than 150°C. These liquid organic compounds may be selected from aliphatic and aromatic hydrocarbons, chlorinated aliphatic hydrocarbons, aliphatic ketones, monohydric aliphatic alcohols, and aliphatic ethers. According to US3920785 the essence of the invention is the discovery that certain liquid organic compounds impart greater porosity to certain open-celled microporous polymer films which are produced from non-porous, crystalline, elastic polymer films. The process for producing these particular open-celled films includes the steps of (1) cold stretching, i.e., cold drawing, the elastic film until porous surface regions or areas which are elongated normal or perpendicular to the stretch direction are formed, (2) hot stretching, i.e., hot drawing, the cold stretched film until fibrils and pores or open cells which are elongated parallel to the stretch direction are formed, and thereafter (3) heating or heat setting the resulting porous film under tension, i.e., at substantially constant length, to impart stability to the film. The elastic film is preferably made from crystalline polymers such as polypropylene by melt extruding the polymer into a film, taking up the extrudate at a drawdown ratio giving an oriented film, and thereafter heating or annealing the oriented film if necessary to improve or enhance the initial crystallinity. One disadvantage of the proposed process is the requirement of an additional step of contacting the film with at least one liquid organic compound, which may be selected form i.a. possibly hazardous liquids, like benzene etc..

[0012] Offord et al., describe in Polymer 54 (2013), p 2796 to 2807, microporous polymer membranes, which were produced from p-nucleated isotactic polypropylene using a solvent-free process involving extrusion and biaxial stretching. Melt blending was used to produce a master batch of 0.5 wt.-% quinacridone quinone (QQ) as p-nucleator in an iPP grade, which was then blended with additional iPP to reach a concentration of 0.1 wt.-% QQ in iPP.

[0013] The films have been check i.a. in view of gas pearmeability. The disadvantage of this approach, is that adding that high amount of beta-nucleating agent (i.e. 1000 ppm) makes the films too soft, which can cause problems during stretching. Although already a great number of breathable films have been proposed, there is still the need to provide new solutions, i.e. new biaxially oriented polypropylene (BOPP) films, which provide high water vapour permeability combined with improved simplicity (in view of above mentioned state of the art solutions, e.g. no additional process step, no inorganic particles involved) and recycl ability.

[0014] Accordingly, it is an object of the present invention to provide a biaxially oriented polypropylene (BOPP) film with high water vapour permeability, improved recyclability and simplicity.

[0015] Summary of the Invention

[0016] Thus, the present invention is, in a first aspect, related to a biaxially oriented polypropylene (BOPP) film comprising at least 95 wt.-%, based on the total weight of the film, of a polypropylene homopolymer composition comprising a) one or more polypropylene homopolymer(s) (PPH) having

[0017] • a melt flow rate MFR2, determined according to ISO 1133 at 230 °C and a load of 2.16 kg, in the range of 1.0 to 5.0 g / 10 min

[0018] • an isotactic pentad regularity <mmmm>, determined by13C-NMR spectroscopy, in the range of 90.0 to 99.9%

[0019] • a xylene cold soluble (XCS) content, determined according to ISO 16152 at 25 °C, in the range of 0.5 to less than 3.8 wt.-%

[0020] • a melting temperature, Tm, measured with DSC according to ISO 11357, in a range of

[0021] 155 to 170 °C,

[0022] • a crystallization temperature, Tc, measured with DSC according to ISO 11357 in a range of 105 to 125 °C,

[0023] • a weight average molecular weight (Mw), determined with GPC, as described in the experimental part, in the range of in the range of 300 to 420 kg / mol, and

[0024] • a polydispersity index (PI), determined at 220 °C, as described in the experimental part, in the range of 4.0 to 6.8 Pa-1, b) 5 to 20 ppm, based on the total weight of the polypropylene homopolymer composition, of at least one beta- nucleating agent, wherein the biaxially oriented polypropylene (BOPP) film has a water vapour transmission rate (WTVR), determined according to ISO 15106-2 of greater than 300 g / m2 / day at 38 °C and at a relative humidity of 90%. In a further aspect, the present invention is related to a process for producing such a BOPP film.

[0025] In a third aspect, the present invention is directed to the use of such BOPP films for laminated fabrics, water vapour permeable fabrics, wearable articles thereof, consumer air and water filters, roof insulation, technical fabrics, diapers.

[0026] Definitions

[0027] Where the term "comprising" is used in the present description and claims, it does not exclude other non-specified elements of major or minor functional importance. For the purposes of the present invention, the term "consisting of" is considered to be a preferred embodiment of the term "comprising of". If hereinafter a group is defined to comprise at least a certain number of embodiments, this is also to be understood to disclose a group, which preferably consists only of these embodiments.

[0028] Whenever the terms "including" or "having" are used, these terms are meant to be equivalent to "comprising" as defined above.

[0029] Where an indefinite or definite article is used when referring to a singular noun, e.g. "a", "an" or "the", this includes a plural of that noun unless something else is specifically stated.

[0030] A “polypropylene homopolymer” in the sense of this disclosure refers to a propylene polymer preferably containing not more than 1.0 wt.-% of comonomer selected from the group of ethylene and / or alpha-olefins having 4 to 10 carbon atoms. More preferably, such propylene polymers will contain less than 0.8 wt.-% or less than 0.5 wt.-% of comonomers, The propylene polymer may also be free of comonomers.

[0031] It is also understood within the meaning of this disclosure that the below described embodiments may be combined.

[0032] It should be understood that any of the lower or upper limits of any of the parameters described for the preferred embodiments of the present invention can be combined with each other. Likewise, any of the lower or upper limits of any of the parameters described for the “other preferred embodiments of the present invention” can be combined with each other.

[0033] Detailed Description of the Invention

[0034] Polypropylene homopolymer composition

[0035] The BOPP film of the present invention comprises a polypropylene homopolymer composition, which comprises, preferably consists of one or more polypropylene homopolymer(s) (PPH) and at least one beta-nucleating agent. It is envisaged in the present invention that conventional additives may be present in the polypropylene homopolymer(s), even in case, the composition is defined in a closed way using “consisting of” wording.

[0036] Polypropylene homopolymer(s) (PPH)

[0037] The polypropylene homopolymer (PPH) suitable for being used in the BOPP film of the present invention is characterized by a melt flow rate MFR2, determined according to ISO 1133 at 230 °C and a load of 2.16 kg, in the range of 1.0 to 5.0 g / 10 min, preferably 1.5 to 4.5 g / 10 min, more preferably 2.0 to 4.0 g / 10 min and even more preferably 2.5 to 3.8 g / 10 min.

[0038] In addition the propylene homopolymer is characterized by a isotactic pentad regularity <mmmm> determined by13C-NMR spectroscopy in the range of 90.0 to 99.9%, preferably in the range of 90.5 to 99.0%, more preferably in the range of 91 .0 to 98.0%.

[0039] The high isotacticity goes along with a high crystallinity of the material. Moreover, the high isotacticity is accompanied by a low xylene cold soluble (XCS) content. Therefore, the polypropylene homopolymer is featured by a rather low xylene cold soluble (XCS) content (ISO 16152; at 25 °C) in the range of 0.5 to less than 3.8 wt.-%, preferably in the range of 0.8 to 3.6 wt.-%, more preferably in the range of 1 .0 to 3.5 wt.-%.

[0040] It is appreciated that the XCS content indicates that the high isotactic homopolymer of propylene is preferably free of any elastomeric polymer component, like an ethylene propylene rubber. In other words, the high isotactic homopolymer of propylene does not correspond to a heterophasic polypropylene, i.e. a system consisting of a polypropylene matrix in which an elastomeric phase is dispersed. Such systems are usually featured by a rather high xylene cold soluble content.

[0041] The polypropylene homopolymer furthermore has a melting temperature, Tm, measured with DSC according to ISO 11357, in a range of 155 to 170 °C, preferably in the range of 158 to 168 °C and more preferably in the range of 160 to 166 °C and a crystallization temperature, Tc, measured with DSC according to ISO 11357 in a range of 105 to 125 °C, preferably in the range of 107 to 120 °C and more preferably in the range of 109 to 118 °C.

[0042] Additionally, the polypropylene homopolymer has a weight average molecular weight (Mw), determined with GPC, as described in the experimental part, in the range of in the range of 300 to 420 kg / mol, preferably 320 to 400 kg / mol, more preferably 330 to 390 kg / mol, most preferably 340 to 380 kg / mol. The polydispersity index (PI), determined as described in the experimental part, of the polypropylene homopolymer is in the range of 4.0 to 6.8 Pa'1, preferably in the range of 4.2 to 6.6 Pa'1and more preferably in the range of 4.4 to 6.4 Pa'1.

[0043] In the scope of the present invention the general principle applies that each of the above properties (here MFR2, pentad regularity <mmmm>, XCS, Tm Tc, Mw, PI) may preferably be individually adjusted into a preferred or more preferred range, while it is even more preferred that two or more, most preferably all, of the above properties may be adjusted into preferred and / or even more preferred ranges in combination. Again, this general principle generally applies throughout the entire application to other mentioned properties (as given below or above) in connection with (preferred) quantifications.

[0044] According to a preferred embodiment, the polypropylene homopolymer has a number average molecular weight Mn (GPC) in the range of 30.0 to 53.0 kg / mol, preferably 32.0 to 51 .0 kg / mol, more preferably 33.0 to 49.0 kg / mol, most preferably 34.0 to 46.0 kg / mol. Within these ranges, the effects of the present invention are more pronounced.

[0045] According to a preferred embodiment, the polypropylene homopolymer has a z-average molecular weight Mz (GPC) in the range of 1000 to 2000. kg / mol, preferably 1100 to 1800 kg / mol, more preferably 1150 to 1700 kg / mol, and even more preferably 1200 to 1650 kg / mol.

[0046] According to another preferred embodiment, the polypropylene homopolymer has a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) [Mw / Mn] of at least 5.0, Mw and Mn both determined with GPC, as described in the experimental part.

[0047] More preferably Mw / Mn is in the range of 5.0 to 12.0, preferably 6.0 to 11.0, and more preferably 7.0 to 10.0.

[0048] Given the general principle, it is apparently preferred that the polypropylene homopolymer, preferably in addition to the above and / or below characteristics, has the Mn and Mw, and more preferably the Mn, Mw and Mz in the above ranges by setting individually or combined the preferred or more preferred ranges.

[0049] According to a preferred embodiment, preferably in addition to the above and / or below characteristics, the polypropylene homopolymer has a zero shear viscosity in the range of 6000 Pa s to 25000 Pa s, preferably 7000 Pa s to 20000 Pa s, more preferably 8000 Pa s to 15000 Pa s, determined at 220 °C, as described in the experimental part.

[0050] The polypropylene homopolymer may also comprise one or more additives, excluding nucleating agents. Preferably the one or more additives are present in a content from 0 to 2.0 wt.-%, more preferably in an amount from 0.05 to 1.0 wt.-%, in particular in an amount from 0.05 to 0.5 wt.-%, based on the total weight of the polypropylene homopolymer.

[0051] The one or more additives may be non-polymeric additives and / or polymeric additives, with non-polymeric additives being preferred. For example, the one or more additives may be selected from the group consisting of antioxidants, stabilizers, acid scavengers, colorants, plasticizers, slip agents, antiscratch agents, dispersing agents, processing aids, lubricants, pigments, antistatic agent, and the like. It is particularly preferred when the one or more additives are selected from the group consisting of antioxidants, stabilizers and acid scavengers and combinations thereof.

[0052] The polypropylene homopolymer composition may comprise one polypropylene homopolymer with the above described properties, or may comprise two or more, preferably two different polypropylene homopolymers, both being characterized by the above described properties.

[0053] In case that the polypropylene homopolymer composition comprises, preferably consists of two different polypropylene homopolymers, the second polypropylene homopolymer is preferably the carrier polymer of a masterbatch, which is used to incorporate the beta nucleating agent(s) into the polypropylene homopolymer composition.

[0054] In case a second polypropylene homopolymer is used as a carrier polymer in a masterbatch for incorporating the beta nucleating agent, the second polypropylene homopolymer is present in the polypropylene homopolymer composition in an amount of 1.0 to 5.0 wt.-%, preferably 1.2 to 4.0 wt.-% and more preferably 1.5 to 3.0 wt.-%, based on the total weight of the polypropylene homopolymer composition.

[0055] The polypropylene homopolymer(s) may be produced by any procedure known in the art. However, there exists a crucial difference in the chain-microstructure between polypropylenes produced by a single site catalyst such as a metallocene catalyst and a Ziegler-Natta catalyst. The chain regularity of metallocene-based polypropylene is reduced by stereo- and regiodefects, whereas the chain regularity of Ziegler-Natta based polypropylenes is only reduced by stereo defects. It is preferred that the polypropylene homopolymer(s) is / are obtained in the presence of a Ziegler-Natta catalyst yielding the polypropylene homopolymer(s) having the above described characteristics especially in terms of high pentad isotacticity <mmmm> with a moderate molecular weight distribution Mw / Mn(MWD) and / or polydispersity index (PI) as described above.

[0056] Preferably, the polypropylene homopolymer(s) is / are polymerized in a slurry polymerization process, wherein at least

[0057] (a) a Ziegler-Natta catalyst, preferably a titanium compound, more preferably TiCh, (b) propylene, and

[0058] (c) a diluent (D) comprising a donor agent, preferably an external donor selected from the group consisting of methyl methacrylate, butyl methacrylate, 2-ethyl 1-hexyl methacrylate, and tridecyl methacrylate, or mixtures therefrom, more preferably methyl methacrylate and / or butyl methacrylate, are fed into at least one polymerization reactor, in case of several polymerization reactors in at least the first polymerization reactor, to conduct polymerization.

[0059] The Ziegler-Natta catalyst system preferably comprises a co-catalyst such as an organic aluminum compound and may contain internal donors.

[0060] Such polymerization processes are described in e.g. WO 2021 / 239594 A 1 and WO 2013 / 004781 A1 and details about the Ziegler-Natta catalyst system including co-catalysts, internal and external donors, and how to prepare Ziegler-Natta catalysed polypropylene polymers can be found in these references..

[0061] Suitable polypropylene homopolymers are also commercial available, for example under the tradenames HC318BF or HC300BF all commercial available from Borealis AG.

[0062] Beta nucleating agent

[0063] The at least one beta nucleating agent is present in an amount of 5 to 20 ppm, preferably 7 to 15 ppm and more preferably 8 to 12 ppm, based on the polypropylene homopolymer composition.

[0064] The term “beta-nucleating agent” refers to any nucleating agent which is suitable for inducing crystallization of propylene polymers in the hexagonal or pseudohexagonal modification. Mixtures of such nucleating agents may also be employed.

[0065] Suitable types of beta-nucleating agents are dicarboxylic acid derivative type diamide compounds from C5-C8-cycloalkyl monoamines or 06-012-aromatic monoamines and 05-08- aliphatic, C5-C8-cycloaliphatic or 06-012 aromatic dicarboxylic acids, e.g.

[0066] N,N'-di-C5-C8-cycloalkyl-2,6-naphthalene dicarboxamide compounds such as

[0067] N,N'-dicyclohexyl-2,6-naphthalene dicarboxamide and

[0068] N,N'-dicyclooctyl-2,6-naphthalene dicarboxamide,

[0069] N,N'-di-C5-C8-cycloalkyl-4,4-biphenyldicarboxamide compounds such as

[0070] N,N'-dicyclohexyl-4,4-biphenyldicarboxamide and N,N'-di cyclopentyl-4, 4-biphenyldicarboxamide,

[0071] N,N'-di-C5-C8-cycloalkyl-terephthalamide compounds such as

[0072] N,N'-dicyclohexylterephthalamide and N,N'-dicyclopentylterephthalamide,

[0073] N,N'-C5-C8-cycloalkyl-1,4-cyclohexanedicarboxamide compounds such as

[0074] N,N'-dicyclo-hexyl-1,4-cyclohexanedicarboxamide and

[0075] N,N'-dicyclohexyl-1 ,4-cyclopentanedicarboxamide, diamine derivative type diamide compounds from C5-C8-cycloalkyl monocarboxylic acids or C6-C12-aromatic monocarboxylic acids and C5-C8-cycloaliphatic or C6-C12-aromatic diamines, e.g.

[0076] N,N'-C6-C12-arylene-bis-benzamide compounds such as

[0077] N,N'-p-phenylene-bis-benzamide and N,N'-1,5-naphthalene-bis-benzamide,

[0078] N,N'-C5-C8-cycloalkyl-bis-benzamide compounds such as

[0079] N,N'-1 ,4-cyclopentane-bis-benzamide and N,N'-1 ,4-cyclohexane-bis-benzamide,

[0080] N,N'-p-C6-C12-arylene-bis-C5-C8-cycloalkyl carboxamide compounds such as

[0081] N,N'-l,5-naphthalene-bis-cyclohexanecarboxamide and

[0082] N,N'-1 ,4-phenylene-bis-cyclohexanecarboxamide, and

[0083] N,N'-C5-C8-cycloalkyl-bis-cyclohexanecarboxamide compounds such as

[0084] N,N'-1 ,4-cyclopentane-bis-cyclohexanecarboxamide and

[0085] N,N'-1 ,4-cyclohexane-bis-cyclohexanecarboxamide, amino acid derivative type diamide compounds from amidation reaction of C5-C8-alkyl, C5- C8-cycloalkyl- or C6-C12-arylamino acids, C5-C8-alkyl-, C5-C8-cycloalkyl- or C6-C12- aromatic monocarboxylic acid chlorides and C5-C8-alkyl-, C5-C8-cycloalkyl- or C6-C12- aromatic monoamines, e.g.

[0086] N-phenyl-5-(N-benzoylamino)pentane amide and

[0087] N-cyclohexyl-4-(N-cyclohexyl-carbonylamino)benzamide.

[0088] Further suitable beta-nucleating agents are: quinacridone type compounds, e.g.

[0089] 5, 12-dihydro-quino[2,3-b]acridine-7, 14-dione (i.e. quinacridone), dimethylquinacridone and dimethoxyquinacridone, quinacridonequinone type compounds, e.g. quino[2,3-b]acridine-6,7,13,14(5H,12H)-tetrone (i.e. quinacridonequinone), and dimethoxyquinacridonequinone and dihydroquinacridone type compounds, e.g. 5,6,12,13- tetrahydroquino[2,3-b]acridine-7, 14-dione (i.e. a dihydroquinacridone), dimethoxy dihydroquinacridone and dibenzodihydroquinacridone.

[0090] Still further suitable beta-nucleating agents are dicarboxylic acid salts of metals from group 11a of periodic table, e.g. pimelic acid calcium salt and suberic acid calcium salt; and mixtures of dicarboxylic acids and salts of metals from group 11a of the periodic table.

[0091] In a particularly preferred embodiment, the nucleating agent is a quinacridone or quinacridonequinone type compound. For example, the nucleating agent is select-ed from the group consisting of 5, 12-dihydro-quino[2,3-b]acridine-7, 14-dione, quino[2,3-b]acridine- 6,7,13,14(5H,12H) tetrone, 5,6,12,13 tetrahydroquino[2,3-b]acridine-7, 14-dione and mixtures thereof.

[0092] As already indicated above, the beta nucleating agent may be incorporated into the polypropylene homopolymer by using a masterbatch.

[0093] Suitable masterbatches comprise a carrier polymer, which is for the present invention a polypropylene homopolymer with the above described parameters and the beta nucleating agent (or a mixture of 2 beta nucleating agents).

[0094] Such masterbatches are prepared for example by melt blending the carrier polymer and the beta nucleating agent.

[0095] Process for producing BOPP film

[0096] The present invention further provides a process for producing a BOPP film comprising the steps of:

[0097] (A) extruding the polypropylene homopolymer composition as defined above to a film,

[0098] (B) orienting the film in the machine direction (MD) and in the transverse direction (TD) to obtain the BOPP film, and (C) recovering the BOPP film having a water vapour transmission rate (WTVR), determined according to ISO 15106-2 of greater than 300 g / m2 / day at 38 °C and at a relative humidity of 90%.

[0099] The polypropylene homopolymer composition as defined above is used to prepare breathable films. The films may be produced either by blowing or casting. Preferably the films produced in the first step (step A) are cast films.

[0100] After the cast film has been prepared, it is stretched, respectively oriented in the machine direction (MD) and in the transverse direction (TD) to obtain a biaxially oriented polypropylene (BOPP) film.

[0101] The film shall be stretched from 2 to 6 times, preferably 2.5 to 4 times, its original length. This ratio between the length of the stretched film and the length of the original film is in referred to as the stretching ratio.

[0102] Preferably the stretch ratio is the same for both directions, e.g. a stretch ratio of 2.5x2.5 or 3x3 or 3.5x3.5 is applied.

[0103] Preferably, the biaxially oriented polypropylene film according to the present invention may be obtained by orienting the film simultaneously in the machine direction and in the transverse direction, more preferably the simultaneous orientation of the film in the machine direction and in the transverse direction to obtain the biaxially oriented polypropylene film is conducted in a continuous process.

[0104] Alternatively, in another preferred embodiment, sequential stretching, first by stretching in machine direction followed by stretching in transverse direction can be employed.

[0105] The thickness of the BOPP film is typically from 5 to 50 pm, preferably from 10 to 40 pm, and more preferably from 20 to 35 pm.

[0106] The biaxially oriented polypropylene (BOPP) film according to the invention may comprise at least 95 wt.-%, more preferably comprises at least 98.0 wt.-%, yet more preferably consists of, the polypropylene homopolymer composition as defined in the present invention.

[0107] Surprisingly, the BOPP films of the present invention have a very high water vapour transmission rate, determined according to ISO 15106-2 of greater than 300 g / m2 / day at 38 °C and at a relative humidity of 90%, preferably greater than 400 g / m2 / day, more preferably greater than 450 g / m2 / day. Such films are therefore suitable for being used for laminated fabrics, water vapour permeable fabrics, wearable articles thereof, consumer air and water filters, roof insulation, technical fabrics and diapers.

[0108] Experimental part

[0109] The nature of the present invention will become more clearly apparent and better to be understood in view of the accompanying examples. The examples are, however, in no way intended to limit the scope of the invention.

[0110] Measurement Methods

[0111] MFR

[0112] Melt flow rate MFR2 was determined according to ISO 1133 at 230 °C under a load of 2.16 kg.

[0113] Quantification of microstructure by NMR spectroscopy

[0114] Quantitative nuclear magnetic resonance (NMR) spectroscopy was used to quantify the isotacticity and regio-regularity of the propylene homopolymers.

[0115] Quantitative13C{1H} NMR spectra were recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for1H and13C respectively. All spectra were recorded using a13C optimised 10 mm extended temperature probehead at 125 °C using nitrogen gas for all pneumatics.

[0116] Approximately 200 mg of material (propylene homopolymer) was dissolved in 1 ,2- tetrachloroethane-d2 (TCE-d2). To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotary oven for at least 1 hour. Upon insertion into the magnet the tube was spun at 10 Hz. This setup was chosen primarily for the high resolution needed for tacticity distribution quantification (Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443; Busico, V.; Cipullo, R., Monaco, G., Vacatello, M., Segre, A.L., Macromolecules 30 (1997) 6251). Standard single-pulse excitation was employed utilising the NOE and bi-level WALTZ16 decoupling scheme (Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, 15 B., J. Mag. Reson. 187 (2007) 225; Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 11289). A total of 8192 (8k) transients were acquired per spectra.

[0117] Quantitative13C{1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs.

[0118] For propylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

[0119] Characteristic signals corresponding to regio defects (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253; Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157; Cheng, H. N., Macromolecules 17 (1984), 1950) or comonomer were observed.

[0120] The tacticity distribution was quantified through integration of the methyl region between 23.6- 19.7 ppm correcting for any sites not related to the stereo sequences of interest (Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443; Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A.L., Macromolecules 30 (1997) 6251).

[0121] By pentad isotacticity is meant the fraction of isotactic pentads (mmmm). xcs

[0122] The XCS content was determined in weight percent at 23 °C according to ISO 16152.

[0123] GPC (Mw, Mn, Mz, MWD)

[0124] Number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity (Mw / Mn, MWD) were determined by Gel Permeation Chromatography (GPC) according to the following method:

[0125] The number average molecular weight (Mn), the weight average molecular weight Mw, the z- average molecular weight Mz, and the polydispersity (Mw / Mn, wherein Mn is the number average molecular weight and Mw is the weight average molecular weight) is measured by a method based on ISO 16014-1 :2003 and ISO 16014-4:2003. A Waters Alliance GPCV 2000 instrument, equipped with refractive index detector and online viscometer was used with 3xTSK-gel columns (GMHXL-HT) from TosoHaas and 1 ,2,4-trichlorobenzene (TCB, stabilized with 200 mg / L 2,6-di tert butyl-4-methyl-phenol) as solvent at 145°C and at a constant flow rate of 1 mL / min. 216.5 pL of sample solution were injected per analysis. The column set was calibrated using relative calibration with 19 narrow MWD polystyrene (PS) standards in the range of 0.5 kg / mol to 11 500 kg / mol and a set of well-characterized broad polypropylene standards. All samples were prepared by dissolving 5-10 mg of polymer in 10 mL (at 160°C) of stabilized TCB (same as mobile phase) and keeping for 3 hours with continuous shaking prior sampling in into the GPC instrument. Rheology (polydispersity index PI and zero shear viscosity)

[0126] Small-amplitude oscillatory shear (SAOS) rheology experiments were done with the Anton Paar MCR501-CTD600 rheometer in nitrogen atmosphere, using a parallel plate setup (gap 1 .3 mm, 25 mm diameter), following ISO 6721-1 . Specimens of circular shape with a diameter of 25 mm and thickness of 2 to 3 mm were prepared first by compression molding (200 °C, load of 100 kg cnr2) of the polymer samples. Specimens were placed between the plates, heated to the measurement temperature (220 °C) and after removing excess material (trimming) the specimen was kept at the measurement temperature for another five minutes before the experiment begun. Frequency sweeps were done in the linear viscoelastic regime (strain 2 -7 %) applying frequencies w within 103to 10'2rad s-1

[0127] The zero shear viscosity was obtained as the fitting parameter r)o of a Carreau-Yasuda fit to the magnitude of the complex shear viscosity | q*| plotted as function of frequency (rad s'1) where rj is the shear visosity (Pa.s), is the infinite-shear viscosity plateau (set to zero, Pa.s). rjo is the zero-shear viscosity plateau (Pa.s) , is an average relaxation time (obtained in seconds when shear frequency is expressed in Hz), n is the power law index describing the slope of the shear thinning power law section (slope = n-1) and parameter a describes the width of the transition from zero-viscosity plateau to power law behaviour.

[0128] The polydispersity index PI (Pa-1) is defined as the inverse of the crossover modulus, Gc. The crossover modulus is the modulus level where elastic modulus of the melt (also called “storage modulus” G’, ) and viscous (loss) modulus G” have the same value. PI = 1 / Gc * 10A5.

[0129] Melting temperature Tm, crystallization temperature Tc

[0130] Differential Scanning Calorimetry (DSC) experiments were run on a TA Instruments Q2000 device calibrated with Indium, Zinc, Tin according to ISO 11357 / 1. The measurements were run under nitrogen atmosphere (50 mL min'1) on 5±0.5 mg samples in a heat / cool / heat cycle with a scan rate of 10 °C / min between -30 °C and 225 °C according to ISO 11357 / 3. Melting (Tm) and crystallisation (Tc) temperatures were taken as the peaks of the endotherms and exotherms in the cooling cycle and the second heating cycle respectively. WVTR

[0131] The water vapour transmission rate was determined at 38 °C and 90% relative humidity according to ISO 15106-2, measured from the face of the stretched film corresponding to the original cast film facing the chill roll.

[0132] Examples

[0133] Materials used for IE1

[0134] Isotactic crystalline polypropylene homopolymers PP1 and PP2 were produced as disclosed in WO2013 / 004781 , using diluent-slurry conditions (reactor cascade of five continuously stirred reactors, CSTR) and a commercial Ziegler Natta catalyst (“Lynx900”).

[0135] For PP1 Lynx900 catalyst was used together with diethylaluminiumchloride (DEAC) as cocatalyst an i-butyl methacrylate as external donor. (Al / Ti 6 mol / mol).

[0136] For PP2 Lynx900 catalyst was used together with diethylaluminiumchloride (DEAC) as cocatalyst an methyl methacrylate as external donor. (Al / Ti 6 mol / mol).

[0137] Quinacridonequinone CGNA-7588 (QQ), supplier BASF.

[0138] Material used for the Comparative Examples CE1 to CE4

[0139] BC545MO: low-blush polypropylene heterophasic copolymer produced by Borealis AG. It has a MFR2 of 3.5 g / 10min, a flexural modulus of 1200 MPa and - 18 wt.-% of rubber. Tm is -166 °C; Tc is -126.7 °C; Mw 350 kg / mol; Mn 45 kg / mol, PD 7.8

[0140] HD905CF: nucleated polypropylene homopolymer, commercial available from Borealis AG. MFR2 of 6.5 g / 10 min, Tm 168 °C; Mw 260 kg / mol, Mn 33 kg / mol, PD 7.9, mmmm 96 %

[0141] Millad NX8000: alpha nucleating agent; 1 ,2,3-trideoxy-4,6:5,7-bis-O-((4-propylphenyl) methylene) nonitol (CAS-no. 882073-43-0) supplier Milliken

[0142] Table 1 shows the properties of the polymers used for IE1 :

[0143] Table 1 :

[0144] For IE1 melt blending was used to produce a masterbatch (MB) of 0.05 wt.-% QQ in the carrier polymer PP2 grade containing 0.45 wt.-% of Irganox 1010 FF. See Table 2, showing the composition of the masterbatch MB.

[0145] Table 2: Composition of masterbatch MB

[0146] This masterbatch was blended with PP1 to reach a concentration of 10 ppm of QQ in the polypropylene homopolymer composition of IE1.

[0147] All CE, IE and MB compositions were compounded at a temperature -220 °C on a co-rotating Coperion twin-screw extruder, process length L / d=22, screw speed -150 rpm, diameter 57 mm.

[0148] In Table 3 the composition of IE1 and CE1 to CE4 are shown

[0149] Table 3:

[0150] The compositions as shown in Table 3 have been obtained in a pelletized form. The pellets have been converted to cast films on a small-scale laboratory mono layer cast film line from company COLLIN Lab & Pilot Solutions GmbH. The line consists of an extruder with a 0 30 mm screw with an L / D ration of 30. The extruder temperature has been set at 235 °C, the melt temperature was 235°C and has been recorded after 45 min of process stabilization. The extruder is followed by a die with a width of 300 mm. The die has a flexible die lip with a die gap of 0.5 - 1.5 mm. The line has been run at a constant throughput of 8 kg / h and a line speed of 10 m / min. The end width of the film was cut to 270 mm.

[0151] The chill roll temperature was 90 °C.

[0152] The cast films have been produced with a thickness of 250 pm (except for CE1 , which had 500 pm).

[0153] For the subsequent biaxial orientation, square specimens were cut out from each film (9 cm by 9 cm samples). These specimens were biaxially stretched on a BOPP machine (“Karo IV laboratory stretcher” Bruckner Maschinenbau GmbH, Germany). The stretching-process was done at a strain rate of 400% / s and temperature of 135-145 °C.

[0154] The films were stretched at a 3x3 ratio, the final thickness of the films was therefore 28 pm (55 pm for CE1) and a total width of 27x27 cm2.

[0155] The central, most homogeneous part of the films was used for the subsequent testing. The water vapour transmission rate was determined at 38 °C and 90% relative humidity according to ISO 15106-2, measured from the face of the stretched film corresponding to the original cast film facing the chill roll. The results can be seen in Table 4.

[0156] Table 4:

[0157] From the Table above it can be seen that the inventive example has much higher WVTR due to the combination of a specific propylene homopolymer and the beta nucleating agent.

Claims

Claims:

1. A biaxially oriented polypropylene (BOPP) film comprising at least 95 wt.-%, based on the total weight of the film, of a polypropylene homopolymer composition comprising a) one or more polypropylene homopolymer(s) (PPH) having• a melt flow rate MFR2, determined according to ISO 1133 at 230 °C and a load of 2.16 kg, in the range of 1.0 to 5.0 g / 10 min• an isotactic pentad regularity <mmmm>, determined by13C-NMR spectroscopy, in the range of 90.0 to 99.9%• a xylene cold soluble (XCS) content, determined according to ISO 16152 at 25 °C in the range of 0.5 to less than 3.8 wt.-%• a melting temperature, Tm, measured with DSC according to ISO 11357, in a range of155 to 170 °C• a crystallization temperature, Tc, measured with DSC according to ISO 11357, in a range of 105 to 125 °C• a weight average molecular weight (Mw), determined with GPC, as described in the experimental part, in the range of in the range of 300 to 420 kg / mol, and• a polydispersity index (PI), determined at 220 °C, as described in the experimental part, in the range of 4.0 to 6.8 Pa_1, b) 5 to 20 ppm, based on the weight of the polypropylene homopolymer composition, of at least one beta-nucleating agent, wherein the biaxially oriented polypropylene (BOPP) film has a water vapour transmission rate (WTVR), determined according to ISO 15106-2 of greater than 300 g / m2 / day at 38 °C and at a relative humidity of 90%.

2. The biaxially oriented polypropylene (BOPP) film according to claim 1 , wherein the one or more polypropylene homopolymer has one or more, preferably all of the following properties: a melt flow rate MFR2, determined according to ISO 1133 at 230 °C and a load of 2.16 kg, in the range of 1.5 to 4.5 g / 10 min, preferably 2.0 to 4.0 g / 10 min and more preferably 2.5 to 3.8 g / 10 min; an isotactic pentad regularity <mmmm> determined by13C-NMR spectroscopy in the range of 90.5 to 99.0%, preferably in the range of 91 .0 to 98.0%; a xylene cold soluble (XCS) content (ISO 16152; at 25 °C) in the range of 0.8 to 3.6 wt.-%, preferably in the range of 1 .0 to 3.5 wt.-%;a melting temperature, Tm, measured with DSC according to ISO 11357, in a range of of 158 to 168 °C and preferably in the range of 160 to 166 °C; a crystallization temperature, Tc, measured with DSC according to ISO 11357 in a range of 107 to 120 °C and preferably in the range of 109 to 118 °C; a weight average molecular weight (Mw), determined with GPC, as described in the experimental part, in the range of 320 to 400 kg / mol, preferably 330 to 390 kg / mol, more preferably 340 to 380 kg / mol, and a polydispersity index (PI), determined at 220 °C, as described in the experimental part, in the range of 4.2 to 6.6 Pa-1and more preferably in the range of 4.4 to 6.4 Pa-1.

3. The biaxially oriented polypropylene (BOPP) film according to claim 1 or 2, wherein the one or more polypropylene homopolymer has one or more, preferably all of the following properties a number average molecular weight Mn (GPC) in the range of 30.0 to 53.0 kg / mol, preferably 32.0 to 51 .0 kg / mol, more preferably 33.0 to 49.0 kg / mol, most preferably 34.0 to 46.0 kg / mol, a z-average molecular weight Mz (GPC) in the range of 1000 to 2000. kg / mol, preferably 1100 to 1800 kg / mol, more preferably 1150 to 1700 kg / mol, and even more preferably 1200 to 1650 kg / mol and a ratio of weight average molecular weight (Mw) to number average molecular weight (Mn) [Mw I Mn] of at least 5.0, Mw and Mn both determined with GPC, as described in the experimental part, in the range of 5.0 to 12.0, preferably 6.0 to 11.0, and more preferably 7.0 to 10.0.

4. The biaxially oriented polypropylene (BOPP) film according to any of the preceding claims, wherein the one or more polypropylene homopolymer has a zero shear viscosity in the range of 6000 Pa s to 25000 Pa s, preferably 7000 Pa s to 20000 Pa s, more preferably 8000 Pa s to 15000 Pa s, determined at 220 °C, as described in the experimental part.

5. The biaxially oriented polypropylene (BOPP) film according to any of the preceding claims, wherein the one or more polypropylene homopolymer is / are polymerized in a slurry polymerization process, wherein at least(a) a Ziegler-Natta catalyst, preferably a titanium compound, more preferably TiCI3,(b) propylene, and(c) a diluent (D) comprising a donor agent, preferably an external donor selected from the group consisting of methyl methacrylate, butyl methacrylate, 2-ethyl 1-hexyl methacrylate, and tridecyl methacrylate, or mixtures therefrom, more preferably methyl methacrylate and / or butyl methacrylate, are fed into at least one polymerization reactor, in case of several polymerization reactors in at least the first polymerization reactor, to conduct polymerization.

6. The biaxially oriented polypropylene (BOPP) film according to any of the preceding claims, wherein the polypropylene homopolymer composition comprises, preferably consists of two different polypropylene homopolymers, the second polypropylene homopolymer is preferably the carrier polymer of a masterbatch, which is used to incorporate the beta nucleating agent(s) into the polypropylene homopolymer composition, whereby the second polypropylene homopolymer is present in the polypropylene homopolymer composition in an amount of 1.0 to 5.0 wt.-%, preferably 1.2 to 4.0 wt.-% and more preferably 1.5 to 3.0 wt.-%, based on the total weight of the polypropylene homopolymer composition.

7. The biaxially oriented polypropylene (BOPP) film according to any of the preceding claims, wherein the beta-nucleating agent(s) wherein the beta-nucleating agent(s) are based on quinacridone type compounds, selected from the group comprising5, 12-dihydro-quino[2,3-b]acridine-7, 14-dione (i.e. quinacridone), dimethylquinacridone and dimethoxyquinacridone, quinacridonequinone type compounds, selected from quino[2,3-b]acridine-6,7,13,14(5H,12H)-tetrone (i.e. quinacridonequinone), and dimethoxyquinacridonequinone and dihydroquinacridone type compounds, selected from 5,6,12,13- tetrahydroquino[2,3- b]acridine-7, 14-dione (i.e. a dihydroquinacridone), dimethoxy dihydroquinacridone and dibenzodihydroquinacridone.

8. The biaxially oriented polypropylene (BOPP) film according to any of the preceding claims, wherein the BOPP film is produced by a process comprising the steps of:(A) extruding the polypropylene homopolymer composition as defined in claims 1 to 7 to a film,(B) orienting the film in the machine direction (MD) and in the transverse direction (TD) to obtain the BOPP film, and(C) recovering the BOPP film having a water vapour transmission rate (WTVR), determined according to ISO 15106-2 of greater than 300 g / m2 / day at 38 °C and at a relative humidity of 90%.

9. The biaxially oriented polypropylene (BOPP) film according to claim 8, wherein the films produced in the first step (step A) are cast films.

10. The biaxially oriented polypropylene (BOPP) film according to any of the preceding claims, wherein the films are stretched in machine as well as in transverse direction from 2 to 6 times, preferably 2.5 to 4 times, its original length.

11. The biaxially oriented polypropylene (BOPP) film according to claim 10, wherein the stretch ratio is the same for both directions, whereby preferably a stretch ratio of 2.5x2.5 or 3x3 or 3.5x3.5 is applied.

12. The biaxially oriented polypropylene (BOPP) film according to any of the preceding claims, wherein the film has a thickness of 5 to 50 pm, preferably from 10 to 40 pm, and more preferably from 20 to 35 pm.

13. Use of the biaxially oriented polypropylene (BOPP) film according to any of the preceding claims for laminated fabrics, water vapour permeable fabrics, wearable articles thereof, consumer air and water filters, roof insulation, technical fabrics and diapers.

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