Polypropylene copolymer biaxially stretched microporous membranes and composite sheets comprising same

Abstract

A biaxially stretched microporous membrane, a composite sheet comprising the same, and a method of making the same, and the microporous membrane comprises: a) 90 to 65 weight percent of a polypropylene copolymer comprising i) a polypropylene homopolymer segment, and ii) an ethylene-containing copolymer segment; and b) 10 to 35 weight percent of a propylene-based elastomer having 5 to 25 weight percent of ethylene derived units and having a melting temperature of less than 110 DEG C; wherein the biaxially stretched film may have a water vapor permeability of 50 g / (24 hours per square meter) or more, and no liquid water passes through the film when exposed to a 0.3 MPa hydrostatic pressure test for 30 minutes.

Description

Background Art

[0001] The present invention relates to biaxially stretched microporous membranes and composite sheets comprising biaxially stretched microporous membranes and their use in a variety of applications where a moisture vapor permeable sheet structure with a high liquid water barrier is desired. Some preferred end uses are in various construction applications in the building industry, including use in breathable waterproof membranes for roofing applications.

[0002] Description of Related Art U.S. Patent Publication No. 2021 / 0095110 to Huang et al. discloses microporous membranes made by sequentially cold and hot stretching an unannealed polypropylene copolymer membrane; wherein the polypropylene copolymer comprises one or more polypropylene homopolymer segments and one or more ethylene-containing copolymer segments.

[0003] Huang et al., U.S. Patent Publication 2022 / 0298340, also discloses a microporous membrane made by sequential cold and hot stretching of an unannealed polymer film. Examples 1 to 17 of the reference utilize membranes, wherein the polymer comprises (a) a polypropylene copolymer comprising one or more polypropylene homopolymer segments and one or more copolymer segments containing ethylene. As shown in Example 15 of the disclosure, a membrane sample made by both cold machine direction (MDO) stretching and hot machine direction (MDO) stretching passes a very strict hydrostatic pressure test of 30 meters of water for at least 30 minutes; however, the biaxially stretched sample made by only a cold MDO stretching step followed by direct hot transverse direction (TDO) stretching without an intermediate hot MDO stretching step does not pass this strict hydrostatic pressure test. This failure to pass the test is attributed to more interconnected pores generated by the biaxial stretching process, which undesirably opens the pores. Examples 18 to 20 of the disclosure further disclose membranes, wherein the polymer comprises (a) a polypropylene copolymer comprising one or more polypropylene homopolymer segments and one or more copolymer segments containing ethylene, and (b) an ethylene-propylene elastomer. All of these films were made using a process that included both cold machine direction (MDO) stretching and hot machine direction (MDO) stretching. Example 20 discloses that the film of Example 18, which was then cold stretched in the machine direction (MDO) and then further hot stretched, was further hot stretched in the transverse direction, and the general properties of the films made by this biaxial stretching process (including increased porosity) and the degree of difference in properties between the machine direction (MDO)-only films and the films made by biaxial stretching were similar to those shown in Examples 13-15 and Example 17. This includes biaxially stretched samples that did not pass the rigorous hydrostatic pressure test when made solely by the method of Example 15, in which the cold machine direction MDO stretching step was followed by hot transverse direction (TDO) stretching without an intermediate hot MDO stretching step.

[0004] Water leakage is a key challenge in using microporous membranes in roofing membranes. While some existing microporous membranes are said to offer water vapor permeability while maintaining an effective barrier to liquid water, the use of excessive machine direction stretching can result in the resulting membrane having an undesirable balance of properties in the machine and transverse directions, where certain machine direction properties are enhanced at the expense of transverse properties. Furthermore, because stretching can potentially damage the membrane, it is desirable to manufacture such membranes using the simplest possible method.

[0005] Understandably, there is a need for a microporous membrane that has a desirable balance of properties and is produced via a process with as few stretching steps as possible to avoid potential damage to the microporous membrane or connecting the membrane pores in an undesirable manner that negatively impacts liquid water barrier. Thus, specifically, there is a need for biaxially stretched microporous membranes and roofing membranes and other sheet structures that can pass this minimum liquid water barrier test and preferably can maintain liquid water barrier at 0.3 MPa water pressure for at least 30 minutes, and ideally for up to 2 hours or more, and that can further be produced in a two-step stretching process. Summary of the Invention

[0006] The present invention relates to a biaxially stretched microporous membrane, the biaxially stretched microporous membrane comprising:

[0007] a) 90 to 65 weight percent of a polypropylene copolymer comprising

[0008] i) 50 to 95 weight percent of polypropylene homopolymer segments, based on the weight of the polyolefin; or 43 to 79 mole percent of polypropylene homopolymer segments, based on the molar content of polymerized units of polypropylene in the polypropylene homopolymer segments as a percentage of the total molar content of polymerized monomer units in the polyolefin; and

[0009] ii) 5 to 50 weight percent of ethylene-containing copolymer segments, based on the weight of the polyolefin; or 21 to 57 mole percent of ethylene-containing copolymer segments, based on the molar content of polymerized monomer units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the polyolefin;

[0010] wherein at least a portion of the ethylene-containing copolymer segments comprises ethylene polymerized units in an amount of at least 45 weight percent based on the weight of the ethylene-containing copolymer segments; or ethylene polymerized units in an amount of at least 55 mole percent based on the molar content of ethylene polymerized units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the ethylene-containing copolymer segments; and

[0011] b) 10 to 35 weight percent of a propylene-based elastomer having 5 to 25 weight percent ethylene-derived units and having a melting temperature of less than 110°C;

[0012] The weight percentages of a) and b) are based on the total weight of a) and b),

[0013] The biaxially stretched microporous film has a water vapor permeability of 50 g / (24 hours·m 2 ) or more, and no liquid water passes through the film when exposed to a 0.3 MPa hydrostatic pressure test for 30 minutes.

[0014] The present invention also relates to a microporous biaxially stretched film, which comprises:

[0015] a) 89 to 65 weight percent of a polypropylene copolymer comprising

[0016] i) 50 to 95 weight percent of polypropylene homopolymer segments, based on the weight of the polypropylene copolymer; or 43 to 79 mole percent of polypropylene homopolymer segments, based on the molar content of polymerized units of polypropylene in the polypropylene homopolymer segments as a percentage of the total molar content of polymerized monomer units in the polypropylene copolymer; and

[0017] ii) 5 to 50 weight percent of ethylene-containing copolymer segments, based on the weight of the polypropylene copolymer; or 21 to 57 mole percent of ethylene-containing copolymer segments, based on the molar content of polymerized monomer units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the polypropylene copolymer;

[0018] wherein at least a portion of the ethylene-containing copolymer segments comprises ethylene polymerized units in an amount of at least 45 weight percent based on the weight of the ethylene-containing copolymer segments; or ethylene polymerized units in an amount of at least 55 mole percent based on the molar content of ethylene polymerized units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the ethylene-containing copolymer segments; and

[0019] b) 10 to 34 weight percent of a propylene-based elastomer having 5 to 25 weight percent ethylene-derived units and having a melting temperature of less than 110°C; and

[0020] c) 1 to 15 weight percent of a sealing additive,

[0021] The weight percentages of a), b) and c) are based on the total combined weight of a), b) and c).

[0022] The present invention also relates to a method for forming a biaxially stretched microporous membrane, the method comprising the steps of:

[0023] A) forming a non-porous film from a composition comprising

[0024] a) 90 to 65 weight percent of a polypropylene copolymer containing i) 50 to 95 weight percent of polypropylene homopolymer segments, based on the weight of the polyolefin; or 43 to 79 mole percent of polypropylene homopolymer segments, based on the molar content of polymerized units of polypropylene in the polypropylene homopolymer segments as a percentage of the total molar content of polymerized monomer units in the polyolefin; and

[0025] ii) 5 to 50 weight percent of ethylene-containing copolymer segments, based on the weight of the polyolefin; or 21 to 57 mole percent of ethylene-containing copolymer segments, based on the molar content of polymerized monomer units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the polyolefin;

[0026] wherein at least a portion of the ethylene-containing copolymer segments comprises ethylene polymerized units in an amount of at least 45 weight percent based on the weight of the ethylene-containing copolymer segments; or ethylene polymerized units in an amount of at least 55 mole percent based on the molar content of ethylene polymerized units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the ethylene-containing copolymer segments; and

[0027] b) 10 to 35 weight percent of a propylene-based elastomer having 5 to 25 weight percent ethylene-derived units and having a melting temperature of less than 110°C;

[0028] The weight percentages of a) and b) are based on the total weight of a) and b),

[0029] B) subjecting the non-porous film to sequential cold and hot biaxial stretching steps consisting of:

[0030] (i) a cold stretching step in a first direction at a temperature in the range of -20°C to 50°C; and

[0031] (ii) a heat stretching step in the second direction at a temperature in the range of 50° C. to 140° C.;

[0032] To produce a biaxially stretched microporous polymer membrane having a water vapor permeability of 50 g / (24 hr·m 2 ) or higher and no liquid water passing through the membrane when exposed to a 0.3 MPa hydrostatic pressure test for 30 minutes.

[0033] The present invention further relates to a method for forming a composite sheet comprising a biaxially stretched microporous membrane, the method comprising the steps of:

[0034] A) forming a non-porous polymer film or layer from a composition comprising

[0035] a) 90 to 65 weight percent of a polypropylene copolymer containing i) 50 to 95 weight percent of polypropylene homopolymer segments, based on the weight of the polyolefin; or 43 to 79 mole percent of polypropylene homopolymer segments, based on the molar content of polymerized units of polypropylene in the polypropylene homopolymer segments as a percentage of the total molar content of polymerized monomer units in the polyolefin; and

[0036] ii) 5 to 50 weight percent of ethylene-containing copolymer segments, based on the weight of the polyolefin; or 21 to 57 mole percent of ethylene-containing copolymer segments, based on the molar content of polymerized monomer units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the polyolefin;

[0037] wherein at least a portion of the ethylene-containing copolymer segments comprises ethylene polymerized units in an amount of at least 45 weight percent based on the weight of the ethylene-containing copolymer segments; or ethylene polymerized units in an amount of at least 55 mole percent based on the molar content of ethylene polymerized units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the ethylene-containing copolymer segments; and

[0038] b) 10 to 35 weight percent of a propylene-based elastomer having 5 to 25 weight percent ethylene-derived units and having a melting temperature of less than 110°C;

[0039] The weight percentages of a) and b) are based on the total weight of a) and b),

[0040] B) combining the non-porous polymer film or layer with a nonwoven fabric to form a composite sheet, and

[0041] C) subjecting the composite sheet to sequential cold and hot biaxial stretching steps comprising:

[0042] (i) at least one cold stretching step in a first direction at a temperature in the range of -20°C to 50°C; and

[0043] (ii) at least one heat stretching step in the second direction at a temperature in the range of 50°C to 140°C;

[0044] to produce a composite sheet comprising a biaxially stretched microporous polymer membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a TEM micrograph of a non-porous polymer film sample comprising 80 weight percent of a polypropylene copolymer comprising a polypropylene homopolymer and an ethylene-containing copolymer in a weight ratio of 70 / 30, and 20 weight percent of a propylene-based elastomer.

[0046] Figure 2 is a TEM micrograph of a "control" non-porous polymer film sample having a phase-separated polypropylene copolymer containing domains of a polypropylene homopolymer (continuous phase) and an ethylene-containing copolymer in a weight ratio of 70 / 30, without any propylene-based elastomer.

[0047] Figure 3 is a TEM micrograph of a non-porous polymer film sample comprising 70 weight percent of a polypropylene copolymer comprising a polypropylene homopolymer and an ethylene-containing copolymer in a 70 / 30 weight ratio, and 30 weight percent of a propylene-based elastomer.

[0048] Figure 4 is a TEM micrograph of a non-porous polymer film sample comprising 60 weight percent of a polypropylene copolymer comprising a polypropylene homopolymer and an ethylene-containing copolymer in a weight ratio of 70 / 30, and 40 weight percent of a propylene-based elastomer.

[0049] Figure 5 is a TEM micrograph of a non-porous polymer film sample comprising 75 weight percent of a polypropylene copolymer comprising a polypropylene homopolymer and an ethylene-containing copolymer in a 70 / 30 weight ratio, and 10 weight percent of a propylene-based elastomer, and 5 weight percent each of two different polyolefin elastomers and a hydrocarbon tackifier.

[0050] Figure 6 is a TEM micrograph of a non-porous polymer film sample comprising 65 weight percent of a polypropylene copolymer comprising a polypropylene homopolymer and an ethylene-containing copolymer in a 70 / 30 weight ratio, and 20 weight percent of a propylene-based elastomer, and 5 weight percent each of two different polyolefin elastomers and a hydrocarbon tackifier.

[0051] Figure 7 is an illustration of one embodiment of a cross-sectional view of a non-porous composite sheet formed by sandwiching a nonwoven fabric between two non-porous films; this is a view before biaxial stretching.

[0052] Figure 8 This is a photograph of a cross-section of a biaxially stretched composite sheet made from 73.5 weight percent of a polypropylene copolymer containing a polypropylene homopolymer and an ethylene-containing copolymer in a weight ratio of 70 / 30, 25 weight percent of a propylene-based elastomer, and 1.5 weight percent of a UV stabilizer, wherein a nonwoven fabric is symmetrically laminated into the composite sheet.

[0053] Figure 9is a diagrammatic representation of a possible continuous process for producing a biaxially stretched microporous membrane or a composite sheet comprising a microporous membrane on an apparatus comprising an extrusion lamination device 50, followed by a machine direction cold stretching device 51, followed by a transverse direction hot stretching device 52, followed by a cooling device 53 and finally a winding device 54. DETAILED DESCRIPTION

[0054] The present invention relates to biaxially stretched polymeric microporous membranes or composite sheets comprising such membranes, which are suitable for use in applications requiring a membrane that is impervious to liquid water but permeable to water vapor, such as roofing and other architectural applications. The polymeric microporous membranes are made from formulations that provide a microporous membrane having a microphase-separated / inclusion morphology and pores induced by sequential cold stretching in one direction followed by hot stretching in a second, different direction. The polymeric microporous membranes or composite sheets comprising such membranes have suitable mechanical properties for the intended application.

[0055] The polymeric microporous membrane or a composite sheet comprising such a membrane has a water vapor permeability of at least 50 g / (24 hours·m²) or higher, while also preventing liquid water from passing through the microporous membrane (or composite sheet) for 30 minutes when exposed to a 0.3 MPa hydrostatic pressure test, and preferably no liquid water passes through the microporous membrane (or composite sheet) for 2 hours when exposed to a 0.3 MPa hydrostatic pressure test. As used herein, the phrase "sheet material" is intended to include any type of membrane or composite sheet comprising a membrane. In addition, the terms "composite sheet comprising a biaxially stretched microporous membrane" and "biaxially stretched composite sheet" are used interchangeably herein.

[0056] It is believed that the compositions of the microporous film (or composite sheet) formulations described herein and the methods for stretching the microporous film (or composite sheet) form a unique pore structure in the biaxially stretched sheet material; providing, for example, uniformly small pores (diameter: 100 nm to 1 micron) with substantially non-interconnected properties, resulting in breathable films that exhibit excellent barriers to liquid water and air while achieving desirable water vapor permeation. In addition, these breathable polymer sheet materials are based on polypropylene, which means they are naturally hydrophobic and thermally stable, as polypropylene has a melting temperature of approximately 165°C.

[0057] The polymeric microporous membrane comprises a mixture of a polypropylene copolymer and a propylene-based elastomer. It is preferably made by casting a non-porous film of the desired formulation and then biaxially stretching the film to form a liquid water-proof, breathable, biaxially stretched microporous membrane structure.

[0058] It is believed that incorporating a propylene-based elastomer with a high number of propylene repeating units into the formulation modifies the micromorphology of the film, resulting in pores formed in the film when the film is stretched in two directions, providing excellent water vapor permeability (through the film) that is sufficient for many uses and can even be far higher than certain industry standards of at least 100 g / (24 hours·m²) for some architectural applications. In fact, water vapor permeability (through the film) can range from 50 g / (24 hours·m²) or slightly lower to as high as almost 600 g / (24 hours·m²) or even higher (specifically exemplified herein as 587.6 g / (24 hours·m²)). This also provides excellent water tightness, with no liquid water passing through the film for at least 30 minutes when exposed to a 0.3 MPa hydrostatic pressure test. This leak-free performance can last for up to 2 hours or more of water exposure. In addition to reducing seam welding time while increasing weld strength, the incorporation of a high propylene-based elastomer also significantly improves the flexibility of the film.

[0059] In some embodiments, the microporous membrane comprises 90 to 65 weight percent of a polypropylene copolymer comprising

[0060] i) 50 to 95 weight percent of polypropylene homopolymer segments, based on the weight of the polyolefin; or 43 to 79 mole percent of polypropylene homopolymer segments, based on the molar content of polymerized units of polypropylene in the polypropylene homopolymer segments as a percentage of the total molar content of polymerized monomer units in the polyolefin; and

[0061] ii) 5 to 50 weight percent of ethylene-containing copolymer segments, based on the weight of the polyolefin; or 21 to 57 mole percent of ethylene-containing copolymer segments, based on the molar content of polymerized monomer units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the polyolefin;

[0062] wherein at least a portion of the ethylene-containing copolymer segments comprises ethylene polymerized units in an amount of at least 45 weight percent based on the weight of the ethylene-containing copolymer segments; or ethylene polymerized units in an amount of at least 55 mole percent based on the molar content of ethylene polymerized units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the ethylene-containing copolymer segments. A suitable polypropylene copolymer is a reactor grade PP copolymer available from Braskem under the product code PP C7054-07NA. It contains 32.9 wt.% of ethylene-propylene copolymer, and the ethylene content of the ethylene-propylene copolymer is 49.7 wt.%. It has a viscosity of 0.9 g / cm 3and a melt mass flow rate of 7 g / 10 min at 230° C. and 2.16 kg. The number average molecular weight (Mn) and weight average molecular weight (Mw) of PP C7054-07NA are 58,000 and 295,000, respectively; this means that this copolymer has an Mw / Mn of about 5.1.

[0063] In some embodiments, the microporous membrane further comprises 10 to 35 weight percent of a propylene-based elastomer having 5 to 25 weight percent ethylene-derived units and having a melting temperature of less than 110° C. The weight percent of the polypropylene copolymer and the weight percent of the propylene-based elastomer are based on the total combined weight of the polypropylene copolymer and the propylene-based elastomer. One suitable propylene-based elastomer is Vistamaxx manufactured by ExxonMobil. TM 6102 is a propylene-based elastomer. It is composed primarily of isotactic propylene repeating units with random ethylene distribution (16 wt.% ethylene content). It has a melt mass flow rate of 1.4 g / 10 min at 190°C and 2.16 kg and a flow rate of 0.862 g / cm 3 It is believed that for adequate biaxial stretching properties, the propylene-based elastomer should have a majority of propylene repeat units, have an ethylene content of about 40 weight percent or less, and preferably about 25 weight percent or less, and most preferably about 20 weight percent or less.

[0064] In some embodiments, the microporous membrane (and / or composite sheet) further comprises up to 15 weight percents of a sealing additive that promotes the seam between the sheet material and itself. The sealing additive can be a single compound or a mixture of different compounds. The phrase "... up to 15 weight percents" in the word "up to" means that at least some sealing additives are present in the composition of the microporous membrane formulation and therefore present in the sheet material, and preferably this amount is an effective amount to increase the seam sealing of the microporous membrane. In some cases, it is believed that this amount accounts for at least 1 weight percent, and preferably at least 3 weight percent, of the microporous membrane formulation. The weight percent of the sealing additive is based on the total combined weight of the sealing additive, the polypropylene copolymer, and the propylene-based elastomer.

[0065] In some preferred embodiments, the sealant additive is a mixture of compounds such as one or more polyolefin elastomers, one or more polyolefin plastomers, one or more hydrocarbon tackifiers, and any mixtures thereof. A preferred mixture comprises two different polyolefin elastomers of different densities and a hydrocarbon tackifier, each present in equal parts by weight.

[0066] Elastomers and plastomers based on polyolefins are generally polymers or rubber or rubber-like compounds; the general rule is that the key difference between elastomers and plastomers is that elastomers exhibit elasticity, while plastomers exhibit both plasticity and elasticity. Elastomers also tend to have a reduced degree of crystallinity compared to plastomers. However, these are general rather than definitive rules of thumb, and it is possible that a particular material used as a plastomer in one application may be used as an elastomer in another application. Polyolefin elastomers and plastomers can be selected from suitable metallocene-catalyzed α-olefin copolymers, as described in: Progress in Polymer Science, Vol. 33, pp. 797-819 (2008). Preferred polyolefin elastomers and plastomers are based on α-olefins containing 1-octene. A non-limiting example of a preferred polyolefin elastomer is ENGAGE® available from Dow. TM 8402 polyolefin elastomer having a melt mass flow rate (MFR) of 30 g / 10 min at 190°C and 2.16 kg and a viscosity of 0.902 g / cm 3 ENGAGE TM 8402 elastomer has a glass transition temperature of -36°C and a melting temperature of 96°C. Plastomers have elastomeric properties like rubber, but can be processed similarly to plastics and are generally tougher than elastomers. A non-limiting example of a preferred elastomer is AFFINITY ® available from Dow TM GA 1900 elastomer, which has a density of 0.87 g / cm 3 A polyolefin elastomer. It has a glass transition temperature of -57.8°C and a melting temperature of 67.8°C. Tackifiers are generally low molecular weight compounds commonly used to increase the viscosity of adhesives. One suitable tackifier is ESCOREZ available from ExxonMobil Corporation. TM 5400, which is an alicyclic hydrocarbon resin with a number average molecular weight (Mn) of 400 g / mol. It is designed to tackify a variety of adhesive polymers. It has a softening point of 103.4°C and a glass transition temperature of 52°C.

[0067] In some specific embodiments, the microporous membrane comprises 89 to 65 weight percent of a polypropylene copolymer as previously described herein in combination with 10 to 34 weight percent of a propylene-based elastomer as previously described herein, and 1 to 15 weight percent of a sealing additive as previously described herein.

[0068] In other words, in some embodiments, the microporous membrane comprises 89 to 65 weight percent of a polypropylene copolymer comprising

[0069] i) 50 to 95 weight percent of polypropylene homopolymer segments, based on the weight of the polyolefin; or 43 to 79 mole percent of polypropylene homopolymer segments, based on the molar content of polymerized units of polypropylene in the polypropylene homopolymer segments as a percentage of the total molar content of polymerized monomer units in the polyolefin; and

[0070] ii) 5 to 50 weight percent of ethylene-containing copolymer segments, based on the weight of the polyolefin; or 21 to 57 mole percent of ethylene-containing copolymer segments, based on the molar content of polymerized monomer units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the polyolefin;

[0071] wherein at least a portion of the ethylene-containing copolymer segments comprises ethylene polymerized units in an amount of at least 45 weight percent based on the weight of the ethylene-containing copolymer segments; or ethylene polymerized units in an amount of at least 55 mole percent based on the molar content of ethylene polymerized units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the ethylene-containing copolymer segments.

[0072] In this embodiment, the microporous membrane also includes 10 to 34 weight percent of a propylene-based elastomer having 5 to 25 weight percent ethylene-derived units and a melting temperature of less than 110°C, and 1 to 15 weight percent of a sealant additive that facilitates the seaming of the sheet to itself. Each of the weight percents of the polypropylene copolymer, the propylene-based elastomer, and the sealant additive is based on the total combined weight of the polypropylene copolymer, the propylene-based elastomer, and the sealant additive. As described herein, the sealant additive is preferably a mixture of compounds, with one preferred mixture being equal parts by weight of a polyolefin elastomer, a polyolefin plastomer, and a hydrocarbon tackifier; or alternatively, two different polyolefin elastomers and a hydrocarbon tackifier.

[0073] The microporous membrane, and preferably the composite sheet comprising the microporous membrane, has a water vapor permeability of 50 g / (24 h·m²) or higher. In some embodiments, a water vapor permeability of 90 g / (24 h·m²) or higher is desirable. In some other embodiments, a water vapor permeability of 190 g / (24 h·m²) or higher is desirable.

[0074] The microporous membrane also allows no liquid water to pass through the membrane for 30 minutes when exposed to a 0.3 MPa hydrostatic pressure test. In some embodiments, the microporous membrane also allows no water to pass through the membrane for 2 hours when exposed to a 0.3 MPa hydrostatic pressure test.

[0075] In some embodiments, the microporous membrane has a density of about 100 to 400 g / m 2In some other embodiments, the microporous membrane has a basis weight of about 200 to 300 g / m 2 basis weight.

[0076] In certain embodiments, the non-porous film made of the composition described herein, and the subsequent biaxially stretched microporous film and the composite sheet made of the non-porous film include a phase-separated polymer, the phase-separated polymer includes a continuous phase and a dispersed phase, the continuous phase includes a polypropylene homopolymer and a propylene-based elastomer, and the dispersed phase includes a domain of an ethylene-propylene copolymer. The dispersed phase is in the form of discrete domains that can be observed by a transmission electron microscope (TEM) according to the method described in paragraph

[0173] of US2021 / 0095110 A1 or an equivalent method. The dispersed phase domain further contains inclusions of at least the polypropylene homopolymer from the continuous phase. Such inclusions can also be observed by the TEM method mentioned above.

[0077] Figure 1 is a TEM micrograph of a non-porous polymer film sample 10 comprising 80 weight percent of a polypropylene copolymer comprising a polypropylene homopolymer and an ethylene-containing copolymer in a 70 / 30 weight ratio, and 20 weight percent of a propylene-based elastomer. In other words, the composition comprises a polypropylene copolymer comprising approximately 67.1 weight percent of a polypropylene homopolymer (light continuous phase 1) and approximately 32.9 weight percent of an ethylene-propylene copolymer (forming part of a darker dispersed phase, domains 2); and 20 weight percent of a propylene-based elastomer, which also forms part of the continuous phase 1. The domains 2 comprising the ethylene-propylene copolymer primarily have a maximum dimension of 0.5 to 2 micrometers (μm) as shown. The domains 2 further contain inclusions 4 of at least the polypropylene homopolymer as present in the continuous phase 1. The inclusions 4 may constitute, for example, 10% to 65% of the total mass of the domains 2. A small fraction (e.g., up to 25%, up to 10%, or up to 5%) of the dispersed phase mass may be in the form of smaller fragmented domains 5 of ethylene-propylene copolymer having a largest dimension of less than 0.5 micrometers (μm). The smaller domains 5 may lack inclusions 4. The relative mass of the dispersed phase can be estimated using nuclear magnetic resonance (NMR) spectroscopy.

[0078] The effect of adding propylene-based elastomers on the copolymer morphology is shown in Figure 2 middle. Figure 2 FIG1 is a TEM micrograph of a "control" non-porous polymer film sample having a phase-separated polypropylene copolymer comprising a 70 / 30 weight ratio of polypropylene homopolymer (continuous phase 11) and domains of ethylene-containing copolymer 12, without any propylene-based elastomer. The ethylene-containing copolymer domains 12 further contain inclusions 14 of polypropylene homopolymer. Figure 2 and Figure 1 The comparison shows that the addition of propylene-based elastomer reduces the size of the dispersed domains, as shown by Figure 1 The comparison is shown.

[0079] Thus, in the presence of a propylene-based elastomer, domain size is reduced relative to the control sample. Preferably, at least 95% of the dispersed phase mass is in the form of domains having a longest dimension of 0.1 to 2 μm. In some embodiments, at least 95% or at least 98% of the dispersed phase is in the form of domains having a longest dimension of 0.1 to 1.0 μm, and in preferred embodiments, at least 95% or at least 98% of the dispersed phase is in the form of domains having a longest dimension of 0.25 to 1.0 μm.

[0080] Figure 3 is a TEM micrograph of a non-porous polymer film sample comprising 70 weight percent of a polypropylene copolymer comprising a polypropylene homopolymer and an ethylene-containing copolymer in a 70 / 30 weight ratio, and 30 weight percent of a propylene-based elastomer. Figure 4 1 is a TEM micrograph of a non-porous polymer film sample containing 60 weight percent of a polypropylene copolymer containing a polypropylene homopolymer and an ethylene-containing copolymer in a weight ratio of 70 / 30, and 40 weight percent of a propylene-based elastomer. As shown, as the amount of the propylene-based elastomer increases, the domains of the dispersed phase become smaller, so that when the amount of the propylene-based elastomer is 40 weight percent, the desired morphology is no longer predominant.

[0081] Figure 5 is a TEM micrograph of a non-porous polymer film sample comprising 75 weight percent of a polypropylene copolymer comprising a polypropylene homopolymer and an ethylene-containing copolymer in a 70 / 30 weight ratio, 10 weight percent of a propylene-based elastomer, and 5 weight percent of each of two different polyolefin elastomers (having different densities) and 5 weight percent of a hydrocarbon tackifier. Figure 6 is a TEM micrograph of a non-porous polymer membrane sample comprising 65 weight percent of a polypropylene copolymer comprising a polypropylene homopolymer and an ethylene-containing copolymer in a 70 / 30 weight ratio, 20 weight percent of a propylene-based elastomer, 5 weight percent of each of two different polyolefin elastomers (having different densities), and 5 weight percent of a hydrocarbon tackifier.

[0082] It is believed that additional polyolefin elastomer and tackifier (15 weight percent total) are further present in the continuous phase, and as shown, the domains of the dispersed phase become smaller as the amount of ethylene-containing copolymer in the total formulation decreases, again indicating that the minimum amount of polypropylene copolymer should not be less than about 65 weight percent to achieve the desired morphology in the film.

[0083] The polypropylene copolymer comprises 50 to 95 weight percent polypropylene homopolymer segments, based on the weight of the polypropylene copolymer. In some embodiments, the polypropylene copolymer may comprise at least 55, at least 60, or at least 70 weight percent polypropylene homopolymer segments and up to 90, up to 88, up to 85, or up to 82 weight percent polypropylene homopolymer segments. The polypropylene copolymer also comprises 5 to 50 weight percent ethylene-containing copolymer segments, based on the weight of the polypropylene copolymer. In some embodiments, the polypropylene copolymer may comprise at least 10, at least 12, at least 15, or at least 18 percent ethylene-containing copolymer segments and up to 45, up to 40, or up to 30 weight percent ethylene-containing copolymer segments.

[0084] At least a portion of the ethylene-containing copolymer segments comprises ethylene polymerized units in an amount of at least 45 weight percent, based on the weight of the ethylene-containing copolymer segments. In some embodiments, at least a portion of the ethylene-containing copolymer segments may comprise ethylene polymerized units in an amount of at least 50, at least 55, or at least 50 weight percent ethylene polymerized units, and may contain, for example, up to 80, up to 75, or up to 75 weight percent ethylene polymerized units.

[0085] The ethylene-containing copolymer segment is a copolymer of ethylene and at least one other copolymerizable monomer. The other copolymerizable monomer is preferably propylene. The ethylene-containing copolymer segment can be, for example, a block, random, pseudo-random and / or graft copolymer of ethylene and the at least one other copolymerizable monomer. In a specific embodiment, the ethylene-containing copolymer segment is a block copolymer of ethylene and propylene or a block copolymer comprising ethylene and propylene. The content of polymerized ethylene units in the polyolefin can be, for example, at least 10, at least 12 or at least 15 weight percent based on the total weight of the polyolefin and, for example, up to 30 or up to 25 weight percent. Other suitable polyolefins are, for example, those described in paragraphs

[0063] to

[0078] of US2021 / 009511 A1.

[0086] The propylene-based elastomer has at least about 60 weight percent propylene-derived units, preferably at least about 75 weight percent propylene-derived units, or at least about 80 weight percent propylene-derived units. The propylene-based elastomer is preferably a random propylene homopolymer or copolymer having crystalline regions interspersed with amorphous regions. The amorphous regions can result from non-crystallizable polypropylene segments and / or regions of inclusion of comonomer units (e.g., ethylene). In the presence of the comonomer, the crystallinity and melting temperature of the propylene-based elastomer are reduced compared to highly isotactic polypropylene. Examples of commercially available propylene-based elastomers include Vistamaxx from ExxonMobil Corporation. TM Performance polymers and VESIFY from Dow TM Elastomer.

[0087] It has been found that the addition of a propylene-based elastomer with a high propylene content promotes the adhesion of biaxially stretched microporous membranes and composite sheets containing biaxially stretched microporous membranes to themselves to form seams. Despite the use of polypropylene copolymers in microporous membranes, microporous membranes and composite sheets containing such membranes can become stiff at colder temperatures, which can make roofing membranes difficult to install in winter. It is desirable to seam the edges of roofing membranes without the use of adhesives by heating the edges of the sheets to a temperature above the melting temperature of the membrane polymer, which bonds the edges of the sheets together. This technique for joining sheets, known as thermal (hot air) welding, provides a strong seam and results in overall time and cost savings in roofing membrane applications. It is believed that the further addition of sealing additives to the compositions used for microporous membranes and composite sheets containing such membranes can further improve the thermal welding (seaming) performance.

[0088] The compositions used to make the biaxially stretched microporous membranes and composite sheets comprising the biaxially stretched microporous membranes may contain other components such as extrusion processing aids, such as lubricants, etc.; antioxidants, titanium dioxide, UV stabilizers, light stabilizers, heat stabilizers, pigments or other colorants, antistatic agents, flame retardants, antiblocking additives, biocides, etc., to the extent that they do not negatively affect the desired properties of the sheet material. UV stabilizers are preferred additives. Examples of stabilizers include various hydroxyphenylbenzotriols, such as those marketed by BASF under the generic trade name Those sold as BASF, or hindered amine stabilizers, such as those sold as or One or more UV stabilizers may be used in combination with one or more antioxidants.

[0089] Although the polypropylene copolymer may contain filler particles, such fillers are preferably absent or, if present, are present only in small amounts, such as up to 3%, up to 2%, up to 1%, or up to 0.5% of the combined weight of the filler particles and the polypropylene copolymer. Such fillers are particulate materials that are thermally stable (i.e., do not melt or thermally degrade) under the conditions of the extrusion lamination process. Fillers may include both inorganic and organic types.

[0090] In some embodiments, the biaxially stretched composite sheet comprising a microporous membrane and a nonwoven fabric has a weight of about 500 to 2000 g / m 2 In some embodiments, the biaxially stretched composite sheet comprising a microporous membrane and a nonwoven fabric has a basis weight of about 300 to 1500 g / m 2 basis weight.

[0091] In some embodiments, the nonwoven fabric in the composite sheet has a weight of about 100 to 400 g / m² as measured according to EN ISO 9864:2016. 2 The preferred basis weight is at least 125 or at least 150 g / m 2 And up to 350 or up to 300g / m 2 At 2kN / m 2 The thickness of the nonwoven fabric under a load of 1000 ft may preferably be 0.25 to 0.95 mm, and for example may be at least 0.3 or at least 0.4 mm and up to 0.9 or up to 0.8 mm, as measured in accordance with EN ISO 9863-1:2005. The nonwoven fabric may have an elongation at break of 30% to 200% in each of the machine direction and the cross direction as measured in accordance with EN ISO 10319:2015. The nonwoven fabric is preferably water permeable and may have a 5×10 -3 to 200×10 -3 m / s, especially 10×10 -3 to 100×10 -3 m / s, or 10×10 -3 to 50×10 -3 m / s permeability (VH50). In some embodiments, the nonwoven fabric comprises fibers or filaments or consists of fibers or filaments that are entangled, spunbonded and / or melt-bonded to form the nonwoven fabric. The nonwoven fabric can be made, for example, by spunbonding, air-laid, spunlace or melt-bonding methods, or can be a mesh.

[0092] The nonwoven fabric is preferably composed of a material that is thermally stable under the conditions of the extrusion lamination step, that is, the material does not melt, unacceptably thermally soften, or degrade so that the nonwoven fabric loses its integrity during the extrusion lamination step. The material can be or comprise an organic polymer, preferably an organic polymer having a crystalline melting temperature or Vicat softening temperature of at least 80° C., preferably at least 100° C. or at least 125° C. Examples of such polymers include polypropylene, polyesters such as poly(ethylene terephthalate), poly(butylene terephthalate), various polyamides (nylon), poly(lactide), cellulosic fibers such as pulped and extruded cellulose fibers. Cellulose acetate, cellulose diacetate, cellulose triacetate and cellulose acetate butyrate, various acrylate polymers, polybenzimidazole, aromatic polyamides, polyvinyl alcohol, polyphenylene sulfide, polyacrylonitrile and acrylonitrile copolymers. The nonwoven fabric may also contain, for example, carbon, wool, metal, mineral wool, silk, jute or other natural fibers, provided that the nonwoven fabric has the elongation at break as mentioned above and preferably also has the permeability as mentioned above.

[0093] Preferred nonwovens are polypropylene nonwovens, polyethylene terephthalate nonwovens or polypropylene-polyethylene terephthalate nonwovens. Polypropylene-polyethylene terephthalate nonwovens can be made from polypropylene-polyethylene bicomponent fibers, wherein the polypropylene forms at least a portion of the surface of these bicomponent fibers. Such bicomponent fibers can be, for example, sheath-and-core or side-by-side bicomponent fibers with a polypropylene sheath.

[0094] When the biaxially stretched microporous membrane or the biaxially stretched composite sheet containing microporous membrane is manufactured by extrusion lamination method, the polypropylene copolymer formulation is melted, and then the molten polypropylene copolymer formulation is forced to pass through a die to form a non-porous polymer film or layer. This step can be carried out using, for example, a single screw extruder or a twin screw extruder, a cumulative extruder or other suitable equipment equipped with a suitable die such as a slit die or a dog-bone die. The polypropylene copolymer formulation is heated to a temperature higher than the crystalline melt temperature of the polypropylene homopolymer of the continuous phase in an extrusion device, and is forced to pass through a die to form a polymer film or layer. Preferred temperature is at least 180°C or at least 200°C and up to 240°C or up to 260°C.

[0095] The extruded non-porous polymer film or layer preferably has a thickness of at least 250 μm, at least 400 μm or at least 500 μm, or at least 1000 μm and up to 10 mm, up to 5 mm, up to 2,000 μm or up to 1,500 μm.

[0096] The extruded polymer film or layer is non-porous. It is preferred to omit the blowing agent and / or gas during the extrusion process to avoid the creation of pores at this stage. For the purposes of the present invention, a sheet is considered non-porous if, after cooling, it exhibits a relative humidity of not more than 2 g / m2 at 37.8°C and 100% relative humidity as measured according to ASTM D1249. 2 -day water vapor transmission rate (WVTR), the sheet is considered "non-porous".

[0097] Preferably, the non-porous polymer film or layer of melting is contacted with the surface of the nonwoven fabric to produce a non-porous polymer layer on the surface. This step is carried out before the sheet is cooled to a temperature lower than its Vicat softening temperature. The contacting step is preferably carried out in 30 seconds, more preferably in 10 seconds, in 5 seconds or in 2 seconds from the time the sheet leaves the extruder die.

[0098] The contacting step is preferably carried out under mechanical (clamping) pressure so that the nonwoven fabric becomes at least partially embedded in the non-porous membrane or polymer layer. "Embedding" means that all or a portion of the polymer penetrates into a portion of the interstitial space between the fibers or filaments in the nonwoven fabric, so that at least a portion of the nonwoven fabric becomes infused with the polymer. The mechanical (clamping) pressure is conveniently applied by passing the nonwoven fabric and the applied polymer layer through one or more calendering rollers; however, other devices such as double-belt laminators are also suitable. In some embodiments, one or more of the calendering rollers can be cooled to simultaneously cool the polymer to a temperature below its Vicat softening temperature (e.g., to 80° C. to 120° C.) and impregnate the nonwoven fabric.

[0099] Extrusion lamination processes can be performed by applying extruded polymer films or layers to both sides of the nonwoven. In such cases, the opposing polypropylene copolymer formulation sheets can be contacted with the nonwoven simultaneously or sequentially.

[0100] Figure 7 FIG is an illustration of one embodiment of a cross-sectional view of a non-porous composite sheet formed by sandwiching a non-woven fabric between two non-porous films. Figure 7As shown, the resulting non-porous composite sheet 20 comprises a nonwoven fabric 21 and (in the embodiment shown) two polypropylene copolymer layers 22 and 22A. As shown, the nonwoven fabric 21 is partially embedded in each of the polypropylene copolymer layers 22 and 22A, wherein a small central portion 23 of the nonwoven fabric 21 is not wetted. In an alternative embodiment, in the non-porous composite sheet, and more particularly in a biaxially stretched composite sheet, the entire nonwoven fabric 21 is preferably wetted and embedded in either or both of the polypropylene copolymer layers 22 and 22A. Also as shown, a portion of each of the polypropylene copolymer layers 22 and 22A extends above and below the nonwoven fabric 21 to form non-reinforced surface layers 24 and 24A, respectively. In alternative embodiments, in a non-porous composite sheet, and more particularly in a biaxially stretched composite sheet, one or both of those non-reinforced surface layers 24 and 24A are not present, in which case the corresponding polypropylene copolymer layer 22 and / or 22A has been fully penetrated into the nonwoven fabric 21.

[0101] In some embodiments, the composite sheet is in the form of an extruded laminate having a nonwoven positioned within the interior of the composite sheet. In some other embodiments, the nonwoven is positioned symmetrically within the composite sheet, at the center of the thickness of the composite sheet.

[0102] The total thickness of the non-porous composite sheet may be at least 1 mm. It may be at least 1.2 mm, and may for example be up to 12.7 mm, up to 6.35 mm, up to 3 mm, up to 2 mm, or up to 1.8 mm.

[0103] The non-porous composite sheet thus formed is preferably cooled to a temperature of 50°C or lower before being subjected to sequential cold and hot stretching processes. Cold stretching is first performed in the machine direction and then hot stretching is performed in the transverse direction. The stretching process can be carried out in the general manner and conditions described in US2021 / 095110 A1. The cold stretching step is carried out with a non-porous composite sheet at a temperature of -20°C to 50°C. The preferred lower temperature limit is 0°C, 10°C or 15°C, and the preferred upper temperature limit is up to 35°C, up to 30°C or up to 25°C. The cold stretch percentage can be, for example, at least 15%, at least 25%, at least 35% or at least 40% and up to 150%, up to 100% or up to 80%. Cold stretching can be performed in a single step or in multiple increments. The stretch percentage is calculated as 100% × [(stretched film length-initial film length) ÷ initial film length)]. As used herein, a "single step" is considered to be a single stretching process used to stretch a sheet material by a certain amount in a specific direction at a specific temperature or temperature range. For example, a "single cold stretching step" may include multiple rollers that work together to incrementally stretch the sheet material with each roller, ultimately stretching the sheet material in one direction by a certain desired percentage.

[0104] If desired, the cold-stretched composite sheet can be annealed before the subsequent hot stretching step. This annealing step is conveniently performed by heating the cold-stretched composite sheet to a temperature of 90°C to 150°C for a period of at least one second, preferably at least two seconds. An annealing period of no more than 30 seconds is typically required. Annealing can fix the pore structure formed during the cold stretching step and can also reduce shrinkage. The annealing step is preferably performed immediately after cold stretching, while maintaining the cold-stretched composite sheet under as much tension as necessary to prevent shrinkage prior to transverse stretching.

[0105] The hot stretching step in the transverse direction is performed with the composite sheet at a temperature of greater than 50°C to 150°C. Preferably, the transverse direction is orthogonal to the cold machine direction stretching. The preferred lower temperature limit is at least 90°C or at least 120°C, and the preferred upper temperature limit is 140°C. The hot stretching can be performed in a single step or in multiple increments. The hot stretch percentage can be, for example, at least 25%, at least 40%, or at least 50% and up to 400%, up to 300%, up to 200%, up to 150%, up to 100% or up to 80%. The hot stretched composite sheet is optionally annealed in the same manner as described for annealing the cold stretched composite sheet.

[0106] Figure 8A cross section of a practical biaxially stretched composite sheet (similar to a sheet made of 73.5 weight percent of a polypropylene copolymer containing a polypropylene homopolymer and an ethylene-containing copolymer in a weight ratio of 70 / 30, 25 weight percent of a propylene-based elastomer, and 1.5 weight percent of a UV stabilizer. Figure 7 ), in which the nonwoven fabric is symmetrically extrusion laminated in the composite sheet.

[0107] When non-porous membrane or composite sheet is produced on film casting, extrusion lamination or other equipment, sheet material will have the machine direction corresponding to the direction of movement through the equipment and perpendicular (or orthogonal) to the transverse or cross direction (in the plane of sheet). Any one of the cold stretching step or the hot stretching step can be carried out uniaxially in the machine direction or in the cross direction, but in order to produce a biaxially stretched microporous membrane or composite sheet, the cold stretching step and the hot stretching step should not be in the same direction, but preferably in the orthogonal direction. In a preferred embodiment, the cold stretching step is carried out in the machine direction, and the hot stretching step is carried out in the transverse or cross direction.

[0108] When one of the stretching steps is performed in the machine direction and the other in the cross direction, the resulting microporous membrane or composite sheet comprising the microporous membrane has a better balance of physical properties such as tensile strength and elongation in the machine and cross directions.

[0109] Non-porous membrane or composite sheet can be biaxially stretched in the continuous operation of the combination involving various devices, these devices first stretch non-porous membrane or composite sheet in the machine direction, such as a series of stretching rollers, then stretch non-porous membrane or composite sheet in the transverse or cross direction, such as using a tenter frame comprising a clamp for clamping the side of non-porous membrane or composite sheet. The clamp is mounted on a pair of tracks, and the pair of tracks separates the non-porous membrane or composite sheet in the moving direction of the device. The clamp travels along the track, carrying non-porous membrane or composite sheet, separates non-porous membrane or composite sheet and therefore biaxially stretches into a biaxially stretched microporous membrane or a biaxially stretched composite sheet. The tenter frame is particularly suitable for stretching sheet material in the cross direction. As previously mentioned, the stretching section (that is, comprising the section separating the tracks) can be a preheating section before, and can be an annealing section and / or a rewinding section afterwards.

[0110] Yet another suitable stretching device is a grooved roller stretcher. This grooved roller stretcher is particularly useful for stretching non-porous membranes or composite sheets in a cross direction. The grooved roller stretcher includes a staggered tooth-groove structure through which the non-porous membrane or composite sheet passes. The tooth-groove structure can be a roller pair as described, for example, in U.S. Patent Nos. 4,368,565, 5,028,289, and 6,843,949, U.S. Patent Application No. 2006 / 0148354, and EP 927 096B1; or an activation member with toothed grooves and a moving belt with complementary toothed grooves such as described in U.S. Patent No. 8,337,190. The grooved roller stretcher can include multiple tooth-groove structures in series. The non-porous membrane or composite sheet is fed into the grooved roller stretcher and conveyed through the tooth-groove structure, wherein the non-porous membrane or composite sheet is stretched transversely to its moving direction. The resulting microporous membrane or composite sheet comprising the microporous membrane is then removed from the device. The stretching operation in a slotted roll stretcher is conveniently performed in a continuous manner by continuously feeding a length of non-porous film or composite sheet through a slotted structure.

[0111] In one embodiment, a composite sheet comprising a microporous membrane is produced in a continuous process comprising the steps of: i) continuously extruding a polypropylene copolymer composition into a non-porous polymer film or layer; ii) contacting the non-porous polymer film or layer with a first side of a nonwoven fabric and then cooling the non-porous polymer film or layer to a temperature below its Vicat softening temperature to produce a composite sheet; iii) cooling the composite sheet to a cold stretching temperature and then iv) cold stretching the composite sheet in a first direction, preferably a machine direction, followed by v) heating the cold stretched composite sheet to a hot stretching temperature and then vi) hot stretching the cold stretched composite sheet in a second direction transverse to the first direction, preferably a cross direction orthogonal to the machine direction, to produce a biaxially stretched composite sheet comprising a microporous membrane.

[0112] If desired, before, after, or during step ii), a second non-porous polymer film or layer can be attached to or in contact with the second, opposite side of the nonwoven fabric to produce a composite sheet having the nonwoven fabric positioned within the interior of the composite sheet after biaxial stretching. In some preferred embodiments, the first and second non-porous polymer films or layers have substantially equal weights such that the nonwoven fabric is symmetrically positioned at or near the center of the thickness of the composite sheet.

[0113] like Figure 9 As shown, the continuous biaxial stretching process can be carried out on an apparatus comprising an extrusion lamination unit 50, followed by a machine direction cold stretching unit 51, followed by a transverse direction hot stretching unit 52, followed by a cooling unit 53 and finally a winding unit 54.

[0114] Extrusion lamination device 50 can comprise for example being equipped with the forcing machine of the mould that is suitable for producing non-porous polymer film or non-porous polymer layer, for non-woven fabric is supplied to the feeding device of laminating machine and laminating machine such as the calendering roller of heating so that polymer film or layer are contacted with non-woven fabric and mechanical compression, to preferably force at least a portion of the polymer from polymer film or layer to enter in the interstitial space in the non-woven fabric to produce composite sheet.Extrusion lamination device can have the calendering roller of heating or cooling according to hope or need.Extrusion lamination device can further comprise the equipment (that is, second forcing machine, casting die, laminating station etc.) for producing or providing the second polymer film or layer, to make the second non-porous polymer film or non-porous polymer layer contact in a similar manner on the opposite side of non-woven fabric, to form wherein non-woven fabric embeds the composite sheet between two polymer films or two polymer layers, form sandwich structure, wherein in the interstitial space between the fiber component in non-woven fabric, have the polymer from polymer film / layer.

[0115] The machine direction cold stretching device 51 can receive the composite sheet from the extrusion lamination device and continuously cold stretch the composite sheet in the machine direction. The machine direction cold stretching device can include a cooling roller or other device (if necessary) for cooling the composite sheet or bringing the composite sheet to a specific stretching temperature and one or more stretching rollers or a set of nip rollers for stretching the composite sheet in the machine direction. This is considered herein as a single machine direction stretching step.

[0116] The transverse direction hot stretching device 52 can receive the cold-stretched composite sheet from the cold stretching device and continuously further heat-stretch the composite sheet in the machine direction. The transverse direction hot stretching device can include a heating roller or other device for heating the composite sheet or bringing it to a specific stretching temperature, and a device for clamping and stretching the heated composite sheet in a direction transverse to the machine direction, such as a transverse spreading roller and / or a tenter frame. This hot stretching device can further include an optional annealing section after the stretching roller for optionally annealing the stretched composite sheet at a desired temperature, for example, using additional temperature-controlled rollers. This is considered herein as a single transverse direction stretching step.

[0117] The cooling device 53 can receive the biaxially stretched composite sheet from the hot stretching device and continuously cool the sheet; the cooling device can include cooling rollers or other equipment (if necessary) to cool the biaxially stretched composite sheet to the desired final temperature for winding into a roll product. The winding device 54 then preferably winds the final biaxially stretched composite sheet onto a core to form a roll of composite sheet containing a biaxially stretched microporous membrane.

[0118] Biaxially stretched microporous membranes can be made by a method similar to that of composite sheets comprising biaxially stretched microporous membranes by simply excluding the nonwoven fabric. That is, one or more of the one or more non-porous polymer films or layers as described above are cast, but the one or more non-porous polymer films or layers are not combined with any nonwoven fabric, and only the one or more non-porous polymer films or layers are cold stretched and hot stretched to form the biaxially stretched microporous membrane.

[0119] The resulting biaxially stretched composite sheet has a thickness of at least 1 mm. The thickness may be at least 1.2 mm, and may be, for example, up to 12.7 mm, up to 6.35 mm, up to 3 mm, up to 2 mm, or up to 1.8 mm. The biaxially stretched microporous membrane and the biaxially stretched composite sheet preferably exhibit a tensile strength of at least 50, at least 90, at least 100, at least 120, or at least 190 g / m² as measured according to ASTM E96 / E96M (ISO 12572:2001). 2 - day water vapor permeability. The water vapor permeability can be, for example, up to 1000, up to 500 or up to 350 g / m 2 -sky.

[0120] The biaxially stretched microporous membrane or the composite sheet comprising the biaxially stretched microporous membrane preferably passes the water tightness test of EN1928:2000 Method B under a pressure of 0.3 MPa for at least 30 minutes without leakage. Preferably, the biaxially stretched microporous membrane or the composite sheet comprising the biaxially stretched microporous membrane does not leak under a pressure of 0.3 MPa for at least two hours.

[0121] Surprisingly, the presence of the nonwoven does not inhibit stretching and micropore formation in the film, and also adheres strongly to the polypropylene copolymer, thereby preventing tearing and the formation of more macroscopic defects in the stretched material. Therefore, the biaxially stretched composite sheet preferably has a high vapor pressure permeability and excellent water tightness.

[0122] The composite sheet preferably exhibits a tear strength in at least one direction as measured according to EN 12310-2: 2000 of at least 200 N, more preferably at least 250 N. More preferably, the tear strength is at least 200 N, more preferably at least 250 N in each of the machine and cross directions.

[0123] The composite sheet preferably exhibits a tensile strength of at least 1250 N / 5 cm, more preferably at least 1500 N / 5 cm, or at least 1750 N / 5 cm, in at least one direction at peak load, as measured in accordance with ASTM D5034-09 at a crosshead speed of 30 cm / min. The composite sheet may exhibit a tensile strength of at least 1250 N / cm, at least 1500 N / cm, or at least 1500 N / cm in one direction (typically the machine direction) and at least 500 N / cm in the orthogonal direction (typically the cross direction) at peak load. The elongation at maximum force, measured in the same manner, is preferably at least 15% in both the machine and cross directions.

[0124] Another advantage of the composite sheet is that it welds easily and securely to itself, despite the presence of the embedded nonwoven. Bond strength is determined by bonding two composite sheets together using a hot air welder operating at a set temperature of 250°C, followed by measuring the peel strength of the resulting bond according to EM 12316-2:2000. The peel force at the weld is typically at least 2 N / mm.

[0125] The biaxially stretched microporous membrane or composite sheet comprising the biaxially stretched microporous membrane can be preferably used as a waterproof membrane or a component of a waterproof membrane in applications requiring air permeability, particularly water vapor permeability, such as roofing applications. In some embodiments, the biaxially stretched microporous membrane or composite sheet comprising the biaxially stretched microporous membrane is a roofing membrane or is used as a roofing membrane. Specific examples of roofing membranes for which the biaxially stretched microporous membrane or composite sheet comprising the biaxially stretched microporous membrane can be used include metal roofing membranes, temporary roofing membranes, and concrete roofing membranes, particularly lightweight concrete roofing membranes.

[0126] Test Method

[0127] Melting temperature and glass transition temperature are determined as follows by differential scanning calorimetry (DSC). The sample to be tested is weighed and sealed in an aluminum sealed DSC pan (P / N 900793.901 pan and 900794.901 lid). The sample weight of each sample is about 1-4 mg. The sample is scanned in a TA Instruments Q2000 DSC (differential scanning calorimeter) (P / N 970001.901) (S / N 2000.0877) with an automatic sampler, a nitrogen purge of 50 ml / min and a mechanical cooling accessory. The operating parameters are -20°C to 200°C, at 10°C / min, and a sampling interval of 0.1 s / pt. for the heating-cooling-heating cycle. The scan is analyzed using Universal Analysis V4.7A TA Instruments software. The melting temperature is obtained by DSC scanning, which is presented as the output of the instrument software and corresponds to the peak temperature in the heat flow relative to the temperature curve diagram on the second heating cycle. The glass transition temperature was determined from the inflection point at the second heating of the DSC curve using a heating / cooling rate of 10°C / min.

[0128] Density is determined by ASTM D792.

[0129] The softening point temperature is determined by ASTM D36-06. The specific Vicat softening temperature is determined by ASTM D1525.

[0130] Melt (mass) flow rate (MFR) is measured according to ASTM D-1238 at 230°C and 2.16 kg, according to Condition L (at 230°C and 2.16 kg) or Condition E (at 190°C and 2.16 kg) as indicated.

[0131] The peel strength is measured according to the GB / T328.21-2007 test standard (Test Methods for Building Sheets for Waterproofing―Part 21:Plastic and Rubber Sheets for Waterproofing-Resistance to Peeling of Joints). Two pieces of 200mm×350mm membrane are cut, and then overlapped and welded together by a hot air gun. The overlapping width is 80mm. The welded sample is cut into 5 pieces, and an unoverlapped portion of at least 100mm is retained; and the width of each piece is 50mm. Each specimen is mounted on the upper and lower fixtures. The 180° peel force test is run at a speed of 100±10mm / min, and the maximum peel force is recorded in N / 50mm. If the sample is broken, the peel force is not recorded or only one peak peel force is recorded. Record the stress-strain curve and remove the first and last quarter zones. The average peel force is the average of the peel forces at 10 equally divided points between the quarter zone and the third quarter zone. The average peel force is the average of 5 specimens.

[0132] The average molecular weight is measured via gel permeation chromatography (GPC) as described in US20210095110 A1.

[0133] The polymer composition was determined by nuclear magnetic resonance (NMR) spectroscopy as described in US20210095110 A1.

[0134] Tensile and elongation tests were performed according to ASTM D882.

[0135] Trapezoidal tear testing was performed according to ASTM D5587.

[0136] Example 1

[0137] The polypropylene copolymer stretch film is made from a formulation containing 80 weight percent polypropylene copolymer and 20 weight percent propylene-based elastomer. The polypropylene copolymer contains a polypropylene homopolymer and an ethylene-containing copolymer in a 70 / 30 weight ratio, meaning the formulation and polypropylene copolymer film contain 56 weight percent polypropylene homopolymer, 24 weight percent ethylene-containing copolymer, and 20 weight percent propylene-based elastomer. The polypropylene copolymer is a reactor-grade resin manufactured by Braskem, in which the polypropylene homopolymer and ethylene-containing copolymer are mixed in a reactor.

[0138] Propylene-based elastomers are primarily composed of isotactic propylene repeat units with random ethylene distribution and are produced using metallocene catalyst technology; they are available from ExxonMobil as Vistamaxx. TM 6102 elastomer available.

[0139] Film casting was performed on a 2-inch diameter single screw extruder with a film casting die. The copolymer formulation was fed into the extruder using a loss-in-weight feeder, and the extruder then melted the ingredients and extruded a non-porous polymer film or layer. The extruded film was then pulled through a roll stack with three rollers set at 250°F (+ / - 10 degrees) to obtain a non-porous film with a uniform and smooth surface.

[0140] Biaxially stretched films were produced by first stretching the film in the machine direction (MDO - parallel to the film production direction) on rollers at room temperature, then preheating the film to a temperature of 120°C and stretching the film in the transverse direction (TDO - perpendicular to the film production direction) using a tenter frame.

[0141] The degree of stretching and resulting properties of these films are shown in Tables 1A and 1B. The final film thickness for all samples ranged from 18.8 to 19.8 mils. Water vapor permeability (WVP) was measured as a wet cup value at 23 (+ / - 0.6)°C and a relative humidity differential of 50 (+ / - 2)%. Hydrostatic pressure measurements were performed using a slotted plate at a pressure of 0.3 MPa for 2 hours. As shown in Table 1A, the films of the present invention passed the hydrostatic pressure test.

[0142] Table 1A

[0143]

[0144]

[0145] Table 1B

[0146]

[0147]

[0148] Example 2

[0149] A composite sheet containing a biaxially oriented film was made using the same polypropylene copolymer formulation from Example 1, containing 80 weight percent polypropylene copolymer and 20 weight percent propylene-based elastomer, and a polypropylene-polyester (PP-PET) nonwoven fabric. The PP-PET nonwoven fabric was a 157 gsm spunbond nonwoven fabric purchased from Low & Bonar, made from sheath / core PP / PET filaments. The nonwoven fabric had MD / CD tensile strengths of 550 and 434 N / 5 cm, respectively, and MD / CD tensile elongations of 75% and 82%, respectively.

[0150] Composite sheet is made by extrusion lamination, promptly first extrude the non-porous membrane layer (or non-porous polymer layer) of polypropylene copolymer formulation and this membrane is combined with nonwoven in the roll gap between one group of rollers, wherein roll gap is set as a side that a part on the surface of the first side of nonwoven is pushed into polymer membrane layer.Then extrude another identical non-porous membrane layer (or non-porous polymer layer) and make it contact with the second side of the nonwoven exposed, and be clamped between one group of rollers again, wherein roll gap is set as the second side of nonwoven is pushed into the second membrane layer of extrusion.The thickness of each membrane layer of extrusion is about 762 microns.After cooling, gained structure forms reinforced membrane, and this reinforced membrane has the sandwich structure of the polypropylene copolymer formulation / nonwoven / extruded of extrusion, and wherein the space between the fibrous material in nonwoven is substantially fully impregnated with or is filled with the copolymer formulation of extrusion.

[0151] The composite sheet was then biaxially stretched as in Example 1, i.e., the film was first stretched 50% in the machine direction (MDO - parallel to the film production direction) on a roller at room temperature, and then stretched 40% in the transverse direction (TDO - perpendicular to the film production direction) in a tenter frame at a temperature of 120° C. The peel strength of the inventive sample (5-1) is shown in Table 2.

[0152] For comparison, a similar composite sheet was produced as above, except that the extruded polymer film layer was made solely of a polypropylene copolymer, rather than a polypropylene copolymer formulation; that is, no propylene-based elastomer was present in the polymer film layer. The composite sheet was then biaxially stretched, first cold-stretched 25% on an MDO and then hot-stretched 50% on a TDO, both at the same temperature as before. The peel strength of this comparative sample (5-A) is also shown in Table 2. As shown, the composite sheet of the present invention with the addition of a propylene-based elastomer exhibits improved peel strength.

[0153] Table 2

[0154]

[0155] Example 3

[0156] The biaxially stretched film is made of two compositions of the embodiment of polypropylene copolymer formulation. In this example, the polypropylene copolymer formulation contains a mixture of polypropylene copolymer, an elastomer based on propylene and a sealing additive. As in Example 1, the polypropylene copolymer contains a polypropylene homopolymer and an ethylene-containing copolymer in a weight ratio of 70 / 30. The first composition has a polypropylene copolymer of 75 weight percents, an elastomer based on propylene of 10 weight percents and a sealing additive of 15 weight percents. The second composition has a polypropylene copolymer of 65 weight percents, an elastomer based on propylene of 20 weight percents and a sealing additive of 15 weight percents. As in Example 1, the polypropylene copolymer contains a polypropylene homopolymer and an ethylene-containing copolymer in a weight ratio of 70 / 30.

[0157] The sealant additive contains equal weight portions of two different polyolefin elastomers with different densities and a hydrocarbon tackifier (each accounting for 5 weight percent of the composition). The two polyolefin elastomers are ENGAGE TM 8402 Polyolefin Elastomer and Affinity TM GA 1900 elastomer, both available from Dow, and the hydrocarbon tackifier is ESCOREZ TM 5400, which is a cycloaliphatic hydrocarbon resin available from ExxonMobil Corporation. Figure 5 is a TEM micrograph of a non-porous film of the first composition before stretching, and Figure 6 is a TEM micrograph of a non-porous film of the second composition before stretching.

[0158] Then, as in Example 1, a non-porous film containing a second composition (65% / 20% / 15% polypropylene copolymer / propylene-based elastomer / sealing additive) was cold stretched 40% in the machine direction and then hot stretched 50% in the transverse direction to form a biaxial film; the biaxially stretched film passed the hydrostatic pressure test (slotted plate) at 0.3 MPa for 2 hours.

Claims

1. A microporous biaxially stretched film, comprising: a) 90 to 65 weight percent of a polypropylene copolymer, said polypropylene copolymer comprising i) 50 to 95 weight percent of polypropylene homopolymer segments, based on the weight of the polypropylene copolymer; or 43 to 79 mole percent of polypropylene homopolymer segments, based on the molar content of polymerized units of polypropylene in the polypropylene homopolymer segments as a percentage of the total molar content of polymerized monomer units in the polypropylene copolymer; and ii) 5 to 50 weight percent of ethylene-containing copolymer segments, based on the weight of the polypropylene copolymer; or 21 to 57 mole percent of ethylene-containing copolymer segments, based on the molar content of polymerized monomer units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the polypropylene copolymer; wherein at least a portion of the ethylene-containing copolymer segment comprises ethylene polymerized units in an amount of at least 45 weight percent based on the weight of the ethylene-containing copolymer segment; or ethylene polymerized units in an amount of at least 55 mole percent based on the molar content of ethylene polymerized units in the ethylene-containing copolymer segment as a percentage of the total molar content of polymerized monomer units in the ethylene-containing copolymer segment; and b) 10 to 35 weight percent of a propylene-based elastomer having 5 to 25 weight percent ethylene-derived units and having a melting temperature of less than 110°C; The weight percentages of a) and b) are based on the total weight of a) and b), The biaxially stretched microporous film has a water vapor permeability of 50 g / (24 hours·m 2 ) or more, and no liquid water passes through the film when exposed to a 0.3 MPa hydrostatic pressure test for 30 minutes. 2 . The biaxially stretched microporous film according to claim 1 , having a water vapor permeability of 90 g / (24 h·m 2 ) or more. 3 . The biaxially stretched microporous film according to claim 2 , having a water vapor permeability of 190 g / (24 h·m 2 ) or more.

4. The biaxially stretched microporous membrane of any one of claims 1 to 3, wherein no liquid water passes through the membrane when exposed to a 0.3 MPa hydrostatic pressure test for 2 hours.

5. A roof membrane comprising the biaxially stretched microporous membrane according to any one of claims 1 to 4.

6. A composite sheet comprising the biaxially stretched microporous membrane according to any one of claims 1 to 4, further comprising a nonwoven fabric embedded therein, wherein the nonwoven fabric has a weight of 100 to 400 g / m 2 basis weight.

7. The composite sheet of claim 6, which is in the form of an extrusion laminated sheet having the nonwoven fabric positioned inside the composite sheet.

8. The composite sheet according to claim 6 or 7, wherein the composite sheet has a density of 500 to 2000 g / m 2 basis weight.

9. A roof membrane comprising the composite sheet according to any one of claims 6 to 8.

10. A microporous biaxially stretched film, comprising: a) 89 to 65 weight percent of a polypropylene copolymer, said polypropylene copolymer comprising i) 50 to 95 weight percent of polypropylene homopolymer segments, based on the weight of the polypropylene copolymer; or 43 to 79 mole percent of polypropylene homopolymer segments, based on the molar content of polymerized units of polypropylene in the polypropylene homopolymer segments as a percentage of the total molar content of polymerized monomer units in the polypropylene copolymer; and ii) 5 to 50 weight percent of ethylene-containing copolymer segments, based on the weight of the polypropylene copolymer; or 21 to 57 mole percent of ethylene-containing copolymer segments, based on the molar content of polymerized monomer units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the polypropylene copolymer; wherein at least a portion of the ethylene-containing copolymer segment comprises ethylene polymerized units in an amount of at least 45 weight percent based on the weight of the ethylene-containing copolymer segment; or ethylene polymerized units in an amount of at least 55 mole percent based on the molar content of ethylene polymerized units in the ethylene-containing copolymer segment as a percentage of the total molar content of polymerized monomer units in the ethylene-containing copolymer segment; and b) 10 to 34 weight percent of a propylene-based elastomer having 5 to 25 weight percent ethylene-derived units and having a melting temperature of less than 110°C; and c) 1 to 15 weight percent of a sealing additive, The weight percentages of a), b) and c) are based on the total combined weight of a), b) and c).

11. The biaxially stretched microporous membrane according to claim 10, wherein The sealing additive is one or more polyolefin elastomers, one or more polyolefin plastomers, one or more hydrocarbon tackifiers, or any mixture thereof.

12. The biaxially stretched microporous membrane according to claim 11, wherein The sealant additive comprises a mixture of two different polyolefin elastomers.

13. A roofing membrane comprising the biaxially stretched microporous membrane according to any one of claims 10 to 12.

14. A composite sheet comprising the biaxially stretched microporous membrane according to any one of claims 10 to 12, wherein the composite sheet comprises a nonwoven fabric embedded therein, wherein the nonwoven fabric has a weight of 100 to 400 g / m 2 basis weight.

15. The composite sheet of claim 14, in the form of an extrusion laminated sheet having the nonwoven fabric positioned inside the composite sheet.

16. The composite sheet according to claim 14 or 15, wherein the composite sheet has a density of 500 to 2000 g / m 2 basis weight.

17. A roof membrane comprising the composite sheet according to any one of claims 14 to 16.

18. A method for forming a biaxially stretched microporous membrane, the method comprising the steps of: A) forming a non-porous film from a composition comprising a) 90 to 65 weight percent of a polypropylene copolymer, said polypropylene copolymer comprising i) 50 to 95 weight percent of polypropylene homopolymer segments, based on the weight of the polypropylene copolymer; or 43 to 79 mole percent of polypropylene homopolymer segments, based on the molar content of polymerized units of polypropylene in the polypropylene homopolymer segments as a percentage of the total molar content of polymerized monomer units in the polypropylene copolymer; and ii) 5 to 50 weight percent of ethylene-containing copolymer segments, based on the weight of the polypropylene copolymer; or 21 to 57 mole percent of ethylene-containing copolymer segments, based on the molar content of polymerized monomer units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the polypropylene copolymer; wherein at least a portion of the ethylene-containing copolymer segment comprises ethylene polymerized units in an amount of at least 45 weight percent based on the weight of the ethylene-containing copolymer segment; or ethylene polymerized units in an amount of at least 55 mole percent based on the molar content of ethylene polymerized units in the ethylene-containing copolymer segment as a percentage of the total molar content of polymerized monomer units in the ethylene-containing copolymer segment; and b) 10 to 35 weight percent of a propylene-based elastomer having 5 to 25 weight percent ethylene-derived units and having a melting temperature of less than 110°C; The weight percentages of a) and b) are based on the total weight of a) and b), B) subjecting the non-porous membrane to a sequential cold and hot biaxial stretching step consisting of: (i) a cold stretching step in a first direction at a temperature in the range of -20°C to 50°C; and (ii) a heat stretching step in the second direction at a temperature in the range of 50° C. to 140° C.; To produce a biaxially stretched microporous polymer membrane having a water vapor permeability of 50 g / (24 hours·m2) or more and no liquid water passing through the membrane when exposed to a 0.3 MPa hydrostatic pressure test for 30 minutes.

19. The method for forming a biaxially stretched microporous membrane according to claim 18, wherein: The second direction is orthogonal to the first direction.

20. The method for forming a biaxially stretched microporous film according to claim 18 or 19, wherein the biaxially stretched microporous film has a water vapor permeability of 190 g / (24 hours·m2) or more.

21. The method for forming a biaxially stretched microporous membrane according to any one of claims 18 to 20, wherein no liquid water passes through the biaxially stretched microporous membrane when exposed to a 0.3 MPa hydrostatic pressure test for 2 hours.

22. The method for forming a biaxially stretched microporous membrane according to any one of claims 18 to 21, wherein The non-porous membrane is made by extruding a polymer layer from a casting die.

23. A method for forming a composite sheet comprising a biaxially stretched microporous membrane, the method comprising the steps of: A) forming a non-porous polymer film or a non-porous polymer layer from a composition comprising a) 90 to 65 weight percent of a polypropylene copolymer, said polypropylene copolymer comprising i) 50 to 95 weight percent of polypropylene homopolymer segments, based on the weight of the polypropylene copolymer; or 43 to 79 mole percent of polypropylene homopolymer segments, based on the molar content of polymerized units of polypropylene in the polypropylene homopolymer segments as a percentage of the total molar content of polymerized monomer units in the polypropylene copolymer; and ii) 5 to 50 weight percent of ethylene-containing copolymer segments, based on the weight of the polypropylene copolymer; or 21 to 57 mole percent of ethylene-containing copolymer segments, based on the molar content of polymerized monomer units in the ethylene-containing copolymer segments as a percentage of the total molar content of polymerized monomer units in the polypropylene copolymer; wherein at least a portion of the ethylene-containing copolymer segment comprises ethylene polymerized units in an amount of at least 45 weight percent based on the weight of the ethylene-containing copolymer segment; or ethylene polymerized units in an amount of at least 55 mole percent based on the molar content of ethylene polymerized units in the ethylene-containing copolymer segment as a percentage of the total molar content of polymerized monomer units in the ethylene-containing copolymer segment; and b) 10 to 35 weight percent of a propylene-based elastomer having 5 to 25 weight percent ethylene-derived units and having a melting temperature of less than 110°C; The weight percentages of a) and b) are based on the total weight of a) and b), B) combining the non-porous polymer film or non-porous polymer layer with a non-woven fabric to form a composite sheet, and C) subjecting the composite sheet to sequential cold and hot biaxial stretching steps comprising: (i) at least one cold stretching step in a first direction at a temperature in the range of -20°C to 50°C; and (ii) at least one heat stretching step in the second direction at a temperature in the range of 50°C to 140°C; to produce a composite sheet comprising a biaxially stretched microporous polymer membrane.

24. The method for forming a composite sheet according to claim 23, wherein: Said sequential cold and hot biaxial stretching steps of step C) consist of: (i) a cold stretching step in a first direction at a temperature in the range of -20°C to 50°C; and (ii) a heat stretching step in the second direction at a temperature in the range of 50°C to 140°C.

25. The method for forming a composite sheet according to claim 23 or 24, wherein: The second direction is orthogonal to the first direction.

26. The method for forming a composite sheet according to any one of claims 23 to 25, wherein: The composite sheet is formed by combining the non-porous polymer film or non-porous polymer layer with a non-woven fabric through extrusion lamination.

27. The method for forming a composite sheet according to any one of claims 23 to 26, wherein: The nonwoven fabric is positioned between two non-porous films or two polymer layers on the interior of the composite sheet.

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