EP4662270A1

EP4662270A1 - Polypropylene copolymer biaxially stretched microporous film and composite sheets containing same

Info

Publication number: EP4662270A1
Application number: EP24753828.3A
Authority: EP
Inventors: Wenyi Huang
Original assignee: DDP Specialty Electronic Materials US LLC
Current assignee: DDP Specialty Electronic Materials US LLC
Priority date: 2023-02-09
Filing date: 2024-02-02
Publication date: 2025-12-17
Also published as: CN120659834A; JP2026507498A; WO2024167783A1; KR20250148615A

Abstract

Biaxially-stretched microporous film and composite sheet containing same, and process for making, and microporous film comprising: a) 90 to 65 percent by weight polypropylene copolymer, the polypropylene copolymer containing i) polypropylene homopolymer chain segments, and ii) ethylene-containing copolymer chain segments; and b) 10to 35 percent by weight propylene-based elastomer, the propylene-based elastomer having 5 to 25 weight percent ethylene derived units and having a melting temperature of less than 110 ⁰C; wherein the biaxially-stretched film can have a water vapor permeability of 50 grams/ (24 hours • m²)or greater and have no liquid water passage through the film for 30 minutes when exposed to a 0.3 MPa hydrohead test.

Description

Title of the Invention

Polypropylene Copolymer Biaxially Stretched Microporous Film and Composite Sheets Containing Same

Background of the Invention

Field of the Invention. This invention is related to biaxially stretched microporous films and composite sheets comprising biaxially stretched microporous films, and their use in a number of applications that desire a moisture vapor permeable sheet structure with a high degree of liquid water holdout. Some preferred end uses are in various building applications in the construction industry, including the use in breathable water resistant membranes for use in roofing applications.

Description of Related Art. US Pat. Publication 2021/0095110 to Huang et al. discloses microporous film via sequential cold and hot stretching of an unannealed polypropylene copolymer film; wherein the polypropylene copolymer comprises one or more polypropylene homopolymer chain segments and one or more ethylene-containing copolymer chain segments.

US Pat. Publication 2022/0298340 to Huang et al. also discloses microporous films made via sequential cold and hot stretching of unannealed polymer film. Examples 1 to 17 of that reference utilize films wherein the polymer comprises (a) polypropylene copolymer comprising one or more polypropylene homopolymer chain segments and one or more ethylene-containing copolymer chain segments. As illustrated in Example 15 of that publication, film samples made by both cold and hot machine-direction (MDO) stretching passed the very stringent hydrohead test of 30 meters of water for at least 30 minutes; however, the biaxially stretched samples made solely via a cold MDO stretching step followed directly by hot transverse direction (TDO) stretching, without an intervening hot MDO stretching step, did not pass this stringent hydrohead test. This failure to pass the test was attributed to the more interconnected pores created by the biaxial stretching process that undesirably pulled open the pores. Examples 18 to 20 of that publication further disclose films wherein the polymer comprises (a) polypropylene copolymer comprising one or more polypropylene homopolymer chain segments and one or more ethylene-containing copolymer chain segments, and (b) ethylene-propylene elastomer. All of these films are made with a process that includes both cold and hot machine-direction (MDO) stretching. Example 20 discloses that the machine direction (MDO) cold- stretched-and-then-further-hot-stretched films of Example 18 were then further hot stretched in the transverse direction, and that the general properties (including increased porosity) of films made by this biaxially-stretching process and the degree of property difference between the solely machine direction (MDO) films and films made by biaxially-stretching were similar to those shown Examples 13-15 & Example 17. This includes the biaxially stretched samples that did not pass the stringent hydrohead test when made solely via the process of Example 15, wherein a cold machine direction MDO stretching step was followed by hot transverse direction (TDO) stretching, without an intervening hot MDO stretching step.

Water leakage is a key challenge for the use of microporous film in a roof membrane. While some prior microporous films are said to provide water vapor permeability while maintaining an effective barrier to liquid water, the use of excessive machine-direction stretch can cause the resulting films to have an undesirable balance of properties in the machine and transverse direction, with certain machine-direction properties being increased at the expense of worse transverse properties. Additionally, as the stretching action on the film can potentially damage the film, it is desirable to make such films by the simplest process possible.

Understandably, there is a need for a microporous film that has both a desirable balance of properties and is made via a process having the fewest number of stretching steps possible to avoid potentially damage to the microporous membrane or by connecting the membrane pores in an undesirable way that negatively affects liquid water holdout. Therefore, specifically, there is a need for a biaxially stretched microporous film and roof membrane and other sheet structures that can pass this minimum liquid water holdout test and preferably can maintain the liquid water holdout at 0.3 MPa of water pressure for at least 30 minutes, and ideally for as long as 2 hours or more and can further be made in a two-step stretching process.

Brief Summary of the Invention

This invention relates to a biaxially-stretched microporous film comprising: a) 90 to 65 percent by weight polypropylene copolymer, the polypropylene copolymer containing i) 50 to 95 weight percent polypropylene homopolymer chain segments, based on the weight of the polyolefin; or 43 to 79 mole percent polypropylene homopolymer chain segments, based on the mole content of polymerized units of polypropylene in the polypropylene homopolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polyolefin; and ii) 5 to 50 weight percent of ethylene-containing copolymer chain segments based on the weight of the polyolefin; or 21 to 57 mole percent of ethylene-containing copolymer chain segments based on the mole content of polymerized monomer units in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polyolefin; wherein at least a portion of the ethylene-containing copolymer chain segments comprise polymerized units of ethylene in an amount of at least 45 weight percent, based on the weight of the ethylene-containing copolymer chain segments; or at least 55 mole percent, based on the mole content of polymerized units of ethylene in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the ethylene-containing copolymer chain segments; and b) 10 to 35 percent by weight propylene-based elastomer, the propylene-based elastomer having 5 to 25 weight percent ethylene derived units and having a melting temperature of less than 110 °C; wherein the percent by weight of a) and b) are based on the total weight of a) and b), the biaxially-stretched microporous film having a water vapor permeability of 50 grams/ (24 hours • m²) or greater and having no liquid water passage through the film for 30 minutes when exposed to a 0.3 MPa hydrohead test.

This invention also relates to a microporous biaxially-stretched film comprising: a) 89 to 65 percent by weight polypropylene copolymer, the polypropylene copolymer containing i) 50 to 95 weight percent polypropylene homopolymer chain segments, based on the weight of the polypropylene copolymer; or 43 to 79 mole percent polypropylene homopolymer chain segments, based on the mole content of polymerized units of polypropylene in the polypropylene homopolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polypropylene copolymer; and ii) 5 to 50 weight percent of ethylene-containing copolymer chain segments based on the weight of the polypropylene copolymer; or 21 to 57 mole percent of ethylene-containing copolymer chain segments based on the mole content of polymerized monomer units in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polypropylene copolymer; wherein at least a portion of the ethylene-containing copolymer chain segments comprise polymerized units of ethylene in an amount of at least 45 weight percent, based on the weight of the ethylene-containing copolymer chain segments; or at least 55 mole percent, based on the mole content of polymerized units of ethylene in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the ethylene-containing copolymer chain segments; and b) 10 to 34 percent by weight propylene-based elastomer, the 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 percent by weight of sealing additive, wherein the percent by weight of a), b), and c) are based on the total combined weight of a), b), and c).

The invention also relates to a process for forming a biaxially-stretched microporous film comprising the steps of:

A) forming a non-porous film from a composition comprising a) 90 to 65 percent by weight polypropylene copolymer, the polypropylene copolymer containing i) 50 to 95 weight percent polypropylene homopolymer chain segments, based on the weight of the polyolefin; or 43 to 79 mole percent polypropylene homopolymer chain segments, based on the mole content of polymerized units of polypropylene in the polypropylene homopolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polyolefin; and ii) 5 to 50 weight percent of ethylene-containing copolymer chain segments based on the weight of the polyolefin; or 21 to 57 mole percent of ethylene-containing copolymer chain segments based on the mole content of polymerized monomer units in the ethylenecontaining copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polyolefin; wherein at least a portion of the ethylene-containing copolymer chain segments comprise polymerized units of ethylene in an amount of at least 45 weight percent, based on the weight of the ethylenecontaining copolymer chain segments; or at least 55 mole percent, based on the mole content of polymerized units of ethylene in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the ethylene-containing copolymer chain segments; and b) 10 to 35 percent by weight propylene-based elastomer, the propylene- based elastomer having 5 to 25 weight percent ethylene derived units and having a melting temperature of less than 110 °C; wherein the percent by weight of a) and b) are based on the total weight of a) and b),

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

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

(ii) a hot stretching step in a second direction at a temperature in a range of from 50 °C to 140 °C; to produce a biaxially-stretched microporous polymer film having a water vapor permeability of 50 grams/ (24 hours • m²) or greater and having no liquid water passage through the film for 30 minutes when exposed to a 0.3 MPa hydrohead test.

This invention also further relates to a process for forming a composite sheet comprising a biaxially-stretched microporous film, comprising the steps of: A) forming a non-porous film or layer of polymer from a composition comprising a) 90 to 65 percent by weight polypropylene copolymer, the polypropylene copolymer containing i) 50 to 95 weight percent polypropylene homopolymer chain segments, based on the weight of the polyolefin; or 43 to 79 mole percent polypropylene homopolymer chain segments, based on the mole content of polymerized units of polypropylene in the polypropylene homopolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polyolefin; and ii) 5 to 50 weight percent of ethylene-containing copolymer chain segments based on the weight of the polyolefin; or 21 to 57 mole percent of ethylene-containing copolymer chain segments based on the mole content of polymerized monomer units in the ethylenecontaining copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polyolefin; wherein at least a portion of the ethylene-containing copolymer chain segments comprise polymerized units of ethylene in an amount of at least 45 weight percent, based on the weight of the ethylenecontaining copolymer chain segments; or at least 55 mole percent, based on the mole content of polymerized units of ethylene in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the ethylene-containing copolymer chain segments; and b) 10 to 35 percent by weight propylene-based elastomer, the propylene- based elastomer having 5 to 25 weight percent ethylene derived units and having a melting temperature of less than 110 °C; wherein the percent by weight of a) and b) are based on the total weight of a) and b),

B) combining the non-porous film or layer of polymer with a nonwoven 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 a range of from -20 °C to 50 °C; and

(ii) at least one hot stretching step in a second direction at a temperature in a range of from 50 °C to 140 °C; to produce a composite sheet comprising a biaxially-stretched microporous polymer film. Brief Description of the Drawings

Fig. 1 is a TEM micrograph of a non-porous polymer film sample that includes 80 percent by weight of polypropylene copolymer containing polypropylene homopolymer and ethylene-containing copolymer in a 70/30 weight ratio, and 20 percent by weight propylene-based elastomer.

Fig. 2 is a TEM micrograph of a “Control” non-porous polymer film sample of a phase-segregated polypropylene copolymer containing polypropylene homopolymer (continuous phase) and domains of ethylene-containing copolymer in a 70/30 weight ratio but without any propylene-based elastomer.

Fig. 3 is a TEM micrograph of a non-porous polymer film sample that includes 70 percent by weight of polypropylene copolymer containing polypropylene homopolymer and ethylene-containing copolymer in a 70/30 weight ratio, and 30 percent by weight propylene-based elastomer.

Fig. 4 is a TEM micrograph of a non-porous polymer film sample that includes 60 percent by weight of polypropylene copolymer containing polypropylene homopolymer and ethylene-containing copolymer in a 70/30 weight ratio, and 40 percent by weight propylene-based elastomer.

Fig. 5 is a TEM micrograph of a non-porous polymer film sample that includes 75 percent by weight of polypropylene copolymer containing polypropylene homopolymer and ethylene-containing copolymer in a 70/30 weight ratio, and 10 percent by weight propylene-based elastomer, and 5 weight percent each of two different polyolefin elastomers, and a hydrocarbon tackifier.

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

Fig. 7 is an illustration of one embodiment of a cross-sectional view of a non-porous composite sheet formed by sandwiching a nonwoven between two non-porous films; this is a view prior to biaxial ly stretching. Fig. 8 is a photo of the cross-section of the biaxially-stretched composite sheet made from 73.5 percent by weight of polypropylene copolymer containing polypropylene homopolymer and ethylene-containing copolymer in a 70/30 weight ratio, and 25 percent by weight propylene-based elastomer and 1 .5 weight percent UV stabilizer, wherein the nonwoven is symmetrically laminated in the composite sheet.

Fig. 9 is a representation of one possible continuous process for making a biaxially-stretched microporous film or a composite sheet comprising a microporous film, on an apparatus comprising an extrusion laminating 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 of the Invention

This invention relates to a polymeric biaxially-stretched microporous film, or a composite sheet comprising such a film, that is suitable for use in applications requiring a liquid water resistant but water vapor permeable membrane, such as, for example, roofing and other construction applications. The polymeric microporous film is made from a formulation than can provide a microporous film having microphase segregation/inclusion morphology, further having pore formation induced by sequential cold stretching in one direction followed by hot stretching in a second different direction. The polymeric microporous film, or a composite sheet comprising such a film, has suitable mechanical properties for the desired use.

The polymeric microporous film, or a composite sheet comprising such a film, has a water vapor permeability of at least 50 grams/ (24 hours • m²) or greater while also preventing liquid water from passing through the microporous film (or composite sheet) for 30 minutes when exposed to a 0.3 MPa hydrohead test, and preferably has no liquid water passage through the microporous film (or composite sheet) for 2 hours when exposed to a 0.3 MPa hydrohead test. As used herein, the phrase “sheet material” is meant to include any type of film or composite sheet comprising a film. Also, the terms “composite sheet comprising a biaxially-stretched microporous film” and “biaxially-stretched composite sheet” are used interchangeably herein.

It is believed the composition of the formulation and process for stretching the microporous film (or composite sheet) described herein forms a unique pore structure in a biaxially-stretched sheet material; providing, for example, uniform smaller pores (diameter: 100 nm - 1 micron) that have a generally noninterconnecting nature, resulting in breathable membranes that exhibit exceptional barrier to liquid water and air while achieving a desirable water vapor permeance. In addition, these breathable polymeric sheet materials are based on a polypropylene, meaning they are naturally hydrophobic and thermally stable, as polypropylene has a melting temperature of about 165 °C.

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

It is believed the incorporation of the propylene-based elastomer having a high quantity of propylene repeat units into the formulation modifies the microphase morphology in the film, such that when the film is stretched in two directions, the pores formed in the film provide both superior water vapor permeability (through the film) that is adequate for many uses and can further be much higher than certain industry standards of at least 100 grams/ (24 hours • m²) for some construction applications. In fact, water vapor permeability (through the film) can range from 50 grams/ (24 hours • m²) or a little lower, to as high as almost 600 grams/(24 hours • m²) or even higher (587.6 grams/(24 hours • m²) is specifically exemplified herein); while also providing superior watertightness by having no liquid water passage through the film when exposed to a 0.3 MPa hydrohead test for a minimum of 30 minutes. This no-leakage performance time can be as high as 2 hours or more of water exposure. The incorporation of the high propylene content propylene-based elastomer also significantly improved the flexibility of the film, in addition to reducing seam welding times while increasing the strength of welded seams.

In some embodiments, the microporous film comprises 90 to 65 percent by weight polypropylene copolymer, the polypropylene copolymer containing i) 50 to 95 weight percent polypropylene homopolymer chain segments, based on the weight of the polyolefin; or 43 to 79 mole percent polypropylene homopolymer chain segments, based on the mole content of polymerized units of polypropylene in the polypropylene homopolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polyolefin; and ii) 5 to 50 weight percent of ethylene-containing copolymer chain segments based on the weight of the polyolefin; or 21 to 57 mole percent of ethylene-containing copolymer chain segments based on the mole content of polymerized monomer units in the ethylenecontaining copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polyolefin; wherein at least a portion of the ethylene-containing copolymer chain segments comprise polymerized units of ethylene in an amount of at least 45 weight percent, based on the weight of the ethylene-containing copolymer chain segments; or at least 55 mole percent, based on the mole content of polymerized units of ethylene in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the ethylene-containing copolymer chain segments. One suitable polypropylene copolymer is a reactor grade PP copolymer available from Braskem under the product code of PP C7054-07NA. It contains 32.9 wt. % ethylene-propylene copolymer, while the ethylene content in ethylene-propylene copolymer is 49.7 wt. %. It has a density of 0.9 g/cm³ and a melt mass flow rate of 7 g/10 min at 230°C and 2.16 kg. The number average molecular weight (Mn) and the weight average molecular weight (Mw) of PP C7054-07NA are 58,000 and 295,000, respectively; which means this copolymer has a Mw/Mn of about 5.1 . In some embodiments, the microporous film also comprises 10 to 35 percent by weight propylene-based elastomer, the propylene-based elastomer having 5 to 25 weight percent ethylene derived units and having a melting temperature of less than 110 °C. The percent by weight of the polypropylene copolymer and percent by weight propylene-based elastomer being based on the total combined weight of the polypropylene copolymer and the propylene-based elastomer. One suitable propylene-based elastomer is Vistamaxx™ 6102 propylene-based elastomer produced by ExxonMobil. It is primarily composed of isotactic propylene repeat 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 density of 0.862 g/cm³ It is believed the propylene-based elastomer should have a majority of propylene repeat units with about 40 weight percent ethylene content or less, and preferably about 25 weight percent ethylene content or less, and most preferably about 20 weight percent or less for proper biaxial stretching performance.

In some embodiments, the microporous film (and/or composite sheet) further comprises up to 15 percent by weight of sealing additive that promotes the seaming of the sheet material to itself. The sealing additive can be a single compound or a mixture of different compounds. The words “up to” in the phrase “... up to 15 percent by weight” means at least some sealing additive is present in the composition of the microporous film formulation and therefore in the sheet materials, and that preferably that amount is an effective amount to increase the seam sealing of the microporous film. In some instances, this is believed to be at least 1 percent by weight, and preferably at least 3 percent by weight, of the microporous film formulation. The percent by weight of the sealing additive is based on the total combined weight of the sealing additive, the weight of the polypropylene copolymer, and the propylene-based elastomer.

In some preferred embodiments, the sealing additive is a mixture of compounds, such as one or more polyolefin elastomer, one or more polyolefin plastomer, one or more hydrocarbon tackifier, and any mixture of these. One preferred mixture includes two different polyolefin elastomers differing by density and a hydrocarbon tackifier, each present in equal parts by weight.

Polyolefin-based elastomers and plastomers are generally polymers or rubber or rubber-like compounds; the general rule is that the key difference between elastomers and plastomers is that elastomers show elasticity, whereas plastomers show both plasticity and elasticity. Elastomers also tend to have reduced crystallinity compared to plastomers. However, these are general and not firm rules of thumb, and it is possible a particular material used as a plastomer in one application can be used as an elastomer in another. Polyolefin elastomers and plastomers can be selected from suitable metallocene-catalyzed alpha-olefin copolymers as described in: Progress in Polymer Science, v. 33, pp 797-819 (2008). Preferred polyolefin elastomers and plastomers are based on an alpha-olefin comprising 1 -octene. A non-limiting example of a preferred polyolefin elastomer is ENGAGE™ 8402 polyolefin elastomer available from Dow, which is an ethylene-octene copolymer with a melt mass flow rate (MFR) of 30 g/10 min at 190 °C and 2.16 kg and a density of 0.902 g/cm³. ENGAGE™ 8402 elastomer has a glass transition temperature of -36 °C and a melting temperature of 96 °C. Plastomers have elastomeric properties like rubbers but can be processed similar to plastics and are generally tougher than elastomers. A non-limiting example of a preferred elastomer is AFFINITY™ GA 1900 elastomer available from Dow, which is a polyolefin elastomer with a density of 0.87 g/cm³. 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 generally used to increase the stickiness of adhesives. One suitable tackifier is ESCOREZ™ 5400 available from ExxonMobil, which is a cycloaliphatic hydrocarbon resin having 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.

In some specific embodiments, the microporous film comprises 89 to 65 percent by weight polypropylene copolymer as previously described herein, combined with 10 to 34 percent by weight propylene-based elastomer as previously described herein, and 1 to 15 percent by weight of the sealing additive as previously described herein.

In other words, in some embodiments, the microporous film comprises 89 to 65 percent by weight polypropylene copolymer, the polypropylene copolymer containing i) 50 to 95 weight percent polypropylene homopolymer chain segments, based on the weight of the polyolefin; or 43 to 79 mole percent polypropylene homopolymer chain segments, based on the mole content of polymerized units of polypropylene in the polypropylene homopolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polyolefin; and ii) 5 to 50 weight percent of ethylene-containing copolymer chain segments based on the weight of the polyolefin; or 21 to 57 mole percent of ethylene-containing copolymer chain segments based on the mole content of polymerized monomer units in the ethylenecontaining copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polyolefin; wherein at least a portion of the ethylene-containing copolymer chain segments comprise polymerized units of ethylene in an amount of at least 45 weight percent, based on the weight of the ethylene-containing copolymer chain segments; or at least 55 mole percent, based on the mole content of polymerized units of ethylene in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the ethylene-containing copolymer chain segments.

In this embodiment, the microporous film also comprises 10 to 34 percent by weight propylene-based elastomer, the propylene-based elastomer having 5 to 25 weight percent ethylene derived units and having a melting temperature of less than 110 °C, and 1 to 15 percent by weight of sealing additive that promotes the seaming of the sheet to itself. Each of the percent by weight of the polypropylene copolymer, the propylene-based elastomer, and the sealing additive are based on the total combined weight of the polypropylene copolymer, the propylene-based elastomer, and the sealing additive. As stated herein, preferably the sealing additive is a mixture of compounds, and one preferred mixture is 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.

The microporous film, and preferably a composite sheet comprising the microporous film, has a water vapor permeability of 50 grams/ (24 hours • m²) or greater. In some embodiments, a water vapor permeability of 90 grams/ (24 hours • m²) or greater is desirable. In some other embodiments, a water vapor permeability of 190 grams/ (24 hours • m²) or greater is desirable.

The microporous film also does not allow any liquid water passage through the film for 30 minutes when exposed to a 0.3 MPa hydrohead test. In some embodiments, the microporous film does not allow any water passage through the film for 2 hours when exposed to a 0.3 MPa hydrohead test.

In some embodiments, the microporous film has a basis weight of about 100 to 400 g/m². In some other embodiments, the microporous film has a basis weight of about 200 to 300 g/m².

In some embodiments the non-porous film made from the composition described herein, and the subsequent biaxially-stretched microporous film and composite sheet made from the non-porous film, comprises a phase-segregated polymer that includes a continuous phase that comprises the polypropylene homopolymer and the propylene-based elastomer, and a dispersed phase that comprises domains of the ethylene-propylene copolymer. The dispersed phase is in the form of discrete domains observable by transmission electron microscopy (TEM) according to the method described in paragraph [0173] of US 2021/0095110 A1 , or equivalent method. The dispersed phase domains further contain inclusions of at least the polypropylene homopolymer from the continuous phase. Such inclusions are also observable by the aforementioned TEM method. Fig. 1 is a TEM micrograph of a non-porous polymer film sample 10 that includes 80 percent by weight of polypropylene copolymer containing polypropylene homopolymer and ethylene-containing copolymer in a 70/30 weight ratio, and 20 percent by weight propylene-based elastomer. In other words, the composition comprised polypropylene copolymer in about 67.1 weight percent polypropylene homopolymer (the light-colored continuous phase 1), and about 32.9 weight percent ethylene-propylene copolymer (forming part of the darker dispersed phase domain 2); and 20 weight percent of propylene-based elastomer, the propylene-based elastomer also forming part of the continuous phase 1. The domains 2 comprising the ethylene-propylene copolymer mainly have largest dimensions of 0.5 to 2 micrometers (pm) as shown. Domains 2 further contain inclusions 4 of a least the polypropylene homopolymer as is present in the continuous phase 1. Inclusions 4 may constitute, for example, 10 to 65% of the total mass of domains 2. A small portion (such as up to 25%, up to 10% or up to 5%) of the mass of the dispersed phase may be in the form of smaller fragmented domains 5 of the ethylene-propylene copolymer having largest dimensions of less than 0.5 micrometers (pm) The smaller domains 5 may lack inclusions 4. The relative mass of the dispersed phase can be estimated using nuclear magnetic resonance (NMR) spectroscopy methods.

The impact on the morphology of the copolymer by the addition of the propylene-based elastomer is illustrated in Fig. 2. Fig. 2 is a TEM micrograph of a “Control” non-porous polymer film sample of a phase-segregated polypropylene copolymer containing polypropylene homopolymer (continuous phase 11) and domains 12 of ethylene-containing copolymer in a 70/30 weight ratio but without any propylene-based elastomer. The domains of ethylenecontaining copolymer 12 further contain inclusions 14 of the polypropylene homopolymer. Comparison of Fig. 2 with Fig. 1 suggests the addition of the propylene-based elastomer reduces the size of the dispersed phase domains as shown by comparison with Fig. 1.

Therefore, with the presence of the propylene-based elastomer, the domain sizes were reduced over the control sample. Preferably, at least 95% of the mass of the dispersed phase is in the form of domains having a longest dimension of 0.1 to 2 pm. 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 pm, 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 pm.

Fig. 3 is a TEM micrograph of a non-porous polymer film sample that includes 70 percent by weight of polypropylene copolymer containing polypropylene homopolymer and ethylene-containing copolymer in a 70/30 weight ratio, and 30 percent by weight propylene-based elastomer. Fig. 4 is a TEM micrograph of a non-porous polymer film sample that includes 60 percent by weight of polypropylene copolymer containing polypropylene homopolymer and ethylene-containing copolymer in a 70/30 weight ratio, and 40 percent by weight propylene-based elastomer. As shown, as the amount of propylene- based elastomer is increased, the domains of the dispersed phase get smaller, such that by the time the amount of propylene-based elastomer is 40 weight percent the desired morphology is no longer primarily present.

Fig. 5 is a TEM micrograph of a non-porous polymer film sample that includes 75 percent by weight of polypropylene copolymer containing polypropylene homopolymer and ethylene-containing copolymer in a 70/30 weight ratio, and 10 percent by weight propylene-based elastomer, and 5 weight percent each of two different polyolefin elastomers (having different densities) and 5 weight percent of a hydrocarbon tackifier. Fig. 6 is a TEM micrograph of a non-porous polymer film sample that includes 65 percent by weight of polypropylene copolymer containing polypropylene homopolymer and ethylenecontaining copolymer in a 70/30 weight ratio, and 20 percent by weight propylene-based elastomer, 5 weight percent each of two different polyolefin elastomers (having different densities) and 5 weight percent of a hydrocarbon tackifier.

The additional polyolefin elastomers and tackifiers (15 weight percent total) are believed to further reside in the continuous phase, and as shown, as the amount of ethylene-containing copolymer in the overall formulation is decreased, the domains of the dispersed phase get smaller, again showing that the minimum amount of polypropylene copolymer should be no less than about 65 weight percent to achieve the desired morphology in the film.

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

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

The ethylene-containing copolymer chain segments are copolymers of ethylene and at least one other copolymerizable monomer. The other copolymerizable monomer preferably is propylene. The ethylene-containing copolymer chain segments may be, for example, block, random, pseudo-random, and/or graft copolymers of ethylene and the at least one other copolymerizable monomer. In specific embodiments, the ethylene- containing copolymer chain segments are or include block copolymers of ethylene and propylene. The content of polymerized ethylene units in the polyolefin may be, for example at least 10, at least 12 or at least 15 weight percent, and for example, up to 30 or up to 25 weight percent, based on the total weight of the polyolefin. Other suitable polyolefins are those such as, for example, described in US 2021/009511 A1 paragraphs [0063] to [0078],

The propylene-based elastomer has at least about 60 weight percent propylene-derived units, preferably at least about 75 weight percent, 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 interrupted by non-crystalline regions. The non-crystalline regions may result from regions of non-crystallizable polypropylene segments and/or the inclusion of comonomer units, for example, ethylene. In the presence of comonomer, the crystallinity and the melting temperature of the propylene- based elastomer are reduced compared to highly isotactic polypropylene. The examples of commercially available propylene-based elastomers include Vistamaxx™ performance polymers from ExxonMobil and VESIFY™ elastomers from Dow Inc.

It has been found that the addition of the high propylene-content propylene-based elastomer promotes the adhesion of the biaxially-stretched microporous film, and of the composite sheet comprising the biaxially-stretched microporous film, to itself to form a seam. Despite the use of a polypropylene copolymer in the microporous film, the microporous film and composite sheet containing said film can stiffen at colder temperatures, which can make installation of roofing membranes difficult in the wintertime. It is desirable for the edges of roof membranes to be seamed without the use of an adhesive, by heating the edges of the sheets to a temperature above the melting temperature of film polymer, which will adhere the sheet edges together. This technique of joining sheets, known as heat (hot air) welding, provides a strong seam and results in overall time and cost savings in the application of roofing membrane. It is believed the further addition of a sealing additive in the composition for the microporous film and composite sheet containing said film can further improve heat welding (seaming) performance.

The composition for making the biaxially-stretched microporous film and composite sheet comprising the biaxially-stretched microporous film can contain other components such as extrusion processing aids such as lubricants and the like; antioxidants, titanium dioxide, UV stabilizers, light stabilizers, thermal stabilizers, pigments or other colorants, antistatic agents, flame retardants, antiblock additives, biocides, and the like, to the degree that they don’t negatively affect the desired performance of the sheet materials. UV stabilizers are preferred additives. Examples of stabilizers include various hydroxyphenylbenzotrioles, such as those sold under the general brand name of Tinuvin® by BASF or hindered amine stabilizers such as those sold as Tinuvin® or Chimassorb® by BASF. One or more UV stabilizers may be used in conjunction with one or more antioxidants.

Although the polypropylene copolymer may contain filler particles, such fillers are preferably absent or, if present, present in only small quantities such as up to 3%, up to 2%, up to 1 %, or up to 0.5% of the combined weight of 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 can include both inorganic and organic types.

In some embodiments, the biaxially-stretched composite sheet comprising the microporous film and a nonwoven has a basis weight of about 500 to 2000 g/m². In some embodiments, the biaxially-stretched composite sheet comprising the microporous film and a nonwoven has a basis weight of about 300 to 1500 g/m².

In some embodiments, the nonwoven in the composite sheet has a basis weight of about 100 to 400 g/m². as measured according to EN ISO 9864:2016. A preferred basis weight is at least 125 or at least 150 g/m² and up to 350 or up to 300 g/m². The nonwoven thickness can be preferably 0.25 to 0.95 mm under a load of 2 kN/m², and can be, for example, at least 0.3 or least 0.4 mm and up to 0.9 or up to 0.8 mm, as measured according to EN ISO 9863-1 :2005. The nonwoven can have an elongation to break of 30 to 200% in each of machine and cross directions, as measured according to EN ISO 10319:2015. The nonwoven is preferably water-permeable and may have a permeability (VH50) of 5 x 10’³ to 200 x 10-³, especially 10 x 10’³ to 100 x 10’³, or 10 x 1 Q-³ to 50 x 10’³, m/s as measured according to EN ISO 11058:2019. The nonwoven in some embodiments comprises or consists of fibers or filaments that are entangled, spun-bonded and/or melt bonded to form the nonwoven. The nonwoven may be made in a spun-bond, air-laying, spunlaced or melt-bond process, for example, or may be a mesh.

The nonwoven is preferably composed of a material that is thermally stable under the conditions of an extrusion lamination step, i.e., the material does not melt, unacceptably heat soften or degrade such that nonwoven loses its integrity during the extrusion lamination step. The material may be or include 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 (nylons), poly(lactide), cellulosic fibers such as pulped and extruded cellulose (Lyocell®), cellulose acetate, cellulose diacetate, cellulose triacetate and cellulose acetate butyrate, various acrylate polymers, polybenzimidazole, aramid, polyvinyl alcohol, polyphenylene sulfide, polyacrylonitrile and acrylonitrile copolymers. The nonwoven may also comprise, for example, carbon, wool, metallic, mineral wool, silk, jute or other natural fibers, provided the nonwoven has the elongation to break and preferably also the permeability as mentioned above.

A preferred nonwoven is a polypropylene nonwoven, a polyethylene terephthalate nonwoven, or a polypropylene-polyethylene terephthalate nonwoven. A polypropylene-polyethylene terephthalate nonwoven can be composed of polypropylene-polyethylene bicomponent fibers, wherein polypropylene forms at least a portion of the surface of the bicomponent fibers. Such bicomponent fibers can be, for example, a sheath-and-core type with a polypropylene sheath, or a side-by-side bicomponent fiber.

When the biaxially-stretched microporous film or biaxially-stretched composite sheet containing the microporous film is made by an extrusion lamination process, the polypropylene copolymer formulation is melted, and the melted polypropylene copolymer formulation is then forced through a die to form a non-porous film or layer of polymer. This step can be performed using, for example, a single-screw or twin-screw extruder, an accumulating extruder, or other suitable apparatus, equipped with a suitable die such as a slit die or dogbone die. The polypropylene copolymer formulation is heated in the extrusion equipment to a temperature above the crystalline melting temperature of the polypropylene homopolymer of the continuous phase and forced through the die to form a film or layer of polymer. A preferred temperature is at least 180°C or at least 200°C and up to 240°C or up to 260°C.

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

The extruded film or layer of polymer is non-porous. It is preferred to omit blowing agents and/or gasses in the extrusion process to avoid producing pores at this stage. For purposes of this invention, a sheet is considered as “non- porous” if, after cooling, it exhibits a water vapor transmission rate (WVTR) of no greater than 2 g/m²-day at 37.8°C, 100% relative humidity, as measured according to ASTM D1249.

Preferably, the molten non-porous film or layer of polymer is contacted with a surface of the nonwoven, to produce a non-porous polymer layer on that surface. This step is preferably performed before the sheet has cooled to below its Vicat softening temperature. The contacting step preferably is performed within 30 seconds, more preferably within 10 seconds, within 5 seconds or within 2 seconds from when the sheet exits the extruder die.

The contacting step is preferably performed under mechanical (nipping) pressure such that the nonwoven becomes at least partially embedded in the non-porous film or polymer layer. By “embedded” it is meant that all or a portion of the polymer penetrates into a portion of the interstitial spaces between the fibers or filaments in the nonwoven, so at least a portion of the nonwoven becomes infused with the polymer. Mechanical (nipping) pressure is conveniently applied by passing the nonwoven and applied polymer layer through one or more calendar rollers; however other devices such as a double-belt laminator are also suitable. In some embodiments one or more of the calender rollers may be chilled to simultaneously cool the polymer to a temperature below its Vicat softening temperature (such as to 80 to 120°C) and impregnate the nonwoven.

The extrusion lamination process may be performed by applying an extruded film or layer of polymer to both sides of the nonwoven. In such a case, the opposing polypropylene copolymer formulation sheets can be contacted with the nonwoven simultaneously or sequentially.

Fig. 7 is an illustration of one embodiment of a cross-sectional view of a non-porous composite sheet formed by sandwiching a nonwoven between two non-porous films. As shown in Fig. 7, the resulting non-porous composite sheet 20 includes nonwoven 21 and (in the embodiment shown) two polypropylene copolymer layers 22 and 22A. As shown, nonwoven 21 is partially embedded into each of polypropylene copolymer layers 22 and 22A, which a small central section 23 of nonwoven 21 being non-infiltrated. In alternative embodiments in the non-porous composite sheet, and more particularly in the biaxially-stretched composite sheet, the entirely of nonwoven 21 is preferably infiltrated by and embedded in either or both of polypropylene copolymer layers 22 and 22A. Also as shown, a portion of each of polypropylene copolymer layers 22 and 22A respectively extend above and below nonwoven 21 to form non-reinforced surface layers 24 and 24A. In alternative embodiments, in the non-porous composite sheet, and more particularly in the biaxially-stretched composite sheet, one or both of those non-reinforced surface layers 24 and 24A are absent, in which case the respective polypropylene copolymer layer 22 and/or 22A has entirely penetrated into nonwoven 21. In some embodiments the composite sheet is in the form of an extrusion laminated sheet having the nonwoven positioned in the interior of the composite sheet. In some other embodiments, the nonwoven is symmetrically positioned in the composite sheet at the center of the thickness of the composite sheet.

The total thickness of the non-porous composite sheet can be at least 1 mm. It can be at least 1.2 mm, and can be up to, for example, 12.7 mm, up to 6.35 mm, up to 3 mm, up to 2 mm or up to 1 .8 mm.

The non-porous composite sheet thus formed is preferably cooled to a temperature of 50°C or less before being subjected to the sequential cold and hot stretching process. The cold stretch in the machine direction is performed first, followed by the hot stretch in a transverse direction. The stretching process may be performed in the general manner and conditions described in US 2021/095110 A1 . The cold stretching step is performed with the non-porous composite sheet at a temperature of -20° to 50°C. A preferred lower temperature is 0°C, 10°C or 15°C, and a preferred upper temperature is up to 35°C, up to 30°C or up to 25°C. The cold stretch percentage may 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%. The cold stretching may be performed in a single step or in multiple increments. Stretch percentage is calculated as 100% x [(stretched film length - initial film length) initial film length)]. As used herein, a “single step” is considered a single stretching process for stretching a sheet material a certain amount in a particular direction at a particular temperature or range of temperatures. For example, a “single cold stretch step” may include multiple rolls that work together to incrementally stretch the sheet material with each roll to ultimately stretch the sheet material a certain desired percentage in one direction.

The cold stretched composite sheet can be annealed prior to performing the subsequent hot stretching step if desired. Such an annealing step is conveniently performed by heating the cold stretched composite sheet to a temperature of 90 to 150°C, for a period of at least one second, preferably at least 2 seconds. Annealing periods of more than 30 seconds are generally unnecessary. Annealing can fix the pore structure formed in the cold stretching step and also reduce shrinkage. The annealing step preferably is performed immediately after cold stretching while maintaining the cold stretched composite sheet under as much tension as required to prevent shrinkage prior to transverse stretching.

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. A preferred lower temperature is at least 90°C or at least 120°C, and a preferred upper temperature is 140°C. The hot stretching may be performed in a single step or in multiple increments. The hot stretch percentage may 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 with regard to annealing the cold stretched composite sheet.

Fig. 8 is a photo of the cross-section (as shown similarly to Fig. 7) of an actual biaxially-stretched composite sheet made from 73.5 percent by weight of polypropylene copolymer containing polypropylene homopolymer and ethylenecontaining copolymer in a 70/30 weight ratio, and 25 percent by weight propylene-based elastomer and 1.5 weight percent UV stabilizer, wherein the nonwoven is symmetrically extrusion laminated in the composite sheet.

When the non-porous film or composite sheet is produced on film casting, extrusion lamination, or other apparatus, the sheet material will have a machine direction corresponding to the direction of movement through the apparatus, and a transverse or cross direction which is perpendicular (or orthogonal) to the machine direction (within the plane of the sheet). Either of the cold or hot stretching steps can be performed uniaxially in the machine direction or in the cross direction, but to create a biaxially-stretched microporous film or composite sheet, the cold and hot stretching steps should not be in the same direction, but preferably be orthogonal. In a preferred embodiment, the cold stretching step is performed in a machine direction and the hot stretching step is performed in the transverse or cross direction.

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

The non-porous film or composite sheet can be biaxially stretched in a continuous operation involving the combination of various devices that first stretch the non-porous film or composite sheet in the machine direction, for example a series of stretching rollers, followed by a stretching the non-porous film or composite sheet in the transverse or cross direction, such as with the use of a tenter frame that includes clips for gripping the sides of non-porous film or composite sheet. The clips are mounted on a pair of rails that diverge in the direction of the movement of the non-porous film or composite sheet through the apparatus. The clips travel along the rails, carrying the non-porous film or composite sheet, diverging and thus biaxially stretching the non-porous film or composite sheet into a biaxially-stretched microporous film or biaxially stretched composite sheet. The tenter frame is particularly well suited for stretching the sheet material in the cross direction. As before, the stretching section (i.e. , the section that includes the diverging rails) can be preceded by a preheating section, which can be followed by an annealing section and/or a rewinding section.

Yet another suitable stretching apparatus is a grooved roller stretcher. Such a grooved roller stretcher is particularly useful for stretching the non-porous film or composite sheet in the cross direction. The grooved roller stretcher comprises interdigitating tooth-and-groove structures through which the non- porous film or composite sheet is passed. The tooth-and-groove structure may be roller pairs as described, for example, in U.S. Patent Nos. 4,368,565, 5,028,289 and 6,843,949, US Published Patent Application No. 2006/0148354 and EP 927 096B1 ; or a toothed-and-grooved activation member and moving belt with complementary teeth-and grooves such as described in US Patent No. 8,337,190. The grooved roller stretcher may include multiple tooth-and-groove structures in series. The non-porous film or composite sheet is fed into the grooved roller stretcher and transported through the tooth-and-grooved structures, where the non-porous film or composite sheet is stretched transversely to the direction of its movement. The resulting microporous film or composite sheet comprising a microporous film is then removed from the apparatus. A stretching operation performed in a grooved roller stretcher is conveniently performed in a continuous manner by continuously transporting a length of the non-porous film or composite sheet through the tooth-and-grooved structures.

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

If desired, before, after, or during the step of ii), a second a non-porous film or layer of polymer can be attached or put in contact with the second opposing side of the nonwoven, which after biaxial stretching produces a composite sheet having the nonwoven positioned in the interior of the composite sheet. In some preferred embodiments, the first and second non-porous films or layers of polymer have essentially equal weight such that the nonwoven is symmetrically positioned at or near the center of the thickness of the composite sheet. As shown in Fig. 9, a continuous biaxially-stretching process can be performed on an apparatus that comprises an extrusion laminating 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.

The extrusion laminating device 50 can include, for example, an extruder equipped with a die adapted to produce a non-porous film or non-porous layer of polymer, a feeding apparatus for supplying the nonwoven to a laminator, and a laminator such as heated calender rolls to contact and mechanically compress the film or layer of polymer with a nonwoven to preferably force at least a portion of polymer from the film or layer of polymer into interstitial spaces in nonwoven to produce a composite sheet. The extrusion laminating device can have heated or cooled calendar rolls as desired or needed. The extrusion laminating device can further include the equipment to produce or provide a second film or layer of polymer (i.e. , a second extruder, casting die, laminating station, etc.) for contacting a second non-porous film or non-porous layer of polymer on the opposing side of the nonwoven in a similar manner to form a composite sheet with the nonwoven embedded between two films or two layers of polymer, forming a sandwich structure with the polymer from the films/layers of polymer in the interstitial spaces between the fibrous components in the nonwoven.

The machine-direction cold-stretching device 51 can receive the composite sheet from the extrusion laminating device and continuously coldstretch the composite sheet in the machine direction, which can include chilled rolls or other equipment, if needed, to cool or bring the composite sheet to a specific stretching temperature, and one or more stretching rollers or sets of nipped rollers for stretching the composite sheet in the machine direction. This is considered a single machine-direction stretching step herein.

The transverse direction hot-stretching device 52 can receive the cold- stretched composite sheet from the cold-stretching device and continuously further hot-stretch the composite sheet in the machine direction, which can include heated rolls or other equipment to heat or bring the composite sheet to a specific stretching temperature, and equipment such as a traverse spreading rollers an/or a tenter frame for gripping and stretching the heated composite sheet in a direction transverse the machine direction. This hot-stretching device can further include an optional annealing section after the stretching rollers for optionally annealing the stretched composite sheet at a desired temperature, for example with additional temperature-controlled rollers. This is considered a single transverse-direction stretching step herein.

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 chilled rolls or other equipment, if needed, to cool the biaxially-stretched composite sheet to a desired final temperature for winding into a roll good. The winding device 54 then preferably winds the final biaxially- stretched composite sheet onto a core to form a roll of the composite sheet comprising the biaxially-stretched microporous film.

A biaxially-stretched microporous film can be made in a similar process to the composite sheet comprising a biaxially-stretched microporous film by simply excluding the nonwoven. That is, casting one or more of the non-porous film(s) or layer(s) of polymer as before, but without combining the non-porous film(s) or layer(s) of polymer with any nonwoven, and cold-stretching and hot-stretching just the non-porous film(s) or layer(s) of polymer to form the biaxially-stretched microporous film.

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 film and the biaxially-stretched composite sheet preferably exhibits a water vapor permeance of at least 50, at least 90, at least 100, at least 120 or at least 190 g/m²-day, as measured according to ASTM E96/E96M (15012572:2001 ). The water vapor permeance may be, for example, up to 1000, up to 500 or up to 350 g/m²-day.

The biaxially-stretched microporous film or the composite sheet comprising a biaxially-stretched microporous film preferably passes the water tightness test of EN1928:2000 Method B without leakage under conditions of 0.3 MPa pressure for at least 30 minutes. Preferably the biaxially-stretched microporous film or a composite sheet comprising a biaxially-stretched microporous film is without leakage under conditions of 0.3 MPa pressure for at least two hours.

Surprisingly, the presence of the nonwoven does not inhibit stretching and micropore formation in the film, and also adheres strongly to the polypropylene copolymer so as to avoid tearing away and forming more macroscopic defects in the stretched material. Therefore, the biaxially-stretched composite sheet preferably has high vapor pressure permeance and excellent water tightness.

The composite sheet preferably exhibits a tear strength in at least one direction of at least 200 N, more preferably at least 250 N, as measured according to EN12310-2:2000. More preferably the tear strength is at least 200 N, more preferably at least 250 N, in each of machine and cross directions.

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

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 operated at a set temperature of 250°C, followed by measuring the peel strength of the resulting bond according to EM12316-2:2000. The peel force at the welded typically is at least 2 N/mm.

The biaxially stretched microporous film or a composite sheet comprising a biaxially stretched microporous film is preferably useful as, or as a component of, a water-proofing membrane in applications that require breathability, especially water vapor transmission, such as roofing applications. In some embodiments, the biaxially stretched microporous film or a composite sheet comprising a biaxially stretched microporous film is or is used as a roofing membrane. Specific examples of roof membranes for which the biaxially stretched microporous film or a composite sheet comprising a biaxially stretched microporous film are useful include metal roof membranes, temporary roof membranes, and concrete roof membranes, especially for lightweight concrete roof membranes.

Test Methods

Melting and glass transition temperatures were determined by Differential Scanning calorimetry (DSC) as follows. A sample to be measured was weighed and sealed in aluminum hermetic DSC pans (P/N 900793.901 pan and 900794.901 lid). The sample weights were roughly 1 -4 mg for each sample. The samples were scanned in a TA Instruments Q2000 DSC (Differential Scanning calorimeter) (P/N 970001.901 ) (S/N 2000.0877) with an auto sampler, nitrogen purge of 50 ml/min and mechanical cooling accessory. The run parameters were -20 °C to 200 °C at 10 °C/min with a sampling interval of 0.1 s/pt. for a heat-cool- heat cycle. The scans were analyzed using Universal Analysis V4.7A TA Instruments software. Melting temperature was obtained from DSC scans presented as the output of the instrument software and correspond to the temperature of the peak in the heat flow versus temperature plot on the second heating cycle. Glass transition temperature was determined from the inflection point on second heatup of the DSC curve using a heating/cooling rate of 10 °C/min.

Densities were determined by ASTM D792.

Softening point temperatures were determined by ASTM D36-06. Specific VICAT softening temperatures were determined by ASTM D1525. The Melt (Mass) Flow Rate (MFR) was measured at 230° C and 2.16 kg according to ASTM D-1238, in accordance with either Condition L (at 230° C and 2.16 kg), or Condition E (at 190° C and 2.16 kg) as noted.

The peel strength was measured according to GB/T328.21-2007 testing standard (Test Methods for Building Sheets for Waterproofing — Part 21 : Plastic and Rubber Sheets for Waterproofing-Resistance to Peeling of Joints). Two pieces of 200 mm x 350 mm membrane were cut and then overlapped and welded together by a hot air gun. The overlapping width was 80 mm. The welded sample was cut into 5 pieces, and at least 100 mm non-overlapping part was retained; and the width of each piece was 50mm. Each specimen was mounted onto the upper and lower clamps. The 180° peel force test was run at a speed of 100 ± 10 mm/min, and the maximum peel force was recorded in the unit of N/50 mm. If the sample was broken, no peel force or only one peak peel force was recorded. The stress-strain curve was recorded, and the first % and last % zones were removed. The average peer force was the average value of the peel forces at 10 equal diversion points between % zone and % zone. The peel force average was the averaged value of 5 specimens.

Average molecular weight was measured via Gel Permeation Chromatography (GPC) as described in US20210095110A1.

Polymer composition was determined by Nuclear Magnetic Resonance (NMR) Spectroscopy as described in US20210095110A1 .

Tensile & Elongation tests were performed following ASTM D882. Trapezoid tear tests were performed following ASTM D5587.

Example 1

Polypropylene copolymer stretched films were made from a formulation containing 80 percent by weight of polypropylene copolymer and 20 percent by weight propylene-based elastomer. The polypropylene copolymer contained polypropylene homopolymer and ethylene-containing copolymer in a 70/30 weight ratio, which meant the formulation and the polypropylene copolymer film contained 56 weight percent polypropylene homopolymer and 24 weight percent was ethylene-containing copolymer with the 20 percent by weight propylene- based elastomer. The polypropylene copolymer is a reactor grade resin manufactured by Braskem, where the polypropylene homopolymer and ethylenecontaining copolymer are mixed in a reactor.

The propylene-based elastomer was primarily composed of isotactic propylene repeat units with random ethylene distribution and was produced using metallocene catalyst technology; it was available as Vistamaxx™ 6102 elastomer from ExxonMobil.

The film casting was done on a 2-inch diameter single-screw extruder with film casting die. The copolymer formulation was fed to the extruder using loss-in- weight feeders and the extruder then melted the ingredients and extruded a non- porous film or non-porous layer of polymer. The extruded film was then pulled through a roll stack having three rolls set at 250 °F (+/- 10 degrees) to achieve a non-porous film having a uniform and smooth surface.

Biaxially-stretched films were made by first stretching the film on rolls in the machine direction (MDO - parallel to the direction of film manufacture) at room temperature, followed by preheating the film to a temperature of 120 °C and stretching the film using a tenter frame in the traverse direction (TDO - perpendicular to the direction of film manufacture).

The degree of stretching and resulting properties of these films are shown in Tables 1A and 1 B. The final film thickness for all samples ranged from 18.8 to 19.8 mils. The water vapor permeability (WVP) was the wet cup measurement at 23 (+/- 0.6) °C with a relative humidity difference of 50 (+/- 2) %. The hydrohead measurement was at a pressure of 0.3 MPa for 2 hours using the slotted plate. As shown in Table 1A, the inventive films passed the hydrohead test.

Table 1A

Table 1B

Example 2

Composite sheets containing biaxially-stretched films were made using the same polypropylene copolymer formulation containing the 80 percent by weight of polypropylene copolymer and 20 percent by weight propylene-based elastomer of Example 1 and a polypropylene-polyester (PP-PET) nonwoven. The PP-PET nonwoven was a 157 gsm spunbonded nonwoven purchased from Low & Bonar, made using sheath/core PP/PET filaments. The nonwoven has MD/CD tensile strengths of 550 and 434 N/5cm, respectively; and MD/CD tensile elongations of 75 and 82 %, respectively.

The composite sheets were made by extrusion lamination, by first extruding a non-porous film layer (or non-porous polymer layer) of the polypropylene copolymer formulation and combining that film layer with the nonwoven in the nip between a set of rolls, with the nip gap set to push a portion of the surface of first side of the nonwoven into one side of the layer of film or polymer. Another identical non-porous film layer (or non-porous polymer layer) was then extruded and contacted with the second side of the exposed nonwoven and again nipped between a set of rolls, with the nip gap set to push the second side of the nonwoven into the second extruded layer of film. Each extruded layer of film was about 762 micrometers thick. After cooling, the resultant structure formed a reinforced film having a sandwich structure of extruded polypropylene copolymer formulation / nonwoven I extruded polypropylene copolymer formulation with voids between the fibrous material in the nonwoven essentially fully impregnated or filled with the extruded copolymer formulation. The composite sheets were then biaxially-stretched as in Example 1 , first by stretching the film on rolls 50 percent in the machine direction (MDO - parallel to the direction of film manufacture) at room temperature, followed by stretching the film in a tenter frame 40 percent in the traverse direction (TDO - perpendicular to the direction of film manufacture) at a temperature of 120 °C. The Peel Strength of this inventive sample (5-1 ) is shown in Table 2.

For a comparison, a similar composite sheet was made as above, except the extruded polymer film layers were made from only the polypropylene copolymer, not the polypropylene copolymer formulation; that is, no propylene- based elastomer was present in the polymer film layers. The composite sheet was then biaxially stretched, first cold-stretched 25 percent in the MDO, followed by hot-stretched 50 percent in the TDO, both at the same temperatures as before. The Peel Strength of this comparison sample (5-A) is also shown in Table 2. The inventive composite sheet with the additional propylene-based elastomer had improved Peel strength as shown.

Table 2

Example 3

Biaxially-stretched films were made from two compositions of embodiments of the polypropylene copolymer formulation, that in this example contained a mixture of the polypropylene copolymer, propylene-based elastomer, and the sealing additive. As in Example 1 , the polypropylene copolymer contained polypropylene homopolymer and ethylene-containing copolymer in a 70/30 weight ratio. The first composition had 75 percent by weight of polypropylene copolymer, 10 percent by weight propylene-based elastomer, and 15 percent by weight sealing additive. The second composition had 65 percent by weight of polypropylene copolymer, 20 percent by weight propylene-based elastomer, and 15 percent by weight sealing additive. As in Example 1 , the polypropylene copolymer contained polypropylene homopolymer and ethylenecontaining copolymer in a 70/30 weight ratio.

The sealing additive contained equal parts by weight of two different polyolefin elastomers having different densities and a hydrocarbon tackifier (5 percent by weight of the composition for each). The two polyolefin elastomers were ENGAGE™ 8402 polyolefin elastomer and AFFINITY™ GA 1900 elastomer, both available from Dow, and the hydrocarbon tackifier was ESCOREZ™ 5400, which is a cycloaliphatic hydrocarbon resin available from ExxonMobil. Fig. 5 is a TEM micrograph of the non-porous film of the first composition prior to stretching and Fig. 6 is a TEM micrograph of a non-porous film of the second composition prior to stretching.

The non-porous film containing the second composition (65/20/15 percent polypropylene copolymer / propylene-based elastomer / sealing additive) was then cold stretched 40 percent in the machine direction followed by hot stretched 50 percent in the transverse direction to form a biaxial film as in Example 1 ; the biaxially-stretched film passed the hydrohead test at 0.3 MPa for 2 hours (slotted plate).

Claims

1 . A microporous biaxially-stretched film comprising: a) 90 to 65 percent by weight polypropylene copolymer, the polypropylene copolymer containing i) 50 to 95 weight percent polypropylene homopolymer chain segments, based on the weight of the polypropylene copolymer; or 43 to 79 mole percent polypropylene homopolymer chain segments, based on the mole content of polymerized units of polypropylene in the polypropylene homopolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polypropylene copolymer; and ii) 5 to 50 weight percent of ethylene-containing copolymer chain segments based on the weight of the polypropylene copolymer; or 21 to 57 mole percent of ethylene-containing copolymer chain segments based on the mole content of polymerized monomer units in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polypropylene copolymer; wherein at least a portion of the ethylene-containing copolymer chain segments comprise polymerized units of ethylene in an amount of at least 45 weight percent, based on the weight of the ethylenecontaining copolymer chain segments; or at least 55 mole percent, based on the mole content of polymerized units of ethylene in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the ethylenecontaining copolymer chain segments; and b) 10 to 35 percent by weight propylene-based elastomer, the propylene- based elastomer having 5 to 25 weight percent ethylene derived units and having a melting temperature of less than 110 °C; wherein the percent by weight of a) and b) are based on the total weight of a) and b), the biaxially-stretched microporous film having a water vapor permeability of 50 grams/ (24 hours • m²) or greater and having no liquid water passage through the film for 30 minutes when exposed to a 0.3 MPa hydrohead test.

2. The biaxially-stretched microporous film of claim 1 having a water vapor permeability of 90 grams/ (24 hours • m²) or greater.

3. The biaxially-stretched microporous film of claim 2 having a water vapor permeability of 190 grams/ (24 hours • m²) or greater.

4. The biaxially-stretched microporous film of any one of claims 1 to 3 having no liquid water passage through the film for 2 hours when exposed to a 0.3 MPa hydrohead test.

5. A roofing membrane comprising the biaxially-stretched microporous film of any one of claims 1 to 4.

6. A composite sheet comprising the biaxially-stretched microporous film of any one of claims 1 to 4, further comprising a nonwoven embedded therein, wherein the nonwoven has basis weight of 100 to 400 g/m².

7. The composite sheet of claim 6 in the form of an extrusion laminated sheet having the nonwoven positioned in the interior of the composite sheet.

8. The composite sheet of claim 6 or 7 having a basis weight of 500 to 2000 g/m².

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

10. A microporous biaxially-stretched film comprising: a) 89 to 65 percent by weight polypropylene copolymer, the polypropylene copolymer containing i) 50 to 95 weight percent polypropylene homopolymer chain segments, based on the weight of the polypropylene copolymer; or 43 to 79 mole percent polypropylene homopolymer chain segments, based on the mole content of polymerized units of polypropylene in the polypropylene homopolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polypropylene copolymer; and ii) 5 to 50 weight percent of ethylene-containing copolymer chain segments based on the weight of the polypropylene copolymer; or 21 to 57 mole percent of ethylene-containing copolymer chain segments based on the mole content of polymerized monomer units in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polypropylene copolymer; wherein at least a portion of the ethylene-containing copolymer chain segments comprise polymerized units of ethylene in an amount of at least 45 weight percent, based on the weight of the ethylenecontaining copolymer chain segments; or at least 55 mole percent, based on the mole content of polymerized units of ethylene in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the ethylenecontaining copolymer chain segments; and b) 10 to 34 percent by weight propylene-based elastomer, the 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 percent by weight of sealing additive, wherein the percent by weight of a), b), and c) are based on the total combined weight of a), b), and c).

11 . The biaxially-stretched microporous film of claim 10, wherein the sealing additive is one or more polyolefin elastomer, one or more polyolefin plastomer, one or more hydrocarbon tackifier, or any mixture thereof.

12. The biaxially-stretched microporous film of claim 11 , wherein the sealing additive includes a mixture of two different polyolefin elastomers.

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

14. A composite sheet comprising the biaxially-stretched microporous film of any one of claims 10 to 12 comprising a nonwoven embedded therein, wherein the nonwoven has basis weight of 100 to 400 g/m²

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

16. The composite sheet of claim 14 or 15 having a basis weight of 500 to 2000 g/m².

17. A roofing membrane comprising the composite sheet of any one of claims

14 to 16.

18. A process for forming a biaxially-stretched microporous film comprising the steps of:

A) forming a non-porous film from a composition comprising a) 90 to 65 percent by weight polypropylene copolymer, the polypropylene copolymer containing i) 50 to 95 weight percent polypropylene homopolymer chain segments, based on the weight of the polypropylene copolymer; or 43 to 79 mole percent polypropylene homopolymer chain segments, based on the mole content of polymerized units of polypropylene in the polypropylene homopolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polypropylene copolymer; and ii) 5 to 50 weight percent of ethylene-containing copolymer chain segments based on the weight of the polypropylene copolymer; or 21 to 57 mole percent of ethylene-containing copolymer chain segments based on the mole content of polymerized monomer units in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polypropylene copolymer; wherein at least a portion of the ethylene-containing copolymer chain segments comprise polymerized units of ethylene in an amount of at least 45 weight percent, based on the weight of the ethylene-containing copolymer chain segments; or at least 55 mole percent, based on the mole content of polymerized units of ethylene in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the ethylene-containing copolymer chain segments; and b) 10 to 35 percent by weight propylene-based elastomer, the propylene-based elastomer having 5 to 25 weight percent ethylene derived units and having a melting temperature of less than 110 °C; wherein the percent by weight of a) and b) are based on the total weight of a) and b),

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

19. The process for forming the biaxially-stretched microporous film of claim 18 wherein the second direction is orthogonal to the first direction.

20. The process for forming the biaxially-stretched microporous film of claim 18 or 19 having a water vapor permeability of 190 grams/ (24 hours • m²) or greater.

21 . The process for forming the biaxially-stretched microporous film of any one of claims 18 to 20 having no liquid water passage through the biaxially-stretched microporous film for 2 hours when exposed to a 0.3 MPa hydrohead test.

22. The process for forming the biaxially-stretched microporous film of any one of claims 18 to 21 wherein the non-porous film is made by extruding a polymeric layer from a casting die.

23. A process for forming a composite sheet comprising a biaxially-stretched microporous film, comprising the steps of:

A) forming a non-porous film or non-porous layer of polymer from a composition comprising a) 90 to 65 percent by weight polypropylene copolymer, the polypropylene copolymer containing i) 50 to 95 weight percent polypropylene homopolymer chain segments, based on the weight of the polypropylene copolymer; or 43 to 79 mole percent polypropylene homopolymer chain segments, based on the mole content of polymerized units of polypropylene in the polypropylene homopolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polypropylene copolymer; and ii) 5 to 50 weight percent of ethylene-containing copolymer chain segments based on the weight of the polypropylene copolymer; or 21 to 57 mole percent of ethylene-containing copolymer chain segments based on the mole content of polymerized monomer units in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the polypropylene copolymer; wherein at least a portion of the ethylene-containing copolymer chain segments comprise polymerized units of ethylene in an amount of at least 45 weight percent, based on the weight of the ethylene-containing copolymer chain segments; or at least 55 mole percent, based on the mole content of polymerized units of ethylene in the ethylene-containing copolymer chain segments as a percentage of the total mole content of polymerized monomer units in the ethylene-containing copolymer chain segments; and b) 10 to 35 percent by weight propylene-based elastomer, the propylene-based elastomer having 5 to 25 weight percent ethylene derived units and having a melting temperature of less than 110 °C; wherein the percent by weight of a) and b) are based on the total weight of a) and b),

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

(ii) at least one hot stretching step in a second direction at a temperature in a range of from 50 °C to 1 0 °C; to produce a composite sheet comprising a biaxially-stretched microporous polymer film.

24. The process for forming the composite sheet of claim 23 wherein the sequential cold and hot biaxial stretching steps of step C) consists of

(ii) a hot stretching step in a second direction at a temperature in a range of from 50 °C to 140 °C;

25. The process for forming the composite sheet of claim 23 or 24 wherein the second direction is orthogonal to the first direction.

26. The process for forming the composite sheet of any one of claims 23 to 25 wherein the composite sheet is formed by combining the non-porous film or non-porous layer of polymer with a nonwoven by extrusion lamination.

27. The process for forming the composite sheet of any one of claims 23 to 26 wherein in the nonwoven is positioned between either two the non-porous films or two layers of polymer in the interior of the composite sheet.