Breathable membrane with uniform micropores

Abstract

A breathable membrane and a method for preparing the breathable membrane are provided. The breathable membrane comprises a filler and a polymer blend comprising a polyolefin and an ethylene copolymer. The method for preparing the breathable membrane includes extruding the polymer blend and the filler, forming a membrane from the extruded polymer blend and the filler, and stretching the membrane to form the breathable membrane. The breathable membrane according to the embodiments disclosed herein can exhibit an increased WVTR value and can reduce filler shedding while providing improved micropore uniformity.

Description

Technical Field

[0001] The embodiments disclosed herein relate generally to breathable membranes and methods for preparing breathable membranes, and more specifically to breathable membranes comprising specific polymer blends. Background Technology

[0002] Breathable membranes are used in a wide variety of applications, including fresh produce packaging, baby diapers, adult incontinence products, surgical gowns, and other hygiene and medical applications. Breathable membranes have a microporous morphology (i.e., micropores) to provide water vapor transmission rate (“WVTR”), which helps allow water vapor to pass through while preventing condensation of water droplets. Breathability, or WVTR, is an important characteristic of many breathable membranes because the membrane can act as a liquid barrier while allowing water vapor to pass through to provide benefits such as protection or comfort. For example, breathable membranes used in plastic food packaging for fruit can help prevent water droplets from condensing on the fruit (which can lead to fungal growth).

[0003] Breathable membranes are typically prepared by incorporating fillers (e.g., CaCO3) into polyolefin resins such as polyethylene or polypropylene to prepare a cast or blown film, and then stretching or orienting the cast or blown film via a stretching roller or via meshing gears, thereby circumferentially or incrementally stretching the film in one or both longitudinally or transversely at a temperature below the melting point of the polyolefin resin. The generation of micropores is partly due to the addition of fillers to the polyolefin in the membrane. Post-extrusion processes, such as longitudinal orientation or the use of interdigitating fibers, also contribute to the generation of micropores in the membrane by creating cavitation around the filler particles at the filler-polyolefin interface.

[0004] The number of micropores, and consequently the WVTR value, can be increased by increasing or adjusting the amount of filler and stretching. However, increasing the amount of filler and stretching leads to filler dropping (e.g., residual filler remaining on the surface of the breathable membrane). It also causes a lack of micropore uniformity, which can result in poor WVTR uniformity and a tendency for membrane tearing or pinholes.

[0005] Therefore, there remains a strong need for breathable membrane formulations and methods for preparing breathable membranes that produce membranes with higher micropore and water vapor permeability uniformity, less filler shedding, and increased or improved WVTR. Summary of the Invention

[0006] The embodiments disclosed herein meet the aforementioned needs by providing a breathable membrane with improved WVTR and micropore uniformity, and reduced filler shedding compared to existing breathable membranes. The breathable membrane according to the embodiments disclosed herein achieves excellent results, such as higher WVTR and less filler shedding, without the need for complex processes. The membrane can be formed by blending materials without requiring additional expensive processing or lamination steps.

[0007] This document discloses a breathable membrane. The breathable membrane comprises (a) a polymer blend comprising: (i) a polyolefin selected from the group consisting of polyethylene, polypropylene, or combinations thereof; (ii) an ethylene copolymer selected from the group consisting of ethylene / ethyl acrylate copolymer, ethylene / methyl acrylate copolymer, ethylene / vinyl acetate copolymer, ethylene / vinyl acrylate copolymer, ethylene / butyl acrylate copolymer, ethylene / acrylic acid copolymer, or combinations thereof; and (b) a filler selected from the group consisting of sodium carbonate, calcium carbonate, magnesium carbonate, barium sulfate, etc. Magnesium sulfate, aluminum sulfate, magnesium oxide, calcium oxide, aluminum oxide, mica, talc, silica, clay, glass beads, titanium dioxide, aluminum hydroxide, zeolite, or combinations thereof; wherein the polyolefin is present in an amount of 35% to 74% by weight based on the total weight of the polymer blend and filler; the ethylene copolymer is present in an amount of 1% to 10% by weight based on the total weight of the polymer blend and filler; and the filler is present in an amount of 25% to 55% by weight based on the total weight of the polymer blend and filler; and wherein the filler has a median particle size (D50) of less than 5 micrometers.

[0008] This article also discloses a method for preparing a breathable membrane. The method for preparing the breathable membrane includes extruding a filler and a polymer blend comprising a polyolefin and an ethylene copolymer, wherein the polyolefin is present in an amount of 35% to 74% by weight based on the total weight of the polymer blend and the filler, and is selected from the group consisting of polyethylene, polypropylene, or combinations thereof, wherein the ethylene copolymer is present in an amount of 1% to 10% by weight based on the total weight of the polymer blend and the filler, and is selected from the group consisting of ethylene / ethyl acrylate copolymer, ethylene / methyl acrylate copolymer, ethylene / vinyl acetate copolymer, ethylene / vinyl acrylate copolymer, ethylene / acrylic acid copolymer, etc. Butyl acetate copolymer, ethylene / acrylic acid copolymer, or combinations thereof, wherein the filler has a median particle size (D50) of less than 5 micrometers, is present in an amount of 25% to 55% by weight based on the total weight of the polymer blend and the filler, and is selected from the group consisting of: sodium carbonate, calcium carbonate, magnesium carbonate, barium sulfate, magnesium sulfate, aluminum sulfate, magnesium oxide, calcium oxide, aluminum oxide, mica, talc, silica, clay, glass beads, titanium dioxide, aluminum hydroxide, zeolite, or combinations thereof; a membrane is formed from the extruded polymer blend and the filler; and the membrane is stretched in the longitudinal, transverse, or both directions to form a breathable membrane.

[0009] These and other implementation schemes are described in more detail in the specific embodiments. Attached Figure Description

[0010] Figure 1 The image shows a SEM image of a breathable membrane sample, depicting nine designated regions of the membrane, namely A1-A9, which can be used to characterize the micropores of the breathable membrane. Detailed Implementation

[0011] The aspects of the disclosed breathable membrane are described in more detail below. Breathable membranes can have a wide variety of applications, including, for example, packaging of fresh produce, baby diapers, adult incontinence products, surgical gowns, and other hygiene and medical applications. However, this disclosure may be implemented in various forms and should not be construed as limiting it to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art.

[0012] As used herein, the term "polymer" refers to a polymeric compound prepared by polymerizing monomers of the same or different types. Therefore, the general term polymer encompasses the term homopolymer (used to refer to a polymer prepared from only one type of monomer) and the term copolymer or interpolymer. Trace impurities (e.g., catalyst residues) may be incorporated into and / or within a polymer. A polymer can be a single polymer, a polymer blend, or a mixture of polymers comprising a mixture of polymers formed in situ during polymerization.

[0013] As used herein, the term "polyolefin" refers to a polymer that contains, in polymeric form, a majority amount of an olefin monomer (e.g., ethylene or propylene) (based on the weight of the polymer) and optionally may contain one or more comonomers.

[0014] As used herein, the term "polyethylene" refers to a polymer containing a majority amount (>50 mol%) of units derived from ethylene monomers.

[0015] As used herein, the term “copolymer” refers to any polymer having two or more monomers.

[0016] As used herein, the term "ethylene copolymer" refers to a copolymer of ethylene and at least one comonomer. Examples of ethylene copolymers include ethylene / ethyl acrylate copolymer (EEA), ethylene / methyl acrylate copolymer (EMA), ethylene / vinyl acetate copolymer, ethylene / vinyl acrylate copolymer, ethylene / butyl acrylate copolymer, ethylene / acrylic acid copolymer, and ethylene / ethyl acrylate copolymer.

[0017] As used in this article, the term "micropore" refers to small holes on the surface of the permeable membrane.

[0018] The terms “comprising,” “including,” “having,” and their derivatives are not intended to exclude the presence of any additional components, steps, or procedures, whether or not such components, steps, or procedures are specifically disclosed. For the avoidance of any doubt, unless stated otherwise, all compositions claimed using the term “comprising” may include any additional additives, adjuvants, or compounds, whether polymerized or otherwise. In contrast, the term “substantially constitutes” excludes any other components, steps, or procedures from any subsequently listed scope, except those that are not essential for operability. The term “consisting of” excludes any ingredients, steps, or procedures not specifically described or listed.

[0019] Polymer blends of breathable membranes

[0020] The breathable membrane disclosed herein comprises a polymer blend and a filler. The polymer blend includes a polyolefin and an ethylene copolymer. In embodiments, the polyolefin is present in an amount of 35% to 74% by weight (“wt.%”) based on the total weight of the polymer blend and the filler; the ethylene copolymer is present in an amount of 1% to 10% by weight based on the total weight of the polymer blend and the filler; and the filler is present in an amount of 25% to 55% by weight based on the total weight of the polymer blend and the filler.

[0021] In the implementation scheme, the polymer blend has a density of 0.910 g / cm³. 3 Up to 0.950 g / cm 3 The density. This document discloses and includes 0.910 g / cm³. 3 Up to 0.950 g / cm 3 All individual values ​​and sub-ranges; for example, polymer blends can have values ​​as low as 0.910 g / cm³. 3 Up to 0.950 g / cm 3 0.910 g / cm 3 Up to 0.940 g / cm 3 0.910 g / cm 3 Up to 0.930 g / cm 3 0.910 g / cm 3 Up to 0.920 g / cm 3 0.915g / cm 3 Up to 0.940 g / cm 3 0.915g / cm 3 Up to 0.930 g / cm 3 or 0.915g / cm 3 Up to 0.920 g / cm 3 The density.

[0022] In addition to the polyolefin and ethylene copolymers of the breathable membranes described herein, the polymer blends used to form the breathable membranes described herein may also contain one or more other polymers, such as propylene-based plasmons or elastomers, polyvinylidene chloride (PVDC), polyethylene terephthalate (PET), oriented polypropylene (OPP), polyacrylamide, butyl acrylate, peroxides (such as peroxidized polymers, e.g., peroxidized olefins), silanes (e.g., epoxysilanes), reactive polystyrene, chlorinated polyethylene, olefin block copolymers, propylene copolymers, ionomers, and graft-modified polymers (e.g., maleic anhydride-grafted polyethylene). One or more other polymers may be present in amounts less than or equal to 25 wt%, 20 wt%, 15 wt%, 12 wt%, 10 wt%, 8 wt%, 5 wt%, 3 wt%, 2 wt%, 1 wt%, or 0.5 wt% based on the total weight of the polymer blends and fillers.

[0023] Polyolefins of polymer blends

[0024] The polymer blend of the breathable membrane comprises a polyolefin. The polyolefin is selected from the group consisting of polyethylene, polypropylene, or combinations thereof. In embodiments, the polyolefin is present in an amount of 34% to 75% by weight based on the total weight of the polymer blend and filler. All individual values ​​and sub-ranges of 34% to 75% by weight of the olefin are disclosed and included herein; for example, the polyolefin may be present in an amount of 40% to 70%, 40% to 60%, 40% to 55%, or 45% to 55% by weight based on the total weight of the polymer blend and filler.

[0025] In this embodiment, the polyolefin is or includes polyethylene. In such embodiments, the polyethylene may have a content of less than or equal to 0.945 g / cm³. 3 The density of the sample is included and disclosed herein. This document includes and discloses samples with a density less than or equal to 0.945 g / cm³. 3 All individual values ​​and sub-ranges; for example, the density of polyethylene can range from the lower limit of 0.870 g / cm³. 3 Up to the upper limit of 0.945 g / cm 3 0.935g / cm 3 0.925g / cm 3 0.920g / cm 3 Or 0.915g / cm 3 In embodiments where polyethylene is part of a polymer blend, the melt index (I2) of the polyethylene may be from 0.3 g / 10 min to 10.0 g / 10 min, from 0.3 g / 10 min to 7.0 g / 10 min, from 0.3 g / 10 min to 5.0 g / 10 min, from 0.3 g / 10 min to 4.0 g / 10 min, or from 1.0 g / 10 min to 4.0 g / 10 min.

[0026] Commercially available examples of polyethylene that can be used as part of a polymer blend for use as a breathable membrane include those that can be named ELITE. TM Those purchased from The Dow Chemical Company, including, for example, ELITE TM 5220G.

[0027] Ethylene copolymers of polymer blends

[0028] The polymer blend of the breathable membrane comprises an ethylene copolymer selected from the group consisting of: ethylene / ethyl acrylate copolymer, ethylene / methyl acrylate copolymer, ethylene / vinyl acetate copolymer, ethylene / vinyl acrylate copolymer, ethylene / butyl acrylate copolymer, ethylene / acrylic acid copolymer, ethylene / ethyl acrylate copolymer, or combinations thereof. In embodiments, the ethylene copolymer is present in an amount of 1% to 10% by weight based on the total weight of the polymer blend and filler. All individual values ​​and sub-ranges of 1% to 10% by weight are disclosed and included herein; for example, the ethylene copolymer may be present in an amount of 1% to 10% by weight, 2% to 8% by weight, 3% to 7% by weight, or 4% to 6% by weight based on the total weight of the polymer blend and filler. Without being bound by theory, adding specific types and amounts of ethylene copolymer to the polymer blend and filler used to form the breathable membrane can enhance the compatibility of the polyolefin and the filler, which can reduce filler dropout, increase WVTR, and improve the number and uniformity of micropores.

[0029] The ethylene copolymer may have a comonomer content of 1% to 40% by weight based on the total weight of the ethylene copolymer. For example, the ethylene copolymer may have a comonomer content of ethyl acrylate (EA), butyl acrylate (BA), methyl acrylate (MA), vinyl acetate, vinyl acrylate, acrylic acid, or combinations thereof of 1% to 40% by weight, 5% to 35% by weight, 10% to 30% by weight, or 15% to 25% by weight. In embodiments, the ethylene copolymer may have a melt index (I2) of 0.1 g / 10 min to 20 g / 10 min, 1 g / 10 min to 20 g / 10 min, 5 g / 10 min to 15 g / 10 min, or 6 g / 10 min to 12 g / 10 min.

[0030] In some embodiments, the ethylene copolymer is or includes an ethylene / methyl acrylate copolymer. In such embodiments, the ethylene / methyl acrylate copolymer may have a methyl acrylate content of 10% to 30% by weight based on the total weight of the ethylene / methyl acrylate copolymer, and may have a melt index (I2) of 0.1 g / 10 min to 20 g / 10 min, 1 g / 10 min to 20 g / 10 min, 5 g / 10 min to 15 g / 10 min, or 6 g / 10 min to 12 g / 10 min.

[0031] Examples of commercially available ethylene copolymers that can be used in some implementations include ELVAX, which is available from Dow Chemical Company in Midland, Michigan. TM 470 and ELVALOY TMAC 1820.

[0032] Filler for breathable membrane

[0033] The breathable membrane comprises a filler selected from the group consisting of sodium carbonate, calcium carbonate, magnesium carbonate, barium sulfate, magnesium sulfate, aluminum sulfate, magnesium oxide, calcium oxide, aluminum oxide, mica, talc, silica, clay, glass beads, titanium dioxide, aluminum hydroxide, zeolite, or combinations thereof. In embodiments, the filler is present in an amount of 25% to 55% by weight based on the total weight of the polymer blend and the filler. All individual values ​​and sub-ranges of 25% to 55% by weight are disclosed and included herein; for example, the filler may be present in an amount of 25% to 55% by weight, 30% to 55% by weight, 40% to 55% by weight, or 50% to 55% by weight based on the total weight of the polymer blend and the filler.

[0034] In embodiments, the filler has a median particle size (D50) of less than 5 micrometers (also referred to as micrometers (μm)). This document discloses and includes all individual values ​​and sub-ranges of less than 5 micrometers. For example, the filler may have a median particle size (D50) of less than 4 micrometers, less than 3 micrometers, less than 2 micrometers, or less than 1 micrometer, or may be in the range of 0.1 micrometers to 4 micrometers, 0.1 micrometers to 3 micrometers, 0.1 micrometers to 2 micrometers, or 0.1 micrometers to 1 micrometer.

[0035] The polymer blends used to form the breathable membranes described herein may incorporate other additives, such as antioxidants (e.g., hindered phenols, such as...). 1010 or 1076, supplied by BASF), phosphites (e.g., 168, also supplied by BASF), processing aids, UV stabilizers, heat stabilizers, pigments, colorants, antistatic additives, flame retardants, slip agents, anti-blocking additives, biocides, antimicrobial agents, and clarifying / nucleating agents (e.g., HYPERFORM). TM HPN-20E, Millad TM 3988, MILLAD TMNX 8000 (available from Milliken Chemical). Other additives may be included in the membrane at levels commonly used in the art to achieve their desired purpose. In some examples, the content range of one or more additives is 0 to 10 wt% based on the total weight of the polymer blend and filler, 0 to 5 wt% based on the total weight of the polymer blend and filler, 0.001 wt% to 5 wt% based on the total weight of the polymer blend and filler, 0.001 wt% to 3 wt% based on the total weight of the polymer blend and filler, 0.05 wt% to 3 wt% based on the total weight of the polymer blend and filler, or 0.05 wt% to 2 wt% based on the total weight of the polymer blend and filler.

[0036] The overall thickness of the breathable membrane is not particularly limited, but in some embodiments it may be less than 20 mils. This document includes and discloses all individual values ​​and sub-ranges less than 20 mils. For example, in some embodiments, the overall thickness of the breathable membrane may be less than 15 mils, 10 mils, 8 mils, 6 mils, 4 mils, 2 mils, or 1.5 mils. In other embodiments, the overall thickness of the breathable membrane may be from 0.1 mil to 6 mils, from 0.1 mils to 4 mils, or from 0.1 mils to 2 mils. In even further embodiments, the overall thickness of the breathable membrane may be from 0.1 mils to 1.5 mils.

[0037] The basis weight of the breathable membrane is not particularly limited, but in some embodiments it can be from 8 gsm to 100 gsm. The basis weight of the breathable membrane can depend on a variety of factors, including the desired properties of the membrane, the end-use application of the membrane, the equipment available for manufacturing the membrane, the cost allowed by the application, and other factors. This document includes and discloses all individual values ​​and sub-ranges from 8 gsm to 100 gsm. For example, in some embodiments, the breathable membrane has a basis weight of 8 gsm to 100 gsm, 8 gsm to 80 gsm, 8 gsm to 50 gsm, 8 gsm to 40 gsm, 8 gsm to 20 gsm, 20 gsm to 100 gsm, 20 gsm to 80 gsm, or 20 gsm to 50 gsm.

[0038] The WVTR of the membrane produced according to the present invention is adjustable, i.e., it can be varied within a certain range by changing the amount and selection of filler and the amount of stretching to meet the needs of the intended application. Generally, a higher WVTR is obtained with a higher filler level, a higher ethylene copolymer level, and a higher stretching level. Compared with membranes formed from polymer blends not formed from the specific polymer blend formulations described herein, the membranes of the present invention exhibit surprisingly and significantly higher WVTR values ​​when stretched at the same stretch ratio (e.g., at 3, 5, and 7 stretch ratios) and when containing the same type and amount of filler. The following examples demonstrate this phenomenon of higher WVTR values ​​of the polymer blends and fillers according to the embodiments disclosed herein.

[0039] In the implementation scheme, the breathable membrane of the present invention can exhibit at least 100 g / m² when measured according to the following test method. 2 *At most 10,000g / m² 2 *days WVTR. In the embodiment, when measured according to the test methods described below, the breathable membrane of the present invention can exhibit a stretch ratio of greater than 100 g / m² at a stretch ratio of 3:1. 2 *Days, or alternatively, greater than 200g / m³ 2 *Days, or alternatively, greater than 300g / m 2 *days of WVTR.

[0040] In the implementation scheme, when measured according to the test methods described below, the breathable membrane of the present invention can exhibit a stretch ratio of greater than 400 g / m² at a stretch ratio of 5:1. 2 *Days, or alternatively, greater than 600g / m³ 2 *Days, or alternatively, greater than 800g / m³ 2 *Days, or alternatively, greater than 1,000 g / m³ 2 *Days, or alternatively, greater than 1,200 g / m³ 2 *days of WVTR.

[0041] In the implementation scheme, when measured according to the test methods described below, the breathable membrane of the present invention can exhibit a stretch ratio of greater than 1,100 g / m² at a stretch ratio of 7:1. 2 *Days, or alternatively, greater than 1,300 g / m³ 2 *Days, or alternatively, greater than 1,500 g / m³ 2 *Days, or alternatively, greater than 1,700 g / m³ 2 *Days, or alternatively, greater than 1,900 g / m³ 2 *days of WVTR.

[0042] In an embodiment, the breathable membrane of the present invention may have micropores with an average diameter of 0.5 micrometers to 5 micrometers, or alternatively 1 micrometers to 3 micrometers, wherein the average diameter of the micropores may be measured according to the test method described below.

[0043] In embodiments, the breathable membrane of the present invention may have a micropore occupancy percentage (%) of 0.5% to 10%, or alternatively 1% to 8%. In embodiments, the breathable membrane of the present invention may have a micropore occupancy percentage of 0.75% to 3% at an elongation ratio of 3, or alternatively 1% to 2% at an elongation ratio of 3. In embodiments, the breathable membrane of the present invention may have a micropore occupancy percentage of 1.5% to 8% at an elongation ratio of 5, or alternatively 3% to 7% at an elongation ratio of 5. In embodiments, the breathable membrane of the present invention may have a micropore occupancy percentage of 4% to 10% at an elongation ratio of 7, or alternatively 6% to 9% at an elongation ratio of 7. The micropore occupancy percentage can be measured according to the test methods described below.

[0044] In one embodiment, the micropore uniformity (expressed as the relative standard deviation (RSD) of the micropore area relative to the average micropore area) of the breathable membrane at a stretch ratio of 3 can be less than 0.020, or alternatively less than 0.010 of the micropore area RSD. In other embodiments, the micropore uniformity (expressed as the relative standard deviation (RSD) of the micropore area relative to the average micropore area) of the breathable membrane at a stretch ratio of 5 can be less than 0.012, or alternatively less than 0.010 of the micropore area RSD. In even other embodiments, the micropore uniformity (expressed as the relative standard deviation (RSD) of the micropore area relative to the average micropore area) of the breathable membrane at a stretch ratio of 7 can be less than 0.0050, or alternatively less than 0.0020 of the micropore area RSD. The micropore uniformity or the relative standard deviation of the micropore area relative to the average micropore area can be calculated according to the test methods described below.

[0045] The breathable membrane described herein can be prepared by a variety of processes. Exemplary processes may include forming the membrane into a blown or cast film, and the membrane may be manufactured by blown, cast, or extrusion coating processes. The breathable membrane may be stretched by longitudinal stretching, transverse stretching, ring rolling stretching, cold drawing, or a combination thereof. In embodiments, the breathable membrane of the present invention may be oriented in the longitudinal and / or transverse directions. In embodiments, the breathable membrane may be oriented in the longitudinal direction at a stretch ratio of 1:1 to 10:1, or alternatively at a stretch ratio of 2:1 to 8:1. In embodiments, the breathable membrane may be oriented in the transverse direction at a stretch ratio of 1:1 to 10:1, or alternatively at a stretch ratio of 2:1 to 8:1. In embodiments, the breathable membrane of the present invention is stretched in the longitudinal direction at a stretch ratio of at least 1.4:1.

[0046] A method for preparing a breathable membrane according to an embodiment disclosed herein is disclosed. The method includes extruding a filler and a polymer blend comprising a polyolefin and an ethylene copolymer, wherein the polyolefin is present in an amount of 35% to 74% by weight based on the total weight of the polymer blend and the filler, and is selected from the group consisting of polyethylene, polypropylene, or combinations thereof, wherein the ethylene copolymer is present in an amount of 1% to 10% by weight based on the total weight of the polymer blend and the filler, and is selected from the group consisting of ethylene / ethyl acrylate copolymer, ethylene / methyl acrylate copolymer, ethylene / vinyl acetate copolymer, ethylene / vinyl acrylate copolymer, ethylene / butyl acrylate copolymer, etc. Polymers, ethylene / acrylic acid copolymers, or combinations thereof, wherein the filler has a median particle size (D50) of less than 5 micrometers, is present in an amount of 25% to 55% by weight based on the total weight of the polymer blend and the filler, and is selected from the group consisting of: sodium carbonate, calcium carbonate, magnesium carbonate, barium sulfate, magnesium sulfate, aluminum sulfate, magnesium oxide, calcium oxide, aluminum oxide, mica, talc, silica, clay, glass beads, titanium dioxide, aluminum hydroxide, zeolite, or combinations thereof; forming a membrane from an extruded polymer blend and filler; and stretching the membrane in the longitudinal, transverse, or both directions to form a breathable membrane.

[0047] It is also anticipated that the breathable membrane according to the embodiments disclosed herein may include co-extruded or additional layers as a laminate. These layers may be selected to provide additional functionality, such as layers providing additional strength, adhesion to another substrate (such as a nonwoven fabric), and / or aesthetic properties (such as feel or appearance).

[0048] Some embodiments of the present invention relate to laminates comprising one or more of the breathable membranes of the present invention. For example, the breathable membranes of the present invention can be used in membrane / nonwoven laminates. Typical nonwovens used in such laminates can be spunbond webs, air-blown webs, carded webs, or composites thereof. Typical nonwoven composites used in laminates having the breathable membranes of the present invention include three-beam spunbond materials (e.g., S / S / S), spunbond / meltblown / spunbond composites (e.g., S / M / S), etc. Common methods for bonding membranes to nonwovens include, for example, adhesive hot-melt bonding, ultrasonic bonding, and thermal bonding achieved by calendering or pressure rollers.

[0049] This invention also relates to articles comprising at least one of the breathable membranes disclosed herein. Articles comprising the breathable membranes of this invention can be used as liquid-impermeable but breathable layers in disposable hygiene and medical products. Examples of articles comprising such breathable membranes include diapers, training pants, feminine hygiene products, adult incontinence products, medical drapes, medical gowns, surgical gowns, etc. In articles such as diapers, training pants, feminine hygiene products, and adult incontinence products, the breathable membrane is also often referred to as a backing film. In medical products, the breathable membrane is often referred to as a “barrier layer” because it prevents contamination of patients by healthcare workers and vice versa. Breathable membranes can be incorporated into such articles based on the teachings herein and using techniques known to those skilled in the art.

[0050] Test methods

[0051] density

[0052] Density was measured according to ASTM D792 and expressed in grams per cubic centimeter. 3 (g / cm 3 )express.

[0053] Melt index (I2)

[0054] Melt index (I2) was measured at 190°C and 2.16 kg according to ASTM D-1238. The value is reported in g / 10 min, which corresponds to the number of grams eluted per 10 minutes.

[0055] Water vapor transmission rate (WVTR)

[0056] Water vapor transmission rate (WVTR) was measured using the standard cup method according to ASTM E96-16 and GB / T12704.2 (2009). 10 ml of distilled water was added to a test dish. The sample was attached to the test dish and sealed with a gasket and ring cap. The weight of the dish assembly was recorded as mass (Wa). The dish assembly was placed in a control chamber with constant temperature (40°C) and humidity (60%). After four (4) hours, the dish assembly was removed from the control chamber and weighed, with the mass recorded as (Wb). WVTR was calculated using the following equation:

[0057]

[0058] WVTR: Water vapor transmission rate, [g / m³] 2 *sky]

[0059] Wa: Quality of the test dish assembly before testing, [g]

[0060] Wb: The quality of the test dish assembly after testing, [g]

[0061] S: Test area = 0.0032m 2 , [m 2 ]

[0062] T: Test time = 4 hours, [h]

[0063] Micropore uniformity analysis

[0064] A 3mm × 3mm sample was cut from the center of the exemplary membrane using a single-edged blade. The sample was then fixed to a sample holder and coated with carbon. Imaging was performed using a Hitachi S-3400N SEM in HV mode with BSE imaging. The SEM parameters were set as follows: accelerating voltage of 5kV, working distance of 6mm, contrast set to maximum, scan area of ​​0.26mm × 0.18mm, and aperture 1 with carbon coating. MATLAB (MathWorks R2017b, 64-bit version) was used for image processing and SEM image analysis. The Image Processing Toolbox (version 9.3) and the Statistics and Machine Learning Toolbox (version 10.1) were used in MATLAB. The following image analysis code was used to calculate the number of micropores, micropore occupancy, average micropore diameter, and micropore uniformity:

[0065] im2 = im2bw(im1, 0.4);

[0066] figure,imshow(im2);

[0067] im3 = ~im2;

[0068] im4 = imfill(im3, 'holes');

[0069] im5 = bwareaopen(im4,30);

[0070] stats=regionprops(im5,'Area','EquivDiameter');

[0071] Nine sections or regions on the membrane sample are designated as A1 to A9. Figure 1 SEM images of the sample breathable membrane are shown, depicting nine sections / regions, A1 to A9. Using the image analysis code and software described above, the diameters of the micropores and the area of ​​each section were calculated to characterize the dispersion of the micropores across the entire membrane. The number of micropores and the average diameter of the micropores (in micrometers) across the entire A1 to A9 region were calculated. The micropore uniformity of the membrane was based on the relative standard deviation (RSD) of the micropore area of ​​A1 to A9 relative to the average micropore area of ​​A1 to A9, calculated using the following equation:

[0072]

[0073] x i It is the area of ​​the micropores A1, A2, A3, A4, A5, A6, A7, A8, or A9.

[0074] It is the average area of ​​the micropores from A1 to A9.

[0075] Micropore occupancy was calculated as a percentage by dividing the total area of ​​the scanned area by the total area of ​​the scanned area (0.26 mm × 0.18 mm) and then multiplying the result by 100. Three independent tests were performed on each membrane sample, with scanned areas of the membrane sample randomly selected, and the average number of micropores, micropore occupancy, micropore diameter, and RSD were reported.

[0076] Example

[0077] The following examples illustrate the features of this disclosure, but are not intended to limit the scope of this disclosure.

[0078] Materials used

[0079] The following materials are included in the exemplary breathable membranes discussed below.

[0080] ELITE TM 5220G is a linear low-density polyethylene resin with a density of 0.915 g / cm³. 3 Furthermore, the melt index (I2) is 3.5 g / 10 min, and it is commercially available from Dow Chemical Company (Midland, Michigan).

[0081] ELVALOY TM AC 1820 is an ethylene copolymer of ethylene and methyl acrylate, having a comonomer content of 20% by weight of acrylate and a density of 0.942 g / cm³. 3 Furthermore, the melt index (I2) is 8 g / 10 min, and it is commercially available from Dow Chemical Company (Midland, Michigan).

[0082] 520, a calcium carbonate filler with a median particle size (D50) of 2 micrometers, is commercially available from Imerys (Paris, France).

[0083] B900, an antioxidant, is commercially available from BASF (Ludwigshafen, Germany).

[0084] Example 1 of the present invention describes a breathable membrane according to the embodiments disclosed herein, formed using the following polymer blend and filler formulation: 45% by weight ELITE TM 5220g, 5% ELVALOY TM AC 1820 and 50% by weight 520, where the weight percentage is based on the total weight of the polymer blend and the filler. The overall density of the polymer blend used to form Example 1 of the present invention is 0.918 g / cm³. 3 .

[0085] Besides using ELITE TM 5220G replaces ELVALOY TM Comparative Example 1 was formed using a formulation almost identical to that of the embodiments of the present invention, except for AC 1820. That is, the comparative example was formed using the following polymer and filler formulation: 50% by weight ELITE TM 5220g and 50% by weight 520, where the weight percentage is based on the total weight of the polymer and filler.

[0086] To form Examples 1 and Comparative Example 1 of the present invention, polymer blends and filler materials were extruded via a twin-screw compounding line. The composition was extruded using a Dr. Collin 5-layer casting line with one 30 mm extruder and three 25 mm extruders to produce samples. All extruders operated with the same composition, such that the films produced in each case were conceptually equivalent to single-layer films. The process conditions used to produce all film examples and samples are given in Tables 1-3. After extrusion, the films underwent reheating, stretching, annealing, cooling, and winding onto rolls. Stretch ratios were set, and the sample films were longitudinally oriented with stretch ratios of 3:1, 5:1, and 7:1. The sample films are represented as Comparative Example 1A (stretch ratio 3:1), Comparative Example 1B (stretch ratio 5:1), Comparative Example 1C (stretch ratio 7:1), Example 1A of the present invention (stretch ratio 3:1), Example 1B of the present invention (stretch ratio 5:1), and Example 1C of the present invention (stretch ratio 7:1). The final basis weight of all films was 18 gsm.

[0087] Table 1: Dr. Collin 5-layer casting line parameters

[0088]

[0089] Table 2: Dr. Collin Casting Line Processing Parameters

[0090]

[0091] Table 3: Longitudinal Orientation Machining Parameters

[0092]

[0093] The WVTR values ​​of each embodiment at different stretch ratios were tested according to the test methods described above. Table 4 below provides the results. As the results show, the breathable membrane of Embodiment 1 of the present invention has a surprisingly and significantly higher WVTR value compared to the breathable membrane of Comparative Example 1.

[0094] Table 4: WVTR values ​​of the examples

[0095]

[0096]

[0097] Add 2000ppm B900 is an antioxidant.

[0098] The exemplary membranes were also visually inspected for filler droplets. The inspection of the membranes clearly showed that, compared to Comparative Examples 1A, 1B, and 1C, Examples 1A, 1B, and 1C of the present invention exhibited surprisingly and significantly less filler droplets.

[0099] Samples of the exemplary membrane were analyzed under a scanning electron microscope equipped with MATLAB according to the test methods described above to measure the number of micropores, micropore occupancy, average diameter of micropores, and micropore uniformity as expressed by relative standard deviation (RSD). Table 5 provides the results. As the results in Table 5 show, the embodiments of the present invention exhibit surprisingly low RSD and therefore better micropore uniformity when compared with comparative membranes at the same stretch ratio, even when the membranes of the present invention have a high number of micropores and a higher micropore occupancy.

[0100] Table 5 - Micropore analysis results obtained by SEM and MATLAB

[0101]

[0102] Unless expressly excluded or otherwise limited, every document cited herein (if any), including any cross-referenced or related patent or application and any patent application or patent claiming priority or benefit to this application, is hereby incorporated in its entirety by reference. No reference to any document acknowledges it as prior art to any invention disclosed or claimed herein, or as teaching, indicating, or disclosing any such invention, alone or in combination with any other referenced document. Furthermore, in the event of any conflict between the meaning or definition of any term in this document and the meaning or definition of the same term in any document incorporated by reference, the meaning or definition given to the term in this document shall prevail.

[0103] While specific embodiments of the invention have been described and illustrated, it will be apparent to those skilled in the art that many other changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, it is intended that all such changes and modifications falling within the scope of the invention be covered in the appended claims.

Claims

1. A breathable membrane, the breathable membrane comprising: (a) A polymer blend comprising: (i) Polyolefins, selected from the group consisting of polyethylene, polypropylene, or combinations thereof; (ii) an ethylene copolymer selected from the group consisting of: ethylene / ethyl acrylate copolymer, ethylene / methyl acrylate copolymer, ethylene / vinyl acetate copolymer, ethylene / vinyl acrylate copolymer, ethylene / butyl acrylate copolymer, ethylene / acrylic acid copolymer, or combinations thereof; and (b) A filler selected from the group consisting of: sodium carbonate, calcium carbonate, magnesium carbonate, barium sulfate, magnesium sulfate, aluminum sulfate, magnesium oxide, calcium oxide, aluminum oxide, mica, talc, silica, clay, glass beads, titanium dioxide, aluminum hydroxide, zeolite, or combinations thereof. The polyolefin is present in an amount of 35% to 74% by weight based on the total weight of the polymer blend and filler; the ethylene copolymer is present in an amount of 1% to 10% by weight based on the total weight of the polymer blend and filler; and the filler is present in an amount of 50% to 55% by weight based on the total weight of the polymer blend and filler; and The filler described herein has a median particle size D50 of less than 5 micrometers. The membrane is a stretched membrane and has at least one of the following characteristics: a) a micropore occupancy percentage of 0.5% to 10%; and b) an average micropore diameter of 0.5 micrometers to 5 micrometers. The breathable membrane is stretched longitudinally at a stretch ratio of 5:1 to 8:

1.

2. The breathable membrane according to claim 1, wherein the ethylene copolymer has a comonomer content of 1% to 40% by weight based on the total weight of the ethylene copolymer.

3. The breathable membrane according to claim 1 or 2, wherein the membrane is stretched in the longitudinal direction at a stretch ratio of 5:1 to 7:

1.

4. The breathable membrane according to claim 1 or 2, wherein the polymer blend has a content of 0.910 g / cm³. 3 Up to 0.950 g / cm 3 The density.

5. The breathable membrane according to claim 1 or 2, wherein the ethylene copolymer is an ethylene / methyl acrylate copolymer having an acrylate content of 10% to 30% by weight and a melt index of 12 of 0.1 g / 10 min to 20 g / 10 min.

6. The breathable membrane according to claim 1 or 2, wherein the membrane has a basis weight of 8 gsm to 100 gsm.

7. The breathable membrane according to claim 1 or 2, wherein the membrane has a strength of at least 400 g / m² when the stretch ratio is 5. 2 *days of WVTR.

8. A method for preparing a breathable membrane, the method comprising: The extrusion filler and the polymer blend comprising a polyolefin and an ethylene copolymer, wherein the polyolefin is present in an amount of 35% to 74% by weight based on the total weight of the polymer blend and the filler, and is selected from the group consisting of polyethylene, polypropylene, or combinations thereof; wherein the ethylene copolymer is present in an amount of 1% to 10% by weight based on the total weight of the polymer blend and the filler, and is selected from the group consisting of ethylene / ethyl acrylate copolymer, ethylene / methyl acrylate copolymer, ethylene / vinyl acetate copolymer, ethylene / vinyl acrylate copolymer, ethylene / butyl acrylate copolymer, ethylene / acrylic acid copolymer, or combinations thereof; and wherein the filler has a median particle size D50 of less than 5 micrometers, is present in an amount of 50% to 55% by weight based on the total weight of the polymer blend and the filler, and is selected from the group consisting of sodium carbonate, calcium carbonate, magnesium carbonate, barium sulfate, magnesium sulfate, aluminum sulfate, magnesium oxide, calcium oxide, aluminum oxide, mica, talc, silica, clay, glass beads, titanium dioxide, aluminum hydroxide, zeolite, or combinations thereof; A film is formed from the extruded polymer blend and fillers; and The membrane is stretched in the longitudinal, transverse, or both directions to form a breathable membrane. The breathable membrane is stretched longitudinally at a stretch ratio of 5:1 to 8:1.

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