Multilayer microporous membranes and uses thereof

Abstract

The present application relates to a multilayer microporous membrane and its use. The multilayer microporous membrane comprises: a first layer; a second layer; and a third layer; the first layer and the third layer are on both sides of the second layer; wherein the second layer comprises 60 wt% to 100 wt% of a homopolypropylene, based on the total weight of the polymers in the second layer, the homopolypropylene has a melt flow rate of 0.2 to 5 g / 10 min at 2.16 kg / 230°C, an isotacticity of ≥ 95%, and a total inorganic element content of ≤ 50 ppm; at least one of the first layer, the second layer and the third layer comprises a copolymer selected from a propylene-based copolymer, an ethylene-based copolymer, or a combination thereof; the thickness of the multilayer microporous membrane is less than 20 μm. The multilayer microporous membrane can be used as a battery separator, enabling film thickness thinning, low defect rate during battery assembly process, and safe operation.

Description

Technical Field

[0001] This application relates to the field of battery separators, and more specifically, to multilayer microporous membranes, methods for preparing the multilayer microporous membranes, and the use of the multilayer microporous membranes as battery separators. Background Technology

[0002] A battery separator (BSF) is a permeable membrane located between the anode and cathode to separate the two electrodes, allowing lithium ions to pass through while hindering electron transport. With the rapid growth in demand for electric vehicles and renewable energy storage, the performance and manufacturing process of BSFs have received widespread attention.

[0003] In terms of raw materials, polypropylene (PP) and polyethylene (PE) are the most commonly used battery separator materials. PP has excellent chemical stability and mechanical strength, while PE is known for its excellent electrical insulation and flexibility. In recent years, the application of PP / PE composite materials (such as PP / PE / PP) has gradually increased. This material combines the advantages of PP and PE, and can improve the strength of the separator while maintaining good ionic conductivity.

[0004] In terms of manufacturing processes, BSF production is mainly divided into dry and wet processes. The dry process typically involves stretching and heat-treating the polymer membrane to separate the lamellar crystals or transform the crystal structure to form a microporous structure. This method can effectively control the membrane's porosity and thickness, thereby optimizing its electrochemical performance. The wet process, on the other hand, prepares the membrane through solvent immersion and phase separation, achieving higher porosity and better ionic conductivity, but it is relatively complex and costly. Currently, the dry process is mainly suitable for single-layer PP membranes, single-layer PE membranes, and multilayer membranes, while the wet process is mainly suitable for single-layer PE membranes.

[0005] Currently, the BSF industry faces two major challenges: high defect rates and low membrane productivity. These not only increase production costs but can also sometimes lead to safety issues after battery assembly. Defect rates are primarily limited by the material's toughness properties, such as elongation at break and puncture resistance, while productivity is mainly determined by the material's melt flow rate (MFR). Furthermore, it is generally desirable for BSFs to be as thin as possible (e.g., less than 20 micrometers, or even as low as 10 micrometers) to improve energy density. Thinning typically requires materials with higher melt strength and lower MFR.

[0006] Homopolymer polypropylene (hPP) with low melt flow rate (MFR) (e.g., S802 M from Korea Petrochemical) is commonly used in the battery cell fuel cell (BSF) industry. This hPP exhibits good tensile and tear strength, and its low MFR allows for lower thicknesses. However, the BSF industry trend is towards further thinning to deliver higher energy density after battery assembly, requiring hPP with higher melt strength and even lower MFR. Under this trend, low MFR presents production challenges; if a production line speed for 2MFR hPP is 120 m / min, the speed for 1MFR hPP would drop to 60 m / min or even lower. Considering cost-saving pressures from automotive OEMs and battery manufacturers, the impact of reduced production line speeds is unacceptable to BSF manufacturers. Furthermore, BSF produced using low MFR hPP exhibits poor toughness, posing safety risks and complicating thinning processes.

[0007] Therefore, the purpose of this invention is to provide an improved solution for hPP, which can solve the above-mentioned problems, improve toughness properties such as elongation at break and puncture resistance, and achieve further thinning of PP-based BSF, thereby increasing the energy density of the battery and reducing the defect rate during battery assembly. Summary of the Invention

[0008] In a first aspect, this disclosure provides a multilayer microporous membrane comprising: a first layer; a second layer; and a third layer; the first layer and the third layer being on opposite sides of the second layer; wherein the second layer comprises 60% to 100% by weight of homopolymer polypropylene, and based on the total weight of the polymer in the second layer, the homopolymer polypropylene has a melt flow rate of 0.2 to 5 g / 10 min at 2.16 kg / 230 °C, an isotactic index of ≥95%, and a total inorganic element content of ≤50 ppm; at least one of the first, second, and third layers comprises a copolymer selected from propylene-based copolymers, ethylene-based copolymers, or combinations thereof, wherein the propylene-based copolymer comprises 75% to 98% by weight of propylene-derived units and 2% to 25% by weight of units derived from C2 or C4-C. 12 α-olefin units and having a strength of 0.85 to 0.92 g / cm³ 3 The density and melt flow rate at 2.16 kg / 230 °C are 1 to 100 g / 10 min; the ethylene-based copolymer comprises 50 wt% to 99 wt% ethylene-derived units and 1 wt% to 50 wt% C3-C-derived units. 12 α-olefin units and having a strength of 0.85 to 0.91 g / cm³ 3The density and melt flow rate at 2.16 kg / 190 °C are 0.1 to 1000 g / 10 min; the thickness of the multilayer microporous membrane is less than 20 μm.

[0009] In a second aspect, this disclosure provides a method for preparing a multilayer microporous membrane as described in the context, comprising: (1) extruding and casting the components of each layer to form a basic multilayer membrane; (2) heat-treating the basic multilayer membrane to form a heat-treated basic multilayer membrane; and (3) stretching the heat-treated basic multilayer membrane multiple times to form a multilayer microporous membrane.

[0010] Thirdly, this disclosure provides the use of multilayer microporous membranes as battery separators, as described in the context.

[0011] Surprisingly, the technical solution of this application can significantly improve toughness properties such as elongation at break and puncture resistance by introducing specific propylene-based elastomers into specific layers of PP-based multilayer microporous membranes, thereby achieving further thinning of PP-based BSF, increasing the energy density of the battery and reducing the defect rate during battery assembly. Attached Figure Description

[0012] Figure 1 Radiographs showing various properties of a control pure PP film and the multilayer film of the present invention are displayed.

[0013] Figure 2 The sealing strength curves of the control pure PP film and the multilayer film of the present invention as a function of temperature are shown.

[0014] Detailed Explanation

[0015] Definition and testing methods

[0016] Unless otherwise stated, the room temperature is 25°C.

[0017] "Battery separator" refers to the membrane material between the positive and negative electrodes of a battery, which prevents electrons from passing through while allowing ions in the electrolyte to pass freely.

[0018] In this paper, “microporous membrane” refers to membrane materials that can be used in battery separators, which typically have nanoscale pore sizes (e.g., 20-40 nm) and porosity of 30-50%.

[0019] An olefin is a linear, branched, or cyclic compound of carbon and hydrogen having at least one double bond.

[0020] A “polymer” has two or more identical or different monomer units. A “homopolymer” is a polymer having identical monomer units. As used herein, the term “polymer” includes, but is not limited to, homopolymers, copolymers, terpolymers, etc. As used herein, the term “polymer” also includes impact, block, graft, random, and alternating copolymers. Unless otherwise specified, the term “polymer” should also include all possible geometries. Such geometries can include isotactic, syndiotactic, and random symmetric geometries.

[0021] As used herein, unless otherwise specified, the term "copolymer" refers to a polymer formed by the polymerization of at least two different monomers (i.e., monomer units). For example, the term "copolymer" includes the copolymerization product of propylene and α-olefins such as ethylene and 1-hexene. A "terpolymer" is a polymer having three monomer units that are different from each other. Therefore, the term "copolymer" also includes copolymer products of terpolymers and quaternary copolymers such as mixtures of ethylene, propylene, 1-hexene, and 1-octene.

[0022] The term "different" used to refer to monomer units means that the monomer units differ from each other by at least one atom or are isomerically different. "Ethylene polymer" or "ethylene copolymer" is a polymer or copolymer containing at least 50 mol% ethylene-derived units, "propylene polymer" or "propylene copolymer" is a polymer or copolymer containing at least 50 mol% propylene-derived units, and so on. For the purposes of this invention, polyethylene is an ethylene polymer.

[0023] As used herein, when a polymer is referred to as “comprising, consisting of, or substantially consisting of monomers,” the monomers are present in the polymer in the form of polymerized / derived monomers. For example, when a copolymer is claimed to have 35% to 55% by weight of “ethylene,” it should be understood that the monomer units in the copolymer are derived from ethylene in the polymerization reaction, and that the derived units are present at 35% to 55% by weight based on the weight of the copolymer. Therefore, a polymer or copolymer claimed to have 90% by weight of “ethylene” content is equivalent to a polymer or copolymer claimed to have 90% by weight of “ethylene-derived” content or 90% by weight of “units derived from ethylene,” etc.

[0024] The terms “polypropylene”, “propylene polymer” and “propylene-based polymer” refer to polymers or copolymers containing at least 50 mol% propylene units (preferably at least 70 mol% propylene units, more preferably at least 80 mol% propylene units, even more preferably at least 90 mol% propylene units, even more preferably at least 95 mol% propylene units or 100 mol% propylene units (in the case of homopolymers)).

[0025] As used herein, "propylene-based" means any polymer containing propylene alone or propylene together with one or more comonomers, wherein propylene is the major component (e.g., more than 50% by weight of propylene).

[0026] Polypropylene may be or may include homopolymer polypropylene (“hPP”), isotactic polypropylene, highly isotactic polypropylene, syndiotactic polypropylene, and copolymers of propylene or mixtures thereof. Products comprising one or more propylene monomers polymerized with one or more additional monomers may be more commonly referred to as random copolymers (RCPs) or impact copolymers (ICPs).

[0027] In this paper, isotactic polypropylene (iPP) is defined as having at least 10% or more isotactic pentads. Highly isotactic polypropylene is defined as having 50% or more isotactic pentads. Metaisotactic polypropylene (sPP) is defined as having 10% or more metaisotactic pentads.

[0028] In this document, polypropylene random copolymer (RCP) is defined as a copolymer of propylene and 1 to 10% by weight of an olefin selected from ethylene and C4-C8 α-olefins, having less than 10% isotactic pentamelist and syndiotactic pentamelist. Preferably, the α-olefin comonomer is ethylene.

[0029] In this article, polypropylene impact copolymers (ICPs) are combinations of crystalline and amorphous polymers (e.g., iPP and rubber), typically multiphase, which provides ICPs with stiffness and toughness greater than that of one or more amorphous polymers and greater toughness than that of one or more crystalline polymers. ICPs can typically be morphologically such that the matrix phase comprises a higher proportion of the crystalline polymer, and the rubber exists in a higher proportion in the dispersed or cocontinuous phase; for example, blends comprising 60 to 95 wt% iPP matrix and 5 to 40 wt% ethylene, propylene, or other polymers with a Tg of 30°C or lower.

[0030] The terms “polyethylene,” “ethylene polymer,” and “ethylene-based polymer” refer to polymers or copolymers containing at least 50 mol% ethylene units (preferably at least 70 mol% ethylene units, more preferably at least 80 mol% ethylene units, even more preferably at least 90 mol% ethylene units, even more preferably at least 95 mol% ethylene units or 100 mol% ethylene units (in the case of homopolymers)).

[0031] As used herein, "ethylene-based" means any polymer containing ethylene alone or ethylene together with one or more comonomers, wherein ethylene is the major component (e.g., more than 50% by weight of ethylene).

[0032] As used herein, the term "elastomer" or "elastomer composition" refers to any polymer, copolymer, or composition of polymers (e.g., polymer blends) conforming to the definition in ASTM D1566. Elastomers include blends of polymers, such as melt blends and / or reactor blends of polymers.

[0033] Molecular weight moments and distributions (Mw, Mn, Mz, Mw / Mn, Mz / Mn, Mz / Mn, etc.), monomer / comonomer content (C2, C4, C6 and / or C8 and / or others, etc.), and g' (vis) were determined using high-temperature gel permeation chromatography (Polymer Char GPC-IR) equipped with an infrared detector IR5 based on a multi-channel bandpass filter, an 18-angle light scattering detector, and a viscometer. Three Agile lent PLgel 10 μm mixed-B LS columns were used for polymer separation. Detailed analytical principles and molecular weight determination methods and g' are described below. vis Paragraphs

[0044] -

[0051] of PCT Publication WO2019 / 246069A1 are described and incorporated herein by reference (note that the equation c = / / / mentioned in paragraph

[0044] regarding the concentration (c) at each point in the chromatogram is c = βI, where β is the mass constant and I is the IR5 broadband signal intensity (I) minus the baseline). Unless specifically mentioned, all molecular weight moments used or mentioned in this disclosure are determined according to absolute determination methods (e.g., those mentioned in paragraphs

[0044] -

[0051] of the previously mentioned disclosure text), note that for the equations in such paragraph

[0044] , a = 0.695 and K = 0.000579 (1 - 0.75Wt) are used, where Wt is the weight fraction of the comonomer, and further note that the comonomer composition is determined by the ratio of the IR5 detector intensities corresponding to the CH2 and CH3 channels calibrated with a series of PE and PP homopolymer / copolymer standards, the nominal values ​​of which are predetermined by NMR or FTIR as indicated in paragraph

[0045] of the previously mentioned PCT disclosure text (providing methyl / 1000 total carbons (CH3 / 1000TC)). Other required parameters can be found in the paragraphs mentioned in the WO2019 / 246069A1 publication, but for convenience, some are included here: TCB at 145°C n = 1.500; I = 665nm; dn / dc = 0.1048mL / mg.

[0034] The density value of the polymer is measured according to ASTM D1505-10.

[0035] For propylene-based polymers, the melt flow rate (MFR) is determined according to ASTM D-1238, under condition L (2.16 kg, 230 °C).

[0036] For ethylene-based polymers, the melt flow rate (MFR) is determined according to ASTM D-1238, under condition L (2.16 kg, 190 °C).

[0037] propylene-based copolymers

[0038] Propylene-based copolymers may include or be based on propylene elastomers. The following description of propylene-based elastomers also applies to propylene-based copolymers.

[0039] The propylene-based elastomer is a random copolymer having crystalline regions interrupted by amorphous regions, comprising ethylene or C4-C12 α-olefin-derived units in the range of 2-25% by weight of the propylene-based elastomer, and optionally diene-derived units, with the balance of the polymer being propylene-derived units. Without being intended to be limited by any theory, it is believed that the amorphous regions may be generated by non-crystallizable polypropylene segments and / or include comonomer units. Compared to highly isotactic polypropylene, the crystallinity and melting point of the propylene-based elastomer are reduced by introducing errors (stereoscopic defects and regional defects) in the propylene insertion and / or by the presence of comonomers. The copolymer contains at least 50% by weight of propylene-derived units, based on the weight of the propylene-based elastomer. In any embodiment, the propylene-based elastomer is a propylene-based elastomer with limited crystallinity and a melting point as described herein, resulting from adjacent isotactic propylene units. In other embodiments, propylene-based elastomers typically exhibit no substantial intermolecular heterogeneity in stereoregularity and comonomer composition, and also typically exhibit no substantial heterogeneity in intramolecular composition distribution.

[0040] The propylene-based elastomer contains more than 50% by weight, preferably more than 60% by weight, more preferably more than 65% by weight, even more preferably more than 75% by weight, and up to 99% by weight, of propylene-derived units based on the total weight of the propylene-based elastomer. In some preferred embodiments, the propylene-based elastomer comprises 75%-95% by weight, more preferably 75%-92.5% by weight, and even more preferably 82.5%-92.5% by weight, and most preferably 82.5%-90% by weight, of propylene-derived units based on the weight of the propylene-based elastomer. Accordingly, units or comonomers derived from at least one of ethylene or C4-C12 α-olefins may be present in an amount of elastomer ranging from a lower limit of 5 or 10 or 14% by weight to an upper limit of about 20, 22 or 25% by weight.

[0041] Adjustable comonomer content allows propylene-based elastomers to have heats of fusion of 100 J / g, 90 J / g, 85 J / g, 80 J / g, 75 J / g, 70 J / g, or 65 J / g or less, and melting points of 100°C, 90°C or less (T).m ), and 2% to 65% crystallinity of isotactic polypropylene, and preferably less than 1,000 g / 10 min melt flow rate (“MFR”) as measured at 230 °C and 2.16 kg weight.

[0042] Propylene-based elastomers may have more than one comonomer. Preferred embodiments of propylene-based elastomers have more than one comonomer, such as propylene-ethylene-octene, propylene-ethylene-hexene, and propylene-ethylene-butene copolymers.

[0043] In embodiments containing more than one comonomer derived from at least one of ethylene or C4-C10 α-olefins, the amount of each comonomer may be less than 25% by weight of the propylene-based elastomer, but the total amount of comonomer is 3% by weight or more based on the weight of the propylene-based monoolefin. In a preferred embodiment, the comonomer is ethylene, 1-hexene, or 1-octene, and preferably in amounts from 3, 5, 10, or 14% by weight to 15, 20, 22, or 25% by weight, based on the total weight of the propylene-based elastomer. The comonomer content of the propylene-based elastomer may also be from about 3 to about 25% by weight, from about 3 to 15% by weight, or from about 10 to 15% by weight, based on the total weight of the propylene-based elastomer.

[0044] In a preferred embodiment, the propylene-based elastomer comprises ethylene-derived units. The propylene-based elastomer may contain 3, 5, 10, or 14% by weight to 15, 20, 22, or 25% by weight of ethylene-derived units, based on the total weight of the propylene-based elastomer. The ethylene content of the propylene-based elastomer may also be about 3 to about 35% by weight, about 3 to 15% by weight, about 10 to 15% by weight, or about 4 to 8% by weight, based on the total weight of the propylene-based elastomer. In any embodiment, the propylene-based elastomer consists essentially of units derived from propylene and ethylene, i.e., the propylene-based elastomer does not contain any other comonomer present in amounts typically used as impurities in the ethylene and / or propylene feed stream used in the polymerization process, or in amounts that would substantially affect the heat of fusion, melting point, crystallinity, or melt flow rate of the propylene-based elastomer, or any other comonomer intentionally added to the polymerization process.

[0045] A propylene-based elastomer may contain at least 50% by weight, at least 60% by weight, at least 70% by weight, at least 75% by weight, at least 80% by weight, at least 85% by weight, at least 90% by weight, or at least 95% by weight of propylene-derived units, based on the total weight of the propylene-based elastomer. A propylene-based elastomer may contain up to 96% by weight, up to 95% by weight, up to 94% by weight, up to 93% by weight, up to 92% by weight, up to 90% by weight, up to 88% by weight, or up to 86% by weight of propylene-derived units, based on the total weight of the propylene-based elastomer.

[0046] In some embodiments, the propylene-based elastomer may also include one or more dienes. The term "diene" is defined as a hydrocarbon compound having two unsaturated sites, i.e., a compound having a double bond with two carbon atoms. Depending on the context, the term "diene" as used herein broadly refers to a diene monomer prior to polymerization (e.g., forming part of a polymerization medium) or a diene monomer after polymerization has begun (also referred to as a diene monomer unit or diene-derived unit). In some embodiments, the diene may be selected from 5-ethimide-2-norbornene (ENB), 1,4-hexadiene, 5-methylene-2-norbornene (MNB), 1,6-octadiene, 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, 1,3-cyclopentadiene, 1,4-cyclohexadiene, vinylnorbornene (VNB), dicyclopentadiene (DCPD), and combinations thereof. When used, the amount of diene comonomer may be equal to or greater than 0.1 wt%, or 0.5 wt%, or 1 wt%, or 1.5 wt%, and less than or equal to 6 wt%, or 4 wt%, or 3 wt%, or 2 wt%, based on the total weight of the propylene-based elastomer.

[0047] Propylene-based elastomers have a heat of fusion (“Hf”) of 100 J / g or less, or 75 J / g or less, 70 J / g or less, 50 J / g or less, or 35 J / g or less, as determined by differential scanning calorimetry (“DSC”). Propylene-based elastomers may have a lower limit of Hf of 0.5 J / g, 1 J / g, or 5 J / g. For example, Hf values ​​may be anywhere from 1.0, 1.5, 3.0, 4.0, 6.0, or 7.0 J / g to 30, 35, 40, 50, 60, 70, or 75 J / g.

[0048] The propylene-based elastomer may have a crystallinity of 2% to 65%, preferably 0.5% to 40%, preferably 1% to 30%, and more preferably 5% to 35% of isotactic polypropylene, as determined according to the DSC procedure described herein. The thermal energy of the highest degree of ordering propylene (i.e., 100% crystallinity) is identified as 189 J / g. In any embodiment, the copolymer has a crystallinity in the range of 0.25% to 25%, or 0.5% to 22% of isotactic polypropylene.

[0049] Propylene-based elastomers may have a ternary stereoregularity (mmm stereoregularity) of 75% or greater, 80% or greater, 85% or greater, 90% or greater, 92% or greater, 95% or greater, or 97% or greater, as measured by 13C NMR. For example, the ternary stereoregularity may be in the range of about 75-about 99%, about 80-about 99%, about 85-about 99%, about 90-about 99%, about 90-about 97%, or about 80-about 97%. The ternary stereoregularity can be determined by the method described in U.S. Patent No. 7,232,871.

[0050] Propylene-based elastomers may have a stereoregularity index m / r ranging from a lower limit of 4 or 6 to an upper limit of 8 or 10 or 12. The stereoregularity index, determined by 13C nuclear magnetic resonance (“NMR”), is expressed herein as “m / r”. The stereoregularity index (m / r) is calculated as defined by HNCheng in Volume 17, MACROMOLECULES, pp. 1950–1955 (1984), which is incorporated herein by reference. The designation “m” or “r” describes the stereochemistry of adjacent propylene group pairs, where “m” indicates meso and “r” indicates racemic. An m / r ratio of 1.0 generally describes a syndiotactic polymer, and an m / r ratio of 2.0 describes a atactic material. Propylene-based elastomers may have a single-peak melt transition as determined by DSC. In any embodiment, the copolymer has a main peak transition of 90°C or less and a broad melt transition endpoint of 110°C or greater. The peak “melting point” (“Tm”) is defined as the temperature at which the sample absorbs the maximum heat within the melting range. However, copolymers may exhibit secondary melting peaks adjacent to the main peak and / or at the melt transition endpoint. For the purposes of this disclosure, such secondary melting peaks are collectively considered as a single melting point, and the highest of these peaks is considered to be the Tm of the propylene-based elastomer. Propylene-based elastomers may have a Tm of 115°C or less, 110°C or less, 100°C or less, 90°C or less, 80°C or less, or 70°C or less. In any embodiment, the propylene-based elastomer may have a Tm of 25 to 115°C, 15 to 110°C, 25°C to 100°C, 25°C to 85°C, 25°C to 75°C, or 25°C to 65°C.

[0051] To determine the thermal properties of the propylene-based elastomers presented herein, differential scanning calorimetry (“DSC”) was used. DSC data were obtained using Perkin-Elmer DSC, with polymer sheets of 7.5 mg to 10 mg to be tested pressed using a die and annealed at room temperature for 48 hours. The samples were then sealed in an aluminum sample pan. DSC data were recorded by first cooling the samples to -50 °C and then gradually heating them to 200 °C at a rate of 10 °C / min. The samples were held at approximately 200 °C for 5 minutes before applying a second cooling-heating cycle. The thermal events of the first and second cycles were recorded. The area under the melt curve was measured and used to determine the heat of fusion and degree of crystallization.

[0052] The percentage crystallinity (X%) is calculated using the formula: X% = [Area under the curve (J / g) / B (J / g)] * 100, where B is the heat of fusion of the homopolymer of the major monomer component. These B values ​​can be found in the Polymer Handbook (4th edition), published by John Wiley and Sons (New York), 1999. The value (B) of 189 J / g is used as the heat of fusion for 100% crystalline polypropylene. The melting temperature is measured and reported during the second heating cycle (or second melt).

[0053] In one or more embodiments, the propylene-based elastomer may have a Mooney viscosity [ML(1+4) at 125°C] of less than 100, less than 75, less than 60, and less than 30, as determined according to ASTM D-1646.

[0054] Propylene-based elastomers can have a density of 0.850 g / cm³. 3 Up to 0.920 g / cm 3 0.860 g / cm 3 Up to 0.900 g / cm 3 or 0.860 g / cm 3 Up to 0.890 g / cm 3 The density, as tested at room temperature according to ASTM D1505.

[0055] Propylene-based elastomers may have melt flow rates (“MFR”) greater than 0.5 dg / min and less than or equal to 1,000 dg / min, or less than or equal to 800 dg / min, 500 dg / min, 200 dg / min, 100 dg / min, or 50 dg / min. Some embodiments may include propylene-based elastomers with an MFR of less than or equal to 25 dg / min, for example, 1-25 dg / min, 1-20 dg / min, or 3-15 dg / min. MFR may also range from a lower limit of about 2.5, 3.5, or 4 g / 10 min to an upper limit of about 10, 15, 20, or 30 g / 10 min. MFR is determined according to ASTM D-1238, condition L (2.16 kg, 230 °C).

[0056] Propylene-based elastomers may have a weight-average molecular weight (“Mw”) of 5,000 to 5,000,000 g / mol, 10,000 to 1,000,000 g / mol, or 50,000 to 400,000 g / mol; a number-average molecular weight (“Mn”) of 2,500 to 2,500,000 g / mol, 10,000 to 250,000 g / mol, or 25,000 to 200,000 g / mol; and / or a z-average molecular weight (“Mz”) of 10,000 to 7,000,000 g / mol, 80,000 to 700,000 g / mol, or 100,000 to 500,000 g / mol. Propylene-based elastomers may have molecular weight distributions (Mw / Mn or “MWD”) of 1.5 to 20, or 1.5 to 15, 1.5 to 5, 1.8 to 5, or 1.8 to 4.

[0057] Propylene-based elastomers may have elongation at break of less than 2000%, less than 1000%, or less than 800%, as measured according to ASTM D412.

[0058] One or more graft monomers can be used to graft (i.e., “functionalize”) a propylene-based elastomer. As used herein, the term “graft” means that the graft monomer is covalently bonded to the polymer chain of the propylene-based elastomer. The graft monomer may be or include at least one olefinically unsaturated carboxylic acid or acid derivative, such as anhydride, ester, salt, amide, imide, or acrylate. Illustrative graft monomers include, but are not limited to, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesocarboxylic acid, maleic anhydride, 4-methylcyclohexene-1,2-dicarboxylic anhydride, bicyclo(2.2.2)octene-2,3-dicarboxylic anhydride, 1,2,3,4,5,8,9,10-octahydronaphthalene-2,3-dicarboxylic anhydride, 2-oxa-1,3-diketospiro(4.4)nonene, bicyclo(2.2.1)heptene-2,3-dicarboxylic anhydride, maleic acridinium, tetrahydrophthalic anhydride, norbornene-2,3-dicarboxylic anhydride, nadic anhydride, methylnadic anhydride, norbornenedihydride, methyl norbornenedihydride, and 5-methylbicyclo(2.2.1)heptene-2,3-dicarboxylic anhydride. Other suitable graft monomers include methyl acrylate and higher alkyl acrylates, methyl methacrylate and higher alkyl methacrylates, acrylic acid, methacrylic acid, hydroxymethyl methacrylate, hydroxyethyl methacrylate and higher hydroxyalkyl methacrylates and glycidyl methacrylate. Maleic anhydride can be used as a graft monomer. In embodiments where the graft monomer is maleic anhydride, the concentration of maleic anhydride in the grafted polymer can be about 6% by weight, at least about 0.5% by weight, or at least about 1.5% by weight, based on the total weight of the propylene-based elastomer.

[0059] In some embodiments, the propylene-based elastomer may be a reactor-blended polymer as defined herein. That is, the propylene-based elastomer is a reactor blend of a first polymer component and a second polymer component. Therefore, the comonomer content of the propylene-based elastomer can be adjusted by adjusting the comonomer content of the first polymer component present in the propylene-based elastomer, adjusting the comonomer content of the second polymer component, and / or adjusting the ratio of the first polymer component to the second polymer component.

[0060] In embodiments where the propylene-based elastomer is a reactor-blended polymer, the α-olefin content of the first polymer component (“R1”) may be greater than 5 wt% α-olefin, greater than 7 wt% α-olefin, greater than 10 wt% α-olefin, greater than 12 wt% α-olefin, greater than 15 wt% α-olefin, or greater than 17 wt% α-olefin, wherein the weight percentage is based on the total weight of the propylene-derived units and α-olefin-derived units of the first polymer component. The α-olefin content of the first polymer component may be less than 30 wt% α-olefin, less than 27 wt% α-olefin, less than 25 wt% α-olefin, less than 22 wt% α-olefin, less than 20 wt% α-olefin, or less than 19 wt% α-olefin, wherein the weight percentage is based on the total weight of the propylene-derived units and α-olefin-derived units of the first polymer component. In some embodiments, the α-olefin content of the first polymer component may be 5 wt%-30 wt% α-olefin, 7 wt%-27 wt% α-olefin, 10 wt%-25 wt% α-olefin, 12 wt%-22 wt% α-olefin, 15 wt%-20 wt% α-olefin, or 17 wt%-19 wt% α-olefin. The first polymer component may contain propylene and ethylene, and in some embodiments, the first polymer component may consist only of propylene and ethylene-derived units.

[0061] In embodiments where the propylene-based elastomer is a reactor-blended polymer, the α-olefin content of the second polymer component (“R2”) may be greater than 1.0 wt% α-olefin, greater than 1.5 wt% α-olefin, greater than 2.0 wt% α-olefin, greater than 2.5 wt% α-olefin, greater than 2.75 wt% α-olefin, or greater than 3.0 wt% α-olefin, wherein the weight percentage is based on the total weight of the propylene-derived units and α-olefin-derived units of the second polymer component. The α-olefin content of the second polymer component may be less than 10 wt% α-olefin, less than 9 wt% α-olefin, less than 8 wt% α-olefin, less than 7 wt% α-olefin, less than 6 wt% α-olefin, or less than 5 wt% α-olefin, wherein the weight percentage is based on the total weight of the propylene-derived units and α-olefin-derived units of the second polymer component. In some embodiments, the α-olefin content of the second polymer component may range from 1.0 wt% to 10 wt% α-olefin, or 1.5 wt% to 9 wt% α-olefin, or 2.0 wt% to 8 wt% α-olefin, or 2.5 wt% to 7 wt% α-olefin, or 2.75 wt% to 6 wt% α-olefin, or 3 wt% to 5 wt% α-olefin. The second polymer component may contain propylene and ethylene, and in some embodiments the first polymer component may consist only of propylene and ethylene-derived units.

[0062] In embodiments where the propylene-based elastomer is a reactor-blended polymer, the propylene-based elastomer may comprise 1-25 wt% of a second polymer component, 3-20 wt% of a second polymer component, 5-18 wt% of a second polymer component, 7-15 wt% of a second polymer component, or 8-12 wt% of a second polymer component, based on the weight of the propylene-based elastomer. The propylene-based elastomer may comprise 75-99 wt% of a first polymer component, 80-97 wt% of a first polymer component, 85-93 wt% of a first polymer component, or 82-92 wt% of a first polymer component, based on the weight of the propylene-based elastomer.

[0063] Propylene-based elastomers can be prepared by any suitable method known in the art. Homogeneous conditions, such as continuous solution polymerization methods, and the use of metallocene catalysts can be used to prepare propylene-based elastomers. In some embodiments, propylene-based elastomers can be prepared in parallel solution polymerization reactors, such that a first reactor component is prepared in a first reactor and a second reactor component is prepared in a second reactor, and reactor effluents from the first and second reactors are combined and blended to form a single effluent from which the final propylene-based elastomer is separated. Exemplary methods for preparing propylene-based elastomers can be found in U.S. Patent Nos. 6,881,800; 7,803,876; 8,013,069 and 8,026,323 and PCT Publications WO 2011 / 087729; WO 2011 / 087730 and WO 2011 / 087731.

[0064] The propylene-based elastomers used in this invention have one or more of the following characteristics:

[0065] (a) comprising 75% to 98% by weight, 80% to 97% by weight, 84% to 96% by weight, 75% to 88% by weight, or 93% to 98% by weight of propylene-derived units and 2% to 25% by weight, 3% to 20% by weight, 4% to 16% by weight, 12% to 25% by weight, or 2% to 7% by weight of C2 or C4-C 12 Units of α-olefins (preferably ethylene) (ethylene is considered an α-olefin for the purposes of this invention);

[0066] (b) Having a concentration of 0.85 to 0.92 g / cm³ 3 0.86 to 0.90 g / cm³ 3 0.85 to 0.87 g / cm³ 3 Or 0.88 to 0.92 g / cm³ 3 The density;

[0067] (c) Having a melt flow rate of 1 to 15 g / 10 min, 2 to 10 g / 10 min, 1 to 5 g / 10 min, or 6 to 15 g / 10 min at 2.16 kg / 230 °C;

[0068] (d) Having a melting temperature of 80 to 115°C, 90 to 110°C, 95 to 110°C, or 100 to 110°C; and

[0069] (e) Having a Vicat softening temperature of 45 to 110°C, 50 to 105°C, 45 to 65°C, or 80 to 105°C.

[0070] Commercially available examples of propylene-based elastomers that can be used in this invention include Vis tamaxx from ExxonMobil Chemical Company. TM High-performance polymers, such as Vis tamaxx TM 6102 and Vistamaxx TM 3588.

[0071] Vis tamaxx TM 6102 is primarily composed of isotactic propylene repeating units and randomly distributed ethylene. The production process utilizes ExxonMobil's proprietary metallocene catalyst technology and contains 16% by weight ethylene, with a concentration of 0.862 g / cm³. 3 Its density, melt flow rate of 3 g / 10 min at 2.16 kg / 230 °C, Shore A hardness of 67, melting temperature of 106 °C, and Vicat softening temperature of 53.9 °C.

[0072] Vis tamaxx TM 3588 is primarily composed of isotactic propylene repeating units and randomly distributed ethylene. Its production process utilizes ExxonMobil's proprietary metallocene catalyst technology and contains 4% wt% ethylene, with a concentration of 0.889 g / cm³. 3 Its density, melt flow rate of 8 g / 10 min at 2.16 kg / 230 °C, Shore hardness D of 50, melting temperature of 108 °C, and Vicat softening temperature of 103 °C.

[0073] Ethylene-based copolymers

[0074] Ethylene-based copolymers may include or may include ethylene-based plastides. The following description of ethylene-based plastides also applies to ethylene-based copolymers.

[0075] Preferred ethylene-based copolymers that can be used in the compositions described herein include those having the following characteristics:

[0076] 1) The ethylene content is 50-99% by weight (preferably 50-90% by weight, 60-85% by weight, or 65-80% by weight, or 65-75% by weight); and / or

[0077] 2) The ethylene content is 80-96 mol% (preferably 82-92 mol%, or 82-88 mol%, or 84-86 mol%); and / or

[0078] 3) The propylene content is 10-20% by weight; and / or

[0079] 4) The butene-1 content is 15% by weight or more (preferably 20% by weight or more, or 25% by weight or more); and / or

[0080] 5) The content of hexene-1 is 20% by weight or more (preferably 25% by weight or more, or 30% by weight or more); and / or

[0081] 6) The octene-1 content is 25% by weight or more (preferably 30% by weight or more, or 35% by weight or more).

[0082] Useful ethylene-based copolymers can possess one or more of the following properties:

[0083] 1) The density is 0.91 g / cm³ 3 or smaller (preferably 0.905 g / cm³) 3 Or smaller, or 0.902 g / cm³ 3 Or smaller, or 0.85 g / cm³ 3 Or larger, or 0.86 g / cm³ 3 Or larger, or 0.87 g / cm³ 3 Or larger, or 0.88 g / cm³ 3 Or larger, or 0.885 g / cm³ 3 Or larger, or 0.85-0.91 g / cm³ 3 Or 0.86-0.91 g / cm³ 3 Or 0.87-0.91 g / cm³ 3 Or 0.88-0.905 g / cm³ 3 Or 0.88-0.902 g / cm³ 3 Or 0.885-0.902 g / cm³ 3 ); and / or

[0084] 2) The heat of fusion (Hf) is 90 J / g or less (preferably 70 J / g or less, or 50 J / g or less, or 30 J / g or less, or 10-70 J / g, or 10-50 J / g, or 10-30 J / g); and / or

[0085] 3) Crystallinity is 40% or less (preferably 30% or less, or 20% or less, preferably at least 5%, or 5-30%, or 5-20%); and / or

[0086] 4) The melting point (Tm, first melting peak) is 100°C or less (preferably 95°C or less, or 90°C or less, or 80°C or less, or 70°C or less, or 60°C or less, or 50°C or less); and / or

[0087] 5) The crystallization temperature (Tc, peak value) is 90°C or less (preferably 80°C or less, or 70°C or less, or 60°C or less, or 50°C or less, or 40°C or less); and / or

[0088] 6) The glass transition temperature (Tg) is -20°C or less (preferably -30°C or less, or -40°C or less); and / or

[0089] 7) Mw is 30-2000 kg / mol (preferably 50-1000 kg / mol, or 90-500 kg / mol); and / or

[0090] 8) Mw / Mn is 1-40 (preferably 1.4-20, or 1.6-10, or 1.8-3.5, or 1.8-2.5); and / or

[0091] 9) The branching index (g”) is 1.4-20 (preferably 1.6-10, or 1.8-10); and / or

[0092] 10) Melt flow rate (MFR, 2.16 kg, 190 °C) is 0.1-1000 g / 10 min (preferably 0.1-100 g / 10 min, 0.3-60 g / 10 min, or 0.5-40 g / 10 min, or 0.7-20 g / 10 min); and / or

[0093] 11) CDBI is at least 60% by weight (preferably at least 70% by weight, or at least 80% by weight, or at least 90% by weight, or at least 95% by weight).

[0094] In a preferred embodiment, the ethylene-based copolymer is an ethylene-based plastide with a density of 0.86-0.91 g / cm³. 3 (Preferred concentration: 0.87-0.91 g / cm³) 3 Or 0.88-0.91 g / cm³ 3 Or 0.88-0.905 g / cm³ 3 Or 0.885-0.902 g / cm³3 The preferred plastic body comprises about 50 to about 85% by weight (preferably about 50 to about 75% by weight) of ethylene-derived units and up to 50% by weight (preferably 20 to 40% by weight) of units derived from propylene and C4-C. 20 A unit of one or more alkenes (preferably 1-butene, 1-hexene and / or 1-octene).

[0095] In another preferred embodiment, the ethylene-based copolymer has a density of less than 0.86 g / cm³. 3 An ethylene elastomer comprising ethylene-derived units and at least 30% by weight of units derived from one or more C4-C4 elastomers. 20 Units of olefins (preferably 1-butene, 1-hexene and / or 1-octene).

[0096] In any implementation, the ethylene-based copolymer can be a random copolymer, a block copolymer, or a blend thereof.

[0097] The method for producing the ethylene-based copolymer is not critical, as it can be produced by slurry, solution, gas phase, high pressure, or other suitable methods using a catalyst system suitable for polyolefin polymerization, such as Ziegler-Natta catalysts, metallocene catalysts, other suitable catalyst systems, or combinations thereof.

[0098] Useful ethylene-based copolymers can be produced using metallocene catalyst systems, i.e., mono- or di-cyclopentadienyl transition metal catalysts combined with aluminoxanes and / or noncoordinate anionic activators in solution, slurry, high pressure, or gas phase. The catalyst and activator can be supported or unsupported, and the cyclopentadienyl ring can be substituted or unsubstituted. For more information on methods and catalysts / activators for producing such mPE homopolymers and copolymers, see WO 94 / 26816; WO 94 / 03506; EPA 277003; EPA 277004; US Patent No. 5153157; US Patent No. 5198401; US ​​Patent No. 5240894; US Patent No. 5017714; CA1268753; US Patent No. 5324800; EPA 129368; US Patent No. 5264405; EPA 520732; WO9200333; US Patent No. 5096867; 5507475; EPA 426637; EPA 573403; EPA 520732; EPA495375; EPA 500944; EPA 570982; WO 91 / 09882; WO 94 / 03506; and U.S. Patent No. 5055438. More generally, preferred plastic bodies are produced using a single-point catalyst, whether or not a metallocene catalyst, and Mw / Mn is 1.5-3 (preferably 1.8-2.5) and CDBI is 70% or greater (preferably 80% or greater, or 90% or greater).

[0099] Plastic bodies that can be used in this invention include those under the trade name EXACT TM (ExxonMobil Chemical Company, Houston, Texas, USA) VERSIFY TM AFFINITY TM ENGAGE TM INFUSE TM (The Dow Chemical Company, Midland, Michigan, USA) and TAFMER TM NOTIO TM Those (Mi tsui Company, Japan) that are no longer sold.

[0100] polypropylene

[0101] The polypropylene used in this invention is preferably a homopolymer polypropylene with high isotacticity, low ash content, and low melt index.

[0102] The homopolymer polypropylene may have one or more of the following characteristics:

[0103] (a) Melt flow rates of 0.2 to 5 g / 10 min, 0.5 to 5 g / 10 min, and 1 to 3 g / 10 min at 2.16 kg / 230 °C;

[0104] (b) ≥95%, ≥96%, ≥97%, or ≥98% of the isotactic index as measured by NMR;

[0105] (c) Total inorganic element content as measured by XRF ≤50ppm, ≤40ppm, ≤30ppm, or ≤20ppm;

[0106] (d) 0.89 to 0.91 g / cm³ 3 or 0.895 to 0.905 g / cm³ 3 density;

[0107] (e) melting temperatures of 160 to 170°C, 162 to 170°C, 164 to 168°C, or 166 to 168°C; and

[0108] (f) Rockwell hardness of 100 to 120, 105 to 115, or 108 to 113 as measured according to ASTM D785.

[0109] Commercially available examples of propylene-based elastomers that can be used in this invention include YUNWA POLYPRO S802 M from Korea Petrochemical.

[0110] S802 M is a homopolymer polypropylene with a melt flow rate of 2.0 g / 10 min at 2.16 kg / 230 °C and a melt flow rate of 0.9 g / cm³. 3 Its density is 15-20 ppm, total inorganic element content is 98.5%, isotactic index is 166-168℃, melting temperature is 111 Rockwell hardness.

[0111] Multilayer microporous membrane

[0112] The multilayer microporous membrane of this disclosure may comprise: a first layer; a second layer; and a third layer; the first and third layers being on opposite sides of the second layer; wherein the second layer comprises 60 wt% to 100 wt% of homopolymer polypropylene as described above, based on the total weight of the polymer in the second layer; at least one of the first, second, and third layers comprises a copolymer selected from propylene-based copolymers (preferably propylene-based elastomers) as described above, ethylene-based copolymers (preferably propylene-based plastomers) as described above, or combinations thereof. The homopolymer polypropylene may have a melt flow rate of 0.2 to 5 g / 10 min at 2.16 kg / 230 °C, an isotactic index of ≥95%, and a total inorganic element content of ≤50 ppm. The propylene-based copolymer may comprise 75 wt% to 98 wt% of propylene-derived units and 2 wt% to 25 wt% of units derived from C2 or C4-C. 12 α-olefin units and having a strength of 0.85 to 0.92 g / cm³ 3 The density and melt flow rate at 2.16 kg / 230 °C are 1 to 100 g / 10 min. The ethylene-based copolymer may contain 50% to 99% by weight of ethylene-derived units and 1% to 50% by weight of C3-C-derived units. 12 α-olefin units and having a strength of 0.85 to 0.91 g / cm³ 3 The density and melt flow rate at 2.16 kg / 190 °C are 0.1 to 1000 g / 10 min. The thickness of the multilayer microporous membrane is less than 20 μm, preferably less than or equal to 19 μm, less than or equal to 18 μm, less than or equal to 17 μm, less than or equal to 16 μm, less than or equal to 15 μm, less than or equal to 14 μm, less than or equal to 13 μm, less than or equal to 12 μm, less than or equal to 11 μm, less than or equal to 10 μm, for example 15-10 μm, 12-10 μm.

[0113] In one embodiment, the second layer may comprise 20% to 40% by weight of a copolymer and 60% to 80% by weight of homopolymer polypropylene; the first layer may comprise 100% by weight of homopolymer polypropylene, based on the total weight of the polymers in the first layer; and the third layer may comprise 100% by weight of homopolymer polypropylene, based on the total weight of the polymers in the third layer. The copolymer may be a propylene-based elastomer. The copolymer may be a first propylene-based elastomer, which may comprise 75% to 88% by weight of propylene-derived units and 12% to 25% by weight of units derived from C2 or C4-C. 12 α-olefin units; and / or having a content of 0.85 to 0.87 g / cm³ 3The density; and / or a melt flow rate of 1 to 5 g / 10 min at 2.16 kg / 230 °C; and / or a Shore hardness A of 45 to 80. In a preferred embodiment, the first propylene-based elastomer may be Vistamaxx from ExxonMobil Chemical Company. TM 6102.

[0114] In another embodiment, the second layer may comprise 100% by weight of a second homopolymer polypropylene, based on the total weight of the polymer in the second layer; and at least one of the first and third layers may comprise 100% by weight of a copolymer, each based on the total weight of the polymer in the first layer or based on the total weight of the polymer in the third layer. In one case, the first layer may comprise 100% by weight of homopolymer polypropylene, based on the total weight of the polymer in the first layer; and the third layer may comprise 100% by weight of a propylene-based elastomer, based on the total weight of the polymer in the third layer. In another case, the first layer may comprise 100% by weight of a copolymer, based on the total weight of the polymer in the first layer; and the third layer may comprise 100% by weight of a copolymer, based on the total weight of the polymer in the third layer. The copolymer may be a propylene-based elastomer. The copolymer may be a second propylene-based elastomer, which may comprise 93% to 98% by weight of propylene-derived units and 2% to 7% by weight of units derived from C2 or C4-C. 12 α-olefin units; and / or having a content of 0.88 to 0.92 g / cm³ 3 The density; and / or a melt flow rate of 6 to 15 g / 10 min at 2.16 kg / 230 °C; and / or a Shore hardness D of 40 to 70. In a preferred embodiment, the second propylene-based elastomer may be Vistamaxx from ExxonMobil Chemical Company. TM 3588.

[0115] The multilayer microporous membrane can be a battery separator, wherein the first and third layers can be called sealing layers, and the second layer can be called the core layer.

[0116] Surprisingly, it was found that by introducing specific copolymers into specific layers of PP-based multilayer microporous membranes, such as Vis tamaxx, TM 6102 can be introduced into the core layer, or Vis tamaxx can be used. TMThe introduction of 3588 into the sealing layer can significantly improve toughness properties such as elongation at break and puncture resistance, while maintaining strength properties such as tensile strength and right-angle tear strength. This will help achieve further thinning of PP-based BSF, as well as increased energy density, reduced defect rate and safe operation.

[0117] Surprisingly, it was also found that adding copolymers can improve sealing performance, manifested in a lower sealing initiation temperature compared to pure PP film, which will help improve production efficiency during battery assembly.

[0118] Compared to the control microporous membrane (which is a single-layer membrane made of pure homopolymer polypropylene with the same thickness as the total thickness of the multilayer microporous membrane), the multilayer microporous membrane has one or more of the following characteristics:

[0119] (a) The needle puncture Fmax / thickness increases by at least 5%, preferably at least 6%, at least 7%, and at least 10%;

[0120] (b) The TD elongation at break increases by at least 30%, preferably at least 40%, at least 50%, or at least 60%;

[0121] (c) The elongation at break of MD increases by at least 5%, preferably at least 6%, at least 7%, and at least 10%;

[0122] (d) The sealing initiation temperature at 5N is reduced by at least 2°C, preferably at least 3°C, at least 4°C, and at least 5°C;

[0123] (e) The reduction in TD tensile strength at break shall not exceed 10%, preferably not exceed 7%, and not exceed 5%;

[0124] (f) The reduction in MD fracture tensile strength shall not exceed 10%, preferably not exceed 7%, and not exceed 5%;

[0125] (g) The reduction in TD right-angle tear strength shall not exceed 10%, preferably not exceed 7%, and not exceed 5%; and

[0126] (h)MD right-angle tear strength reduction shall not exceed 10%, preferably not exceed 7%, and not exceed 5%.

[0127] Preparation method of multilayer microporous membrane

[0128] The multilayer microporous membrane of the present invention can be prepared using conventional methods for preparing battery separators. Methods for preparing battery separators include dry and wet methods, with dry methods including dry uniaxial stretching and dry biaxial stretching. The multilayer microporous membrane of the present invention is preferably prepared by dry uniaxial stretching.

[0129] In the dry uniaxial stretching process, the polymers for each layer and optional additives are first fed into an extruder. After melt mixing in the extruder, the mixture is extruded through a multilayer film die and then cooled and shaped on a casting roll to obtain a basic multilayer film. Under the stress field of high-speed stretching on the casting roll, PP crystallizes, resulting in a lamellar structure with parallel crystals perpendicular to the extrusion direction. Second, the basic multilayer film is heat-treated to eliminate defects in the crystalline regions, further improve the lamellar structure, and increase crystallinity. Third, the heat-treated basic multilayer film is stretched. Typically, it is first stretched at a low temperature to form micro-defects such as silver streaks, and then stretched again at a high temperature to break up the defects and form micropores. The microporous film is then shaped at a specific temperature and stretch ratio to obtain a multilayer microporous film. Finally, as needed, the multilayer microporous film is cut to form the finished microporous film.

[0130] Typical preparation process conditions include:

[0131] (i) The extrusion temperature is about 200°C to about 240°C, for example about 210°C to about 230°C, the casting roll temperature is room temperature (about 25°C) to about 155°C, for example about 40°C to about 80°C, and the draw ratio is about 1 to about 4, for example about 1 to about 3;

[0132] (ii) The heat treatment temperature is about 100°C to about 200°C, for example about 120°C to about 160°C, and the time is about 20 to about 100 minutes, for example about 30 to about 60 minutes;

[0133] (iii) The cold stretching temperature is from room temperature (about 25°C) to about 60°C, for example from about 25°C to about 40°C, and the stretching ratio is from about 1 to about 3, for example from about 1 to about 2;

[0134] (iv) The hot stretching temperature is about 90°C to about 150°C, for example about 110°C to about 140°C, and the stretching ratio is about 1 to about 5, for example about 2 to about 4.

[0135] (v) The setting temperature is about 100°C to about 160°C, for example about 120°C to about 150°C, and the stretch ratio is about 0.7 to about 1, for example about 0.8 to about 0.9.

[0136] Unless otherwise stated, all numerical values ​​used in this specification and the related claims to represent quantities of ingredients, properties such as molecular weight, reaction conditions, etc., should be understood to be modified by the term "about" in all cases. Therefore, unless the contrary is indicated, the numerical parameters listed in the following specification and the appended claims are approximate values ​​and may vary depending on the desired properties sought to be obtained by the embodiment of the invention. At least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be interpreted based at least on the reported significant figures and by applying ordinary rounding techniques.

[0137] This document presents one or more illustrative embodiments including one or more inventive elements. For clarity, not all features of the physical implementation are described or shown in this application. It should be understood that in the development of physical embodiments including one or more elements of the present invention, many implementation-specific decisions must be made to achieve the developer's objectives, such as complying with system-related, business-related, governmental-related, and other constraints, which vary from time to time as implementation progresses. While the developer's efforts may be time-consuming, such efforts are a routine task for those skilled in the art who benefit from this disclosure.

[0138] While compositions and methods are described herein with respect to “comprising” various components or steps, they may also be described as “consistently composed of various components and steps” or “components of various components and steps.” In the context of compositions, “consistently…” composition allows for 25 ppm or less of impurities (each).

[0139] Other implementation plans

[0140] The present invention also relates to the following embodiments.

[0141] 1. A multilayer microporous membrane, comprising:

[0142] First layer;

[0143] The second layer; and

[0144] The third layer;

[0145] The first and third layers are on either side of the second layer;

[0146] The second layer comprises 60% to 100% by weight of homopolymer polypropylene, and based on the total weight of the polymer in the second layer, the homopolymer polypropylene has a melt flow rate of 0.2 to 5 g / 10 min at 2.16 kg / 230 °C, an isotactic index of ≥95%, and a total inorganic element content of ≤50 ppm.

[0147] At least one of the first, second, and third layers comprises a copolymer selected from propylene-based copolymers, ethylene-based copolymers, or combinations thereof.

[0148] The propylene-based copolymer comprises 75% to 98% by weight of propylene-derived units and 2% to 25% by weight of units derived from C2 or C4-C. 12 α-olefin units and having a strength of 0.85 to 0.92 g / cm³ 3 The density and melt flow rate of 1 to 100 g / 10 min at 2.16 kg / 230 °C;

[0149] The ethylene-based copolymer comprises 50% to 99% by weight of ethylene-derived units and 1% to 50% by weight of C3-C-derived units. 12 α-olefin units and having a strength of 0.85 to 0.91 g / cm³ 3 The density and melt flow rate at 2.16 kg / 190 °C are 0.1 to 1000 g / 10 min.

[0150] The thickness of the multilayer microporous membrane is less than 20 μm.

[0151] 2. The multilayer microporous membrane according to embodiment 1, wherein the propylene-based copolymer:

[0152] Contains 80% to 97% by weight of propylene-derived units and 3% to 20% by weight of C2 or C4-C-derived units. 12 α-olefin units; and / or

[0153] The C2 or C4-C mentioned above 12 α-olefins are ethylene or butene; and / or

[0154] It has a concentration of 0.86 to 0.90 g / cm³. 3 The density; and / or

[0155] It has a melt flow rate of 2 to 10 g / 10 min at 2.16 kg / 230 °C; and / or

[0156] Having a melting temperature of 80 to 115°C; and / or

[0157] It is an elastomer based on propylene.

[0158] 3. The multilayer microporous membrane according to embodiment 1, wherein the ethylene-based copolymer:

[0159] Contains 60% to 85% by weight of ethylene-derived units and 15% to 40% by weight of C3-C-derived units. 12 α-olefin units; and / or

[0160] The C3-C 12 α-olefins are butene or octene; and / or

[0161] It has a concentration of 0.86 to 0.91 g / cm³. 3 The density; and / or

[0162] It has a melt flow rate of 0.1 to 100 g / 10 min at 2.16 kg / 190 °C; and / or

[0163] Having a melting temperature of 100°C or lower; and / or

[0164] It is a plastic based on ethylene.

[0165] 4. The multilayer microporous membrane according to embodiment 1, wherein:

[0166] The second layer comprises 20% to 40% by weight of copolymer and 60% to 80% by weight of homopolymer polypropylene;

[0167] The first layer comprises 100% by weight homopolymer polypropylene, based on the total weight of the polymer in the first layer; and

[0168] The third layer comprises 100% by weight homopolymer polypropylene, based on the total weight of the polymer in the third layer.

[0169] 5. The multilayer microporous membrane according to embodiment 4, wherein the copolymer is a first propylene-based elastomer, the first propylene-based elastomer being:

[0170] Contains 75% to 88% by weight of propylene-derived units and 12% to 25% by weight of C2 or C4-C-derived units. 12 α-olefin units; and / or

[0171] It has a concentration of 0.85 to 0.87 g / cm³. 3 The density; and / or

[0172] It has a melt flow rate of 1 to 5 g / 10 min at 2.16 kg / 230 °C; and / or

[0173] It has a Shore A hardness of 45 to 80.

[0174] 6. The multilayer microporous membrane according to embodiment 1, wherein:

[0175] The second layer comprises 100% by weight homopolymer polypropylene, based on the total weight of the polymer in the second layer; and

[0176] At least one of the first layer and the third layer comprises 100% by weight of copolymer, each based on the total weight of the polymer in the first layer or the total weight of the polymer in the third layer.

[0177] 7. The multilayer microporous membrane according to embodiment 6, wherein:

[0178] The first layer comprises 100% by weight homopolymer polypropylene, based on the total weight of the polymer in the first layer; and

[0179] The third layer comprises 100% by weight of copolymer, based on the total weight of the polymer in the third layer.

[0180] 8. The multilayer microporous membrane according to embodiment 6 or 7, wherein the copolymer is a second propylene-based elastomer, the second propylene-based elastomer being:

[0181] Contains 93% to 98% by weight of propylene-derived units and 2% to 7% by weight of C2 or C4-C derivatives. 12 α-olefin units; and / or

[0182] It has a concentration of 0.88 to 0.92 g / cm³. 3 The density; and / or

[0183] It has a melt flow rate of 6 to 15 g / 10 min at 2.16 kg / 230 °C; and / or

[0184] It has a Shore hardness (D) of 40 to 70.

[0185] 9. The multilayer microporous membrane according to any one of embodiments 1-8, wherein the homopolymer polypropylene has one or more of the following characteristics:

[0186] 0.89 to 0.91 g / cm³ 3 The density;

[0187] Melting temperature of 160 to 170°C; and

[0188] Rockwell hardness of 100 to 120.

[0189] 10. The multilayer microporous membrane according to any one of embodiments 1-8, wherein

[0190] The multilayer microporous membrane is a three-layer membrane; and / or

[0191] The thickness ratio of the first, second, and third layers is 1:1 to 3:1.

[0192] 11. A three-layer microporous membrane, comprising:

[0193] First layer;

[0194] The second layer; and

[0195] The third layer;

[0196] The first and third layers are on either side of the second layer;

[0197] The first layer comprises 100% by weight homopolymer polypropylene, based on the total weight of the polymer in the first layer;

[0198] The second layer comprises 30% by weight of a propylene-based elastomer and 70% by weight of homopolymer polypropylene; and

[0199] The third layer comprises 100% by weight homopolymer polypropylene, based on the total weight of the polymer in the third layer;

[0200] The homopolymer polypropylene described herein has a melt flow rate of 2 g / 10 min at 2.16 kg / 230 °C; an isotactic index of 98.5%; a total inorganic element content of 15-20 ppm; and a melt flow rate of 0.9 g / cm³. 3 The density;

[0201] The propylene-based elastomer comprises 84 wt% propylene-derived units and 16 wt% ethylene-derived units and has a density of 0.862 g / cm³. 3 The density and melt flow rate of 3 g / 10 min at 2.16 kg / 230 °C;

[0202] The thickness of the multilayer microporous membrane is less than 20 μm.

[0203] 12. A three-layer microporous membrane, comprising:

[0204] First layer;

[0205] The second layer; and

[0206] The third layer;

[0207] The first and third layers are on either side of the second layer;

[0208] The first layer comprises 100% by weight homopolymer polypropylene, based on the total weight of the polymer in the first layer;

[0209] The second layer comprises 100% by weight homopolymer polypropylene, based on the total weight of the polymer in the second layer;

[0210] The third layer comprises 100% by weight of a propylene-based elastomer, based on the total weight of the polymer in the third layer;

[0211] The homopolymer polypropylene described herein has a melt flow rate of 2 g / 10 min at 2.16 kg / 230 °C; an isotactic index of 98.5%; a total inorganic element content of 15-20 ppm; and a melt flow rate of 0.9 g / cm³. 3 The density;

[0212] The propylene-based elastomer comprises 96 wt% propylene-derived units and 4 wt% ethylene-derived units and has a density of 0.889 g / cm³. 3 The density and melt flow rate of 8 g / 10 min at 2.16 kg / 230 °C;

[0213] The thickness of the multilayer microporous membrane is less than 20 μm.

[0214] 13. A method for preparing a multilayer microporous membrane according to any one of embodiments 1-12, comprising:

[0215] (1) The components of each layer are extruded and cast to form a basic multilayer film;

[0216] (2) Heat-treating the base multilayer film to form a heat-treated base multilayer film; and

[0217] (3) The heat-treated base multilayer film is stretched multiple times to form a multilayer microporous film.

[0218] 14. Use of the multilayer microporous membrane according to any one of embodiments 1-12 as a battery separator. Detailed Implementation

[0219] To facilitate a better understanding of embodiments of the present invention, the following preferred or representative embodiments are provided. These embodiments should not be construed as limiting or restricting the scope of the invention.

[0220] Example

[0221] Test methods

[0222] Measure peak puncture force according to CEN 14477.

[0223] Tensile strength and elongation at break were measured according to ASTM D-882.

[0224] Right-angle tear strength was measured according to ASTM D 1004-09.

[0225] The sealing strength (N / 15mm) test is performed according to the following procedures. The seal is prepared under the following conditions: 30mm wide strip, 0.5N / mm. 2 Sealing pressure, sealing time 0.5 seconds, sealing area 50mm x 5mm. After preparing the seal, the specimens were cut into 15mm strips. After conditioning the samples at 23℃ ± 3℃ and 50% RH ± 5% RH for at least 24 hours, the sealing strength of the 15mm wide specimens was determined using a Zwick tensile tester under the following conditions: speed 100mm / min, force sensor 200N, and clamping distance 50mm. The specimens were placed between the clamps, and the clamps were moved apart at a speed of 100mm / min. Four specimens were measured, and the maximum force was recorded and averaged. Sealing strength is the force at which the specimen fails. The sealing initiation temperature is the temperature at which a sealing strength of 5N is achieved.

[0226] Table 1 shows the polymers used in the examples.

[0227] Table 1 describes the polymers used in the examples.

[0228]

[0229] Six membrane samples were prepared using the formulations shown in Table 2, with Example 1 (made of pure PP) serving as a reference example. Example 2 had two sealing layers made of pure PP, and the core layer was made of 15 wt% 6102 + 85 wt% PP; Example 3 had two sealing layers made of pure PP, and the core layer was made of 30 wt% 6102 + 70 wt% PP; Example 4 had one sealing layer and core layer made of pure PP, and the other sealing layer was made of 100 wt% 3588; Example 5 had one sealing layer and core layer made of pure PP, and the other sealing layer was made of 25 wt% 3980 + 75 wt% PP; Example 6 had one sealing layer and core layer made of pure PP, and the other sealing layer was made of 25 wt% 6102 + 75 wt% PP.

[0230] Table 2 shows the formulations of the samples in the examples.

[0231]

[0232] Multilayer films were prepared on an SML multifunctional cast film production line according to the formulations in Table 2. The process conditions included: extrusion temperature of 220°C, casting roll temperature of 50°C, draw ratio of 1, and production line speed of 150 m / min. Example 1 was a single-layer film made of pure PP with a thickness of 19 μm and a width of 1 m. Examples 2-6 were three-layer films with a total thickness of 19 μm and a width of 1 m, and a film structure of 1 / 2 / 1.

[0233] The performance of the above six membrane samples was tested, and the results are shown in Table 3 and... Figure 1 and 2 As shown.

[0234] Table 3 Performance of the samples in the examples

[0235]

[0236] From Table 3 and Figure 1 The results show that, compared with pure PP film (Example 1), introducing 6102 into the core layer (Examples 2 and 3) can significantly improve the TD elongation at break of the film, while other mechanical properties remain comparable. Compared with pure PP film (Example 1), introducing 3588 into the sealing layer (Example 4) can significantly improve the puncture resistance of the film, while other mechanical properties remain comparable. Furthermore, compared with pure PP film (Example 1), introducing 3980 or 6102 into the sealing layer (Examples 5 and 6) can slightly improve the TD elongation at break of the film.

[0237] From Table 3 and Figure 2The results show that, compared with pure PP film (Example 1), introducing propylene-based elastomers (Examples 2-6) into the core layer or sealing layer can reduce the sealing initiation temperature.

[0238] In summary, the inventors of this application have surprisingly discovered that by introducing specific propylene-based elastomers into specific layers of PP-based multilayer microporous membranes, such as Vis tamaxx, TM 6102 can be introduced into the core layer, or Vis tamaxx can be used. TM The introduction of 3588 into the sealing layer significantly improves toughness properties such as elongation at break and puncture resistance, while maintaining strength properties such as tensile strength and right-angle tear strength. This will help achieve further thinning of PP-based BSF, as well as increased energy density, reduced defect rate, and safer operation. Furthermore, the addition of a propylene-based elastomer can also improve sealing performance, manifested in a lower sealing initiation temperature compared to pure PP film. This will help improve production efficiency during battery assembly and facilitate improved hot-pressing efficiency after battery stacking.

[0239] Therefore, the present invention is highly suitable for achieving the results and advantages mentioned and inherent therein. The specific embodiments and constructions disclosed above are merely illustrative, as it will be apparent to those skilled in the art, who benefit from the teachings herein, that different but equivalent means can be employed to modify and implement the invention. Furthermore, the details of the constructions or designs shown herein are not intended to be limited except as set forth in the following claims. It will thus be apparent that the specific illustrative embodiments disclosed above can be changed, combined, or modified, and all such changes are considered to be within the scope and spirit of the invention. The invention disclosed herein may be suitably implemented even in the absence of any elements not specifically disclosed herein and / or any optional elements disclosed herein.

[0240] While compositions and methods are described as "comprising," "containing," or "including" various components or steps, they may also be described as "substantially composed of various components and steps" or "composed of various components and steps." All the values ​​and ranges disclosed above may be modified to a certain extent.

[0241] Whenever a range of values ​​with a lower and upper limit is disclosed, it specifically discloses any value falling within that range and any included range. In particular, the range of each value disclosed herein (having the form "from about a to about b", or equivalently "from about a to b", or equivalently "from about ab") should be understood as listing every value and range contained within a wider range of values. Similarly, when multiple ranges are disclosed (e.g., 1-100 or 10-90, e.g., 30 to 75), it specifically covers the range from any disclosed lower end to any disclosed upper end (e.g., 10-75).

[0242] Furthermore, the terms in the claims have their ordinary, general meanings unless otherwise explicitly and clearly defined by the patentee. Additionally, the indefinite articles “a” or “an” used in the claims are defined herein as referring to one or more elements they introduce.

Claims

1. A battery separator, the battery separator being a multilayer microporous membrane comprising: a first layer; a second layer; and a third layer; the first and third layers being on either side of the second layer; wherein (1) the second layer comprises 20 to 40 wt% of a copolymer and 60 to 80 wt% of a homopolymer polypropylene; the first layer comprises 100 wt% of a homopolymer polypropylene, based on the total weight of polymer in the first layer; and the third layer comprises 100 wt% of a homopolymer polypropylene, based on the total weight of polymer in the third layer; or (2) the second layer comprises 100 wt% of a homopolymer polypropylene, based on the total weight of polymer in the second layer; the first layer comprises 100 wt% of a homopolymer polypropylene, based on the total weight of polymer in the first layer; and the third layer comprises 100 wt% of a copolymer, based on the total weight of polymer in the third layer; said homopolypropylene having a density of 0.89 to 0.91 g / cm 3 0.2 to 5 g / 10 min melt flow rate at 2.16 kg / 230°C, an isotacticity of > 95% and a total inorganic element content of < 50 ppm; for composition (1), the copolymer is a first propylene-based elastomer, the first propylene-based elastomer: comprising 75 to 88 wt% units derived from propylene and 12 to 25 wt% units derived from C2or C4-C 12 units of an α-olefin; having a density of 0.85 to 0.87 g / cm 3 and having a melt flow rate at 2.16 kg / 230°C of 1 to 5 g / 10 min; for composition (2), the copolymer is a second propylene-based elastomer, the second propylene-based elastomer: comprising 93 to 98 weight percent of units derived from propylene and 2 to 7 weight percent of units derived from C2or C4-C 12 units of an α-olefin; having a density of 0.88 to 0.92 g / cm3 3 and having a melt flow rate at 2.16 kg / 230°C of 6 to 15 g / 10 min; the multilayer microporous membrane having a thickness of less than 20 pm.

2. The battery separator of claim 1, wherein the first propylene-based elastomer: has a Shore hardness A of 45 to 80.

3. The battery separator of claim 1, wherein the second propylene-based elastomer: has a Shore hardness D of 40 to 70.

4. The battery separator of any one of claims 1-3, wherein the homopolymer polypropylene has one or more of the following characteristics: a melting temperature of 160 to 170°C; and a Rockwell hardness of 100 to 120.

5. The battery separator of any one of claims 1-3, wherein the multilayer microporous membrane is a three-layer membrane; and / or the layer thickness ratio of the first, second, and third layers is 1:1-3:

1.

6. A battery separator, the battery separator being a three-layer microporous membrane comprising: a first layer; a second layer; and a third layer; the first and third layers being on either side of the second layer; wherein the first layer comprises 100 wt% of a homopolymer polypropylene, based on the total weight of polymer in the first layer; the second layer comprises 30 wt% of a propylene-based elastomer and 70 wt% of a homopolymer polypropylene; and the third layer comprises 100 wt% of a homopolymer polypropylene, based on the total weight of polymer in the third layer; wherein the homopolypropylene has a melt flow rate of 2 g / 10 min at 2.16 kg / 230°C; an isotacticity of 98.5%; a total inorganic element content of 15-20 ppm; and a density of 0.9 g / cm 3 3. The propylene-based elastomer comprises 84 wt% of units derived from propylene and 16 wt% of units derived from ethylene and has a density of 0.862 g / cm 3 and a melt flow rate at 2.16 kg / 230°C of 3 g / 10 min; the three-layer microporous membrane having a thickness of less than 20 pm.

7. A battery separator, the battery separator being a three-layer microporous membrane comprising: a first layer; a second layer; and a third layer; the first and third layers being on either side of the second layer; wherein the first layer comprises 100 wt% of a homopolymer polypropylene, based on the total weight of polymer in the first layer; the second layer comprises 100 wt% of a homopolymer polypropylene, based on the total weight of polymer in the second layer; the third layer comprises 100 wt% of a homopolymer polypropylene, based on the total weight of polymer in the third layer. the third layer comprises 100 wt% propylene-based elastomer, based on the total weight of polymer in the third layer; wherein the homopolypropylene has a melt flow rate of 2 g / 10 min at 2.16 kg / 230°C; an isotacticity of 98.5%; a total inorganic element content of 15-20 ppm; and a density of 0.9 g / cm 3 3. The propylene-based elastomer comprises 96 wt% of units derived from propylene and 4 wt% of units derived from ethylene and has a density of 0.889 g / cm 3 and a melt flow rate at 2.16 kg / 230°C of 8 g / 10 min; the three-layer microporous membrane has a thickness of less than 20 pm.

8. The method of claim 1-7, comprising: (1) extrusion casting the components of each layer to form a base multilayer film; (2) heat treating the base multilayer film to form a heat treated base multilayer film; and (3) stretching the heat treated base multilayer film multiple times to form a multilayer microporous membrane.

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