TWI423499B - Multi-layer, microporous membrane, battery separator and battery - Google Patents

Description

Multilayer microporous membrane, battery separator and battery

The present invention relates to a multilayer microporous polyolefin film having suitable permeability, pin puncture strength, shutdown temperature, shutdown speed, melting temperature, and thickness uniformity. The invention also relates to a battery separator formed from, for example, a multilayer microporous membrane, and a battery comprising the separator. Another aspect of the present invention relates to a method of producing the multilayer microporous polyolefin film, a method of manufacturing a battery using the film as a separator, and a method using a battery.

The porous polyolefin film can be used, for example, as a battery separator for primary and secondary lithium batteries, lithium polymer batteries, nickel hydrogen batteries, nickel cadmium batteries, nickel zinc batteries, silver zinc batteries, and the like. When a microporous polyolefin membrane is used in a battery separator (especially a lithium ion battery separator), the effectiveness of the membrane can significantly affect the properties, productivity, and safety of the battery. Therefore, the microporous polyolefin film should have appropriate mechanical properties, heat resistance, permeability, dimensional stability, shutdown properties, melting properties, and the like. As is well known, batteries should have a relatively low shutdown temperature and a relatively high melting temperature to improve battery safety, especially during manufacturing, charging, recharging, use, and/or storage. For batteries exposed to high temperatures. Improvements in the permeability of the separator generally result in an improvement in the storage capacity of the battery. The high speed shutdown speed is required to improve battery safety, especially when the battery is operated under overcharge conditions. Improved pin pressure resistance is desired Because the roughness of the electrode of the battery will pierce the separator during manufacturing, causing a short circuit to occur. Improved thickness uniformity is desirable because variations in thickness can cause manufacturing difficulties when the film is wound onto the core. Variations in thickness can also cause anisotropic temperature variations within the cell, which can result in battery hot spots (higher temperatures) when the separator is relatively thin.

In general, a microporous film containing only polyethylene (that is, a film composed of polyethylene or substantially composed of polyethylene) has a low melting temperature, and a microporous film containing only polypropylene has a high The temperature of the shutdown. Therefore, a microporous film comprising polyethylene and polypropylene as main components has been proposed as an improved battery separator. Therefore, a microporous film formed of a polyethylene resin and a polypropylene resin, and a multilayer microporous film containing polyethylene and polypropylene are provided.

For example, JP 7-216118 A discloses a battery separator having an appropriate shutdown temperature and mechanical strength. This patent application discloses a battery separator comprising a multilayer porous film having two microporous layers. Both layers may contain polyethylene and polypropylene, but the relative amounts are different. For example, in the first microporous layer, the percentage of polyethylene is 0% by weight to 20% by weight, and in the second microporous layer is 21% by weight to 60% by weight (based on the total weight of polyethylene and polypropylene) ). The total amount of polyethylene in the film (i.e., the two microporous layers) is from 2% by weight to 40% by weight based on the weight of the multilayer microporous film.

JP 10-195215 A discloses a relatively thin battery separator having acceptable closure and pin-pulling characteristics. "on the pin The term "pin pulling" refers to the relative ease with which a metal pin is pulled from a laminate of a separator, a cathode sheet and an anode sheet which is wound around a pin to form an annular laminate. The multilayer porous film contains polyethylene and polypropylene, but differs in relative amounts. The percentage of polyethylene in the inner layer is from 0% by weight to 20% by weight, and in the outer layer is from 61% by weight to 100% by weight (based on the total weight of polyethylene and polypropylene).

JP 10-279718 A discloses a separator designed to prevent an unacceptably large temperature increase in a lithium battery when the battery is overcharged. The separator is formed of a multilayer porous film made of polyethylene and polypropylene, and the relative amounts of polyethylene and polypropylene in each layer are different. The film has a polyethylene-deficient layer having a polyethylene content of from 0% by weight to 20% by weight based on the weight of the polyethylene-deficient layer. The second layer is a polyethylene-rich layer containing 0.5% by weight or more of polyethylene having a melt index of 3 or higher and having a polyethylene content of 61% by weight to 100% by weight (based on the rich The weight of the polyethylene layer).

It is also necessary to further improve the permeability of the microporous polyolefin film, the pin pressure resistance, and the shutdown speed. In addition, there is a need to further improve the thickness uniformity of the microporous polyolefin film, and to reduce the possibility of short circuits when used as a battery separator.

General theory of invention

In one system, the invention relates to a multilayer microporous membrane comprising: a first layer of material comprising a first polyethylene and a first polypropylene and a second layer of material comprising a second layer of polyethylene And a second polypropylene having (1) a weight average molecular weight of 6 × 10 ⁵ or more, (2) a heat of fusion of 90 J/g or more, and (3) a molecular weight of 5 × 10 ⁴ or For fewer parts, this part is 5% or less (based on the mass of the second polypropylene).

The multilayer film can comprise, for example, a first microporous layer comprising a first microporous layer material and a second microporous layer comprising a second microporous layer material. For example, the multilayer film of claim 1 may include: a first microporous layer containing a first microporous layer material; a third microporous layer containing a first microporous layer material; Two microporous layers comprising a second microporous layer material, the second microporous layer being located between the first and third microporous layers.

In an alternative form, the multilayer microporous membrane may comprise: a first microporous layer comprising a second microporous layer material; and a third microporous layer comprising a second microporous layer material; And a second microporous layer comprising a first microporous layer material, the second microporous layer being between the first and third microporous layers.

In another system, the present invention relates to a method of producing a microporous membrane comprising: (1) combining a first polyethylene resin, a first polypropylene resin, and a first processing solvent to form a first a polyolefin solution in which the first polyethylene resin and the first polypropylene resin together constitute a first polyolefin composition; and wherein the first polyethylene in the first polyolefin composition The amount is at least about 80% by weight (based on the weight of the first polyolefin composition); and (2) combining the second polyethylene resin, the second polypropylene resin, and the second processing solvent to form a second polyolefin solution, wherein the second polyethylene resin and the second polypropylene resin together form a second polyolefin composition; and wherein the second polyethylene in the second polyolefin composition The amount is at least about 50% by weight based on the weight of the second polyolefin composition; the second polypropylene resin has (a) a weight average molecular weight of 6 × 10 ⁵ or more, and (b) heat of fusion 90 J / g or more and 5 × 10 ⁴ or smaller part (c) molecular weight The line portion or 5% less (based on the weight of the second polypropylene resin).

In one system, the invention further comprises: (3) extruding at least a portion of the first polyolefin solution through the die and coextruding at least a portion of the second polyolefin solution to form a multilayer extrudate, (4) The multilayer extrudate is cooled to form a multilayer sheet, (5) removing at least a portion of the processing solvent from the multilayer sheet to form a solvent-removed sheet, and (6) from the sheet At least a portion of any volatile species is removed to form a multilayer microporous membrane.

In yet another system, the present invention is directed to a battery comprising an anode, a cathode, and an electrolyte, and a multilayer film of the foregoing system, wherein the multilayer film isolates at least the anode from the cathode. This battery can be used as a source of charge Or a tank.

Detailed description of the invention [1] Composition and structure of multilayer micro-polybiolefin film

In a system, the multilayer microporous membrane comprises two layers. The first layer (eg, the upper layer) comprises a first microporous layer material and the second layer (eg, the bottom layer) comprises a second microporous layer material. For example, the film has a planar top layer (when viewed from above on an axis that is at right angles to the transverse and mechanical directions of the film), while the bottom layer is hidden beneath it when viewed from the top. In another system, the multilayer microporous membrane comprises three or more layers, wherein the outer layer (also referred to as a "surface" or "skin" layer) comprises a first microporous layer material, and at least one intermediate layer comprises Two microporous layers of material. In a related system, when the multilayer microporous membrane comprises two layers, the first layer consists essentially of (or consists of) the first microporous layer material, and the second layer consists essentially of (or It consists of a second microporous material. In a related system in which the multilayer microporous membrane comprises two or more layers, the outer layer consists essentially of (or consists of) the first microporous layer material, and at least one of the intermediate layers is substantially (or It consists of a second microporous layer of material. The film may be referred to as a "polyolefin film" when it contains a polyolefin. Although the film may contain only a polyolefin, this is not essential, and within the scope of the present invention, the film may contain a polyolefin as well as a non-polyolefin.

In yet another system in which the multilayer microporous membrane comprises three or more layers, the surface layer comprises (either consists essentially of or consists of: a second microporous layer material, In the middle of at least one layer The layer comprises (either consists essentially of or consists of: the first microporous layer material). When the multilayer microporous membrane has three or more layers, the multilayer microporous polyolefin membrane has at least one layer comprising a first microporous layer material and at least one layer comprising a second microporous layer material.

In a system, the sum of the thicknesses of the layers comprising the second layer of material is typically in the range of from about 3% to about 90%, or from about 10% to about 60%, of the total thickness of the multilayer microporous membrane.

In one system, the first microporous layer material comprises a first polypropylene and a first polyethylene. The second microporous layer material comprises a second polyethylene and a second polypropylene. The total amount of polyethylene in the multilayer microporous polyolefin film can be, for example, from about 9.5% to about 95% by weight, or from about 10% to about 60% by weight, or from about 50% to about 85% by weight. Within the range of % (based on the weight of the multilayer microporous polyolefin film). The total amount of polypropylene in the multilayer microporous polyolefin film can be, for example, from about 1.4% to about 90.5% by weight, or from about 10% to about 60% by weight, or from about 50% to about 85% by weight. Within the range (based on the weight of the multilayer microporous polyolefin film). In a system, the first microporous layer material is present in the first amount in the range of from about 50% by weight to about 99% by weight (based on the weight of the first microporous layer material). Within the microporous layer material; the first polypropylene is present in the first amount in the range of from about 1% by weight to about 50% by weight (based on the weight of the first microporous layer material) Within the microporous layer material; the second polyethylene is from about 5% by weight to about 95% by weight (based on the second microporous layer material) The second amount of polyethylene in the range of weight) is present in the second microporous layer material; and the second polypropylene is in the range of from about 5% by weight to about 95% by weight (based on the second microporous layer material) The second amount of polypropylene in the range of weights is present in the second microporous layer material.

The first and second polyethylenes, as well as the first and second polypropylenes, are described in more detail below.

A. The first polyethylene in a system, the first polyethylene Mw is from about 1 x 10 ⁴ to about 1 x 10 ⁷ , or from about 1 x 10 ⁵ to about 5 x 10 ⁶ , or about 2 Polyethylene in the range of from 10 ⁵ to about 3 × 10 ⁶ . The first polyethylene can be one or more polyethylenes, for example, PE1, PE2, and the like. PE1 comprises polyethylene having a Mw in the range of from about 1 x 10 ⁴ to about 5 x 10 ⁵ . Optionally, PE1 can be one or more high density polyethylene (HPDE), medium density polyethylene, branched low density polyethylene, or linear low density polyethylene. Although not strictly limited, the Mw of the high density polyethylene may range, for example, from about 1 x 10 ⁵ to about 5 x 10 ⁵ , or from about 2 x 10 ⁵ to about 4 x 10 ⁵ . In one system, PE1 is at least one of the following: (i) an ethylene homopolymer or (ii) a third amount of ethylene and a third alpha olefin typically less than the amount of ethylene (such as a copolymer of propylene, butene-1, hexene-1, etc.). For example, the copolymer can be produced by using a single catalyst.

In a system, the first polyethylene comprises a second polyethylene, PE2. PE2 comprising polyethylene Mw of at least about 1 × 10 ⁶ in. For example, PE2 can be ultra high molecular weight polyethylene (UHMWPE). In one system, PE2 is at least one of: (i) an ethylene homopolymer or (ii) ethylene and a fourth alpha-olefin (typically, compared to the amount of ethylene, the amount thereof) Less) copolymer. The fourth α-olefin may be, for example, one or more of propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, vinyl acetate. , methyl methacrylate, or styrene. Although not strictly limited, the Mw of PE2 may be, for example, from about 1 x 10 ⁶ to about 15 x 10 ⁶ , or from about 1 x 10 ⁶ to about 5 x 10 ⁶ , or from about 1 x 10 ⁶ to about 3 x 10 Within ⁶ limits.

In a system, the first polyethylene contains both PE1 and PE2. In this case, the amount of PE2 in the first polyethylene may range, for example, from 0% by weight to about 50% by weight, or from about 1% by weight to about 50% by weight (based on the weight of the first polyethylene) ).

In a system, the first polyethylene has one or more of the following independently selected features: (1) The first polyethylene comprises PE1.

(2) The first polyethylene system consists essentially of or consists of PE1.

(3) The PE1 is one or more high density polyethylene, medium density polyethylene, branched low density polyethylene, or linear low density polyethylene.

(4) PE1 is one or more high density polyethylene having a Mw in the range of from about 1 x 10 ⁵ to about 5 x 10 ⁵ or from about 2 x 10 ⁵ to about 4 x 10 ⁵ .

(5) PE1 is one of at least (i) an ethylene homopolymer or (ii) a copolymer of ethylene and a third α-olefin (selected from propylene, butene-1, hexene-1).

(6) The first polyethylene contains both PE1 and PE2.

(7) PE2 has a range of from about 1 x 10 ⁶ to about 15 x 10 ⁶ , or optionally from about 1 x 10 ⁶ to about 5 x 10 ⁶ , or optionally from about 1 x 10 ⁶ to about 3 x 10 ⁶ Mw inside.

(8) PE2 is an ultra high molecular weight polyethylene.

(9) PE2 is at least one of (i) an ethylene homopolymer or (ii) a copolymer of ethylene and a third α-olefin (selected from propylene, butene-1, hexene-1).

(10) The first polyethylene has a molecular weight distribution (Mw/Mn) of from about 5 to about 300, or from about 5 to about 100, or optionally from about 5 to about 30.

B. Second polyethylene The second polyethylene may comprise PE1, PE2, or both PE1 and PE2. When the second polyethylene comprises PE1 and PE2, the amount of PE2 in the second polyethylene may range from about 0% to about 50% by weight, or from about 1% to about 50% by weight (based on the second The weight of a polyethylene).

C. First Polypropylene In addition to polyethylene, the first and second microporous layer materials also comprise polypropylene. The polypropylene can be, for example, one or more (i) propylene homopolymer or (ii) a copolymer of propylene and a fifth olefin. The copolymer can be a random or block copolymer. The fifth olefin may be, for example, one or more alpha-olefins (such as ethylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1) , vinyl acetate, methyl methacrylate, and styrene); and diolefins (such as butadiene, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene, etc.) Wait). The amount of the fifth olefin in the copolymer is preferably within a range which does not adversely affect the properties of the multilayer microporous film such as heat resistance, pressure resistance, heat shrinkage resistance and the like. For example, the amount of the fifth olefin can be less than 10 mole percent (based on 100 mole percent of the total copolymer). Optionally, the polypropylene may have one or more of the following properties: (i) the polypropylene has a Mw in the range of from about 1 x 10 ⁴ to about 4 x 10 ⁶ , or from about 3 x 10 ⁵ to about 3 x 10 ⁶ (ii) the polypropylene has a Mw/Mn system in the range of from about 1.01 to about 100, or from about 1.1 to about 50; (iii) the stereotacticity of the polypropylene is isotactic; Iv) the heat of fusion of the polypropylene is at least about 90 J/g; (v) the second melting peak of the polypropylene (second melting) is at least about 160 ° C; (vi) when at a temperature of about 230 ° C The specific measured Trouton's ratio of the polypropylene measured at a strain rate of 25 sec ^-1 is at least about 15; and/or (vii) at a temperature of about 230 ° C and a strain rate of 25 seconds. ^{At -1} , the polypropylene has a tensile viscosity of at least about 50,000 Pa seconds. Optionally, the polypropylene has an Mw/Mn ranging from about 1.01 to about 100, or from about 1.1 to about 50.

D. The second polypropylene second polypropylene preferably has a weight average molecular weight of 6 × 10 ⁵ or more, and a heat of fusion ΔHm of 90 J/g or higher (according to JIS K7122, by differential scanning calorimetry The polypropylene portion having a molecular weight of 5 × 10 ⁴ or less was measured by a meter (DSC) to be 5% by mass or less. The temperature rise rate for measuring the heat of fusion is preferably 3-20 ° C / min, usually 10 ° C / min. Since the polypropylene having a weight average molecular weight of less than 6 × 10 ⁵ has low dispersibility in the polyethylene resin, its use makes stretching difficult, and imparts a large amount of microscopic roughness to the surface of the second porous layer and makes the multilayer micro The thickness variation of the porous film is large. When the molecular weight is 5 x 10 ⁴ or less, the portion of the polypropylene is more than 5% (based on the mass of the polypropylene), the multilayer microporous film may have an undesirable low melting property. When the heat of fusion ΔHm of polypropylene is less than 90 J/g, the resulting multilayer microporous membrane has low melting properties and permeability.

The weight average molecular weight of the second polypropylene is preferably 6.5 × 10 ⁵ or more, more preferably 8 × 10 ⁵ or more. The polypropylene portion having a molecular weight of 5 × 10 ⁴ or less is preferably 4.5% by mass or less, more preferably 3% by mass or less (based on the mass of the polypropylene). The heat of fusion ΔHm of the polypropylene is preferably 95 J/g or more, more preferably 100 J/g or more. The molecular weight distribution, Mw/Mn, is preferably 5 or less, more preferably 4 or less, most preferably 2.5 or less.

Preferably, (1) if the weight average molecular weight of the polypropylene is from 6 × 10 ⁵ to 1 × 10 ⁶ or less, the Mw / Mn of the polypropylene is 2.5 or less; (2) if the weight average molecular weight is 1.5×10 ⁶ or less, Mw/Mn is 3 or less; (3) Mw/Mn is 4 or less if the weight average molecular weight is 2×10 ⁶ or less; and (4) If the weight When the average molecular weight is 2 × 10 ⁶ or more, the Mw / Mn is 5 or less.

The amount of polypropylene in the second layer of material can be, for example, about 5-95 mass Within the range of %, but preferably 20-80% by mass, more preferably 30-70% by mass (based on the mass of the second layer material). When the amount of polypropylene is less than 20% by mass, the melting temperature may be less desirable. When the amount of polypropylene exceeds 80% by mass, the multilayer microporous film tends to have an undesired thickness uniformity and permeability.

As long as the weight average molecular weight, the molecular weight of 5 × 10 ⁴ or less (measured by the molecular weight distribution), and the heat of fusion are satisfied, the type of the polypropylene is not particularly limited, but it may be propylene. The polymer, a copolymer of propylene with other α-olefins or a mixture thereof, is preferably a homopolymer. The copolymer can be a clutter or block copolymer. The α-olefin, comonomer in the polypropylene copolymer may include, for example, ethylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene, vinyl acetate. Ester, methyl methacrylate, styrene, and combinations thereof. Optionally, the polypropylene may have one or more of the following properties: (i) the polypropylene has a Mw of from about 1 x 10 ⁴ to about 4 x 10 ⁶ , or from about 6 x 10 ⁵ to about 3 x 10 ⁶ (ii) the polypropylene has a Mw/Mn in the range of from about 1.01 to about 100, or from about 1.1 to about 50; (iii) the stereoregularity of the polypropylene is uniform; (iv) The polypropylene has a heat of fusion of at least about 95 J/g; (v) the polypropylene has a melting peak (second melt) of at least about 160 ° C; (vi) when at about 230 ° C The specific Trowton's ratio of the polypropylene measured at a temperature and measured at a strain rate of 25 sec ^-1 is at least about 15; and/or (vii) at a temperature of about 230 ° C and a strain rate of 25 sec ^-1, extensional viscosity of the polypropylene is at least about 50,000 Pa sec.

The Mw and Mn of the polypropylene can be measured by, for example, GPC under the following conditions. Measuring device: Alliance 2000 GPC, available from Waters Corp.; column: three PL Gel Mix-B, available from Polymer Laboratories. Column temperature: 145 ° C, solvent (mobile phase): 1,2,4-trichlorobenzene, stabilized with 0.1% by weight of BHT, 6 g / 4L. Solvent flow rate: 1.0 ml/min. Sample concentration: 0.25 mg/mL (dissolved at 175 ° C for 1 hour). Injection volume: 300 μl. Detector: Differential Refractometer, available from Waters Corp. Calibration curve: A pre-measured conversion constant was generated from a calibration curve for a set of monodisperse, standard polystyrene samples.

The heat of fusion ΔHm of polypropylene can be measured according to JIS K7122 as follows: in a sample holder of a differential scanning calorimeter (DSC-System 7, available from Perkin Elmer Inc.), The PP sample was heat-treated at 190 ° C for 10 minutes in a nitrogen atmosphere, cooled to 40 ° C at a rate of 10 ° C / minute, kept at 40 ° C for 2 minutes, and heated at 10 ° C / minute to 190 ° C. As shown in the first figure, the line through the point on the DSC curve (melting curve) obtained by the temperature rise process at 85 ° C and 175 ° C can be plotted as a baseline, and the amount of heat can be surrounded by the baseline and the DSC curve. The diagonal portion of the area is calculated by the area S1. The heat of fusion (unit: J) is divided by the amount of heat (unit: J) to determine the heat of fusion ΔHm (unit: J/g).

The percentage (based on mass) of the polypropylene fraction having a molecular weight of 5 × 10 ⁴ or less can be measured as follows. The GPC curve in the second graph and the oblique portion around the base clue, region S2, can be measured to determine the amount of the entire polypropylene sample. The region S3 in the third graph can be measured to determine the amount of the molecular weight system having a portion of 5 × 10 ⁴ or less. The percentage of the fraction having a molecular weight of 5 × 10 ⁴ or less is calculated from (S3 / S2) × 100 (% by mass).

[2] Substance for producing a multilayer microporous polyolefin film

A. Polymer resin used to make the first microporous layer material In one system, the first microporous layer material is made from the first polyolefin solution. The first polyolefin solution comprises a first polyolefin composition and a first processing solvent. Since this process produces a multilayer microporous membrane, the processing solvent is also referred to as a diluent or film forming solvent. The resins used to make the first polyolefin composition are described in more detail below.

(1) The first polyethylene resin In a system, the first polyethylene resin comprises a first polyethylene, the first of which is as described in the previous paragraph [1]. For example, the first polyethylene resin may be a mixture of a polyethylene resin having a lower Mw than UHMWPE (such as HDPE) and a UHMWPE resin.

The molecular weight distribution (Mw/Mn) of the polyethylene in the first polyethylene resin is not strictly limited. Mw/Mn is a measure of molecular weight distribution, and the larger the value, the broader the molecular weight distribution. Although not strictly limited, the polyethylene Mw/Mn in the first polyethylene resin may be, for example, in the range of from about 5 to about 300, or in the range of from about 5 to about 100, or at about 5 to Approximately 30. When Mw/Mn is less than 5, it will be more difficult to squeeze out the first A polyethylene resin. On the other hand, when Mw/Mn is more than 300, it is more difficult to produce a relatively strong multilayer microporous film. A multistage polymerization process can be used to obtain the Mw/Mn in the first polyethylene resin desired. For example, a two-stage polymerization process can be employed to form a relatively higher molecular weight polymer component in the first stage and a relatively lower molecular weight polymer component in the second stage. Although not essential, for example, when the first polyethylene resin contains PE1, this method can be employed. When the first polyethylene resin comprises PE1 and PE2, the Mw/Mn ratio of the desired polyethylene resin can be selected by adjusting the relative molecular weight and relative amount of the first and second polyethylenes.

(2) The first polypropylene resin In addition to the first polyethylene resin, the first polyethylene composition also contained the first polypropylene resin. In a system, the first polypropylene resin comprises a first polypropylene, wherein the first polypropylene is as described in the previous paragraph [1]. The first polypropylene resin can be, for example, one or more (i) propylene homopolymer or (ii) a copolymer of propylene and a fifth olefin. The copolymer can be a clutter or block copolymer. The fifth olefin may be, for example, one or more alpha-olefins (such as ethylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1) , vinyl acetate, methyl methacrylate, and styrene, etc.; and diolefins (such as butadiene, 1,5-hexadiene, 1,7-octadiene, 1,9-fluorene) Alkene, etc.). The amount of the fifth olefin in the copolymer should not be such as to the properties of the multilayer microporous membrane (such as heat resistance, pressure resistance, heat shrinkage, etc.) There are negative effects within the scope. For example, the amount of the fifth olefin can be less than 10 mole percent (based on 100 mole percent of the total copolymer).

Although not strictly limited, the Mw of the polypropylene in the first polypropylene resin may be, for example, in the range of about 1 × 10 ⁴ to about 4 × 10 ⁶ or about 3 × 10 ⁵ to about 3 × 10 ⁶ Within the scope. Although not strictly limited, the molecular weight distribution (Mw/Mn) of the polypropylene in the first polypropylene resin may range from about 1.01 to about 100, or from about 1.1 to about 50.

(3) Formula The amount of processing solvent in the first polyolefin solution can range, for example, from about 25% to about 99% by weight based on the weight of the first polyolefin solution. In one system, the amount of polyethylene resin in the first polyolefin composition can range, for example, from about 50% to about 99% by weight based on the weight of the first polyolefin composition. The remainder of the first polyolefin composition is polypropylene.

B. Polymer used to make the second microporous layer material In one system, the second microporous layer material is made from a second polyolefin solution (the selection of which is independent of the first polyolefin solution). The second polyolefin solution comprises a second polyolefin composition and a second processing solvent (this solvent can be the same as the first processing solvent). As in the case of the first polyolefin solution, the second processing solvent can be referred to as a second film forming solvent or a second diluent. In one system, the second polyolefin composition comprises a second polyethylene resin and a second polypropylene resin. second The polyethylene resin may comprise the second polyethylene described in the above paragraph [1]. The second polypropylene resin comprises the second polypropylene described in the above paragraph [1].

The amount of processing solvent in the second polyolefin reaction solution can range, for example, from about 25% to about 99% by weight based on the weight of the second polyolefin solution. In one system, the amount of the second polyethylene resin in the second polyolefin composition can range, for example, from about 5% by weight to about 95% by weight based on the weight of the second polyolefin composition. . The remainder of the second polyolefin composition can be a second polypropylene.

C. The third polyolefin, although not essential, each of the first and second polyolefin compositions may further comprise a third polyolefin selected from the group consisting of polybutene-1, polypentene-1, poly 4-methylpentene-1, polyhexene-1, polyoctene-1, polyvinyl acetate, polymethyl methacrylate, polystyrene, and ethylene alpha-olefin copolymer (except ethylene-propylene copolymer) Outside). In the system in which the third polyolefin is used, the third polyolefin may, for example, have a Mw in the range of from about 1 x 10 ⁴ to about 4 x 10 ⁶ . In addition to the third olefin, the first and/or second polyolefin composition may further comprise a polyethylene wax, for example, having a Mw in the range of from about 1 x 10 ³ to about 1 x 10 ⁴ . When used, such species should be present in an amount that is less than would cause the desired properties (e.g., melting, shutdown, etc.) of the multilayer microporous membrane to deteriorate. When the third polyolefin is one or more of the following: polybutene-1, polypentene-1, poly-4-methylpentene-1, polyhexene-1, polyoctene-1, poly Vinyl acetate, polymethyl methacrylate, and polystyrene, the third polyolefin need not be a homopolymer, but may be a copolymer containing other α-olefins.

Multilayer microporous membranes typically comprise a polyolefin for forming a polyolefin solution. It is also possible that a small amount of cleaning solvent and/or processing solvent is present, which is typically less than 1% by weight (based on the weight of the microporous polyolefin film). A small amount of polyolefin molecular weight reduction may occur during processing, but this is acceptable. In a system, if the molecular weight decreases during the processing, the Mw/Mn value of the polyolefin in the film is different from the Mw/Mn of the first or second polyolefin solution by no more than about 50%. Or no more than about 1%, or no more than about 0.1%.

[3] Method for producing multilayer microporous polyolefin film

In a system, the microporous polyolefin membrane is a bilayer membrane. In another system, the microporous polyolefin membrane has at least three layers. For the sake of brevity, the manufacture of microporous polyolefin membranes will mainly be described by two-layer and three-layer membranes, but it is recognized by those skilled in the art that the same technique can be applied to membranes or membranes having at least four layers. Manufacturing.

In one system, the three-layer microporous polyolefin film comprises first and third layers of microporous layers constituting the outer layer of the microporous polyolefin film, and between the first and third layers (and optionally with The second layer, which is in a plane contact. In one system, the first and third layers are produced from a first polyolefin solution and the second layer (inner layer) is produced from a second polyolefin solution. In another system, the first and third layers are produced from a second polyolefin solution and the second layer is produced from a first polyolefin solution.

A. The first manufacturing method The first method of making a multilayer film comprises the steps of: (1) preparing a first polyolefin solution by combining a first polyolefin composition and a film forming solvent (for example, by melt blending), (2) Forming a second polyolefin solution by combining a second polyolefin composition with a second film, (3) extruding the first and second polyolefin solutions (preferably simultaneously) through at least a mold to form an extrudate, (4) cooling the extrudate to form a cooled extrudate, for example, a multi-layer gel-like sheet, (5) removing the film from the multi-layer sheet Forming a solvent to form a solvent-removed sheet, and (6) drying the solvent-removed gel-like sheet to remove any volatile species present to form a multilayer microporous polyolefin membrane. Optionally, between steps (4) and (5), a selective stretching step (7) and a selective thermal solvent treatment step (8) may be performed. If necessary, after step (6), a selective step (9) of stretching the multilayer microporous membrane, a selective heat treatment step (10), a selective crosslinking step (11) using free radiation, and Selective hydrophilic treatment step (12) and the like. The order in which these optional steps are performed is not important.

(1) Preparation of the first polyolefin solution The first polyolefin composition comprises a polyolefin resin as hereinbefore described which can form a solvent with a suitable film, for example, by dry mixing or melt blending, and combined to produce a first polyolefin solution. Optionally, the first multiolefin The solution may contain various additives such as one or more of the following: an antioxidant, a fine cerium oxide powder (a substance forming a pore), etc., provided that the concentration range used by them does not significantly lower the multilayer micro The desired properties of porous polyolefin membranes.

The first processing solvent (i.e., the first film forming solvent) is preferably a solvent which is liquid at room temperature. While not wishing to be bound by any theory or mode, it is believed that the use of a liquid solvent to form the first polyolefin solution makes it possible to stretch the gelatinous sheet at a relatively high draw ratio. In a system, the first film forming solvent may be at least one of the following: an aliphatic, alicyclic or aromatic hydrocarbon such as decane, decane, decahydronaphthalene, p-xylene, undecane. , dodecane, liquid paraffin, etc.; a mineral oil distillate having a boiling point comparable to the aforementioned hydrocarbons; and a phthalate liquid at room temperature, such as dibutyl phthalate, dioctyl phthalate, and the like. In a system for obtaining a multi-layered gel-like sheet having a stable liquid solvent content, a non-volatile liquid solvent such as liquid paraffin may be used alone or in combination with other solvents. Optionally, a solvent which is miscible with polyethylene in a melt blending state but which is solid at room temperature may be used, which may be used alone or in combination with a liquid solvent. The solid solvent may include, for example, stearyl alcohol, cetyl alcohol, paraffin wax, and the like. Although not strictly limited, it is more difficult to stretch the gel-like sheet or the obtained film evenly when the solution does not contain a liquid solvent.

The viscosity of the liquid solvent is not a decisive parameter. For example, the viscosity of the liquid solvent can range from about 30 cSt to about 500 cSt, or from about 30 cSt to about 200 cSt (25 ° C). Although it is not a decisive parameter However, when the viscosity at 25 ° C is less than about 30 cSt, it is more difficult to prevent foaming of the polyolefin solution, which causes difficulty in blending. On the other hand, when the viscosity is greater than about 500 cSt, it is more difficult to remove the liquid solvent from the multilayer microporous polyolefin film.

In a system, the resin or the like for producing the first polyolefin composition is, for example, a twin roll extruder or a mixer, and is subjected to dry mixing or melt blending. For example, conventional extruders (or mixers or mixer-extruders), such as twin-roll extruders, can be used to combine resins and the like to form a first polyolefin composition. A film forming solvent may be added to the polyolefin composition (or alternatively added to the resin used to produce the polyolefin composition) at any convenient point in the process. For example, when the first olefin composition is melt blended with the first film forming solvent, the solvent may be (i) melt blended in the first polyolefin composition before (i) starting melt blending. During the period, or (iii) any point after melt blending, added to the polyolefin composition (or a component thereof), for example, by a second extruder or located for melt blending the polyolefin composition In the region of the extruder downstream of the extruder zone, the first film forming solvent is added to the melt blended or partially melt blended polyolefin composition.

When melt blending is employed, there is no strict limit to the melt blending temperature. For example, the melt blending temperature of the first polyolefin solution may be about 10 ° C higher than the melting point Tm _{1 of the} first polyethylene resin. It is about 20 ° C higher than Tm ₁ temperature range. For the sake of brevity, the range can be expressed as Tm ₁ +10 ° C to Tm ₁ +120 ° C. In the system wherein the first polyethylene resin has a melting point of from about 130 ° C to about 140 ° C, the melt blending temperature may range from about 140 ° C to about 250 ° C, or from about 170 ° C to about 240 ° C.

When an extruder (such as a twin roll extruder) is used for melt blending, the parameters of the roll are not critical. For example, the roll may be characterized in that the ratio L/D of the roll length L to the roll diameter D of the twin roll extruder may range, for example, from about 20 to about 100, or from about 35 to about 70. Although there are no strict limits on this parameter, melt blending will be more difficult when L/D is less than about 20, and when L/D is greater than about 100, faster extruder speeds may be required to prevent The residence time of the polyolefin solution in the twin roll extruder is too long (this can result in undesirable molecular weight reduction). Although not a decisive parameter, the extrusion barrel (or orifice) of the twin roll extruder can have, for example, an inner diameter in the range of from about 40 mm to about 100 mm.

The amount of the first polyolefin composition in the first polyolefin solution is not strictly limited. In one system, the amount of the first polyolefin composition in the first olefin solution may range from about 1% by weight to about 75% by weight (based on the weight of the polyolefin solution), for example, about 20% by weight to About 70% by weight. Although the amount of the first polyolefin composition in the first polyolefin solution is not strictly limited, when the amount is less than about 1% by weight, it will be more difficult to produce a multilayer microporous at an acceptable sufficient rate. Polyolefin film. Further, when the amount is less than 1% by weight, it will be more difficult to prevent swelling or narrowing at the exit of the mold during extrusion, and it is difficult to form and support the multilayered gel-like sheet (which is formed during the manufacturing process) Precursor of the membrane). On the other hand, when the first polyolefin composition in the first polyolefin solution When the amount is more than 75% by weight, it will be more difficult to form a multilayer gel-like sheet. The amount of the first polyethylene is preferably from 1 to 50% by mass, more preferably from 20 to 40% by mass (relative to the first polyolefin solution per 100% by mass). When the polyethylene resin is less than 1% by mass, during the extrusion of the first olefin solution to form a gel-like molded article, expansion or narrowing occurs at the exit of the mold, resulting in molding of the gel-like molded product. Sex and self-supporting are reduced. On the other hand, when the polyethylene resin is less than 50% by mass, the moldability of the gel-like molded product is deteriorated.

(2) Preparation of a second polyolefin solution The second polyolefin solution can be prepared by the same method as used in the preparation of the first polyolefin solution. For example, a second polyolefin solution can be prepared by melt blending a second polyolefin composition with a second film forming solvent. The second film forming solvent may be selected from the same solvent as the first film forming solvent. Although the second film forming solvent may (and usually is) independently selected from the first film forming solvent, the second film forming solvent may be the same as the first film forming solvent, and may form a solvent with the first film. The same relative concentration is used for the first olefin solution.

The second polyolefin composition is typically independently selected from the first olefin composition. The second olefin composition comprises a second polyethylene and a second polypropylene resin.

In a system, the method for preparing the second polyolefin solution differs from the method for preparing the first polyolefin solution in that the mixing temperature is preferably at the melting point (Tm ₂ ) of the second polypropylene to Tm ₂ +90 ° C. The amount of the polyolefin composition is preferably in the range of from 1 to 50% by mass, more preferably from 20 to 40% by mass.

(3) Squeeze In one system, the first polyolefin solution is directed from the first extruder to the first mold and the second polyolefin solution is directed from the second extruder to the second mold. From the first and second molds, a layered, sheet-like extrudate (i.e., an object having a substantially larger planar direction than the thickness direction) can be extruded. Optionally, the first and second polyolefin solutions are coextruded from the first and second molds such that the planar surface of the first extrudate layer formed by the first polyolefin solution The planar surface of the second extrudate layer formed by the second polyolefin solution is in contact. The planar surface of the extrudate can be defined by a first vector in the machine direction of the extrudate and a second vector in the transverse direction of the extrudate.

In a system, a module can be used, wherein a die assembly includes a first mold and a second mold, as, for example, when the first mold and the second mold are shared in the module The area of one polyolefin solution and the module contain the same compartment between the second area of the second polyolefin solution.

In another system, multiple molds can be used, each mold being attached to an extruder to direct the first or second polyolefin solution to the mold. For example, in one system, the first extruder containing the first polyolefin solution is attached to the first mold and the third mold, and the extruder containing the second polyolefin solution is attached to The second mold. As in the case of the foregoing system, the resulting layered extrudate can be from the first, second, and third modes. Coextruding (eg, simultaneously) to form a three layer extrudate comprising first and third layers (eg, top and bottom layers) constituting the surface layer formed from the first polyolefin solution, and constituting An intermediate layer of the extrudate and a second layer between the two surface layers in planar contact with the second layer, wherein the second layer is formed from a second polyolefin solution.

In yet another system, the same module is used, but the polyolefin solution is reversed, that is, the second extruder containing the second polyolefin solution is connected to the first mold and the third The mold, and the first extruder containing the first polyolefin solution is attached to the second mold.

In any of the foregoing systems, conventional die extrusion equipment can be used for die extrusion. For example, the extrusion can be performed by a flat die or an inflation die. In a system that can be used to coextrude a multilayer gel-like sheet, a multi-manifold extrusion can be employed in which the first and second polyolefin solutions are directed to a multilayer extrusion die. The individual manifolds are layered on the lip outlet. In another system, a block extrusion process may be employed in which the first and second polyolefin solutions are first combined into a laminar flow (i.e., previously), and then the laminar flow can be attached to the mold. . Since the multi-port extrusion method and the block extrusion method are known to those skilled in the art of polyolefin film processing, for example, as disclosed in JP06-122142 A, JP 06-106599 A, they are Methods are considered as learners and their operation methods are not described in detail.

The selection of the mold is not strictly limited, and for example, a flat mold or an inflatable mold which is conventionally used to form a multilayer sheet may be employed. The mold gap is not strictly limited. For example, a flat mold forming a multilayer sheet may have about 0.1 mm To a mold gap of about 5 mm. The mold temperature and extrusion speed are also not strictly set parameters. For example, during extrusion, the mold can be heated to a mold temperature in the range of from about 140 °C to about 250 °C. The extrusion speed can range, for example, from about 0.2 m/min to about 15 m/min. The layer thickness of the layered extrudate can be selected independently. For example, the gelatinous layer may have a relatively thicker surface layer (or "skin" layer) (as compared to the thickness of the intermediate layer of the layered extrudate).

Although the extrusion process has been illustrated by the system for producing two and three layers of extrudate, the extrusion steps are not limited to those systems. For example, a plurality of molds and/or modules can be used to produce a multilayer extrudate having four or more layers using the methods described in the foregoing systems. In such a layered extrudate, each surface or intermediate layer can be made using a first polyolefin solution and/or a second polyolefin solution.

(4) Formation of multilayer gelatinous sheet The multilayer extrudate can be formed into a multi-layer gel-like sheet by, for example, cooling. The cooling rate and cooling temperature are not particularly limited. For example, the multilayer gel-like sheet can be cooled to a temperature at a cooling rate of at least about 50 ° C/min to a temperature at which the multilayer gel-like sheet (cooling temperature) is approximately equal to the gelation of the multilayer gel-like sheet. Temperature (or lower temperature). In a system, the extrudate is cooled to a temperature of about 25 ° C or less to form a multilayer gel-like sheet. While not wishing to be bound by any theory or mode, it is believed that the cooling of the layered extrudate determines the polyamines of the first and second polyolefin solutions separated by one or several film forming solvents. Hydrocarbon microphase. I have observed that, in general, a slower cooling rate (for example, less than 50 ° C / min) can provide a multi-layer gel-like sheet with a larger pseudo-cell unit, resulting in coarser The higher-order structure. On the other hand, a relatively fast cooling rate (for example, 80 ° C / min) will result in a denser unit cell. Although not a decisive parameter, when the cooling rate of the extrudate is less than 50 ° C / min, the crystallinity of the polyolefin in the layer may be increased, so that the multilayer gel-like sheet in the subsequent stretching step The processing of the object is difficult to carry out. The choice of cooling method is not strictly limited. For example, a conventional sheet cooling method can be employed. In a system, the cooling process involves contacting the layered extrudate with a cooling medium such as cooling air, cooling water, and the like. Also. Alternatively, the extrudate may be cooled by contact with a roller cooled by a cooling medium or the like.

(5) removing the first and second film forming solvents in a system, removing (or replacing) at least a portion of the first and second film forming solvents from the multilayer gel-like sheet to form A gelatinous sheet in which the solvent has been removed. The substitution and (or "cleaning" of the solvent) can be used to remove (wash off, or replace) the first and second film forming solvents. While not wishing to be bound by any theory or mode, we believe that the polyolefin phase and film forming solvent in the multilayer gel-like sheet produced by the first polyolefin solution and the second polyolefin solution Separately, the removal of the film forming solvent provides a porous film composed of fibrils forming a fine three-dimensional network structure and having pores which are three-dimensionally and irregularly communicated. The choice of cleaning solvent is not critical as long as it is capable of dissolving or replacing at least a portion of the first and/or second film forming solvent. Suitable cleaning solvents include, for example, one or more volatile solvents such as saturated hydrocarbons such as pentane, hexane, heptane, etc.; chlorinated hydrocarbons such as dichloromethane, tetrachlorinated Carbon or the like; ethers such as diethyl ether, dioxane, etc.; ketones such as methyl ethyl ketone and the like; linear fluorocarbons such as trifluoroethane, C ₆ F ₁₄ , C ₇ F ₁₆ or the like; a cyclic hydrofluorocarbon such as C ₅ H ₃ F ₇ or the like; a hydrofluoroether compound such as C ₄ F ₉ OCH ₃ , C ₄ F ₉ OC ₂ H _{5 ,} etc.; a fluoroether compound such as C ₄ F ₉ OCF ₃ , C ₄ F ₉ OC ₂ F ₅ or the like.

The method of removing the film forming solvent is not critical, and any method capable of removing a significant amount of a solvent, including a conventional solvent removal method, may be employed. For example, the multilayer gel-like sheet can be washed by immersing the multi-layer gel-like sheet in a washing solvent and/or rinsing with a washing solvent. The amount of cleaning solvent used is not critical and is generally dependent upon the method chosen to remove the film forming solvent. For example, the amount of cleaning solvent used can range from about 300 to about 30,000 parts by mass based on the mass of the gelatinous sheet. Although there is no particular strict limit on the amount of solvent for forming a film, when at least a large amount of the first and second film forming solvents are removed from the gel-like sheet, it usually causes a higher quality. A (more porous) film is produced. In a system, the film forming solvent is removed from the gel-like sheet (for example, by washing) until the amount of the remaining film forming solvent in the multilayer gel-like sheet becomes less than 1% by weight (based on the gel) The weight of the sheet is as long as it is.

(6) drying the gel-like sheet from which the solvent has been removed in a system, and drying the solvent-removed multilayer gel-like sheet obtained by removing at least a part of the film forming solvent to remove the cleaning solvent . Any method capable of removing the cleaning solvent may be employed, including conventional methods such as heat drying, air drying (moving air), and the like. The temperature of the gelatinous sheet (i.e., the drying temperature) during drying is not strictly limited. For example, the drying temperature may be equal to or lower than the crystal dispersion temperature Tcd. Tcd-based polyethylene resin of the first crystal dispersion temperature _{Tcd. 1} and the second polyethylene resin (if using the time) of the crystal dispersion temperature Tcd of the lower _2. For example, the drying temperature may be at least less than 5 ° C than the crystal dispersion temperature Tcd. The crystal dispersion temperature of the first and second polyethylene resins can be determined by measuring the temperature characteristics of the dynamic viscoelasticity of the polyethylene resin in accordance with ASTM D 4065. In one system, at least one of the first or second polyethylene resins has a crystal dispersion temperature in the range of from about 90 °C to about 100 °C.

Although not strictly set, the drying can be carried out until the amount of the remaining cleaning solvent is about 5% by weight or less (dry basis, that is, based on the weight of the dried multilayer microporous polyolefin film). In another system, the drying is carried out until the amount of the remaining washing solvent is about 3% by weight or less (dry basis). Insufficient drying is identifiable because it generally results in an undesirable increase in the porosity of the multilayer microporous membrane. If this is observed, the drying temperature should be increased and/or the drying time increased. Removal of the cleaning solvent by, for example, drying or other methods can result in the production of a multilayer microporous polyolefin film.

(7) Stretching Prior to the step of removing the film forming solvent (i.e., before step 5), the multilayer gel-like sheet may be stretched to obtain a stretched multilayer gel-like sheet. It is believed that the presence of the first and second film forming solvents in the multilayer gel-like sheet can result in a relatively uniform draw ratio. Heating the multilayer gel-like sheet, especially at the beginning of stretching or at a relatively early stage of stretching (for example, before 50% of the stretching is completed), is believed to contribute to the uniformity of stretching.

Regardless of the choice of stretching method or the degree of stretching ratio, there are no particularly strict limits. For example, any method capable of stretching a multilayer gel-like sheet to a predetermined rate (including any selective heating) can be used. In a system, it can be accomplished by one or more of the following: tenter-stretching, roller-stretching, or inflation stretching (for example, Use air). Although there are no strict limits on the selection, the stretching can be performed either uniaxially (i.e., in the machine or transverse direction) or biaxially (in the machine and transverse directions). In a system, biaxial stretching can be employed. In the case of biaxial stretching (also known as biaxial orientation), the stretching can be simultaneous biaxial stretching, first along a plane axis and then along another axis, or in multiple stages of stretching. Stretching (for example, a combination of simultaneous biaxial stretching and continuous stretching). In a system, simultaneous biaxial stretching is employed.

The draw ratio is not strictly limited. In a system employing uniaxial stretching, the linear stretching ratio may be, for example, about 2 times or more, or about 3 Up to about 30 times. In the system employing biaxial stretching, the linear stretching ratio may be, for example, about 3 times or more (in the plane direction). In another system, the area magnification produced by stretching is at least about 9 times, or at least about 16 times, or at least about 25 times. Although not a decisive parameter, the multilayer microporous polyolefin film will have a relatively high pin compressive strength when stretch results in an area multiplication of at least about 9 times. When an area magnification greater than about 400 times is reached, it will be more difficult to operate the stretching device.

The temperature (i.e., stretching temperature) of the multilayer gel-like sheet during stretching is not strictly limited. In a system, the temperature of the gelatinous sheet during stretching may be about (Tm + 10 ° C) or lower, or optionally in a range higher than Tcd but lower than Tm, wherein Tm a first melting point of the polyethylene-based and the second polyethylene Tm ₁ (if used) of a melting point Tm ₂ is smaller. Although this parameter is not strictly limited, when the stretching temperature is higher than about the melting point Tm + 10 ° C, at least one of the first or second polyethylene is in a molten state, which causes multiple layers during stretching. The orientation of the polyolefin molecular chains within the gelatinous sheet is more difficult. And when the stretching temperature is lower than about Tcd, at least one of the first or second polyethylene may be insufficiently softened, and it is difficult to stretch the multilayer gel-like sheet without breaking or tearing. This will result in the desired draw ratio not being achieved. In one system, the stretching temperature is in the range of from about 90 ° C to about 140 ° C, or in the range of from about 100 ° C to about 130 ° C.

While not wishing to be bound by any theory or mode, it is believed that stretching would cause peeling between the thin layers of polyethylene, making the polyethylene phase more slender and forming a large amount of fibrils. These fibrils form a three-dimensional network structure (Dimensional irregularly connected mesh structure). Thus, stretching, if employed, generally results in a relatively high mechanical strength and a relatively large pore size multilayer microporous polyolefin film that is easier to manufacture. Such as a multilayer microporous membrane is considered to be particularly suitable for use as a battery separator.

Optionally, the stretching can be carried out in the presence of a temperature gradient in the thickness direction (i.e., in a direction approximately perpendicular to the planar surface of the multilayer microporous polyolefin film). In this case, it is easy to manufacture a multilayer microporous polyolefin film having improved mechanical strength. The details of this method are described in Japanese Patent No. 3347854.

(8) Hot solvent treatment steps Although not required, between steps (4) and (5), the multilayer gel-like sheet may be treated with a hot solvent. In use, it is believed that the thermal solvent treatment can provide a relatively thick vein structure for fibrils, such as those formed by stretching a multi-layer gel-like sheet. The term "leaf vein" refers to a thin fiber in which the fibrils have a thick backbone and which extend out of a network structure. The details of this method are described in WO 2000/20493.

(9) Stretching of a multilayer microporous membrane ("dry stretching") In a system, the dried multilayer microporous membrane of step (6) can be at least uniaxially stretched. There is no strict limitation on the selected stretching method, and a conventional stretching method such as stretching by a tenter type or the like can be employed. Although not strictly limited, the film can be heated during the stretching process. Although there are no strict restrictions on the selection, the stretching can be uniaxial or biaxial. When adopted In biaxial stretching, the stretching may be carried out simultaneously in two axial directions, or alternatively, the multilayer microporous polyolefin film may be stretched in a continuous manner, for example, first in the machine direction and then in the transverse direction. In a system, simultaneous biaxial stretching is employed. When the multilayer gel-like sheet has been stretched as described in the step (7), the stretching of the dried multilayer microporous polyolefin film of the step (9) is referred to as dry stretching, re-stretching or dry orientation. (dry-orientation).

The temperature of the dried multilayer microporous film during stretching ("dry stretching temperature") is not strictly limited. In a system, the drying stretching temperature is approximately equal to the melting point Tm or lower, for example, in the range of from about the crystal dispersion temperature Tcd to about the melting point Tm. When the drying stretching temperature is higher than Tm, it will be more difficult to produce a relatively high pressure resistance and have relatively uniform air permeability characteristics, especially in the transverse direction (when the dried multilayer microporous polyolefin film is transversely pulled) When stretched out). When the stretching temperature is lower than Tcd, it will be more difficult to sufficiently soften the first and second polyolefins, causing tearing during stretching, and lacking uniform stretching. In a system, the dry stretching temperature can range from about 90 ° C to about 135 ° C, or from about 95 ° C to about 130 ° C.

When dry stretching is employed, the draw ratio is not strictly limited. For example, the stretching ratio of the multilayer microporous film may be in the range of about 1.1 times to about 1.8 times in at least one plane (for example, the side) direction. Therefore, in the case of uniaxial stretching, the stretching ratio in the longitudinal direction (i.e., the "mechanical direction" or the transverse direction (depending on the longitudinal or transverse stretching of the film system) may be about 1.1 times to about Within a range of 1.8 times, uniaxial stretching can also be done along a plane axis between the longitudinal and transverse directions.

In a system, biaxial stretching is carried out at a draw ratio of about 1.1 times to about 1.8 times along two stretching axes (for example, both in the machine direction and in the cross direction). The stretching ratio in the longitudinal direction need not be the same as the stretching ratio in the transverse direction. In other words, in the case of biaxial stretching, the stretching ratio can be independently selected. In one system, the dry draw ratios in the two directions of stretching are the same.

(10) Heat treatment In a system, the dried multilayer microporous membrane can be heat treated in accordance with step (6). It is believed that the heat treatment stabilizes the polyolefin crystals in the dried multilayer microporous polyolefin film to form a uniform thin layer. In one piece, the heat treatment comprises heat setting and/or annealing. When heat setting is employed, it can be carried out using conventional methods such as a tenter type method and/or a roller type method. Although not strictly limited, the temperature of drying the multilayer microporous polyolefin film (i.e., "heat setting temperature") during heat setting may range from Tcd to about Tm. In one system, the heat setting temperature may be in the range of about ± 5 ° C of the dry stretching temperature of the multilayer microporous polyolefin film, or about ± 3 ° C of the dry stretching temperature of the multilayer microporous polyolefin film.

Annealing differs from heat setting in that it is a heat treatment without applying a load to the multilayer microporous polyolefin film. The selection of the annealing method is not strictly limited, and it can be carried out by using, for example, a heating chamber equipped with a belt conveyor or an air floating heating chamber. Alternatively, the annealing may be performed after heat setting (tenter clips relaxation). The temperature (i.e., annealing temperature) of the multilayer microporous polyolefin film during annealing is not strictly limited. In a system, the annealing temperature can be about the melting point Tm Or lower, or in the range of about 60 ° C to (Tm - 10 ° C). I believe that annealing will make the fabrication of multilayer microporous polyolefin membranes with relatively high permeability and strength less difficult.

(11) Cross-linking In a system, after step (6), the multilayer microporous polyolefin film can be crosslinked (e.g., by free radiation rays such as alpha rays, beta rays, gamma rays, electron beams, etc.). For example, when a beam of radiation electrons is used for crosslinking, the amount of electron beam radiation can range from about 0.1 Mrad to about 100 Mrad, and the acceleration voltage employed is in the range of about 100 kV to about 300 kV. It is believed that the cross-linking treatment will make the fabrication of the multilayer microporous polyolefin film having a relatively high melting temperature less difficult.

(12) Hydrophilic treatment In a system, the multilayer microporous polyolefin membrane can be subjected to a hydrophilic treatment (i.e., a treatment that makes the multilayer microporous polyolefin membrane more hydrophilic). The hydrophilic treatment may be, for example, a monomer graft treatment, a surfactant treatment, a corona treatment, or the like. In a system, after the crosslinking treatment, a monomer graft treatment is employed.

When a surfactant is employed, any of the nonionic surfactants, cationic surfactants, anionic surfactants, and zwitterionic surfactants can be used, for example, alone or in combination. In a system, a nonionic surfactant is used. There is no strict limit to the choice of surfactant. For example, a multilayer microporous polyolefin membrane can be immersed in interfacial activity The solution is applied to a solution of water and a lower alcohol (such as methanol, ethanol, isopropanol, etc.) or, for example, by a casting method.

B. The second manufacturing method A second method for making a multilayer microporous polyolefin film comprises the steps of: (1) forming a first polyolefin composition with a first film to form a solvent (eg, by melt blending) to prepare a first a polyolefin solution, (2) forming a second polyolefin composition with a second film to form a second polyolefin solution, and (3) extruding the first polyolefin solution through the first Moulding and extruding the second solution through the second mold, then laminating the extruded first and second polyolefin solutions to obtain a multilayer extrudate, (4) the multilayer The extrudate is cooled to form a multi-layer gel-like sheet, (5) removing at least a portion of the film-forming solvent from the multi-layer gel-like sheet to form a gel-like sheet from which the solvent has been removed, and 6) The solvent-like gel-like sheet is dried to form a multilayer microporous film. Optionally, an optional stretching step (7) and optionally a thermal solvent treatment step (8) and the like may be carried out between steps (4) and (5). After step (6), optional step (9) of stretching the multilayer microporous membrane, optional heat treatment step (10), optional step (11) of crosslinking by free radiation, and optional Hydrophilic treatment step (12) and the like.

The process steps and conditions of the second manufacturing process are generally the same as those described in the section relating to the first manufacturing step, except for step (3). Therefore, step (3) will be explained in detail.

There is no strict limit to the mold used, as long as the mold can form a laminateable extrudate. In a system, a sheet mold (which is adjacent or joined together) is used to form the extrudate. The first and second sheet molds are respectively connected to the first and second extruders, wherein the first extruder contains the first polyolefin solution and the second extruder contains the first Two polyolefin solutions. Although not strictly limited, lamination is generally easier when the first and second polyolefin solutions that are extruded are still at about the extrusion temperature. Other conditions can be the same as in the first method.

In another system, the first, second and third sheet molds are joined to the first, second and third extruders, wherein the first and third sheets are The mold contains the first polyolefin solution and the second sheet mold contains the second polyolefin solution. In this system, the resulting laminated extrudate is comprised of an outer layer comprising an extruded first polyolefin solution and an intermediate layer comprising an extruded second polyolefin solution.

In yet another system, the first, second, and third sheet molds are coupled to the first, second, and third extruders, wherein the second sheet mold is The first polyolefin solution is included, and the first and third sheet molds contain a second polyolefin solution. In this system, the resulting layered extrudate is comprised of an outer layer comprising an extruded second polyolefin solution and an intermediate layer comprising an extruded first polyolefin solution.

C. The third manufacturing method A third method for producing a multilayer microporous polyolefin film comprises the steps of: (1) forming a first polyolefin by combining a first polyolefin composition and a film forming solvent (for example, by melt blending) a solution, (2) combining a second polyolefin composition and a second film forming solution to prepare a second polyolefin solution, and (3) extruding the first polyolefin solution through at least one first mold Forming at least one first extrudate, (4) extruding the second polyolefin solution through at least one second die to form at least one second extrudate, (5) placing the first And the second extrudate is cooled to form at least one first gelatinous sheet and at least one second gelatinous sheet, (6) for the first and second gelatinous sheets Laminating to form a multi-layered gel-like sheet, (7) removing the at least part of the film-forming solvent from the resulting multi-layer gel-like sheet, and forming a gel-like solvent to remove the solvent a sheet, and (8) drying the solvent-like gel-like sheet to form a multilayer microporous filmOptionally, between step (5) and (6), or between steps (6) and (7), an optional stretching step (9), and optionally a thermal solvent treatment step (10) )and many more. After step (8), optional step (11) of stretching the multilayer microporous membrane, optional heat treatment step (12), and optional crosslinking step with free radiation, and optionally hydrophilicity may be performed. Sexual processing steps (14) and so on.

The main difference between the third manufacturing method and the second manufacturing method is the order of the lamination and cooling steps.

In the second manufacturing method, lamination of the first and second polyolefin solutions is performed prior to the cooling step. In the third manufacturing method, One and the second polyolefin solution are cooled prior to the lamination step.

Steps (1), (2), (7), and (8) in the third manufacturing method may be combined with steps (1), (2), (5), and (6) in the first manufacturing method described above. )the same. The condition of the step (3) of the second manufacturing method is used for the step (3) of the third manufacturing method in terms of the extrusion of the first polyolefin solution through the first mold. In the case where the second polyolefin solution is extruded through the second mold, the condition of the step (4) of the third manufacturing method may be the same as the condition of the step (3) of the second manufacturing method. In a system, either the first or second polyolefin solution is extruded through a third mold. In this manner, the resulting multilayer laminate can have a two layer produced from the first polyolefin solution and a single layer produced from the second polyolefin solution, or vice versa.

The step (5) of the third manufacturing method may be the same as the step (4) of the first manufacturing method, except that in the third manufacturing method, the first and second gel-like sheets are separately formed. outer.

The step (6) of laminating the first and second gel-like sheets will be described in detail below. The method of lamination is not strictly limited, and the multilayer gel-like sheet can be laminated using a conventional lamination method such as heat-induced lamination methods. Other suitable lamination methods include, for example, heat sealing, impulse-sealing, ultrasonic-bonding, and the like, which may be used singly or in combination. The heat sealing process can be carried out, for example, by one or more pairs of heated rollers, wherein the gel-like sheet is guided through at least one pair of heated rollers. Although for heat The sealing temperature and pressure are not critical, but sufficient heating and pressure should be applied for a sufficient period of time to ensure that the gel-like sheets are properly joined to provide a multilayer microporous membrane having relatively uniform properties and a low tendency to delamination. In a system, the heat sealing temperature can be, for example, from about 90 ° C to about 135 ° C, or from about 90 ° C to about 115 ° C. In a system, the heat seal pressure can range from about 0.1 MPa to about -50 MPa.

a layer formed from the first and second polyolefin solutions (i.e., a layer comprising the first and second microporous layer materials) as in the case of the first and second manufacturing methods The thickness can be adjusted by adjusting the thickness of the first and second gel-like sheets and by the amount of stretching (stretching ratio and dry stretching ratio) (when one or more stretching steps are used) ), to control. Optionally, the laminating step and the stretching step can be combined by passing the gel-like sheet through a multi-stage heating roller.

In a system, the third manufacturing process forms a multilayer polyolefin gel-like sheet having at least three layers. For example, after cooling two extruded first polyolefin solutions and one extruded second polyolefin solution to form a gel-like sheet, the multilayer gel-like sheet can contain extrusion The outer layer of the first polyolefin solution and the intermediate layer comprising the extruded second polyolefin solution are laminated. In another system, after cooling the two extruded second polyolefin solution and an extruded first polyolefin solution to form a gel-like sheet, the multilayer gel-like sheet can be combined with An outer layer comprising the extruded second polyolefin solution and an intermediate layer comprising the extruded first polyolefin solution are included.

The stretching step (9) and the hot solvent treatment step (10) may be the same as the stretching step (7) and the hot solvent treatment step (8) described in the first preparation method, but the stretching step (9) and the hot solvent Treatment step (10) can be carried out on the first and/or second gelatinous sheet. The stretching temperatures of the first and second gel-like sheets are not strictly limited. For example, the stretching temperature of the first gel-like sheet may be, for example, Tm ₁ + 10 ° C or lower, or optionally about Tcd ₁ or higher but lower than Tm ₁ . The stretching temperature of the second gel-like sheet may be, for example, Tm ₂ + 10 ° C or lower, or optionally about Tcd ₂ or higher but less than about Tm ₂ .

D. Fourth manufacturing method A fourth method for producing a multilayer microporous polyolefin film comprises the steps of: (1) forming a first polyolefin by forming a first polyolefin composition with a film forming solvent (for example, by melt blending) Solution (2) forming a second polyolefin composition with a second film to form a second polyolefin solution, and (3) extruding the first polyolefin solution through at least one first mold, Forming at least one first extrudate, (4) extruding a second polyolefin solution through at least one second die to form at least one second extrudate, (5) forming the first The second extrudate is cooled to form at least one first gelatinous sheet and at least one second gelatinous sheet, (6) from the first and second gelatinous sheets Removing at least a portion of the second and second film forming solvents to form the first and second gel-like sheets from which the solvent has been removed, and (7) removing the first and second solvents The gelatinous sheet is dried to form at least one first polyolefin film and at least one second polyolefin film to And (8) laminating the first and second porous polyolefin films to form a multilayer microporous polyolefin film.

A stretching step (9), a thermal solvent treatment step (10), and the like may be performed between the steps (5) and (6) as needed. A stretching step (11), a heat treatment step (12), and the like may be performed between the steps (7) and (8) as needed. If necessary, after the step (8), the step (13) of stretching the multilayer microporous membrane, the heat treatment step (14), the crosslinking step (15) using free radiation, the hydrophilic treatment step (16), etc. may be performed. .

The steps (1) and (2) in the fourth production method can be carried out under the same conditions as the steps (1) and (2) in the first production method. Steps (3), (4), and (5) in the fourth manufacturing method can be carried out under the same conditions as the steps (3), (4), and (5) in the third method. The step (6) in the fourth manufacturing method can be carried out under the same conditions as the step (5) of the first manufacturing method, but the film is removed from the first and second gel-like sheets to form a solvent. Except for some. The step (7) in the fourth manufacturing method can be carried out under the same conditions as the step (6) of the first manufacturing method, but in the fourth manufacturing method, the first and second solvent-removed The gelatinous flakes are separately dried. The step (8) in the fourth production method can be carried out under the same conditions as the step (6) of the third production method, except for the portion where the first and second polyolefin microporous membranes are laminated. The stretching step (9) and the hot solvent treatment step (10) in the fourth manufacturing method can be carried out under the same conditions as the steps (9) and (10) of the third manufacturing method. The stretching step (11) and the heat treatment step (12) in the fourth manufacturing method may be in steps with the first manufacturing method (9) and (10) are carried out under the same conditions, but in the fourth manufacturing method, the first and second polyolefin microporous membranes are subjected to stretching and/or heat treatment.

In a system, in the stretching step (11) of the fourth manufacturing method, the stretching temperature of the first polyolefin microporous film may be about Tm ₁ or lower, or optionally Tcd ₁ to About Tm ₁ , and the stretching temperature of the second polyolefin microporous film may be about Tm ₂ or lower, or optionally about Tcd ₂ to about Tm ₂ .

In a system, the heat treatment step (12) in the fourth manufacturing method may be HS and/or annealing. For example, in the heat treatment step (12) of the fourth manufacturing method, the heat setting temperature of the first polyolefin microporous film may be from about Tcd ₁ to about Tm ₁ , or optionally about dry stretching temperature ± 5 ° C, or optionally about dry stretching temperature ± 3 ° C. In a system, in the heat treatment step (12) of the fourth manufacturing method, the heat setting temperature of the second microporous film may be from about Tcd ₂ to about Tm ₂ , or optionally dry stretching temperature ± 5 ° C, or optionally dry stretching temperature ± 3 ° C. When HS is employed, it can be carried out, for example, by a tenter method or a roller method.

In a system, in the heat treatment step (12) of the fourth manufacturing method, the annealing temperature of the first microporous film may be about Tm ₁ or lower, or optionally about 60 ° C to about (Tm). ₁ -10 ° C). In a system, in the heat treatment step (12) of the fourth manufacturing method, the annealing temperature of the second microporous film may be about Tm ₂ or lower, or optionally about 60 ° C to about (Tm ₂ -10 ° C).

The fourth step (13), the heat treatment step (14), the crosslinking step (15) using the free radiation, and the conditions of the hydrophilic treatment step (16) and the first production in the fourth manufacturing method The steps (9), (10), (11) and (12) of the method are the same.

[4] Properties of multilayer microporous polyolefin membranes

In one system, the multilayer microporous polyolefin film has a thickness in the range of from about 3 μm to about 200 μm, or in the range of from about 5 μm to about 50 μm. Optionally, the multilayer microporous polyolefin membrane has one or more of the following characteristics.

A. Porosity is about 25% to about 80% When the porosity is less than 25%, the multilayer microporous polyolefin film generally does not exhibit the desired gas permeability for use as a battery separator. When the porosity exceeds 80%, it is more difficult to manufacture a battery separator having a desired strength, which increases the possibility of short circuits of the internal electrodes.

B1. Gas permeability is about 20 sec / 100 cm ³ to about 700 sec / 100 cm ³ (converted to a value at a thickness of 20 - μm) when the gas permeability of the multilayer microporous polyolefin film (as measured according to JIS P8117) is When it is in the range of about 20 seconds / 100 cm ³ to about 700 seconds / 100 cm ³ , it is less difficult to form a battery having a desired charge storage capacity and a desired charge and discharge cycle. When the gas permeability is less than about 20 seconds / 100 cm ³ , it is more difficult to manufacture a battery having the desired shutdown characteristics, especially when the temperature inside the battery rises. According to JIS P8117, the gas permeability P ₁ measured on the multilayer microporous film having the thickness T ₁ can be converted into a gas permeability of 20 μm in thickness by the equation P ₂ = (P ₁ x 20) / T ₁ .

B2. Gas permeability after hot compression is about 100 sec / 100 crri ³ to about 1000 sec / 100 cm ³ When the glass is thermally compressed at 90 ° C under a pressure of 2.2 MPa for 5 minutes, the multilayer microporous film of the present invention has gas permeability. (measured according to JIS P8117) is about 100 seconds / 100 cm ³ or less, such as about 100 to about 1000 seconds / 100 cm ³ . A battery such as a film has a suitably large capacity and charge and discharge cycle. The gas permeability after heat compression is preferably, for example, 950 sec / 100 cm ³ or less.

C. Pin puncture strength is about 2,000 mN / 20 μm or more The pin compressive strength (converted to a value of 20 μm film thickness) means that a needle having a diameter of 1 mm having a spherical end surface (curvature radius R: 0.5 mm) is used for piercing at a speed of 2 mm/sec. The maximum load measured for a multilayer microporous polyolefin membrane. When the pin-to-hole compressive strength of the multilayer microporous polyolefin film is less than 2,000 mN/20 μm, it is more difficult to manufacture a battery having desired mechanical integrity, durability, and toughness.

D. The standard deviation of the thickness is about 5 μm or less. When the standard deviation of the multilayer microporous polyolefin film exceeds about 5 μm, it will be more difficult to manufacture a battery having the desired protection for the internal short circuit. The standard deviation of the multilayer microporous polyolefin film can be measured in a 10 cm x 10 cm area film by a contact thickness meter at intervals of 10 mm. The standard deviation of the thickness is preferably 3 μm or less, more preferably 1 μm or less.

E. The shutdown temperature is about 140 ° C or lower. When the shutdown temperature of the multilayer microporous polyolefin film exceeds 140 ° C, it is more difficult to manufacture a battery separator which is required to close the reaction when the battery is overheated. One of the methods for determining the shutdown temperature involves measuring the temperature at which the inflection point is observed near the melting point of the multilayer microporous polyolefin film under the following conditions: a test of 3 mm in the longitudinal direction and 10 mm in the lateral direction at a rate of 5 ° C/min. The sheet was heated from room temperature while the test piece was stretched in the longitudinal direction under a load of 2 g. In a system, the shutdown temperature is in the range of about 120-140 °C.

F. The melting temperature is at least about 170 ° C In a system, the melting temperature can range from about 170 °C to about 190 °C. One of the methods of measuring the melting temperature involves measuring the temperature at which the multilayer microporous polyolefin film test piece of 3 mm in the longitudinal direction and 10 mm in the transverse direction is broken by melting under the following conditions: heating the test piece at a heating rate of 5 ° C / minute while The test piece was stretched under a load of 2 g.

G. Battery capacity recovery rate is 70% or higher (anti-attenuation properties of lithium secondary batteries) When a lithium ion secondary battery including a separator formed of a multilayer microporous membrane is stored at 80 ° C for 30 days, the desired battery capacity recovery rate [(capacity after storage at a high temperature) / (starting capacity)] ×100 (%) should be 70% or higher. The battery capacity recovery rate should be 75% or higher.

H. The thickness variation rate after hot compression is 20% or less The thickness variation rate after hot compression at 90 ° C under a pressure of 2.2 MPa for 5 minutes is generally 20% or less, preferably less than 10%, per 100% of the thickness before compression. A battery including a membrane separator having a variation rate of 20% or less has a suitably large capacity and a good charge and discharge cycle.

[5] battery separator

In one system, the battery separator formed by the multilayer microporous polyolefin film has a thickness in the range of from about 3 μm to about 200 μm, or from about 5 μm to about 50 μm. Depending on, for example, the choice of electrolyte, the swelling of the separator may increase the final thickness to a value greater than 200 μm.

[6]Battery

In a system, a multilayer microporous polyolefin film can be used as a separator for primary and secondary batteries, such as a lithium ion battery, a lithium-polymer secondary battery, a nickel-hydrogen secondary battery, a nickel-cadmium secondary battery, A nickel-zinc secondary battery, a silver-zinc secondary battery, and specifically a lithium ion secondary battery. Hereinafter, a lithium ion secondary battery will be described.

A lithium secondary battery includes a cathode, an anode, and a separator between the anode and the cathode. The separator usually contains an electrolytic solution (electrolyte). The structure of the electrode is not strictly limited, and a conventional electrode structure can be used. The electrode structure may be, for example, a button type (in which the disk-shaped cathode and the anode are opposite); a stacked type (where the planar sheet cathode and the anode are alternately laminated with at least one separator between the anode and the cathode) ; and ring type (where the strip cathode and anode are wound together), and so on.

The cathode generally includes a current collector and a cathode active material layer capable of absorbing and releasing lithium ions (which is formed on the current collector). The cathode active material may be, for example, an inorganic compound such as a transition metal oxide, a composite oxide of lithium and a transition metal (lithium composite oxide), a transition metal sulfide, or the like. The transition metal can be, for example, V, Mn, Fe, Co, Ni, or the like. In one system, the lithium composite oxide may be lithium nickelate, lithium cobaltate, lithium manganate, a layered lithium composite oxide based on α-NaFeO ₂ , or the like. The anode generally includes a current collector and a negative electrode active material layer formed on the current collector. The negative electrode active material may be, for example, a carbon substance such as natural graphite, artificial graphite, coke, carbon black, or the like.

The electrolytic solution can be obtained by dissolving a lithium salt in an organic solvent. There are no strict restrictions on the choice of solvent and/or lithium salt and conventional solvents and salts can be employed. The lithium salt may be, for example, LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , a lower aliphatic carboxylate of lithium, LiAlCl ₄ or the like. Lithium salts can be used singly or in combination. The organic solvent may be an organic solvent having a relatively high boiling point (compared to the shutdown temperature of the battery) and a high dielectric constant. Suitable organic solvents include: ethylene carbonate, propylene carbonate, ethyl methyl carbonate, γ-butyrolactone, etc.; organic solvents having a low boiling point and a low viscosity, such as tetrahydrofuran, 2-methyltetrahydrofuran, diethyl Oxyethane, dioxane, dimethyl carbonate, diethyl carbonate, and the like, including mixtures thereof. Since organic solvents which generally have a high dielectric constant often have a high viscosity, and vice versa, a mixture of high and low viscosity solvents can be used.

When the battery is assembled, the separator is usually impregnated with an electrolytic solution to provide ion permeability to the separator (multilayer microporous membrane). There is no strict restriction on the choice of the soaking method, and a conventional soaking method can be employed. For example, the impregnation treatment can be performed by immersing the multilayer microporous membrane in an electrolytic solution at room temperature.

There is no strict limitation on the method of selecting a battery for combination, and a conventional battery combination method can be employed. For example, in the case of combining cylindrical batteries, a cathode sheet, a separator formed of a multilayer microporous film, and an anode sheet are sequentially laminated, and the resultant laminate is wound into a ring electrode combination. It may be necessary to have a second baffle to prevent short circuits of the windings. As a result, the obtained electrode combination can be embedded in the battery, then impregnated with the aforementioned electrolytic solution, and a battery cover equipped with a safety valve as a cathode terminal is filled in the battery via a gasket to manufacture a battery.

The invention is described in more detail with reference to the following non-limiting examples.

Example 1

(1) Preparation of First Polyolefin Solution A first polyolefin composition comprising (a) 82% PE1 having a weight average molecular weight of 3.0 × 10 ⁵ and a molecular weight distribution of 8.6 was prepared by dry blending. (b) 8% PE2 having a weight average molecular weight of 2.0 × 10 ⁶ and a molecular weight distribution of 8, (c) 10% of the first polypropylene resin having a weight average molecular weight of 1.01 × 10 ⁶ and a heat of fusion of 108.2 J / g, a portion having a molecular weight of 5 × 10 ⁴ or less and the portion is 4.3%, and a molecular weight distribution of 4.3 (the percentage is based on the weight of the first polyolefin composition). The polyethylene in the composition had a melting point of 135 ° C and a crystal dispersion temperature of 100 ° C.

25 parts by weight of the resulting polyolefin composition was charged into a strongly blended twin roll extruder (having an inner diameter of 58 mm and an L/D of 42), and 75 parts by mass via a side feeder Liquid paraffin (50 cst at 40 ° C) was supplied to the twin roll extruder. Melt blending was carried out at 210 ° C and 200 rpm to prepare a first polyolefin solution.

(2) Preparation of Second Polyolefin Solution A second polyolefin solution was prepared in the same manner as described above except for the following. A second polyolefin composition comprising: (a) 47% PEI having a weight average molecular weight of 3.0 x 10 ⁵ and a molecular weight distribution of 8.6, and (b) 3% PE2, is prepared by dry blending. Having a weight average molecular weight of 2.0×10 ⁶ and a molecular weight distribution of 8, and (c) 50% of a second polypropylene resin having a weight average molecular weight of 1.01×10 ⁶ , a heat of fusion of 108.2 J/g, and a molecular weight of 5×10 ⁴ Or a smaller portion and the portion is 4.3% and the molecular weight distribution is 4.3 (the percentage is based on the weight of the second polyolefin composition). The polyethylene resin in the composition had a melting point of 135 ° C and a crystal dispersion temperature of 100 ° C. The second polyolefin composition obtained as a result of 35 parts by weight was placed in a strongly blended twin roll extruder (inner diameter 58 mm and L/D 42), and 65 mass by side feeder A portion of the liquid paraffin (50 cst at 40 ° C) was supplied to the twin roll extruder. Melt blending was carried out at 210 ° C and 200 rpm to prepare a second polyolefin solution.

(3) Film manufacturing The first and second polyolefin solutions were supplied to the three-layer extruded T-die by their respective twin roll extruders, and extruded from the mold to form a layer thickness of 42.5/10/42.5. An extrudate of the first polyolefin solution layer/second polyolefin solution layer/first polyolefin solution layer (also referred to as a laminate). The extrudate was cooled while passing through a cooling roller controlled at 20 ° C to form a three-layer gel-like sheet, which was stretched at 118 ° C by a tenter type machine while being in the machine ( In the longitudinal direction and the transverse direction, it is simultaneously biaxially stretched and stretched to a magnification of 5 times. The stretched three-layer gel-like sheet was fixed on a 20 cm × 20 cm aluminum frame, and immersed in a dichloromethane bath controlled at 25 ° C to 100 The rpm was shaken (for 3 minutes), the liquid paraffin was removed, and it was dried by air flow at room temperature. The dried film was further stretched to a magnification of 1.4 times at 125 ° C in a transverse direction by a batch-stretching machine. The restretched film (which was still fixed on a batch stretching machine) was heat-set at 125 ° C for 10 minutes to produce a three-layer microporous film.

Example 2

Example 1 was repeated, but the dried three-layer film was not redrawn.

Example 3

Example 1 was repeated, but the first and second microporous polyolefin membranes were in the order of the first microporous membrane / the second microporous membrane / the first microporous membrane, with a layer of 25/50/25 The thickness ratio is laminated.

Example 4

Example 1 was repeated, but the first polypropylene in the first polyolefin composition had a weight average molecular weight of 6.6 × 10 ⁵ , a heat of fusion of 103.3 J/g, and a fraction having a molecular weight of 5 × 10 ⁴ or less. And this part accounts for 14.2% and 11 molecular weight distribution.

Example 5

Example 1 was repeated, however, the first polypropylene in the first polyolefin composition had a weight average molecular weight of 6.8 × 10 ⁵ , a heat of fusion of 94.6 J/g, and a fraction of molecular weight of 5 × 10 ⁴ or less. And this part accounts for 8.4%, and a molecular weight distribution of 5.9.

Example 6

Example 1 was repeated, but the first polypropylene in the first polyolefin composition had a weight average molecular weight of 3.0 × 10 ⁵ , a heat of fusion of 88.9 J/g, a portion having a molecular weight of 5 × 10 ⁴ or less and This fraction accounts for 4.9% and a molecular weight distribution of 4.9.

Example 7

Example 1 was repeated, but the second polypropylene in the second polyolefin composition had a weight average molecular weight of 1.82 × 10 ⁶ , a heat of fusion of 107.2 J/g, a portion having a molecular weight of 5 × 10 ⁴ or less and This fraction accounts for 0.08%, and a molecular weight distribution of 2.6.

Example 8

Example 1 was repeated, but the second polypropylene in the second polyolefin composition had a weight average molecular weight of 0.90 × 10 ⁶ , a heat of fusion of 109.7 J/g, a portion having a molecular weight of 5 × 10 ⁴ or less and This fraction accounts for 1.2% and a molecular weight distribution of 2.4.

Example 9

Example 1 was repeated, but the first polyolefin composition in the first polyolefin solution contained 90% PE1 and 10% first polypropylene resin ( The percentage is based on the weight of the first polyolefin composition). In this first polyolefin composition, there is no second polyethylene resin.

Example 10

Example 1 was repeated, but the second polyolefin composition in the second polyolefin solution contained 50% PE1 and 50% first polypropylene resin (the percentage is based on the weight of the second polyolefin composition). In this second polyolefin composition, there is no second polyethylene resin.

Comparative Example 1

Example 1 was repeated, but the first polyolefin composition in the first polyolefin solution contained 82% of the first polyethylene resin and 18% of the second polyethylene resin, and the first polypropylene resin was not added (percentage Based on the weight of the first polyolefin composition).

Comparative Example 2

Example 1 was repeated except for the first polyolefin composition of the first polyolefin solution. There is no first polyolefin composition.

Comparative Example 3

Comparative Example 1 was repeated, but the first polypropylene resin in the first polyolefin composition had a weight average molecular weight of 6.8 × 10 ⁵ , a heat of fusion of 94.6 J/g, and a fraction of molecular weight of 5 × 10 ⁴ or less. And the portion accounts for 8.4%, and a molecular weight distribution of 5.9, and the second polypropylene in the second polyolefin composition has a weight average molecular weight of 6.8 × 10 ⁵ , a heat of fusion of 94.6 J / g, a molecular weight of 5 × A portion of 10 ⁴ or less and this portion accounts for 8.4%, and a molecular weight distribution of 5.9.

Comparative Example 4

Example 1 was repeated, but the first polypropylene resin in the first polyolefin composition had a weight average molecular weight of 1.56 × 10 ⁶ , a heat of fusion of 78.4 J/g, a portion having a molecular weight of 5×10 ⁴ or less and Part of the molecular weight distribution of 1.2% and 3.2, and the second polypropylene resin in the second polyolefin composition has a weight average molecular weight of 1.56 × 10 ⁶ , a heat of fusion of 78.4 J / g, a molecular weight of 5 × 10 A portion of ⁴ or less and this portion accounts for 1.2%, and a molecular weight distribution of 3.2.

Comparative Example 5

Comparative Example 1 was repeated except for the second polyolefin composition in the second polyolefin solution. There is no second polyolefin composition.

nature

The properties of the multilayer microporous membranes of Examples 1-6 and Comparative Example 1.8 were measured by the following methods. The results are shown in Tables 1 and 2.

(1) Average thickness (μm) The thickness of each microporous film was measured by a contact thickness meter on a film of an area of 10 cm × 10 cm at intervals of 10 mm, and averaged. Take The thickness meter used is a Litematic manufactured by Mitsutoyo Corporation.

(2) Standard deviation of thickness (μm) The thickness of each microporous membrane was measured as described above. Based on the thickness data, the standard deviation of the thickness is calculated.

(3) Air permeability (sec/100 cm ³ / 20 μm) The air permeability P measured in each of the microporous films each having a thickness T ₁ according to JIS P8117 by the equation P ₂ = (P ₁ × 20) / T _{1 1 was} converted into a gas permeability P ₂ having a thickness of 20 μm.

(4) Porosity (%) It was measured by gravimetric method using the following formula: % porosity = 100 x (w2-w1) / w2, where "w1" is the actual weight of the film, and "w2" is the assumed weight of 100% polyethylene.

(5) Pin compressive strength (mN/20 μm) When the speed was 2 mm/sec, a needle having a diameter of 1 mm having a spherical end surface (curvature radius R: 0.5 mm) was used to puncture the thickness to The maximum load was measured when the multilayer microporous polyolefin film of T was used. The measured maximum load L _{1 is} converted into the maximum load L ₂ at a thickness of 20 μm by the equation L ₂ = (L ₁ × 20) / T ₁ and used as the pin compressive strength.

(6) Thickness variation rate after heat compression (%) The microporous film sample was placed between a pair of highly flat sheets, and pressed at 2.2 MPa (22 kgf/cm ² ) at 90 ° C by a punch. The heat was compressed for 5 minutes, and the average thickness was measured in the same manner as described above. The thickness variation rate is calculated by the equation: (average thickness after compression - average thickness before compression) / (average thickness before compression) × 100, which can be expressed as an absolute value.

(7) Air permeability after hot compression (sec/100 cm ³ ) Under the above conditions, each of the multilayer microporous membranes having a thickness T ₁ was thermally compressed, and the gas permeability P ₁ was measured in accordance with JIS P8117.

(8) Absorption rate of electrolytic solution A multilayer surface microporous membrane sample was immersed at 18 ° C using a dynamic surface tension measuring device (DCAT 21 equipped with a high-precision electronic balance, available from Eiko Instruments Co., Ltd.). Electrolytic solution (electrolyte: 1 mol/L LiPF ₆ , solvent: 3/7 by volume of ethylene carbonate / dimethyl carbonate) by the equation: [microporous membrane weight increase (g) / micro before absorption The weight of the porous membrane (g)] was used to determine the absorption rate of the electrolytic solution. The absorption rate of the electrolytic solution is expressed by a relative value, and it is assumed that the absorption rate of the electrolytic solution of the microporous membrane of Comparative Example 5 is 1.

(9) Shutdown temperature (°C) The shutdown temperature was measured by cutting a piece of a 3 mm x 50 mm triangular sample from the microporous membrane such that the longitudinal direction of the sample was in line with the transverse direction of the microporous membrane and was fixed to a thermomechanical analyzer ( TMA/SS6000, available from Seiko Instruments, Inc., has a chuck distance of 10 mm. A load of 19.6 mN was applied to the lower end of the sample, and the temperature was raised at a rate of 5 ° C/min to measure the change in size. The temperature at which the inflection point is observed near the melting point is defined as the shutdown temperature.

(10) Melting temperature (°C) The melting temperature was measured using a thermomechanical analyzer (TMA/SS6000, available from Seiko Instruments, Inc.) in the same manner as the aforementioned shutdown temperature. The melting temperature is the temperature at which the membrane breaks.

(11) Capacity recovery rate The recovery rate of a lithium ion battery containing a multilayer microporous membrane as a separator was measured as follows: First, the discharge capacity of the lithium ion battery was measured by a charge/discharge tester before high temperature storage (starting) capacity). After storage at 80 ° C for 30 days, the discharge capacity was measured again by the same method, and the capacity after high-temperature storage was obtained. The capacity recovery rate (%) of the battery is determined by the following equation: capacity recovery rate (%) = [(capacity after high temperature storage) / (starting capacity)] × 100.

Note (1) LMWF represents a low molecular weight portion having a molecular weight of 5.0 × 10 ⁴ or less (% by mass). (2) (I) shows the first polyolefin solution, and (II) shows the second polyolefin solution. (3) (MD × TD) shows the magnification in the longitudinal direction (MD) and the transverse direction (TD).

It can be noted from Table 1 that the multilayer microporous membrane of the present invention has balanced properties including standard deviation of thickness, gas permeability, pin pressure resistance, shutdown temperature, and melting temperature, as well as excellent absorption of electrolytic solution. The thickness and the gas permeability after heat compression are small. The lithium ion secondary battery comprising the multilayer microporous membrane of the present invention has a capacity recovery ratio of 70% or more, indicating that it has a desired high temperature anti-attenuation property.

On the other hand, the microporous membrane product of the comparative example exhibited a poor balance of properties.

The multilayer microporous membrane of the present invention has a balanced property and, if it is a multilayer microporous membrane, as a battery separator, provides a battery having excellent safety, heat resistance, attenuation resistance, and productivity.

Figure 1 is a diagram showing an example of a typical DSC curve.

Figure 2 is a diagram showing another example of a typical GPC curve.

Figure 3 is a diagram showing the same GPC curve as in the second figure, where low The portion of the molecular weight is slashed.

Figure 4 is a diagram showing an example of a typical TMA measurement, with the off temperature being indicated by an arrow.

Claims (27)

A multilayer microporous membrane comprising: a first layer of material comprising a first polyethylene and a first polypropylene, and a second layer of material comprising a second polyethylene and a second polypropylene, The second polypropylene has (1) a weight average molecular weight of 6 × 10 ⁵ or more, (2) a heat of fusion of 90 J/g or more, and (3) a portion having a molecular weight of 5 × 10 ⁴ or less, the portion Is 5% or less (based on the mass of the second polypropylene), wherein the multilayer microporous membrane comprises: a first microporous layer containing the first layer material and a material containing the second layer The second microporous layer. The multilayer microporous membrane of claim 1, wherein the multilayer microporous membrane comprises: a first microporous layer containing the first layer material; and a third microporous layer containing the first a layer of material; and a second microporous layer comprising the second layer of material; the second microporous layer being between the first and third microporous layers. The multilayer microporous membrane of claim 1, wherein the multilayer microporous membrane comprises: a first microporous layer containing the second layer material; and a third microporous layer containing the second a layer of material; and a second microporous layer comprising the first layer of material; the second microporous layer being between the first and third microporous layers. The multilayer microporous membrane of claim 1, 2, or 3, wherein: the first polyethylene is in the range of 50% by weight to 99% by weight (based on the weight of the first layer of the substance) An amount of polyethylene present in the first layer of material, the first polypropylene being at a first concentration ranging from 1% to 50% by weight based on the weight of the first layer of material An amount of propylene present in the first layer of material, the second polyethylene being in a second amount of polyethylene in the range of from 5% by weight to 95% by weight based on the weight of the second layer of material, Existing in the second layer of material, and the second polypropylene is present in the second amount of polypropylene in the range of 5 wt% to 95 wt% (based on the weight of the second layer of material) The second layer of matter. The multilayer microporous membrane of any one of claims 1 to 3 wherein: (a) the first and/or second polyethylene comprises PE1 polyethylene, PE2 polyethylene, or both PE1 and PE2 polyethylene, wherein (1) the first and/or second polyethylene has a Mw in the range of 1 x 10 ⁴ to 1 x 10 ⁷ ; (2) the first and/or second Polyethylene has a Mw in the range of 1 × 10 ⁴ to 5 × 10 ⁵ ; (3) PE1 is one or more of the following: high density polyethylene, medium density polyethylene, branched low density polyethylene, or linear Low density polyethylene; (4) PE1 is at least one of the following: (i) an ethylene homopolymer or (ii) ethylene and a third alpha selected from the group consisting of propylene, butene-1, and hexene-1. a copolymer of an olefin; (5) PE2 having a Mw of at least 1 × 10 ⁶ ; (6) PE2 is at least one of the following: (i) an ethylene homopolymer or (ii) ethylene and a catalyst selected from the group consisting of propylene, a copolymer of butene-1, a fourth alpha-olefin of hexene-1; (7) an amount of PE1 in the first layer of the material is from 70% by weight to 90% by weight based on the first layer Within the range of the weight of the substance; (8) the amount of PE2 in the first layer of material is 0% by weight 10% by weight (based on the weight of the first layer of material); (9) the amount of PE1 in the second layer of material is between 40% and 60% by weight (based on the second layer of material) (10) the amount of PE2 in the second layer material is in the range of 0% by weight to 10% by weight (based on the weight of the second layer material); (11) the first And/or the second polyethylene has a molecular weight distribution ("Mw/Mn") of 5 to 300; (b) the first polypropylene has at least one property selected from the group consisting of: (1) the first One or more of the following: (i) a propylene homopolymer or (ii) a copolymer of propylene and a fifth olefin selected from one or more of the following alpha olefins: ethylene, butyl Alkenyl-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, vinyl acetate, methyl methacrylate, styrene, butadiene, 1,5-hexyl Diene, 1,7-octadiene and 1,9-decadiene; (2) the first polypropylene has a Mw system in the range of 1 × 10 ⁴ to 4 × 10 ⁶ ; (3) The first polypropylene has a Mw/Mn in the range of 1.01 to 100; (4) the first polypropylene is in the gauge; (5) a heat of fusion of the first polypropylene of at least 90 J/g; (6) a melting peak (second melting) of the first polypropylene is at least 160 ° C; and (c) the second polypropylene has At least one property selected from the group consisting of (1) Mw/Mn is 2.5 or less; (2) a weight average molecular weight of 6.5 × 10 ⁵ or more; (3) a heat of fusion of 95 J/g or more; 4) The second polypropylene portion having a molecular weight of 5 × 10 ⁴ or less is 4.5% or less (based on the mass of the second polypropylene). The multilayer microporous membrane of claim 4, wherein: (a) the first and/or second polyethylene comprises PE1 polyethylene, PE2 polyethylene, or both PE1 and PE2 polyethylene, wherein 1) the first and/or second polyethylene has a Mw in the range of 1 x 10 ⁴ to 1 x 10 ⁷ ; (2) the Mw of the first and/or second polyethylene In the range of 1×10 ⁴ to 5×10 ⁵ ; (3) PE1 is one or more of the following: high density polyethylene, medium density polyethylene, branched low density polyethylene, or linear low density polyethylene; 4) PE1 is at least one of the following: (i) an ethylene homopolymer or (ii) a copolymer of ethylene and a third alpha-olefin selected from the group consisting of propylene, butene-1, and hexene-1; 5) PE2 has a Mw of at least 1 × 10 ⁶ ; (6) PE2 is at least one of the following: (i) an ethylene homopolymer or (ii) ethylene and a selected from the group consisting of propylene, butene-1, and a copolymer of a fourth alpha-olefin of alkene-1; (7) a range of PE1 in the first layer of matter ranging from 70% by weight to 90% by weight based on the weight of the first layer of the material (8) The amount of PE2 in the first layer of material is between 0% and 10% by weight (based on Within the range of the weight of the first layer of matter; (9) the amount of PE1 in the second layer of matter is in the range of 40% by weight to 60% by weight (based on the weight of the second layer of material) (10) the amount of PE2 in the second layer of material is in the range of 0% by weight to 10% by weight (based on the weight of the second layer of material); (11) the first and/or the first The two polyethylenes have a molecular weight distribution ("Mw/Mn") of 5 to 300; (b) the first polypropylene has at least one property selected from the group consisting of: (1) the first polypropylene is the following One or more of: (i) a propylene homopolymer or (ii) a copolymer of propylene with a fifth olefin selected from one or more of the following alpha olefins: ethylene, butene-1, pentane Alkenyl-1, hexene-1, 4-methylpentene-1, octene-1, vinyl acetate, methyl methacrylate, styrene, butadiene, 1,5-hexadiene, 1, 7-octadiene and 1,9-decadiene; (2) the first polypropylene has a Mw in the range of 1 × 10 ⁴ to 4 × 10 ⁶ ; (3) the first polypropylene The Mw/Mn is in the range of 1.01 to 100; (4) the first polypropylene is uniform; (5) the first is The heat of fusion of the ene is at least 90 J/g; (6) the melting peak (second melting) of the first polypropylene is at least 160 ° C; and (c) the second polypropylene has at least one selected from the group consisting of Characteristics: (1) Mw/Mn is 2.5 or less; (2) weight average molecular weight is 6.5 × 10 ⁵ or more; (3) heat of fusion is 95 J/g or more; and (4) has molecular weight of 5 × The second polypropylene portion of 10 ⁴ or less is 4.5% or less (based on the mass of the second polypropylene). The multilayer microporous membrane of claim 1, wherein the first and/or second polyethylene has a Mw in the range of 2 x 10 ⁵ to 3 x 10 ⁶ . The multilayer microporous membrane of claim 1, wherein the first and/or second polyethylene has a weight average molecular weight in the range of from 1 × 10 ⁴ to 5 × 10 ⁵ . A multilayer microporous membrane according to claim 5, wherein the PE1 is a high density polyethylene and the PE2 is an ultrahigh molecular weight polyethylene. A multilayer microporous membrane according to claim 6, wherein the PE1 is a high density polyethylene and the PE2 is an ultrahigh molecular weight polyethylene. a multilayer microporous membrane as claimed in claim 5, wherein The first and/or second polyethylene comprises 10% by weight or less of PE2 and 90% by weight or more of PE1. The multilayer microporous membrane of claim 6, wherein the first and/or second polyethylene comprises 10% by weight or less of PE2 and 90% by weight or more of PE1. A method of manufacturing a microporous membrane comprising: (1) combining a first polyethylene resin, a first polypropylene resin, and a first processing solvent to form a first polyolefin solution, wherein the first a polyethylene resin and the first polypropylene resin together constitute a first polyolefin composition; and (2) a second polyethylene resin, a second polypropylene resin, and a second processing solvent are combined Forming a second polyolefin solution, wherein the second polyethylene resin and the second polypropylene resin together constitute a second polyolefin composition; the second polypropylene resin having (a) a weight average molecular weight of 6× 10 ⁵ or more, (b) heat of fusion of 90 J/g or more, and (c) part of molecular weight of 5 × 10 ⁴ or less, which is 5% or less (based on the second polypropylene) The quality of the resin). The method of claim 13, further comprising: (3) extruding at least a portion of the first polyolefin solution through a mold or a plurality of molds and coextruding at least a portion of the second polyolefin solution to Forming a multilayered extrudate, (4) cooling the multilayer extrudate to form a multilayer sheet, (5) removing at least a portion of the processing solvent from the multilayer sheet to form a solvent-removed sheet Object, and (6) removing at least a portion of any volatile species from the sheet to form the multilayer microporous membrane. The method of claim 13, further comprising: (3) extruding at least a portion of the first polyolefin solution through the first mold to form a first extrudate, and at least a portion of the first The two polyolefin solutions are extruded through a second die to form a second extrudate, and then the first and second extrudates are laminated to form a multilayer extrudate, (4) The multilayer extrudate is cooled to form a multilayer sheet, (5) removing at least a portion of the processing solvent from the multilayer sheet to form a solvent-removed sheet, and (6) from the sheet At least a portion of any volatile species is removed to form the multilayer microporous membrane. The method of claim 13, further comprising: (3) extruding at least a portion of the first polyolefin solution through the first mold to form a first extrudate, and (4) causing at least a portion of the The second polyolefin solution is extruded through the second die to form a second extrudate, (5) the first and second extrudates are cooled to form at least one first sheet and at least a second sheet, (6) laminating the first and second sheets to form a multilayer sheet, (7) removing at least a portion of the processing solvent from the multilayer sheet, and Forming a sheet of solvent removed, and (8) removing at least a portion of any volatile species from the sheet to form the multilayer microporous membrane. The method of claim 13, wherein the first polyolefin solution is extruded through the first mold to form a first extrudate, the method further comprising: (3) making at least a portion of the first The polyolefin solution is extruded through the first die to form a first extrudate, and (4) at least a portion of the second polyolefin solution is extruded through at least a second die to form a second extrudate, 5) cooling the first and second extrudates to form at least one first sheet and at least one second gel sheet, (6) from the first and second sheets Removing at least a portion of the first and second processing solvents, (7) removing at least a portion of any volatile species from the first and second sheets to form at least one first micro The porous polyolefin film and the at least one second microporous polyolefin film, and (8) laminating the first and second microporous polyolefin films to form a multilayer microporous polyolefin film. The method of claim 13, further comprising: (3) extruding at least a portion of the first polyolefin solution through the first mold, coextruding at least a portion of the second polyolefin solution, and Extruding at least a portion of the first or second polyolefin solution, wherein the extrudate is a multilayer extrudate comprising: (i) first and third layers comprising the first extruded Polyolefin a second layer comprising the extruded second polyolefin solution between the first and third layers; or (ii) first and third layers comprising the extruded portion Two polyolefin solutions; and a second layer comprising the extruded first polyolefin solution between the first and third layers; and then, (4) cooling the multilayer extrudate to form a multilayer sheet, (5) removing at least a portion of the first and second processing solvents from the multilayer sheet to form a solvent-removed sheet, and (6) removing the sheet from the sheet At least a portion of any volatile species forms the multilayer microporous membrane. The method of claim 13, further comprising: (3) extruding at least a portion of the first polyolefin solution through the first mold to form a first extrudate; at least a portion of the second The polyolefin solution is extruded through a second die to form a second extrudate; and at least a portion of the first or second polyolefin solution is extruded through the third die to form a third extrudate; The first, second, and third extrudates are then laminated to form a multilayer extrudate comprising: (i) first and third layers comprising the first extruded a polyolefin solution; and a second layer comprising the extruded second polyolefin solution between the first and third layers; or (ii) first and third layers comprising the extruded a second polyolefin solution; and a second layer comprising the extruded first polyolefin solution between the first and third layers; (4) cooling the multilayer extrudate to form Multi-layer sheet, (5) removing at least a portion of the first and second processing solvents from the multilayer sheet to form a solvent-removed sheet, and (6) removing at least a portion of any volatile species from the sheet The multilayer microporous membrane is formed. The method of claim 13, further comprising: (3) extruding at least a portion of the first polyolefin solution through the first mold to form a first extrudate, and (4) causing at least a portion of the The second polyolefin solution is extruded through the second die to form a second extrudate and at least a portion of the first or second polyolefin solution is extruded through the third die to produce a third extrusion Produce, (5) cool the first, second and third extrudates to form the first, second and third sheets, (6) the first, the first Two and a third sheet are laminated to form a multi-layer sheet, (7) removing at least a portion of the first and the second processing solvent from the multilayer sheet to form a solvent-removed sheet And (8) removing at least a portion of any volatile species from the multilayer sheet to form the multilayer microporous membrane. The method of claim 13, further comprising: (3) extruding at least a portion of the first polyolefin solution through the first mold to form a first extrudate, and (4) causing at least a portion of the The second polyolefin solution is extruded through the second die to form a second extrudate and at least a portion of the first Or the second polyolefin solution is extruded through the third mold to form a third extrudate, (5) the first, second and third extrudates are cooled to form the first, first Two and third sheets, (6) removing at least a portion of the first and second processing solvents from the first, second and third sheets, (7) from the The first, second and third sheets remove at least a portion of any volatile species to form a first, second, and third microporous polyolefin film, and (8) the first The second, second, and third microporous polyolefin films are laminated to form a multilayer microporous polyolefin film. The method of claim 13, wherein: the first polyethylene resin is present in the range of 0.5% by weight to 71.3% by weight (based on the weight of the first polyolefin solution) In a polyolefin solution, the first polypropylene resin is present in the first polyolefin solution in an amount ranging from 0.5% by weight to 37.25% by weight (based on the weight of the first polyolefin solution) The second polyethylene resin is present in the second polyolefin solution in an amount ranging from 0.1% by weight to 71.3% by weight (based on the weight of the second polyolefin solution), the second a polypropylene resin is present in the second polyolefin solution in an amount ranging from 0.1% by weight to 71.3% by weight (based on the weight of the second polyolefin solution), The first processing solvent is present in the first polyolefin solution in an amount ranging from 25% by weight to 99% by weight (based on the weight of the first polyolefin solution), and the second processing The solvent is present in the second polyolefin solution in an amount ranging from 25% to 99% by weight, based on the weight of the second polyolefin solution. The method of claim 13, wherein (a) the first and/or second polyethylene resin comprises PE1 polyethylene, PE2 polyethylene, or both PE1 and PE2 polyethylene, wherein (1) The first and/or second polyethylene resin has a Mw in the range of 1 × 10 ⁴ to 1 × 10 ⁷ ; (2) the Mw of the first and/or second polyethylene resin 1×10 ⁴ to 5×10 ⁵ ; (3) PE1 is one or more of the following: high density polyethylene, medium density polyethylene, branched low density polyethylene, or linear low density polyethylene; (4) PE1 is at least one of: (i) an ethylene homopolymer or (ii) a copolymer of ethylene and a third alpha-olefin selected from the group consisting of propylene, butene-1, and hexene-1; PE2 has a Mw of at least 1 × 10 ⁶ ; (6) PE2 is at least one of the following: (i) an ethylene homopolymer or (ii) ethylene and a selected from the group consisting of propylene, butene-1, hexene a copolymer of a fourth alpha-olefin of -1; (7) an amount of PE1 in the first polyolefin composition of from 70% by weight to 90% by weight based on the weight of the first polyolefin composition Within the range of (8) the amount of PE2 in the first polyolefin composition In the range of 0% by weight to 10% by weight (based on the weight of the first polyolefin composition); (9) the amount of PE1 in the second polyolefin composition is 40% by weight to 60% by weight (based on the weight of the second polyolefin composition); (10) the amount of PE2 in the second polyolefin composition is from 0% by weight to 10% by weight based on the second polyolefin (1) The first and/or second polyethylene resin has a molecular weight distribution ("Mw/Mn") of 5 to 300; (12) PE1 is a high density poly Ethylene and PE2 are ultrahigh molecular weight polyethylene; (b) the first polypropylene resin has at least one property selected from the group consisting of: (1) the first polypropylene resin is one or more of the following: (i a propylene homopolymer or (ii) a copolymer of propylene with a fifth olefin selected from one or more of the following alpha olefins: ethylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, vinyl acetate, methyl methacrylate, styrene, butadiene, 1,5-hexadiene, 1,7-octadiene, and 1,9 - decadiene; (2) the first polypropylene resin Mw is in the range of 1 × 10 ⁴ to 4 × 10 ⁶ ; (3) the first polypropylene resin has a Mw / Mn in the range of 1.01 to 100; (4) the first polypropylene resin system (5) the heat of fusion of the first polypropylene resin is at least 90 J/g; (6) the melting peak (second melting) of the first polypropylene resin is at least 160 ° C; and (c) The second polypropylene resin has at least one property selected from the group consisting of (1) Mw/Mn is 2.5 or less; (2) weight average molecular weight is 6.5 × 10 ⁵ or more; (3) heat of fusion is 95 J/g or more; and (4) having a second molecular weight of 5 × 10 ⁴ or less, the second polypropylene resin portion is 4.5% or less (based on the mass of the second polypropylene resin). A battery comprising an anode, a cathode, an electrolyte, and the multilayer microporous membrane of the first aspect of the invention, wherein the multilayer microporous membrane of the first aspect of the patent application is at least separated from the anode and the cathode. A battery according to claim 24, wherein the electrolyte contains lithium ions and the battery is a secondary battery. The battery of claim 24, wherein the multilayer film has a porosity of 25 to 80%, a gas permeability of 20 to 700 seconds/100 cc (a value converted to a thickness of 20 μm), and a pin puncture strength. 2,000 mN / 20 μm or more, shutdown temperature 120 to 140 ° C, melting temperature 170 ° C or higher, and battery capacity The response rate is 70% or higher. A battery as claimed in claim 24, which is used as a source of charge or a reservoir.