JP5661101B2 - Microporous membrane and methods for making and using such membranes - Google Patents

Description

(Cross-reference of related applications)
This application claims priority from US Provisional Patent Application No. 61 / 175,159, filed May 4, 2009, and European Patent Application No. 09162567.3, filed June 12, 2009, The disclosure is incorporated herein by reference in its entirety.

  The present invention relates to a multilayer microporous polymer membrane suitable for use as a battery separator film. The present invention also relates to a method for producing such a membrane, a battery containing such a membrane as a battery separator film, a method for producing such a battery, and a method for using such a battery.

  The microporous membrane can be used as a battery separator in, for example, lithium primary batteries and secondary batteries, lithium polymer batteries, nickel metal hydride batteries, nickel cadmium batteries, nickel zinc batteries, silver zinc secondary batteries, and the like. When a polyolefin microporous membrane is used for a battery separator, particularly a lithium ion battery separator, the properties of the membrane greatly affect the characteristics, productivity, and performance of the battery. Therefore, it is desirable that the microporous membrane is resistant to heat shrinkage, particularly at high temperatures. Resistance to thermal shrinkage (ie, “thermal shrinkage”) can improve the protection of the battery against internal short circuits.

  Such internal shorts include a loss of dimensional stability, particularly near the edges of the battery separator film. If the width of the film is reduced at a temperature higher than the film shutdown temperature, the negative electrode and the positive electrode may come into contact with each other. This is especially true for prismatic and cylindrical batteries, where any change in film width can lead to contact between the negative and positive electrodes at or near the edges of the battery.

  Traditionally, heat shrink characteristics have been determined at about 105 ° C, but the shutdown temperature of microporous membranes is typically in the range of 130 ° C to 140 ° C. Thus, the heat shrink properties at 130 ° C. can be a better indicator for identifying films that perform better under shutdown conditions. However, it has been found that the heat shrinkage characteristic at 130 ° C. cannot generally be predicted only from the heat shrinkage characteristic of the film at 105 ° C. In other words, a separator that exhibits good heat shrinkage characteristics at 105 ° C. does not necessarily exhibit sufficient performance at 130 ° C. Therefore, a need still remains for a battery separator film having improved heat shrinkage characteristics at 130 ° C.

In one aspect, an embodiment of the present invention is a multilayer microporous membrane comprising polypropylene having a Mw of greater than 1.0 × 10 ⁶ , and having a temperature of 130 ° C. of 9.5% or less in at least one planar direction providing a film having the following regular air permeability thermal shrinkage and 300 seconds / 100cm ³ / 20μm. Specific membranes are: (a) 1% to 20% by weight polyethylene based on the weight of the first layer, and Mw greater than 1.0 × 10 ⁶ and 80% based on the weight of the first layer. % to 99 each containing a polyethylene having a weight percent of 1.0 × 10 ⁶ or less of Mw, the first and third layers, (b) 5 wt% to 40 wt% of 1.0 × 10 ⁶ exceeds the Mw A polyethylene having a Mw greater than 0% by weight and less than or equal to 10% by weight and greater than 1.0 × 10 ⁶ , and a polyethylene having a Mw of 60% to 95% by weight less than or equal to 1.0 × 10 ⁶ (by weight The second layer located between the first and third layers, the percentage comprising a total polypropylene content of greater than 0 wt% and less than or equal to 10 wt% , 300 sec / 100 cm ^3/20 [mu] m or less regular moisture vapor It has a temperature and a TD heat shrinkage at 130 ° C. of 5% or less.

In another aspect, an embodiment of the present invention is a method of manufacturing a microporous membrane, wherein (a) the first layer includes a first polyolefin and at least a first diluent, and the second layer Comprises a second polyolefin and at least a second diluent, wherein the second polyolefin comprises polypropylene in an amount ranging from 1% to 40% by weight based on the weight of the second polyolefin, A multilayer extrudate comprising at least a first and a second layer having a Mw of greater than 0 × 10 ⁶ and a ΔHm of 110 J / g or more is stretched to at least one of MD or TD, and (b) first and second Removing at least a portion of the diluent from the stretched extrudate to produce a dry film having a first width along TD; (c) removing the film from the first width from about 1.1 to A second width greater than the first width at a second magnification in the range of about 1.8. And then (d) reduce the second width to a third width ranging from the first width to about 1.1 to about 1.6 times the first width. A method comprising:

In yet another embodiment, the present invention provides a battery comprising a negative electrode, a positive electrode, an electrolyte, and a multilayer microporous membrane comprising a polypropylene having a Mw greater than 1.0 × 10 ⁶ and a ΔHm greater than 112 J / g. The membrane has a heat shrinkage of 130 ° C. in at least one plane direction of 9.5% or less and a normalized air permeability of 400 sec / 100 cm ³ or less, and at least a negative electrode by a multilayer microporous membrane A battery is provided in which the positive electrode and the positive electrode are separated. Such battery systems can be used in many applications such as powering electric or hybrid electric vehicles.

It is a cross-sectional perspective view which shows an example of the cylindrical lithium ion secondary battery provided with the electrode assembly of this invention.

It is sectional drawing which shows the battery of FIG.

It is an expanded sectional view which shows the part A of FIG.

The present invention relates to the discovery of microporous membranes with improved heat shrink properties, ie better dimensional stability at high temperatures. Improvements in heat shrink properties are not only at relatively low temperatures (eg, below about 110 ° C., which is within the operating temperature range of conventional lithium ion batteries), but also at relatively high temperatures (eg, above 125 ° C., or above 135 ° C. For example, it is recognized also in the shutdown temperature vicinity of the conventional battery separator film for lithium ion batteries.
Structure and composition of multilayer microporous membrane

  In certain embodiments, the microporous membrane includes first and second layers. The first layer includes a first layer material and the second layer includes an independently selected second layer material. The first and second layer materials may be, for example, independently selected polyolefins. For example, the film has a top layer that is flat when viewed from an axially upper direction substantially perpendicular to the plane axis along the length and width of the film, and a flat bottom layer that is parallel or substantially parallel to the top layer. . In another embodiment, the multilayer microporous membrane is a membrane having three or more layers, eg, first and third layers and a second layer located between the first and third layers. including. The third layer may comprise an independently selected third layer material, but this is not essential. When the multilayer microporous membrane has more than two layers, at least one layer includes a first microporous layer material and at least one layer includes a second microporous layer material. In some embodiments, the first and third layers are made from (and generally include) substantially the same polymer or mixture of polymers (eg, both are made from the first layer material). ).

  In some embodiments, the multilayer microporous membrane includes a first and third layer (also referred to as a “surface” layer or “skin” layer) that constitutes the outer layer of the membrane, and a second layer that is coupled with the first layer. It includes three layers, an intermediate layer (or “core” layer) located between the third layers. In related embodiments, the multilayer microporous membrane may include additional layers, ie, layers other than the two skin layers and the core layer. For example, the membrane may contain an additional core layer between the first layer and the third layer. The membrane may be a coated membrane, i.e. there may be one or more additional layers above the first and third layers, or one or more of the first and third layers. These layers may be applied. In general, the second layer of the membrane has a thickness of 5% to 15% of the total thickness of the membrane, and the first and third layers of the membrane have the same thickness, The thickness of each of the three layers ranges from 42.5% to 47.5% of the total thickness of the membrane.

  Optionally, the core layer is in planar contact with one or more of the skin layers that are stacked face-to-face, for example in an A / B / A arrangement. If the membrane contains a polyolefin, the membrane may be referred to as a “polyolefin membrane”. The membrane may contain only polyolefins, but this is not essential and it is within the scope of the present invention for the polyolefin membrane to contain polyolefins and non-polyolefin materials. Suitable polyolefins can be made by a variety of suitable processes, such as polymerization in the presence of a chromium catalyst, Ziegler-Natta catalyst, or polymerization with one or more single site polymerization catalysts.

  Hereinafter, the first and second layer materials will be described in more detail.

In certain embodiments, the first layer comprises polyethylene. As used herein, the term polyethylene refers to a polyolefin homopolymer or copolymer containing repeating units derived from ethylene. Such polyethylenes include, but are not limited to, polyethylene homopolymers and / or copolymers in which at least 85% (number basis) of repeat units are derived from ethylene. The polyethylene may be a mixture of individual polyethylenes or a reactor blend, such as a mixture of two or more polyethylenes. In one embodiment, the polyethylene comprises a first polyethylene having a weight average molecular weight (“Mw”) of 1.0 × 10 ⁶ or less and a second polyethylene having a Mw of greater than 1.0 × 10 ⁶ . The third layer material includes a first polyethylene having a Mw of 1.0 × 10 ⁶ or less and a second polyethylene having a Mw greater than 1.0 × 10 ⁶ . The second layer material includes polypropylene. As used herein, the term polypropylene refers to a polyolefin homopolymer or copolymer containing propylene-derived repeat units. Such polypropylenes include, but are not limited to, polypropylene homopolymers and / or copolymers in which at least 85% (number basis) of repeat units are derived from propylene. The polypropylene may be a mixture of individual polypropylenes or a reactor blend, such as a mixture of two or more polypropylenes. For example, in certain embodiments, the second layer material is a first polyethylene having a Mw of 1.0 × 10 ⁶ or less, a polypropylene having a Mw greater than 1.0 × 10 ⁶ , and optionally 1.0 × A second polyethylene having a Mw greater than 10 ⁶ is included. Optionally, the first polyethylene of the second and / or third layer material is the same as the first polyethylene of the first layer material. Optionally, the second polyethylene of the second and / or third layer material is the same as the second polyethylene of the first layer material. In some embodiments, none of the first and third layer materials contain polypropylene in an amount greater than 0.5% by weight. In a related embodiment, the first and / or third layer material consists essentially of polyethylene, such as substantially the same polyethylene or a combination of polyethylenes.

  In certain embodiments, the first layer material comprises from about 80% to about 99% by weight first polyethylene, such as from 92.5% to about 97.5%, and from about 1% to about 9%. It contains 20% by weight, in particular about 1% to about 5% by weight of a second polyethylene, the weight percentage being based on the weight of the first layer material. In some embodiments, the polyethylene of the third layer material is selected from among substantially the same polyethylene in the same concentration range as the first layer material.

  In some embodiments, the second layer material comprises a first polyethylene, polypropylene, eg, up to 40% by weight polypropylene, and optionally a second polyethylene. For example, the second layer material may be about 60% to about 95% by weight first polyethylene, about 5% to about 40% polypropylene, and about 0% to about 10% second polyethylene. The weight percent is based on the weight of the second layer material. In another embodiment, the second layer material comprises about 60% to about 75% by weight first polyethylene, about 25% to about 35% polypropylene, and about 0.5% to about It contains 5% by weight of the second polyethylene, and the weight percent is based on the weight of the second layer material. In some embodiments, the microporous membrane comprises 1.5 to 5 wt% polypropylene, 75 to 98 wt% first polyethylene, and greater than 0 and up to 5 wt% second polyethylene; The weight percent is based on the weight of the second layer material.

  The microporous membrane may also contain copolymers, inorganic species (such as species containing silicon and / or aluminum atoms), and / or heat resistant polymers such as the polymers described in PCT Publication WO2007 / 132294 and WO2008 / 016174. Good, but these are not essential. In certain embodiments, the membrane is substantially free of such materials. Substantially free in this context means that the amount of such material in the microporous membrane is less than 1% by weight, based on the total weight of the polymer used to make the microporous membrane.

  The final microporous membrane typically contains the polymer used to produce the extrudate. Small amounts of diluent or other species introduced during processing may also be present, generally in an amount of less than 1% by weight, based on the weight of the microporous membrane. During processing, the molecular weight of the polymer may be reduced by a small amount, which is acceptable. In some embodiments, the Mw of the polymer in the membrane is reduced, for example by no more than about 10%, no more than about 1%, or no more than about 0.1% of the Mw of the polymer used to make the membrane.

Hereinafter, the diluent used for the production of polypropylene, first and second polyethylene, and extrudate and microporous membrane will be described in more detail.
Materials used in the production of microporous membranes

In some embodiments, the first and third layer materials are prepared from a first diluent and first and second polyethylenes, and the second layer material is a second diluent, first polyethylene. , Polypropylene, and optionally a second polyethylene. Optionally, polymers described in inorganic species (such as species containing silicon and / or aluminum atoms) and / or PCT publications WO 2007/132294 and WO 2008/016174, both of which are hereby incorporated by reference in their entirety. The first, second, and / or third layer material may be prepared using a heat resistant polymer such as In some embodiments, these optional species are not used.
A. First polyethylene

The first polyethylene has a Mw of 1.0 × 10 ⁶ or less, such as in the range of about 1.0 × 10 ⁵ to about 9 × 10 ⁵ , for example, about 4 × 10 ⁵ to about 8 × 10 ⁵ . Optionally, the first polyethylene has a molecular weight distribution (“MWD”) in the range of about 1 to about 100, such as about 3 to about 20. For example, the first polyethylene may be one or more of high density polyethylene (“HPDE”), medium density polyethylene, branched low density polyethylene, or linear low density polyethylene.

  In some embodiments, the first polyethylene has 0.2 or more terminal unsaturated groups per 10,000 carbon atoms, such as 5 or more per 10,000 carbon atoms or 10 or more per 10,000 carbon atoms. Have quantity. The amount of terminal unsaturated groups can be measured, for example, according to the procedure described in PCT Publication WO 97/23554.

In some embodiments, the first polyethylene is a comonomer such as (i) an ethylene homopolymer, or (ii) ethylene and 10 mol% or less of an α-olefin (eg, propylene, butene-1, hexene-1, etc.). And at least one of the copolymers. Such polymers or copolymers can be made by any convenient polymerization method such as a Ziegler-Natta catalyst process, a chromium catalyst process, or a single site catalyst process. Optionally, the comonomer is one or more of propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, vinyl acetate, methyl methacrylate, or styrene, or other monomers. It is.
B. Second polyethylene

The second polyethylene is 1.0, for example in the range of 1.1.0 × 10 ⁶ to about 5 × 10 ⁶ , for example about 1.2 × 10 ⁶ to about 3 × 10 ⁶ , for example about 2 × 10 ⁶ . * Mw greater than 10 ⁶ The second polyethylene has a MWD in the range of about 2 to about 100, such as about 3 to about 10. For example, the second polyethylene may be ultra high molecular weight polyethylene (“UHMWPE”). In some embodiments, the first polyethylene is at least one of (i) an ethylene homopolymer, or (ii) a copolymer of ethylene and no more than 10 mole% comonomer such as an α-olefin. Optionally, the comonomer is one or more of propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, vinyl acetate, methyl methacrylate, or styrene, or other monomers. It is. Such polymers or copolymers can be made by any convenient polymerization method such as a Ziegler-Natta catalyst process, a chromium catalyst process, or a single site catalyst process.
C. polypropylene

  If desired, the polypropylene may be propylene and up to 10.0 mole percent comonomer (such as one or more α-olefins), such as ethylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1. , Octene-1, vinyl acetate, methyl methacrylate, styrene and the like; diolefins such as butadiene, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene; and copolymers with other comonomers .

In some embodiments, the polypropylene comprises a first polypropylene, which itself comprises one or more polypropylene homopolymers or copolymers of propylene (random or block). The first polypropylene has a Mw of 5 × 10 ⁵ or more, for example, about 5.0 × 10 ⁵ to about 2.0 × 10 ⁶ , for example, about 1.1 × 10 ⁶ to about 1.5 × 10 ^6. . Optionally, the polypropylene has an MWD of 100 or less, such as from about 1 to about 50, or from 2.0 to 6.0, and / or such as from 110.0 J / g to 120.0 J / g, such as about 113.0 J / g. It has a heat of fusion (“ΔHm”) of 100.0 J / g or more, such as ˜119.0 J / g or 114.0 J / g to about 116.0 J / g. ΔHm is measured using differential scanning calorimetry according to JIS K7122, as described in PCT Patent Publication No. WO2007 / 132294.

Optionally, the polypropylene has one or more of the following properties: (i) the polypropylene is isotactic; (ii) at least about 50,000 Pa seconds at a temperature of 230 ° C. and a strain rate of 25 seconds ^−1. (Iii) a melting peak of at least about 160 ° C. (second melting); and / or (iv) a Truton ratio of at least about 15 when measured at a temperature of about 230 ° C. and a strain rate of 25 sec ^−1. .

The Mw and MWD of polyethylene and polypropylene are determined using a high temperature size exclusion chromatograph equipped with a differential refractometer (DRI), ie “SEC” (GPC PL 220, manufactured by Polymer Laboratories). The measurement is performed according to the procedure disclosed in “Macromolecules, Vol. 34, No. 19, pp. 6812-6820 (2001)”. Three PLgel Mixed-B columns (Polymer Laboratories) are used to determine Mw and MWD. For polyethylene, the nominal flow rate is 0.5 cm ³ / min, the nominal injection volume is 300 μL, and the transfer line, column, and DRI detector are contained in an oven maintained at 145 ° C. For polypropylene, the nominal flow rate is 1.0 cm ³ / min, the nominal injection volume is 300 μL, and the transfer line, column, and DRI detector are contained in an oven maintained at 160 ° C.

  The GPC solvent used is a filtered, Aldrich reagent grade 1,2,4-trichlorobenzene (TCB) containing about 1000 ppm butylated hydroxytoluene (BHT). The TCB is degassed with an online degasser prior to introduction into the SEC. The same solvent is used as the SEC eluent. A polymer solution is prepared by placing the dried polymer in a glass container, adding the desired amount of TCB solvent, and then heating the mixture at 160 ° C. with continuous stirring for about 2 hours. The concentration of the polymer solution is 0.25 to 0.75 mg / ml. The sample solution is filtered off-line with a 2 μm filter using Model SP260 Sample Prep Station (manufactured by Polymer Laboratories) before being injected into GPC.

The column set separation efficiency is calibrated with a calibration curve generated using 17 different polystyrene standards with Mp ("Mp" defined as the peak at Mw) in the range of about 580 to about 10,000,000. Polystyrene standards are obtained from Polymer Laboratories (Amherst, Mass.). A calibration curve (logMp vs. retention capacity) is created by recording the retention capacity at the peak of the DRI signal for each PS standard and fitting this data set to a second order polynomial. Samples are analyzed using IGOR Pro manufactured by Wave Metrics, Inc.
Method for producing microporous membrane

  In certain embodiments, the multilayer microporous membrane of the present invention is a bilayer membrane. In another embodiment, the multilayer microporous membrane has at least three layers. The present invention is not limited thereto, but mainly includes first and third layers including a first layer material, and a second layer located between the first layer and the third layer. A method for manufacturing a microporous film will be described with respect to a three-layer film having a second layer containing a material.

  One method for producing a multilayer microporous membrane of the present invention includes multilayering by laminating or coextrusion of extrudates or membranes, such as single layer extrudates or single layer microporous membranes. For example, the one or more layers comprising a first layer material can be one or both sides of one or more layers comprising a second layer material, eg, a layer (or layers) comprising a second layer material. May be co-extruded with the layer comprising the first layer material located at.

In the membrane manufacturing process, a multilayer having a first planar direction (eg, the machine direction of extrusion or “MD”) and a second orthogonal planar direction (eg, a direction transverse to the MD, transverse direction or “TD”) The extrudate is cooled. The extrudate may include at least first, second, and third layers, wherein the second layer is located between the first layer and the third layer. The first and third layers of the extrudate include a first layer material and at least a first diluent, and the second layer of the extrudate includes a second layer material and at least a second diluent. . The first and third layers may be outer layers of the extrudate, also called skin layers. One skilled in the art will appreciate that the third layer of the extrudate can be formed from a different layer material, such as the third layer material, and may have a different thickness than the first layer. Can understand. The process also includes first stretching in the first planar direction by stretching the cooled extrudate to MD and / or TD and removing at least a portion of the first and second diluents from the stretched extrudate. A dry membrane having a dry length and a first dry width in the second planar direction is also produced. The process then involves the formation of the final film by stretching the dry film along TD and optionally MD. Hereinafter, an embodiment for producing a three-layer film will be described in more detail.
Mixing the first layer material with the first diluent

  The first layer material is produced by mixing the first polyethylene and optionally the second polyethylene, for example by dry blending or melt blending. The mixed polymer may be mixed with one or more diluents to form a mixture of polymer and diluent. The polymer may be in the form of a polymer resin. The diluent may be, for example, a solvent for the polymer of the first layer material. When the diluent is such a solvent, the diluent can be referred to as a film-forming solvent and the mixture of polymer and diluent can be referred to as a polymer solution, such as a polyolefin solution. The combined first layer material and diluent may contain one or more additives such as antioxidants as desired. In certain embodiments, the amount of such additives does not exceed 1% by weight, based on the weight of the polymer and diluent mixture.

  Optionally, the first diluent is a solvent that is liquid at room temperature. Without wishing to be bound by any theory or model, the extrudate (usually a gel-like sheet) is stretched at a relatively high stretch ratio by forming a first polyolefin solution using a liquid solvent. It will be possible.

  As the diluent of the present invention, any species that can be combined with the resin at the extrusion temperature to form a single phase may be used. Diluents include aliphatic or cyclic hydrocarbons such as nonane, decane, decalin, and paraffin oil, and phthalate esters such as dibutyl phthalate and dioctyl phthalate. Paraffin oil having a kinematic viscosity at 40 ° C. of 20 to 200 cst may be used. The selection of the first diluent, mixing conditions, extrusion conditions, etc., for example, may be the same as that disclosed in PCT Patent Publication No. WO 2008/016174, which is incorporated herein by reference in its entirety. Good.

The amount of the first diluent in the mixture of diluent and first layer material in the first polyolefin solution is not critical. In some embodiments, the amount of the first diluent is 20 wt% to 99 wt%, preferably 60 wt% to 80 wt%, based on the combined weight of the first diluent and the first layer material. It is in the range of wt%. It is believed that higher concentrations of diluent contribute at least in part to improving the heat shrink properties of some of the films described herein.
Mixing the second layer material with the second diluent

  The second layer material and the second diluent may be mixed by a method similar to the method used for mixing the first layer material and the first diluent. For example, the polymer comprising the second layer material may be mixed by melt blending the first polyethylene, polypropylene, and optionally the second polyethylene. The second diluent may be selected from the same diluent as the first diluent. The second diluent may be selected independently of the first diluent (and usually selected independently), but the diluent may be the same as the first diluent. Alternatively, the first diluent may be used in the same relative concentration as used in the first polyolefin solution.

In some embodiments, 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 in the range of the melting point of polypropylene (Tm2) to Tm2 + 90 ° C. ing.
Extrusion

  In some embodiments, the combined first layer material and the first diluent are directed from the first extruder to the first and third dies to combine the combined second layer material and the second. The diluent is led from the second extruder to the second die. A sheet-like layered extrudate (ie, an object that is significantly larger in the planar direction than in the thickness direction) is extruded (eg, co-extruded) from the first, second, and third dies and the combined first A multilayer extrudate can be produced having a skin layer of the first and second layer materials and a core layer of the combined second layer material and second diluent.

The selection of the die or dies and extrusion conditions may be the same as that disclosed, for example, in PCT Publication No. WO 2008/016174.
Cooling multilayer extrudates

The multilayer extrudate can be exposed to temperatures ranging from 15 ° C to 25 ° C to form a cooled extrudate. The cooling rate is not particularly important. For example, the extrudate may be cooled at a cooling rate of at least about 30 ° C./min until the temperature of the extrudate (cooled temperature) is approximately the same as (or below) the gel temperature of the extrudate. . The cooling process conditions may be the same as those disclosed in, for example, PCT Publication No. WO2008 / 01617. In some embodiments, the cooled extrudate has a thickness of 10 mm or less, such as in the range of 0.1 mm to 10 mm, or 0.5 mm to 5 mm. Typically, the second layer of the cooled extrudate has a thickness of 5% to 15% of the total thickness of the cooled extrudate, and the first and third layers of the cooled extrudate are substantially the same. Each having a thickness, the thickness of the first and third layers each ranging from 42.5% to 47.5% of the total thickness of the cooled extrudate.
Drawing of cooled extrudate

  The cooled extrudate is then stretched (referred to as “wet” stretching) in at least one direction (eg, at least one planar direction such as MD or TD) to produce a stretched extrudate. If desired, the extrudate is stretched simultaneously in the transverse and machine directions to a magnification in the range of 4-6. Suitable stretching methods are described, for example, in PCT Publication No. WO2008 / 016174. Although not essential, the MD and TD magnifications may be the same. In some embodiments, the draw ratio is equal to 5 in MD and TD. In certain embodiments, stretching is performed at a deformation rate of about 850% / min or less, 800% / min or less, 775% / min or less, or 700% / min or less. Deformation rates in the range of 600% / min to about 800% / min, or 700% / min to 800% / min are useful. Although a biaxially stretched film is stretched in both MD and TD dimensions, the term “deformation rate” as used herein refers to at least one planar dimension of the film (eg, MD, TD, or combinations thereof). Refers to the rate at which increases. For example, a film that is stretched 5 times to MD and TD during the 1-minute biaxial stretching process will have a deformation rate of 500% / min for both MD and TD, with 500% deformation It can be described as stretched at a speed.

  Although not required, stretching may be performed while subjecting the extrudate to temperatures in the range of approximately Tcd temperature to Tm. Tcd and Tm are defined as the crystal dispersion temperature and the melting point of the lowest melting polyethylene among the polyethylenes used to make the extrudate (ie, the first and second polyethylenes). The crystal dispersion temperature is determined by measuring the temperature characteristics of dynamic viscoelasticity according to ASTM D 4065. In embodiments where the Tcd is in the range of about 90-100 ° C, the stretching temperature is about 90-125 ° C, preferably about 100-125 ° C, more preferably 105-125 ° C, even more preferably 119-about 125. It may be ° C. It is considered that when the stretching temperature is higher, a film with less shrinkage under operating conditions may be obtained.

  In some embodiments, the stretched extrudate is optionally subjected to a heat treatment prior to diluent removal. In heat treatment, the stretched extrudate is exposed to a temperature that is higher (warm) than the temperature at which the extrudate is exposed during stretching. In some embodiments, the stretched extrudate is exposed to a temperature in the range of 120 ° C. to 125 ° C. for a time in the range of 1 second to 100 seconds, during which time, for example, using a tenter clip, the stretched extrudate is By holding along the outer periphery, the wet length and wet width are kept constant. In another embodiment, the stretched extrudate is exposed to a temperature that is not higher, preferably lower (cold) than the temperature to which the extrudate is exposed during stretching. In some embodiments, the stretched extrudate is subjected to a time in the range of 1 second to 100 seconds, 90 ° C to 120 ° C, particularly when the stretch temperature is 119 to 120 ° C, particularly in the range of about 90 ° C to 100 ° C. In the meantime, the wet length and the wet width are kept constant, for example, by holding the stretched extrudate along its outer periphery using a tenter clip. While the stretched extrudate is exposed to its higher temperature, the planar dimensions (MD length and TD width) of the stretched extrudate can be kept constant. Since the extrudate contains polymer and diluent, its length and width are referred to as “wet” length and “wet” width. In other words, there is no expansion or contraction (ie dimensional change) of the stretched extrudate to MD or TD during heat treatment.

  In this process, and in other processes such as dry stretching and heat setting that expose the sample (eg, extrudates, dry extrudates, membranes, etc.) to high temperatures, such exposure heats the air and then brings the heated air close to the sample. Can be done by carrying it on. The temperature of the heated air is usually controlled to a set value equal to the desired temperature, and then directed toward the sample through a plenum or the like. Other methods of exposing the sample to high temperatures may be used with or in place of heated air, including conventional methods such as exposing the sample to a heated surface, infrared heating in an oven, and the like.

While not wishing to be bound by any particular theory, it is believed that a relatively higher stretching temperature allows for relaxation of polymer chain entanglement, thereby reducing thermal shrinkage at higher temperatures. The optional heat treatment is also considered to contribute to the improvement of heat shrinkage characteristics at higher temperatures.
Removal of first and second diluents

  In certain embodiments, at least a portion of the first and second diluents (eg, film-forming solvents) are removed (or replaced) from the stretched extrudate to form a dry film. A replacement (or “wash”) solvent may be used to remove (wash or replace) the first and second diluents. The processing conditions for removing the first and second diluents may be the same as those disclosed, for example, in PCT Publication No. WO2008 / 016174. The term “dry film” refers to an extrudate from which at least a portion of the diluent has been removed. Although it is not necessary to remove all of the diluent from the stretched extrudate, it may be desirable to do so because removing the diluent increases the porosity of the final membrane.

In some embodiments, at least a portion of any remaining volatile species, such as a cleaning solvent, may be removed from the dry film at any point after the diluent is removed. Any method capable of removing the cleaning solvent may be used, including conventional methods such as heat drying and air drying (moving air). The processing conditions for removing volatile species such as cleaning solvents may be the same as those disclosed, for example, in PCT Publication Nos. WO2008 / 016174 and WO2007 / 132294.
Stretching of dry film

  The dried film is stretched to at least TD (referred to as “dry stretching”). A dry film that has been stretched dry is referred to as a “stretched” film. Prior to dry stretching, the dry film has an initial size of MD (first dry length) and an initial size of TD (first dry width). As used herein, the term “first drying width” refers to the size of the dry film in the transverse direction before the start of dry stretching. The term “first dry length” refers to the size of the dry film in the machine direction before the start of dry stretching. For example, a tenter stretching apparatus of the type described in International Publication No. 2008/016174 can be used.

  The dry film is stretched from the first dry width to the TD to a second dry width wider than the first dry width at a magnification in the range of about 1.1 to about 1.8 (“TD dry draw ratio”). May be. If desired, when dry stretching is used, the dry film is converted from a first dry length to a second dry length that is longer than the first dry length at a certain magnification ("MD dry stretch ratio"). You may extend | stretch. Stretching (also called restretching because the extrudate containing the diluent has already been stretched) may be performed sequentially or simultaneously in MD and TD. Usually, the TD heat shrinkage rate has a larger influence on the battery characteristics than the MD heat shrinkage rate. Therefore, the size of the TD dry magnification does not normally exceed the size of the MD dry magnification. When TD dry stretching is used, dry stretching may be performed simultaneously or sequentially with MD and TD. When dry stretching is sequential, MD stretching is usually performed first, followed by TD stretching.

  Dry stretching is usually performed while subjecting the dried film to temperatures below Tm, for example in the range of about Tcd-30 ° C. to Tm. In embodiments where the membrane is a multilayer membrane having first and third layers comprising polyethylene and a second layer comprising polypropylene located between the first and third layers, the stretching temperature Is usually performed on a film exposed to a temperature in the range of about 70 to about 135 ° C., for example about 80 ° C. to about 132 ° C., in particular 125 ° C. to 132 ° C. or 128 ° C. to 131 ° C.

  In some embodiments, the MD has a dry draw ratio in the range of about 1.1 to about 1.5, such as 1.2 to 1.4, and the TD has a dry draw ratio of, for example, 1.15 to 1. The range is from about 1.1 to about 1.3, such as .25, with MD stretching first followed by stretching in the TD direction.

The stretching rate is preferably 3% / second or more in the stretching direction (MD or TD), and this rate may be independently selected for MD and TD stretching. The stretching rate is preferably 5% / second or more, more preferably 10% / second or more, for example, in the range of 5% / second to 25% / second. Although not particularly important, the upper limit of the stretching rate is preferably 50% / second in order to prevent the film from bursting.
Controlled film width reduction

  Subsequent to dry stretching, the dry film is subjected to controlled width reduction from the second dry width to the third width, the third dry width being from the first dry width to the first dry width. The range is about 1.1 to about 1.6 times, particularly 1.3 to 1.5 times. The reduction in width is usually performed while subjecting the film to a temperature above Tcd-30 ° C. but below Tm. For example, during width reduction, the membrane may be exposed to a temperature in the range of about 70 ° C. to about 135 ° C., such as about 127 ° C. to about 132 ° C., eg, about 128 ° C. to about 131 ° C. In some embodiments, the film width reduction is performed while subjecting the film to a temperature below Tm. In certain embodiments, the third drying width is in the range of 1.0 to about 1.6 times, or 1.2 to 1.5 times the first drying width.

It is believed that, during controlled width reduction, subjecting the film to a temperature above that at which the film was exposed during TD stretching will make the final film more resistant to thermal shrinkage.
Any heat set

  Optionally, the film is thermally treated (heat set) one or more times after removal of the diluent, eg, after dry stretching, after controlled width reduction, or both. It is considered that the heat set stabilizes the crystals and forms a uniform lamellar layer in the film. In certain embodiments, the heat set causes the film to range from Tcd to Tm, such as a temperature in the range of about 100 ° C to about 135 ° C, such as in the range of about 127 ° C to about 132 ° C, or about 129 ° C to about 131 ° C. It is performed while exposed to the temperature of. Generally, the heat setting is performed for a time sufficient to form a uniform lamellar layer in the film, for example, in the range of 1 to 100 seconds. In some embodiments, the heat set is performed under typical heat set “heat set” conditions. The term “heat setting” refers to heat setting performed while maintaining the length and width of the membrane substantially constant, for example, by holding the outer periphery of the membrane with a tenter clip during heat setting.

  If desired, an annealing treatment may be performed after the heat setting step. Annealing is a heat treatment that does not apply a load to the film, and may be performed using, for example, a heating chamber equipped with a belt conveyor or an air-floating-type heating chamber. Annealing may be performed continuously with the tenter loosened after heat setting. During annealing, the membrane may be exposed to temperatures in the range of Tm or lower, such as in the range of about 60 ° C to about Tm-5 ° C. Annealing is thought to improve the permeability and strength of the microporous membrane.

  Optional hot roller treatment, hot solvent treatment, crosslinking treatment, hydrophilic treatment, and coating treatment may be performed as desired, for example, as described in PCT Publication No. WO 2008/016174.

  If desired, an annealing treatment may be performed before, during, or after heat setting. Annealing is a heat treatment that does not apply a load to the membrane, and may be performed using, for example, a heating chamber equipped with a belt conveyor or an air floating heating chamber. Annealing may be performed continuously with the tenter loosened after heat setting, for example. The temperature at which the film is exposed during annealing (annealing temperature) may be, for example, in the range of about 126.9 ° C. to 128.9 ° C. It is considered that the heat shrinkage and strength of the microporous membrane are improved by annealing.

Optional hot roller treatment, hot solvent treatment, crosslinking treatment, hydrophilic treatment, and coating treatment may be performed as desired, for example, as described in PCT Publication No. WO 2008/016174.
Characteristics of multilayer microporous membrane

  In certain embodiments, the membrane is a multilayer microporous membrane. The thickness of the film is usually in the range of 3 μm or more. For example, the membrane may have a thickness in the range of about 5 μm to about 200 μm, for example about 10 μm to about 50 μm. The thickness of the film can be measured, for example, with a contact thickness meter over the width of 10 cm at 1 cm intervals in the longitudinal direction, and then an average value can be obtained to obtain the film thickness. Thickness gauges such as Mitutoyo Corporation Lightmatic are suitable. As will be described later, this method is also suitable for measuring a change in thickness after thermal compression. Non-contact thickness measurement methods such as optical thickness measurement methods are also suitable.

Optionally, the membrane has one or more of the following properties:
A. Porosity

In some embodiments, the membrane has a porosity of 25% or greater, such as in the range of about 25% to about 80%, or 30% to 60%. Membrane porosity is measured by conventional methods by comparing the actual weight of the membrane with the weight of an equivalent non-porous membrane of the same composition (equivalent in the sense of having the same length, width, and thickness) To do. Next, a porosity is calculated | required using the following formula | equation: Porosity% = 100x (w2-w1) / w2. Where “w1” is the actual weight of the microporous membrane and “w2” is the weight of an equivalent non-porous membrane having the same size and thickness.
B. Normalized air permeability

In some embodiments, a regular air permeability (Gurley value) of the film is less than 400 seconds / 100cm ³ / 20μm. Normalized air permeability is measured according to JIS P8117, and the result is normalized to the air permeability value of an equivalent membrane having a thickness of 20 μm using the formula A = 20 μm * (X) / T ₁ To do. Where X is the measured value of the air permeability of the membrane having the actual thickness T ₁ and A is the normalized air permeability of an equivalent membrane having a thickness of 20 μm. Air permeability value for normalizing the film thickness of 20 [mu] m, air permeability value is expressed in units of "seconds / 100 cm ^3/20 [mu] m." In some embodiments, the regular air permeability is 20.0 sec / 100 cm ^3/20 m to about 400 seconds / 100 cm ^3/20 [mu] m or 150 seconds / 100cm ³ / 20μm~250 sec / 100 cm ^3/20 [mu] m range, It is.
C. Normalized puncture strength

In some embodiments, the membrane has a puncture strength of 130 mN / μm or greater, such as in the range of 130 mN / μm to 250 mN / μm. Puncture strength is a microporous membrane having a thickness T _1, terminal (a radius of curvature R: 0.5 mm) spherical define the maximum load measured when piercing a diameter 1mm needle is at 2 mm / sec rate of a Is done. This puncture strength is expressed by an equation of S ₂ = 1 μm * (S ₁ ) / T ₁ (where S ₁ is an actual measurement value of puncture strength, S ₂ is a normalized puncture strength, and T ₁ is an average of the film) Is normalized to a value at a film thickness of 1 μm.
D. Tensile strength

In some embodiments, the membrane has an MD tensile strength of 55,000 kPa or higher, such as in the range of 58,000 to 90,000 kPa, and / or 70,000 kPa or higher, such as in the range of 75,000 kPa to 110,000 kPa. Has TD tensile strength. Tensile strength is measured in MD and TD according to ASTM D-882A.
E. Tensile elongation ≧ 100%

Tensile elongation is measured according to ASTM D-882A. In some embodiments, the MD and TD tensile elongation of the membrane is 150% or more, each in the range of, for example, 150% to 350%. In another embodiment, the membrane has an MD tensile elongation in the range of, for example, 150% to 250%, and a TD tensile elongation in the range of, for example, 150% to 250%.
F. Shutdown temperature

In certain embodiments, the membrane has a shutdown temperature of 140 ° C. or less, such as in the range of about 132 ° C. to about 138 ° C. The shutdown temperature of the microporous membrane is measured by the method disclosed in PCT Publication WO 2007/052663, which is incorporated herein by reference in its entirety. According to this method, the microporous membrane is exposed to a rising temperature (5 ° C./min), during which the air permeability of the membrane is measured. The shutdown temperature of the microporous membrane is defined as the temperature at which the air permeability (Gurley value) of the microporous membrane is 100,000 seconds / 100 cm ³ . The air permeability of the microporous membrane is measured according to JIS P8117 using an air permeability meter (Asahi Seiko Co., Ltd., EGO-1T).
G. Fracture temperature

  In some embodiments, the membrane breaking temperature is 170 ° C. or higher, such as in the range of 171 ° C. to 200 ° C., or 172 ° C. to 190 ° C. The film breaking temperature is measured as follows. A 5 cm × 5 cm microporous membrane was sandwiched between blocks each having a circular opening having a diameter of 12 mm, and a tungsten carbide sphere having a diameter of 10 mm was placed on the microporous membrane in the circular opening. The membrane is then exposed to increasing temperature at a rate of 5 ° C./min. The membrane breaking temperature is defined as the temperature at which the sphere first breaks through the membrane. The meltdown temperature of the membrane is defined as the temperature at which the sphere completely penetrates the sample, ie the temperature at which the sample breaks.

In some embodiments, the membrane breaking temperature is in the range of 180 ° C to 190 ° C. Since the membrane has a desired high tear temperature, it is suitable for use as a battery separator in high-power, high-capacity lithium-ion batteries such as batteries used to power electric and hybrid electric vehicles. It is.
H. Meltdown temperature

The meltdown temperature is measured by the following procedure: A rectangular sample of 3 mm × 50 mm is cut out from the liquid-permeable microlayer membrane so that the long axis of the sample is aligned with TD and the short axis is aligned with MD. . This sample is set in a thermomechanical analyzer (TMA / SS6000 manufactured by Seiko Instruments Inc.) with a distance between chucks of 10 mm. That is, the distance from the upper chuck to the lower chuck is 10 mm. The lower chuck is fixed, and a load of 19.6 mN is applied to the sample with the upper chuck. Both chucks and sample are enclosed in a heatable tube. Starting at 30 ° C, increasing the temperature inside the tube at a rate of 5 ° C / min, measuring the change in sample length under a load of 19.6 mN at 0.5 second intervals and recording with increasing temperature To do. The temperature is raised to 200 ° C. The meltdown temperature of a sample is defined as the temperature at which the sample breaks, and is usually in the range of about 145 ° C to about 200 ° C. In some embodiments, the meltdown temperature is 180 ° C or higher, such as in the range of 180 ° C to 200 ° C, such as 185 ° C to about 195 ° C.
I. Thermal shrinkage at 105 ° C. in at least one plane direction of about 1% or less

In certain embodiments, the membrane is at 105 ° C. in at least one planar direction (eg, MD or TD) of 1% or less, such as 0.5% or less, eg, in the range of 0.1% to 0.25%. Has heat shrinkage. The shrinkage of the membrane at 105 ° C. to MD and TD is measured as follows: (i) The microporous membrane specimen size at ambient temperature is measured for both MD and TD; The porous membrane specimens are allowed to equilibrate for 8 hours at a temperature of 105 ° C. without loading, and then (iii) the membrane size is measured for both MD and TD. Thermal (ie, “thermal”) shrinkage to MD and TD can be obtained by dividing measurement result (i) by measurement result (ii) and expressing the resulting quotient as a percentage.
J. et al. Thermal shrinkage at 130 ° C

  In certain embodiments, the membrane has a TD heat shrinkage measured at 130 ° C. of 8% or less, such as 1% to 7.5%. The temperature of 130 ° C. is generally within the operating temperature range of the lithium ion secondary battery during charging and discharging, but is close to the upper end (shutdown) of this temperature range. The value of can be particularly important.

The measured value is slightly different from the measured thermal shrinkage at 105 ° C., which means that the edge of the film, which is parallel to the TD of the film, is usually fixed in the cell, especially parallel to the MD of the film. Reflects the fact that there is a limited degree of freedom to allow expansion or reduction (shrinkage) to TD near the center of an edge. Therefore, a sample of a microporous film having a square shape of 50 mm along TD and 50 mm along MD is fixed to a frame (by tape or the like) with an end parallel to TD, and 35 mm in MD and 50 mm in TD. Leave the opening that is and install it on the frame. Next, the frame to which the sample is attached is heated for 30 minutes at a temperature of 130 ° C. (in an oven or the like) in a thermal equilibrium state and then cooled. In general, the TD heat shrinkage causes the end of the film parallel to the MD to bend inwardly (towards the center of the frame opening). Shrinkage to TD (expressed in percent) is equal to the TD length of the sample before heating divided by the shortest length (in frame) of the sample TD after heating multiplied by 100 percent.
K. Maximum heat shrinkage in the molten state

  The maximum shrinkage in the molten state in the plane direction of the film is measured by the following procedure.

  Record the length of the sample measured in the temperature range of 135 ° C. to 145 ° C. using the TMA procedure described in Measuring Melt Down Temperature. The membrane shrinks and the distance between chucks decreases as the membrane shrinks. Maximum shrinkage in the molten state is the minimum length (equal to L2) measured in the range of about 135 ° C to about 145 ° C, usually from the length of the sample between the chucks measured at 23 ° C (L1: equal to 10 mm) Is divided by L1, ie, [L1-L2] / L1 * 100%. When measuring the TD maximum shrinkage, a 3 mm × 50 mm rectangular sample to be used is prepared at the same time as the microporous membrane is produced by this process, and the long axis of the sample is aligned with the transverse direction of the microporous membrane, and Cut from the microporous membrane so that the short axis is aligned with the machine direction. When measuring the MD maximum shrinkage, a 3 mm × 50 mm rectangular sample to be used is manufactured at the same time as the microporous membrane is manufactured in this process, and the long axis of the sample is aligned with the machine direction of the microporous membrane, and Cut from the microporous membrane so that the minor axis is aligned with the transverse direction.

In some embodiments, the maximum MD heat shrinkage of the film in the molten state is 25% or less or 20% or less, such as in the range of 1% to 25% or 2% to 20%. In some embodiments, the maximum TD heat shrink rate of the film in the molten state is 11% or less, or 6% or less, such as in the range of 1% to 10% or 2% to 5.5%.
battery

  The microporous membrane of the present invention is useful as a battery separator in, for example, lithium ion primary batteries and secondary batteries. Such a battery is described in PCT Publication WO 2008/016174, which is incorporated herein by reference in its entirety.

  FIG. 1 shows an example of a cylindrical lithium ion secondary battery provided with two battery separators. The microporous membrane of the present invention is suitable for use as a battery separator for this type of battery. The battery includes a wound electrode assembly 1 including a first separator 10, a second separator 11, a positive electrode sheet 13, and a negative electrode sheet 12. The scale of the thickness of the separator is not a fixed ratio, but is greatly enlarged for illustration. For example, the wound electrode assembly 1 may be wound such that the second separator 11 is disposed outside the positive electrode sheet 13 and the first separator 10 is disposed inside the positive electrode sheet. In this example, as shown in FIG. 2, the second separator 11 is disposed on the inner surface side of the wound electrode assembly 1.

  In this example, as shown in FIG. 3, the negative electrode active material layer 12b is formed on both sides of the current collector 12a, and the positive electrode active material layer 13b is formed on both sides of the current collector 13a. As shown in FIG. 2, the negative electrode lead 20 is attached to the end portion of the negative electrode sheet 12, and the positive electrode lead 21 is attached to the end portion of the positive electrode sheet 13. The negative electrode lead 20 is connected to the battery lid 27, and the positive electrode lead 21 is connected to the battery can 23.

  Although the cylindrical battery has been described, the present invention is not limited to this, and the separator of the present invention is, for example, a negative electrode that is alternately connected in parallel with a separator positioned between the stacked negative electrode and the positive electrode. Suitable for use in prismatic batteries, such as batteries containing electrodes in the form of laminated plates of (one or more) 12 and positive electrode (3) 13.

  When assembling the battery, the negative electrode sheet 12, the positive electrode sheet 13, and the first and second separators 10 and 11 are impregnated with an electrolytic solution, so that ions passing through the separators 10 and 11 can be moved. The impregnation treatment can be performed, for example, by immersing the electrode assembly 1 in an electrolytic solution at room temperature. In the cylindrical lithium ion secondary battery, the wound electrode assembly 1 (see FIG. 1) is inserted into a battery can 23 having an insulating plate 22 at the bottom, and an electrolyte is injected into the battery can 23 to insulate the electrode assembly 1. It can be manufactured by covering with the plate 22 and caulking the battery lids (24, 25, 26, and 27) to the battery can 23 via the gasket 28. The battery lid functions as a negative electrode terminal.

  FIG. 3 (assuming that the battery lid of FIG. 1, ie, the negative electrode terminal is on the right side) has the advantage of using a separator that has less tendency to shrink laterally (with respect to the separator manufacturing process) as the temperature of the battery increases. Is illustrated. One of the roles of the separator is to prevent contact between the negative electrode active material layer and the positive electrode active material layer. When there is a significant amount of TD heat shrink, the thin ends of separators 10 and 11 are peeled away from the battery lid (moved to the left in FIG. 3) so that the negative electrode active material layer and the positive electrode active material layer are in contact. Short circuit occurs. Since the separator may be quite thin, usually less than 200 μm, the negative electrode active material layer and the positive electrode active material layer may be quite close to each other. For this reason, the resistance of the battery to an internal short circuit can be greatly improved by only slightly reducing the TD shrinkage of the separator when the battery is hot. Therefore, the thermal shrinkage characteristic of the separator at a temperature close to shutdown is important.

  Batteries are useful as a power source from one or more electrical or electronic components, such as passive elements such as resistors, capacitors, inductors, etc., including transformers, motors, generators, etc. And electronic devices such as diodes, transistors, and integrated circuits. These components can be connected to the battery in series and / or parallel electrical circuits to form a battery system. The circuit may be connected directly or indirectly to the battery. For example, the electricity flowing from the battery can be electrochemically (eg, by secondary or fuel cells) and / or (eg, generating electricity) before the electricity is dissipated or stored in one or more of these components. Can be converted electromechanically (by the electric motor moving the machine). The battery system can be used as a power source for driving an electric vehicle or a hybrid electric vehicle, for example. In one embodiment, the battery is electrically connected to an electric motor and / or generator for powering the electric vehicle or hybrid electric vehicle.

  The invention will now be described in more detail with reference to the following examples, without intending to limit the scope of the invention.

Example 1
(1) Preparation of the first polyolefin solution
(a) 68.6% by weight of a first polyethylene resin having a Mw of 5.62 × 10 ⁵ and a MWD of 4.05; and (b) having a Mw of 1.95 × 10 ⁶ and a MWD of 5.09. By dry blending 1.4% by weight of a second polyethylene resin and (c) 30% by weight of a polypropylene resin having a Mw of 1.1 × 10 ^6, a heat of fusion of 114 J / g, and an MWD of 5; A first polyolefin composition is prepared. The percentage is based on the weight of the first polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 ° C and a Tcd of 100 ° C.

30% by weight of the resulting first polyolefin composition was filled into a first strongly mixed twin screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 parts by weight of liquid paraffin (50 cst at 40 ° C.). % Is fed to the twin screw extruder via a side feeder to make a first polyolefin solution. The weight percent is based on the weight of the first polyolefin solution. The melt blending is performed at 210 ° C. and 200 rpm.
(2) Preparation of second polyolefin solution

In a manner similar to that described above, (a) 82% by weight of a first polyethylene resin having Mw of 5.62 × 10 ⁵ and MWD of 4.05; and (b) Mw of 1.95 × 10 ⁶ and 5. A second polyolefin solution is prepared by dry blending with 18% by weight of a second polyethylene resin having a MWD of 09. The percentage is based on the weight of the second polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 ° C and a Tcd of 100 ° C.

25% by weight of the resulting second polyolefin composition was charged into a second strongly mixed twin screw extruder having an inner diameter of 58 mm and an L / D of 42, and 75 parts by weight of liquid paraffin (50 cst at 40 ° C.). % Is fed through a side feeder to a twin screw extruder to make a second polyolefin solution. The weight percent is based on the weight of the second polyolefin solution. The melt blending is performed at 210 ° C. and 200 rpm.
(3) Production of membrane

  First and second polyolefin solutions are fed from respective twin screw extruders to a three-layer extrusion T-die and extruded from there to produce a second polyolefin solution layer / first polyolefin solution layer / second polyolefin. A layered extrudate (also referred to as a laminate) having a solution layer thickness ratio of 45.3 / 9.4 / 45.3 is produced. The extrudate is cooled while passing through a cooling roller controlled at 20 ° C. to produce an extrudate in the form of a three-layer gel sheet. The gel-like sheet is heated to a temperature of 119.5 ° C. for 150 seconds and then exposed to a temperature of 119.5 ° C. (“biaxial stretching temperature”), with a tenter stretching machine at an average deformation rate of 750% / min. Each of MD and TD is biaxially stretched (simultaneously) at a magnification of 5 times. The stretched gel-like sheet is heat-treated at 120.0 ° C. for 18 seconds. The stretched three-layer gel sheet is fixed to a 20 cm × 20 cm aluminum frame, immersed in a methylene chloride bath controlled at 25 ° C. for 3 minutes to remove liquid paraffin, and air-dried at room temperature to produce a dry film. .

Prior to dry stretching, the dry film has an initial dry length (MD) and an initial dry width (TD). The dried film is dried and stretched to TD at a magnification of 1.6 times while being exposed to a temperature of 129.5 ° C. to obtain a second drying width. The film length (MD) remains approximately equal to the initial dry length during TD dry stretching. Following TD dry stretching, controlled width reduction (TD) from the second dry width to a final magnification of 1.4 times while exposing the membrane to a temperature of 129.5 ° C. (“width reduction temperature”). ). The final magnification is based on the width of the first film at the start of dry stretching. The membrane length (MD) remains approximately equal to the second dry length during width reduction. The membrane remains fixed to the batch stretcher, but the membrane is then heat set while exposed to a temperature of 129.5 ° C. (“heat set temperature”) for 10 minutes to produce the final multilayer microporous membrane. Next, the dried film is stretched by drying.
Example 2
(1) Preparation of the first polyolefin solution

(a) 68.6% by weight of a first polyethylene resin having a Mw of 5.62 × 10 ⁵ and a MWD of 4.05; and (b) having a Mw of 1.95 × 10 ⁶ and a MWD of 5.09. By dry blending 1.4% by weight of a second polyethylene resin and (c) 30% by weight of a polypropylene resin having a Mw of 1.1 × 10 ^6, a heat of fusion of 114 J / g, and an MWD of 5; A first polyolefin composition is prepared. The percentage is based on the weight of the first polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 ° C and a Tcd of 100 ° C.

30% by weight of the resulting first polyolefin composition was filled into a first strongly mixed twin screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 parts by weight of liquid paraffin (50 cst at 40 ° C.). % Is fed to the twin screw extruder via a side feeder to make a first polyolefin solution. The weight percent is based on the weight of the first polyolefin solution. The melt blending is performed at 210 ° C. and 200 rpm.
(2) Preparation of second polyolefin solution

In the same manner as above, (a) 98% by weight of a first polyethylene resin having Mw of 5.62 × 10 ⁵ and MWD of 4.05; and (b) Mw of 1.95 × 10 ⁶ and 5. A second polyolefin solution is prepared by dry blending with 2% by weight of a second polyethylene resin having a MWD of 09. The percentage is based on the weight of the second polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 ° C and a Tcd of 100 ° C.

30% by weight of the resulting second polyolefin composition was loaded into a second strongly mixed twin screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 parts by weight of liquid paraffin (50 cst at 40 ° C.). % Is fed through a side feeder to a twin screw extruder to make a second polyolefin solution. The weight percent is based on the weight of the second polyolefin solution. The melt blending is performed at 210 ° C. and 200 rpm.
(3) Production of membrane

  First and second polyolefin solutions are fed from respective twin screw extruders to a three-layer extrusion T-die and extruded from there to produce a second polyolefin solution layer / first polyolefin solution layer / second polyolefin. A layered extrudate (also referred to as a laminate) having a solution layer thickness ratio of 45.5 / 9.0 / 45.5 is produced. The extrudate is cooled while passing through a cooling roller controlled at 20 ° C. to produce an extrudate in the form of a three-layer gel sheet. The gel-like sheet was heated to a temperature of 119.3 ° C. for 150 seconds and then exposed to a temperature of 119.3 ° C. (“biaxial stretching temperature”), with a tenter stretching machine at an average deformation rate of 710% / min. Each of MD and TD is biaxially stretched (simultaneously) at a magnification of 5 times. The stretched gel-like sheet is heat-treated at 95.0 ° C. for 18 seconds. The stretched three-layer gel sheet is fixed to a 20 cm × 20 cm aluminum frame, immersed in a methylene chloride bath controlled at 25 ° C. for 3 minutes to remove liquid paraffin, and air-dried at room temperature to produce a dry film. .

Prior to dry stretching, the dry film has an initial dry length (MD) and an initial dry width (TD). The dried film is dried and stretched to TD at a magnification of 1.5 times while being exposed to a temperature of 129.0 ° C. to obtain a second dry width. The film length (MD) remains approximately equal to the initial dry length during TD dry stretching. Following TD dry stretching, controlled width reduction (TD) from the second dry width to a final magnification of 1.3 times while exposing the membrane to a temperature of 129.0 ° C. (“width reduction temperature”). ). The final magnification is based on the width of the first film at the start of dry stretching. The membrane length (MD) remains approximately equal to the second dry length during width reduction. The membrane remains fixed in the batch stretcher, but the membrane is then heat set while exposed to a temperature of 129.0 ° C. (“heat set temperature”) for 10 minutes to produce the final multilayer microporous membrane. Next, the dried film is stretched by drying.
Comparative Example 1
(1) Preparation of the first polyolefin solution

(a) 68.6% by weight of a first polyethylene resin having a Mw of 5.62 × 10 ⁵ and a MWD of 4.05; and (b) having a Mw of 1.95 × 10 ⁶ and a MWD of 5.09. By dry blending 1.4% by weight of a second polyethylene resin and (c) 30% by weight of a polypropylene resin having a Mw of 1.1 × 10 ^6, a heat of fusion of 114 J / g, and an MWD of 5; A first polyolefin composition is prepared. The percentage is based on the weight of the first polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 ° C and a Tcd of 100 ° C.

30% by weight of the resulting first polyolefin composition was filled into a first strongly mixed twin screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 parts by weight of liquid paraffin (50 cst at 40 ° C.). % Is fed to the twin screw extruder via a side feeder to make a first polyolefin solution. The weight percent is based on the weight of the first polyolefin solution. The melt blending is performed at 210 ° C. and 200 rpm.
(2) Preparation of second polyolefin solution

In a manner similar to that described above, (a) 82% by weight of a first polyethylene resin having Mw of 5.62 × 10 ⁵ and MWD of 4.05; and (b) Mw of 1.95 × 10 ⁶ and 5. A second polyolefin solution is prepared by dry blending with 18% by weight of a second polyethylene resin having a MWD of 09. The percentage is based on the weight of the second polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 ° C and a Tcd of 100 ° C.

25% by weight of the resulting second polyolefin composition was charged into a second strongly mixed twin screw extruder having an inner diameter of 58 mm and an L / D of 42, and 75 parts by weight of liquid paraffin (50 cst at 40 ° C.). % Is fed through a side feeder to a twin screw extruder to make a second polyolefin solution. The weight percent is based on the weight of the second polyolefin solution. The melt blending is performed at 210 ° C. and 200 rpm.
(3) Production of membrane

  First and second polyolefin solutions are fed from respective twin screw extruders to a three-layer extrusion T-die and extruded from there to produce a second polyolefin solution layer / first polyolefin solution layer / second polyolefin. A layered extrudate (also referred to as a laminate) having a solution layer thickness ratio of 45.8 / 8.4 / 45.8 is produced. The extrudate is cooled while passing through a cooling roller controlled at 20 ° C. to produce an extrudate in the form of a three-layer gel sheet. The gel-like sheet was heated to a temperature of 117.0 ° C. for 120 seconds, and then exposed to a temperature of 117.0 ° C. (“biaxial stretching temperature”), with a tenter stretching machine at a deformation rate of 940% / min. And TD are biaxially stretched (simultaneously) to a magnification of 5 times. The stretched gel-like sheet is heat-treated at 95.0 ° C. for 15 seconds. The stretched three-layer gel sheet is fixed to a 20 cm × 20 cm aluminum frame, immersed in a methylene chloride bath controlled at 25 ° C. for 3 minutes to remove liquid paraffin, and air-dried at room temperature to produce a dry film. .

Prior to dry stretching, the dry film has an initial dry length (MD) and an initial dry width (TD). The dried film is dried and stretched to TD at a magnification of 1.6 times while being exposed to a temperature of 128.7 ° C. to obtain a second dry width. The film length (MD) remains approximately equal to the initial dry length during TD dry stretching. Following TD dry stretching, the film is subjected to a temperature of 128.7 ° C. (“width reduction temperature”) while a controlled width reduction (TD) from the second drying width to a final magnification of 1.4 times. ). The final magnification is based on the width of the first film at the start of dry stretching. The membrane length (MD) remains approximately equal to the second dry length during width reduction. Although the membrane remains fixed in the batch stretcher, the membrane is then heat treated for 10 minutes while exposed to a temperature of 128.7 ° C. (“heat treatment temperature”) to produce the final multilayer microporous membrane. Next, the dried film is stretched by drying.
Comparative Example 2
(1) Preparation of the first polyolefin solution

(a) 68.6% by weight of a first polyethylene resin having a Mw of 5.62 × 10 ⁵ and a MWD of 4.05; and (b) having a Mw of 1.95 × 10 ⁶ and a MWD of 5.09. By dry blending 1.4% by weight of a second polyethylene resin and (c) 30% by weight of a polypropylene resin having a Mw of 1.1 × 10 ^6, a heat of fusion of 114 J / g, and an MWD of 5; A first polyolefin composition is prepared. The percentage is based on the weight of the first polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 ° C and a Tcd of 100 ° C.

30% by weight of the resulting first polyolefin composition was filled into a first strongly mixed twin screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 parts by weight of liquid paraffin (50 cst at 40 ° C.). % Is fed to the twin screw extruder via a side feeder to make a first polyolefin solution. The weight percent is based on the weight of the first polyolefin solution. The melt blending is performed at 210 ° C. and 200 rpm.
(2) Preparation of second polyolefin solution

In the same manner as above, (a) 82% by weight of a first polyethylene resin having Mw of 5.62 × 10 ⁵ and MWD of 4.05; and (b) Mw of 1.95 × 10 ⁶ and 5. A second polyolefin solution is prepared by dry blending with 18% by weight of a second polyethylene resin having a MWD of 09. The percentage is based on the weight of the second polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 ° C and a Tcd of 100 ° C.

25% by weight of the resulting second polyolefin composition was charged into a second strongly mixed twin screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 parts by weight of liquid paraffin (50 cst at 40 ° C.). % Is fed through a side feeder to a twin screw extruder to make a second polyolefin solution. The weight percent is based on the weight of the second polyolefin solution. The melt blending is performed at 210 ° C. and 200 rpm.
(3) Production of membrane

  First and second polyolefin solutions are fed from respective twin screw extruders to a three-layer extrusion T-die and extruded from there to produce a second polyolefin solution layer / first polyolefin solution layer / second polyolefin. A layered extrudate (also referred to as a laminate) having a solution layer thickness ratio of 45.3 / 9.4 / 45.3 is produced. The extrudate is cooled while passing through a cooling roller controlled at 20 ° C. to produce an extrudate in the form of a three-layer gel sheet. The gel-like sheet was heated to a temperature of 115.5 ° C. for 129 seconds, and then exposed to a temperature of 115.5 ° C. (“biaxial stretching temperature”), with a tenter stretching machine at a deformation rate of 880% / min. And TD are biaxially stretched (simultaneously) to a magnification of 5 times. The stretched gel sheet is heat-treated at 95.0 ° C. for 16 seconds. The stretched three-layer gel sheet is fixed to a 20 cm × 20 cm aluminum frame, immersed in a methylene chloride bath controlled at 25 ° C. for 3 minutes to remove liquid paraffin, and air-dried at room temperature to produce a dry film. .

Prior to dry stretching, the dry film has an initial dry length (MD) and an initial dry width (TD). The dried film is dried and stretched to TD at a magnification of 1.6 times while being exposed to a temperature of 127.3 ° C. to obtain a second dry width. The film length (MD) remains approximately equal to the initial dry length during TD dry stretching. Following TD dry stretching, controlled width reduction (TD) from the second dry width to a final magnification of 1.3 times while exposing the membrane to a temperature of 127.3 ° C. (“width reduction temperature”). ). The final magnification is based on the width of the first film at the start of dry stretching. The membrane length (MD) remains approximately equal to the second dry length during width reduction. The membrane remains fixed to the batch stretcher, but the membrane is then heat set while exposed to a temperature of 127.3 ° C. (“heat set temperature”) for 10 minutes to produce the final multilayer microporous membrane. Next, the dried film is stretched by drying.
Comparative Example 3
(1) Preparation of the first polyolefin solution

(a) 82% first polyethylene with Mw of 5.6 × 10 ⁵ and Mw / Mn of 4.05, (b) No. 1 with Mw of 1.9 × 10 ⁶ and Mw / Mn of 5.09 A first polyolefin composition comprising 18% polyethylene of 2 is prepared by dry blending. The polyethylene resin in the composition has a melting point of 135 ° C and a crystal dispersion temperature of 100 ° C.

25 parts by weight of the obtained first polyolefin composition was charged into a strongly mixed twin screw extruder having an inner diameter of 58 mm and an L / D of 42, and 65 parts by mass of liquid paraffin (50 cst at 40 ° C.) A polyolefin solution is prepared by feeding to a twin screw extruder through a side feeder. Melt blending is performed at 210 ° C. and 200 rpm to prepare a first polyolefin solution.
(2) Preparation of second polyolefin solution

A second polyolefin solution is prepared in the same manner as described above except for the following. By weight of the second polyolefin composition, (a) 63.7% of a first polyethylene having 5.6 × 10 ⁵ Mw and 4.05 Mw / Mn, (b) 1.3% A second polyethylene having Mw / Mn of 1.9 × 10 ⁶ and 5.09, and (c) 35% of 1.6 × 10 ⁶ Mw, 5.2 Mw / Mn, and 114. A second polyolefin composition comprising a polypropylene resin having a ΔHm of 0 J / g is prepared by dry blending. The polyethylene resin in the composition has a melting point of 135 ° C and a crystal dispersion temperature of 100 ° C. 30 parts by weight of the obtained second polyolefin composition was charged into a strongly mixed twin screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 parts by weight of liquid paraffin (50 cst at 40 ° C.) Side feeder melt blending is performed at 210 ° C. and 200 rpm to prepare a second polyolefin solution.
(3) Production of membrane

  The first and second polyolefin solutions are fed from their respective twin screw extruders to a three-layer extrusion T-die and extruded from there for the first polyolefin solution layer / second polyolefin solution layer / first polyolefin An extrudate (also referred to as a laminate) having a layer thickness ratio of the solution layer of 46.45 / 7.1 / 46.45 is formed. The extrudate is cooled while passing through a cooling roller controlled at 20 ° C. to form a three-layer gel-like sheet, and this is 119 at a magnification of 5 times in both the machine (longitudinal) and transverse directions with a tenter stretching machine. Simultaneous biaxial stretching at 3 ° C. The stretched three-layer gel-like sheet is fixed to a 20 cm × 20 cm aluminum frame, immersed in a methylene chloride bath controlled at 25 ° C., and liquid paraffin is removed by vibration at 100 rpm for 3 minutes, followed by drying at room temperature. Let The dried film was re-stretched in the transverse direction (TD) at a magnification of 1.5 times while being exposed to a temperature of 127.3 ° C., and then relaxed to a TD magnification of 1.3 times at the same temperature ( The tenter clip is readjusted to a narrower width) (the magnification is based on the width (TD) of the film before dry stretching before re-stretching). The restretched membrane remains fixed on the batch stretcher, but this is heat set at 127.3 ° C. for 10 minutes to produce a three-layer microporous membrane.

Table 1 shows the compositions and treatment conditions of Examples and Comparative Examples of multilayer microporous membranes. Table 2 shows the characteristics of the multilayer microporous membranes of Examples and Comparative Examples.

  From Table 2, the microporous membranes of Examples 1 and 2 have important characteristics with good balance such as a heat shrinkage rate at 130 ° C. of 9.5% or less, particularly a TD heat shrinkage rate at 130 ° C. of 9.5% or less. It can be seen that Compared to the films of Comparative Examples 1 and 2, Examples 1 and 2 of the present invention maintain a good heat shrinkage of 105 ° C. while improving the heat shrinkage at 130 ° C. and in the molten state. On the other hand, Comparative Example 3 has a small heat shrinkage rate in the molten state and a good heat shrinkage rate of 105 ° C., but the properties at 130 ° C. are relatively poor. Examples 1 and 2 provide membranes that achieve heat shrink properties in a range of conditions that are not achieved in the comparative example while maintaining other properties such as permeability and piercing.

  The multilayer microporous membrane of the present invention having well-balanced characteristics and the use of such multilayer microporous membrane as a battery separator provide a battery having excellent safety, heat resistance, holding characteristics, and productivity. .

  All patents, test procedures, and other references cited herein, including priority documents, are fully incorporated by reference, and such incorporation is permitted, to the extent that such disclosure does not contradict the present invention. All permissions are fully integrated.

  While the exemplary forms disclosed herein are described with particularity, various other modifications will be apparent to those skilled in the art and depart from the spirit and scope of the disclosure by those skilled in the art. It will be understood that this can easily be done without. Accordingly, the scope of the claims appended hereto is not limited to the examples and descriptions set forth herein, which are claimed by those skilled in the art to which this disclosure belongs. It is intended to be construed as including all patentable, novel features provided herein, including all features treated as equivalents.

  Where numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated.

Claims (4)

A method for producing a microporous membrane, comprising:
(a) The first layer is 1.0 × 10% by weight of 1% to 20% by weight based on the weight of the first polyolefin. ⁶ A first polyolefin comprising polyethylene having an Mw of greater than and at least a first diluent;
The third layer is 1.0 × 10% by weight of 1-20% by weight based on the weight of the third polyolefin. ⁶ A third polyolefin comprising polyethylene having an Mw greater than and at least a third diluent;
The second layer comprises a second polyolefin and at least a second diluent;
The second polyolefin is 1.1 x 10 in an amount ranging from 1 wt% to 40 wt% based on the weight of the second polyolefin. ⁶ ~ 1.5 × 10 ⁶ A polypropylene having a Mw of
Stretching a multilayer extrudate comprising first and third layers and a second layer located between the first and third layers at a rate of 850% / min or less in at least one planar direction; Then
(b) removing at least a portion of the first, second and third diluents from the stretched extrudate to provide a dry film having a first length along MD and a first width along TD. The step of preparing, followed by
(c) stretching the film from the first width to the second width wider than the first width at a magnification in the range of 1.1 to 1.8, and thereafter
(d) reducing the second width to a third width in a range from the first width to 1.1 to 1.6 times the first width. The first and third polyolefins are 1% to 5% by weight of 1.0 × 10 ⁶ The method of claim 1 comprising polyethylene having an Mw of greater. A method for producing a microporous membrane, comprising:
(a) the first layer comprises a first polyolefin and at least a first diluent;
The second layer comprises a second polyolefin and at least a second diluent;
The second polyolefin is 1.1 x 10 in an amount ranging from 1 wt% to 40 wt% based on the weight of the second polyolefin. ⁶ ~ 1.5 × 10 ⁶ A polypropylene having a Mw of
Stretching a multi-layer extrudate comprising at least a first and second layer in at least one planar direction at a rate of 850% / min or less;
(b) removing at least a portion of the first and second diluents from the stretched extrudate to prepare a dry film having a first length along MD and a first width along TD. ,continue
(c) stretching the film from the first width to the second width wider than the first width at a second magnification in the range of 1.1 to 1.8, and thereafter
(d) reducing the second width to a third width in a range from the first width to 1.1 to 1.6 times the first width. The method according to any one of claims 1 to 3, wherein a stretching speed in the step (a) is 600% / min to 800% / min.

Images