KR20130016211A - Microporous membranes, methods for making these membranes, and the use of these membranes as battery separator films - Google Patents

Abstract

The present invention relates to microporous membranes having high meltdown temperatures and useful electrolyte affinity. The present invention also relates to the preparation of these membranes and the use of these membranes as battery separator films.

Description

MICROPOROUS MEMBRANES, METHODS FOR MAKING THESE MEMBRANES, AND THE USE OF THESE MEMBRANES AS BATTERY SEPARATOR FILMS}

The present invention relates to a microporous membrane having a high meltdown temperature and affinity useful for the polymer electrolyte of a lithium ion polymer battery. The present invention also relates to the production of these membranes and the use of these membranes as battery separator films.

The microporous membrane is useful as a battery separator film ("BSF") for primary batteries and secondary batteries. Such batteries include lithium ion secondary batteries, lithium ion polymer secondary batteries, nickel-hydrogen batteries, nickel-cadmium batteries, nickel-zinc batteries, silver-zinc batteries, and the like.

The microporous polymer film can be used, for example, as a battery separator film ("BSF") of a lithium ion battery. Such membranes have high polymer mobility at high cell temperatures and significantly reduce air permeability. This effect is beneficial for BSF because the decrease in air permeability reduces the cell's electrochemical activity, reducing the risk of battery failure under overcharge, rapid discharge or other high temperature cell conditions. Since the internal temperature of the battery can continue to increase even when the electrochemical activity decreases (eg, from a temperature overshoot), it is desirable to increase the thermal stability of the film at high temperatures to further reduce the risk of battery failure. This can be accomplished by including high melting point species (eg polypropylene) in the polymer of the membrane. Melting point temperature differences between polyethylene and polypropylene and their physical incompatibility make it difficult to produce membranes containing both polymers, especially when the membranes are thin.

For example, lithium theory cells ("lithium ion polymer cells"), in which the electrolyte is a gel electrolyte or a polymer electrolyte contained within a polymer medium, generally exhibit a polymer compatibility (eg, affinity) with the polymer medium in which the electrolyte is included. Use the included BSF. In general, BSFs for lithium ion polymer batteries are significantly thinner, for example, compared to BSFs commonly used in cylindrical and prismatic lithium ion batteries.

Therefore, it is preferable to produce a relatively thin polymer film having affinity for the polymer used as the electrolyte medium in the polymer battery and having dimensional stability at high temperature.

In one embodiment, the wt% of the film based on the weight of the polymer in the invention is at least 1% by weight of polyethylene and 5.0 × l0 ⁵ less than 4.0% by weight or more and having a Mw 80.0J / g ΔHm ~ 20.0% by weight It relates to a film comprising a polypropylene of; The membrane is microporous and has a thickness of 12.0 μm or less.

In another embodiment, the present invention provides a process for producing a microporous membrane:

(1) a process of extruding a mixture of diluent and polymer, the polymer comprising an amount of A ₁ of polyethylene, and an amount of A ₂ of polypropylene, wherein the weight percent is based on the weight of the polymer in the polymer-diluent mixture A ₁ is 1.0% by weight or more, for example, in the range of 80.0% by weight to 96.0% by weight, wherein A ₂ is a step of extruding a mixture of polymers in the range of 4.0% by weight to 20.0% by weight; (2) drawing the extrudate in at least one planar direction; And (3) removing at least a portion of the diluent from the stretched extrudate.

(Effects of the Invention)

Membranes of the invention have both improved meltdown temperatures and sufficient electrolyte affinity.

It was confirmed that the microporous membrane containing polyethylene and having a thickness of 12.0 µm or less usually had a meltdown temperature of less than 145.0 ° C. When the polyethylene is combined with polypropylene, these membranes increase the meltdown temperature, but also reduce the affinity for the polymer electrolyte. The invention provides that at least in part by weight, based on the weight percent of the membrane, at least 1.0 weight percent polyethylene and 5.0 × 10 ⁵ If the membrane comprises a mixture of at least 4.0 weight percent to 20.0 weight percent (based on the weight of the membrane) having a weight average molecular weight ("Mw") and a heat of fusion ("ΔHm") of at least 80.OJ / g, It is based on the finding that the difficulty can be solved. These membranes have both improved meltdown temperatures and sufficient electrolyte affinity useful as BSFs in lithium ion polymer cells.

For the purposes of this specification and the appended claims, the term "polymer" means a composition comprising a plurality of polymers comprising repeating units derived from one or more monomers. The polymer may vary in size, molecular structure, atomic content, and the like. The term "polymer" includes polymers such as copolymers, terpolymers, and the like. "Polyethylene" means a polyolefin comprising at least 50% (by number) repeating units derived from ethylene, preferably polyethylene homopolymers and / or polyethylene copolymers wherein at least 85% (by number) of repeating units are ethylene units do. "Polypropylene" comprises at least 50.0% (by number) of repeating units derived from propylene, preferably polypropylene homopolymers and / or polypropylene copolymers wherein at least 85% (by number) of repeating units are propylene units It means polyolefin. The term isotactic polypropylene (based on the total moles of isotactic polypropylene) is polypropylene having a meso pentad fraction of at least about 50.0 mol% mmmm pentad, preferably at least 96.0 mol% mmmm pentad Means. The "microporous membrane" is a thin film having micropores in which 90.0% or more (volume basis) of the micropore volume of the membrane is present in the micropores having an average diameter in the range of 0.01 µm to 10.0 µm. For membranes made of extrudate, the machine direction (“MD”) is defined as the direction in which the extrudate is produced from the die. The transverse direction (“TD”) is defined as the direction perpendicular to both the MD direction and the thickness direction of the extrudate. MD and TD are referred to as the planar direction of the membrane, and the term "planar" in this context means the direction which lies mainly in the plane of the membrane when the membrane is flat.

(Composition of Microporous Membrane)

In one or more embodiments, the present invention relates to a membrane comprising polyethylene and polypropylene, being microporous and having a thickness of 12.0 μm or less. In one embodiment, the microporous membrane comprises an amount of polyethylene (A ₁ ), and an amount of polypropylene (A ₂ ) having a Mw of at least 5.0 × 10 ⁵ and a ΔHm of at least 80.0 J / g. A ₁ and A ₂ may be expressed as weight percent based on the weight of the polymer in the film. For example, the weight percent can be, for example, A ₁ + A ₂ = 100 weight percent based on the combined weight of polyethylene and polypropylene in the membrane. In another embodiment, the weight percent is relative to the weight of the membrane, for example if the membrane consists essentially of polyethylene and polypropylene only (or even if it consists of polyethylene and polypropylene).

For example, in one or more embodiments, A ₁ is in the range of 80.0 wt% to 96.0 wt%, A ₂ is in the range of 4.0 wt% to 20.0 wt%, and the wt% of A ₁ and A ₂ is 100 wt% For the combined weight of A ₁ and A ₂ equal to. As needed, A <_1> is the range of 84.5 weight%-95.5 weight%, for example, the range of 94.75 weight%-95.25 weight%. As needed, A <_2> is the range of 4.5 weight%-15.5 weight%, for example, the range of 4.75 weight%-5.25 weight%.

While selected embodiments of polyethylene and polypropylene are described in greater detail, this description is not meant to exclude other embodiments that are within the broad scope of the invention.

(Polyethylene)

In certain embodiments, the polyethylene ("PE") may comprise a mixture or reactor blend of polyethylene, such as a mixture of two or more polyethylenes ("PE1", "PE2", "PE3", etc., as described below). . For example, the PE may comprise a blend of (i) the first PE (PEl) and / or the second PE (PE2) and (ii) the third PE (PE3).

(PE1)

In one embodiment, the first PE (“PE1”) is less than 1.0 × 10 ⁶ , for example, MW in the range of about 1.0 × 10 ⁵ to about 0.90 × 10 ⁶ ; MWD in the range of about 50.0 or less, for example about 2.0 to about 20.0; And PE having a terminal unsaturation of less than 0.20 per 1.0 x 10 ⁴ carbon atoms. If desired, PE1 has a Mw in the range of about 4.0 × 10 ⁵ to about 6.0 × 10 ⁵ , and a molecular weight distribution of about 3.0 to about 10.0 (“MWD”, defined as Mw divided by the number average molecular weight). If necessary, PE1 is the carbon atom to 1.O × 1O ⁴ per O.14 or less, or a carbon atom 1.O × 1O ⁴ per O.12 or less, for example, the carbon atom to 1.0 × 10 ⁴ per one range of 0.05 to 0.14 It has an amount of terminal unsaturation of (for example, below the detection limit of the measurement).

(PE2)

In one embodiment, the second PE (“PE2”) is, for example, less than 1.0 × 10 ⁶ , for example, MW in the range of about 2.0 × 10 ⁵ to about 0.9 × 10 ⁶ , 50.0 or less, for example about MWD in the range of 2 to about 50, and PE having a terminal unsaturation of at least 0.20 per 1.0 x 10 ⁴ carbon atoms. If necessary, PE2 is the carbon atom to 1.0 × 10 ⁴ per O.30 or more, carbon atoms per O.5O 1.O × 1O ⁴ or more, for example, the range of carbon atoms 1.O × 1O ⁴ per 0.6 ~ 10.0 Terminal unsaturated amount. Non-limiting examples of PE2 are those having a range of about 3.0 × 10 ⁵ to about 8.O × 10 ⁵ , for example, Mw of about 7.5 × 10 ⁵ , and MWD of about 4 to about 15.

PE1 and / or PE2 can be, for example, an ethylene homopolymer, or an ethylene / α-olefin copolymer comprising up to 5.0 mol% based on 100 mol% of the copolymer in one or more comonomers such as α-olefins. have. If desired, the α-olefin is at least one of propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, vinylacetate, methylmethacrylate or styrene. Such PE may have a melting point of at least 132 ° C. PE1 can be produced, for example, by a process using a Ziegler-Natta catalyst or a single site polymerization catalyst, but this is not necessary. Terminal unsaturation can be measured, for example, according to the procedure described in PCT publication WO 97/23554. PE2 can be produced, for example, using a chromium containing catalyst.

(PE3)

In one embodiment, the third PE (“PE3”) is, for example, 1.0 × 10 ⁶ or more, for example, Mw in the range of about 1.0 × 10 ⁶ to about 5.0 × 10 ⁶ , and about 1.2 to about 50.0. PE with MWD. Non-limiting examples of PE3 include Mw of about 1.0 × 10 ⁶ to about 3.0 × 10 ⁶ , for example about 2.0 × 10 ⁶ , and up to 20.0, for example about 2.0 to about 20.0, preferably about 4.0 to about Have an MWD of 15.0. PE3 can be, for example, an ethylene homopolymer, or an ethylene / α-olefin copolymer comprising up to 5.0 mol% based on 100 mol% of the copolymer in one or more comonomers such as α-olefins. The comonomer can 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. Such polymers or copolymers may be prepared using Ziegler-Natta catalysts or single site catalysts, but this is not necessary. Such PE may have a melting point of at least 134 ° C. The melting point of PE1-PE3 can be obtained, for example, using the method disclosed in PCT Patent Publication No. WO 2008/140835.

In one or more embodiments, the PE comprises an amount of B ₁ of PE1 and / or PE2, and an amount of B ₂ of PE3. In one embodiment, B ₁ and B _2% by weight of in the range of the basis is 60.O% by weight to 96.0% by weight of B ₁ on the weight of polymer in the film, B ₂ is O.0 to 20.0% by weight Range by weight. If necessary, B ₁ is in the range of 69.5% by weight to 90.5% by weight based on the total polymer in the film, for example, in the range of 80.0% by weight to 85.0% by weight. If necessary, B ₂ is in the range of 5.0% by weight to 15.0% by weight based on the total polymer in the membrane, for example, in the range of 9.75% by weight to 15.25% by weight. In one embodiment, B ₁ is in the range of 79.0% to 95.0% by weight, and B ₂ is in the range of 0.1% to 16.0% by weight. When B ₂ is less than about 7.5% by weight, in one embodiment the membrane is at least 145 ° C., for example 147 ° C., because it is more difficult to produce a membrane having a meltdown temperature of at least 145 ° C., for example at least 147 ° C. It has a meltdown temperature of at least 8 and also has at least 8.0% by weight of B ₂ , such as at least 10.0% by weight.

(Polypropylene)

In one embodiment, the polypropylene (“PP”) is 6.O × 10 ⁵ Or above 7.5 × 10 ⁵ 5.0 × 10 ⁵ or more as described above, for example, having a Mw in the range of about 0.8 × 10 ⁶ to about 3.O × 10 ⁶ , such as in the range of 0.9 × 10 ⁶ to 2.O × 10 ⁶ It may be polypropylene. If desired, the PP has a Tm of at least 160.0 ° C. and a ΔHm of at least 80.0 J / g, such as at least 90.0 J / g, such as in the range of 110 J / g to 120 J / g, or at least 100.0 J / g. If desired, PP has an MWD of 20.0 or less, for example in the range of about 1,5 to about 10.0, such as in the range of about 2.0 to about 8.5. If desired, PP is a copolymer (random or block) of propylene and up to 5.0 mol% of comonomer, the comonomer being for example ethylene, butene-1, pentene-1, hexene-1, 4-methylpentene- One or more α-olefins such as 1, octene-1, vinyl acetate, methyl methacrylate and styrene; Or diolefins such as butadiene, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene and the like.

In one embodiment, PP is isotactic polypropylene. In one embodiment, the PP comprises: (a) at least about 90.0 mole% mmmm pentad, if necessary at least 96.0 mole% of mmmm pentad, preferably at least 96.0 mole% of meso pentad fraction; And (b) carbon atoms 1.O × 1O ⁴ per about 5.O or less, for example, the carbon atom to 1.O × 1O ⁴ per about 5.0 carbon atoms, such as less than 1.O × 1O ⁴ per about 2O or less, or It has a stereo defect amount of less than about 10.0 per ⁴ carbon atoms of 1.0O10. If desired, PP has the following characteristics: (1) a Tm of at least 162.0 ° C .; (ii) an elongational viscosity of at least about 5.0 × 10 ⁴ Pa sec at a temperature of 230 ° C. and a strain rate of 25 sec ⁻¹ ; (iii) a Towton ratio of at least about 15 when measured at a temperature of about 230 ° C. and a strain rate of ²⁵ sec ⁻¹ ; (iv) a melt index (“MFR”) of about 0.ldg / min or less, for example about 0.0ldg / min or less (ie, the value is so low that the MFR is not measurable); ASTM D- at 230 ° C. and 2.16 kg. 1238-95 condition L); Or (v) at least 0.5% by weight, based on the weight of the PP, for example at least 0.2% by weight of extractable species, such as 0.1% by weight or less, extractable by contacting PP with boiling xylene Have

In one embodiment, the PP is MwD in the range of about 0.9 × 10 ⁶ to about 2.O × 10 ⁶ , MWD in the range of 8.5 or less, for example in the range of 2.0 to 8.5, for example in the range of 2.5 to 6.0. And isotactic PP having a ΔHm of at least 90.0 J / g. In general, these PP has a meso pentad fraction, the carbon atom to 1.O × 1O ⁴ stereo defects per unit volume, and Tm more than 162.0 ℃ of about 5.0 or less of 94.0 mol% or more in mmmm penta de. In one embodiment, the weight percent comprises at least 90.0 wt.% Isotactic polypropylene having at least 6.0 × 10 ⁵ Mw, at most 8.5 MWD, and at least 90.0 J / g ΔHm based on the weight of the PP. do.

Non-limiting examples of PP, and methods of determining the Tm, meso pentad fraction, stereoregularity, intrinsic viscosity, throat tone ratio, stereo defects, and extractable amount of PP of PP, are incorporated herein by reference in their entirety. PCT Patent Publication No. WO2008 / 140835.

ΔHm of PP is measured by the method disclosed in PCT Publication No. WO2007 / 132942, which is incorporated by reference in its entirety. Tm can be determined from differential scanning calorimetry (DSC) data obtained using PerkinElmer Instrument, Pyris l DSC. Fill a weight sample of about 5.5-6.5 mg into an aluminum sample pan. DSC data is first recorded by heating a sample called first fusion (data not recorded) at 230 ° C. at a rate of 10 ° C./min. The sample is held at 230 ° C. for 10 minutes before applying the cooling heating cycle. The sample is then cooled to about 230 ° C. to about 25 ° C. at a rate of 10 ° C./min, called “crystallization”, held at 25 ° C. for 10 minutes, and then heated to 230 ° C. at a rate of 10 ° C./min (“ Second fusion "). The thermal image on both crystallization and second fusion is recorded. Melting temperature T _m is the peak temperature of the second melting curve, and crystallization temperature T _c is the peak temperature of the crystallization peak.

(Other species)

If desired, inorganic species (eg, species comprising silicon and / or aluminum atoms such as silica and / or alumina), and / or PCT patent publication WO2007 / 132942 and PCT patent publication WO2008 / 016174 (both of which The heat resistant polymer as described in the entirety of which is incorporated herein by reference may be present in the membrane. In one embodiment, the membrane comprises less than 1.0 weight percent of such material based on the weight of the membrane.

For example, small amounts of diluents or other species as processing aids may be present in the membrane, generally in amounts of less than 1.0 weight percent based on the weight of the membrane.

When the microporous membrane is produced by extrusion, the final microporous membrane generally comprises the polymer used to produce the extrudate. In addition, small amounts of diluent or other species introduced during the process may generally be present in amounts of less than 1.0% by weight, based on the weight of the membrane. Small amounts of polymer molecular weight degradation may occur during the process, but this is acceptable. In one form, if molecular weight degradation occurs during the process, the value of the MWD of the polymer in the membrane may be, for example, about 10% or less, or about 1%, of the MWD (eg, before extrusion) of the polymer used to make the membrane. Or less than or about 0,1%.

(Measurement of Mw and MWD)

The Mw and MWD of the polymer can be measured using “SEC” (GPC PL 220, Polymer Laboratories) equipped with high temperature size exclusion chromatography or differential refractive index detector (DRI). The measurement is made according to the procedure disclosed in "Macromolecules, Vol. 34, No. 19, pp. 6812-6820 (2001)". Three PLgel Mixed-B columns (Polymer Laboratories) for the measurement of Mw and MWD are used. Nominal flow rate for PE is 0.5 cm 3 / min; Nominal injection volume is 30 [mu] l; Transfer lines, columns and DRI detectors are included in the oven maintained at 145 ° C. Nominal flow rate for PP is 1.0 cm 3 / min; Nominal injection volume is 300 μl; Transfer lines, columns, and DRI detectors are included in an oven maintained at 160 ° C.

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

The separation efficiency of the column set is calibrated by calibration curves drawn using 17 polystyrene standards, each with Mp ("Mp" defined as peak in Mw) ranging from about 580 to about 10,000,000. Polystyrene standards are obtained from Polymer Laboratories (Amherst, Mass.). The calibration curve (1ogMp vs. retention volume) records the retention volume at the peak of the DRI signal for each PS standard and writes this data into a second order polynomial. Wave Metrics, Inc. Samples are analyzed using the IGOR Pro product.

(membrane)

This invention is further demonstrated by the following embodiment. This description is not meant to exclude other embodiments that are within the broad scope of the invention.

In one embodiment, the invention is directed to a membrane comprising 79.0 wt% to 86.0 wt% PE1, 9.0 wt% to 16.0 wt% PE3, and 4.0 wt% to 6.0 wt% PP, wherein ( i) PE1 has a Mw in the range of about 4.0 × 10 ⁵ to about 6.0 × 10 ⁵ , a MWD of about 3.0 to about 10.0, an amount of terminal unsaturation of 0.14 or less per 1.0 × 10 ⁴ carbon atoms, and a melting point of at least 132 ° C .; (ii) PE 3 has a Mw in the range of about 1.0 × 10 ⁶ to about 3.0 × 10 ⁶ , a MWD in the range of about 4.0 to about 15.0, and a melting point of at least 134 ° C .; (iii) PP is Mw in the range of about 0.9 × 10 ⁶ to about 2.0 × 10 ⁶ , 8.5 or less, for example MWD in the range of 2.0 to 8.5, for example in the range of 2.5 to 6.0, and at least 90.0 J / g For example, isotactic PP having a ΔHm of at least 100,0 J / g (% by weight is relative to the weight of the membrane); (iv) the membrane is microporous; In addition, the film (v) has a thickness of 12.0 μm or less, such as 8.0 μm or less. If necessary, the film is a monolayer film. If desired, the membrane comprises up to 1.0 wt.% PE2, based on the weight of the membrane. Such membranes may have a meltdown temperature of at least 148.0 ° C., such as at least 145.0 ° C., for example at least 150.0 ° C .; Standardized electrolyte affinity of 0.20 sec / μm or less, such as 0.24 sec / μm or less, for example 0.18 sec / μm or less: and 2.85 × 10 ² mN / μm or more, for example 2.90 × 10 ² mN / μm or more Has strength. In one embodiment, the membrane has a thickness of 9.0 μm or less, a standardized puncture strength of 2.85 × 10 ² mN / μm or more, NEA of 0.18 seconds / μm or less, and a porosity of 35.0% or more. If desired, the combined weight of PE1, PE2 and PP is at least 95.0% by weight, such as at least 95.0% by weight, for example at least 99.0% by weight of the membrane.

In another embodiment, the present invention relates to a membrane comprising 79.0 wt% to 86.0 wt% PE2, 9.0 wt% to 16.0 wt% PE3, and 4.0 wt% to 6.0 wt% PP, wherein (i ) PE2 has a Mw in the range of about 3.0 × 10 ⁵ to about 8.0 × 10 ⁵ , a MWD in the range of about 4 to about 15, a terminal unsaturation of at least 0.20 per 1.0 × 10 ⁴ carbon atoms, and a melting point of at least 132 ° C .; (ii) PE3 has a Mw in the range of about 1.0 × 10 ⁶ to about 3.0 × 10 ⁶ , a MWD in the range of about 4.0 to about 15.0, and a melting point of at least 134 ° C .; (iii) PP is Mw in the range from about 0.9 × 10 ⁶ to about 2.0 × 10 ⁶ , MWD in the range of from 8.5 to below 8.5, for example from 2.0 to 8.5, such as in the range from 2.5 to 6.0, and at least 90.0 J / g, eg For example isotactic PP having a ΔHm of at least 100.0 J / g; (iv) the membrane is microporous; In addition, the film (v) has a thickness of 12.0 μm or less, for example, 8.0 μm. Weight percent is relative to the weight of the membrane. If desired, the membrane comprises up to 1.0 wt.% PE1 based on the weight of the membrane. Such membranes have a meltdown temperature of at least 145.0 ° C., for example at least 150.0 ° C., and a standardized electrolyte affinity of at most 0.16 seconds / μm, for example at most 0.14 seconds / μm, and a standardized puncture strength of less than 2.90 × 10 ² mN / μm. Has If necessary, the film is a monolayer film. If desired, the combined weight of PE1, PE2 and PP is at least 98.0% by weight, such as at least 95.0% by weight of the membrane, for example at least 99.0% by weight.

Although this is not limited to the above, the present invention includes the use of the membrane of any of the above-described embodiments as a battery separator film in a lithium ion polymer battery, particularly a secondary lithium ion polymer battery. Although not limited to any theory or model, it is believed that the use of PE2 instead of PE1 increases the affinity of the membrane for the polymer electrolyte but decreases the membrane strength, while the relative amounts of PP and PE3 in the membrane remain largely constant. .

Hereinafter, the manufacturing method of a microporous membrane is demonstrated in detail. Although this invention is demonstrated about the monolayer film | membrane manufactured by extrusion, this invention is not limited to this and this description does not mean to exclude other embodiment in the wide range of this invention.

(Method of manufacturing membrane)

In one or more embodiments, the first polymer (ie PE) and the second polymer (ie PP) (eg, by dry blending or melt mixing) may be combined with optional components such as diluents and inorganic fillers. The microporous membrane can be prepared by forming a mixture and then extruding the mixture to form an extrudate. At least a portion of the diluent is removed from the extrudate to form the microporous membrane. For example, a blend of PE1 and / or PE2 and PE3 and PP may be combined with a diluent such as liquid paraffin to form a mixture, and the mixture may be extruded and processed to form a monolayer film having a thickness of 12.0 μm or less. have. If desired, additional layers can be applied to the extrudate to provide the final membrane, for example with a low shutdown function. That is, a single layer extrudate or a single layer microporous membrane can be laminated or coextruded to form a multilayer membrane.

In at least one embodiment, the process of preparing the membrane comprises stretching the extrudate in at least l direction prior to diluent removal. In these or other embodiments, the process includes stretching the membrane in at least one direction after diluent removal. The process for preparing the membrane may require, for example, removing at least some of any residual volatiles from the membrane at any time after diluent removal, and heat treating (eg, heating setting or annealing) before or after diluent removal. According to more include. As described in PCT Patent Publication No. WO2008 / 016174, a selective solvent treatment, a selective heating setting, a crosslinking to selective ionizing radiation, a hydrophilic treatment process and the like can be carried out as necessary. The order of the numbers of the optional processes is not important either.

(Preparation of Polymer-Diluent Mixture)

In one or more embodiments, a first and a second polymer (e.g., PEl (and / or PE2) and PE3 as first polymer and PP3 as a second polymer, as described above) is added with one or more diluents And mix to form a polymer-diluent mixture. For example, the first and second polymers can be combined to form a polymer blend, and the blend can be combined with a diluent (which is a mixture of diluents, for example a solvent mixture) to produce a polymer-diluent mixture. Mixing can be carried out in an extruder, for example a reaction extruder. Such extruders include, but are not limited to, twin screw extruders, ring extruders, and planetary extruders. The practice of the present invention is not limited to the type of extruder used. Optional species, for example fillers, antioxidants, stabilizers and / or heat resistant polymers, may be included in the polymer-diluent mixture. The kind and amount of these optional species may be the same as described in PCT Publication No. WO2007 / 132942, PCT Publication No. WO2008 / 016174 and PCT Publication No. WO2008 / 140835, which are hereby incorporated by reference in their entirety. .

Diluents are generally compatible with the polymers used to make the extrudate. For example, the diluent can be any species or combination of species capable of forming a single phase with the resin at the extrusion temperature. Examples of diluents include aliphatic or alicyclic hydrocarbons such as nonane, decane, decalin, and paraffin oils, and phthalic acid esters such as dibutylphthalate and dioctylphthalate. For example, paraffin oil having a fluid viscosity of 20-200 cSt at 40 ° C. may be used. Diluents can be the same as described in US 2008/0057388 and US 2008/0057389, which are incorporated by reference in their entirety.

In one embodiment, the polymer blend in the polymer-diluent mixture comprises an amount of A ₁ of the first polymer (eg, PE1 and PE3) and an amount of A ₂ of the second polymer (eg, PP) . In one embodiment, A ₁ is 1.0% by weight or more, for example, in the range of 80.0% by weight to 96.0% by weight, A ₂ is in the range of 4.0% by weight to 20.0% by weight, and A ₁ and A ₂ in Weight percent is relative to the weight of the polymer in the mixture. As needed, A <_1> is the range of 84.5 weight%-95.5 weight%, for example, the range of 94.75 weight%-95.25 weight%. If desired, A ₂ is in the range of 4.5% by weight to 15.5, for example in the range of 4.75 to 5.25% by weight, based on the total weight of the polymer in the mixture. If desired, the polymer-diluent mixture comprises up to 45.0% by weight of the polymer, based on the weight of the mixture, for example, in the range of 30.0% to 40.0% by weight, based on the total weight of the polymer in the mixture. The remainder of the mixture may be a diluent.

In one or more embodiments, the amount of A ₁ in PE in the polymer-diluent mixture may include the amount of B ₁ in PE1 and / or PE2 and the amount of B ₂ in PE3. In one embodiment, B ₁ is in the range of 60.0 wt% to 96.0 wt%, B ₂ is in the range of 0.0 wt% to 20.0 wt%, and wt% of B ₁ and B ₂ is relative to the weight of the polymer in the mixture. will be. If desired, B ₁ is in the range of 69.5% to 90.5% by weight, for example 80.0% to 85.0% by weight, based on the total polymer in the mixture. If desired, B ₂ is in the range of 5.0% by weight to 15.0, for example 9.75% by weight to 15.25% by weight, based on the total polymer in the mixture.

In one embodiment, the polymer-diluent mixture is exposed to a temperature in the range of 140 ° C. to 250 ° C., for example 210 ° C. to 230 ° C. during extrusion.

(Production of Extruded Products)

In one embodiment, the polymer-diluent mixture is run from the extruder through a die to produce the extrudate. The extrudate must have a suitable thickness to produce a final film having the desired thickness (generally 12.0 μm or less) after the process step. For example, the extrudate may have a thickness in the range of about 1.0 μm to about 10.0 μm, or about 3.0 μm to about 8.0 μm. In one or more embodiments, the final film has a final film thickness (after processing) of 12.0 μm or less, for example 10.0 μm or less.

Extrusion is generally carried out in a molten polymer-diluent mixture. When using a sheet-forming die, the die lip is generally heated at a high temperature, for example in the range of 180 ° C to 240 ° C. Suitable process conditions for achieving extrusion are disclosed in PCT Patent Publication WO2007 / 132942 and PCT Patent Publication WO2008 / 016174.

If desired, the extrudate can be exposed to a temperature in the range of about 10 ° C. to about 45 ° C. to form a cooled extrudate. The cooling rate is not particularly important. For example, the extrudate can be cooled at a cooling rate of at least about 30 ° C./minute until the extrudate's temperature (cooled temperature) is approximately equal (or below) the extrudate's gelling temperature. Process conditions for cooling may be the same as those disclosed, for example, in PCT Patent Publication No. WO2007 / 132942, PCT Patent Publication No. WO2008 / 016174, and PCT Patent Publication No. WO2008 / 140835.

(Stretching of extrudates (upstream stretching))

The extrudate or cooled extrudate can be stretched in at least one direction, for example in a planar direction such as MD or TD (referred to as "upstream stretch" or "wet stretch"). As a result of this stretching, the polymer in the extrudate is considered to be at least a predetermined orientation. This orientation is referred to as the "upstream" orientation. The extrudate can be drawn by the tenter method, the roll method, the inflation method, or a combination thereof, as described, for example, in PCT Publication No. WO2008 / 016174. Stretching may be performed either uniaxially or biaxially; In certain embodiments, the extrudate is stretched biaxially. In the case of biaxial stretching, any one of simultaneous biaxial stretching, sequential stretching or multistage stretching (eg, a combination of simultaneous biaxial stretching and sequential stretching) can be used; In certain embodiments, the extrudate is simultaneously biaxially stretched. When using biaxial stretching, the magnification amount does not need to be the same in each stretching direction.

The draw ratio may be, for example, 2 times or more and 3 to 30 times in the case of uniaxial stretching. In the case of biaxial stretching, the stretching magnification can be, for example, three times or more, that is, nine times or more, for example, 16 times or more, 25 times or more in area magnification in any direction. Examples of such stretching processes include stretching from about 9 times to about 49 times in area magnification. In addition, the draw amount in each direction does not need to be the same. The magnification acts as a multiplication to the size of the membrane. For example, a film with an initial width (TD) of 2.0 cm drawn at 4 times magnification by TD will have a final width of 8.0 cm.

Stretching can be performed while extruded products are exposed to temperatures in the range of about Tcd to Tm (upstream stretching temperature), in which case Tcd and Tm have the lowest melting point among the crystal dispersion temperatures and the polyethylene used to make the extrudate. It is defined as the melting point of PE (typically PE such as PE1 or PE3). Crystal dispersion temperature is obtained by measuring the temperature characteristics of the dynamic viscoelasticity according to ASTM D4065. In an embodiment in which the Tcd is in the range of about 90 ° C to about 100 ° C, the stretching temperature is 90.0 ° C to 122.0 ° C; For example, it may be 108.0 ° C to 116.0 ° C, such as 110.0 ° C to 114.0 ° C.

When exposing a sample (eg, extrudate, dried extrudate, membrane, etc.) to high temperatures, this exposure can be achieved by heating the air and moving the heated air near the sample. In general, the temperature of the heated air is controlled to the same setpoint as the desired temperature, and is then moved towards the sample, for example through a plenum. Other methods of exposing the sample to high temperatures, including conventional methods such as exposing the sample to a heating surface, infrared heating in an oven, and the like, can be used with or instead of heated air.

(Removal of diluent)

In one embodiment, at least a portion of the diluent is removed (or substituted) from the stretched extrudate to form a dried film. For example, a diluent may be removed (cleaned or substituted) using a substituted (or "washed") solvent, as described in PCT Publication No. WO2008 / 016174.

In one embodiment, at least some of any remaining volatile species (eg, cleaning solvent) is removed from the dried membrane after diluent removal. Any method capable of removing the cleaning solvent can be used, and conventional methods such as heat drying, blow drying (air movement), and the like are included. Process conditions for removing volatiles, such as cleaning solvents, may be the same as those disclosed, for example, in PCT Publication No. WO2008 / 016174.

(Extension (downstream stretching) of selective membrane)

The dried membrane may be stretched in at least one direction, for example MD and / or TD (called “downstream stretching” or “dry stretching” since at least a portion of the diluent has been removed or substituted). It is contemplated that, as a result of this stretching, the polymer can be performed in at least a predetermined orientation in the film. This orientation is called the downstream orientation. The membrane dried prior to downstream stretching has an initial MD size (first drying length) and an initial TD size (first drying width). As used herein, the term "first dry width" refers to the TD size of the dried membrane before the start of dry stretching. The term "first dry length" refers to the MD size of the dried membrane before the start of dry stretching. For example, tenter stretching apparatus of the type described in WO2008 / 016174 can be used.

The dried membrane is MD by a magnification ("MD dry draw ratio") in the range of about 1.0 to about 1.6, for example in the range of about 1.1 to 1.5, from the first drying length to the second drying length longer than the first drying length. Can be stretched to. When using TD dry stretching, the dried film may be stretched to TD by a magnification (“TD dry draw ratio”) from the first drying width to a second drying width wider than the first drying width. As needed, TD dry draw ratio is more than MD dry draw ratio. The TD dry draw ratio may range from about 1.1 to about 1.6, for example from about 1.1 to 1.5. Dry stretching can be sequential or simultaneous with MD and TD. When biaxial dry stretching is used, dry stretching can be simultaneous or sequential with MD and TD. In the case where dry stretching is sequential, MD stretching is generally preferred, followed by TD stretching.

In certain embodiments, dry stretching is to be avoided or minimized, particularly when practicing embodiments of the present invention in view of the thickness of the particular film produced according to the present invention. For example, the process step of making a film with the desired thickness is free of any dry stretching steps. In another embodiment, the process step includes dry stretching at a magnification of 1.1 or less, in another embodiment up to 1.08, in other embodiments up to 1.05, and in other embodiments up to 1.03.

Dry stretching can be performed while exposing the dried film to a temperature below Tm (downstream stretching temperature), for example, in the range of about Tcd-20 ° C to Tm. In one embodiment, the stretching temperature is performed with a film exposed to a temperature in the range of about 70.0 ° C to about 135.0 ° C, such as about 110.0 ° C to about 132.0 ° C, such as about 120.0 ° C to about 130.0 ° C.

In one embodiment, the MD dry draw ratio is about 1.0; The TD dry draw ratio is no greater than 1.6, for example in the range of about 1.05 to about 1.5, such as about 1.1 to 1.5; Dry stretching is performed while exposing the membrane to a temperature in the range of about 120.0 ° C to about 130.0 ° C.

Dry stretching speed is not important. In one embodiment, the dry draw rate is at least 1% / sec in the draw direction (MD or TD), and the rate may be independently selected for MD and TD draw. If desired, the stretching speed is at least 3% / second, such as at least 2% / second, for example at least 10% / second. In one embodiment, the stretching speed is in the range of 2% / second to 25% / second. Although not particularly important, the upper limit of the stretching speed may be 50% / second to prevent breakage of the membrane.

(Controlled reduction of membrane width)

Following the dry stretching, the dried membrane is subjected to a reduction in the controlled width from the second drying width to the third drying width as needed, and the third drying width is from about 0.9 times the first drying width to about 1.5 greater than the first drying width. The range of the ship. As needed, a 2nd dry width is the range of 1.25-1.35 of a 1st dry width, and a 3rd dry width is the range of 0.95-1.05 of a 1st dry width. The width reduction is generally above Tcd-30 ° C., but about 110.0 ° C. to about 132.0 ° C., such as temperatures below Tm, such as temperatures ranging from about 70.0 ° C. to about 135.0 ° C., for example about 120.0 ° C. to about 130.0 ° C. It is performed while exposing to temperature.

The temperature during the controlled width reduction may be equal to the downstream stretching temperature, but this is not essential, and in one embodiment, the temperature at which the membrane is exposed during the controlled width reduction is at least 1.01 times the downstream stretching temperature, for example 1.05 times. It is in the range of ~ 1.1 times. In one embodiment, the width reduction of the membrane is performed while exposing the membrane to a temperature of 130.0 ° C. or lower, and the third drying width is in the range of 0.95 to 1.05 of the first drying width.

(Heating set)

For example, the membrane is heat treated (heat set) at least once following dry stretching as needed, after a controlled decrease in width, or after both, followed by diluent removal. It is believed that the crystals stabilize and form a uniform layered layer in the film by the heating set. In one embodiment, the heating setting is applied to the membrane at a temperature in the range of Tcd to Tm, for example in the range of about 70.0 ° C to about 135.0 ° C, for example about 110.0 ° C to about 120.0 ° C, such as about 120.0 ° C to about 130.0 ° C. It is performed while exposing.

The heating set temperature may be equal to the downstream stretching temperature, but this is not necessary. In one embodiment, the temperature at which the membrane is exposed during the heating setting ranges from at least 1.01 times the downstream stretching temperature, for example, from 1.05 times to 1.1 times. In general, the heating setting is carried out for a time sufficient to form a uniform layered in the film, for example for a time in the range of 1000 seconds or less, for example 1 to 600 seconds. In one embodiment, the heating setting is performed under conventional heating set "heat set" conditions. The term "heat fixation" refers to a heating setting that is made while keeping the length and width of the membrane largely constant, for example by fixing the perimeter of the membrane using a tenter clip during the heating setting.

If necessary, an annealing treatment may be performed after the heat set step. Annealing is a heat treatment with no load applied to the membrane, and can be done using, for example, a drying chamber with a belt conveyor or an air floating type drying chamber. In addition, annealing can be performed continuously in the state which relaxed the tenter after heating setting. During annealing the membrane may be exposed to temperatures in the range of Tm or below, for example in the range of about 60 ° C to about Tm-5 ° C. Annealing is thought to improve the air permeability and strength of the microporous membrane.

Optional heating rollers, heating solvents, crosslinking, hydrophilicity, and coating treatments can be carried out as required, for example, as described in PCT Publication No. WO2008 / 016174.

(Characteristic of the film)

In one or more embodiments, the membrane is a microporous membrane that is permeable to liquids (aqueous and non-aqueous) at atmospheric pressure. Thus, the membrane can be used as a battery separator, a filtration membrane, or the like. Microporous membranes are particularly useful as BSFs for secondary batteries such as nickel-hydrogen batteries, nickel-cadmium batteries, nickel-zinc batteries, silver-zinc batteries, lithium-ion batteries, lithium-ion polymer batteries and the like. In one embodiment, the present invention relates to a lithium ion secondary battery comprising a BSF comprising a membrane. Such cells are described in PCT patent publication WO2008 / 016174, which is incorporated herein by reference in its entirety.

In one or more embodiments, the microporous membrane is a monolayer useful as a BSF for polymer cells, such as lithium ion polymer cells. The term "polymer electrolyte" as used herein may be used in the conventional sense to denote an electrolyte in a polymer cell. As will be appreciated by those skilled in the art, polymer cells include electrolytes that are dispersed, suspended or dissolved in a polymer medium such as lithium ions. Thus, electrolyte affinity or permeability refers to the ability to permeate through the membrane of an electrolyte, such as a polymer medium and / or lithium ions.

The membrane may have one or more of the following properties.

(thickness)

In one embodiment, the thickness of the final film is 12.0 μm or less, such as 10.0 μm or less, for example in the range of about 1.0 μm to about 10.0 μm. For example, the monolayer film may have a thickness in the range of about 4.5 μm to about 9.5 μm. The thickness of the film can be measured, for example, by a contact thickness meter at 1 cm length intervals over 10 cm width and then averaged to obtain a film thickness. 746-3 Gokanjima, Fuji-shi, Shizuoka-ken, Japan Maysun, Inc. Thickness gauges such as the RC-1 Rotary Caliper, or "Litematic" from Mitsutoyo Corporation are suitable. The non-contact thickness measuring method is also suitable, for example, the optical thickness measuring method.

(Porosity)

The porosity of the membrane is measured by conventional methods by comparing the actual weight of the membrane with the weight of the same nonporous membrane (the same in terms of polymer composition, length, width and thickness) of 100% polymer. The porosity is then calculated using the following formula: Porosity (expressed in%) = 99% x (w1 / w2), where "w1" is the actual weight of the membrane and "w2" is the same size and thickness (the same polymer ) The weight of the non-porous membrane. In one embodiment, the porosity of the membrane is at least 20.0%, for example at least 31.0%, such as at least 35.0%. For example, the porosity of the membrane can range from 20.0% to 80.0%, such as 36.0% to 40.0%.

(Standardization speculation)

In one embodiment, the membrane has a thickness of about 10.0 seconds / 1OO or less, such as about 15.0 seconds / 1OO cm 3 / μm to about 40.0 seconds / 1OO cm 3 / μm It has a standardized air permeability in the range of cm 3 / μm to about 45.0 sec / 1OO cm 3 / μm. Since the air permeability value is normalized to the value for the same film having a film thickness of 1.0 μm, the air permeability value of the film is expressed in units of “second / 10 cm 3 / μm”. Normalized air permeability is measured according to JIS P8117, and the results are normalized to the air permeability values of the same membrane having a thickness of 1.0 μm using the formula A = 1.0 μm * (X) / T ₁ , where X is the actual thickness The measured air permeability of the membrane, T ₁ , and A is the standardized air permeability of the same membrane with a thickness of 1.0 μm.

(Standardized puncture strength)

The puncture strength of the membrane is expressed as the puncture strength of the same membrane having a thickness of 1.0 mu m and a porosity of 30%, and has a unit of [mN / mu m]. The puncture strength is defined as the maximum load measured at ambient temperature when a membrane of thickness T _l punctures a spherical surface (bending radius R: 0.5 mm) at a speed of 2 mm / sec with a needle of diameter 1 mm. This puncture strength ("S") is obtained by using the formula S ₂ = [30% * 1.0 μm * (S ₁ )] / [T ₁ * (100% -P)] with a thickness of 1.0 μm and a porosity of 50%. Normalized to the puncture strength value of the same membrane, where S ₁ is the measured puncture strength, S ₂ is the normalized puncture strength, P is the measured porosity of the membrane, and T ₁ is the average thickness of the membrane. In one embodiment, the standardized puncture strength of the membrane is at least 2.50 × 10 ² mN / μm, for example at least 2.90 × 10 ² mN / μm. If necessary, the standardized puncture strength of the membrane is at least 3.0 × 10 ² mN / μm, such as in the range of 3.05 × 10 ² mN / μm to 4.5 × 10 ² mN / μm.

(Shutdown Temperature)

The shutdown temperature of the microporous membrane is measured by the method disclosed in PCT Patent Publication No. WO2007 / 052663, which is incorporated by reference herein in its entirety. Following this method, the microporous membrane is exposed to increasing temperature (5 ° C./min) starting at 25 ° C. while measuring the air permeability of the increasing temperature (5 ° C./min) membrane starting at 25 ° C. The shutdown temperature of the microporous membrane is defined as the temperature at which the air permeability (Gurley value) of the microporous membrane exceeds 1.0 × 10 ⁵ seconds / 1OO cm ³ for the first time. The air permeability of the microporous membrane is measured using an air permeability measuring instrument (EGO-1T, manufactured by Asahi Seiko Co., Ltd.) in accordance with JIS P8117. In one embodiment, the shutdown temperature is at most 136 ° C, for example in the range from 132.5 ° C to 134.5 ° C.

(Meltdown temperature)

The shutdown temperature of the microporous membrane is measured using the same procedure as the measurement of the shutdown temperature. According to this method, the microporous membrane is exposed to increasing temperature (5 ° C./minute) starting at 25 ° C., which is a temperature exceeding the membrane's shutdown temperature, while measuring the air permeability of the membrane. The membrane is continuously heated and the meltdown temperature of the microporous membrane is defined as the temperature at which the air permeability (Gurley value) of the microporous membrane is first reduced to a value of 1.0O ⁵ sec / 1OO cm ³ . The air permeability of the microporous membrane is measured using an air permeability measuring instrument (EGO-1T, manufactured by Asahi Seiko Co., Ltd.) in accordance with JIS P8117. In one embodiment, the meltdown temperature of the membrane of the present invention is at least 150.0 ° C, such as at least 165.0 ° C, for example at least 160.0 ° C. In one embodiment, the meltdown temperature is in the range of 146.0 ° C to 170.0 ° C, for example in the range of 150.0 ° C to 165 ° C.

(105 ℃ heat shrink)

In one embodiment, the membrane has heat shrinkage at 105 ° C. in at least one planar direction (eg MD or TD) of at least 10.0%, for example at least 6.0%, such as in the range of 1.0% to 5.0%. The membrane shrinkage at 105.0 ° C. of MD and TD is measured as follows: (i) the size of the test piece of the microporous membrane at ambient temperature is measured with both MD and TD; (ii) equilibrate the specimen of the microporous membrane at a temperature of 105 ° C. for 8 hours to which no load was applied; (Iii) the membrane size is then measured in both MD and TD. Thermal (or “heat”) shrinkage of the MD and TD can be obtained by dividing the measurement result (i) by the measurement result and (ii) expressing the obtained value as a percentage.

(The tensile strength)

In one embodiment, the membranes each have an MD and TD tensile strength in the range of 1.4 × 10 ⁵ kPa or more, for example 1.5 × 10 ⁵ kPa to 2.0 × 10 ⁵ kPa. Tensile strength is measured by MD and TD according to ASTM D-882A.

(Standardized Electrolyte Affinity)

A film sample of 50 mm x 50 mm (thickness of 12.0 µm or less) is prepared and placed on a flat glass substrate having a larger area than the film. The film is irradiated from the top using visible light, and the film at the start of the measurement is opaque. 500.0 µl of droplets of propylene carbonate (purity is 99 vol% or more) is applied to the surface of the film using a film at 25 ° C and +/- 3 ° C. The electrolyte affinity ("EA") of a membrane is defined as the average elapsed time from contacting the film at the beginning of the droplets until the film becomes transparent. The measurement is repeated five times to obtain an average value.

Normalized electrolyte affinity (“NEA”) is defined as EA / (average film thickness of μm). NEA has a unit of [seconds / μm]. In one embodiment, the membrane has a NEA in the range of 5.0 seconds / μm or less, such as 0.1 seconds / μm to 0.9 seconds / μm, such as 2.5 seconds / μm or less.

(Example)

The invention will be explained in more detail without restricting the scope of the invention with reference to the following examples.

(Example 1)

(1) Preparation of polymer-diluent mixture

The polymer-diluent mixture is prepared as follows by combining a polymer blend of two kinds of polyethylene, PE1 and PE3 and PP with a diluent. The weight percents are based on the weight of the combined polymer and the polymer blends are (a) 5.6 × 10 ⁵ Mw, 4.0 MWD, up to 0.14 terminal unsaturation per 1.0 × 10 ⁴ carbon atoms, and Tm of 136.0 ° C. 90.0% by weight of PE (PEl), (b) 1.9 × 10 ⁶ Mw, 5.1 MWD, and 5.0% by weight PE (PE3) with Tm of 136.0 ° C., and (c) 5.3 × 10 ⁵ of 5.0 wt% isotactic PP (PP2) with Mw and ΔHm of about 80 J / g.

Subsequently, 35.0 wt% polymer blend was charged into a strong blending twin screw extruder having an internal diameter of 58 mm and L / D of 42, and 65.0 wt% of liquid paraffin (50 cst at 40 ° C.) was passed through a side feeder. To feed. Mixing at 220 ° C. and 320 rpm produces a polymer-diluent mixture, wherein the weight percentages are relative to the weight of the polymer-diluent mixture.

(2) Production of membranes

The polymer-diluent mixture is subjected to a sheet forming die (in the form of a sheet) from an extruder to form an extrudate. The temperature of the die is about 210 ° C. (or as specifically described in Table 1). The extrudate is cooled in contact with a controlled cooling roller at 20 ° C. The cooled extrudate is 5 times simultaneous biaxial stretching (upstream stretching) to both MD and TD at about 112.5 ° C. (as specifically shown in the table) by a tenter stretching machine. The stretched three-layer gel-like sheet is then immersed in a methylene chloride bath controlled at 25 ° C. to remove the liquid paraffin in an amount of 1.0 wt% or less based on the weight of the liquid paraffin in the polymer-diluent mixture. The membrane is then dried by airflow at room temperature. Subsequently, the membrane is heated and set at 128.8 ° C. for 10 minutes (as shown in the table) while keeping the size of the membrane largely constant to produce the final microporous membrane. Selected starting materials, process conditions and membrane properties are shown in Table 1.

(Example 2)

Example 1 other than what is described in Table 1 is repeated. Starting materials and process conditions were as used in Example 1 other than those listed in the table. For example, PP1 may be substituted for polypropylene (PP1) having Mw of 1.1 × 10 ⁶ and ΔHm of 114J / g; PE1 may be substituted for PE1 (PE2) having a Mw of 7.46 × 10 ⁵ , a Tm of 134.0 ° C., and a terminal unsaturation of at least 0.20 per 1.0 × 10 ⁴ carbon atoms. The membranes of Examples 4 and 5 are drawn at a TD magnification of 1.4 downstream of the diluent removal (downstream) with exposure to temperatures of 130.2 ° C. (Example 4) and 130.0 ° C. (Example 5), respectively, before heat setting.

(Review)

It is shown in Examples 1-5 that relatively thin microporous membranes having a useful meltdown temperature (eg, 145.0 ° C. or higher) can be prepared from at least 4.0 wt% PP based on the weight of the PE and the membrane. Such membranes are useful as BSFs in lithium ion batteries such as lithium ion polymer cells using thin BSFs. As shown by Example 5, increasing the concentration of PP significantly increased NEA. For films containing 20.0% by weight or more of PP, the larger the NEA value, the more difficult it is to use the film as BSF for polymer batteries. On the other hand, the data indicate that a limiting amount of PP is necessary to achieve a useful meltdown temperature, while increasing the amount of PP has an undesirable effect on the NEA. Comparative Example 1 represents BSF without PP. These membranes also have useful NEA, but also have relatively low meltdown temperatures, relatively low porosity, and relatively low normalized puncture strength.

All patents, test procedures, and other documents, including the priorities listed in the present invention, are hereby fully incorporated by reference in the scope and jurisdiction in which these publications are permitted.

Although the exemplary forms disclosed herein have been described in detail, it will be apparent to those skilled in the art that various other changes may be made without departing from the spirit and scope of the invention. Thus, although the scope of the claims appended to the present invention is not intended to be limited to the embodiments and descriptions set forth herein, the claims encompass all of the patentable novelty features present in the present invention and are disclosed by those skilled in the art It is configured to include all of the properties considered to be the same as included.

When the water droplet lower limit and water droplet upper limit are described in this invention, it is considered that it is a range of arbitrary lower limits-arbitrary upper limits.

(Industrial availability)

The microporous membrane of the present invention is suitable for use as a battery separator film.

Claims (23)

A film comprising at least 1.0 weight percent polyethylene and at least 4.0x10 ⁵ Mw and at least 4.0% to 20.0 weight percent polypropylene having a ΔHm of at least 80.0 J / g, where the weight percent is based on the weight of the polymer in the membrane. :
The membrane is microporous and has a thickness of 12.0 µm or less. The method of claim 1,
The amount of the polypropylene is in the range of 4.5% by weight to 15.5% by weight based on the weight of the membrane, wherein the membrane has a thickness of less than 10.0㎛. 3. The method according to claim 1 or 2,
A membrane characterized by having a meltdown temperature of 145.0 ° C. or higher and a standardized electrolyte affinity of 2.5 seconds / μm or less. The method according to any one of claims 1 to 3,
A membrane having a porosity in the range of 20% to 80%, a standardized air permeability of 50.0 seconds / 100 cm 3 / m or less, and a standardized puncture strength of 2.5 × 10 ² mN / m or more. The method according to any one of claims 1 to 4,
The polypropylene has a Mw of 6.0 × 10 ⁵ or more, MWD of 8.5 or less, and ΔHm of 90.0 J / g or more and comprises 90.0% by weight or more of isotactic polypropylene based on the weight of the polymer in the film. Just about to. 6. The method according to any one of claims 1 to 5,
(i) wherein said polyethylene comprises a first polyethylene having a first polyethylene and 1.0 × 10 ⁶ or more Mw having a Mw of less than 1.0 × 10 ^6; (ii) the first polyethylene is present in an amount of B ₁ in the range of 69.5% to 90.5% by weight; (iii) the second polyethylene is present in an amount of B ₂ in the range of 5.0% to 15.0% by weight, whereby% by weight is based on the weight of the polymer in the membrane. The method according to claim 6,
The amount of the first polyethylene is in the range of 72.0% to 90.0% by weight, the amount of the second polyethylene is in the range of 5.0% to 20.0% by weight, and the amount of the polypropylene is 5.0% by weight based on the weight of the polymer in the membrane. Membrane characterized by the range of% to 8.0% by weight. The method of claim 7, wherein
The first polyethylene has a Mw in the range of 4.0 × 10 ⁵ to 6.0 × 10 ⁵ and a MWD in the range of 3.0 to 10.0, and the second polyethylene has a Mw in the range of 1.0 × 10 ⁶ to 3.0 × 10 ⁶ and 4.0 to Membrane having an MWD in the range of 15.0. The method of claim 8,
The first polyethylene film, characterized in that having a terminal unsaturation amount of less than carbon atoms 1.O × 10 ⁴ per 0.20. The microporous membrane of any one of Claims 1-9 is included, The battery separator film characterized by the above-mentioned. (1) A process of extruding a mixture of diluent and polymer, wherein the polymer comprises A ₁ amount of polyethylene and A ₂ amount polypropylene, wherein A ₁ is based on the weight of the polymer in the polymer in the polymer-diluent mixture 1.0 wt% or more, wherein A ₂ is in the range of 4.0 wt% to 20.0 wt%;
(2) drawing the extrudate in at least one planar direction: and
(3) removing at least a portion of the diluent from the stretched extrudate. The method of claim 11,
A ₁ is in the range of 84.5% by weight to 99.5% by weight based on the weight of the polymer in the polymer-diluent mixture, wherein the polyethylene has a Mw of less than 1.0 × 10 ⁶ . 13. The method according to claim 11 or 12,
(i) A ₂ is in the range of 4.5% to 15.5% by weight; (ii) the polypropylene comprises isotactic polypropylene having a Mw of at least 6.0 × 10 ⁵ , a HWD of at most 8.5 and a ΔHm of at least 90.0 J / g, of at least 90.0% by weight based on the weight of the polypropylene. Method for producing a microporous membrane to be. 14. The method according to any one of claims 11 to 13,
(i) The polyethylene is, based on the total weight of the first polyethylene and 1.0 × 10 ⁶ polymer in the second polyethylene, and, (ii) a mixture including having at least Mw having a Mw of less than 1.0 × 10 ⁶ of the first The polyethylene is present in an amount of B ₁ in the range of 69.5% to 90.5% by weight, and (iii) the second polyethylene is present in an amount of B ₂ in the range of 5.0% to 15.0% by weight. Method for producing a porous membrane. 15. The method according to any one of claims 11 to 14,
Method for producing a microporous membrane further comprises the step of cooling the extrudate prior to the step (2). The method according to any one of claims 11 to 15,
And a step of stretching the membrane in at least one direction following the step (3) and a step of heat treating the membrane following the step (3). 17. The method of claim 16,
The drawing direction is a method for producing a microporous membrane, characterized in that TD. 18. The method according to any one of claims 11 to 17,
The stretching of the step (2) is carried out biaxially at a magnification in the range of 9 times to 49 times the area while exposing the extrudate to a temperature in the range of 90.0 ° C to 125.0 ° C. 19. The method according to any one of claims 11 to 18,
A method of producing a microporous membrane, further comprising the step of removing any volatile species remaining after the step (3) from the membrane. The membrane product according to any one of claims 11 to 19. A battery comprising a negative electrode, a positive electrode, an electrolyte, and a battery separator positioned between the negative electrode and the positive electrode:
The battery separator includes the membrane according to any one of claims 1 to 10. 22. The method of claim 21,
The membrane has a thickness of 10.0 μm or less, and the battery is a lithium ion polymer battery. An electric vehicle or a hybrid electric vehicle, comprising a power means electrically connected to the battery according to claim 21.