JPWO2020075794A1 - Polyolefin microporous membrane, multilayer polyolefin microporous membrane, battery - Google Patents

Polyolefin microporous membrane, multilayer polyolefin microporous membrane, battery Download PDF

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JPWO2020075794A1
JPWO2020075794A1 JP2020500906A JP2020500906A JPWO2020075794A1 JP WO2020075794 A1 JPWO2020075794 A1 JP WO2020075794A1 JP 2020500906 A JP2020500906 A JP 2020500906A JP 2020500906 A JP2020500906 A JP 2020500906A JP WO2020075794 A1 JPWO2020075794 A1 JP WO2020075794A1
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crystallinity
polyolefin microporous
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敏彦 金田
敏彦 金田
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Toray Industries Inc
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00Layered products comprising a layer of synthetic resin
    • B32B27/32Layered products comprising a layer of synthetic resin comprising polyolefins
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B5/00Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
    • B32B5/22Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed
    • B32B5/32Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed at least two layers being foamed and next to each other
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/26Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409Separators, membranes or diaphragms characterised by the material
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/491Porosity
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries

Abstract

セパレータとして電池に組み入れた際にシャットダウン特性に優れたポリオレフィン微多孔膜を提供する。
広角X線回折測定により算出される室温における膜厚方向の結晶化度と面内方向の結晶化度との差が25%以下であり、前記膜厚方向の結晶化度が前記面内方向の結晶化度よりも大きく、前記室温における面内方向の結晶化度と広角X線測定により算出されるシャットダウン温度における面内方向の結晶化度との差が58%以上であるポリオレフィン微多孔膜。
Provided is a polyolefin microporous membrane having excellent shutdown characteristics when incorporated into a battery as a separator.
The difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction at room temperature calculated by wide-angle X-ray diffraction measurement is 25% or less, and the crystallinity in the film thickness direction is the in-plane direction. A polyolefin microporous film that is larger than the crystallinity and the difference between the in-plane crystallinity at room temperature and the in-plane crystallinity at the shutdown temperature calculated by wide-angle X-ray measurement is 58% or more.

Description

本発明は、ポリオレフィン微多孔膜、多層ポリオレフィン微多孔膜および電池に関するものである。 The present invention relates to a polyolefin microporous membrane, a multilayer polyolefin microporous membrane and a battery.

微多孔膜は、ろ過膜、透析膜などのフィルター、電池用セパレータや電解コンデンサー用のセパレータなどの種々の分野に用いられる。これらの中でも、ポリオレフィンを樹脂材料とする微多孔膜は、耐薬品性、絶縁性、機械的強度などに優れ、シャットダウン特性を有するため、近年、二次電池用セパレータとして広く用いられる。 Microporous membranes are used in various fields such as filters for filtration membranes and dialysis membranes, separators for batteries and separators for electrolytic capacitors. Among these, microporous membranes made of polyolefin as a resin material are excellent in chemical resistance, insulating property, mechanical strength, etc., and have shutdown characteristics, and are therefore widely used as separators for secondary batteries in recent years.

二次電池用セパレータには捲回体や電池内への異物混入などによる短絡を防ぐため機械強度や電池の熱暴走を抑制するために高温時にセパレータの孔が閉塞することで電極間に流れる電流を遮断するシャットダウン特性が求められる。なお、シャットダウン特性は孔が閉塞する温度(シャットダウン温度)が低くなるほど一般には良いとされる。 The current that flows between the electrodes of the separator for secondary batteries is due to the holes in the separator being blocked at high temperatures in order to prevent short circuits due to foreign matter entering the winding body and batteries, and to suppress mechanical strength and thermal runaway of the batteries. Shutdown characteristics are required. It should be noted that the shutdown characteristic is generally considered to be better as the temperature at which the hole is closed (shutdown temperature) becomes lower.

特許文献1では、特性粘度が5×10Pa・s以上5×10Pa・s以下であって、非ニュートン流動性が0.15以上0.4以下であるポリオレフィンを含み、結晶化度が65%以上85%以下である多孔質基材と、前記多孔質基材の少なくとも片面に設けられ、耐熱性樹脂を含む耐熱性多孔質層と、を備えた非水電解質電池用セパレータが開示されている。優れた機械強度とシャットダウン特性を有すると共に、高温下での耐短絡性に優れた非水電解質電池用セパレータが提供されると記載されている。Patent Document 1 contains a polyolefin having a characteristic viscosity of 5 × 10 5 Pa · s or more and 5 × 10 6 Pa · s or less and a non-Newton fluidity of 0.15 or more and 0.4 or less, and has a degree of crystallinity. Disclosed is a separator for a non-aqueous electrolyte battery comprising a porous base material having a value of 65% or more and 85% or less, and a heat-resistant porous layer provided on at least one surface of the porous base material and containing a heat-resistant resin. Has been done. It is stated that a separator for a non-aqueous electrolyte battery having excellent mechanical strength and shutdown characteristics and excellent short-circuit resistance at high temperatures will be provided.

特許文献2では、DSCにより測定を行ったときに、結晶化度が65〜85%であり、結晶に占めるラメラ晶の割合が30〜85%であり、結晶長が5nm〜50nmであり、非晶長が3nm〜30nmである、ポリオレフィン微多孔膜が開示されている。耐熱性多孔質層と複合化した場合にも、優れた機械強度およびシャットダウン特性が得られ、かつ、電解液の液枯れを防止可能なポリオレフィン微多孔膜が提供されると記載されている。 In Patent Document 2, when measured by DSC, the crystallinity is 65 to 85%, the ratio of lamellar crystals to the crystals is 30 to 85%, the crystal length is 5 nm to 50 nm, and the amorphous material is not. A polyolefin microporous film having a crystal length of 3 nm to 30 nm is disclosed. It is described that a polyolefin microporous membrane capable of obtaining excellent mechanical strength and shutdown characteristics and preventing the electrolytic solution from withering even when combined with the heat-resistant porous layer is provided.

特許文献3では、重量平均分子量1×10以上の分率(a)が、21〜60重量%、重量平均分子量1×10以上1×10未満の分率(b)と重量平均分子量1×10未満の分率(c)との合計が40〜79重量%、前記分率(c)が30重量%以下であり、且つ重量平均分子量/数平均分子量が7〜50であり、バブルポイント値が980kPaを超えることを特徴とするポリオレフィン微多孔膜が開示されている。透気度、空孔率、孔径、バブルポイント値、機械的強度、寸法安定性、シャットダウン特性及びメルトダウン特性のバランスに優れたポリオレフィン微多孔膜及びその製造方法が提供されると記載されている。In Patent Document 3, a weight average molecular weight 1 × 10 6 or more fraction (a) is 21 to 60 wt%, the weight average molecular weight of 1 × 10 4 to 1 × 10 min of less than 6 (b) and the weight average molecular weight 1 × 10 min of less than 4 total 40-79% by weight of (c), the fraction (c) is 30 wt% or less, and the weight average molecular weight / number average molecular weight of 7 to 50, A polyolefin microporous film characterized by a bubble point value of more than 980 kPa has been disclosed. It is stated that a polyolefin microporous membrane having an excellent balance of air permeability, porosity, pore diameter, bubble point value, mechanical strength, dimensional stability, shutdown characteristics and meltdown characteristics and a method for producing the same are provided. ..

特開2012−129115号公報Japanese Unexamined Patent Publication No. 2012-129115 WO2011/118660WO2011 / 118660 特開2002−284918号公報JP-A-2002-284918

二次電池、例えばリチウムイオン二次電池は、エネルギー密度が高いため、パーソナルコンピュータ、携帯電話などに用いる電池として広く使用されている。また、二次電池は、電気自動車やハイブリッド自動車のモータ駆動用電源、定置用蓄電池としても期待されている。 A secondary battery, for example, a lithium ion secondary battery, has a high energy density and is therefore widely used as a battery used in personal computers, mobile phones, and the like. Secondary batteries are also expected to be used as power sources for driving motors of electric vehicles and hybrid vehicles, and as stationary storage batteries.

近年、二次電池のエネルギー密度の高密度化が要求されており、電極体積を増加させるためにセパレータの薄膜化や高容量電極の適用が望まれる。しかしながら、セパレータの薄膜化に伴い機械強度が失われ、捲回体や電池内への異物混入などによる短絡が発生しやすくなる。また、高容量電極として高ニッケル系材料が検討されているが、高ニッケル系材料は過充電時の温度上昇で酸素が正極材結晶から遊離し、発火や爆発を誘引するなど安全性に対する懸念が大きい。従って、電池用セパレータに用いる微多孔膜には、シャットダウン特性の向上が求められている。しかしながら、特許文献1〜3のポリオレフィン微多孔膜は、エネルギー密度が高密度化された電池においてシャットダウン特性の効果が十分ではない。 In recent years, there has been a demand for higher energy densities of secondary batteries, and in order to increase the electrode volume, it is desired to reduce the thickness of the separator and apply a high-capacity electrode. However, as the separator becomes thinner, the mechanical strength is lost, and a short circuit is likely to occur due to foreign matter mixed in the wound body or the battery. In addition, high-nickel materials are being studied as high-capacity electrodes, but there are concerns about safety such as oxygen being released from the positive electrode crystal due to the temperature rise during overcharging, which induces ignition and explosion. big. Therefore, the microporous membrane used for the battery separator is required to have improved shutdown characteristics. However, the polyolefin microporous membranes of Patent Documents 1 to 3 do not have a sufficient effect of shutdown characteristics in a battery having a high energy density.

本発明は、上記事情に鑑みて、膜全体の構造バランスに優れ、電池用セパレータとして用いた場合、優れたシャットダウン特性を示す高い電池安全性を有するポリオレフィン微多孔膜を提供することを目的とする。 In view of the above circumstances, it is an object of the present invention to provide a polyolefin microporous membrane having excellent structural balance of the entire membrane and having high battery safety showing excellent shutdown characteristics when used as a battery separator. ..

本発明者らは、上記課題を解決すべく鋭意検討を重ねた結果、高度に延伸された微多孔膜は機械強度に優れるが、面内方向と膜厚方向の構造が異方的であり、シャットダウンに至るまでの構造変化が高度に延伸されていない微多孔膜と比較して、より低い温度で起こりにくく、その結果、シャットダウン温度を低くすることが難しいことを見出した。そして、膜厚方向の結晶化度と面内方向の結晶化度の差を所定の値とすることで膜面内方向と膜厚方向の構造バランスを調整し、上記課題を解決可能なポリオレフィン微多孔膜を提供することができることを見出して、本発明を完成するに至った。 As a result of diligent studies to solve the above problems, the present inventors have excellent mechanical strength in the highly stretched microporous membrane, but the structures in the in-plane direction and the film thickness direction are anisotropic. We have found that structural changes leading up to shutdown are less likely to occur at lower temperatures than microporous membranes that are not highly stretched, and as a result, it is difficult to lower the shutdown temperature. Then, by setting the difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction to a predetermined value, the structural balance between the in-plane direction and the film film direction can be adjusted, and the polyolefin fine can solve the above-mentioned problems. They have found that they can provide a porous membrane and have completed the present invention.

上記課題を解決するため本発明の多孔性フィルムは次の構成を有する。
(1)広角X線回折測定による室温における膜厚方向の結晶化度と面内方向の結晶化度との差が25%以下であり、前記膜厚方向の結晶化度が前記面内方向の結晶化度よりも大きく、広角X線測定によるシャットダウン温度における面内方向の結晶化度と前記室温における面内方向の結晶化度との差が58%以上であるポリオレフィン微多孔膜。
(2)示差走査熱量測定の2回目の昇温で観測されるポリオレフィン微多孔膜の融解ピーク温度が115℃以上132℃以下である(1)記載のポリオレフィン微多孔膜。
(3)前記ポリオレフィン微多孔膜を形成する樹脂組成物の分子量分布が5以上30以下である(1)または(2)に記載のポリオレフィン微多孔膜。
(4)9μm換算の突刺強度が2.25N以上である(1)〜(3)のいずれか一つに記載のポリオレフィン微多孔膜。
(5)ポリオレフィンがポリエチレンを含む、(1)〜(4)のいずれか一つに記載のポリオレフィン微多孔膜。
(6)膜厚が9μm以下である(1)〜(5)のいずれか1つに記載のポリオレフィン微多孔膜。
(7)(1)〜(6)のいずれか1つに記載のポリオレフィン微多孔膜に、他の多孔質層を1層以上積層してなる多層微多孔膜。
(8)(1)〜(6)のいずれか1つに記載のポリオレフィン微多孔膜または(7)に記載の多層微多孔膜を含む電池用セパレータ。
(9)(8)に記載の電池用セパレータを備える電池。
In order to solve the above problems, the porous film of the present invention has the following constitution.
(1) The difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction at room temperature by wide-angle X-ray diffraction measurement is 25% or less, and the crystallinity in the film thickness direction is the in-plane direction. A polyolefin microporous film that is larger than the crystallinity and the difference between the in-plane crystallinity at the shutdown temperature by wide-angle X-ray measurement and the in-plane crystallinity at room temperature is 58% or more.
(2) The polyolefin microporous film according to (1), wherein the melting peak temperature of the polyolefin microporous film observed at the second temperature rise of the differential scanning calorimetry is 115 ° C. or higher and 132 ° C. or lower.
(3) The polyolefin microporous film according to (1) or (2), wherein the resin composition forming the polyolefin microporous film has a molecular weight distribution of 5 or more and 30 or less.
(4) The polyolefin microporous membrane according to any one of (1) to (3), wherein the puncture strength in terms of 9 μm is 2.25 N or more.
(5) The polyolefin microporous membrane according to any one of (1) to (4), wherein the polyolefin contains polyethylene.
(6) The microporous polyolefin membrane according to any one of (1) to (5), which has a film thickness of 9 μm or less.
(7) A multilayer microporous membrane formed by laminating one or more other porous layers on the polyolefin microporous membrane according to any one of (1) to (6).
(8) A battery separator comprising the polyolefin microporous membrane according to any one of (1) to (6) or the multilayer microporous membrane according to (7).
(9) A battery including the battery separator according to (8).

本発明のポリオレフィン微多孔膜はシャットダウン温度が低く、電池用セパレータとして用いたとき電池に優れたシャットダウン性能を付与することができる。 The microporous polyolefin membrane of the present invention has a low shutdown temperature and can impart excellent shutdown performance to a battery when used as a battery separator.

1.ポリオレフィン微多孔膜
以下、本実施形態のポリオレフィン微多孔膜について説明する。なお、本発明は以下説明する実施形態に限定されるものではない。
1. 1. Polyolefin Microporous Membrane Hereinafter, the polyolefin microporous membrane of this embodiment will be described. The present invention is not limited to the embodiments described below.

本発明によるポリオレフィン微多孔膜は、広角X線回折測定による室温における膜厚方向の結晶化度と面内方向の結晶化度との差が25%以下であり、前記膜厚方向の結晶化度が前記面内方向の結晶化度よりも大きく、広角X線測定によるシャットダウン温度における面内方向の結晶化度と前記面内方向の結晶化度との差が58%以上である。 In the polyolefin microporous film according to the present invention, the difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction at room temperature by wide-angle X-ray diffraction measurement is 25% or less, and the crystallinity in the film thickness direction is 25% or less. Is larger than the in-plane crystallization degree, and the difference between the in-plane crystallization degree and the in-plane crystallization degree at the shutdown temperature by wide-angle X-ray measurement is 58% or more.

ここで膜厚方向とは、ポリオレフィン微多孔膜の表面に垂直な方向を表す。面内方向とは、ポリオレフィン微多孔膜の膜厚面に垂直な方向を表す。また結晶化度は測定サンプルを室温から昇温しながらX線照射する広角X線回折測定により得られる回折スペクトルから非晶質ハローと結晶性ピークのフィッティングを行い結晶のピーク面積と非晶のピーク面積が得られ、下記の式から求めることができる。
式:結晶化度(%)=(結晶のピーク面積)÷(結晶と非晶のピーク面積)×100
室温における膜厚方向の結晶化度と面内方向の結晶化度は、それぞれ膜厚方向と面内方向にX線照射したときの室温における回折スペクトルから求めた各結晶化度の差分とする。シャットダウン温度における面内方向の結晶化度は、面内方向にX線照射したときのシャットダウン温度における回折スペクトルから求めた各結晶化度の差分とする。ここで、シャットダウン温度とは、微多孔膜を室温(25℃)から5℃/分の昇温速度で加熱しながら、透気度計(旭精工株式会社製、EGO−1T)により測定する透気抵抗度が検出限界である1×10秒/100cmAirに到達した温度をいう。
(室温(25℃)における膜厚方向の結晶化度と面内方向の結晶化度との差)
シャットダウン特性の制御には膜厚方向の構造と面内方向の構造のバランスを制御することが重要である。膜厚方向の構造と面内方向の構造バランスは各方向の結晶化度の差から知ることができる。広角X線回折測定による室温における膜厚方向の結晶化度と面内方向の結晶化度との差が25%以下であり、前記膜厚方向の結晶化度が前記面内方向の結晶化度よりも大きいと、膜厚方向と面内方向の構造差が小さくなり、従来のシャットダウン温度より低い温度で面内方向の構造に変化が起こるようになり、シャットダウン特性が向上する。室温(25℃)における膜厚方向の結晶化度と面内方向の結晶化度との差が25%を超えると、面内方向の熱的安定構造が多くなり、シャットダウン特性の制御に重要な面内方向の変化が抑制され、シャットダウン特性が低下する。
Here, the film thickness direction represents a direction perpendicular to the surface of the polyolefin microporous film. The in-plane direction represents a direction perpendicular to the film thickness plane of the polyolefin microporous film. The crystallinity is determined by fitting the amorphous halo and the crystalline peak from the diffraction spectrum obtained by X-ray irradiation of the measurement sample while raising the temperature from room temperature to the peak area of the crystal and the peak of the crystallinity. The area is obtained and can be calculated from the following formula.
Formula: Crystallinity (%) = (Crystal peak area) ÷ (Crystal and amorphous peak area) x 100
The crystallinity in the film thickness direction and the crystallinity in the in-plane direction at room temperature are the differences between the crystallinities obtained from the diffraction spectra at room temperature when X-rays are irradiated in the film thickness direction and the in-plane direction, respectively. The in-plane crystallization degree at the shutdown temperature is the difference between the crystallization degrees obtained from the diffraction spectrum at the shutdown temperature when X-rays are irradiated in the in-plane direction. Here, the shutdown temperature is a transparency measured by an air permeability meter (manufactured by Asahi Seiko Co., Ltd., EGO-1T) while heating the microporous film from room temperature (25 ° C.) at a heating rate of 5 ° C./min. The temperature at which the air resistance reaches the detection limit of 1 × 10 5 seconds / 100 cm 3 Air.
(Difference between crystallinity in the film thickness direction and crystallinity in the in-plane direction at room temperature (25 ° C))
In order to control the shutdown characteristics, it is important to control the balance between the structure in the film thickness direction and the structure in the in-plane direction. The structural balance in the film thickness direction and the structural balance in the in-plane direction can be known from the difference in crystallinity in each direction. The difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction at room temperature by wide-angle X-ray diffraction measurement is 25% or less, and the crystallinity in the film thickness direction is the crystallinity in the in-plane direction. If it is larger than, the structural difference between the film thickness direction and the in-plane direction becomes small, the structure in the in-plane direction changes at a temperature lower than the conventional shutdown temperature, and the shutdown characteristics are improved. When the difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction at room temperature (25 ° C.) exceeds 25%, the thermally stable structure in the in-plane direction increases, which is important for controlling the shutdown characteristics. Changes in the in-plane direction are suppressed, and shutdown characteristics are reduced.

室温(25℃)における膜厚方向の結晶化度と面内方向の結晶化度との差の上限は20%以下が好ましい。膜厚方向の結晶化度と面内方向結晶化度の差の下限としては、特に制限はないが、5%以上であることが好ましく、8%以上であることがさらに好ましい。膜厚方向の結晶化度と面内方向の結晶化度の差が5%以上であると、面内方向の構造が安定化し、シャットダウン特性のバランスに優れた膜となる。 The upper limit of the difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction at room temperature (25 ° C.) is preferably 20% or less. The lower limit of the difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction is not particularly limited, but is preferably 5% or more, and more preferably 8% or more. When the difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction is 5% or more, the structure in the in-plane direction is stabilized, and the film has an excellent balance of shutdown characteristics.

また、膜厚方向の結晶化度が面内方向の結晶化度よりも大きくすることで面内方向の熱的安定構造が膜厚方向に比べ少なくなり、シャットダウン特性の制御に重要な面内方向の変化が促進されることでシャットダウン特性が向上する。 Further, by making the crystallinity in the film thickness direction larger than the crystallinity in the in-plane direction, the thermally stable structure in the in-plane direction is smaller than that in the film thickness direction, and the in-plane direction is important for controlling the shutdown characteristics. Shutdown characteristics are improved by promoting the change of.

室温における膜厚方向の結晶化度と面内方向の結晶化度との差は、ポリオレフィン微多孔膜を製造する際、例えば、核剤の含有量、原料とする樹脂組成物の重量平均分子量(Mw)、分子量分布(MwD)、延伸条件、特に、後述する乾燥後のフィルムの延伸温度などを調整することで上記範囲とすることができる。 The difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction at room temperature is, for example, the content of the nucleating agent and the weight average molecular weight of the resin composition used as a raw material when producing the polyolefin microporous film. The above range can be obtained by adjusting the Mw), the molecular weight distribution (MwD), the stretching conditions, particularly the stretching temperature of the film after drying, which will be described later.

(シャットダウン温度における面内方向の結晶化度と前記室温における面内方向の結晶化度との差)
シャットダウン特性の向上には、面内方向の構造変化が優先的に起こることも重要である。シャットダウンに至るまでの面内方向の構造変化は、後述する昇温しながらの広角X線測定で得られるシャットダウン温度における面内向の結晶化度と室温における面内方向の結晶化度との差から知ることができる。シャットダウン時の面内向の結晶化度と室温における面内方向の結晶化度との差は58%以上である。この差が58%未満であると、面内方向の変化(結晶融解)が抑制され、シャットダウン特性が低下する。
(Difference between in-plane crystallinity at shutdown temperature and in-plane crystallinity at room temperature)
In order to improve the shutdown characteristics, it is also important that structural changes in the in-plane direction occur preferentially. The in-plane structural change leading up to shutdown is based on the difference between the in-plane crystallinity at the shutdown temperature and the in-plane crystallinity at room temperature obtained by wide-angle X-ray measurement while raising the temperature, which will be described later. You can know. The difference between the in-plane crystallization degree at shutdown and the in-plane crystallization degree at room temperature is 58% or more. When this difference is less than 58%, the change in the in-plane direction (crystal melting) is suppressed, and the shutdown characteristic is deteriorated.

シャットダウン温度における面内向の結晶化度と室温における面内方向の結晶化度の下限は60%以上であることが好ましく、65%以上であることがより好ましい。上限としては、特に制限はないが、90%以下であることが好ましく、85%以下であることがより好ましい。上記範囲内である場合、面内方向の結晶融解が優先的に進んでいることを示しており、シャットダウン特性が向上する。この差が90%を超えると面内方向の熱的不安定構造が多くなり過ぎて、機械強度の低下がおきたり、膜全体の熱的安定性が著しく下がるため、例えば、車載の高温部近傍に配置された場合、熱的安定性に懸念がある。 The lower limit of the in-plane crystallization degree at the shutdown temperature and the in-plane crystallization degree at room temperature is preferably 60% or more, more preferably 65% or more. The upper limit is not particularly limited, but is preferably 90% or less, and more preferably 85% or less. When it is within the above range, it indicates that the crystal melting in the in-plane direction is proceeding preferentially, and the shutdown characteristic is improved. If this difference exceeds 90%, the number of thermally unstable structures in the in-plane direction will increase too much, causing a decrease in mechanical strength and a significant decrease in the thermal stability of the entire film. There are concerns about thermal stability when placed in.

シャットダウン温度における面内方向の結晶化度と前記室温における面内方向の結晶化度との差は、ポリオレフィン微多孔膜を製造する際、例えば、核剤の含有量、原料とする原料とする樹脂組成物の重量平均分子量(Mw)、分子量分布(MwD)、延伸条件、特に、後述する乾燥後のフィルムの延伸温度などを調整することで上記範囲とすることができる。 The difference between the in-plane crystallinity at the shutdown temperature and the in-plane crystallinity at room temperature is, for example, the content of the nucleating agent and the resin used as the raw material when producing the polyolefin microporous film. The above range can be obtained by adjusting the weight average molecular weight (Mw), molecular weight distribution (MwD), stretching conditions of the composition, particularly the stretching temperature of the film after drying, which will be described later.

(示差走査熱量測定(DSC)による2回目の昇温(2nd heat)で観測されるポリオレフィン微多孔膜の融解ピーク温度)
ポリオレフィン微多孔膜の融解ピーク温度は、窒素雰囲気下(20mL/分)で測定温度範囲を0℃〜200℃、昇温速度10℃/分で200℃に到達してから保持時間を10分として(第1回目の昇温)、その後、窒素雰囲気下(20mL/分)、降温速度30℃/分で降温する。さらに、窒素雰囲気下(20mL/分)で測定温度範囲を0℃〜200℃、昇温速度10℃/minで200℃に到達してから保持時間を5分とする2回目の昇温を行う。2回目の昇温で得られたDSC曲線から0℃と200℃を結ぶ直線をベースラインとし、融解吸熱ピーク時の温度を読み取り、ポリオレフィン微多孔膜のDSCによる2回目の昇温で観測される融解ピーク温度とする。ピークが2山以上観測される場合は、最も吸熱している方のピークから微多孔膜の融点ピーク温度を読み取る。
(Melting peak temperature of polyolefin microporous membrane observed at the second temperature rise (2nd heat) by differential scanning calorimetry (DSC))
The melting peak temperature of the polyolefin microporous film is 0 ° C. to 200 ° C. under a nitrogen atmosphere (20 mL / min), and the holding time is 10 minutes after reaching 200 ° C. at a heating rate of 10 ° C./min. (First temperature rise), then the temperature is lowered in a nitrogen atmosphere (20 mL / min) at a temperature lowering rate of 30 ° C./min. Further, in a nitrogen atmosphere (20 mL / min), the measurement temperature range is 0 ° C. to 200 ° C., and the temperature rise rate is 10 ° C./min. .. From the DSC curve obtained by the second temperature rise, the straight line connecting 0 ° C. and 200 ° C. is used as the baseline, the temperature at the peak endothermic reaction of melting is read, and it is observed by the second temperature rise by DSC of the polyolefin microporous film. Let it be the melting peak temperature. When two or more peaks are observed, the melting point peak temperature of the microporous membrane is read from the peak that absorbs the most heat.

DSCの2nd heatで観測されるポリオレフィン微多孔膜の融解ピーク温度は、115℃以上132℃以下が好ましく、より好ましくは120以上130℃以下であり、さらに好ましくは122℃以上130℃以下である。ポリオレフィン微多孔膜のDSCの2nd heatで観測される融解ピーク温度を115℃以上132℃以下とすることで、湿式延伸または乾式延伸時に応力が抑制され、面内方向と膜厚方向に熱に不安定な構造が多くなり、シャットダウン特性の制御に重要な面内方向の構造変化が起こることになり、シャットダウン特性が向上する。ポリオレフィンの融解ピーク温度は後述する示差走査型熱量測定(DSC)法により求めることができる。 The melting peak temperature of the polyolefin microporous membrane observed in the 2nd heat of DSC is preferably 115 ° C. or higher and 132 ° C. or lower, more preferably 120 or higher and 130 ° C. or lower, and further preferably 122 ° C. or higher and 130 ° C. or lower. By setting the melting peak temperature observed in the 2nd heat of the DSC of the polyolefin microporous film to 115 ° C. or higher and 132 ° C. or lower, stress is suppressed during wet stretching or dry stretching, and heat is not applied in the in-plane direction and the film thickness direction. The number of stable structures will increase, and in-plane structural changes that are important for controlling the shutdown characteristics will occur, and the shutdown characteristics will improve. The melting peak temperature of polyolefin can be determined by the differential scanning calorimetry (DSC) method described later.

(ポリオレフィン微多孔膜の分子量分布(MwD))
ポリオレフィン微多孔膜の分子量分布は、5以上30以下が好ましく、より好ましくは16以上25以下であり、さらに好ましくは17以上23以下である。ポリオレフィン微多孔膜の分子量分布を上記範囲とすることで、融点が著しく低下したり結晶化度が減少して機械強度が低下するのを防ぐことができ、また、延伸時の面内方向の熱的安定構造の形成が抑制されているため、優れたシャットダウン特性を示し、電池安全性が向上する。ポリオレフィン微多孔膜の分子量分布は後述するゲルパーミエーションクロマトグラフィー(GPC)法により求めることができる。
(Molecular Weight Distribution of Polyolefin Microporous Membrane (MwD))
The molecular weight distribution of the polyolefin microporous membrane is preferably 5 or more and 30 or less, more preferably 16 or more and 25 or less, and further preferably 17 or more and 23 or less. By setting the molecular weight distribution of the polyolefin microporous membrane in the above range, it is possible to prevent the melting point from being significantly lowered or the crystallinity from being lowered to reduce the mechanical strength, and the heat in the in-plane direction during stretching can be prevented. Since the formation of a stable structure is suppressed, excellent shutdown characteristics are exhibited and battery safety is improved. The molecular weight distribution of the polyolefin microporous membrane can be determined by the gel permeation chromatography (GPC) method described later.

ポリオレフィン微多孔膜の分子量分布は、ポリオレフィン微多孔膜を製造する工程において、例えば、分岐ポリエチレン及び酸化防止剤の少なくとも一方を含有させたり、混練条件(特に、温度、スクリュー回転数)を調整したりすることなどにより、上記範囲とすることができる。 The molecular weight distribution of the polyolefin microporous membrane is determined by, for example, containing at least one of branched polyethylene and an antioxidant in the process of producing the polyolefin microporous membrane, and adjusting kneading conditions (particularly temperature and screw rotation speed). By doing so, the above range can be obtained.

(膜厚)
ポリオレフィン微多孔膜の膜厚の上限は、特に限定されないが、例えば、20μm以下が好ましく、より好ましくは12μm以下、さらに好ましくは9μm以下である。膜厚の下限は、特に限定されないが、例えば、1μm以上が好ましく、より好ましくは3μm以上である。膜厚が上記範囲内であるとポリオレフィン微多孔膜を電池用セパレータとして使用する際、電池容量が向上する。
(Film thickness)
The upper limit of the film thickness of the polyolefin microporous film is not particularly limited, but is, for example, preferably 20 μm or less, more preferably 12 μm or less, and further preferably 9 μm or less. The lower limit of the film thickness is not particularly limited, but is preferably 1 μm or more, more preferably 3 μm or more, for example. When the film thickness is within the above range, the battery capacity is improved when the polyolefin microporous membrane is used as a battery separator.

(空孔率)
ポリオレフィン微多孔膜の空孔率の下限は、特に限定されないが、例えば、20%以上であり、より好ましくは30%以上であり、さらに好ましくは40%以上である。空孔率の上限は、特に限定されないが、例えば、70%以下であることが好ましく、60%以下であることがより好ましく、50%以下であることがさらに好ましい。空孔率が上記範囲であることにより、電解液の保持量を高め、高いイオン透過性を確保することができる。さらに、高空孔率とした場合でも、優れたシャットダウン特性のため、電池安全性を確保できる。また、空孔率の下限はイオン透過性及びレート特性をより高めるという観点から、空孔率が20%以上であることが好ましい。空孔率は、製造過程において、ポリオレフィンの構成成分の配合割合や延伸倍率、熱固定条件などを調節することにより、上記範囲とできる。
(Porosity)
The lower limit of the porosity of the polyolefin microporous membrane is not particularly limited, but is, for example, 20% or more, more preferably 30% or more, still more preferably 40% or more. The upper limit of the porosity is not particularly limited, but for example, it is preferably 70% or less, more preferably 60% or less, and further preferably 50% or less. When the porosity is in the above range, the retention amount of the electrolytic solution can be increased and high ion permeability can be ensured. Furthermore, even when the porosity is high, battery safety can be ensured due to the excellent shutdown characteristics. Further, the lower limit of the porosity is preferably 20% or more from the viewpoint of further enhancing the ion permeability and the rate characteristics. The porosity can be set within the above range by adjusting the blending ratio of the polyolefin constituents, the stretching ratio, the heat fixing conditions, and the like in the manufacturing process.

(シャットダウン温度)
ポリオレフィン微多孔膜のシャットダウン温度は昇温透気抵抗度測定から得られる透気抵抗度が検出限界である1×10秒/100cmAirに到達した温度とした。シャットダウン温度は110℃以上135℃未満であり、好ましくは110℃以上134℃以下、より好ましくは110℃以上133℃以下、さらにより好ましくは110℃以上132℃以下である。シャットダウン温度が135℃未満であると従来の微多孔膜に比べ、高温時の電池熱暴走を抑制でき、安全性が向上する。また、シャットダウン温度が110℃未満の場合は、例えば、車載高温部近傍に配置された場合の熱的安定性懸念や熱固定時に透気抵抗度が急激に悪化する懸念がある。
(Shutdown temperature)
The shutdown temperature of the polyolefin microporous membrane was set to the temperature at which the air permeability resistance obtained from the temperature rise air permeability resistance measurement reached the detection limit of 1 × 10 5 seconds / 100 cm 3 Air. The shutdown temperature is 110 ° C. or higher and lower than 135 ° C., preferably 110 ° C. or higher and 134 ° C. or lower, more preferably 110 ° C. or higher and 133 ° C. or lower, and even more preferably 110 ° C. or higher and 132 ° C. or lower. When the shutdown temperature is less than 135 ° C., the battery thermal runaway at high temperature can be suppressed and the safety is improved as compared with the conventional microporous membrane. Further, when the shutdown temperature is less than 110 ° C., for example, there is a concern about thermal stability when the vehicle is placed in the vicinity of a high temperature portion in a vehicle, and there is a concern that the air permeation resistance may deteriorate sharply at the time of heat fixation.

(9μm換算突刺強度)
ポリオレフィン微多孔膜の9μm換算突刺強度の下限は、好ましくは1.35N以上であり、より好ましくは1.80N以上であり、さらに好ましくは2.25Nである。9μm換算突刺強度の上限は、特に限定されないが、例えば、3.6N以下である。9μm換算突刺強度が上記範囲である場合、ポリオレフィン微多孔膜の膜強度に優れる。このポリオレフィン微多孔膜をセパレータとして用いた二次電池は、電極の短絡の発生が抑制することができる。9μm換算突刺強度は、ポリオレフィン微多孔膜を製造する際、核剤を含有させたり、重量平均分子量Mwや分子量分布MwD、延伸条件(特に、後述する乾燥後のフィルムの延伸温度)を調整したりすることなどにより、上記範囲とすることができる。
(9 μm equivalent puncture strength)
The lower limit of the 9 μm-equivalent puncture strength of the polyolefin microporous membrane is preferably 1.35 N or more, more preferably 1.80 N or more, and further preferably 2.25 N. The upper limit of the 9 μm equivalent puncture strength is not particularly limited, but is, for example, 3.6 N or less. When the puncture strength in terms of 9 μm is within the above range, the membrane strength of the polyolefin microporous membrane is excellent. A secondary battery using this polyolefin microporous membrane as a separator can suppress the occurrence of short-circuiting of electrodes. The 9 μm equivalent puncture strength can be adjusted by adding a nucleating agent, adjusting the weight average molecular weight Mw, molecular weight distribution MwD, and stretching conditions (particularly, the stretching temperature of the film after drying, which will be described later) when producing a polyolefin microporous film. By doing so, the above range can be obtained.

(熱収縮率)
ポリオレフィン微多孔膜の105℃8時間における機械方向及び幅方向の熱収縮率は、12%以下が好ましく、6%以下であることがより好ましく、4%以下であることがさらに好ましい。機械方向及び幅方向の熱収縮率の下限は、特に限定されないが、0.5%以上であるのが好ましい。機械方向及び幅方向の熱収縮率が12%以下であるとき、電池に用いたとき電池内部での変形や端部での短絡のリスクを低減することができる。また、機械方向及び幅方向の熱収縮率が0.5%以上であるとき、熱収縮による空孔閉塞が起こりやすく、シャットダウン特性が悪化することを防ぐことができる。
(Heat shrinkage rate)
The heat shrinkage of the polyolefin microporous membrane at 105 ° C. for 8 hours in the mechanical direction and the width direction is preferably 12% or less, more preferably 6% or less, and further preferably 4% or less. The lower limit of the heat shrinkage rate in the mechanical direction and the width direction is not particularly limited, but is preferably 0.5% or more. When the heat shrinkage in the mechanical direction and the width direction is 12% or less, the risk of deformation inside the battery and short circuit at the end can be reduced when used in a battery. Further, when the heat shrinkage rate in the machine direction and the width direction is 0.5% or more, vacancies are likely to be closed due to heat shrinkage, and it is possible to prevent the shutdown characteristics from deteriorating.

2.ポリオレフィン微多孔膜の製造方法
ポリオレフィン微多孔膜の製造方法としては、例えば、乾式の製膜方法及び湿式の製膜方法が挙げられる。本実施形態のポリオレフィン微多孔膜の製造方法としては、膜の構造及び物性の制御の観点から湿式と乾式を組み合わせた製膜方法が好ましい。
2. Method for Producing Polyolefin Microporous Membrane Examples of the method for producing a polyolefin microporous membrane include a dry film forming method and a wet film forming method. As a method for producing the microporous polyolefin membrane of the present embodiment, a film forming method combining a wet method and a dry method is preferable from the viewpoint of controlling the structure and physical properties of the film.

以下、ポリオレフィン微多孔膜の製造方法について説明する。なお、以下の説明は、製造方法の一例であって、この方法に限定されるものではない。 Hereinafter, a method for producing a polyolefin microporous membrane will be described. The following description is an example of a manufacturing method, and is not limited to this method.

まず、ポリオレフィンと成膜用溶剤とを溶融混練して樹脂溶液を調製する。溶融混練方法としては、例えば日本国特許第2132327号および日本国特許第3347835号の明細書に記載の二軸押出機を用いる方法を利用することができる。 First, a resin solution is prepared by melt-kneading the polyolefin and the solvent for film formation. As the melt-kneading method, for example, a method using a twin-screw extruder described in Japanese Patent No. 2132327 and Japanese Patent No. 3347835 can be used.

ポリオレフィンは、ポリエチレン、ポリプロピレンなどが挙げられる。ポリエチレンとしては、種々のポリエチレンを用いることができ、超高分子量ポリエチレン、高密度ポリエチレン、分岐高密度ポリエチレン、中密度ポリエチレン、分岐状低密度ポリエチレン、直鎖状低密度ポリエチレンなどが挙げられる。微多孔膜の機械強度の向上、シャットダウン特性の向上の観点からは、分岐高密度ポリエチレンを用いることがより好ましい。ポリエチレンは、エチレン単独重合体であってもよく、エチレンと他のα−オレフィンとの共重合体であってもよい。α−オレフィンとしては、プロピレン、ブテン−1、ヘキセン−1、ペンテン−1、4−メチルペンテン−1、オクテン、酢酸ビニル、メタクリル酸メチル、スチレン等が挙げられる。ポリエチレンはポリオレフィン微多孔膜100質量%に対して50質量%以上含むことができる。 Examples of the polyolefin include polyethylene and polypropylene. As the polyethylene, various types of polyethylene can be used, and examples thereof include ultrahigh molecular weight polyethylene, high density polyethylene, branched high density polyethylene, medium density polyethylene, branched low density polyethylene, and linear low density polyethylene. From the viewpoint of improving the mechanical strength of the microporous membrane and improving the shutdown characteristics, it is more preferable to use branched high-density polyethylene. Polyethylene may be an ethylene homopolymer or a copolymer of ethylene and another α-olefin. Examples of the α-olefin include propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, octene, vinyl acetate, methyl methacrylate, styrene and the like. Polyethylene can be contained in an amount of 50% by mass or more with respect to 100% by mass of the polyolefin microporous membrane.

特に高密度ポリエチレンを含むことが好ましい。高密度ポリエチレンを含有した場合、溶融押出特性に優れ、均一な延伸加工特性に優れる。特に高密度ポリエチレン(密度:0.920g/m以上0.970g/m以下)は溶融押出特性に優れ、均一な延伸加工特性に優れる。高密度ポリエチレンの重量平均分子量(Mw)は1×10以上1×10未満が好ましい。In particular, it is preferable to contain high-density polyethylene. When high-density polyethylene is contained, it is excellent in melt extrusion characteristics and uniform drawing processing characteristics. In particular, high-density polyethylene (density: 0.920 g / m 3 or more and 0.970 g / m 3 or less) is excellent in melt extrusion characteristics and uniform drawing processing characteristics. The weight average molecular weight of high density polyethylene (Mw) of less than 1 × 10 4 or more 1 × 10 6 is preferable.

高密度ポリエチレンの含有量は、ポリオレフィン微多孔膜100質量%に対して、下限は50質量%以上が好ましく、上限は100質量%以下が好ましい。 The content of the high-density polyethylene is preferably 50% by mass or more at the lower limit and 100% by mass or less at the upper limit with respect to 100% by mass of the microporous polyolefin membrane.

分岐高密度ポリエチレンは、重量平均分子量は1×10以上1×10未満であり、かつ分子量分布が10以上30以下であり、融点は115℃以上132℃以下であることが好ましい。この範囲のポリエチレンを用いると結晶性を調整しやすく、ポリオレフィン微多孔膜の分子量分布、膜厚方向と面内方向の結晶化度差を適当な範囲に調整しやすくなり、シャットダウン特性が向上する。分岐高密度ポリエチレンを含む場合は、面内配向が進みにくく、シャットダウン温度を低下できるため、より好ましい。Branched high-density polyethylene has a weight average molecular weight is less than 1 × 10 6 1 × 10 4 or more and has a molecular weight distribution of 10 to 30, it preferably has a melting point is 132 ° C. or less 115 ° C. or higher. When polyethylene in this range is used, the crystallinity can be easily adjusted, the molecular weight distribution of the polyolefin microporous film, and the difference in crystallinity between the film thickness direction and the in-plane direction can be easily adjusted within an appropriate range, and the shutdown characteristics can be improved. When branched high-density polyethylene is contained, in-plane orientation is difficult to proceed and the shutdown temperature can be lowered, which is more preferable.

超高分子量ポリエチレンは、重量平均分子量(Mw)が1×10以上が好ましく、より好ましくは1×10以上8×10以下である。超高分子量ポリエチレンのMwが上記範囲である場合、成形性が良好となる。超高分子量ポリエチレンは少なくとも1種を含むことができる。例えばMwの異なる二種以上の超高分子量ポリエチレンを混合して原料として用いてもよい。Ultra high molecular weight polyethylene has a weight average molecular weight (Mw) is preferably 1 × 10 6 or more, more preferably 8 × 10 6 or less 1 × 10 6 or more. When the Mw of the ultra-high molecular weight polyethylene is in the above range, the moldability is good. The ultra high molecular weight polyethylene can contain at least one kind. For example, two or more types of ultra-high molecular weight polyethylene having different Mw may be mixed and used as a raw material.

また、超高分子量ポリエチレンを含有した場合、ポリオレフィン微多孔膜を薄膜化した際にも高い機械的強度を得ることができる。超高分子量ポリエチレンの含有量は、ポリオレフィン微多孔膜100質量%に対して、0質量%以上70質量%以下含むことができる。超高分子量ポリエチレンの含有量が10質量%以上60質量%以下である場合、ポリオレフィン微多孔膜の分子量分布(MwD)を後述する特定の範囲に容易に制御しやすく、かつ押出性や混練性などの生産性に優れる傾向がある。 Further, when the ultra-high molecular weight polyethylene is contained, high mechanical strength can be obtained even when the polyolefin microporous film is thinned. The content of the ultra-high molecular weight polyethylene can be 0% by mass or more and 70% by mass or less with respect to 100% by mass of the polyolefin microporous membrane. When the content of the ultra-high molecular weight polyethylene is 10% by mass or more and 60% by mass or less, the molecular weight distribution (MwD) of the polyolefin microporous membrane can be easily controlled within a specific range described later, and the extrudability, kneadability, etc. Tends to be more productive.

ポリオレフィンの分子量分布は、5以上30以下が好ましく、より好ましくは16以上25以下であり、さらに好ましくは17以上23以下である。ポリオレフィンの分子量分布を15以上30以下とすることで、湿式延伸または乾式延伸時に応力が抑制され、面内方向と膜厚方向に熱に不安定な構造が多くなり、シャットダウン特性の制御に重要な面内方向の構造変化が起こることになり、シャットダウン特性が向上する。原料の分子量分布は後述するゲルパーミエーションクロマトグラフィー(GPC)法により求めることができる。 The molecular weight distribution of the polyolefin is preferably 5 or more and 30 or less, more preferably 16 or more and 25 or less, and further preferably 17 or more and 23 or less. By setting the molecular weight distribution of polyolefin to 15 or more and 30 or less, stress is suppressed during wet stretching or dry stretching, and many structures are thermally unstable in the in-plane direction and the film thickness direction, which is important for controlling shutdown characteristics. Structural changes in the in-plane direction will occur, improving shutdown characteristics. The molecular weight distribution of the raw material can be determined by the gel permeation chromatography (GPC) method described later.

ポリオレフィン微多孔膜を製造する工程において、例えば、分岐ポリエチレン及び酸化防止剤の少なくとも一方を含有させたり、混練条件(特に、温度、スクリュー回転数)を調整したりすることなどにより、ポリオレフィンの分子量分布を上記範囲とすることができる。 In the process of producing a microporous polyolefin membrane, for example, the molecular weight distribution of polyolefin is distributed by containing at least one of branched polyethylene and an antioxidant, or adjusting kneading conditions (particularly, temperature and screw rotation speed). Can be in the above range.

ポリオレフィンは、必要に応じて、ポリエチン及びポリプロピレン以外のその他の樹脂成分を含むことができる。その他の樹脂成分としては、例えば、耐熱性を付与する樹脂などを用いることができる。また、本発明の効果を損なわない範囲において、酸化防止剤、熱安定剤、帯電防止剤、紫外線吸収剤、ブロッキング防止剤や充填剤、結晶造核剤、結晶化遅延剤等の各種添加剤を含有させてもよい。 Polyolefins can optionally contain other resin components other than polyethane and polypropylene. As the other resin component, for example, a resin that imparts heat resistance can be used. In addition, various additives such as antioxidants, heat stabilizers, antistatic agents, ultraviolet absorbers, blocking inhibitors and fillers, crystal nucleating agents, and crystallization retarders can be used as long as the effects of the present invention are not impaired. It may be contained.

樹脂溶液は、上記のポリオレフィン及び成膜用溶剤以外の成分を含んでもよく、例えば、結晶造核剤(核剤)、酸化防止剤などを含んでもよい。核剤としては、特に限定されず、公知の化合物系、微粒子系結晶造核剤などが使用できる。核剤としては、核剤を予めポリオレフィンに混合、分散したマスターバッチであってもよい。 The resin solution may contain components other than the above-mentioned polyolefin and solvent for film formation, and may contain, for example, a crystal nucleating agent (nuclear agent), an antioxidant and the like. The nucleating agent is not particularly limited, and known compound-based or fine-grained crystal nucleating agents can be used. The nucleating agent may be a masterbatch in which the nucleating agent is mixed and dispersed in polyolefin in advance.

結晶造核剤を含有しない場合、ポリオレフィンは、上記の分岐ポリエチレンと高密度ポリエチレンとを含有することが好ましい。また、ポリオレフィン微多孔膜は、高密度ポリエチレン、分岐ポリエチレン及び核剤を含んでもよい。これらを含むことにより、突刺強度をより向上させることができる。 When the crystalline nucleating agent is not contained, the polyolefin preferably contains the above-mentioned branched polyethylene and high-density polyethylene. Further, the polyolefin microporous membrane may contain high-density polyethylene, branched polyethylene and a nucleating agent. By including these, the puncture strength can be further improved.

次いで、溶融樹脂を押出し、冷却してゲル状シートを形成する。例えば、上記で調整した樹脂溶液を押出機から1つのダイに送給し、シート状に押し出し、形成体を得る。得られた成形体を冷却することにより、ゲル状シートを形成する。 Next, the molten resin is extruded and cooled to form a gel-like sheet. For example, the resin solution prepared above is fed from an extruder to one die and extruded into a sheet to obtain a formed body. A gel-like sheet is formed by cooling the obtained molded product.

ゲル状シートの形成方法として、例えば日本国特許第2132327号公報および日本国特許第3347835号公報に開示の方法を利用することができる。冷却は少なくともゲル化温度までは50℃/分以上の速度で行うのが好ましい。冷却は25℃以下まで行うのが好ましい。冷却速度が上記範囲内であると結晶化度が適度な範囲に保たれ、延伸に適したゲル状シートとなる。冷却方法としては冷風、冷却水等の冷媒に接触させる方法、冷却ロールに接触させる方法等を用いることができるが、冷媒で冷却したロールに接触させて冷却させることが好ましい。 As a method for forming the gel-like sheet, for example, the methods disclosed in Japanese Patent No. 2132327 and Japanese Patent No. 3347835 can be used. Cooling is preferably performed at a rate of 50 ° C./min or higher, at least up to the gelation temperature. Cooling is preferably performed up to 25 ° C. or lower. When the cooling rate is within the above range, the crystallinity is maintained in an appropriate range, and a gel-like sheet suitable for stretching is obtained. As a cooling method, a method of contacting with a refrigerant such as cold air or cooling water, a method of contacting with a cooling roll, or the like can be used, but it is preferable to contact with a roll cooled with the refrigerant for cooling.

次いで、ゲル状シートを延伸する。ゲル状シートの延伸(第一の延伸)は、湿式延伸ともいう。湿式延伸は、少なくとも一軸方向に行う。ゲル状シートは溶剤を含むので、均一に延伸できる。ゲル状シートは、加熱後、テンター法、ロール法、インフレーション法、又はこれらの組合せにより所定の倍率で延伸するのが好ましい。延伸は一軸延伸でも二軸延伸でもよいが、二軸延伸が好ましい。二軸延伸の場合、同時二軸延伸、逐次延伸及び多段延伸(例えば同時二軸延伸及び逐次延伸の組合せ)のいずれでもよい。 Then, the gel-like sheet is stretched. Stretching of the gel-like sheet (first stretching) is also referred to as wet stretching. Wet stretching is performed in at least uniaxial directions. Since the gel-like sheet contains a solvent, it can be uniformly stretched. After heating, the gel-like sheet is preferably stretched at a predetermined magnification by a tenter method, a roll method, an inflation method, or a combination thereof. The stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferable. In the case of biaxial stretching, any of simultaneous biaxial stretching, sequential stretching and multi-stage stretching (for example, a combination of simultaneous biaxial stretching and sequential stretching) may be used.

湿式延伸における、最終的な面積延伸倍率(面倍率)は、例えば、一軸延伸の場合、3倍以上が好ましく、4倍以上30倍以下がより好ましい。また、二軸延伸の場合、最終的な面積延伸倍率は9倍以上が好ましく、16倍以上がより好ましく、25倍以上がさらに好ましい。最終的な面積延伸倍率の上限は100倍以下が好ましく、64倍以下がより好ましい。また、長手方向及び幅方向のいずれでも最終的な面積延伸倍率は3倍以上が好ましく、機械方向と幅方向での延伸倍率は、互いに同じでも異なってもよい。延伸倍率を5倍以上とすると、突刺強度の向上が期待できる。なお、湿式延伸倍率とは、湿式延伸前のゲル状シートを基準としたときの、湿式延伸倍後のゲル状シートの延伸倍率のことをいう。 In the wet stretching, the final area stretching ratio (plane magnification) is preferably 3 times or more, more preferably 4 times or more and 30 times or less in the case of uniaxial stretching, for example. Further, in the case of biaxial stretching, the final area stretching ratio is preferably 9 times or more, more preferably 16 times or more, still more preferably 25 times or more. The upper limit of the final area stretching ratio is preferably 100 times or less, more preferably 64 times or less. Further, the final area stretching ratio is preferably 3 times or more in both the longitudinal direction and the width direction, and the stretching ratios in the mechanical direction and the width direction may be the same or different from each other. When the draw ratio is 5 times or more, improvement in puncture strength can be expected. The wet stretching ratio refers to the stretching ratio of the gel-like sheet after the wet stretching ratio when the gel-like sheet before the wet stretching is used as a reference.

延伸温度は、ポリオレフィンの結晶分散温度(Tcd)〜Tcd+30℃の範囲内にするのが好ましく、結晶分散温度(Tcd)+10℃〜結晶分散温度(Tcd)+28℃の範囲内にするのがより好ましく、Tcd+15℃〜Tcd+26℃の範囲内にするのが特に好ましい。延伸温度が上記範囲内であるとポリオレフィン延伸時の応力が調整され、面内方向と膜厚方向に熱的不安定構造が多くなり、シャットダウン特性の制御に重要な面内方向の変化が優先的に起こることになり、シャットダウン特性が向上する。ここで結晶分散温度(Tcd)とは、ASTM D4065に基づいて動的粘弾性の温度特性測定により求められる値をいう。上記の超高分子量ポリエチレン、超高分子量ポリエチレン以外のポリエチレン及びポリエチレン組成物は、約90〜100℃の結晶分散温度を有する。従って、原料としてポリエチレンを用いる場合の延伸温度は、例えば、90℃以上130℃以下とすることができる。 The stretching temperature is preferably in the range of the polyolefin crystal dispersion temperature (Tcd) to Tcd + 30 ° C., and more preferably in the range of crystal dispersion temperature (Tcd) + 10 ° C. to crystal dispersion temperature (Tcd) + 28 ° C. , Tcd + 15 ° C. to Tcd + 26 ° C. is particularly preferable. When the stretching temperature is within the above range, the stress during polyolefin stretching is adjusted, the number of thermally unstable structures increases in the in-plane direction and the film thickness direction, and the change in the in-plane direction, which is important for controlling the shutdown characteristics, is prioritized. Will occur in, and the shutdown characteristics will be improved. Here, the crystal dispersion temperature (Tcd) means a value obtained by measuring the temperature characteristics of dynamic viscoelasticity based on ASTM D4065. Polyethylene and polyethylene compositions other than the above ultra-high molecular weight polyethylene and ultra-high molecular weight polyethylene have a crystal dispersion temperature of about 90 to 100 ° C. Therefore, when polyethylene is used as a raw material, the stretching temperature can be, for example, 90 ° C. or higher and 130 ° C. or lower.

以上のような原料選択と延伸によりポリエチレンラメラ間に開裂が起こり、ポリエチレン相が微細化し、多数のフィブリルが形成される。フィブリルは三次元的に不規則に連結した網目構造を形成する。かつ、面内方向と膜厚方向に熱的不安定構造が多くなり、シャットダウン特性の制御に重要な面内方向の変化を優先的に起こすことができる構造となる。このため、より安全で高性能な電池用セパレータに好適である。 Cleavage occurs between the polyethylene lamellas due to the selection and stretching of the raw materials as described above, the polyethylene phase becomes finer, and a large number of fibrils are formed. Fibrils form a three-dimensionally irregularly connected network structure. In addition, the number of thermally unstable structures increases in the in-plane direction and the film thickness direction, and the structure can preferentially cause changes in the in-plane direction, which is important for controlling the shutdown characteristics. Therefore, it is suitable for a safer and higher performance battery separator.

次いで、上記延伸後のゲル状シートから成膜用溶剤を除去して微多孔膜(フィルム)とする。成膜用溶剤の除去は、洗浄溶媒を用いた洗浄により行う。洗浄溶媒およびこれを用いた成膜用溶剤の除去方法は公知であるので説明を省略する。例えば日本国特許第2132327号明細書や特開2002−256099号公報に開示の方法を利用することができる。 Next, the film-forming solvent is removed from the stretched gel-like sheet to form a microporous film (film). The film-forming solvent is removed by cleaning with a cleaning solvent. Since the cleaning solvent and the method for removing the film-forming solvent using the cleaning solvent are known, the description thereof will be omitted. For example, the method disclosed in Japanese Patent No. 2132327 and Japanese Patent Application Laid-Open No. 2002-256099 can be used.

次いで、成膜用溶剤を除去した微多孔膜を、加熱乾燥法又は風乾法により乾燥する。 次いで、乾燥後の微多孔膜を延伸する。乾燥後の微多孔膜の延伸は第二の延伸と第三の延伸からなり乾式延伸ともいう。乾式延伸は乾燥後の微多孔膜フィルムを、少なくとも一軸方向に延伸する。二軸延伸の場合、同時二軸延伸及び逐次延伸のいずれでもよいが、逐次延伸が好ましい。逐次延伸の場合、機械方向に延伸(第二の延伸)した後、連続して、幅方向に延伸(第三の延伸)することが好ましい。乾式延伸の方法は、加熱しながらテンター式延伸機やロール式延伸機などにより行うことができる。 Next, the microporous film from which the film-forming solvent has been removed is dried by a heat drying method or an air drying method. Next, the dried microporous membrane is stretched. The stretching of the microporous membrane after drying consists of a second stretching and a third stretching, and is also called a dry stretching. Dry stretching stretches the dried microporous membrane film at least in the uniaxial direction. In the case of biaxial stretching, either simultaneous biaxial stretching or sequential stretching may be used, but sequential stretching is preferable. In the case of sequential stretching, it is preferable to stretch in the mechanical direction (second stretching) and then continuously stretch in the width direction (third stretching). The dry stretching method can be performed by a tenter stretching machine, a roll stretching machine, or the like while heating.

乾式延伸の面積延伸倍率(面倍率)は、1.1倍以上であることが好ましく、1.2倍以上9.0倍以下であることがより好ましい。面倍率を上記範囲とすることにより、突刺強度やシャットダウン温度等を所望の範囲に容易に制御することができる。一軸延伸の場合、例えば、機械方向又は幅方向に1.2倍以上、好ましくは1.2倍以上3.0倍以下とする。二軸延伸の場合、機械方向及び幅方向の延伸倍率として各々1.0倍以上3.0倍以下とし、機械方向と幅方向での延伸倍率が互いに同じでも異なってもよいが、機械方向と幅方向での延伸倍率がほぼ同じであることが好ましい。乾式延伸は、機械方向に1.0倍超3.0倍以下で延伸(第二の延伸)した後、連続して、幅方向に1.0倍超3.0倍以下で延伸(第三の延伸)することが好ましい。特に機械方向の延伸はロール延伸を用いる場合、1.4倍未満が好ましく、1.3倍未満がより好ましい。上記範囲とすることで、ポリオレフィン延伸時の応力が調整され、面内方向と膜厚方向に熱的不安定構造が多くなり、シャットダウン特性の制御に重要な面内方向の変化が優先的に起こる構造となる。なお、乾式延伸倍率とは、乾式延伸後前の微多孔膜を基準としたときの、乾式延伸後の微多孔膜の延伸倍率のことをいう。また、第二の延伸は3段延伸以上であることが好ましく、4段延伸以上であることがより好ましく、5段延伸以上であることがさらに好ましい。こうすることで一段辺りの応力が分散され、延伸ムラなどを抑制することができる。 The area stretching ratio (surface magnification) of the dry stretching is preferably 1.1 times or more, and more preferably 1.2 times or more and 9.0 times or less. By setting the surface magnification within the above range, the puncture strength, shutdown temperature, and the like can be easily controlled within a desired range. In the case of uniaxial stretching, for example, it is 1.2 times or more, preferably 1.2 times or more and 3.0 times or less in the mechanical direction or the width direction. In the case of biaxial stretching, the stretching ratios in the machine direction and the width direction are 1.0 times or more and 3.0 times or less, respectively, and the stretching ratios in the machine direction and the width direction may be the same or different from each other, but they are different from those in the machine direction. It is preferable that the draw ratios in the width direction are substantially the same. In the dry stretching, after stretching in the mechanical direction by more than 1.0 times and 3.0 times or less (second stretching), it is continuously stretched in the width direction by more than 1.0 times and 3.0 times or less (third stretching). (Stretching) is preferable. In particular, when roll stretching is used, the stretching in the mechanical direction is preferably less than 1.4 times, more preferably less than 1.3 times. Within the above range, the stress during polyolefin stretching is adjusted, the number of thermally unstable structures increases in the in-plane direction and the film thickness direction, and in-plane changes that are important for controlling shutdown characteristics occur preferentially. It becomes a structure. The dry stretching ratio refers to the stretching ratio of the microporous membrane after the dry stretching when the microporous membrane before the dry stretching is used as a reference. Further, the second stretching is preferably three-step stretching or more, more preferably four-step stretching or more, and further preferably five-step stretching or more. By doing so, the stress in one step is dispersed, and uneven drawing and the like can be suppressed.

乾式延伸温度は、延伸応力制御の観点から、通常90〜135℃であり、より好ましくは100〜135℃、さらに好ましくは105℃〜135℃である。特に第二の延伸温度は100℃以上120℃以下が好ましく、110℃以上120℃以下がより好ましい。上記範囲とすることで、ポリオレフィン延伸時の応力が調整され、面内方向と膜厚方向に熱的不安定構造が多くなり、シャットダウン特性の制御に重要な面内方向の変化が優先的に起こる構造となる。第二の延伸温度を120℃以下とすることで、膜の一部融解などが起こり第二の延伸以降の微多孔膜に外観ムラが発生するのを防ぐことができる。 The dry stretching temperature is usually 90 to 135 ° C., more preferably 100 to 135 ° C., and even more preferably 105 ° C. to 135 ° C. from the viewpoint of stretching stress control. In particular, the second stretching temperature is preferably 100 ° C. or higher and 120 ° C. or lower, and more preferably 110 ° C. or higher and 120 ° C. or lower. Within the above range, the stress during polyolefin stretching is adjusted, the number of thermally unstable structures increases in the in-plane direction and the film thickness direction, and in-plane changes that are important for controlling shutdown characteristics occur preferentially. It becomes a structure. By setting the second stretching temperature to 120 ° C. or lower, it is possible to prevent the microporous film after the second stretching from causing uneven appearance due to partial melting of the film or the like.

また、乾燥後の微多孔膜は、熱処理が行われてもよい。熱処理方法としては、熱固定処理及び熱緩和処理の少なくとも一方を用いることができる。熱固定処理とは、膜の幅方向の寸法が変わらないように幅方向における両端部を保持しながら加熱する熱処理である。熱固定処理は、テンター方式またはロール方式により行うのが好ましい。熱緩和処理とは、膜を加熱中に機械方向や幅方向に熱収縮させる熱処理である。例えば、熱緩和処理方法としては特開2002−256099号公報に開示の方法があげられる。熱処理温度は第2のポリオレフィンの(Tcd)〜(Tm:融点)の範囲内が好ましく、微多孔膜の延伸温度±5℃の範囲内がより好ましく、微多孔膜の第二の延伸温度±3℃の範囲内が特に好ましい。 Further, the microporous membrane after drying may be heat-treated. As the heat treatment method, at least one of a heat fixing treatment and a heat relaxation treatment can be used. The heat fixing treatment is a heat treatment in which the film is heated while holding both ends in the width direction so that the dimensions in the width direction do not change. The heat fixing treatment is preferably performed by a tenter method or a roll method. The heat relaxation treatment is a heat treatment in which the membrane is heat-shrinked in the mechanical direction and the width direction during heating. For example, as a heat relaxation treatment method, the method disclosed in JP-A-2002-256099 can be mentioned. The heat treatment temperature is preferably in the range of (Tcd) to (Tm: melting point) of the second polyolefin, more preferably in the range of the stretching temperature of the microporous membrane ± 5 ° C., and the second stretching temperature of the microporous membrane ± 3. The range of ° C. is particularly preferable.

例えば、第三の延伸後に、熱処理及び熱緩和処理をしてもよい。熱緩和処理において、緩和温度は、例えば、80℃以上135℃以下、好ましくは90℃以上133℃以下である。また、熱緩和処理を行った場合、最終乾式延伸倍率は、例えば、1.0倍以上9.0倍以下、好ましくは1.2倍以上4.0倍以下である。緩和率は、0%以上70%以下とすることができる。 For example, heat treatment and heat relaxation treatment may be performed after the third stretching. In the heat relaxation treatment, the relaxation temperature is, for example, 80 ° C. or higher and 135 ° C. or lower, preferably 90 ° C. or higher and 133 ° C. or lower. Further, when the heat relaxation treatment is performed, the final dry stretching ratio is, for example, 1.0 times or more and 9.0 times or less, preferably 1.2 times or more and 4.0 times or less. The mitigation rate can be 0% or more and 70% or less.

本発明のポリオレフィン微多孔膜は、単層であってもよいが、異なるポリマー種、分子量、またそれらの配合比等、異なる組成の樹脂組成物を積層して形成したものであってもよい。 The microporous polyolefin membrane of the present invention may be a single layer, but may be formed by laminating resin compositions having different compositions such as different polymer species, molecular weights, and blending ratios thereof.

また、本発明のポリオレフィン微多孔膜に、他の多孔質層を積層して多層多孔質膜としてもよい。他の多孔質層としては、特に限定されないが、例えば、バインダーと無機粒子とを含む無機粒子層などの多孔質層を積層してもよい。無機粒子層を構成するバインダー成分としては、特に限定されず、公知の成分を用いることができ、例えば、アクリル樹脂、ポリフッ化ビニリデン樹脂、ポリアミドイミド樹脂、ポリアミド樹脂、芳香族ポリアミド樹脂、ポリイミド樹脂などを用いることができる。無機粒子層を構成する無機粒子としては、特に限定されず、公知の材料を用いることができ、例えば、アルミナ、ベーマイト、硫酸バリウム、酸化マグネシウム、水酸化マグネシウム、炭酸マグネシウム、ケイ素などを用いることができる。また、多層ポリオレフィン多孔質膜としては、多孔質化した前記バインダー樹脂がポリオレフィン微多孔質膜の少なくとも一方の表面に積層されたものであってもよい。 Further, another porous layer may be laminated on the polyolefin microporous membrane of the present invention to form a multilayer porous membrane. The other porous layer is not particularly limited, and for example, a porous layer such as an inorganic particle layer containing a binder and inorganic particles may be laminated. The binder component constituting the inorganic particle layer is not particularly limited, and known components can be used, for example, acrylic resin, polyvinylidene fluoride resin, polyamideimide resin, polyamide resin, aromatic polyamide resin, polyimide resin and the like. Can be used. The inorganic particles constituting the inorganic particle layer are not particularly limited, and known materials can be used. For example, alumina, boehmite, barium sulfate, magnesium oxide, magnesium hydroxide, magnesium carbonate, silicon and the like can be used. can. Further, as the multilayer polyolefin porous membrane, the porous binder resin may be laminated on at least one surface of the polyolefin microporous membrane.

以下、本発明を実施例によりさらに詳細に説明する。なお、本発明はこれらの例に限定されるものではない。 Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention is not limited to these examples.

1.測定方法と評価方法
[結晶化度]
ポリオレフィン微多孔膜の幅方向の中心位置から3cm×3cmに5箇所を切り出し、重ねたものを測定サンプルとして、放射光施設において室温(25℃)〜160℃程度まで5℃/minで昇温しながら広角X線回折測定を行った。測定サンプルの表面(ポリオレフィン微多孔膜の表面)に対してX線を垂直に入射し、測定して膜厚方向の回折スペクトルを得た。また、測定サンプルの膜厚(ポリオレフィン微多孔膜の膜厚)に対して垂直にX線を入射し、測定して面内方向の回折スペクトルを得た。いずれの方向も室温とシャットダウン温度でサンプル中心付近を1回、測定した。得られた回折スペクトルから非晶質ハローと結晶性ピークのフィッティングを行い、結晶のピーク面積と非晶のピーク面積を求めた。各方向の結晶化度は以下の式を用いて算出した。
式:結晶化度(%)=(結晶のピーク面積)÷(結晶と非晶のピーク面積)×100
室温における膜厚方向の結晶化度と面内方向の結晶化度は、それぞれ膜厚方向と面内方向にX線照射したときの室温における回折スペクトルから求めた各結晶化度の差分とした。シャットダウン温度における面内方向の結晶化度は、面内方向にX線照射したときのシャットダウン温度における回折スペクトルから求めた各結晶化度の差分とした。ここで、シャットダウン温度は後述する方法で測定される温度とした。
1. 1. Measurement method and evaluation method [Crystallinity]
Five points were cut out from the center position in the width direction of the polyolefin microporous film in a width direction of 3 cm × 3 cm, and the stacked ones were used as measurement samples and heated to about room temperature (25 ° C) to 160 ° C at 5 ° C / min in a synchrotron radiation facility. However, wide-angle X-ray diffraction measurement was performed. X-rays were vertically incident on the surface of the measurement sample (the surface of the microporous polyolefin membrane) and measured to obtain a diffraction spectrum in the film thickness direction. Further, X-rays were incident perpendicularly to the film thickness of the measurement sample (the film thickness of the microporous polyolefin film) and measured to obtain a diffraction spectrum in the in-plane direction. In each direction, the measurement was performed once near the center of the sample at room temperature and shutdown temperature. From the obtained diffraction spectrum, the amorphous halo and the crystalline peak were fitted, and the peak area of the crystal and the peak area of the amorphous were obtained. The crystallinity in each direction was calculated using the following formula.
Formula: Crystallinity (%) = (Crystal peak area) ÷ (Crystal and amorphous peak area) x 100
The crystallinity in the film thickness direction and the crystallinity in the in-plane direction at room temperature are the differences between the crystallinities obtained from the diffraction spectra at room temperature when X-rays are irradiated in the film thickness direction and the in-plane direction, respectively. The in-plane crystallization degree at the shutdown temperature was defined as the difference between the crystallization degrees obtained from the diffraction spectrum at the shutdown temperature when X-rays were irradiated in the in-plane direction. Here, the shutdown temperature is the temperature measured by the method described later.

(装置/測定条件)
放射光広角X線を用いて、下記条件により測定した。
(1)放射光施設 SPring−8 BL08B2
(2)波長 0.10 nm
(3)ビーム径 縦0.35mm、横0.40mm
(4)カメラ長 54.2mm
(5)検出器 浜松ホトニクス社製フラットパネルC9728DK 画素サイズ50um角
(6)露光時間 5sec(面内方向の測定時) 、2sec(膜厚方向の測定時)
(7)測定間隔 約0.4℃ステップ
(8)測定範囲 5 ≦ q ≦ 25nm−1
[示差走査熱量測定(DSC)による2回目の昇温(2nd heat)で観測される融解ピーク温度]
Perkin−Elmer社製のDSC 8500を用いて測定した。ポリオレフィン微多孔膜の幅方向の中心箇所が試験片となるように幅方向に対してほぼ等間隔になるように5箇所を選び、試験片が6mgとなるように切り出して重ねて、アルミニウム製標準容器に詰めた。第1回目の昇温は窒素雰囲気下(20mL/分)で測定温度範囲を0℃〜200℃、昇温速度は10℃/分とし、200℃に到達したとき保持時間を10分とした。その後、窒素雰囲気下(20mL/分)、降温速度30℃/分で降温した。次に、第2回目の昇温(再昇温)を窒素雰囲気下(20mL/分)で測定温度範囲を0℃〜200℃、昇温速度は10℃/min、200℃に到達したときの保持時間を5分とした。第2回目の昇温により得られたDSC曲線から0℃と200℃を結ぶ直線をベースラインとし、融解吸熱ピーク時の温度を読み取り、ポリオレフィン微多孔膜のDSCによる再昇温で観測される融解ピーク温度とした。(ピークが2山以上観測される場合は、最も吸熱している方のピークから微多孔膜の融点ピーク温度を読み取る。)。
(Device / measurement conditions)
It was measured under the following conditions using synchrotron radiation wide-angle X-rays.
(1) Synchrotron radiation facility SPring-8 BL08B2
(2) Wavelength 0.10 nm
(3) Beam diameter 0.35 mm in length and 0.40 mm in width
(4) Camera length 54.2 mm
(5) Detector Hamamatsu Photonics Flat Panel C9728DK Pixel size 50um square
(6) Exposure time 5 sec (when measuring in the in-plane direction), 2 sec (when measuring in the film thickness direction)
(7) Measurement interval Approximately 0.4 ° C step
(8) Measurement range 5 ≤ q ≤ 25 nm -1
[Melting peak temperature observed at the second temperature rise (2nd heat) by differential scanning calorimetry (DSC)]
The measurement was performed using a DSC 8500 manufactured by Perkin-Elmer. Five locations were selected so that the central location in the width direction of the polyolefin microporous membrane was approximately equal to the width direction so that the test piece would be the test piece. Packed in a container. For the first temperature rise, the measurement temperature range was 0 ° C. to 200 ° C., the temperature rise rate was 10 ° C./min, and the holding time was 10 minutes when the temperature reached 200 ° C. under a nitrogen atmosphere (20 mL / min). Then, the temperature was lowered under a nitrogen atmosphere (20 mL / min) at a temperature lowering rate of 30 ° C./min. Next, when the second temperature rise (re-heat temperature) was performed in a nitrogen atmosphere (20 mL / min), the measurement temperature range reached 0 ° C. to 200 ° C., and the temperature rise rate reached 10 ° C./min and 200 ° C. The holding time was 5 minutes. From the DSC curve obtained by the second temperature rise, the straight line connecting 0 ° C and 200 ° C is used as the baseline, the temperature at the endothermic peak of melting is read, and the melting observed by reheating the polyolefin microporous film by DSC is performed. The peak temperature was used. (When two or more peaks are observed, the melting point peak temperature of the microporous membrane is read from the peak that absorbs the most heat.)

[ポリオレフィンの重量平均分子量/分子量分布]
ポリオレフィンの重量平均分子量(Mw)、および分子量分布(MwD)は以下の条件でゲルパーミエーションクロマトグラフィー(GPC)法により求めた。
・測定装置:Waters Corporation製GPC−150C
・カラム:昭和電工株式会社製Shodex UT806M
・カラム温度:135℃
・溶媒(移動相):o−ジクロルベンゼン
・溶媒流速:1.0 ml/分
・試料濃度:0.1 wt%(溶解条件:135℃/1h)
・インジェクション量:500μl
・検出器:Waters Corporation製ディファレンシャルリフラクトメーター(RI検出器)
・検量線:単分散ポリスチレン標準試料を用いて得られた検量線から、ポリエチレンか換算係数(0.46)を用いて作成した。
[Weight average molecular weight / molecular weight distribution of polyolefin]
The weight average molecular weight (Mw) and the molecular weight distribution (MwD) of the polyolefin were determined by the gel permeation chromatography (GPC) method under the following conditions.
-Measuring device: GPC-150C manufactured by Waters Corporation
-Column: Showa Denko Corporation Shodex UT806M
-Column temperature: 135 ° C
-Solvent (mobile phase): o-dichlorobenzene-Solvent flow rate: 1.0 ml / min-Sample concentration: 0.1 wt% (dissolution condition: 135 ° C./1 h)
・ Injection amount: 500 μl
-Detector: Waters Corporation differential refractometer (RI detector)
-Calibration curve: Prepared from a calibration curve obtained using a monodisperse polystyrene standard sample using polyethylene or a conversion factor (0.46).

[ポリオレフィン微多孔膜の重量平均分子量/分子量分布]
ポリオレフィン微多孔膜の重量平均分子量(Mw)、および分子量分布(MwD)は以下の条件でゲルパーミエーションクロマトグラフィー(GPC)法により求めた。
・測定装置:Waters Corporation製GPC−150C
・カラム:昭和電工株式会社製Shodex UT806M
・カラム温度:135℃
・溶媒(移動相):o−ジクロルベンゼン
・溶媒流速:1.0 ml/分
・試料濃度:0.1 wt%(溶解条件:135℃/1h)
・インジェクション量:500μl
・検出器:Waters Corporation製ディファレンシャルリフラクトメーター(RI検出器)
・検量線:単分散ポリスチレン標準試料を用いて得られた検量線から、ポリエチレンか換算係数(0.46)を用いて作成した。
[Weight average molecular weight / molecular weight distribution of polyolefin microporous membrane]
The weight average molecular weight (Mw) and the molecular weight distribution (MwD) of the polyolefin microporous membrane were determined by the gel permeation chromatography (GPC) method under the following conditions.
-Measuring device: GPC-150C manufactured by Waters Corporation
-Column: Showa Denko Corporation Shodex UT806M
-Column temperature: 135 ° C
-Solvent (mobile phase): o-dichlorobenzene-Solvent flow rate: 1.0 ml / min-Sample concentration: 0.1 wt% (dissolution condition: 135 ° C./1 h)
・ Injection amount: 500 μl
-Detector: Waters Corporation differential refractometer (RI detector)
-Calibration curve: Prepared from a calibration curve obtained using a monodisperse polystyrene standard sample using polyethylene or a conversion factor (0.46).

[シャットダウン温度]
微多孔膜を室温(25℃)から5℃/分の昇温速度で加熱しながら、透気度計(旭精工株式会社製、EGO−1T)により透気抵抗度を測定し、透気抵抗度が検出限界である1×10秒/100cmAirに到達した温度を求め、シャットダウン温度(℃)とした。
[Shutdown temperature]
While heating the microporous membrane from room temperature (25 ° C) at a heating rate of 5 ° C / min, the air permeability resistance was measured with an air permeability meter (EGO-1T, manufactured by Asahi Seiko Co., Ltd.), and the air permeability resistance was measured. The temperature at which the degree reached the detection limit of 1 × 10 5 seconds / 100 cm 3 Air was determined and used as the shutdown temperature (° C.).

測定セルはアルミブロックで構成され、微多孔膜の直下に熱電対を有する構造とし、サンプルを5cm×5cm角に切り取り、周囲をОリングで固定しながら昇温測定した。 The measurement cell was composed of an aluminum block and had a structure having a thermocouple directly under the microporous membrane. The sample was cut into 5 cm × 5 cm squares, and the temperature was measured while fixing the periphery with an О ring.

[膜厚]
微多孔膜の50mm×50mmの範囲内における5点の膜厚を接触厚み計(株式会社ミツトヨ製ライトマチック)により測定し、平均値を求め、膜厚T(μm)とした。
[Film thickness]
The film thickness at 5 points within the range of 50 mm × 50 mm of the microporous membrane was measured with a contact thickness meter (Lightmatic manufactured by Mitutoyo Co., Ltd.), and the average value was calculated and set to T 0 (μm).

[空孔率(%)]
ポリオレフィン微多孔膜をXcm×Ycmに切り出したサンプルについて、下記の式により算出した。
[Porosity (%)]
A sample obtained by cutting out a microporous polyolefin membrane into X cm × Y cm was calculated by the following formula.

空孔率(%)=〔1−(10000×W/ρ)/(X×Y×T)〕×100
W:サンプル重量(g) ρ:ポリエチレンの樹脂密度0.95(g/m
:サンプル厚み(μm)
なお、ρは原料に用いている樹脂の密度を用いる。
Porosity (%) = [1- (10000 × W / ρ) / (X × Y × T 0 )] × 100
W: Sample weight (g) ρ: Polyethylene resin density 0.95 (g / m 2 )
T 0 : Sample thickness (μm)
In addition, ρ uses the density of the resin used as a raw material.

[突刺強度(N)]
突刺し試験機NDG5(KatoTech製)を用いて、先端が球面(曲率半径R:0.5mm)の直径1mmの針で、ポリオレフィン微多孔膜を2mm/秒の速度で突刺したときの最大荷重(N)を測定した。突刺強度は最大荷重(N)を9μm換算した下記の式で求める値である。
突刺強度=最大荷重(N)×9(μm)/ポリオレフィン微多孔膜の膜厚T(μm)
[熱収縮]
105℃8時間の機械方向の熱収縮率および幅方向の熱収縮率は、次のようにして測定した。
(1)室温におけるポリオレフィン微多孔膜の幅方向の中心位置で5cm×5cmでダンベルカッターにより切り出したものを試験片とした。これを長手方向に3か所繰り返し、n=3のサンプルとした。(5cm×5cmに切り出せない場合は、ポリオレフィン微多孔膜の幅方向長さの50%に相当する長さで長手方向/幅方向にダンベルカッターで切り出す。)切り出したサンプルの機械方向の長さ(L0MD)および幅方向(L0TD)における長さをそれぞれ測定した。
(2)切り出したサンプルを、荷重をかけず、把持もせずに、オーブンで8時間105℃の温度にて熱処理した後、室温25℃に戻し、平衡化した。
(3)熱処理したサンプルについて機械方向の長さ(L1MD)および幅方向(L1TD)における長さをそれぞれ測定した。
(4)機械方向および幅方向の熱収縮は下記の式で表される。
[Puncture strength (N)]
The maximum load (maximum load) when a polyolefin microporous film is pierced at a speed of 2 mm / sec with a needle having a spherical tip (radius of curvature R: 0.5 mm) and a diameter of 1 mm using a piercing tester NDG5 (manufactured by Kato Tech). N) was measured. The puncture strength is a value calculated by the following formula obtained by converting the maximum load (N) into 9 μm.
Puncture strength = maximum load (N) x 9 (μm) / film thickness of polyolefin microporous membrane T 0 (μm)
[Heat shrinkage]
The heat shrinkage in the mechanical direction and the heat shrinkage in the width direction at 105 ° C. for 8 hours were measured as follows.
(1) A test piece cut out by a dumbbell cutter at a center position in the width direction of the polyolefin microporous film at room temperature at a size of 5 cm × 5 cm was used as a test piece. This was repeated in three places in the longitudinal direction to obtain a sample with n = 3. (If it cannot be cut out to 5 cm x 5 cm, it is cut out with a dumbbell cutter in the longitudinal / width direction with a length corresponding to 50% of the widthwise length of the polyolefin microporous membrane.) The mechanical length of the cut out sample ( L 0MD) and length in the width direction (L 0TD) were measured.
(2) The cut-out sample was heat-treated in an oven at a temperature of 105 ° C. for 8 hours without applying a load or gripping, and then returned to room temperature of 25 ° C. for equilibration.
(3) For the heat-treated sample, the length in the mechanical direction (L 1MD ) and the length in the width direction (L 1TD ) were measured, respectively.
(4) The heat shrinkage in the machine direction and the width direction is expressed by the following formula.

機械方向の熱収縮率(%)=(1−L1MD)÷L0MD)×100
幅方向の熱収縮率(%)=(1−L1TD)÷L0TD)×100
(実施例1)
Mw3×10、分子量分布20の高密度ポリエチレン(ポリエチレン1)を表1に示す樹脂濃度となるように成膜用溶剤として流動パラフィンを添加し、二軸押出機にて溶融混練し、ポリオレフィン樹脂溶液を調製した。ポリオレフィン樹脂溶液を、二軸押出機からTダイに供給し、押し出して冷却ロールで引き取りながら冷却し、ゲル状シートを形成した。ゲル状シートを、テンター延伸機により110℃で機械方向及び幅方向ともに5倍で同時二軸延伸(第一の延伸)した。延伸したゲル状シートを塩化メチレン浴中に浸漬し、流動パラフィンを除去した後、乾燥させた。乾燥後の膜を、バッチ式延伸機を用いて、110℃で幅方向に1.1倍で延伸(第二の延伸)した。その後、115℃で10分間熱固定を行いポリオレフィン微多孔質膜を得た。ポリオレフィン微多孔質膜の製造条件および測定結果を表1に記載した。
Heat shrinkage rate in the machine direction (%) = (1-L 1MD ) ÷ L 0MD ) × 100
Thermal shrinkage in the width direction (%) = (1-L 1TD ) ÷ L 0TD ) × 100
(Example 1)
Mw3 × 10 5, a high density polyethylene having a molecular weight distribution 20 (polyethylene 1) was added liquid paraffin as a membrane-forming solvent so that the resin concentration shown in Table 1 was melt-kneaded in a twin-screw extruder, the polyolefin resin The solution was prepared. The polyolefin resin solution was supplied to the T-die from a twin-screw extruder, extruded and cooled while being taken up by a cooling roll to form a gel-like sheet. The gel-like sheet was simultaneously biaxially stretched (first stretch) at 110 ° C. by a tenter stretching machine at a ratio of 5 times in both the mechanical direction and the width direction. The stretched gel sheet was immersed in a methylene chloride bath to remove liquid paraffin and then dried. The dried film was stretched 1.1 times in the width direction at 110 ° C. using a batch type stretching machine (second stretching). Then, it was heat-fixed at 115 ° C. for 10 minutes to obtain a polyolefin microporous film. Table 1 shows the production conditions and measurement results of the polyolefin microporous membrane.

(実施例2)
機械方向及び幅方向ともに8倍で同時二軸延伸、第二の延伸を100℃で機械方向に1.2倍で延伸した以外は、実施例1と同様にしてポリオレフィン微多孔膜を得た。
(Example 2)
A polyolefin microporous film was obtained in the same manner as in Example 1 except that simultaneous biaxial stretching was performed 8 times in both the mechanical direction and the width direction, and the second stretching was performed 1.2 times in the mechanical direction at 100 ° C.

(実施例3)
Mw5×10、分子量分布5の高密度ポリエチレン(ポリエチレン1)を表1に示す樹脂濃度となるように成膜用溶剤として流動パラフィンを添加し、二軸押出機にて溶融混練し、機械方向及び幅方向ともに5倍で同時二軸延伸、第二の延伸を、ロール延伸機を用いて115℃で機械方向に1.2倍で延伸をして、その後、125℃で10分間の熱固定を行った以外は、実施例1と同様にしてポリオレフィン微多孔膜を得た。
(Example 3)
High-density polyethylene (polyethylene 1) with Mw 5 × 105 and molecular weight distribution 5 is added with liquid paraffin as a film-forming solvent so as to have the resin concentration shown in Table 1, melt-kneaded with a twin-screw extruder, and machine-oriented. Simultaneous biaxial stretching and second stretching at 5 times in both the width direction and 1.2 times in the mechanical direction at 115 ° C. using a roll stretching machine, and then heat-fixed at 125 ° C. for 10 minutes. A polyolefin microporous film was obtained in the same manner as in Example 1 except that

(比較例1)
表1に示すMw5×10、分子量分布5の高密度ポリエチレン(ポリエチレン1)とMwが1×10、分子量分布8の超高分子量ポリエチレン(ポリエチレン2)からなるポリエチレン樹脂組成物を表1に示す樹脂濃度となるように成膜用溶剤として流動パラフィンを添加し、二軸押出機にて溶融混練し、第一の延伸をテンター延伸機により90℃で機械方向及び幅方向ともに5倍で同時二軸延伸し、第二の延伸を90℃で機械方向に1.2倍で延伸をして、その後、125℃で10分間の熱固定を行った以外は、実施例1と同様にしてポリオレフィン微多孔膜を得た。
(Comparative Example 1)
Table 1 shows a polyethylene resin composition composed of high-density polyethylene (polyethylene 1) having Mw 5 × 105 and molecular weight distribution 5 and ultra-high molecular weight polyethylene (polyethylene 2) having Mw 1 × 10 6 and molecular weight distribution 8 shown in Table 1. Liquid paraffin was added as a film-forming solvent to the indicated resin concentration, melt-kneaded with a twin-screw extruder, and the first stretching was performed simultaneously at 90 ° C. with a tenter stretching machine at 90 ° C. in both the mechanical direction and the width direction at 5 times. Polyethylene was biaxially stretched, the second stretch was stretched 1.2 times in the mechanical direction at 90 ° C., and then heat-fixed at 125 ° C. for 10 minutes in the same manner as in Example 1. A microporous film was obtained.

(比較例2)
第一の延伸をテンター延伸機により90℃で機械方向及び幅方向ともに9倍に同時二軸延伸し、第二の延伸を90℃で機械方向に1.2倍で延伸をして、その後、125℃で10分間の熱固定を行った以外は、実施例1と同様にしてポリオレフィン微多孔膜を得た。
(Comparative Example 2)
The first stretching was simultaneously biaxially stretched 9 times in both the mechanical direction and the width direction at 90 ° C. by a tenter stretching machine, the second stretching was stretched 1.2 times in the mechanical direction at 90 ° C., and then. A microporous polyolefin membrane was obtained in the same manner as in Example 1 except that the heat was fixed at 125 ° C. for 10 minutes.

Figure 2020075794
Figure 2020075794

(評価)
実施例1〜3のポリオレフィン微多孔膜は、室温(25℃)における膜厚方向の結晶化度と面内方向の結晶化度との差が25%以下であり、膜厚方向の結晶化度が面内方向の結晶化度よりも大きく、広角X線測定によるシャットダウン温度における面内方向の結晶化度と室温における面内方向の結晶化度との差が58%以上であり、シャットダウン温度が135℃以下となり、シャットダウン特性に優れることが示された。
(evaluation)
In the polyolefin microporous films of Examples 1 to 3, the difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction at room temperature (25 ° C.) is 25% or less, and the crystallinity in the film thickness direction is 25% or less. Is larger than the in-plane crystallization degree, the difference between the in-plane crystallization degree at the shutdown temperature by wide-angle X-ray measurement and the in-plane crystallization degree at room temperature is 58% or more, and the shutdown temperature is It was shown to be excellent in shutdown characteristics at 135 ° C or lower.

以上から、室温(25℃)における膜厚方向の結晶化度と面内方向の結晶化度との差が25%以下であり、膜厚方向の結晶化度が面内方向の結晶化度よりも大きく、広角X線測定によるシャットダウン温度における面内方向の結晶化度と室温における面内方向の結晶化度との差が58%以上である微多孔膜は、シャットダウン特性に優れることが明らかとなった。 From the above, the difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction at room temperature (25 ° C.) is 25% or less, and the crystallinity in the film thickness direction is higher than the crystallinity in the in-plane direction. It is clear that the microporous film, which has a difference of 58% or more between the in-plane crystallinity at the shutdown temperature and the in-plane crystallinity at room temperature by wide-angle X-ray measurement, has excellent shutdown characteristics. became.

本発明のポリオレフィン微多孔膜は、セパレータとして二次電池に組み入れた際、シャットダウン特性に優れる。よって、高容量化が要求される二次電池用セパレータに好適に用いることができる。
The polyolefin microporous membrane of the present invention has excellent shutdown characteristics when incorporated into a secondary battery as a separator. Therefore, it can be suitably used for a separator for a secondary battery, which is required to have a high capacity.

Claims (9)

広角X線回折測定による室温における膜厚方向の結晶化度と面内方向の結晶化度との差が25%以下であり、前記膜厚方向の結晶化度が前記面内方向の結晶化度よりも大きく、広角X線測定によるシャットダウン温度における面内方向の結晶化度と前記室温における面内方向の結晶化度との差が58%以上であるポリオレフィン微多孔膜。 The difference between the crystallinity in the film thickness direction and the crystallinity in the in-plane direction at room temperature by wide-angle X-ray diffraction measurement is 25% or less, and the crystallinity in the film thickness direction is the crystallinity in the in-plane direction. A polyolefin microporous film having a difference of 58% or more between the in-plane crystallinity at the shutdown temperature by wide-angle X-ray measurement and the in-plane crystallinity at room temperature. 示差走査熱量測定の2回目の昇温で観測されるポリオレフィン微多孔膜の融解ピーク温度が115℃以上132℃以下である請求項1に記載のポリオレフィン微多孔膜。 The polyolefin microporous film according to claim 1, wherein the melting peak temperature of the polyolefin microporous film observed at the second temperature rise of the differential scanning calorimetry is 115 ° C. or higher and 132 ° C. or lower. 前記ポリオレフィン微多孔膜を形成する樹脂組成物の分子量分布が5以上30以下である請求項1または2に記載のポリオレフィン微多孔膜。 The polyolefin microporous film according to claim 1 or 2, wherein the resin composition forming the polyolefin microporous film has a molecular weight distribution of 5 or more and 30 or less. 9μm換算の突刺強度が2.25N以上である請求項1〜3のいずれか一項に記載のポリオレフィン微多孔膜。 The polyolefin microporous membrane according to any one of claims 1 to 3, wherein the puncture strength in terms of 9 μm is 2.25 N or more. ポリオレフィンがポリエチレンを含む、請求項1〜4いずれか一項に記載のポリオレフィン微多孔膜。 The polyolefin microporous membrane according to any one of claims 1 to 4, wherein the polyolefin contains polyethylene. 膜厚が9μm以下である請求項1〜5のいずれか一項に記載のポリオレフィン微多孔膜。 The polyolefin microporous membrane according to any one of claims 1 to 5, wherein the film thickness is 9 μm or less. 請求項1〜6のいずれか一項に記載のポリオレフィン微多孔膜に、他の多孔質層を1層以上積層してなる多層微多孔膜。 A multilayer microporous membrane formed by laminating one or more other porous layers on the polyolefin microporous membrane according to any one of claims 1 to 6. 請求項1〜6のいずれか一項に記載のポリオレフィン微多孔膜または請求項7に記載の多層微多孔膜を含む電池用セパレータ。 A battery separator comprising the polyolefin microporous membrane according to any one of claims 1 to 6 or the multilayer microporous membrane according to claim 7. 請求項8に記載の電池用セパレータを備える電池。


A battery comprising the battery separator according to claim 8.


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