JP3699561B2 - Polyolefin microporous membrane and method for producing the same - Google Patents
Polyolefin microporous membrane and method for producing the same Download PDFInfo
- Publication number
- JP3699561B2 JP3699561B2 JP12025597A JP12025597A JP3699561B2 JP 3699561 B2 JP3699561 B2 JP 3699561B2 JP 12025597 A JP12025597 A JP 12025597A JP 12025597 A JP12025597 A JP 12025597A JP 3699561 B2 JP3699561 B2 JP 3699561B2
- Authority
- JP
- Japan
- Prior art keywords
- weight
- polyolefin
- temperature
- microporous membrane
- composition
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- Y—GENERAL 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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Description
【０００１】
【発明の属する技術分野】
本発明は、ポリオレフィン微多孔膜に関するものであって、より詳しくは電池用セパレータ等に使用される、透過性能及び機械的強度に優れるとともに、溶融破断温度の優れた機能を有するポリオレフィン微多孔膜に関するものである。
【０００２】
【従来の技術】
微多孔膜は、各種の分離膜や、電池用セパーレーター、電解コンデンサー用セパレーター等に使用されている。特にリチウム電池においては、リチウム金属、リチウムイオンが用いられているために非プロトン性極性有機溶媒が電解液溶媒として用いられ、また、電解質としては、リチウム塩を用いている。したがって正極と負極との間に設置するセパレーターには、有機溶媒に不溶でありかつ電解質や電極活物質に対して安定なポリエチレン、ポリプロピレンなどのポリオレフィン系材料を微多孔膜や不織布に加工したものをセパレーターとして用いている。
【０００３】
最近、超高分子量のポリオレフィンを用いて高強度および高弾性の微多孔膜が開発されてきている。例えば、重量平均分子量が７×１０5以上の超高分子量ポリオレフィンを溶媒中で加熱溶解した溶液からゲル状シートを成形し、前記ゲル状シート中の溶媒量を脱溶媒処理により調整し、次いで加熱延伸した後、残留溶媒を除去することにより、微多孔膜を製造する方法が提案されている（特開昭６０−２４２０３５号他）。また、超高分子量ポリオレフィンの高濃度溶液からのポリオレフィン微多孔膜の製法として、超高分子量ポリオレフィンを含有するポリオレフィン組成物の分子量分布を特定の値にする方法が提案されている（特開平３−６４３３４号）。
【０００４】
ところで、上記ポリオレフィン微多孔膜を電池、例えばリチウム電池用セパレーター等に用いる場合には、電極が短絡して電池内部の温度が上昇した時に、発火等の事故が生じるのを防止する必要がある。このため、リチウムの発火以前に溶融してその孔を目詰りさせ、電流をシャットダウンさせる機能の他に、シャトダウン後に温度がさらに上昇した時に、セパレーター自身が溶融破断（メルトダウン）すると、電池の発火、爆発の危険性があるため、メルトダウン温度を高くすることが望まれている。また、シャットダウン温度とメルトダウン温度の差が大きいほど、高温特性が良好で安全性の高い電池用セパレーターになりうると考えられる。例えば、特開昭６３−３０８８６６号公報や、特開平２−７７１０８号公報では、低融点のポリエチレンおよび高融点のポリプロピレンからなる単膜を積層化することにより、高強度かつ優れた高温特性を有する微孔性多孔膜を得る方法が開示されているが、積層のため、セパレーターの電気抵抗が高くなり、高性能電池用セパレーターとしては不向きのものとなる。さらに、特開平２−７７１０８号公報では、積層押出という手法をとるため、製造工程の複雑化および製造コストという点で生産性に劣るものとなる。
【０００５】
【発明が解決しようとする課題】
したがって、本発明の目的は、透過性能及び機械的強度に優れるとともに、低温でのシャットダウン温度と高いメルトダウン温度を有し、メルトダウン温度とシャットダウン温度の差の幅が広く、かつ熱収縮率の低いポリオレフィン微多孔膜を提供することである。
【０００６】
【課題を解決するための手段】
本発明は、上記目的を達成するため、超高分子量ポリエチレンまたはその組成物に特定のポリプロピレンを加えることにより、透過性能及び機械的強度に優れるとともに、メルトダウン温度が高くなり、さらにシャットダウン温度とメルトダウン温度幅が大きい、かつ熱収縮率が低い微多孔膜が得られることを見い出し本発明に想到した。
【０００７】
すなわち、本発明は、重量平均分子量が５×１０５以上のポリエチレンまたはそのポリエチレン組成物６５〜９５重量％と、重量平均分子量が３×１０５以上でエチレン含量が１．０重量％以下のポリプロピレン５〜３５重量％を含有する組成物からなるポリオレフィン微多孔膜でであって、重量平均分子量が５×１０ ５ 以上のポリエチレンまたはそのポリエチレン組成物の分子量分布が５〜５０であり、当該微多孔膜の破断強度が１０００ｋｇ／ｃｍ ２ 以上で、かつ熱収縮率（１００℃／８時間）が５％以下であるポリオレフィン微多孔膜を提供するものである。このポリオレフィン微多孔膜は、重量平均分子量が５×１０５以上のポリエチレンまたはそのポリエチレン組成物６５〜９５重量％と、重量平均分子量が３×１０５以上でエチレン含量が１．０重量％以下のポリプロピレン５〜３５重量％を含有する組成物１０〜５０重量％と、溶媒５０〜９０重量％とからなる溶液を調製し、前記溶液をダイより押出し、冷却してゲル状組成物を形成し、前記ゲル状組成物をポリエチレン組成物の融点＋１０℃以下の温度で延伸し、しかる後残存溶媒を除去することによって好適に製造される。
【０００８】
【発明の実施の形態】
本発明で用いるポリエチレンは、重量平均分子量が５×１０５以上、好ましくは１×１０６〜１５×１０６の超高分子量のポリエチレンである。重量平均分子量が５×１０５未満では、微多孔膜の製造時の延伸工程において最大延伸倍率が低く、目的の微多孔膜が得られない。一方、上限は特に限定的ではないが１５×１０６を超えるものは、微多孔膜の製造時のゲル状成形物の形成において成形性に劣る。また、本発明においては、後述のポリオレフィン溶液の高濃度化と微多孔膜の強度の向上を図るために、重量平均分子量１×１０６以上の超高分子量ポリエチレンと重量平均分子量１×１０５以上５×１０５未満の高密度ポリエチレンとの組成物を用いることができる。超高分子量ポリエチレンのポリエチレン組成物中の含有量は、ポリエチレン組成物全体を１００重量％として１重量％以上が好ましく、より好ましくは１０〜７０重量％である。さらに前記ポリエチレンまたはそのポリエチレン組成物の分子量分布の尺度として用いられる重量平均分子量／数平均分子量は、５〜５０である。
【０００９】
本発明で用いるポリプロピレンとしては、重量平均分子量が３．０×１０5以上、好ましくは３．５×１０5〜７．５×１０5のホモポリプロピレン又はエチレン含有量が１．０重量％以下のエチレンプロピレンランダムコポリマー、エチレンプロピレンブロックコポリマー等を用いることができる。重量平均分子量が３．０×１０5未満では、得られるポリオレフィン微多孔膜の開孔が困難になり、エチレン含有量が１．０重量％を超えるとポリオレフィンの結晶性が低くなり、ポリオレフィン微多孔膜の開孔が困難になる。
【００１０】
ポリプロピレンをポリエチレンまたはそのポリエチレン組成物に加えることにより、ポリオレフィン微多孔膜をリチウム電池等のセパレーターとして用い、電極が短絡して電池内部の温度が上昇した場合は、低温でのシャットダウン機能に加えてメルトダウン温度が高くなり、安全性の高い電池が得られる。
本発明で用いるポリプロピレンの量は、ポリオレフィン全体の５〜３５重量％、好ましくは、１５〜２０重量％である。５重量％未満では、メルトダウン温度の上昇効果はみられず、３５重量％を超えるとポリオレフィン微多孔膜の強度が著しく低下し、さらに多くなるとシート成形時にポリエチレンとポリプロピレンが相分離してしまい、成形が困難になる。
また、本発明のポリオレフィン組成物にはポリオレフィン微多孔膜をリチウム電池等のセパレーターとして用い、電極が短絡して電池内部の温度が上昇した時、低温でシャットダウンする機能を増大させる低密度ポリエチレンや低分子量ポリエチレン等を加えることができる。
【００１１】
本発明のポリオレフィン微多孔膜はポリエチレンにポリプロピレンを加えた樹脂成分に有機液状体または固体を混合し、溶融混練後押出成形し、抽出、延伸を施すことにより得られる。また、樹脂成分および有機液状体または固体の混合物に無機微粉体を添加しても何等差し支えない。本発明のポリオレフィン微多孔膜を得る好ましい方法としては、ポリオレフィン組成物にポリオレフィンの良溶媒を供給しポリオレフィン組成物の溶液を調製して、この溶液を押出機のダイよりシート状に押し出した後、冷却してゲル状組成物を形成して、このゲル状組成物を加熱延伸し、しかる後残存する溶媒を除去する方法である。
【００１２】
本発明において、原料となるポリオレフィン組成物の溶液は、上述のポリオレフィン組成物を、溶媒に加熱溶解することにより調製する。この溶媒としては、ポリオレフィンを十分に溶解できるものであれば特に限定されない。例えば、ノナン、デカン、ウンデカン、ドデカン、流動パラフィンなどの脂肪族または環式の炭化水素、あるいは沸点がこれらに対応する鉱油留分などがあげられるが、溶媒含有量が安定なゲル状成形物を得るためには流動パラフィンのような不揮発性の溶媒が好ましい。加熱溶解は、ポリオレフィンが完全に溶解する温度で強力に撹拌または押出機で混練しながら行う。その温度は、例えば１４０〜２５０℃の範囲が好ましい。またポリオレフィン溶液の濃度は、１０〜５０重量％好ましくは１０〜４０重量％である。濃度が１０重量％未満では、使用する溶媒量が多く経済的でないばかりか、シート状に成形する際に、ダイス出口でスウェルやネックインが大きくシートの成形が困難となる。なお、加熱溶解にあたってはポリオレフィンの酸化を防止するために酸化防止剤を添加するのが好ましい。
【００１３】
次にこのポリオレフィン組成物の加熱溶液を好ましくはダイから押し出して成形する。ダイは、通常長方形の口金形状をしたシートダイが用いられるが、２重円筒状のインフレーションダイなども用いることができる。シートダイを用いた場合のダイギャップは通常０．１〜５ｍｍであり、押し出し成形温度は１４０〜２５０℃である。この際押し出し速度は、通常２０〜３０ｃｍ/分ないし１０ｍ/分である。
【００１４】
このようにしてダイから押し出された溶液は、冷却することによりゲル状シートに成形される。冷却は少なくともゲル化温度以下までは５０℃／分以上の速度で行うのが好ましい。一般に冷却速度が遅いと、得られるゲル状シートの高次構造が粗くなり、それを形成する疑似細胞単位も大きなものとなるが、冷却速度が速いと、密な細胞単位となる。冷却速度が５０℃／分未満では、結晶化度が上昇し、延伸に適したゲル状シートとなりにくい。冷却方法としては、冷風、冷却水、その他の冷却媒体に直接接触させる方法、冷媒で冷却したロールに接触させる方法などを用いることができる。なお、ダイから押し出された溶液は、冷却前あるいは冷却中に好ましくは１〜１０、より好ましくは１〜５の引き取り比で引取ってもよい。引き取り比が１０以上になるとネックインが大きくなり、また延伸時に破断を起こしやすくなり好ましくない。
【００１５】
次に、このゲル状成形物に延伸を行う。延伸はゲル状シートを加熱し、通常のテンター法、ロール法、インフレーション法、圧延法もしくはこれらの方法の組み合わせによって所定の倍率で行う。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。また、二軸延伸の場合は、縦横同時延伸または逐次延伸のいずれでもよい。延伸温度はポリオレフィンの融点＋１０℃以下、好ましくはポリオレフィンの結晶分散温度から結晶融点未満の範囲である。また延伸倍率は原反の厚さによって異なるが、一軸延伸では２倍以上が好ましく、より好ましくは３〜３０倍である。二軸延伸では面倍率で１０倍以上が好ましく、より好ましくは１５〜４００倍である。面倍率が１０倍未満では延伸が不十分で高弾性、高強度の微多孔膜が得られない。一方、面倍率が４００倍を超えると、延伸操作などで制約が生じる。
【００１６】
得られた延伸成形物は、溶剤で洗浄し残留する溶媒を除去する。洗浄溶剤としては、ペンタン、ヘキサン、ヘプタンなどの炭化水素、塩化メチレン、四塩炭素などの塩素化炭化水素、三フッ化エタンなどのフッ化炭化水素、ジエチルエーテル、ジオキサンなどのエーテル類などの易揮発性のものを用いることができる。これらの溶剤はポリオレフィン組成物の溶解に用いた溶媒に応じて適宜選択し、単独もしくは混合して用いる。洗浄方法は、溶剤に浸漬し抽出する方法、溶剤をシャワーする方法、またはこれらの組合せによる方法などにより行うことができる。
【００１７】
上述のような洗浄は、延伸成形物中の残留溶媒が１重量％未満になるまで行う。その後洗浄溶剤を乾燥するが、洗浄溶剤の乾燥方法は加熱乾燥、風乾などの方法で行うことができる。乾燥した延伸成形物は、結晶分散温度〜融点の温度範囲で熱固定することが望ましい。
【００１８】
以上のようにして製造したポリオレフィン微多孔膜は、破断強度が１０００ｋｇ／ｃｍ２以上で、メルトダウン温度は１７５℃以上、シャットダウン温度とメルトダウン温度との差の幅は４０〜４５℃、熱収縮率（１００℃／８時間）が５％以下となり、セパレーターとして用いると、その安全性は向上する。
なお、得られたポリオレフィン微多孔膜は、必要に応じてさらに、プラズマ照射、界面活性剤含浸、表面グラフト等の親水化処理などの表面修飾を施すことができる。
【００１９】
【実施例】
以下に本発明について実施例を挙げてさらに詳細に説明するが、本発明は実施例に特に限定されるものではない。なお、実施例における試験方法は次の通りである。
（１）膜厚：断面を走査型電子顕微鏡により測定。
（２）破断強度：幅１５ｍｍ短冊状試験片の破断強度をＡＳＴＭ Ｄ８８２に準拠して測定。
（３）透気度：ＪＩＳ Ｐ８１１７に準拠して測定。
（４）シャットダウン温度：所定温度に加熱することによって、透気度が１０万ｓｅｃ／１００ｃｃ以上となる温度として測定。
（５）メルトダウン温度：所定温度に加熱することによって、膜が溶けて破膜する温度として測定。
（６）熱収縮率：膜を１００℃の雰囲気下に８時間放置し、ＭＤ方向およびＴＤ方向のそれぞれの長さの変化から求めた。
【００２０】
実施例１
重量平均分子量が２．５×１０6の超高分子量ポリエチレン（ＵＨＭＷＰＥ）２０重量％、３．３×１０5の高密度ポリエチレン（ＨＤＰＥ）６０重量％及び重量平均分子量が５．３×１０5のポリプロピレンが２０重量％からなるポリオレフィン組成物１００重量部に酸化防止剤０．３７５重量部を加えたポリオレフィン組成物を得た。このポリオレフィン組成物３０重量部を二軸押出機（５８mmφ、Ｌ／Ｄ＝４２、強混練タイプ）に投入した。またこの二軸押出機のサイドフィーダーから流動パラフィン７０重量部を供給し、２００ｒｐｍで溶融混練して、押出機中にてポリオレフィン溶液を調製した。
【００２１】
続いて、この押出機の先端に設置されたＴダイから１９０℃で押し出し、冷却ロールで引取りながらゲル状シートを成形した。続いてこのゲル状シートを、１１５℃で５×５に同時２軸延伸を行い、延伸膜を得た。得られた延伸膜を塩化メチレンで洗浄して残留する流動パラフィンを抽出除去した後、乾燥および熱処理を行いポリオレフィン微多孔膜を得た。このポリオレフィン微多孔膜の物性評価の結果を第１表に示す。
【００２２】
実施例２〜３
実施例１において、高密度ポリエチレン及びポリプロピレンの使用量を表１に示す値に変更した以外は、実施例１と同様にして微多孔膜を得た。得られた微多孔膜は表１の物性を有していた。
【００２３】
実施例４
実施例１において、高密度ポリエチレンを用いない以外は、実施例１と同様にして微多孔膜を得た。得られた微多孔膜は表１の物性を有していた。
【００２４】
実施例５〜７
実施例１において、ポリプロピレンの重量平均分子量及びエチレン含有量が表１に示すものを用いる以外は、実施例１と同様にして微多孔膜を得た。得られた微多孔膜は表１の物性を有していた。
【００２５】
比較例１
実施例１において、ポリプロピレンを用いない以外は、実施例１と同様にして微多孔膜を得た。得られた微多孔膜は表２の物性を有していた。
【００２６】
比較例２
実施例１において、高密度ポリエチレン及びポリプロピレンの使用量を表２に示す様に変更した以外は、実施例１と同様にして微多孔膜を得た。得られた微多孔膜は表２の物性を有していた。
【００２７】
比較例３
実施例１において、ポリプロピレンの重量平均分子量が表２に示すものを用いる以外は、実施例１と同様にして微多孔膜を得た。得られた微多孔膜は表２の物性を有していた。
【００２８】
比較例４
実施例１において、ポリプロピレンの重量平均分子量及びエチレン含有量が表２示すものを用いる以外は、実施例１と同様にして微多孔膜を得た。得られた微多孔膜は表２の物性を有していた。
【００２９】
比較例５
ポリエチレンとポリプロピレンを積層した積層微多孔膜の膜物性を表２に示す。
【００３０】
表１及び表２から明らかなように、実施例１〜７に例示されている本発明のポリオレフィン微多孔膜は高破断強度、高メルトダウン温度を有し、シャットダウン温度とメルトダウン温度との差の幅が広くなり、かつ熱収縮率は低く、リチウム電池の電池セパレーターとして使用される場合の安全性が高い。
【００３１】
【表１】
【表２】
【発明の効果】
本発明のポリオレフィン微多孔膜は、高強度かつ高メルトダウン特性を有しており、シャットダウン温度とメルトダウン温度との差の幅が広くなり、さらに低熱収縮率であることから安全性が高く、リチウム電池用セパレーターとして用いる場合は安全性の点でおおいに信頼できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polyolefin microporous membrane, and more particularly relates to a polyolefin microporous membrane that is used in battery separators and the like and has excellent permeability and mechanical strength and has an excellent function of melt fracture temperature. Is.
[0002]
[Prior art]
Microporous membranes are used in various separation membranes, battery separators, electrolytic capacitor separators, and the like. Particularly in lithium batteries, since a lithium metal and lithium ions are used, an aprotic polar organic solvent is used as an electrolyte solvent, and a lithium salt is used as an electrolyte. Therefore, the separator installed between the positive electrode and the negative electrode is made by processing a polyolefin-based material such as polyethylene or polypropylene that is insoluble in an organic solvent and stable to an electrolyte or an electrode active material into a microporous film or a nonwoven fabric. Used as a separator.
[0003]
Recently, high-strength and high-elasticity microporous membranes have been developed using ultra-high molecular weight polyolefins. For example, a gel-like sheet is formed from a solution obtained by heating and dissolving an ultra-high molecular weight polyolefin having a weight average molecular weight of 7 × 10 5 or more in a solvent, and the solvent amount in the gel-like sheet is adjusted by a desolvation treatment, and then heated There has been proposed a method for producing a microporous membrane by removing the residual solvent after stretching (Japanese Patent Laid-Open No. 60-242035). Further, as a method for producing a polyolefin microporous membrane from a high-concentration solution of ultra-high molecular weight polyolefin, there has been proposed a method in which the molecular weight distribution of a polyolefin composition containing ultra-high molecular weight polyolefin is set to a specific value (Japanese Patent Laid-open No. Hei 3- 64334).
[0004]
By the way, when the polyolefin microporous membrane is used for a battery, for example, a lithium battery separator, it is necessary to prevent an accident such as ignition from occurring when the electrode is short-circuited and the temperature inside the battery is increased. For this reason, in addition to the function of melting before lithium ignition and clogging its holes and shutting down the current, when the temperature further rises after shutdown, the separator itself melts and breaks (melts down). Since there is a risk of ignition and explosion, it is desired to increase the meltdown temperature. In addition, it is considered that the larger the difference between the shutdown temperature and the meltdown temperature, the better the high temperature characteristics and the higher the safety of the battery separator. For example, in Japanese Patent Application Laid-Open No. 63-308866 and Japanese Patent Application Laid-Open No. 2-77108, a single film made of low melting point polyethylene and high melting point polypropylene is laminated to have high strength and excellent high temperature characteristics. Although a method for obtaining a microporous porous membrane has been disclosed, because of the lamination, the electrical resistance of the separator becomes high, making it unsuitable as a separator for high-performance batteries. Furthermore, in Japanese Patent Application Laid-Open No. 2-77108, since a technique called lamination extrusion is used, the productivity is inferior in terms of the complexity of the manufacturing process and the manufacturing cost.
[0005]
[Problems to be solved by the invention]
Therefore, the object of the present invention is excellent in permeation performance and mechanical strength, has a shutdown temperature at a low temperature and a high meltdown temperature, has a wide range of differences between the meltdown temperature and the shutdown temperature, and has a high heat shrinkage rate. It is to provide a low polyolefin microporous membrane.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention adds a specific polypropylene to ultrahigh molecular weight polyethylene or a composition thereof, thereby improving the permeation performance and mechanical strength, increasing the meltdown temperature, and further reducing the shutdown temperature and the melt temperature. The inventors have found that a microporous film having a large down temperature range and a low thermal shrinkage rate can be obtained, and the present invention has been conceived.
[0007]
That is, the present invention relates to polyethylene having a weight average molecular weight of 5 × 10 5 or more or 65 to 95% by weight of the polyethylene composition, and polypropylene having a weight average molecular weight of 3 × 10 5 or more and an ethylene content of 1.0% by weight or less. A polyolefin microporous membrane comprising a composition containing 5 to 35% by weight, wherein the polyethylene or the polyethylene composition having a weight average molecular weight of 5 × 10 5 or more has a molecular weight distribution of 5 to 50, and the microporous A polyolefin microporous membrane having a membrane breaking strength of 1000 kg / cm 2 or more and a heat shrinkage (100 ° C./8 hours) of 5% or less is provided. This polyolefin microporous membrane has a polyethylene having a weight average molecular weight of 5 × 10 5 or more or 65 to 95% by weight of the polyethylene composition, a weight average molecular weight of 3 × 10 5 or more and an ethylene content of 1.0% by weight or less. Preparing a solution comprising 10 to 50% by weight of a composition containing 5 to 35% by weight of polypropylene and 50 to 90% by weight of a solvent, extruding the solution from a die, and cooling to form a gel-like composition; The gel composition is preferably produced by stretching at a temperature not higher than the melting point of the polyethylene composition + 10 ° C. and then removing the residual solvent.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The polyethylene used in the present invention is an ultra high molecular weight polyethylene having a weight average molecular weight of 5 × 10 5 or more, preferably 1 × 10 6 to 15 × 10 6 . When the weight average molecular weight is less than 5 × 10 5 , the maximum stretching ratio is low in the stretching step during the production of the microporous membrane, and the desired microporous membrane cannot be obtained. On the other hand, although the upper limit is not particularly limited, those exceeding 15 × 10 6 are inferior in moldability in the formation of a gel-like molded product during production of the microporous membrane. In the present invention, in order to increase the concentration of the polyolefin solution described later and improve the strength of the microporous membrane, the ultrahigh molecular weight polyethylene having a weight average molecular weight of 1 × 10 6 or more and the weight average molecular weight of 1 × 10 5 or more are used. Compositions with high density polyethylene of less than 5 × 10 5 can be used. The content of the ultrahigh molecular weight polyethylene in the polyethylene composition is preferably 1% by weight or more, more preferably 10 to 70% by weight, based on 100% by weight of the entire polyethylene composition. Furthermore the weight average molecular weight / number-average molecular weight used as a measure of the molecular weight distribution of the polyethylene or polyethylene composition is 5-50.
[0009]
The polypropylene used in the present invention has a weight average molecular weight of 3.0 × 10 5 or more, preferably 3.5 × 10 5 to 7.5 × 10 5 homopolypropylene or ethylene content of 1.0% by weight or less. An ethylene propylene random copolymer, an ethylene propylene block copolymer, etc. can be used. When the weight average molecular weight is less than 3.0 × 10 5 , it becomes difficult to open the resulting polyolefin microporous membrane. When the ethylene content exceeds 1.0% by weight, the crystallinity of the polyolefin decreases, and the polyolefin microporous Membrane opening becomes difficult.
[0010]
When polypropylene is added to polyethylene or its polyethylene composition, the polyolefin microporous membrane is used as a separator for lithium batteries, etc., and when the electrode is short-circuited and the temperature inside the battery rises, in addition to the shutdown function at low temperature, The down temperature increases and a battery with high safety can be obtained.
The amount of polypropylene used in the present invention is 5 to 35% by weight, preferably 15 to 20% by weight, based on the whole polyolefin. If it is less than 5% by weight, the effect of increasing the meltdown temperature is not observed, and if it exceeds 35% by weight, the strength of the polyolefin microporous film is remarkably reduced, and if it is further increased, polyethylene and polypropylene are phase-separated during sheet molding, Molding becomes difficult.
In the polyolefin composition of the present invention, a polyolefin microporous membrane is used as a separator for lithium batteries, etc., and when the electrode is short-circuited and the temperature inside the battery rises, low density polyethylene or low Molecular weight polyethylene or the like can be added.
[0011]
The polyolefin microporous membrane of the present invention is obtained by mixing an organic liquid or solid with a resin component obtained by adding polypropylene to polyethylene, followed by melt-kneading, extrusion molding, extraction, and stretching. Moreover, there is no problem even if inorganic fine powder is added to the resin component and the organic liquid or solid mixture. As a preferred method of obtaining the polyolefin microporous membrane of the present invention, a polyolefin good solvent is supplied to the polyolefin composition to prepare a solution of the polyolefin composition, and this solution is extruded into a sheet form from a die of an extruder. This is a method of cooling to form a gel composition, heating and stretching the gel composition, and then removing the remaining solvent.
[0012]
In the present invention, a solution of a polyolefin composition as a raw material is prepared by dissolving the above-described polyolefin composition in a solvent by heating. The solvent is not particularly limited as long as it can sufficiently dissolve the polyolefin. For example, aliphatic or cyclic hydrocarbons such as nonane, decane, undecane, dodecane, liquid paraffin, or mineral oil fractions with boiling points corresponding to these, but gel-like molded products with a stable solvent content can be used. Nonvolatile solvents such as liquid paraffin are preferred for obtaining. The dissolution by heating is performed while vigorously stirring or kneading with an extruder at a temperature at which the polyolefin is completely dissolved. The temperature is preferably in the range of 140 to 250 ° C, for example. The concentration of the polyolefin solution is 10 to 50% by weight, preferably 10 to 40% by weight. If the concentration is less than 10% by weight, the amount of solvent used is large and not economical, and when forming into a sheet, swell and neck-in are large at the die outlet, making it difficult to form the sheet. In addition, it is preferable to add an antioxidant in order to prevent the polyolefin from being oxidized upon heating and dissolving.
[0013]
Next, the heated solution of the polyolefin composition is preferably extruded from a die. As the die, a sheet die having a rectangular base shape is usually used, but a double cylindrical inflation die or the like can also be used. When a sheet die is used, the die gap is usually 0.1 to 5 mm, and the extrusion temperature is 140 to 250 ° C. At this time, the extrusion speed is usually 20 to 30 cm / min to 10 m / min.
[0014]
The solution thus extruded from the die is formed into a gel-like sheet by cooling. Cooling is preferably performed at a rate of 50 ° C./min or more at least up to the gelation temperature or less. In general, if the cooling rate is slow, the higher order structure of the resulting gel-like sheet becomes coarse, and the pseudo cell unit forming the gel sheet becomes large, but if the cooling rate is fast, the cell unit becomes a dense cell unit. When the cooling rate is less than 50 ° C./min, the degree of crystallinity increases and it is difficult to obtain a gel-like sheet suitable for stretching. As a cooling method, a method of directly contacting cold air, cooling water, or another cooling medium, a method of contacting a roll cooled by a refrigerant, or the like can be used. The solution extruded from the die may be taken out at a take-up ratio of preferably 1 to 10, more preferably 1 to 5, before or during cooling. When the take-up ratio is 10 or more, the neck-in becomes large, and breakage tends to occur during stretching, which is not preferable.
[0015]
Next, the gel-like molded product is stretched. Stretching is performed at a predetermined magnification by heating the gel-like sheet and using a normal tenter method, roll method, inflation method, rolling method, or a combination of these methods. The stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferred. In the case of biaxial stretching, either longitudinal or transverse simultaneous stretching or sequential stretching may be used. The stretching temperature is the melting point of the polyolefin + 10 ° C. or less, preferably in the range from the crystal dispersion temperature of the polyolefin to less than the crystal melting point. Moreover, although a draw ratio changes with thickness of an original fabric, in uniaxial stretching, 2 times or more are preferable, More preferably, it is 3 to 30 times. In biaxial stretching, the surface magnification is preferably 10 times or more, more preferably 15 to 400 times. If the surface magnification is less than 10 times, stretching is insufficient and a highly elastic, high-strength microporous film cannot be obtained. On the other hand, when the surface magnification exceeds 400 times, a restriction occurs in a stretching operation or the like.
[0016]
The obtained stretched molded product is washed with a solvent to remove the remaining solvent. Cleaning solvents include hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and tetrasalt carbon, fluorinated hydrocarbons such as ethane trifluoride, and ethers such as diethyl ether and dioxane. Volatile ones can be used. These solvents are appropriately selected according to the solvent used for dissolving the polyolefin composition, and used alone or in combination. The cleaning method can be performed by a method of immersing and extracting in a solvent, a method of showering a solvent, or a method using a combination thereof.
[0017]
Washing as described above is performed until the residual solvent in the stretched molded product is less than 1% by weight. Thereafter, the cleaning solvent is dried. The cleaning solvent can be dried by heat drying, air drying, or the like. The dried stretched molded product is preferably heat-set within the temperature range of the crystal dispersion temperature to the melting point.
[0018]
The polyolefin microporous membrane produced as described above has a breaking strength of 1000 kg / cm 2 or more, a meltdown temperature of 175 ° C or more, a difference between the shutdown temperature and the meltdown temperature of 40 to 45 ° C, and heat shrinkage. The rate (100 ° C./8 hours) is 5% or less, and when used as a separator, its safety is improved.
In addition, the obtained polyolefin microporous film can be further subjected to surface modification such as plasma irradiation, surfactant impregnation, and hydrophilic treatment such as surface grafting.
[0019]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not particularly limited to the examples. In addition, the test method in an Example is as follows.
(1) Film thickness: The cross section was measured with a scanning electron microscope.
(2) Breaking strength: The breaking strength of a strip-shaped test piece having a width of 15 mm was measured according to ASTM D882.
(3) Air permeability: Measured according to JIS P8117.
(4) Shutdown temperature: measured as a temperature at which the air permeability becomes 100,000 sec / 100 cc or more by heating to a predetermined temperature.
(5) Meltdown temperature: measured as the temperature at which the film melts and breaks when heated to a predetermined temperature.
(6) Thermal contraction rate: The film was allowed to stand in an atmosphere of 100 ° C. for 8 hours, and obtained from changes in length in the MD direction and the TD direction.
[0020]
Example 1
20% by weight of ultra high molecular weight polyethylene (UHMWPE) with a weight average molecular weight of 2.5 × 10 6 , 60% by weight of high density polyethylene (HDPE) with 3.3 × 10 5 and a weight average molecular weight of 5.3 × 10 5 A polyolefin composition was obtained by adding 0.375 parts by weight of an antioxidant to 100 parts by weight of a polyolefin composition comprising 20% by weight of polypropylene. 30 parts by weight of this polyolefin composition was charged into a twin screw extruder (58 mmφ, L / D = 42, strong kneading type). Further, 70 parts by weight of liquid paraffin was supplied from the side feeder of this twin screw extruder, and melt kneaded at 200 rpm to prepare a polyolefin solution in the extruder.
[0021]
Subsequently, a gel-like sheet was formed while being extruded at 190 ° C. from a T die installed at the tip of the extruder and being taken up by a cooling roll. Subsequently, this gel-like sheet was subjected to simultaneous biaxial stretching at 115 ° C. in 5 × 5 to obtain a stretched film. The obtained stretched membrane was washed with methylene chloride to extract and remove the remaining liquid paraffin, followed by drying and heat treatment to obtain a polyolefin microporous membrane. The results of the physical property evaluation of this polyolefin microporous membrane are shown in Table 1.
[0022]
Examples 2-3
In Example 1, a microporous membrane was obtained in the same manner as in Example 1 except that the usage amounts of high-density polyethylene and polypropylene were changed to the values shown in Table 1. The obtained microporous membrane had the physical properties shown in Table 1.
[0023]
Example 4
In Example 1, a microporous film was obtained in the same manner as in Example 1 except that high-density polyethylene was not used. The obtained microporous membrane had the physical properties shown in Table 1.
[0024]
Examples 5-7
In Example 1, a microporous membrane was obtained in the same manner as in Example 1 except that polypropylene having a weight average molecular weight and an ethylene content shown in Table 1 was used. The obtained microporous membrane had the physical properties shown in Table 1.
[0025]
Comparative Example 1
In Example 1, a microporous membrane was obtained in the same manner as in Example 1 except that polypropylene was not used. The obtained microporous membrane had the physical properties shown in Table 2.
[0026]
Comparative Example 2
A microporous membrane was obtained in the same manner as in Example 1, except that the amounts of high-density polyethylene and polypropylene used were changed as shown in Table 2. The obtained microporous membrane had the physical properties shown in Table 2.
[0027]
Comparative Example 3
In Example 1, a microporous membrane was obtained in the same manner as in Example 1 except that polypropylene having a weight average molecular weight shown in Table 2 was used. The obtained microporous membrane had the physical properties shown in Table 2.
[0028]
Comparative Example 4
In Example 1, a microporous membrane was obtained in the same manner as in Example 1 except that polypropylene having a weight average molecular weight and an ethylene content shown in Table 2 was used. The obtained microporous membrane had the physical properties shown in Table 2.
[0029]
Comparative Example 5
Table 2 shows the film physical properties of the laminated microporous film in which polyethylene and polypropylene are laminated.
[0030]
As is apparent from Tables 1 and 2, the polyolefin microporous membranes of the present invention exemplified in Examples 1 to 7 have a high breaking strength and a high meltdown temperature, and the difference between the shutdown temperature and the meltdown temperature. And the heat shrinkage rate is low, and the safety when used as a battery separator of a lithium battery is high.
[0031]
[Table 1]
[Table 2]
【The invention's effect】
The polyolefin microporous membrane of the present invention has high strength and high meltdown characteristics, and the width of the difference between the shutdown temperature and the meltdown temperature is widened. When used as a lithium battery separator, it is very reliable in terms of safety.
Claims (4)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12025597A JP3699561B2 (en) | 1997-04-23 | 1997-04-23 | Polyolefin microporous membrane and method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12025597A JP3699561B2 (en) | 1997-04-23 | 1997-04-23 | Polyolefin microporous membrane and method for producing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH10298324A JPH10298324A (en) | 1998-11-10 |
| JP3699561B2 true JP3699561B2 (en) | 2005-09-28 |
Family
ID=14781680
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP12025597A Expired - Lifetime JP3699561B2 (en) | 1997-04-23 | 1997-04-23 | Polyolefin microporous membrane and method for producing the same |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3699561B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009123015A1 (en) | 2008-03-31 | 2009-10-08 | 旭化成イーマテリアルズ株式会社 | Polyolefin microporous membrane and products of winding |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4812919B2 (en) * | 1999-09-24 | 2011-11-09 | 日本板硝子株式会社 | Non-aqueous electrolyte battery separator |
| JP4927243B2 (en) * | 2000-01-13 | 2012-05-09 | 東レバッテリーセパレータフィルム合同会社 | Polyolefin microporous membrane |
| KR100557380B1 (en) * | 2001-05-17 | 2006-03-06 | 아사히 가세이 케미칼즈 가부시키가이샤 | Microporous Polyolefin Film |
| JP4943599B2 (en) * | 2001-08-09 | 2012-05-30 | セイコーエプソン株式会社 | Resin filter for inkjet recording equipment |
| JP2004303475A (en) * | 2003-03-28 | 2004-10-28 | Sanyo Electric Co Ltd | Nonaqueous electrolyte battery |
| WO2007015416A1 (en) | 2005-08-03 | 2007-02-08 | Asahi Kasei Chemicals Corporation | Polyolefin microporous film |
| US8338017B2 (en) | 2007-10-12 | 2012-12-25 | Toray Battery Separator Film Co., Ltd. | Microporous membrane and manufacturing method |
| JP5183435B2 (en) * | 2008-11-21 | 2013-04-17 | 日立マクセル株式会社 | Battery separator and lithium secondary battery |
| JP5942145B2 (en) * | 2012-05-09 | 2016-06-29 | 旭化成株式会社 | Polyolefin microporous membrane and method for producing the same |
| CN108026376B (en) | 2015-09-28 | 2021-04-09 | 日本瑞翁株式会社 | Microporous membrane, separator, and secondary battery |
| CN114128028A (en) * | 2019-07-30 | 2022-03-01 | 株式会社Lg化学 | Composite separator for electrochemical device and electrochemical device comprising the same |
-
1997
- 1997-04-23 JP JP12025597A patent/JP3699561B2/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009123015A1 (en) | 2008-03-31 | 2009-10-08 | 旭化成イーマテリアルズ株式会社 | Polyolefin microporous membrane and products of winding |
| CN101983219B (en) * | 2008-03-31 | 2014-03-12 | 旭化成电子材料株式会社 | Polyolefin microporous membrane and products of winding |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH10298324A (en) | 1998-11-10 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| KR100667052B1 (en) | Microporous Polyolefin Membrane And Method For Producing The Same | |
| JP4927243B2 (en) | Polyolefin microporous membrane | |
| JP5497635B2 (en) | Polyolefin microporous membrane, method for producing the same, battery separator and battery | |
| JP3699562B2 (en) | Polyolefin microporous membrane and method for producing the same | |
| JP4280381B2 (en) | Polyolefin microporous membrane and method for producing the same | |
| KR20080027233A (en) | Method for producing polyolefin microporous membrane | |
| WO2006106783A1 (en) | Microporous polyolefin film and process for producing the same | |
| JP4677663B2 (en) | Polyolefin microporous membrane | |
| JP2003103626A (en) | Polyolefin microporous film and method for manufacturing the same | |
| JP4817567B2 (en) | Polyolefin microporous membrane and method for producing the same | |
| JP3699561B2 (en) | Polyolefin microporous membrane and method for producing the same | |
| JP3549290B2 (en) | Polyolefin microporous membrane and method for producing the same | |
| KR101354708B1 (en) | Method of manufacturing a multi-component separator film with ultra high molecule weight polyethylene for lithium secondary battery and a multi-component separator film for lithium secondary battery therefrom | |
| JPWO2019163935A1 (en) | Porous polyolefin film | |
| JP3682120B2 (en) | Composite membrane for battery separator and battery separator | |
| JPH11269290A (en) | Polyoelfin fine porous membrane | |
| JP2003105122A (en) | Polyolefin minute porous film and method of its manufacture | |
| JP4008516B2 (en) | Polyolefin porous membrane, method for producing the same, and battery separator using the same | |
| JP4280371B2 (en) | Polyolefin microporous membrane and method for producing the same | |
| JP3989081B2 (en) | Polyethylene microporous membrane | |
| JP4374105B2 (en) | Multilayer composite film | |
| JP2003105121A (en) | Polyolefin minute porous film and method of its manufacture | |
| JP2001200082A (en) | Polyethylene microporous membrane and its manufacturing method | |
| JP3252016B2 (en) | Method for producing polyolefin microporous membrane | |
| JP4682347B2 (en) | Method for producing polyolefin microporous membrane |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20040621 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20040713 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20040902 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20050125 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20050218 |
|
| TRDD | Decision of grant or rejection written | ||
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20050621 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20050708 |
|
| R150 | Certificate of patent or registration of utility model |
Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20080715 Year of fee payment: 3 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20090715 Year of fee payment: 4 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20090715 Year of fee payment: 4 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20100715 Year of fee payment: 5 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20110715 Year of fee payment: 6 |
|
| S111 | Request for change of ownership or part of ownership |
Free format text: JAPANESE INTERMEDIATE CODE: R313113 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20110715 Year of fee payment: 6 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20110715 Year of fee payment: 6 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120715 Year of fee payment: 7 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120715 Year of fee payment: 7 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130715 Year of fee payment: 8 |
|
| S533 | Written request for registration of change of name |
Free format text: JAPANESE INTERMEDIATE CODE: R313533 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130715 Year of fee payment: 8 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |
|
| R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |
|
| R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |
|
| R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |
|
| R250 | Receipt of annual fees |
Free format text: JAPANESE INTERMEDIATE CODE: R250 |
|
| EXPY | Cancellation because of completion of term |