JP4302834B2 - Totally aromatic polyamide porous membrane and method for producing the same - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、全芳香族ポリアミド多孔膜及びその全芳香族ポリアミド多孔膜を製造する方法に関する。更に詳細には、本発明は、全芳香族ポリアミドからなる、高強度、高耐熱性でかつ物質透過性の高い新規な多孔膜並びにその多孔膜を工業的に安定して製造する方法に関する。
【０００２】
【従来の技術】
近年、高分子重合体からなる多孔質膜は、分離ろ過用のフィルター、低強度フィルムや構造体用の支持膜、電気二重層キャパシター、電池用セパレーター等に使用されている。このような高分子多孔膜としては、例えば、特開平３−６４３３４号公報等に記載されているようにポリエチレン、ポリプロピレンに代表わされるポリオレフィン多孔膜があり、また、特公昭５４−３４７９０号公報、特開昭５８−１７９２４３号公報、特開昭５８−２１０９３４号公報に記載されているようなポリエステル多孔膜等がある。
【０００３】
しかし、このような従来の高分子多孔膜は、耐熱性、機械的強度が要求される用途では使用が難しい。例えば、近年ではポリエチレン多孔膜がリチウムイオン二次電池のセパレータ等に用いられているが、リチウムイオン二次電池では可燃性の有機溶媒を電解液に使用している関係で、非常に安全性が重要であるにもかかわらず、特に外部短絡等による異常昇温時に、容易に溶融してしまい、電池内部で更に電極短絡してしまうという問題がある。また、高温溶液のろ過等では、たとえ多孔膜が溶融する温度以下であっても、多孔膜の機械強度が急激に低下してしまい、破断し易くなる。
【０００４】
また、特開平６−２６３９０４号公報、特開平６−２６３９０６号公報等に記載されているように、脂肪族ポリアミド、半芳香族ポリアミドの多孔膜が提案されているが、これらも必ずしも十分な機械強度、耐熱性があるわけではなく、その用途が限定されている。
【０００５】
一方、全芳香族ポリアミドにおいては、機械強度が高く、耐熱性に優れているという特性を有するため、既に、全芳香族ポリアミドの繊維はこのような機械強度、耐熱性が要求される繊維用途で利用されている。更に、高強度の耐熱性フィルムとして、全芳香族ポリアミドフィルムが「繊維学会誌」Ｖｏｌ．４８，Ｎｏ．１（１９９２）４３−４８で提案されている。
【０００６】
また、特開平５−２９０８２２号公報、特開平５−３３５００５号公報、特開平７−３７５７１号公報では、全芳香族ポリアミド繊維を用いた不織布が耐熱性の観点から提案されている。しかしながら、より高度な市場要求とされる薄さに関しては、このような不織布では機械的強度を保つために厚みを１００μｍ程度より薄くすることは難しい。単純に不織布を加圧プレスして機械強度を保ったまま厚みを下げることは可能であるが、その場合、不織布の空隙率が低下するため、ガス、液体等の透過度が低下してしまう。また、不織布表面はいわゆる多孔膜に比べて不均一で、微視的には場所によりガス、液体等の透過度に大きな差が生じる場合がある。
【０００７】
ところで、全芳香族ポリアミドは、その高い耐熱性のため溶融押出製膜技術を用いた製膜が困難である。そのため、膜（フィルム）状物は、溶液流延法によって製膜されるのが一般的である。そこで、膜厚が薄い全芳香族ポリアミド多孔膜についても、次のような製造法が提案されている。
【０００８】
すなわち、特公昭５９−１４４９４号公報には、全芳香族ポリアミド溶液を基板上に流延し、０℃以下の温度で冷却固化した後、引き続きその近傍の温度で溶媒を抽出するという技術が紹介されている。しかしながら、この場合、冷却温度によって形成される膜の空孔形状が異なる、あるいは、冷却温度が十分に制御されていても溶液流延した時の溶液膜厚の変動により空孔形状にバラツキが生じる、という問題があり、実際の製造工程では均一な空孔形状の多孔膜を製膜するのが難しい。また、特公昭５９−３６９３９号公報、特開昭５３−１４４９７４号公報、特公昭６１−５１９２８号公報、特開昭５９−５９２１３号公報、特公平４−１２１７１号公報、特開平２−２２２４３０号公報、特開平１０−６４５３号公報等には、全芳香族ポリアミド溶媒溶液を溶液流延後凝固浴中に浸漬することで全芳香族ポリアミド多孔質膜を製膜するという、いわゆる湿式凝固製膜法が記載されている。しかし、この場合も、「繊維学会誌」Ｖｏｌ．４８，Ｎｏ．２（１９９２）４９−６７で報告されているように、膜厚方向で空孔の形状が異なったり、多孔膜表面に皮膜層が形成されたり、凝固条件の変動で空孔形状が異なってしまう場合がある。
【０００９】
このように単純な湿式凝固製膜法では、空孔形状が均一な全芳香族ポリアミド多孔膜を形成するのが難しい。そこで本発明者らは、先に、全芳香族ポリアミドと、該全芳香族ポリアミドを溶解する溶媒とからなる溶液に、この溶媒に溶解しない微粒子を分散させた混合溶液を用い、これから溶液流延乾燥法又は湿式製膜法で製膜した後、該微粒子を溶解除去することにより多孔膜化するという方法を提案した（特願平１０−２９６６３４号）。この方法によれば、全芳香族ポリアミドの多孔膜が安定かつ効率的に製造できるが、一段と高度な性能を要求される分野に使用できるよう、更に高品質の多孔膜が求められている。
【００１０】
【発明が解決しようとする課題】
本発明は、このように単純な湿式凝固製膜法では空孔形状が均一なものを形成するのが難しい全芳香族ポリアミド多孔膜について、先の特願平１０−２９６６３４号で提案した方法を改善し、高耐熱性、高強度でかつ物質透過性の良好な全芳香族ポリアミド多孔膜及びその製造方法を提供することを目的とする。更に本発明は、特に薄い全芳香族ポリアミド多孔膜が要求される耐熱性分離ろ過膜、電池用セパレーター等に好適に利用することができる新規な全芳香族ポリアミド多孔膜及びその製造方法を提供することを目的とする。
【００１１】
【課題を解決するための手段】
本発明の新規な多孔膜は、金属酸化物微粒子を分散した全芳香族ポリアミド溶液を製膜した金属酸化物微粒子分散膜から該微粒子を溶解除去して形成した実質的に全芳香族ポリアミドからなる多孔膜であって、マクミラン数が１より大きく４０以下であり、かつ１００℃における引張弾性率が１００ｋｇｆ／ｍｍ2以上であって、更に多孔膜に残存する金属酸化物の量が該金属酸化物を構成する金属元素の組成比で溶解除去処理前の１％以下であることを特徴とする全芳香族ポリアミド多孔膜に係るものである。
【００１２】
本発明では、このような全芳香族ポリアミド多孔膜に関し、次の各発明も包含する。
１）前記全芳香族ポリアミドが下記式（１）で表わされるくり返し単位から実質的になることを特徴とする全芳香族ポリアミド多孔膜。
【００１３】
【化４】
−ＮＲ1−Ａｒ1−ＮＲ2−ＣＯ−Ａｒ2−ＣＯ− （１）
（ここで、Ｒ1及びＲ2は、同一もしくは相異なり、水素原子、ハロゲン原子及び炭素数５以下のアルキル基からなる群から選ばれ、Ａｒ1及びＡｒ2は、同一もしくは相異なり、置換基を有してもよいオルトフェニレン基、メタフェニレン基、パラフェニレン基、１，４ナフチレン基、１，５ナフチレン基、２，６ナフチレン基、２，５ピリジレン基及び下記式（２）で示される２価の基から選択される。）
【００１４】
【化５】
（ここで、Ｘはエーテル基、スルフィド基、メチレン基、カルボニル基及びスルフォニル基からなる群から選ばれる。）
２）前記全芳香族ポリアミドが、上記式（１）で表わされる繰り返し単位中のＡｒ1及びＡｒ2の合計量の少なくとも７．５モル％以上が下記式（３）で表わされる全芳香族ポリアミド多孔膜である。
【００１６】
【化６】
そして、この本発明の全芳香族ポリアミド多孔膜は、特に薄さと耐熱性と大きな強度を併せもつ高分子多孔膜が要求される耐熱性分離ろ過膜、電池用セパレーター等に好適に利用することができるものである。
【００１８】
また、本発明の製造方法は、全芳香族ポリアミド溶液中に、該溶液を構成する溶媒には不溶又は難溶性の金属酸化物微粒子が分散している全芳香族ポリアミド溶液から製膜した金属酸化物微粒子分散全芳香族ポリアミド膜を、該全芳香族ポリアミドを溶解せずかつ該金属酸化物微粒子を溶解し得る液からなる浴中に浸漬し、該金属酸化物微粒子を溶解除去した後、洗浄することによって、マクミラン数が１より大きく４０以下で、１００℃における引張弾性率が１００ｋｇｆ／ｍｍ2以上であり、かつ、金属酸化物の残存量が該金属酸化物を構成する金属元素の組成比で１％以下である全芳香族ポリアミド多孔膜の製造方法に係るものである。
【００１９】
この製造方法の発明に関し、次の各発明も本発明に包含される。
１）前記金属酸化物微粒子が、酸化銅（I）、酸化銅（II）、酸化インジウム、酸化マグネシウム、酸化ニッケル、酸化錫（II）、酸化亜鉛からなる微粒子の１種又は２種以上である全芳香族ポリアミド多孔膜の製造方法。
２）前記金属酸化物微粒子の平均粒子径が、製膜した微粒子分散膜の厚さの１／５０〜１／５の範囲にある全芳香族ポリアミド多孔膜の製造方法。
３）前記金属酸化物微粒子分散溶液中の固形分の内、全芳香族ポリアミドの割合が１０〜７０容量％である全芳香族ポリアミド多孔膜の製造方法。
４）前記金属酸化物微粒子を溶解しうる浸漬浴液が、５規定以下の濃度のアルカリ水溶液あるいは５規定以下の濃度の酸水溶液である全芳香族ポリアミド多孔膜の製造方法。
５）前記全芳香族ポリアミドの金属酸化物微粒子分散溶液から、流延乾燥工程と湿式凝固工程とをこの順で実施することで製膜する全芳香族ポリアミド多孔膜の製造方法。
６）前記全芳香族ポリアミド多孔膜を、前記金属酸化物微粒子を溶解除去する工程の前又は後に、少なくとも一方向に１．２倍以上延伸する全芳香族ポリアミド多孔膜の製造方法。
７）前記微粒子溶解除去処理及び洗浄処理により、多孔膜中の金属酸化物の量を、製膜直後に比べ、金属酸化物を構成する金属元素の組成比で除去処理前の１％以下に低下させる全芳香族ポリアミド多孔膜の製造方法。
【００２０】
上記の如き本発明の方法によれば、特に薄い耐熱性で強度の大きな高分子多孔膜が要求される耐熱性分離ろ過膜、電池用セパレーター等に好適に有用な全芳香族ポリアミド多孔膜を安定的に製造することが可能となる。
【００２１】
【発明の実施の形態】
本発明の多孔膜を構成する全芳香族ポリアミドは、下記式（１）の繰り返し単位を有するポリアミドである。
【００２２】
【化７】
−ＮＲ1−Ａｒ1−ＮＲ2−ＣＯ−Ａｒ2−ＣＯ− （１）
【００２３】
上記式（１）において、Ｒ1及びＲ2は、同一もしくは相異なり、水素原子、ハロゲン原子及び炭素数５以下のアルキル基からなる群から選ばれるものであり、Ａｒ1及びＡｒ2は、同一もしくは相異なり、オルトフェニレン基、メタフェニレン基、パラフェニレン基、１，４ナフチレン基、１，５ナフチレン基、２，６ナフチレン基、２，５ピリジレン基及び下記式（２）で示される２価の基から選択される２価の有機基である。なお、これらの基の芳香核を構成する水素原子の一部又は全部がハロゲン原子もしくは低級アルキル基で置換されていてもよい。
【００２４】
【化８】
上記式（２）において、Ｘは、エーテル基、スルフィド基、メチレン基、カルボニル基又はスルフォニル基を示す。
【００２６】
本発明で用いる全芳香族ポリアミドは、上記繰り返し単位の複数の組み合わせからなるもの、すなわち共重合されたものでもよい。
【００２７】
上記のような全芳香族ポリアミドのうち、本発明で使用できる全芳香族ポリアミドとしては、揮発乾燥できる溶媒あるいは溶液抽出できる溶媒に可溶な全芳香族ポリアミドであればよく、その種類は特に限定されない。そのような全芳香族ポリアミドには、オルト配向全芳香族ポリアミド、メタ配向全芳香族ポリアミド、パラ配向全芳香族ポリアミド、メタパラ配向全芳香族ポリアミドが含まれる。しかしながら、多孔膜として望まれる機械的強度の観点からは、この中でもパラ配向芳香族ポリアミドを主成分とする全芳香族ポリアミドの方がより好ましい。
【００２８】
このようなパラ配向全芳香族ポリアミドには、ポリ（パラフェニレンテレフタルアミド）に代表わされるような完全パラ配向全芳香族ポリアミドも包含される。しかしながら、溶液調製の容易性、溶液安定性、耐薬品性、かつ、機械強度が高いという観点から上記式（１）の繰り返し単位中のＡｒ1、Ａｒ2の合計量の少なくとも７．５モル％以上、特に７．５〜５０モル％、が下記式（３）で表わされるパラ配向全芳香族ポリアミドであることが、本発明では好ましい。
【００２９】
【化９】
特に、Ａｒ1はパラフェニレン基と上記式（３）の基との組み合わせ（Ａｒ１とＡｒ２の合計量に対し、上記式（３）の基は１５モル％以上５０モル％以下）であり、Ａｒ2はパラフェニレン基であることが更に好ましい。
【００３１】
全芳香族ポリアミドはフィルム形成能を有し、その重合度は、全芳香族ポリアミド多孔膜の機械的強度を十分に発現するために、高いものが好ましい。具体的には、０．５ｇ／１００ｍｌの濃度で３０℃で測定した対数粘度で１．０以上が好ましく、更に１．７以上がより好ましい。
【００３２】
本発明に係る多孔膜は、主たる構成成分が全芳香族ポリアミドであれば、必要に応じて、それ以外の有機、無機の充填剤、添加剤等を含んでもよい。
【００３３】
この多孔膜は、実質的に連通した微細孔を有し、その透過性は、マクミラン数が１より大きく４０以下であり、更に１００℃における引張弾性率が１００ｋｇｆ／ｍｍ2という耐熱性と強度を有し、かつ、多孔膜に残存する金属酸化物の量が、該金属酸化物を構成する金属元素の組成比で製膜時の１％以下であるという特徴を有する。
【００３４】
すなわち、多孔膜のイオン導電性、すなわち物質の移動のし易さを表す１つの指標として、マクミラン数があるが、本発明の多孔膜は、この数値が１より大きく４０以下の範囲にある。
【００３５】
マクミラン数は測定に用いる電解液の比抵抗に対し、多孔膜に電解液を満たした状態で、見た目の比抵抗が相対的に何倍となるかを示すものであり、理論的には１以上である。一方、４０という上限値は、それ以上高い値であると、良好に物質が移動できるとは言い難くなってくる値である。従来の全芳香族ポリアミド多孔膜では、このようなマクミラン数を有するものは知られていない。
【００３６】
ここで、多孔膜のイオン導電性を表すパラメーターであるマクミラン数は次のように求められる。まず、プロピレンカーボネートとエチレンカーボネートを等重量比混合した有機溶媒に四弗化ホウ酸リチウムを１モル／リットル溶解した有機電解液の比抵抗１を求める。次いで、多孔膜をこの溶液に浸漬し、十分浸透した後、半径１ｃｍの円盤状ステンレス電極間に挟み込み、「ソーラトロン」１２６０型インピーダンスアナライザーで１００ｋＨｚ〜１Ｈｚの間で複素インピーダンスを測定し、測定した高周波数側のデータ曲線を実数軸に外挿することで実測抵抗値を求める。そして、これらの測定値に基づき下記式（ａ）によりマクミラン数が算出される。
マクミラン数＝（実測抵抗値×電極面積／多孔膜膜厚）／比抵抗１ （ａ）
【００３７】
更に、本発明の多孔膜は、耐熱性と機械的強度を表す１つの指標である、加熱引張弾性率が１００℃で１００ｋｇｆ／ｍｍ2以上を示す。この加熱引張弾性率は、１００℃の高温でも高い弾性率を維持し、製造工程上、取り扱い上、十分な機械的強度を有する値として１００ｋｇｆ／ｍｍ2以上であることが望まれる。
【００３８】
加熱引張弾性率は加熱下の引張試験で測定される。この引張試験は、ＪＩＳ規格Ｋ７１２７に準じて、インストロン型引張試験機により１００℃の環境下で１０ｃｍ／分の引張り速度で行われる。測定サンプルは後延伸の方向に、長さ５ｃｍ、幅１ｃｍとなるように切り出し、２ｃｍ間隔で引張試験を実施し、その測定値を引張弾性率で表示する。
【００３９】
本発明の多孔膜は、更に、金属酸化物微粒子の残存量が、金属酸化物微粒子を構成する金属元素の組成比で製膜時の１％以下であるという特徴を有する。多孔膜中の金属酸化物微粒子が実質的な割合で残存すると、該多孔膜の空孔率、透気度、イオン透過性等を低減させることになる。また、残存金属酸化物により、多孔膜の電気特性、化学的特性に好ましくない影響を与えることもある。そのため、最終的に得られる金属酸化物微粒子の残存量が、金属酸化物微粒子を構成する金属元素の組成比で溶解除去処理前の１％以下に低減されていることが好ましい。
【００４０】
溶解除去処理を施し洗浄処理した後の金属酸化物微粒子の残存量の測定は、公知の蛍光Ｘ線測定装置を用い次のようにして行う。まず、金属酸化物微粒子を構成する金属元素について、金属酸化物微粒子分散膜に金属酸化物微粒子の溶解除去処理を施す前の蛍光ピーク強度Ａ1を事前に測定し、次に、金属酸化物微粒子の溶解除去処理を施した後の、同じ蛍光ピーク強度Ａ2を測定し、Ａ2／Ａ1の百分率で該多孔膜における金属酸化物微粒子残存割合とする。
【００４１】
本発明の多孔膜では、この値が１％以下と小さく、該多孔膜の空孔率、透気度、イオン透過性等が良好である。
【００４２】
次に、上記のような特徴をもつ本発明の多孔膜の製造方法を説明する。
（金属酸化物粒子分散全芳香族ポリアミド溶液の調製）
本発明では、まず、全芳香族ポリアミド溶液中に、該溶液を構成する溶媒には不溶性又は難溶性の金属酸化物微粒子が分散している全芳香族ポリアミド溶液（以下、これを金属酸化物微粒子分散溶液と略称することがある）を調製する。
【００４３】
全芳香族ポリアミドとしては前述のものが使用され、これを溶解する溶媒としては、全芳香族ポリアミドを溶解して安定な溶液を形成でき、かつ、後述する製膜工程で揮発乾燥除去できるか又は凝固浴で抽出除去できるものを使用する。
【００４４】
ここで実質的に揮発乾燥除去できる溶媒としては、種々の有機溶媒を用いることが出来るが、溶解性の観点から、好ましい溶媒としてアミド系溶媒を挙げることが出来る。このようなアミド系溶媒としては、例えば、テトラメチル尿素、ヘキサメチルホスホルアミド、Ｎ，Ｎ−ジメチルアセトアミド、Ｎ−メチルピロリドン−２，Ｎ−メチルピペリドン−２、Ｎ，Ｎ−ジメチルエチレン尿素、Ｎ，Ｎ，Ｎ’，Ｎ’−テトラメチルアロン酸アミド、Ｎ−メチルカプロラクタム、Ｎ−アセチルピロリジン、Ｎ，Ｎ−ジエチルアセトアミド、Ｎ−エチルピロリドン−２、Ｎ，Ｎ−ジメチルプロピオン酸アミド、Ｎ，Ｎ−ジメチルイソブチルアミド、Ｎ−メチルホルムアミド、Ｎ，Ｎ−ジメチルプロピレン尿素及びそれらの混合系が挙げられる。更に好ましくは、Ｎ−メチルピロリドン−２、ヘキサメチルホスホルアミド、Ｎ，Ｎ−ジメチルアセトアミド及びそれらの混合系を挙げることが出来る。これらの溶媒には、必要に応じ、塩化カルシウム等の溶解促進剤を含んでもよい。
【００４５】
また、溶液抽出できる溶媒として、種々の酸溶液、有機溶媒を用いることが出来るが、具体的には無水濃硫酸や上述したアミド系溶媒を挙げることが出来る。但し、工程上無水濃硫酸の使用は危険性が高く、アミド系溶媒を使用した方がより好ましい。
【００４６】
すなわち、本発明では、揮発乾燥による除去と凝固浴での溶媒抽出除去がともに可能な、アミド系溶媒が好ましく、Ｎ−メチルピロリドン−２、Ｎ，Ｎ−ジメチルアセトアミド及びそれらの混合系が特に好適である。
【００４７】
このような溶媒に溶解する全芳香族ポリアミドの溶液中のポリマー濃度としては、全芳香族ポリアミドの重合度、溶解度、溶液粘度、製膜手段にもよるが、膜を効率的に作製するという観点から、（ポリマー＋溶媒）の重量を基準に１〜５０重量％、特に３〜２０重量％、の範囲が好ましい。
【００４８】
なお、本発明では全芳香族ポリアミドの溶液は、予め製造した全芳香族ポリアミドを上記の溶媒に溶解して使用してもよく、溶液重合で得た全芳香族ポリアミド溶液を必要に応じ濃度調整して使用してもよい。
【００４９】
一方、本発明で用いる金属酸化物微粒子は、全芳香族ポリアミドを溶解する溶媒には不溶で、それとは異なる溶媒には溶解するもので、その平均粒子径が製膜した金属酸化物微粒子分散膜の厚さの１／５０〜１／５の範囲にあることが好ましい。
【００５０】
ここで製膜した金属酸化物微粒子分散膜とは、後述する溶液流延乾燥法及び／又は湿式製膜法で製膜した時点の膜のことで、用途によってその膜の厚さは選択される。構造材料の支持材等で使用する場合には膜厚は特に限定されないが、気体、液体等、物質を通過させるための膜として使用する場合、あるいは製造上、膜中に分散した金属酸化物微粒子を効率よく溶解除去しなければならない場合、膜厚として１ｍｍ以下、好ましくは０．５ｍｍ以下がよい。膜厚の下限値は特に限定されないが、製膜後の取り扱い性の観点から１μｍ以上が好ましい。
【００５１】
金属酸化物微粒子の平均粒子径は製膜した時点の膜厚に応じて選択されるが、膜厚の１／５０よりも小さい場合、金属酸化物微粒子溶解時に溶解液が浸透しにくく、溶解処理後でも残留しやすくなる上、空孔が出来たとしてもその膜の空孔として有効に作用しなくなってくる。すなわち、物質透過性が相対的に低下してしまう。一方、膜厚の１／５よりも大きくなる場合、多孔膜の機械的強度が極端に低下してくる。したがって、膜厚の１／５０〜１／５の範囲内が好ましい。
【００５２】
一方、このような金属酸化物微粒子の適当な添加量は、該微粒子分散溶液中の全芳香族ポリアミドの量で左右され、前記金属酸化物微粒子分散溶液中の固形分、すなわち、全芳香族ポリアミド自体と金属酸化物微粒子等、金属酸化物微粒子分散溶液中の溶媒成分を除去したときの残留成分量の内、全芳香族ポリアミドの割合が１０〜７０容量％となるようにすることが好ましい。全芳香族ポリアミドが１０容量％よりも少なくなると、多孔膜としては空孔割合が大きくなるが、本発明の目的とする強度のある多孔膜が出来にくい。また、７０容量％を超えると製膜した金属酸化物微粒子分散膜中で微粒子が孤立しやすくなる。このような孤立金属酸化物微粒子は溶解除去し難くなる上、溶解できたとしても孤立空孔では多孔膜として物質透過性に全く寄与しない。より好ましい全芳香族ポリアミドの割合は全固形分に対し２０〜６０容量％である。
【００５３】
このような金属酸化物微粒子の種類としては、前述のとおり、全芳香族ポリアミドを溶解する溶媒には不溶又は難溶で、全芳香族ポリアミドを溶解しない溶媒には可溶なものであるが、具体的には５規定以下の濃度のアルカリ水溶液あるいは５規定以下の濃度の酸水溶液に溶解するものが好ましい。これより強いアルカリ、酸溶液を溶解除去に用いる場合、全芳香族ポリアミドの分解、劣化が顕著になり、出来る多孔膜の機械強度が極端に低下してしまう場合がある。また、無水酸は全芳香族ポリアミドを溶解する場合があるので好ましくない。
【００５４】
ここで、特に金属酸化物微粒子を選択する理由は、ポリマーを扱う温度範囲、例えば３００℃での延伸時に変形しにくいこと、金属微粒子のように酸化して溶解特性が大きく変わることがないことが挙げられる。
【００５５】
このような微粒子を形成する好適な金属酸化物材料としては、酸化銅（Ｉ）、酸化銅（II)、酸化インジウム、酸化マグネシウム、酸化ニッケル、酸化錫(II)、酸化亜鉛等を挙げることが出来、特に酸化亜鉛が好ましいが、これのみに限定されるものではない。
【００５６】
このような金属酸化物微粒子分散全芳香族ポリアミド溶液を調製するには、予め調製した全芳香族ポリアミド溶液に金属酸化物微粒子を添加してもよく、全芳香族ポリアミドを溶かす溶媒に金属酸化物微粒子を分散させておきこれに全芳香族ポリアミドを溶解させてもよい。
【００５７】
（製膜）
上記の金属酸化物微粒子分散全芳香族ポリアミド溶液から、溶液流延乾燥法及び／又は湿式製膜法で製膜し、膜（フィルム）状とする。前述のとおり、その膜の厚さは多孔膜の用途によって選択される。構造材料の支持材等として使用する場合には膜厚は特に限定されないが、気体、液体等、物質を通過させるための膜(例えば電池用セパレーター）として使用する場合、あるいは製造上、分散した金属酸化物微粒子を効率よく溶解除去しなければならない場合、膜厚として１ｍｍ以下、好ましくは０．５ｍｍ以下がよい。膜厚の下限値は特に限定するものではないが、製膜後の取り扱い性の観点から１μｍ以上が好ましい。
【００５８】
本発明における溶液流延乾燥工程とは、高分子を溶解した溶液を、ガラス、金属、プラスチック等の基板、ベルトよりなる支持体上に一定溶液厚みになるように流延し、溶媒揮発除去によって残留固形分からなる膜を基板上に形成するという工程である。溶液流延法には公知の技術が利用可能であり、溶液厚み、粘度等によってグラビアコーティング、ロールコーティング、ダイコーティング法等のコーティング技術から選択できる。また、溶媒揮発除去は具体的には加熱乾燥、真空乾燥、真空加熱乾燥等、公知の乾燥技術が適用できる。
【００５９】
また、湿式凝固工程とは、高分子を溶解した溶液を、ガラス、金属、プラスチック等の基板上に一定溶液厚みになるように流延し、全芳香族ポリアミドの貧溶媒で、かつ全芳香族ポリアミド溶解に使用している溶媒に対しては親和性がある凝固溶液中に浸漬し、全芳香族ポリアミド溶液の溶媒成分を凝固浴中へ抽出除去し、残留固形分からなる膜を基板上あるいは凝固浴液中に形成するという工程である。この際の流延には上述した公知の溶液流延法が採用できる。
【００６０】
本発明では、これらを組み合わせ、溶液流延乾燥工程で完全に溶媒を揮発乾燥するのではなく、揮発途中で湿式凝固工程に切り替え、効果的に溶媒を除去することが好ましい。本発明者らの研究によれば、これら２つの溶媒除去工程を上記の順で組み合わせることにより、単に溶媒を効率的に除去するという効果に加えて、（ａ）生成した膜を支持体から容易に剥離することが可能になるということ、（ｂ）最終的に作製した全芳香族ポリアミド多孔膜の、支持体に接触していた膜面（支持体面）とその反対面（空気面）の表面性状が非常に近くいずれの面も良好な物質透過性を示すということ、更に（ｃ）湿式凝固法単独ではその凝固条件により多孔膜の構造が大きく変化してしまう点を抑制できること、等が明らかとなった。
【００６１】
このとき、多孔膜の物質透過性を一段と上げるためには、溶液流延乾燥工程において、その乾燥温度を（該全芳香族ポリアミドを溶解し、かつ該微粒子を溶解しない溶媒の沸点−６０℃）以上とすることが好ましい。このように乾燥温度を上げる理由は、単に溶媒揮発速度が上がり乾燥工程の時間が短縮されるという、製造工程上の効果だけではなく、溶媒の早い揮発により、特に微粒子分散膜表面に微細空孔ができ易いという効果も発現するためである。その結果、物質透過性が特に良好な多孔質膜が得られる。
【００６２】
（金属酸化物粒子の除去）
次に、上述のように製膜した金属酸化物微粒子分散膜を浴液中で処理し、該膜中から金属酸化物微粒子を溶解除去する。このような浴液(溶解溶液）としては、膜を構成する全芳香族ポリアミドを溶解又は分解せず金属酸化物微粒子を選択的に溶解除去できるものであれば特に制限されないが、工業的には、前述のように、５規定以下の濃度のアルカリ水溶液あるいは５規定以下の濃度の酸水溶液が好適に使用される。ここで、酸としては硝酸、塩酸、硫酸等の無機酸が好ましく、また、アルカリとしては水酸化ナトリウム、水酸化カリウムが好ましく使用される。
【００６３】
これより強いアルカリ、酸溶液を溶解除去に用いる場合、全芳香族ポリアミドの分解、劣化が顕著になり、出来る多孔膜の機械的強度が極端に低下してしまう場合があり、また、無水酸は全芳香族ポリアミドの溶解が生じることがあるので好ましくない。
【００６４】
不活性微粒子の溶解除去は、該微粒子を含む全芳香族ポリアミド膜（微粒子分散膜）を上記の溶解溶液の浴中に浸漬することにより行われる。浸漬浴は液が流動する浴でも、液が流動しない浴でもよい。また、浴中で微粒子分散膜を静置してもよく移動させてもよい。
【００６５】
金属酸化物微粒子の溶解除去の条件としては、金属酸化物微粒子の溶解速度、飽和溶解度、これを溶解する液の凝固点、沸点等にもよるが、０〜１００℃の温度範囲で、２４時間以内に溶解除去する方が製造工程上好ましい。
【００６６】
このように金属酸化物微粒子分散溶液から、製膜し、膜中から金属酸化物微粒子の溶解除去を行うことで良好な全芳香族ポリアミド多孔膜を形成することが出来るが、必要に応じ、前記金属酸化物微粒子分散溶液中に、更に空孔発生を促進するための有機物質（以下、空孔発生促進剤ということがある）を添加して製膜してもよい。
【００６７】
すなわち、溶液溶解する金属酸化物微粒子の分散に加え、更に、全芳香族ポリアミドと実質的に互いに溶け合わず、かつ全芳香族ポリアミドを溶解するための有機溶媒に溶解し、かつ、全芳香族ポリアミドが溶解しない溶媒に溶解する有機物質を空孔発生促進剤として用い、金属酸化物微粒子と上記有機物質とを分散した全芳香族ポリアミド膜を製膜した後、該金属酸化物微粒子及び有機物質を円滑に溶解除去する方法を採用することが出来る。
【００６８】
空孔発生促進剤としての有機物質は、言い換えれば全芳香族ポリアミドを溶解する溶媒に溶解するが、製膜時の溶媒除去と共に全芳香族ポリアミドと相分離するものである。このような有機物質（空孔発生促進剤）としては、作業性の観点から３０℃で固体のもの、すなわち、製膜後にその有機物質によって膜がべとつかないものが好ましい。そしてより好ましくは、金属酸化物微粒子溶解処理工程で一緒に溶解するものがよい。そのような空孔発生促進剤としては、ポリ（エチレンオキサイド）、ポリ（プロピレンオキサイド）等のポリ（アルキレンオキサイド）が好ましい。更に、水溶性がより高いという観点からポリ（エチレンオキサイド）を挙げることが出来る。但し、ポリ（エチレンオキサイド）の溶解性、融点等の特性はその平均分子量によって大きく変わるため、平均分子量が１５００から７５００の間にあるものがよい。平均分子量が１５００よりも低い場合、全芳香族ポリアミドとの相分離時に好適な多孔膜構造とはならず、全芳香族ポリアミドとポリ（エチレンオキサイド）の二層積層構造になる場合がある。また、ポリ（エチレンオキサイド）は平均分子量１５０以下では液体であり、前述したように、べとつきのため作業性が低下する場合がある。平均分子量が１５００よりも低い場合でも、製膜後にも全芳香族ポリアミド溶液の溶媒を含浸してべとつく場合がある。一方、平均分子量が７５００よりも大きくなる場合、全芳香族ポリアミドを含んだ微粒子分散溶液に溶解しにくくなる。たとえ、溶解させても、混合溶液がペースト状になり、流延し難くなる。また、溶解除去時に溶解しにくくなる。
【００６９】
このような金属酸化物微粒子及び空孔発生促進剤の添加量は、それらの合計量が、前記金属酸化物微粒子分散溶液中の固形分の内、全芳香族ポリアミドの割合が１０〜７０容量％となるようにすることが好ましい。１０容量％よりも全芳香族ポリアミドが少なくなると、多孔膜としては空孔割合が大きくなるが、本発明の目的とする強度のある多孔膜が出来にくい。また、７０容量％以上では製膜した金属酸化物微粒子分散膜中で金属酸化物微粒子が孤立しやすくなる。このような孤立金属酸化物微粒子は溶解除去し難くなる上、溶解できたとしても孤立空孔では多孔膜として物質透過性に全く寄与しない。より好ましい全芳香族ポリアミドの割合は既に述べたように２０〜６０容量％である。空孔形成促進剤の量は全芳香族ポリアミドに対し５０〜３００容量％が好ましい。
【００７０】
（延伸）
金属酸化物微粒子除去処理を行った膜はこの時点で多孔質性を発現するが、より透過性を上げる、あるいは機械強度を上げるためには、延伸処理を施す方が、全芳香族ポリアミドの利点を引き出すという点で好ましい。そのような延伸処理としては一軸延伸、逐次二軸延伸、同時二軸延伸、圧延等が挙げられる。延伸処理の順序は金属酸化物微粒子除去処理の前でもよいし、処理の後でもよい。その延伸倍率としては、少なくとも多孔膜の一方向に１．２倍以上延伸しなければ延伸による機械的強度の向上効果が顕著となりにくい。そして破断しない範囲内で高い倍率である方が好ましい。
【００７１】
（後処理）
このようにして製造した全芳香族ポリアミドの多孔膜は、最後に洗浄され、乾燥されて製品となる。洗浄は常温又は加熱下の純水洗浄が好ましく、乾燥は自然乾燥又は乾燥器による乾燥が採用できる。
【００７２】
【実施例】
次に、本発明の各実施例及び比較例を詳述する。なお、これらの例中に記載の各種の指標のうち、既に述べたもの以外については、以下の要領にて評価を行った。
１）対数粘度：重合した全芳香族ポリアミドの対数粘度は、溶媒として濃硫酸を用い、０．５ｇ／１００ｍｌの濃度で３０℃で測定した値で示した。
２）延伸倍率：延伸は逐次二軸延伸を行った。そして、それぞれの延伸倍率は前延伸倍率×後延伸倍率で表示した。
【００７３】
［実施例１］
フラスコ中で窒素気流下、３，４’−ジアミノジフェニルエーテル６．９６８ｇとパラフェニレンジアミン３．７６４ｇを脱水精製したＮ−メチルピロリドン−２の３００ｇに溶解させた後、氷水浴で冷却した。冷却後、この溶液にテレフタル酸ジクロライドの粉末１４．１３６ｇを速やかに加えて、激しく攪拌した。更に溶液の温度が反応熱によって５０℃を越えたところで８５℃に昇温し、１時間攪拌した。その後、水酸化カルシウムを５．１５ｇ添加し、副生塩酸を中和したところ、黄色透明な高粘度溶液となった。この溶液における全芳香族ポリアミド濃度は６．０重量％であった。
【００７４】
測定のため、この溶液の一部を取り出して水と混合し、沈殿した重合体を分離して水洗、乾燥の後、対数粘度を測定したところ、３．２であった。また、この全芳香族ポリアミドの比重は１．３４であった。
【００７５】
そして、上記の溶液１００重量部に、Ｎ−メチルピロリドン−２の４９重量部、界面活性剤（花王製「ホモゲノール」Ｌ−１８）１重量部及び平均粒子径１μｍの酸化亜鉛微粒子（高純度化学製、比重５．４７）３２．８重量部を、窒素気流下で７０℃で均一に分散混合し、酸化亜鉛微粒子分散溶液を得た。その後、更にレベリング剤（信越化学製ＳＨ２８ＰＡ）０．１６重量部を添加混合した。そして、８０℃のガラス板上にこの混合液を０．８ｍｍ厚となるように流延し、１３０℃の乾燥炉中で１２分乾燥処理し、引き続いて、水中で２分間浸漬を行って溶媒を除去した。そして、これを取り出して乾燥処理し、自己支持性の白色膜を得た。
【００７６】
この白色膜を３１０℃の環境下で１．５倍×１．５倍に逐次二軸延伸を行した後、引き続き、５％硝酸水溶液に３０分間浸漬して、白色膜中に分散した酸化亜鉛微粒子を溶解除去した。そして、純水洗浄を行った後、乾燥処理を実施し、多孔膜を得た。
【００７７】
このようにして作製した全芳香族ポリアミド多孔膜の特性を評価した結果を表１の実施例１欄に示す。これより、本発明の多孔膜は、良好な強度、イオン導電性を有し、かつ金属酸化物残存割合が低いことがわかる。
【００７８】
［実施例２］
実施例１で溶液重合した全芳香族ポリアミド溶液１００重量部に、Ｎ−メチルピロリドン−２の３２．７重量部、界面活性剤（花王製「ホモゲノール」Ｌ−１８）０．７重量部及び平均粒子径１μｍの酸化亜鉛微粒子（高純度化学製、比重５．４７）２１．９重量部を、窒素気流下で７０℃で均一に分散混合し、酸化亜鉛微粒子分散溶液を得た。その後、更にレベリング剤（信越化学製ＳＨ２８ＰＡ）０．１６重量部を混合した。そして、８０℃のガラス板上にこの混合液を０．６ｍｍ厚となるように流延し、１３０℃の乾燥炉中で８分間乾燥処理し、引き続いて水中で２分間浸漬を行った。その後、乾燥処理して、自己支持性の白色膜を得た。
【００７９】
この白色膜を３１０℃の環境下で１．５倍×１．５倍に逐次二軸延伸を行った。次に、この延伸白色膜を５％硝酸水溶液に３０分間浸漬し、白色膜中に分散した酸化亜鉛微粒子を溶解除去した。そして純水洗浄を行ったあと、乾燥させて多孔膜を得た。
【００８０】
このようにして作製した全芳香族ポリアミド多孔膜の特性を評価した結果を表１の実施例２欄に示す。これより、この多孔膜は、良好な強度、イオン導電性を有し、かつ金属酸化物残存割合が低いことがわかる。
【００８１】
［実施例３］
実施例２で調製した酸化亜鉛微粒子分散溶液に、同様にレベリング剤（信越化学製ＳＨ２８ＰＡ）０．１６重量部を混合した。そして、８０℃のガラス板上にこの混合液を０．６ｍｍ厚となるように流延し、１５０℃の乾燥炉中で１０分乾燥処理し、引き続いて水中で２分間浸漬を行った。そして、乾燥処理後、自己支持性の白色膜を得た。
【００８２】
この白色膜を３１０℃の環境下で１．５倍×１．５倍に逐次二軸延伸を行った。次に、この延伸白色膜を５％硝酸水溶液に３０分間浸漬し、白色膜中に分散した酸化亜鉛微粒子を溶解除去した。そして純水洗浄を行った後、乾燥させて多孔膜を得た。
【００８３】
このようにして作製した全芳香族ポリアミド多孔膜の特性を評価した結果を表１の実施例３欄に示す。これより、この多孔膜は、良好な強度、イオン導電性を有し、かつ金属酸化物残存割合が低いことがわかる。
【００８４】
［実施例４］
実施例２で調製した酸化亜鉛微粒子分散溶液に、同様にレベリング剤（信越化学製ＳＨ２８ＰＡ）０．１６重量部を混合した。そして、８０℃のガラス板上にこの混合液を０．６ｍｍ厚となるように流延し、１８０℃の乾燥炉中で８分間乾燥処理、引き続き、水中で２分間浸漬を行い、更に乾燥処理後、自己支持性の白色膜を得た。
【００８５】
この白色膜を３１０℃の環境下で１．５倍×１．５倍に逐次二軸延伸を行った。次に、この延伸白色膜を５％硝酸水溶液に３０分間浸漬し、白色膜中に分散した酸化亜鉛微粒子を溶解除去した。そして、純水洗浄を行った後、乾燥させて多孔膜を得た。
【００８６】
このようにして作製した全芳香族ポリアミド多孔膜の特性を評価した結果を表１の実施例４欄に示す。これより、この多孔膜は、良好な強度、イオン導電性、低い金属酸化物残存割合を有することがわかる。
【００８７】
［比較例１］
実施例１で重合した全芳香族ポリアミド溶液１００重量部にＮ−メチルピロリドン−２を５０重量部、平均粒子径３μｍのアルミニウム微粒子（高純度化学製、比重２．６９９）１８．４重量部、ポリエチレンオキサイド（平均分子量６０００）６重量部を８０℃で均一に分散混合し、微粒子分散溶液を得た。そして、８０℃のガラス板上にこの混合液を０．４ｍｍ厚となるように流延し、１３０℃の乾燥炉中で４０分間乾燥処理を行った。この乾燥処理後、自己支持性の灰色膜を得た。
【００８８】
しかる後、この灰色膜を１５０℃環境下で１．５倍×１．５倍に逐次二軸延伸を行った。次に、この延伸灰色膜を３．５％水酸化ナトリウム水溶液に１．５時間浸漬し、灰色膜中に分散したアルミニウム微粒子及びポリエチレンオキサイドを溶解除去した。そして純水洗浄を行って多孔膜を得た。
【００８９】
このようにして作製した全芳香族ポリアミド多孔膜の特性を評価した結果を表１の比較例１欄に示す。これより、この多孔膜は、金属酸化物微粒子が多量に残存する膜であり、かつイオン導電性も若干劣ることがわかる。
【００９０】
［比較例２］
実施例１で重合した全芳香族ポリアミド溶液１００重量部にＮ−メチルピロリドン−２を５０重量部混合し、製膜溶液を得た。そして、８０℃のガラス板上にこの混合液を０．７ｍｍ厚となるように流延し、そのまま２５℃の純水中に浸漬した。５分後に膜がガラス板から自然剥離した。その膜を純水で洗浄後、定長で乾燥処理して、自己支持性の淡黄色膜を得た。そして、この淡黄色膜を１５０℃環境下で２倍×２倍に逐次二軸延伸を行った。
【００９１】
このようにして作製した全芳香族ポリアミド多孔膜の特性を評価した結果を表１の比較例２欄に示す。これより、このものはイオン導電性が極めて悪いことがわかる。
【００９２】
［比較例３］
実施例１で重合した全芳香族ポリアミド溶液１００重量部にＮ−メチルピロリドン−２を５０重量部混合し、製膜溶液を得た。そして、８０℃のガラス板上にこの混合液を０．９ｍｍ厚となるように流延し、そのまま２５℃のｎ−オクタノール中に浸漬した。１時間後膜がガラス板から自然剥離した。その膜を引き上げ、メタノールで洗浄後、定長で乾燥処理して、自己支持性の白色膜を得た。そして、この白色膜を１５０℃の環境下で１．４倍×２倍に逐次二軸延伸を行った。
【００９３】
このようにして作製した全芳香族ポリアミド多孔膜の特性を評価した結果を表１の比較例３欄に示す。これより、この多孔膜はイオン導電性が悪いことがわかる。
【００９４】
［比較例４］
実施例１で重合した全芳香族ポリアミド溶液１００重量部にＮ−メチルピロリドン−２を５０重量部、ポリエチレンオキサイド（平均分子量３０００）９重量部を８０℃で均一に分散混合し、製膜溶液を得た。そして、１００℃のガラス板上にこの混合液を０．７ｍｍ厚となるように流延し、１５０℃の乾燥炉中で２５分間乾燥処理を行った。乾燥処理後、自己支持性の淡黄色膜を得た。そしてこの淡黄色膜を１５０℃の環境下で２倍×２倍に逐次二軸延伸を行った。次に、この延伸淡黄色膜を７０℃純水中に１０分間浸漬し、更にそのまま超音波洗浄処理を１０間分行い、黄色膜分散したポリエチレンオキサイドを溶解除去した。そして、純水洗浄を行って、多孔膜を得た。
【００９５】
このようにして作製した全芳香族ポリアミド多孔膜の特性を評価した結果を表１の比較例４欄に示す。これより、イオン導電性が極めて悪いことがわかる。
【００９６】
［比較例５］
実施例１で調製した酸化亜鉛微粒子分散溶液に、同様にレベリング剤（信越化学製ＳＨ２８ＰＡ）０．１６重量部を混合した。そして、８０℃のガラス板上にこの混合液を０．６ｍｍ厚となるように流延し、１８０℃の乾燥炉中で１５分間乾燥処理を行った。乾燥処理後、自己支持性の白色膜を得た。その後、この白色膜を３１０℃の環境下で１．５×１．５に逐次二軸延伸を行った。次に、この延伸白色膜を５％硝酸水溶液に３０分浸漬し、分散した酸化亜鉛微粒子を溶解除去した。そして純水洗浄を行って多孔膜を得た。
【００９７】
このようにして作製した全芳香族ポリアミド多孔膜の特性を評価した結果を表１の比較例５欄に示す。これより、この多孔膜は、イオン導電性がやや悪いことがわかる。
【表１】
【発明の効果】
以上のように、本発明の技術を用いることにより、物質透過性が良好で、かつ耐熱性、機械強度、外観が良好な全芳香族ポリアミド多孔膜を提供することが出来る。そして本発明の全芳香族ポリアミド多孔膜は、その特性を生かして、特に薄くて高性能の全芳香族ポリアミド多孔膜が要求される、耐熱性分離ろ過膜、電池用セパレーター等に好適に利用することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wholly aromatic polyamide porous membrane and a method for producing the wholly aromatic polyamide porous membrane. More specifically, the present invention relates to a novel porous membrane made of wholly aromatic polyamide and having high strength, high heat resistance and high material permeability, and a method for industrially producing the porous membrane.
[0002]
[Prior art]
In recent years, porous membranes made of a polymer have been used in filters for separation and filtration, low strength films and support membranes for structures, electric double layer capacitors, battery separators, and the like. Examples of such a polymer porous membrane include a polyolefin porous membrane represented by polyethylene and polypropylene as described in JP-A-3-64334 and the like, and Japanese Patent Publication No. Sho 54-34790. And polyester porous membranes as described in JP-A Nos. 58-179243 and 58-210934.
[0003]
However, such conventional polymer porous membranes are difficult to use in applications that require heat resistance and mechanical strength. For example, in recent years, polyethylene porous membranes have been used as separators for lithium ion secondary batteries, etc., but lithium ion secondary batteries are extremely safe because of the use of flammable organic solvents as electrolytes. Despite being important, there is a problem that it melts easily at the time of abnormal temperature rise due to an external short circuit or the like, and the electrode is further short-circuited inside the battery. Further, in filtration of a high-temperature solution or the like, even if the temperature is equal to or lower than the temperature at which the porous membrane melts, the mechanical strength of the porous membrane is abruptly lowered and is easily broken.
[0004]
Further, as described in JP-A-6-263904, JP-A-6-263906, and the like, porous membranes of aliphatic polyamides and semi-aromatic polyamides have been proposed. It does not have strength and heat resistance, and its use is limited.
[0005]
On the other hand, wholly aromatic polyamides have the properties of high mechanical strength and excellent heat resistance. Therefore, the fibers of wholly aromatic polyamides are already used for fibers that require such mechanical strength and heat resistance. It's being used. Furthermore, as a high-strength heat-resistant film, a wholly aromatic polyamide film is disclosed in “Journal of the Textile Society” Vol. 48, no. 1 (1992) 43-48.
[0006]
Further, in Japanese Patent Application Laid-Open Nos. 5-290822, 5-335005, and 7-37571, nonwoven fabrics using wholly aromatic polyamide fibers are proposed from the viewpoint of heat resistance. However, with regard to the thinness required for higher market demand, it is difficult to make the thickness thinner than about 100 μm in such a nonwoven fabric in order to maintain the mechanical strength. Although it is possible to reduce the thickness by simply pressing and pressing the nonwoven fabric while maintaining the mechanical strength, in that case, the porosity of the nonwoven fabric is lowered, and the permeability of gas, liquid, etc. is lowered. Further, the surface of the nonwoven fabric is non-uniform compared to a so-called porous film, and microscopically, there may be a large difference in the permeability of gas, liquid, etc. depending on the location.
[0007]
By the way, it is difficult to form a film using a melt extrusion film forming technique because of its high heat resistance. Therefore, a film (film) is generally formed by a solution casting method. Therefore, the following manufacturing method has also been proposed for a wholly aromatic polyamide porous film having a small film thickness.
[0008]
That is, Japanese Patent Publication No. 59-14494 introduces a technique in which a wholly aromatic polyamide solution is cast on a substrate, cooled and solidified at a temperature of 0 ° C. or lower, and then the solvent is extracted at a temperature in the vicinity thereof. Has been. However, in this case, the pore shape of the film formed varies depending on the cooling temperature, or even if the cooling temperature is sufficiently controlled, the pore shape varies due to variations in the solution film thickness when the solution is cast. In the actual manufacturing process, it is difficult to form a uniform porous porous film. JP-B-59-36939, JP-A-53-144974, JP-B-61-51928, JP-A-59-59213, JP-B-4-12171, JP-A-2-222430. Japanese Patent Laid-Open No. 10-6453 discloses a so-called wet coagulation film forming method in which a wholly aromatic polyamide solvent solution is cast into a coagulating bath after casting to form a wholly aromatic polyamide porous film. The law is described. However, in this case as well, “Journal of the Textile Society” Vol. 48, no. 2 (1992) 49-67, the shape of the pores is different in the film thickness direction, a coating layer is formed on the surface of the porous membrane, or the pore shape is different due to fluctuations in solidification conditions. There is a case.
[0009]
As described above, it is difficult to form a wholly aromatic polyamide porous film having a uniform pore shape by a simple wet coagulation film forming method. Therefore, the present inventors previously used a mixed solution in which fine particles not dissolved in this solvent are dispersed in a solution comprising a wholly aromatic polyamide and a solvent in which the wholly aromatic polyamide is dissolved. A method of forming a porous film by dissolving and removing the fine particles after forming a film by a dry method or a wet film forming method has been proposed (Japanese Patent Application No. 10-296634). According to this method, a wholly aromatic polyamide porous membrane can be produced stably and efficiently, but there is a need for a higher quality porous membrane so that it can be used in fields that require even higher performance.
[0010]
[Problems to be solved by the invention]
The present invention uses the method proposed in Japanese Patent Application No. 10-296634 for a wholly aromatic polyamide porous membrane that is difficult to form a uniform pore shape by such a simple wet coagulation film forming method. An object of the present invention is to provide a wholly aromatic polyamide porous membrane having improved heat resistance, high strength and good material permeability, and a method for producing the same. Furthermore, the present invention provides a novel wholly aromatic polyamide porous membrane that can be suitably used for heat-resistant separation and filtration membranes, battery separators and the like that require a particularly thin wholly aromatic polyamide porous membrane, and a method for producing the same. For the purpose.
[0011]
[Means for Solving the Problems]
The novel porous membrane of the present invention comprises a substantially wholly aromatic polyamide formed by dissolving and removing the fine particles from a metal oxide fine particle dispersed film obtained by forming a wholly aromatic polyamide solution in which metal oxide fine particles are dispersed. A porous membrane having a Macmillan number greater than 1 and less than or equal to 40, and a tensile modulus at 100 ° C. of 100 kgf / mm 2 A wholly aromatic polyamide porous material characterized in that the amount of metal oxide remaining in the porous membrane is not more than 1% of the composition ratio of metal elements constituting the metal oxide before dissolution removal treatment. It concerns the membrane.
[0012]
In the present invention, the following each invention is included regarding such a wholly aromatic polyamide porous membrane.
1) A wholly aromatic polyamide porous membrane, wherein the wholly aromatic polyamide consists essentially of repeating units represented by the following formula (1):
[0013]
[Formula 4]
-NR 1 -Ar 1 -NR 2 -CO-Ar 2 -CO- (1)
(Where R 1 And R 2 Are the same or different and are selected from the group consisting of a hydrogen atom, a halogen atom and an alkyl group having 5 or less carbon atoms; 1 And Ar 2 Are the same or different and may have a substituent such as orthophenylene group, metaphenylene group, paraphenylene group, 1,4 naphthylene group, 1,5 naphthylene group, 2,6 naphthylene group, 2,5 pyridylene group And a divalent group represented by the following formula (2). )
[0014]
[Chemical formula 5]
(Here, X is selected from the group consisting of an ether group, a sulfide group, a methylene group, a carbonyl group and a sulfonyl group.)
2) The wholly aromatic polyamide is Ar in the repeating unit represented by the above formula (1). 1 And Ar 2 Is a wholly aromatic polyamide porous film represented by the following formula (3).
[0016]
[Chemical 6]
The wholly aromatic polyamide porous membrane of the present invention can be suitably used for heat-resistant separation / filtration membranes, battery separators and the like that require a polymer porous membrane having particularly low thickness, heat resistance and high strength. It can be done.
[0018]
Further, the production method of the present invention comprises a metal oxide film formed from a wholly aromatic polyamide solution in which finely divided metal oxide particles insoluble or hardly soluble in the solvent constituting the solution are dispersed in the wholly aromatic polyamide solution. The fine particle-dispersed wholly aromatic polyamide film is immersed in a bath made of a liquid that does not dissolve the wholly aromatic polyamide and can dissolve the metal oxide fine particles, and the metal oxide fine particles are dissolved and removed, and then washed. By doing so, the Macmillan number is greater than 1 and less than or equal to 40, and the tensile modulus at 100 ° C. is 100 kgf / mm. 2 Thus, the present invention relates to a method for producing a wholly aromatic polyamide porous membrane in which the remaining amount of the metal oxide is 1% or less in terms of the composition ratio of the metal elements constituting the metal oxide.
[0019]
Regarding the invention of this production method, the following inventions are also included in the present invention.
1) The metal oxide fine particles are one kind or two or more kinds of fine particles composed of copper oxide (I), copper oxide (II), indium oxide, magnesium oxide, nickel oxide, tin (II) oxide, and zinc oxide. A method for producing a wholly aromatic polyamide porous membrane.
2) A method for producing a wholly aromatic polyamide porous film in which the average particle diameter of the metal oxide fine particles is in the range of 1/50 to 1/5 of the thickness of the formed fine particle dispersion film.
3) A method for producing a wholly aromatic polyamide porous membrane in which the proportion of the wholly aromatic polyamide is 10 to 70% by volume in the solid content in the metal oxide fine particle dispersion solution.
4) A method for producing a wholly aromatic polyamide porous membrane, wherein the immersion bath liquid capable of dissolving the metal oxide fine particles is an alkaline aqueous solution having a concentration of 5 N or less or an acid aqueous solution having a concentration of 5 N or less.
5) A method for producing a wholly aromatic polyamide porous film, in which a cast drying process and a wet coagulation process are performed in this order from the metal oxide fine particle dispersion solution of the wholly aromatic polyamide.
6) A method for producing a wholly aromatic polyamide porous membrane in which the wholly aromatic polyamide porous membrane is stretched 1.2 times or more in at least one direction before or after the step of dissolving and removing the metal oxide fine particles.
7) The amount of metal oxide in the porous film is reduced to 1% or less before the removal treatment by the composition ratio of the metal elements constituting the metal oxide, compared to immediately after the film formation, by the fine particle dissolution and removal treatment and the washing treatment. A method for producing a wholly aromatic polyamide porous membrane.
[0020]
According to the method of the present invention as described above, it is possible to stabilize a wholly aromatic polyamide porous membrane suitably useful for a heat-resistant separation / filtration membrane, a battery separator, and the like that require a particularly thin heat-resistant and high-strength polymer porous membrane. Can be manufactured automatically.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
The wholly aromatic polyamide constituting the porous membrane of the present invention is a polyamide having a repeating unit of the following formula (1).
[0022]
[Chemical 7]
-NR 1 -Ar 1 -NR 2 -CO-Ar 2 -CO- (1)
[0023]
In the above formula (1), R 1 And R 2 Are the same or different and are selected from the group consisting of a hydrogen atom, a halogen atom and an alkyl group having 5 or less carbon atoms, and Ar 1 And Ar 2 Are the same or different and are represented by orthophenylene group, metaphenylene group, paraphenylene group, 1,4 naphthylene group, 1,5 naphthylene group, 2,6 naphthylene group, 2,5 pyridylene group and the following formula (2). A divalent organic group selected from divalent groups. In addition, some or all of hydrogen atoms constituting the aromatic nucleus of these groups may be substituted with a halogen atom or a lower alkyl group.
[0024]
[Chemical 8]
In the above formula (2), X represents an ether group, sulfide group, methylene group, carbonyl group or sulfonyl group.
[0026]
The wholly aromatic polyamide used in the present invention may be composed of a plurality of combinations of the above repeating units, that is, a copolymerized one.
[0027]
Of the wholly aromatic polyamides as described above, the wholly aromatic polyamides that can be used in the present invention may be wholly aromatic polyamides that are soluble in a solvent that can be evaporated and dried or a solvent that can be solution extracted. Not. Such fully aromatic polyamides include ortho-oriented fully aromatic polyamides, meta-oriented fully aromatic polyamides, para-oriented fully aromatic polyamides, meta-para-oriented fully aromatic polyamides. However, from the viewpoint of the mechanical strength desired as a porous film, among these, a wholly aromatic polyamide mainly composed of para-oriented aromatic polyamide is more preferable.
[0028]
Such para-oriented wholly aromatic polyamides also include fully para-oriented wholly aromatic polyamides as typified by poly (paraphenylene terephthalamide). However, Ar in the repeating unit of the above formula (1) from the viewpoints of ease of solution preparation, solution stability, chemical resistance, and high mechanical strength 1 , Ar 2 In the present invention, at least 7.5 mol% or more, particularly 7.5 to 50 mol%, of the total amount of is a para-oriented wholly aromatic polyamide represented by the following formula (3).
[0029]
[Chemical 9]
In particular, Ar 1 Is a combination of a paraphenylene group and a group of the above formula (3) (the group of the above formula (3) is 15 mol% or more and 50 mol% or less with respect to the total amount of Ar1 and Ar2), and Ar 2 Is more preferably a paraphenylene group.
[0031]
The wholly aromatic polyamide has a film-forming ability, and the degree of polymerization is preferably high in order to sufficiently exhibit the mechanical strength of the wholly aromatic polyamide porous membrane. Specifically, the logarithmic viscosity measured at 30 ° C. at a concentration of 0.5 g / 100 ml is preferably 1.0 or more, and more preferably 1.7 or more.
[0032]
If the main component is a wholly aromatic polyamide, the porous membrane according to the present invention may contain other organic and inorganic fillers, additives, and the like as necessary.
[0033]
This porous film has micropores that are substantially in communication, and its permeability is greater than 1 and less than or equal to 40, and the tensile modulus at 100 ° C. is 100 kgf / mm. 2 The amount of the metal oxide remaining in the porous film is 1% or less at the time of film formation in terms of the composition ratio of the metal elements constituting the metal oxide.
[0034]
That is, as one index representing the ionic conductivity of the porous film, that is, the ease of movement of the substance, there is the Macmillan number, but the numerical value of the porous film of the present invention is greater than 1 and 40 or less.
[0035]
The Macmillan number indicates how many times the specific resistivity of the electrolyte is relatively large when the porous membrane is filled with the electrolyte relative to the resistivity of the electrolyte used for the measurement. It is. On the other hand, the upper limit value of 40 is a value higher than that, and it is difficult to say that the substance can move well. No conventional fully aromatic polyamide porous membrane has such a Macmillan number.
[0036]
Here, the Macmillan number, which is a parameter representing the ionic conductivity of the porous membrane, is obtained as follows. First, the specific resistance 1 of an organic electrolyte obtained by dissolving 1 mol / liter of lithium tetrafluoroborate in an organic solvent in which propylene carbonate and ethylene carbonate are mixed at an equal weight ratio is obtained. Next, the porous membrane was immersed in this solution and sufficiently permeated, then sandwiched between disc-shaped stainless steel electrodes having a radius of 1 cm, and the complex impedance was measured between 100 kHz and 1 Hz with a “Solartron” 1260 type impedance analyzer. The measured resistance value is obtained by extrapolating the frequency-side data curve to the real axis. Based on these measured values, the Macmillan number is calculated by the following formula (a).
Macmillan number = (measured resistance value × electrode area / porous film thickness) / specific resistance 1 (a)
[0037]
Furthermore, the porous membrane of the present invention is one index representing heat resistance and mechanical strength, and the heating tensile elastic modulus is 100 kgf / mm at 100 ° C. 2 The above is shown. This heating tensile elastic modulus maintains a high elastic modulus even at a high temperature of 100 ° C., and is 100 kgf / mm as a value having sufficient mechanical strength in the manufacturing process and handling. 2 It is desirable that it is the above.
[0038]
The heated tensile modulus is measured by a tensile test under heating. This tensile test is performed according to JIS standard K7127 by an Instron type tensile tester at a tensile rate of 10 cm / min in an environment of 100 ° C. The measurement sample is cut out in the direction of post-stretching so that the length is 5 cm and the width is 1 cm, a tensile test is performed at intervals of 2 cm, and the measured value is displayed as a tensile elastic modulus.
[0039]
The porous film of the present invention is further characterized in that the remaining amount of metal oxide fine particles is 1% or less of the metal element composing the metal oxide fine particles at the time of film formation. If the metal oxide fine particles in the porous film remain in a substantial proportion, the porosity, air permeability, ion permeability, etc. of the porous film are reduced. In addition, the residual metal oxide may adversely affect the electrical properties and chemical properties of the porous membrane. Therefore, it is preferable that the residual amount of the metal oxide fine particles finally obtained is reduced to 1% or less before the dissolution and removal treatment by the composition ratio of the metal elements constituting the metal oxide fine particles.
[0040]
The residual amount of metal oxide fine particles after the dissolution removal treatment and the washing treatment are measured as follows using a known fluorescent X-ray measurement apparatus. First, with respect to the metal elements constituting the metal oxide fine particles, the fluorescence peak intensity A before the metal oxide fine particle dispersed film is subjected to the dissolution removal treatment of the metal oxide fine particles 1 Is measured in advance, and then the same fluorescence peak intensity A after the metal oxide fine particles are dissolved and removed. 2 Measure A 2 / A 1 The percentage of metal oxide fine particles remaining in the porous film is defined as the percentage.
[0041]
In the porous membrane of the present invention, this value is as small as 1% or less, and the porosity, air permeability, ion permeability and the like of the porous membrane are good.
[0042]
Next, the manufacturing method of the porous film of the present invention having the above characteristics will be described.
(Preparation of metal oxide particle-dispersed wholly aromatic polyamide solution)
In the present invention, first, a wholly aromatic polyamide solution in which metal oxide fine particles insoluble or hardly soluble in a solvent constituting the solution are dispersed in a wholly aromatic polyamide solution (hereinafter referred to as metal oxide fine particles). (Sometimes abbreviated as dispersion solution).
[0043]
As the wholly aromatic polyamide, the above-mentioned ones are used, and as a solvent for dissolving this, the wholly aromatic polyamide can be dissolved to form a stable solution, and it can be removed by volatile drying in the film forming step described later or Use one that can be extracted and removed in a coagulation bath.
[0044]
Here, various organic solvents can be used as the solvent that can be substantially volatilely dried and removed. From the viewpoint of solubility, an amide solvent can be mentioned as a preferable solvent. Examples of such amide solvents include tetramethylurea, hexamethylphosphoramide, N, N-dimethylacetamide, N-methylpyrrolidone-2, N-methylpiperidone-2, N, N-dimethylethyleneurea, N , N, N ′, N′-tetramethylaronic acid amide, N-methylcaprolactam, N-acetylpyrrolidine, N, N-diethylacetamide, N-ethylpyrrolidone-2, N, N-dimethylpropionic acid amide, N, Examples thereof include N-dimethylisobutyramide, N-methylformamide, N, N-dimethylpropyleneurea and mixed systems thereof. More preferable examples include N-methylpyrrolidone-2, hexamethylphosphoramide, N, N-dimethylacetamide and a mixed system thereof. These solvents may contain a dissolution accelerator such as calcium chloride, if necessary.
[0045]
Moreover, various acid solutions and organic solvents can be used as a solvent that can be solution-extracted, and specific examples include anhydrous concentrated sulfuric acid and the above-mentioned amide solvents. However, the use of concentrated sulfuric acid anhydride is highly dangerous in the process, and it is more preferable to use an amide solvent.
[0046]
That is, in the present invention, an amide solvent that can be removed by volatile drying and solvent extraction in a coagulation bath is preferable, and N-methylpyrrolidone-2, N, N-dimethylacetamide and a mixed system thereof are particularly preferable. It is.
[0047]
The polymer concentration in the solution of the wholly aromatic polyamide dissolved in such a solvent depends on the degree of polymerization of the wholly aromatic polyamide, the solubility, the solution viscosity, and the film forming means, but the viewpoint of efficiently producing the membrane Therefore, the range of 1 to 50% by weight, particularly 3 to 20% by weight based on the weight of (polymer + solvent) is preferable.
[0048]
In the present invention, the wholly aromatic polyamide solution may be used by dissolving a previously produced wholly aromatic polyamide in the above solvent, and the concentration of the wholly aromatic polyamide solution obtained by solution polymerization is adjusted as necessary. May be used.
[0049]
On the other hand, the metal oxide fine particles used in the present invention are insoluble in a solvent that dissolves the wholly aromatic polyamide, and are dissolved in a different solvent. It is preferable that it exists in the range of 1/50-1/5 of the thickness of this.
[0050]
The metal oxide fine particle dispersion film formed here is a film at the time of film formation by a solution casting drying method and / or a wet film formation method to be described later, and the thickness of the film is selected depending on the application. . When used as a support material for structural materials, the film thickness is not particularly limited. However, when used as a film for allowing a substance such as gas or liquid to pass through, or for manufacturing, metal oxide fine particles dispersed in the film Is to be dissolved and removed efficiently, the film thickness is 1 mm or less, preferably 0.5 mm or less. The lower limit of the film thickness is not particularly limited, but is preferably 1 μm or more from the viewpoint of handleability after film formation.
[0051]
The average particle diameter of the metal oxide fine particles is selected according to the film thickness at the time of film formation. However, when the metal oxide fine particles are smaller than 1/50 of the film thickness, it is difficult for the solution to penetrate when the metal oxide fine particles are dissolved. In addition to remaining easily afterwards, even if vacancies are formed, they do not function effectively as vacancies in the film. That is, the material permeability is relatively lowered. On the other hand, when it becomes larger than 1/5 of the film thickness, the mechanical strength of the porous film is extremely lowered. Therefore, the range of 1/50 to 1/5 of the film thickness is preferable.
[0052]
On the other hand, the appropriate addition amount of such metal oxide fine particles depends on the amount of the wholly aromatic polyamide in the fine particle dispersion, and the solid content in the metal oxide fine particle dispersion, ie, the wholly aromatic polyamide. It is preferable that the ratio of the wholly aromatic polyamide is 10 to 70% by volume in the residual component amount when the solvent component in the metal oxide fine particle dispersion solution such as itself and the metal oxide fine particle is removed. If the total aromatic polyamide content is less than 10% by volume, the porous membrane has a high percentage of pores, but it is difficult to obtain a porous membrane having the intended strength of the present invention. On the other hand, if it exceeds 70% by volume, the fine particles are likely to be isolated in the formed metal oxide fine particle dispersion film. Such isolated metal oxide fine particles are difficult to dissolve and remove, and even if dissolved, the isolated pores do not contribute to the material permeability as a porous film. A more preferable proportion of wholly aromatic polyamide is 20 to 60% by volume based on the total solid content.
[0053]
As described above, the kind of metal oxide fine particles is insoluble or hardly soluble in a solvent that dissolves a wholly aromatic polyamide and soluble in a solvent that does not dissolve a wholly aromatic polyamide, Specifically, those which are soluble in an alkaline aqueous solution having a concentration of 5 N or less or an acid aqueous solution having a concentration of 5 N or less are preferable. When a stronger alkali or acid solution is used for dissolution and removal, the decomposition and deterioration of the wholly aromatic polyamide become remarkable, and the mechanical strength of the resulting porous film may be extremely reduced. Moreover, an acid anhydride is not preferable because it may dissolve a wholly aromatic polyamide.
[0054]
Here, the reason why metal oxide fine particles are particularly selected is that they are not easily deformed when stretched at a temperature range in which the polymer is handled, for example, 300 ° C., and that the dissolution characteristics are not greatly changed by oxidation like metal fine particles. Can be mentioned.
[0055]
Suitable metal oxide materials for forming such fine particles include copper (I) oxide, copper (II) oxide, indium oxide, magnesium oxide, nickel oxide, tin (II) oxide, zinc oxide and the like. In particular, zinc oxide is preferable, but is not limited thereto.
[0056]
In order to prepare such a metal oxide fine particle-dispersed wholly aromatic polyamide solution, the metal oxide fine particles may be added to a previously prepared wholly aromatic polyamide solution, and the metal oxide is dissolved in a solvent that dissolves the wholly aromatic polyamide. Fine aromatic particles may be dispersed and the wholly aromatic polyamide may be dissolved therein.
[0057]
(Film formation)
A film is formed from the metal oxide fine particle-dispersed wholly aromatic polyamide solution by a solution casting drying method and / or a wet film forming method. As described above, the thickness of the membrane is selected depending on the use of the porous membrane. The film thickness is not particularly limited when used as a support material for structural materials, but when used as a film (for example, a battery separator) for passing a substance such as a gas or liquid, or a metal dispersed in manufacturing. When the oxide fine particles must be efficiently dissolved and removed, the film thickness is 1 mm or less, preferably 0.5 mm or less. The lower limit of the film thickness is not particularly limited, but is preferably 1 μm or more from the viewpoint of handleability after film formation.
[0058]
The solution casting drying step in the present invention is a method in which a solution in which a polymer is dissolved is cast so as to have a constant solution thickness on a substrate made of glass, metal, plastic, or a belt, and then removed by solvent evaporation. This is a process of forming a film of residual solid content on a substrate. A known technique can be used for the solution casting method, and it can be selected from coating techniques such as gravure coating, roll coating, and die coating, depending on the solution thickness and viscosity. For the solvent volatilization removal, specifically, known drying techniques such as heat drying, vacuum drying, and vacuum heat drying can be applied.
[0059]
In addition, the wet coagulation step refers to casting a solution in which a polymer is dissolved on a glass, metal, plastic, or other substrate so as to have a constant solution thickness. Immerse it in a coagulation solution that has affinity for the solvent used to dissolve the polyamide, extract the solvent component of the wholly aromatic polyamide solution into the coagulation bath, and remove the solid solid film on the substrate or coagulate. It is a process of forming in a bath solution. The known solution casting method described above can be used for casting at this time.
[0060]
In the present invention, it is preferable to combine these and not completely evaporate and dry the solvent in the solution casting drying step, but switch to the wet coagulation step in the course of volatilization and effectively remove the solvent. According to the researches of the present inventors, by combining these two solvent removal steps in the order described above, in addition to the effect of simply removing the solvent, (a) the formed membrane can be easily removed from the support. (B) The surface of the finally produced wholly aromatic polyamide porous membrane that was in contact with the support (the support surface) and the opposite surface (the air surface). It is clear that the properties are very close and both surfaces show good material permeability, and that (c) the wet coagulation method alone can suppress the point that the structure of the porous membrane changes greatly depending on the coagulation conditions. It became.
[0061]
At this time, in order to further increase the material permeability of the porous membrane, in the solution casting drying step, the drying temperature (the boiling point of the solvent that dissolves the wholly aromatic polyamide and does not dissolve the fine particles −60 ° C.) The above is preferable. The reason for raising the drying temperature in this way is not only the effect on the manufacturing process, that is, the solvent volatilization rate is increased and the time of the drying process is shortened. This is because the effect that it is easy to perform is also exhibited. As a result, a porous membrane having particularly good substance permeability can be obtained.
[0062]
(Removal of metal oxide particles)
Next, the metal oxide fine particle dispersion film formed as described above is treated in a bath solution, and the metal oxide fine particles are dissolved and removed from the film. Such a bath solution (dissolving solution) is not particularly limited as long as it can selectively dissolve and remove the metal oxide fine particles without dissolving or decomposing the wholly aromatic polyamide constituting the membrane, but industrially. As described above, an alkaline aqueous solution having a concentration of 5 N or less or an acid aqueous solution having a concentration of 5 N or less is preferably used. Here, the acid is preferably an inorganic acid such as nitric acid, hydrochloric acid or sulfuric acid, and the alkali is preferably sodium hydroxide or potassium hydroxide.
[0063]
When a stronger alkali or acid solution is used for dissolution and removal, the degradation and deterioration of the wholly aromatic polyamide may become significant, and the mechanical strength of the porous film that may be produced may be extremely reduced. This is not preferable because dissolution of wholly aromatic polyamide may occur.
[0064]
The inert fine particles are dissolved and removed by immersing a wholly aromatic polyamide film (fine particle dispersed film) containing the fine particles in a bath of the above-described dissolved solution. The immersion bath may be a bath in which the liquid flows or a bath in which the liquid does not flow. Further, the fine particle dispersed film may be allowed to stand in the bath or moved.
[0065]
The conditions for dissolving and removing the metal oxide fine particles depend on the dissolution rate of metal oxide fine particles, the saturation solubility, the freezing point of the liquid in which the metal oxide fine particles are dissolved, the boiling point, etc., but within a temperature range of 0 to 100 ° C. within 24 hours. It is preferable in terms of the production process to dissolve and remove.
[0066]
Thus, by forming a film from the metal oxide fine particle dispersion solution and dissolving and removing the metal oxide fine particles from the film, a good wholly aromatic polyamide porous film can be formed. An organic substance for promoting the generation of vacancies (hereinafter sometimes referred to as a vacancy generation accelerator) may be added to the metal oxide fine particle dispersion solution to form a film.
[0067]
That is, in addition to the dispersion of the metal oxide fine particles dissolved in the solution, the fully aromatic polyamide is substantially incompatible with each other and is dissolved in the organic solvent for dissolving the fully aromatic polyamide, and the fully aromatic polyamide An organic substance dissolved in a solvent in which polyamide does not dissolve is used as a vacancy generation accelerator, and after forming a wholly aromatic polyamide film in which metal oxide fine particles and the organic substance are dispersed, the metal oxide fine particles and the organic substance are formed. It is possible to adopt a method of smoothly dissolving and removing the above.
[0068]
In other words, the organic substance as the pore generation accelerator dissolves in the solvent that dissolves the wholly aromatic polyamide, but phase-separates from the wholly aromatic polyamide as the solvent is removed during film formation. As such an organic substance (vacancy generation accelerator), from the viewpoint of workability, a solid substance at 30 ° C., that is, a substance in which the film does not stick to the organic substance after film formation is preferable. More preferably, the metal oxide fine particles are dissolved together in the metal oxide fine particle dissolution treatment step. As such a vacancy generation accelerator, poly (alkylene oxide) such as poly (ethylene oxide) and poly (propylene oxide) is preferable. Furthermore, poly (ethylene oxide) can be mentioned from the viewpoint of higher water solubility. However, since the properties of poly (ethylene oxide) such as solubility and melting point vary greatly depending on the average molecular weight, those having an average molecular weight between 1500 and 7500 are preferred. When the average molecular weight is lower than 1500, a suitable porous membrane structure may not be obtained at the time of phase separation with the wholly aromatic polyamide, and a two-layer laminated structure of the wholly aromatic polyamide and poly (ethylene oxide) may be obtained. In addition, poly (ethylene oxide) is liquid at an average molecular weight of 150 or less, and as described above, workability may be reduced due to stickiness. Even when the average molecular weight is lower than 1500, the film may be sticky after impregnation with the solvent of the wholly aromatic polyamide solution. On the other hand, when the average molecular weight is larger than 7500, it becomes difficult to dissolve in the fine particle dispersion containing the wholly aromatic polyamide. Even if it is dissolved, the mixed solution becomes pasty and difficult to cast. Moreover, it becomes difficult to dissolve at the time of dissolution removal.
[0069]
The added amount of such metal oxide fine particles and pore generation accelerator is such that the total amount thereof is 10 to 70% by volume of the total aromatic polyamide in the solid content in the metal oxide fine particle dispersion. It is preferable that When the amount of wholly aromatic polyamide is less than 10% by volume, the porosity ratio of the porous film increases, but it is difficult to obtain a porous film having the intended strength of the present invention. Further, when the content is 70% by volume or more, the metal oxide fine particles are easily isolated in the formed metal oxide fine particle dispersion film. Such isolated metal oxide fine particles are difficult to dissolve and remove, and even if dissolved, the isolated pores do not contribute to the material permeability as a porous film. A more preferable ratio of wholly aromatic polyamide is 20 to 60% by volume as described above. The amount of the pore formation accelerator is preferably 50 to 300% by volume with respect to the wholly aromatic polyamide.
[0070]
(Stretching)
The membrane that has been subjected to the metal oxide fine particle removal treatment will exhibit porosity at this point, but in order to increase the permeability or mechanical strength, it is better to apply the stretching treatment to obtain a fully aromatic polyamide. It is preferable in that Examples of such stretching treatment include uniaxial stretching, sequential biaxial stretching, simultaneous biaxial stretching, and rolling. The order of the stretching treatment may be before the metal oxide fine particle removal treatment or after the treatment. As the stretching ratio, the effect of improving the mechanical strength due to stretching is not prominent unless the film is stretched at least 1.2 times in one direction of the porous membrane. And it is preferable that it is a high magnification within the range which does not fracture.
[0071]
(Post-processing)
The porous membrane of the wholly aromatic polyamide thus produced is finally washed and dried to obtain a product. Washing is preferably pure water washing at room temperature or under heating, and drying can be performed by natural drying or drying with a drier.
[0072]
【Example】
Next, each example and comparative example of the present invention will be described in detail. Of the various indices described in these examples, those other than those already described were evaluated in the following manner.
1) Logarithmic viscosity: The logarithmic viscosity of the polymerized wholly aromatic polyamide was shown as a value measured at 30 ° C. at a concentration of 0.5 g / 100 ml using concentrated sulfuric acid as a solvent.
2) Stretch ratio: Stretching was performed sequentially by biaxial stretching. And each draw ratio was displayed by the pre-draw ratio x the post-draw ratio.
[0073]
[Example 1]
Under a nitrogen stream in a flask, 6.968 g of 3,4'-diaminodiphenyl ether and 3.764 g of paraphenylenediamine were dissolved in 300 g of dehydrated and purified N-methylpyrrolidone-2, and then cooled in an ice-water bath. After cooling, 14.136 g of terephthalic acid dichloride powder was quickly added to this solution and stirred vigorously. Further, when the temperature of the solution exceeded 50 ° C. due to reaction heat, the temperature was raised to 85 ° C. and stirred for 1 hour. Thereafter, 5.15 g of calcium hydroxide was added to neutralize the by-product hydrochloric acid to obtain a yellow transparent high-viscosity solution. The total aromatic polyamide concentration in this solution was 6.0% by weight.
[0074]
For measurement, a part of this solution was taken out and mixed with water. The precipitated polymer was separated, washed with water, dried, and then its logarithmic viscosity was measured to be 3.2. The wholly aromatic polyamide had a specific gravity of 1.34.
[0075]
Then, to 100 parts by weight of the above solution, 49 parts by weight of N-methylpyrrolidone-2, 1 part by weight of a surfactant (“Homogenol” L-18 manufactured by Kao) and zinc oxide fine particles having an average particle diameter of 1 μm (high purity chemical) 32.8 parts by weight of a specific gravity of 5.47) was uniformly dispersed and mixed at 70 ° C. under a nitrogen stream to obtain a zinc oxide fine particle dispersed solution. Thereafter, a leveling agent (SH28PA manufactured by Shin-Etsu Chemical Co., Ltd.) 0.16 parts by weight was further added and mixed. The mixture is cast on a glass plate at 80 ° C. to a thickness of 0.8 mm, dried in a drying furnace at 130 ° C. for 12 minutes, and subsequently immersed in water for 2 minutes to obtain a solvent. Was removed. And this was taken out and dried, and a self-supporting white film was obtained.
[0076]
The white film was sequentially biaxially stretched 1.5 times x 1.5 times in an environment of 310 ° C., and then immersed in a 5% nitric acid aqueous solution for 30 minutes to disperse the zinc oxide dispersed in the white film. Fine particles were dissolved and removed. And after performing pure water washing | cleaning, the drying process was implemented and the porous film was obtained.
[0077]
The results of evaluating the properties of the wholly aromatic polyamide porous membrane thus prepared are shown in the Example 1 column of Table 1. From this, it can be seen that the porous film of the present invention has good strength and ionic conductivity, and the metal oxide remaining ratio is low.
[0078]
[Example 2]
To 100 parts by weight of the wholly aromatic polyamide solution solution-polymerized in Example 1, 32.7 parts by weight of N-methylpyrrolidone-2, 0.7 parts by weight of a surfactant (“Homogenol” L-18 manufactured by Kao) and an average 21.9 parts by weight of zinc oxide fine particles having a particle diameter of 1 μm (product of high purity chemical, specific gravity 5.47) were uniformly dispersed and mixed at 70 ° C. under a nitrogen stream to obtain a zinc oxide fine particle dispersed solution. Thereafter, a leveling agent (SH28PA manufactured by Shin-Etsu Chemical Co., Ltd.) 0.16 parts by weight was further mixed. Then, this mixed solution was cast on a glass plate at 80 ° C. so as to have a thickness of 0.6 mm, dried in a drying furnace at 130 ° C. for 8 minutes, and subsequently immersed in water for 2 minutes. Then, it dried and obtained the self-supporting white film.
[0079]
This white film was sequentially biaxially stretched 1.5 times x 1.5 times in an environment of 310 ° C. Next, this stretched white film was immersed in a 5% nitric acid aqueous solution for 30 minutes to dissolve and remove the zinc oxide fine particles dispersed in the white film. And after performing pure water washing | cleaning, it was made to dry and the porous film was obtained.
[0080]
The results of evaluating the properties of the wholly aromatic polyamide porous membrane thus prepared are shown in Example 2 column of Table 1. This shows that this porous film has good strength and ionic conductivity, and the metal oxide remaining ratio is low.
[0081]
[Example 3]
Similarly, 0.16 part by weight of a leveling agent (SH28PA manufactured by Shin-Etsu Chemical Co., Ltd.) was mixed with the zinc oxide fine particle dispersion prepared in Example 2. Then, this mixed solution was cast on a glass plate at 80 ° C. so as to have a thickness of 0.6 mm, dried in a drying furnace at 150 ° C. for 10 minutes, and subsequently immersed in water for 2 minutes. After the drying treatment, a self-supporting white film was obtained.
[0082]
This white film was sequentially biaxially stretched 1.5 times x 1.5 times in an environment of 310 ° C. Next, this stretched white film was immersed in a 5% nitric acid aqueous solution for 30 minutes to dissolve and remove the zinc oxide fine particles dispersed in the white film. And after performing pure water washing | cleaning, it was made to dry and the porous film was obtained.
[0083]
The results of evaluating the properties of the wholly aromatic polyamide porous membrane thus prepared are shown in Example 3 column of Table 1. This shows that this porous film has good strength and ionic conductivity, and the metal oxide remaining ratio is low.
[0084]
[Example 4]
Similarly, 0.16 part by weight of a leveling agent (SH28PA manufactured by Shin-Etsu Chemical Co., Ltd.) was mixed with the zinc oxide fine particle dispersion prepared in Example 2. Then, this mixed solution is cast to a thickness of 0.6 mm on a glass plate at 80 ° C., dried in a drying furnace at 180 ° C. for 8 minutes, subsequently immersed in water for 2 minutes, and further dried. Later, a self-supporting white film was obtained.
[0085]
This white film was sequentially biaxially stretched 1.5 times x 1.5 times in an environment of 310 ° C. Next, this stretched white film was immersed in a 5% nitric acid aqueous solution for 30 minutes to dissolve and remove the zinc oxide fine particles dispersed in the white film. And after performing pure water washing | cleaning, it was made to dry and the porous film was obtained.
[0086]
The results of evaluating the properties of the wholly aromatic polyamide porous membrane thus produced are shown in Example 4 column of Table 1. This shows that this porous film has good strength, ionic conductivity, and a low metal oxide residual ratio.
[0087]
[Comparative Example 1]
100 parts by weight of the wholly aromatic polyamide solution polymerized in Example 1, 50 parts by weight of N-methylpyrrolidone-2, 18.4 parts by weight of aluminum fine particles having an average particle size of 3 μm (high purity chemical, specific gravity 2.699), 6 parts by weight of polyethylene oxide (average molecular weight 6000) was uniformly dispersed and mixed at 80 ° C. to obtain a fine particle dispersion solution. And this liquid mixture was cast so that it might become a thickness of 0.4 mm on a 80 degreeC glass plate, and the drying process was performed for 40 minutes in a 130 degreeC drying furnace. After this drying treatment, a self-supporting gray film was obtained.
[0088]
Thereafter, the gray film was sequentially biaxially stretched 1.5 times x 1.5 times in a 150 ° C environment. Next, this stretched gray film was immersed in a 3.5% aqueous sodium hydroxide solution for 1.5 hours to dissolve and remove the aluminum fine particles and polyethylene oxide dispersed in the gray film. Then, pure water was washed to obtain a porous film.
[0089]
The results of evaluating the properties of the wholly aromatic polyamide porous membrane thus prepared are shown in the Comparative Example 1 column of Table 1. This indicates that this porous film is a film in which a large amount of metal oxide fine particles remain and is slightly inferior in ionic conductivity.
[0090]
[Comparative Example 2]
50 parts by weight of N-methylpyrrolidone-2 was mixed with 100 parts by weight of the wholly aromatic polyamide solution polymerized in Example 1 to obtain a film forming solution. And this liquid mixture was cast so that it might become 0.7 mm thickness on an 80 degreeC glass plate, and it was immersed in the pure water of 25 degreeC as it was. After 5 minutes, the film spontaneously separated from the glass plate. The membrane was washed with pure water and then dried at a constant length to obtain a self-supporting pale yellow membrane. Then, this pale yellow film was sequentially biaxially stretched 2 × 2 times in an environment of 150 ° C.
[0091]
The results of evaluating the properties of the wholly aromatic polyamide porous membrane thus produced are shown in the Comparative Example 2 column of Table 1. This shows that this thing has very bad ionic conductivity.
[0092]
[Comparative Example 3]
50 parts by weight of N-methylpyrrolidone-2 was mixed with 100 parts by weight of the wholly aromatic polyamide solution polymerized in Example 1 to obtain a film forming solution. And this liquid mixture was cast so that it might become 0.9 mm thickness on a 80 degreeC glass plate, and it immersed in 25 degreeC n-octanol as it was. After 1 hour, the film spontaneously separated from the glass plate. The membrane was pulled up, washed with methanol, and dried at a constant length to obtain a self-supporting white membrane. The white film was sequentially biaxially stretched 1.4 times x 2 times in an environment of 150 ° C.
[0093]
The results of evaluating the properties of the wholly aromatic polyamide porous membrane thus produced are shown in the Comparative Example 3 column of Table 1. This shows that this porous film has poor ionic conductivity.
[0094]
[Comparative Example 4]
To 100 parts by weight of the wholly aromatic polyamide solution polymerized in Example 1, 50 parts by weight of N-methylpyrrolidone-2 and 9 parts by weight of polyethylene oxide (average molecular weight 3000) were uniformly dispersed and mixed at 80 ° C. Obtained. And this liquid mixture was cast so that it might become 0.7 mm thickness on a 100 degreeC glass plate, and the drying process was performed for 25 minutes in a 150 degreeC drying furnace. After drying, a self-supporting light yellow film was obtained. The pale yellow film was successively biaxially stretched 2 × 2 times in an environment of 150 ° C. Next, this stretched pale yellow film was immersed in 70 ° C. pure water for 10 minutes, and further subjected to ultrasonic cleaning for 10 minutes as it was to dissolve and remove the polyethylene oxide dispersed in the yellow film. And the pure water washing | cleaning was performed and the porous film was obtained.
[0095]
The results of evaluating the properties of the wholly aromatic polyamide porous membrane thus produced are shown in Comparative Example 4 of Table 1. This shows that the ionic conductivity is extremely poor.
[0096]
[Comparative Example 5]
Similarly, 0.16 part by weight of a leveling agent (SH28PA manufactured by Shin-Etsu Chemical Co., Ltd.) was mixed with the zinc oxide fine particle dispersion prepared in Example 1. And this liquid mixture was cast so that it might become 0.6 mm thickness on a 80 degreeC glass plate, and the drying process was performed for 15 minutes in a 180 degreeC drying furnace. After drying, a self-supporting white film was obtained. Thereafter, the white film was sequentially biaxially stretched to 1.5 × 1.5 in an environment of 310 ° C. Next, this stretched white film was immersed in a 5% nitric acid aqueous solution for 30 minutes to dissolve and remove the dispersed zinc oxide fine particles. Then, pure water was washed to obtain a porous film.
[0097]
The results of evaluating the properties of the wholly aromatic polyamide porous membrane thus prepared are shown in Comparative Example 5 of Table 1. From this, it is understood that this porous film has a slightly poor ionic conductivity.
[Table 1]
【The invention's effect】
As described above, by using the technique of the present invention, it is possible to provide a wholly aromatic polyamide porous film having good material permeability and good heat resistance, mechanical strength, and appearance. The wholly aromatic polyamide porous membrane of the present invention is suitably used for heat-resistant separation filtration membranes, battery separators, etc. that require a particularly thin and high-performance wholly aromatic polyamide porous membrane, taking advantage of its properties. be able to.
Claims (11)
【化１】
−ＮＲ1−Ａｒ1−ＮＲ2−ＣＯ−Ａｒ2−ＣＯ− （１）
（ここで、Ｒ1及びＲ2は、同一もしくは相異なり、水素原子、ハロゲン原子及び炭素数５以下のアルキル基からなる群から選ばれ、Ａｒ1及びＡｒ2は、同一もしくは相異なり、置換基を有してもよいオルトフェニレン基、メタフェニレン基、パラフェニレン基、１，４ナフチレン基、１，５ナフチレン基、２，６ナフチレン基、２，５ピリジレン基及び下記式（２）で示される２価の基から選択される。）
[Chemical 1]
—NR 1 —Ar 1 —NR 2 —CO—Ar 2 —CO— (1)
(Wherein R 1 and R 2 are the same or different and are selected from the group consisting of a hydrogen atom, a halogen atom and an alkyl group having 5 or less carbon atoms; Ar 1 and Ar 2 are the same or different and are a substituent; An orthophenylene group, a metaphenylene group, a paraphenylene group, a 1,4 naphthylene group, a 1,5 naphthylene group, a 2,6 naphthylene group, a 2,5 pyridylene group, and the following formula (2) Selected from divalent groups.)
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| JP2006160888A (en) * | 2004-12-07 | 2006-06-22 | Nakajima Kogyo:Kk | Gas-permeable film and method for producing the same |
| WO2013105300A1 (en) | 2012-01-13 | 2013-07-18 | 東レ株式会社 | Aromatic polyamide porous film, separator for batteries and battery |
| JP6299168B2 (en) * | 2012-12-25 | 2018-03-28 | 東レ株式会社 | Aromatic polyamide porous membrane and battery separator |
| JP6358663B2 (en) * | 2013-06-07 | 2018-07-18 | 公立大学法人首都大学東京 | Method for producing separator for secondary battery and method for producing lithium secondary battery |
| JP2020158640A (en) * | 2019-03-27 | 2020-10-01 | 帝人株式会社 | Para-type total aromatic polyamide film and method for producing the same, and separator containing said film |
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