JP4599787B2

JP4599787B2 - Method for producing hollow fiber membrane and hollow fiber membrane

Info

Publication number: JP4599787B2
Application number: JP2002015563A
Authority: JP
Inventors: 利之石崎; 進一峯岸; 浩一旦; 昌弘辺見
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2002-01-24
Filing date: 2002-01-24
Publication date: 2010-12-15
Anticipated expiration: 2022-01-24
Also published as: JP2003210954A

Description

【０００１】
【発明の属する技術分野】
本発明は、河川水や地下水などの除濁や工業用水の清澄化など浄水処理分野に好適に使用できる分離用中空糸膜の製造方法に関する。
【０００２】
【従来の技術】
膜分離法は省エネルギー、省スペース、省力化などの特長を有するために様々な分野で利用されている技術である。分離対象物によって精密ろ過膜、限外ろ過膜および逆浸透膜などの平膜や中空糸膜などを使用する。近年、精密ろ過用、あるいは限外ろ過用の分離膜として、河川水や地下水除濁、工業用水の清澄化、あるいは排水の高度処理などの分野に適用しようとする動きが活発に行われている。しかし、長期運転を目的とするような浄水処理分野への適用には、除菌性、透水性、機械的特性、耐薬品性などに高い特性が要求されている。ポリビニリデンフルオライド系樹脂を素材として用いた場合、耐薬品性、耐熱性、機械的特性など優れた諸特性を持つために分離膜としての期待が非常に高い。これまでにポリビニリデンフルオライド系樹脂からなる分離膜の製造方法としては、溶液製膜法、溶融製膜法などが提示されている。溶液製膜法では、例えば特公平１−２２００３号公報に開示されているポリビニリデンフルオライド系樹脂を有機溶媒に溶解させ、非溶媒中で固液、あるいは液液相分離させて製膜する方法が開示されている、しかし膜構造が不均一で表面近くにマクロボイドを形成するために機械的強度に課題が有った。また、溶融製膜法では、例えば特許２８９９９０３号公報に開示されているようにポリビニリデンフルオライド系樹脂の溶融成形物から可塑剤や無機微粉体を抽出して、孔を形成させる方法が提案されているもので、溶液製膜で得られる膜よりも高い機械的強度を示すものであった。しかし、溶融成型物から無機微粉体をアルカリ抽出する手間と工程が複雑化している。さらに使用されるフタル酸ジブチル、フタル酸ジオクチルなどの可塑剤にも環境上の影響に懸念が残るものである。
【０００３】
【発明が解決しようとする課題】
本発明は、簡素なプロセスを用いて、河川水や地下水除濁、工業用水の清澄化、あるいは排水の高度処理などの分野に好適に使用できる高強度で高透水性のポリビニリデンフルオライド系中空糸膜の製造方法を提供するものである。
【０００４】
【課題を解決するための手段】
上記の課題を達成するために以下の構成からなる。すなわち本発明の中空糸膜の製造方法は、少なくともポリビニリデンフルオライド系樹脂を含む溶液を、球晶構造を発達させながら凝固させて中空糸を得、該中空糸を１．１〜４倍の範囲で延伸し、さらに延伸後の中空糸を弛緩率０．１〜１０％の範囲で弛緩させることを特徴とするものである。
【０００５】
【発明の実施の形態】
本発明におけるポリビニリデンフルオライド系樹脂とは、ビニリデンフルオライドホモポリマー、ビニリデンフルオライド共重合体あるいは、両者の混合物などが挙げられるが、好ましくはビニリデンフルオライドホモポリマーを８５重量％以上（より好ましくは９０重量％以上、さらに好ましくは９５重量％以上）含むものである。ビニリデンフルオライド共重合体としては、ポリマー構造にビニリデンフルオライドモノマー残基構造を有するようなポリマーがあり、ビニリデンフルオライド−テトラフルオロエチレン共重合体、ビニリデンフルオライド−６フッ化プロピレン共重合体等のビニリデンフルオライドを原料モノマーとして製造し得るポリマーの他、エチレン−４フッ化エチレン共重合体のように、ビニリデンフルオライド以外の原料モノマーから製造し得るものも挙げられる。また、ポリビニリデンフルオライド系樹脂の重量平均分子量は、中空糸膜の機械的特性や透水性を考慮すると５万〜７０万が好ましく、溶媒の溶解性や紡糸性を考慮した場合、１０万〜５０万が好ましい。より好ましくは１５万〜４５万である。ここで親水化のために溶液中にポリエチレングリコール、ポリプロピレングリコール、ポリビニルアルコール、ポリ酢酸ビニル、ポリビニルピロリドン、ポリアクリル酸などの水溶性ポリマー、およびグルセリンなどの多価アルコールを添加することも可能である。
【０００６】
本発明におけるポリビニリデンフルオライド系樹脂を含む溶液の溶媒として、Ｎ−メチル−２−ピロリドン、ジメチルスルホキシド、ジメチルアセトアミド、ジメチルホルムアミド、メチルエチルケトン、アセトン、テトラヒドロフラン、テトラメチル尿素、リン酸トリメチル、シクロヘキサノン、イソホロン、γ−ブチロラクトン、メチルイソアミルケトン、フタル酸ジメチル、プロピレングリコールメチルエーテル、プロピレンカーボネート、ジアセトンアルコール、グリセロールトリアセテートなどを例示することができる。これらを単独で用いても良いし、２種類以上を混合して用いても良い。さらに溶媒以外の成分を添加しても良い。例えば、ポリエチレングリコール、ポリビニルアルコール、ポリビニルピロリドン、グリセリンなどである。また非溶媒としては、水、ヘキサン、ペンタン、ベンゼン、メタノール、トルエンなどのプロトン性溶媒、もしくは非極性溶媒が例示できるが、取り扱い容易な水が好ましく用いられる。
【０００７】
前記のポリビニリデンフルオライド系樹脂は溶媒に完全に溶解することが好ましいが、例え溶けきれなかった固形物が残ってもフィルターろ過により除去すれば問題ない。つまり、溶解温度６０〜１７０℃の温度範囲に調製されたポリビニリデンフルオライド系樹脂を含む溶液（以下、単にポリマー溶液ともいう）を、好ましくは５〜１００μｍの範囲のステンレス製フィルターなどでろ過した後に、チューブインオリフィスを使った紡糸方法で中空糸状に賦形して製造することが好ましい。なおオリフィスの温度すなわち紡糸温度は、溶解温度と同様、６０〜１７０℃の温度範囲が好ましく、オリフィス温度と溶解温度が異なっても構わない。溶解温度については、溶解を短時間に均一に行うという点から、オリフィス温度より高い温度設定することも好ましく採用できる。ここでチューブインオリフィスとは、金属製などの円形ノズル内に円形チューブ（パイプ）が挿入されており、円形ノズルと円形チューブに一定の間隙を設けた２重管状のノズルをいう。
【０００８】
本発明においては、前記のポリマー溶液を凝固浴へ押し出して凝固させ、中空糸を得ることが好ましい。凝固に際して、非溶媒による相分離よりも、球晶構造の発達が優先するように、低温凝固が支配的な熱誘起相分離による凝固が起こるようにすることが必須である。そのため、凝固浴に用いる凝固液としては、前記のような溶媒、あるいは６０重量％以上、好ましくは７０重量％以上の溶媒を含む水溶液が好ましい。凝固浴の温度としては、５０℃以下が好ましく、より好ましくは４０℃、さらに好ましくは３０℃以下である。溶媒濃度が６０重量％を下回ると中空糸表面が緻密化し易く透水性が低くなる傾向がある。また凝固浴の温度が５０℃を越すと中空糸の形状不良が起こり易い。
【０００９】
前記のチューブインオリフィスの寸法は、製造する中空糸膜の寸法と膜構造により適宜選択すれば良いが、おおよそオリフィス外径０．７〜１０ｍｍ、チューブ管外径０．５〜５ｍｍ、チューブ管内径０．２５〜４ｍｍの範囲にあることが好ましい。このオリフィス外径とチューブ管外径の間隙にポリマー溶液を流し、チューブ管内径内に中空部形成用液体を流すものである。また、紡糸ドラフト（引取り速度／原液の口金吐出線速度）は、好ましくは０．８〜５０、より好ましくは０．９〜４０、さらに好ましくは０．９〜３０の範囲、乾式長は好ましくは０．１〜８０ｃｍ、より好ましくは０．３〜５０ｃｍ、さらに好ましくは０．５〜３０ｃｍの範囲である。前記の通りオリフィスからポリマー溶液を吐出させて中空糸に中空部を形成させるにはチューブから中空部形成用液体を吐出することが好ましい。中空部形成用液体としては、前記の凝固液と同種類のものが好適である。チューブに中空部形成用液体を注入する際して、溶媒濃度が６０重量％を下回ると凝固が速く、膜内表面の緻密化により透水性が低くなる傾向を示す。
【００１０】
本発明においては、前記の中空糸を１．１〜４倍、より好ましくは１．１〜３倍、さらに好ましくは１．１〜２倍の範囲で延伸することが特徴である。これにより、透水性や阻止率などの特性を容易に制御できる。延伸は、５０〜１６５℃の温度範囲の熱媒中に２〜３０ｍ／分、好ましくは３〜２０ｍ／分、さらに好ましくは３〜１５ｍ／分の範囲の供給速度で供給して、延伸することが好ましい。延伸方法としては、繊維工業などに常法として用いられている湿熱延伸法、あるいは乾熱延伸法を用いることができる。ここでの延伸倍（数）とは、延伸ゾーンにおけるライン速度の比（引取速度／供給速度）を云う。熱媒としては、水、ポリエチレングルコール、グリセリン、蒸気、空気および窒素から選ばれた１つ以上を用いることが好ましい。通常、熱媒浴を用いて延伸する場合、中空糸と熱媒の接触時間は、５秒以上、好ましくは７秒以上、さらに好ましくは１０秒以上であるが、熱交換を効果的にするために浴槽における循環や対流方向を調整して、温度差を設けることであっても良く。また、熱媒は延伸に際して中空糸の有機溶媒を含む、あるいは含まないものであっても目的が達成できるもので何らかまわない。
【００１１】
前記の延伸が４倍を超えると中空糸の表面に巨視的な開裂が生じ易く、分画性能の低下や機械的強度低下の傾向を示す。また１．１倍未満であると中空糸の形状がほとんど変化しないために透水量の増加が期待できない。前記の媒体温度が５０℃未満で行うと中空糸を均一に伸ばすことが難しくなる。さらに１６５℃を越えるとポリビニリデンフルオライド系樹脂の融点近くになるので膜表面の細孔が部分的に消失する場合がある。前記の供給速度を２ｍ／分未満に行うと連動する前工程のライン速度を下げることになり、最適な紡糸ドラフトが得ることができず曳糸性不良などの問題が生じる場合がある。また、３０ｍ／分を越すと中空糸の形状安定性が低下しやすくなる。通常、熱媒との接触時間が５秒未満であると中空糸の延伸に好適な温度を得ることが難しいが、予備加熱を行えば５秒未満であっても目的を達成できる。
【００１２】
本発明においては、延伸後の中空糸を弛緩率０．１〜１０％の範囲で弛緩させることも特徴である。弛緩処理は、浴槽、あるいはチャンバー内において５０〜１６５℃の温度範囲にある水、水蒸気、空気などの熱媒と中空糸を５秒以上に接触させて、緊張下に弛緩率が０．１〜１０％の範囲になるように引取速度を減速調整させることが良い。ここで弛緩（率）は、〔１−（引取速度／供給速度）〕×１００で示す。ここで緊張下とは、中空糸に張力がかかった状態を云うが、中空糸の熱収縮などを考慮して適宜に張力を決めれば良い。緊張下に置くことで残留する収縮応力を緩和して、高い透水性と高い機械的特性をバランスさせることができる。さらにモジュール作製上における乾燥収縮などを軽減できる。なお、弛緩率が１０％を越えると伸度の低下が大きくなり、モジュール化した後の物理洗浄などに不都合が生じることがある。さらに上記の製造方法で製造された中空糸膜を用いた、中空糸膜モジュールも浄水処理、排水処理、工業用水製造に活用できるので好ましい。
【００１３】
ここで本発明の中空糸膜の形態を次のように評価した。
（１）中空糸膜割断面の走査電子顕微鏡写真から外径、および内径を求めた。
（２）純水透過水量ｍ³／（ｍ²・ｈ・１００ｋＰａ）は、本発明の中空糸状中空糸膜４本からなる長さ２０ｃｍのミニチュアモジュールを作製し、温度２５℃、ろ過差圧１６ｋＰａの条件下に、実質的に微粒子などの固形分を含まない純水の外圧全ろ過を３０分間行い、その透過量（ｍ³）を単位時間（ｈ）、および有効膜面積（ｍ²）あたりの値に圧力（１００ｋＰａ）換算した値とした。
（３）引張り強度および伸度は、引張り試験機（ＴＥＮＳＩＬＯＮ／ＲＴＭ−１００）（東洋ボールドウィン社製）を用いて、長さ５０ｍｍの試料を引張り速度５０ｍｍ／分で試料を代えて３０回測定し、その平均を測定値とした。
【００１４】
【実施例】
実施例１
重量平均分子量４２万のフッ化ビニリデンホモポリマー３０重量％とジメチルスルホキシドを７０重量％を１２０℃で溶解させてポリマー溶液を得た。乾式長２ｃｍでチューブインオリフィス（オリフィス外径２．０ｍｍ、チューブ外径０．８ｍｍ、チューブ内径０．５ｍｍ）のオリフィスから前記ポリマー溶液を、チューブから８０重量％ジメチルスルホキシド水溶液を共に押出して、液温２５℃の８０重量％ジメチルスルホキシド水溶液中で凝固させ、中空糸を得た。得られた中空糸を３０℃で水洗した。引き続き８０℃の熱水浴に８ｍ／分で供給して、熱水浴中で１．５倍（引取速度１２ｍ／分）に延伸した後、さらに緊張下に１１．２ｍ／分に減速して７％の弛緩率で弛緩させ、７０℃の温水中で脱溶媒して中空糸膜を得た。この中空糸膜は、純水透過量３．１ｍ³／（ｍ²・ｈ・１００ｋＰａ）、内径０．８６ｍｍ、外径１．３２ｍｍ、強度５．２ＭＮ／ｍ²以上、伸度８７％であった。
【００１５】
実施例２
重量平均分子量２８万のフッ化ビニリデンホモポリマー４５重量％とジメチルスルホキシドを５５重量％を１２０℃で溶解させてポリマー溶液を得た。乾式長１０ｃｍでチューブインオリフィス（オリフィス外径２．０ｍｍ、チューブ外径０．８ｍｍ、チューブ内径０．５ｍｍ）のオリフィスから前記ポリマー溶液を、チューブから８０重量％ジメチルスルホキシド水溶液を共に押出して、液温１５℃の８０重量％ジメチルスルホキシド水溶液中で凝固させ、中空糸を得た。得られた中空糸を７０℃で水洗浴で脱溶媒してから延伸、および弛緩処理を行った。延伸は、９５℃の熱水浴に８ｍ／分で供給して、熱水浴中で２．２倍（引取速度１７．６ｍ／分）に延伸した後、さらに緊張下に１７ｍ／分に減速して弛緩率３％で弛緩させた。得られた中空糸膜は、純水透過量３．５ｍ³／（ｍ²・ｈ・１００ｋＰａ）、内径０．８８ｍｍ、外径１．１８ｍｍ、強度４．８ＭＮ／ｍ²以上、伸度６８％であった。
【００１６】
実施例３
重量平均分子量４２万のフッ化ビニリデンホモポリマー３５重量％とγ−ブチロラクトンを６５重量％を１７０℃で溶解させてポリマー溶液を得た。次に乾湿式紡糸法を用いて、乾式長２ｃｍでチューブインオリフィス（オリフィス外径３．０ｍｍ、チューブ外径０．８ｍｍ、チューブ内径０．５ｍｍ）のオリフィスから前記溶液を、チューブから１００重量％γ−ブチロラクトン液を共に押出して、液温２５℃の８５重量％γ−ブチロラクトン水溶液中で中空糸状に凝固させ、中空糸を得た。引き続き６０℃の温水浴を経て９０℃の熱水浴に１０ｍ／分で供給して、熱水浴中で１．６倍（引取速度１６ｍ／分）に延伸した後、さらに緊張下に１５．５ｍ／分に減速して弛緩率３％で弛緩させ、６０℃の温水で脱溶媒した。得られた中空糸膜は、純水透過量５．８ｍ³／（ｍ²・ｈ・１００ｋＰａ）、内径０．８２ｍｍ、外径１．３１ｍｍ、強度１０．８ＭＮ／ｍ²以上、伸度１２７％であった。
【００１７】
実施例４
重量平均分子量４２万のフッ化ビニリデンホモポリマー５０重量％とγ−ブチロラクトンを５０重量％を１７０℃で溶解させてポリマー溶液を得た。乾式長１５ｃｍでチューブインオリフィス（オリフィス外径３．０ｍｍ、チューブ外径０．８ｍｍ、チューブ内径０．５ｍｍ）のオリフィスから前記ポリマー溶液を、チューブから１００重量％γ−ブチロラクトン液を共に押出して、液温３５℃の９０重量％γ−ブチロラクトン水溶液中で凝固させ、中空糸を得た。得られた中空糸を８５℃の熱水浴で脱溶媒させた。引き続き１２０℃のグリセリン浴に８ｍ／分で供給し、グリセリン浴中で２．８倍（引取速度２２．４ｍ／分）に延伸した後、さらに緊張下に２０．６ｍ／分に減速して弛緩率８％で弛緩させて中空糸膜を得た。この中空糸膜は、純水透過量３．５ｍ³／（ｍ²・ｈ・１００ｋＰａ）、内径０．８８ｍｍ、外径１．０２ｍｍ、強度８．７ＭＮ／ｍ²以上、伸度８８％であった。
【００１８】
比較例１
実施例３と同じポリマー溶液を用いて、乾式長２ｃｍでチューブインオリフィス（オリフィス外径３．０ｍｍ、チューブ外径０．８ｍｍ、チューブ内径０．５ｍｍ）のオリフィスから前記溶液を、チューブから１００重量％γ−ブチロラクトン液を共に押出して、液温２５℃の８５重量％γ−ブチロラクトン水溶液中で凝固させ、中空糸を得た。得られた中空糸を８０℃で脱溶媒して中空糸膜を得た。延伸および弛緩は行なわなかった。この中空糸膜は、純水透過量０．５７ｍ³／（ｍ²・ｈ・１００ｋＰａ）、内径０．８６ｍｍ、外径１．６２ｍｍ、強度９．１ＭＮ／ｍ²以上、伸度２１２％であった。
【００１９】
比較例２
実施例３と同じポリマー溶液を用いて、乾式長２ｃｍでチューブインオリフィス（オリフィス外径３．０ｍｍ、チューブ外径０．８ｍｍ、チューブ内径０．５ｍｍ）のオリフィスから前記溶液を、チューブから１００重量％γ−ブチロラクトン液を共に押出して、液温２５℃の８５重量％γ−ブチロラクトン水溶液中で凝固させ、中空糸を得た。引き続き１２０℃のグリセリン浴に８ｍ／分で供給し、グリセリン浴中で４．２倍（引取速度３３．６ｍ／分）に延伸した後、さらに緊張下に３２ｍ／分に減速して弛緩率４％で弛緩させた。得られた中空糸膜は、純水透過量２．７ｍ³／（ｍ²・ｈ・１００ｋＰａ）、内径０．８１ｍｍ、外径１．０４ｍｍ、強度７．８ＭＮ／ｍ²以上、伸度３９％であった。
【００２０】
比較例３
実施例３と同じポリマー溶液を用いて、乾式長２ｃｍでチューブインオリフィス（オリフィス外径３．０ｍｍ、チューブ外径０．８ｍｍ、チューブ内径０．５ｍｍ）のオリフィスから前記溶液を、チューブから１００重量％γ−ブチロラクトン液を共に押出して、液温２５℃の８５重量％γ−ブチロラクトン水溶液中で凝固させ、中空糸を得た。引き続き６０℃の温水浴を経て９０℃の熱水浴に１０ｍ／分で供給して、熱水浴中で１．６倍（引取速度１６ｍ／分）に延伸した後、延伸後の中空糸の緊張状態が保てない１３ｍ／分まで減速した（弛緩率１９％）。得られた中空糸膜は、純水透過量２．４ｍ³／（ｍ²・ｈ・１００ｋＰａ）、内径０．８４ｍｍ、外径１．２９ｍｍ、強度５．４ＭＮ／ｍ²以上、伸度２２％であった。
【００２１】
【発明の効果】
本発明の中空糸膜は、透水性、機械的特性、および耐薬品性に優れた精密ろ過膜、限外ろ過膜、各種フィルターなどの使用分野に好適に使用される。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a separation hollow fiber membrane that can be suitably used in the field of water purification such as turbidity of river water and groundwater and clarification of industrial water.
[0002]
[Prior art]
Membrane separation is a technology used in various fields because it has features such as energy saving, space saving, and labor saving. Depending on the object to be separated, flat membranes such as microfiltration membranes, ultrafiltration membranes and reverse osmosis membranes and hollow fiber membranes are used. In recent years, as a separation membrane for microfiltration or ultrafiltration, there has been an active movement to apply it to fields such as clarification of river water and groundwater, clarification of industrial water, or advanced treatment of wastewater. . However, application to the field of water purification treatment for the purpose of long-term operation requires high characteristics such as sterilization, water permeability, mechanical characteristics, and chemical resistance. When a polyvinylidene fluoride resin is used as a raw material, it has excellent properties such as chemical resistance, heat resistance and mechanical properties, so it has high expectations as a separation membrane. So far, a solution casting method, a melt casting method and the like have been proposed as a method for producing a separation membrane comprising a polyvinylidene fluoride resin. In the solution casting method, for example, a method of forming a film by dissolving a polyvinylidene fluoride-based resin disclosed in Japanese Patent Publication No. 1-2003 in an organic solvent and solid-liquid or liquid-liquid phase separation in a non-solvent. However, there is a problem in mechanical strength because the film structure is non-uniform and macrovoids are formed near the surface. Further, in the melt film forming method, for example, as disclosed in Japanese Patent No. 2899903, a method of forming pores by extracting a plasticizer or an inorganic fine powder from a melt-formed product of polyvinylidene fluoride resin is proposed. Therefore, it showed higher mechanical strength than the film obtained by solution casting. However, the labor and process of alkali-extracting inorganic fine powder from the melt-molded product are complicated. Furthermore, plasticizers such as dibutyl phthalate and dioctyl phthalate used are still concerned about the environmental impact.
[0003]
[Problems to be solved by the invention]
The present invention is a high-strength and highly water-permeable polyvinylidene fluoride-based hollow that can be suitably used in fields such as river water and groundwater clarification, industrial water clarification, or advanced wastewater treatment using a simple process. A method for producing a yarn membrane is provided.
[0004]
[Means for Solving the Problems]
In order to achieve the above-mentioned problem, the following configuration is provided. That is, in the method for producing a hollow fiber membrane of the present invention, a solution containing at least a polyvinylidene fluoride resin is solidified while developing a spherulite structure to obtain a hollow fiber, and the hollow fiber is 1.1 to 4 times larger. The hollow fiber is stretched within a range, and the hollow fiber after stretching is further relaxed within a range of a relaxation rate of 0.1 to 10% .
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Examples of the polyvinylidene fluoride resin in the present invention include vinylidene fluoride homopolymer, vinylidene fluoride copolymer, or a mixture of both. Preferably, 85% by weight or more (more preferably) vinylidene fluoride homopolymer is used. Is 90% by weight or more, more preferably 95% by weight or more). As vinylidene fluoride copolymers, there are polymers having a vinylidene fluoride monomer residue structure in the polymer structure, such as vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-6-fluoropropylene copolymer, etc. In addition to polymers that can be produced using the above-mentioned vinylidene fluoride as a raw material monomer, those that can be produced from a raw material monomer other than vinylidene fluoride, such as an ethylene-tetrafluoroethylene copolymer. Further, the weight average molecular weight of the polyvinylidene fluoride-based resin is preferably 50,000 to 700,000 in view of the mechanical properties and water permeability of the hollow fiber membrane, and in consideration of solvent solubility and spinnability, 100,000 to 500,000 is preferable. More preferably, it is 150,000 to 450,000. Here, water-soluble polymers such as polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinyl pyrrolidone, and polyacrylic acid, and polyhydric alcohols such as glycerin can be added to the solution for hydrophilization. .
[0006]
As the solvent of the solution containing the polyvinylidene fluoride resin in the present invention, N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, acetone, tetrahydrofuran, tetramethylurea, trimethyl phosphate, cyclohexanone, isophorone Γ-butyrolactone, methyl isoamyl ketone, dimethyl phthalate, propylene glycol methyl ether, propylene carbonate, diacetone alcohol, glycerol triacetate and the like. These may be used alone or in combination of two or more. Furthermore, components other than the solvent may be added. For example, polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, glycerin and the like. Examples of non-solvents include water, hexane, pentane, benzene, methanol, toluene, and other protic solvents, and nonpolar solvents. Water that is easy to handle is preferably used.
[0007]
The polyvinylidene fluoride-based resin is preferably completely dissolved in a solvent, but there is no problem if it is removed by filter filtration even if solids that have not been completely dissolved remain. That is, a solution containing a polyvinylidene fluoride-based resin prepared in a temperature range of 60 to 170 ° C. (hereinafter also simply referred to as a polymer solution) is preferably filtered through a stainless steel filter having a range of 5 to 100 μm. Thereafter, it is preferable to produce the hollow fiber by a spinning method using a tube-in orifice. The temperature of the orifice, that is, the spinning temperature, is preferably in the temperature range of 60 to 170 ° C., similarly to the melting temperature, and the orifice temperature and the melting temperature may be different. Regarding the melting temperature, it is preferable to set a temperature higher than the orifice temperature from the viewpoint that the melting is performed uniformly in a short time. Here, the tube-in orifice refers to a double tubular nozzle in which a circular tube (pipe) is inserted in a circular nozzle made of metal or the like, and a certain gap is provided between the circular nozzle and the circular tube.
[0008]
In the present invention, it is preferable to obtain a hollow fiber by extruding the polymer solution into a coagulation bath and coagulating it. During solidification, it is essential to cause solidification by heat-induced phase separation, in which low-temperature solidification is dominant, so that the development of the spherulite structure is prioritized over phase separation by a non-solvent. Therefore, as the coagulation liquid used in the coagulation bath, an aqueous solution containing the above-mentioned solvent or 60% by weight or more, preferably 70% by weight or more is preferable. As a temperature of a coagulation bath, 50 degrees C or less is preferable, More preferably, it is 40 degrees C, More preferably, it is 30 degrees C or less. When the solvent concentration is less than 60% by weight, the hollow fiber surface tends to be densified and the water permeability tends to be low. Further, when the temperature of the coagulation bath exceeds 50 ° C., the hollow fiber is liable to have a defective shape.
[0009]
The dimensions of the tube-in orifice may be appropriately selected according to the dimensions of the hollow fiber membrane to be manufactured and the membrane structure, but the orifice outer diameter is approximately 0.7 to 10 mm, the tube tube outer diameter is 0.5 to 5 mm, and the tube tube inner diameter is approximately It is preferable to be in the range of 0.25 to 4 mm. A polymer solution is caused to flow through a gap between the outer diameter of the orifice and the outer diameter of the tube tube, and a liquid for forming a hollow portion is caused to flow into the inner diameter of the tube tube. The spinning draft (take-off speed / stock solution discharge linear speed) is preferably 0.8 to 50, more preferably 0.9 to 40, still more preferably 0.9 to 30, and the dry length is preferable. Is in the range of 0.1 to 80 cm, more preferably 0.3 to 50 cm, still more preferably 0.5 to 30 cm. As described above, in order to discharge the polymer solution from the orifice to form the hollow portion in the hollow fiber, it is preferable to discharge the hollow portion forming liquid from the tube. As the liquid for forming the hollow portion, the same type as the above-mentioned coagulating liquid is preferable. When the liquid for forming the hollow part is injected into the tube, if the solvent concentration is less than 60% by weight, the solidification is fast, and the water permeability tends to decrease due to the densification of the inner surface of the membrane.
[0010]
In the present invention, the hollow fiber is stretched in a range of 1.1 to 4 times, more preferably 1.1 to 3 times, and still more preferably 1.1 to 2 times. Thereby, characteristics such as water permeability and rejection can be easily controlled. Stretching is performed by supplying a heating medium in the temperature range of 50 to 165 ° C. at a supply speed of 2 to 30 m / min, preferably 3 to 20 m / min, more preferably 3 to 15 m / min. Is preferred. As the stretching method, a wet heat stretching method or a dry heat stretching method which is commonly used in the textile industry or the like can be used. The stretching ratio (number) here refers to the ratio of the line speed in the stretching zone (take-up speed / feeding speed). As the heat medium, it is preferable to use one or more selected from water, polyethylene glycol, glycerin, steam, air and nitrogen. Usually, when drawing using a heat medium bath, the contact time between the hollow fiber and the heat medium is 5 seconds or more, preferably 7 seconds or more, and more preferably 10 seconds or more, in order to make heat exchange effective. It is also possible to provide a temperature difference by adjusting the circulation and convection direction in the bathtub. In addition, the heating medium may achieve the purpose even if it contains or does not contain a hollow fiber organic solvent during drawing.
[0011]
When the above stretching exceeds 4 times, macroscopic cleavage is likely to occur on the surface of the hollow fiber, which tends to decrease fractionation performance and mechanical strength. Moreover, since the shape of a hollow fiber hardly changes that it is less than 1.1 times, the increase in water permeability cannot be expected. When the medium temperature is less than 50 ° C., it is difficult to uniformly extend the hollow fiber. Further, when the temperature exceeds 165 ° C., the melting point of the polyvinylidene fluoride resin becomes close to the melting point, so that the pores on the film surface may partially disappear. If the supply speed is less than 2 m / min, the line speed of the preceding process is lowered, and an optimum spinning draft cannot be obtained, and problems such as poor spinnability may occur. Moreover, when it exceeds 30 m / min, the shape stability of the hollow fiber tends to be lowered. Usually, when the contact time with the heat medium is less than 5 seconds, it is difficult to obtain a temperature suitable for drawing the hollow fiber. However, if preheating is performed, the object can be achieved even if the temperature is less than 5 seconds.
[0012]
In the present invention, the hollow fiber after stretching is also relaxed in the range of a relaxation rate of 0.1 to 10%. In the relaxation treatment, a heating medium such as water, water vapor, and air in a temperature range of 50 to 165 ° C. in a bathtub or chamber is brought into contact with the hollow fiber for 5 seconds or more, and the relaxation rate is 0.1 to 0.1 under tension. It is preferable to reduce the take-up speed so as to be in the range of 10%. Here, the relaxation (rate) is represented by [1- (take-off speed / supply speed)] × 100. Here, “under tension” refers to a state where tension is applied to the hollow fiber, but the tension may be determined appropriately in consideration of thermal contraction of the hollow fiber . Relaxes contraction stress remaining in putting down tensions, it is possible to balance the high water permeability and high mechanical properties. Furthermore, drying shrinkage and the like during module production can be reduced. In addition, when the relaxation rate exceeds 10%, the decrease in elongation increases, which may cause inconvenience in physical cleaning after modularization. Furthermore, since the hollow fiber membrane module using the hollow fiber membrane manufactured with said manufacturing method can also be utilized for water purification treatment, wastewater treatment, and industrial water manufacture, it is preferable.
[0013]
Here, the form of the hollow fiber membrane of the present invention was evaluated as follows.
(1) The outer diameter and inner diameter were determined from a scanning electron micrograph of a hollow fiber membrane split section.
(2) The amount of pure water permeated water m ³ / (m ² · h · 100 kPa) is a miniature module having a length of 20 cm comprising four hollow fiber-like hollow fiber membranes of the present invention, temperature 25 ° C., filtration differential pressure 16 kPa. Under the above conditions, the external pressure total filtration of pure water substantially free of solids such as fine particles is performed for 30 minutes, the permeation amount (m ³ ) per unit time (h), and the effective membrane area (m ² ) The pressure was converted to a pressure (100 kPa).
(3) Tensile strength and elongation were measured 30 times using a tensile tester (TENSILON / RTM-100) (manufactured by Toyo Baldwin) by changing the sample at a tensile speed of 50 mm / min and changing the sample 30 times. The average was taken as the measured value.
[0014]
【Example】
Example 1
30% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 420,000 and 70% by weight of dimethyl sulfoxide were dissolved at 120 ° C. to obtain a polymer solution. The polymer solution was extruded through an orifice of 2 cm in dry length and a tube-in orifice (orifice outer diameter 2.0 mm, tube outer diameter 0.8 mm, tube inner diameter 0.5 mm), and an 80 wt% dimethyl sulfoxide aqueous solution was extruded from the tube together. A hollow fiber was obtained by coagulation in an 80% by weight dimethyl sulfoxide aqueous solution at a temperature of 25 ° C. The obtained hollow fiber was washed with water at 30 ° C. Then, after supplying to a hot water bath at 80 ° C. at 8 m / min and stretching 1.5 times (take-off speed 12 m / min) in the hot water bath, it was further decelerated to 11.2 m / min under tension. A hollow fiber membrane was obtained by relaxing at a relaxation rate of 7% and removing the solvent in warm water at 70 ° C. This hollow fiber membrane had a pure water permeation rate of 3.1 m ³ / (m ² · h · 100 kPa), an inner diameter of 0.86 mm, an outer diameter of 1.32 mm, a strength of 5.2 MN / m ² or more, and an elongation of 87%. It was.
[0015]
Example 2
A polymer solution was obtained by dissolving 45% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 280,000 and 55% by weight of dimethyl sulfoxide at 120 ° C. The polymer solution was extruded through an orifice with a dry length of 10 cm and a tube-in orifice (orifice outer diameter 2.0 mm, tube outer diameter 0.8 mm, tube inner diameter 0.5 mm), and an 80 wt% aqueous dimethyl sulfoxide aqueous solution from the tube. A hollow fiber was obtained by coagulation in an 80% by weight dimethyl sulfoxide aqueous solution at a temperature of 15 ° C. The obtained hollow fiber was desolvated in a water washing bath at 70 ° C., and then subjected to stretching and relaxation treatment. Stretching was carried out at a rate of 8 m / min in a hot water bath at 95 ° C., stretched 2.2 times in the hot water bath (take-off speed 17.6 m / min), and further decelerated to 17 m / min under tension. Then, it was relaxed at a relaxation rate of 3%. The obtained hollow fiber membrane has a pure water permeation amount of 3.5 m ³ / (m ² · h · 100 kPa), an inner diameter of 0.88 mm, an outer diameter of 1.18 mm, a strength of 4.8 MN / m ² or more, and an elongation of 68%. Met.
[0016]
Example 3
A polymer solution was obtained by dissolving 35% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 420,000 and 65% by weight of γ-butyrolactone at 170 ° C. Next, using the dry-wet spinning method, the solution is discharged from the orifice of a 2 cm dry length and a tube-in orifice (orifice outer diameter 3.0 mm, tube outer diameter 0.8 mm, tube inner diameter 0.5 mm), and 100% by weight from the tube. The γ-butyrolactone solution was extruded together and coagulated into a hollow fiber in an 85 wt% γ-butyrolactone aqueous solution at a liquid temperature of 25 ° C. to obtain a hollow fiber. Subsequently, the hot water bath at 60 ° C. was supplied to the hot water bath at 90 ° C. at a rate of 10 m / min and stretched 1.6 times (take-off speed 16 m / min) in the hot water bath. It was decelerated to 5 m / min, relaxed at a relaxation rate of 3%, and desolvated with hot water at 60 ° C. The obtained hollow fiber membrane has a pure water permeation rate of 5.8 m ³ / (m ² · h · 100 kPa), an inner diameter of 0.82 mm, an outer diameter of 1.31 mm, a strength of 10.8 MN / m ² or more, and an elongation of 127%. Met.
[0017]
Example 4
A polymer solution was obtained by dissolving 50% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 420,000 and 50% by weight of γ-butyrolactone at 170 ° C. Extruding the polymer solution from the orifice of a dry length 15 cm and a tube-in orifice (orifice outer diameter 3.0 mm, tube outer diameter 0.8 mm, tube inner diameter 0.5 mm) and 100 wt% γ-butyrolactone solution from the tube together, A hollow fiber was obtained by coagulation in a 90 wt% γ-butyrolactone aqueous solution having a liquid temperature of 35 ° C. The obtained hollow fiber was desolvated in a hot water bath at 85 ° C. Subsequently, the mixture was supplied to a glycerin bath at 120 ° C. at 8 m / min, stretched 2.8 times (take-off speed 22.4 m / min) in the glycerin bath, and further decelerated to 20.6 m / min under tension. A hollow fiber membrane was obtained by relaxation at a rate of 8%. This hollow fiber membrane had a pure water permeation of 3.5 m ³ / (m ² · h · 100 kPa), an inner diameter of 0.88 mm, an outer diameter of 1.02 mm, a strength of 8.7 MN / m ² or more, and an elongation of 88%. It was.
[0018]
Comparative Example 1
Using the same polymer solution as in Example 3, the above-mentioned solution was obtained from an orifice of a dry-type 2 cm tube-in orifice (orifice outer diameter 3.0 mm, tube outer diameter 0.8 mm, tube inner diameter 0.5 mm), and 100 weight from the tube. % Γ-butyrolactone solution was extruded together and coagulated in an aqueous 85 wt% γ-butyrolactone solution at a liquid temperature of 25 ° C. to obtain a hollow fiber. The obtained hollow fiber was desolvated at 80 ° C. to obtain a hollow fiber membrane. Stretching and relaxation were not performed. This hollow fiber membrane had a pure water permeation of 0.57 m ³ / (m ² · h · 100 kPa), an inner diameter of 0.86 mm, an outer diameter of 1.62 mm, a strength of 9.1 MN / m ² or more, and an elongation of 212%. It was.
[0019]
Comparative Example 2
Using the same polymer solution as in Example 3, the above-mentioned solution was obtained from an orifice of a dry-type 2 cm tube-in orifice (orifice outer diameter 3.0 mm, tube outer diameter 0.8 mm, tube inner diameter 0.5 mm), and 100 weight from the tube. % Γ-butyrolactone solution was extruded together and coagulated in an aqueous 85 wt% γ-butyrolactone solution at a liquid temperature of 25 ° C. to obtain a hollow fiber. Subsequently, the mixture was supplied to a glycerin bath at 120 ° C. at a rate of 8 m / min, stretched 4.2 times in the glycerin bath (take-up speed: 33.6 m / min), and further decelerated to 32 m / min under tension to achieve a relaxation rate of 4 %. The obtained hollow fiber membrane has a pure water permeation amount of 2.7 m ³ / (m ² · h · 100 kPa), an inner diameter of 0.81 mm, an outer diameter of 1.04 mm, a strength of 7.8 MN / m ² or more, and an elongation of 39%. Met.
[0020]
Comparative Example 3
Using the same polymer solution as in Example 3, the above-mentioned solution was obtained from an orifice of a dry-type 2 cm tube-in orifice (orifice outer diameter 3.0 mm, tube outer diameter 0.8 mm, tube inner diameter 0.5 mm), and 100 weight from the tube. % Γ-butyrolactone solution was extruded together and coagulated in an aqueous 85 wt% γ-butyrolactone solution at a liquid temperature of 25 ° C. to obtain a hollow fiber. Subsequently, the hot water bath at 60 ° C. was supplied to the hot water bath at 90 ° C. at a rate of 10 m / min and stretched 1.6 times (take-off speed 16 m / min) in the hot water bath. The vehicle was decelerated to 13 m / min where the tension was not maintained (relaxation rate 19%). The obtained hollow fiber membrane has a pure water permeation of 2.4 m ³ / (m ² · h · 100 kPa), an inner diameter of 0.84 mm, an outer diameter of 1.29 mm, a strength of 5.4 MN / m ² or more, and an elongation of 22%. Met.
[0021]
【The invention's effect】
The hollow fiber membrane of the present invention is suitably used in fields of use such as microfiltration membranes, ultrafiltration membranes and various filters that are excellent in water permeability, mechanical properties, and chemical resistance.

Claims

A solution containing at least polyvinylidene fluoride-based resin is added to N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, acetone, tetrahydrofuran, tetramethylurea, trimethyl phosphate, cyclohexanone, isophorone, γ-butyrolactone. , methyl isoamyl ketone, dimethyl phthalate, propylene glycol methyl ether, propylene carbonate, diacetone alcohol, at least one solvent selected from the group consisting of glycerol triacetate, or at least one solvent selected from 60 wt% or more of the group comprising an aqueous solution containing, by discharging to a temperature 50 ° C. below the coagulation bath, and thermally induced phase separation, solidifying while developed spherulitic structure hollow fiber The resulting method of manufacturing a hollow fiber membrane hollow fiber was stretched in a range of 1.1 to 4 times, to further the hollow fiber after stretching is relaxed in the range of relaxation of from 0.1 to 10%.

The method for producing a hollow fiber membrane according to claim 1, wherein the drawing of the hollow fiber is performed by supplying the hollow fiber into a heating medium having a temperature range of 50 to 165 ° C at a supply rate of 2 to 30 m / min.

The method for producing a hollow fiber membrane according to claim 2, wherein at least one selected from water, polyethylene glycol, glycerin, steam, air and nitrogen is used as the heat medium.

The method for producing a hollow fiber membrane according to any one of claims 1 to 3, wherein the relaxation is performed under tension in a heating medium having a temperature range of 50 to 165 ° C.