JP3682897B2 - High strength hydrophilic polyvinylidene fluoride porous membrane and method for producing the same - Google Patents
High strength hydrophilic polyvinylidene fluoride porous membrane and method for producing the same Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、液体の濾過に使用する親水性ポリフッ化ビニリデン多孔質膜に関するものである。
【０００２】
【従来の技術】
親水性ポリフッ化ビニリデン多孔質膜は、電子工業用水、製薬、食品用水等の多くの分野で除菌・精製濾過に広く利用されており、特に、フィルタ−の滅菌を伴うような用途においては、優れた耐熱性、高い機械的強度、寸法安定性を有する膜の要望が高まっている。
【０００３】
従来、ポリフッ化ビニリデン多孔質膜のような疎水性ポリマー膜を親水化処理する方法については、多くの研究が成されており、特公昭６１−２００５号公報には、疎水性ポリフッ化ビニリデン膜を非イオン性表面活性剤で親水化処理する方法が開示されている。しかし、この製造方法による親水性ポリフッ化ビニリデン膜は、非イオン性表面活性剤が膜に固定化されていないため、濾液がその溶出物により汚染されるという問題がある。
【０００４】
また、特開平７−３０４３号公報には、疎水性膜に親水性ポリマーとしてポリビニルピロリドンを固定化させる方法が開示されている。しかし、この方法によって得られた多孔質膜は、高温での繰り返し滅菌により、多孔質膜の親水性が失われるという欠点がある。
【０００５】
他方、膜自体の機械的強度を高める方法についても多くの研究が成されており、特表平７−５０７２３７号公報には、不織布やフィラメントのグリッドを膜と一体化することによって機械的強度を高める方法が開示されている。しかし、この方法においては、不織布等が膜中に埋設されているため、多孔質膜の空孔率が低くなり、ひいては濾過流量が低下し、実用上問題となっている。
【０００６】
【発明が解決しようとする課題】
本発明は、これらの状況に鑑み、溶出物成分を含まず、優れた親水性を有し、且つ高い機械的強度、寸法安定性を有する高強度親水性ポリフッ化ビニリデン膜を得ることを目的とする。
【０００７】
【課題を解決するための手段】
上記課題を解決するため、本発明は、疎水性ポリフッ化ビニリデン多孔質膜を、溶剤にて湿潤化した後、ポリビニルピロリドンと重合開始剤とを含む溶液に接触させ、もしくは湿潤可能な溶剤にポリビニルピロリドンと重合開始剤とを溶解した溶液に接触させ、湿潤状態を保持したまま、１２０℃以上の温度条件下にて、ポリビニルピロリドンが架橋し、水不溶化するのに十分な時間曝すことにより、優れた親水性と同時に膜の高い機械的強度を有する高強度親水性ポリフッ化ビニリデン多孔質膜を得る。
【０００８】
【実施の形態】
本発明に用いられるポリフッ化ビニリデンは、特に限定されるものでなく、ポリフッ化ビニリデンホモポリマー、フッ化ビニリデン−テトラフルオロエチレンコポリマー、フッ化ビニリデン−ヘキサフルオロプロピレンコポリマー、フッ化ビニリデン−テトラフルオロエチレン−ヘキサフルオロプロピレンコポリマー、及びこれらの混合物などが挙げられる。疎水性ポリフッ化ビニリデン多孔質膜の膜厚は通常２０μｍ〜２００μｍ、好ましくは５０μｍ〜１５０μｍである。また、膜の孔径は、通常０．０１μｍ〜１０μｍ、好ましくは０．０５μｍ〜５μｍである。
【０００９】
多孔質膜の表面及び内部に架橋させるポリビニルピロリドンは、次ぎの数式１に示すＫ値が１５〜１２０のものであり、また平均分子量が１０，０００〜２，８００，０００のものを単独または混合して使用できる。
【００１０】
【数式１】
η rel ：溶媒に対する溶液の粘度
【００１１】
重合開始剤としては、過硫酸塩類であり、例えば過硫酸カリウム、過硫酸アンモニウム等を用いることができる。
【００１２】
ポリビニルピロリドン及び重合開始剤の溶液中の濃度は、その種類によって決定されるが、通常、ポリビニルピロリドンは０．１〜２０ｗｔ％、好ましくは１〜１０ｗｔ％、重合開始剤は０．１〜３０ｗｔ％、好ましくは１〜２０ｗｔ％である。
【００１３】
また、疎水性ポリフッ化ビニリデン多孔質膜をポリビニルピロリドン及び重合開始剤とを含む溶液に接触させる前、もしくはポリビニルピロリドン及び重合開始剤とを含む溶液に接触させる際に湿潤化する場合の溶剤は、疎水性ポリフッ化ビニリデン多孔質膜に対し、溶解力を有する溶剤以外であり、且つ次の重合・架橋反応を阻害しないものであれば使用することができ、例えばエタノール、イソプロピルアルコール等の低級アルコール類であり、好ましくはコストの点からイソプロピルアルコールである。
【００１４】
また更に、疎水性ポリフッ化ビニリデン多孔質膜を前記溶剤にて湿潤化させた後にポリビニルピロリドン及び重合開始剤とを含む溶液に接触させる場合、ポリビニルピロリドン及び重合開始剤とを溶解する溶剤としては、重合・架橋反応を阻害しないものであれば使用することができ、最も好ましい溶剤は水である。しかし、水は大気圧においてその沸点が１００℃であることから、水が蒸発して膜が乾燥し反応を阻害するのを防ぐため、加圧した密閉容器内で反応を行う必要がある。もし反応中に膜が乾燥すると、その部分には親水性が付与されないこととなる。
【００１５】
疎水性ポリフッ化ビニリデン多孔質膜をポリビニルピロリドンと重合開始剤とを含む溶液に接触させる方法としては、浸漬や塗布、噴霧等の方法を用いることができる。
【００１６】
反応を行う温度及び時間については、ポリフッ化ビニリデンの種類や本発明で得られる親水性ポリフッ化ビニリデン多孔質膜の用途で任意に選択できる。例えば、ポリフッ化ビニリデンとしてホモポリマーを用い、１２１℃でのオートクレーブ滅菌操作を伴う用途に使用する場合、使用温度以上からポリフッ化ビニリデンホモポリマーの融点以下の温度、具体的には、１２１℃以上１７０℃以下の温度範囲で反応を行う。反応時間は、膜の形状や量によって異なるが、一般的に温度が高いほど短時間でよい。この架橋反応時の温度が少なくとも１２０℃以上であることにより、反応が促進されて繰り返しの加熱後も親水性が低下しない優れた耐熱性を有し、且つ所謂アニーリング効果が生じて高い機械的強度、寸法安定性を有する膜が得られる。
【００１７】
【実施例】
以下に実施例によって、本発明を具体的に説明する。
【００１８】
【実施例１〜３】
孔径０．２μｍ、膜厚１００μｍの疎水性ポリフッ化ビニリデンホモポリマー膜（５０ｍｍ幅×１ｍ長）を用意した。この膜をイソプロピルアルコールで湿潤させ、その後水洗してイソプロピルアルコールを水で置換した。次いで、ポリビニルピロリドン（Ｋ−３０、平均分子量４０，０００、和光純薬工業製）と重合開始剤として過硫酸カリウム（１級、関東化学製）を表１に示す濃度で水溶液（反応溶液）として用意し、水で湿潤した疎水性ポリフッ化ビニリデン膜を前記溶液に３分間浸漬させて、水を反応溶液と置換した。前記膜をポリエチレンテレフタレート製のフィルムに挟み、ステンレス製ロールに巻き取り耐圧密閉容器に入れ、表１に示す反応条件で架橋反応を進行させた。反応終了後は充分水洗・乾燥し、本発明の多孔質膜を得た。
またこれら実施例に対し、先行技術である特開平７−３０４３号公報記載の技術に基づいた比較例１についても、同様に表１に併記した。
【００１９】
【表１】
【比較例２】
さらに従来の一般的手法である、疎水性ポリフッ化ビニリデンホモポリマー膜をプルロニックＬ１２１（ポリオキシエチレンとポリオキシプロピレンのブロック共重合体から成る非イオン性表面活性剤）を５ｗｔ％含むメタノール溶液に浸漬した後、５０℃にて１５分間乾燥し、親水化膜を得、これを比較例２として、以下に比較例１とともに本発明の各実施例と対比した。
【００２１】
【実施例１〜３及び比較例１〜２の親水性評価試験及び結果】
実施例１〜３及び比較例１〜２で得られた膜を、１２６℃６０分のオートクレーブ滅菌を繰り返し行い、滅菌後の親水性を評価した。結果を表２に示す。
【００２２】
【表２】
実施例１〜３で得られた膜は、オートクレーブ滅菌後も親水性を保ち、比較例１〜２で得られた膜と比べ、明らかに加熱後も親水性が低下しない優れた耐熱性を有した。
【００２４】
【実施例１〜３及び比較例１〜２の機械的強度評価試験及び結果】
実施例１〜３及び比較例１〜２で得られた膜をφ４７ｍｍに打ち抜き、その中心点（φ１１ｍｍ）に圧力をかけて、膜が割れる時の圧力（破裂強度）を測定した。結果を表３に示す。
【００２５】
【表３】
膜の強度（ｋｇ／ｃｍ2）
実施例１ １．４
実施例２ １．６
実施例３ １．７
比較例１ ０．７
比較例２ ０．７
【００２６】
実施例１〜３で得られた膜は、比較例１〜２で得られた膜と比べ約２倍以上破裂強度（機械的強度）が強い。
【００２７】
【実施例１〜３及び比較例１〜２の寸法安定性の性能評価試験及び結果】
実施例１〜３及び比較例で得られた膜をφ４７mmに打ち抜き、１２６℃６０分のオートクレーブ滅菌を行い、滅菌前後の寸法変化を評価した。結果を表４に示す。
【００２８】
【表４】
実施例１〜３で得られた膜は、比較例１〜２で得られた膜と比べ、オートクレーブ滅菌後の寸法変化率が小さく、優れた寸法安定性を有している。
【００３０】
【発明の効果】
以上述べた如く、本発明によって得られる親水性ポリフッ化ビニリデン多孔質膜は、溶出成分を含まず、優れた親水性を有し、且つ機械的強度，寸法安定性が高い膜である。
従って、本発明によって得られる高強度親水性ポリフッ化ビニリデン多孔質膜は、熱による滅菌操作等を伴う、過酷な条件下において非常に有用である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrophilic polyvinylidene fluoride porous membrane used for liquid filtration.
[0002]
[Prior art]
Hydrophilic polyvinylidene fluoride porous membranes are widely used for sterilization and purification filtration in many fields such as water for electronics industry, pharmaceuticals, and water for foods, especially in applications involving sterilization of filters. There is a growing demand for films having excellent heat resistance, high mechanical strength, and dimensional stability.
[0003]
Conventionally, many studies have been made on a method for hydrophilizing a hydrophobic polymer film such as a porous polyvinylidene fluoride film. Japanese Patent Publication No. 61-2005 discloses a hydrophobic polyvinylidene fluoride film. A method of hydrophilizing with a nonionic surfactant is disclosed. However, the hydrophilic polyvinylidene fluoride membrane produced by this production method has a problem that the filtrate is contaminated by the eluate because the nonionic surfactant is not immobilized on the membrane.
[0004]
Japanese Patent Application Laid-Open No. 7-3043 discloses a method of immobilizing polyvinyl pyrrolidone as a hydrophilic polymer on a hydrophobic membrane. However, the porous membrane obtained by this method has a drawback that the hydrophilicity of the porous membrane is lost by repeated sterilization at high temperature.
[0005]
On the other hand, many studies have been made on methods for increasing the mechanical strength of the membrane itself. In Japanese Patent Publication No. 7-507237, the mechanical strength is increased by integrating a nonwoven fabric or a grid of filaments with the membrane. A method for enhancing is disclosed. However, in this method, since a nonwoven fabric or the like is embedded in the membrane, the porosity of the porous membrane is lowered, and as a result, the filtration flow rate is lowered, which is a practical problem.
[0006]
[Problems to be solved by the invention]
In view of these circumstances, the present invention aims to obtain a high-strength hydrophilic polyvinylidene fluoride film that does not contain an eluate component, has excellent hydrophilicity, and has high mechanical strength and dimensional stability. To do.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention is directed to a method in which a hydrophobic polyvinylidene fluoride porous membrane is wetted with a solvent and then contacted with a solution containing polyvinylpyrrolidone and a polymerization initiator. By contacting with a solution in which pyrrolidone and a polymerization initiator are dissolved and maintaining a wet state, the polymer is exposed to a sufficient time to crosslink and insolubilize polyvinylpyrrolidone under a temperature condition of 120 ° C. or higher. A high-strength hydrophilic polyvinylidene fluoride porous membrane having high mechanical strength as well as high hydrophilicity is obtained.
[0008]
Embodiment
The polyvinylidene fluoride used in the present invention is not particularly limited. Polyvinylidene fluoride homopolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene- Examples thereof include hexafluoropropylene copolymers and mixtures thereof. The film thickness of the hydrophobic polyvinylidene fluoride porous membrane is usually 20 μm to 200 μm, preferably 50 μm to 150 μm. The pore diameter of the membrane is usually 0.01 μm to 10 μm, preferably 0.05 μm to 5 μm.
[0009]
Polyvinylpyrrolidone to be crosslinked on the surface and inside of the porous membrane has a K value of 15 to 120 shown in the following formula 1 and an average molecular weight of 10,000 to 2,800,000 alone or in combination. Can be used.
[0010]
[Formula 1]
Examples of the polymerization initiator include persulfates, such as potassium persulfate and ammonium persulfate.
[0012]
The concentration of the polyvinyl pyrrolidone and the polymerization initiator in the solution is determined depending on the type thereof. Usually, the polyvinyl pyrrolidone is 0.1 to 20 wt%, preferably 1 to 10 wt%, and the polymerization initiator is 0.1 to 30 wt%. , Preferably 1 to 20 wt%.
[0013]
In addition, the solvent when the hydrophobic polyvinylidene fluoride porous membrane is wetted before contacting with the solution containing polyvinylpyrrolidone and the polymerization initiator or when contacting with the solution containing polyvinylpyrrolidone and the polymerization initiator, For the hydrophobic polyvinylidene fluoride porous membrane, it can be used as long as it is a solvent other than a solvent and does not inhibit the subsequent polymerization / crosslinking reaction. For example, lower alcohols such as ethanol and isopropyl alcohol Preferably, isopropyl alcohol is used from the viewpoint of cost.
[0014]
Furthermore, when the hydrophobic polyvinylidene fluoride porous membrane is wetted with the solvent and then contacted with a solution containing polyvinyl pyrrolidone and a polymerization initiator, as a solvent for dissolving the polyvinyl pyrrolidone and the polymerization initiator, Any solvent that does not inhibit the polymerization / crosslinking reaction can be used, and the most preferred solvent is water. However, since the boiling point of water is 100 ° C. at atmospheric pressure, it is necessary to carry out the reaction in a pressurized sealed container in order to prevent the water from evaporating and the membrane from drying and inhibiting the reaction. If the membrane dries during the reaction, the portion will not be hydrophilic.
[0015]
As a method for bringing the hydrophobic polyvinylidene fluoride porous membrane into contact with a solution containing polyvinylpyrrolidone and a polymerization initiator, methods such as dipping, coating and spraying can be used.
[0016]
The temperature and time for performing the reaction can be arbitrarily selected depending on the type of polyvinylidene fluoride and the use of the hydrophilic polyvinylidene fluoride porous membrane obtained in the present invention. For example, when a homopolymer is used as polyvinylidene fluoride and used for an application involving an autoclave sterilization operation at 121 ° C., the temperature is from the use temperature to the melting point of the polyvinylidene fluoride homopolymer, specifically, 121 ° C. to 170 ° C. The reaction is carried out in the temperature range below ℃. The reaction time varies depending on the shape and amount of the film, but generally the shorter the temperature, the higher the temperature. When the temperature during this crosslinking reaction is at least 120 ° C. or higher, the reaction is promoted, and has excellent heat resistance that does not deteriorate hydrophilicity even after repeated heating, and has a so-called annealing effect and high mechanical strength. A film having dimensional stability is obtained.
[0017]
【Example】
The present invention will be specifically described below with reference to examples.
[0018]
Examples 1 to 3
A hydrophobic polyvinylidene fluoride homopolymer film (50 mm width × 1 m length) having a pore diameter of 0.2 μm and a film thickness of 100 μm was prepared. The membrane was moistened with isopropyl alcohol and then washed with water to replace the isopropyl alcohol with water. Next, polyvinyl pyrrolidone (K-30, average molecular weight 40,000, manufactured by Wako Pure Chemical Industries, Ltd.) and potassium persulfate (first grade, manufactured by Kanto Chemical Co., Ltd.) as a polymerization initiator as an aqueous solution (reaction solution) at the concentrations shown in Table 1. A hydrophobic polyvinylidene fluoride membrane prepared and wetted with water was immersed in the solution for 3 minutes to replace the water with the reaction solution. The membrane was sandwiched between polyethylene terephthalate films, wound on a stainless steel roll, placed in a pressure-resistant airtight container, and the crosslinking reaction was allowed to proceed under the reaction conditions shown in Table 1. After completion of the reaction, it was sufficiently washed with water and dried to obtain a porous membrane of the present invention.
For these examples, Comparative Example 1 based on the technology described in JP-A-7-3043, which is a prior art, is also shown in Table 1.
[0019]
[Table 1]
[Comparative Example 2]
In addition, a conventional polyvinylidene fluoride homopolymer membrane is immersed in a methanol solution containing 5 wt% of Pluronic L121 (a nonionic surfactant made of a block copolymer of polyoxyethylene and polyoxypropylene). Then, it was dried at 50 ° C. for 15 minutes to obtain a hydrophilized film, which was referred to as Comparative Example 2 and compared with Comparative Example 1 below in each example of the present invention.
[0021]
[Hydrophilicity evaluation test and results of Examples 1-3 and Comparative Examples 1-2]
The membranes obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were repeatedly autoclaved at 126 ° C. for 60 minutes, and the hydrophilicity after sterilization was evaluated. The results are shown in Table 2.
[0022]
[Table 2]
The membranes obtained in Examples 1 to 3 remain hydrophilic even after autoclave sterilization and have excellent heat resistance so that the hydrophilicity does not deteriorate even after heating as compared with the membranes obtained in Comparative Examples 1 and 2. did.
[0024]
[Mechanical strength evaluation test and results of Examples 1-3 and Comparative Examples 1-2]
The films obtained in Examples 1 to 3 and Comparative Examples 1 to 2 were punched out to 47 mm, pressure was applied to the center point (11 mm), and the pressure at which the film was broken (rupture strength) was measured. The results are shown in Table 3.
[0025]
[Table 3]
Film strength (kg / cm 2 )
Example 1 1.4
Example 2 1.6
Example 3 1.7
Comparative Example 1 0.7
Comparative Example 2 0.7
[0026]
The films obtained in Examples 1 to 3 have a burst strength (mechanical strength) that is about twice or more that of the films obtained in Comparative Examples 1 and 2.
[0027]
[Performance evaluation test and results of dimensional stability of Examples 1-3 and Comparative Examples 1-2]
The membranes obtained in Examples 1 to 3 and the comparative example were punched out to φ47 mm, autoclaved at 126 ° C. for 60 minutes, and the dimensional change before and after sterilization was evaluated. The results are shown in Table 4.
[0028]
[Table 4]
The membranes obtained in Examples 1 to 3 have a small dimensional change rate after autoclave sterilization and excellent dimensional stability compared to the membranes obtained in Comparative Examples 1 and 2.
[0030]
【The invention's effect】
As described above, the hydrophilic polyvinylidene fluoride porous membrane obtained by the present invention does not contain an elution component, has excellent hydrophilicity, and has high mechanical strength and dimensional stability.
Therefore, the high-strength hydrophilic polyvinylidene fluoride porous membrane obtained by the present invention is very useful under severe conditions involving sterilization operation by heat and the like.
Claims (4)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13123198A JP3682897B2 (en) | 1998-04-24 | 1998-04-24 | High strength hydrophilic polyvinylidene fluoride porous membrane and method for producing the same |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13123198A JP3682897B2 (en) | 1998-04-24 | 1998-04-24 | High strength hydrophilic polyvinylidene fluoride porous membrane and method for producing the same |
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| Publication Number | Publication Date |
|---|---|
| JPH11302438A JPH11302438A (en) | 1999-11-02 |
| JP3682897B2 true JP3682897B2 (en) | 2005-08-17 |
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| Application Number | Title | Priority Date | Filing Date |
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| JP13123198A Expired - Fee Related JP3682897B2 (en) | 1998-04-24 | 1998-04-24 | High strength hydrophilic polyvinylidene fluoride porous membrane and method for producing the same |
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| JP (1) | JP3682897B2 (en) |
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1998
- 1998-04-24 JP JP13123198A patent/JP3682897B2/en not_active Expired - Fee Related
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|---|---|
| JPH11302438A (en) | 1999-11-02 |
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