JP3914302B2 - Method for producing porous film made of polytetrafluoroethylene - Google Patents
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Description
【０００１】
【発明の技術分野】
本発明は、ポリテトラフルオロエチレン製多孔質膜の製造方法に関し、さらに詳しくは、機械的強度、透ガス量、透水量に優れ、しかも円形に近く比較的均一な孔を有するポリテトラフルオロエチレン製多孔質膜の製造方法に関する。
【０００２】
【発明の技術的背景】
ポリテトラフルオロエチレン樹脂（以下ＰＴＦＥと略記することがある）は、優れた耐薬品性、耐熱性、機械的特性を有するため、種々の分野で用いられている。たとえばＰＴＦＥからなる多孔質膜は、上記のような特性を利用して、腐食性物質あるいは高温物質のフィルタとして広く用いられており、また、電解隔膜、燃料電池などとしても用いられている。
【０００３】
従来ＰＴＦＥ樹脂から多孔質膜を製造するには、テトラフルオロエチレンの乳化重合により得られる平均粒子径０.１〜０.４μｍのファインパウダーと称されるＰＴＦＥ微粒子に液状潤滑剤を配合して圧縮予備成形し、次いで押出または圧延あるいはこの両者を含む方法によりフィルム状とし、次に液状潤滑剤を除去した後、得られたＰＴＦＥ膜を通常加熱条件下で一軸または二軸延伸するという方法が採られていた。（特公昭４２−１３５６０号公報、特開昭４９−１１８７６０号公報、特公昭５１−４０９０２号公報、特公昭５１−１８９９１号公報参照）
また特公昭５３−４２７９４号公報には、焼成されたＰＴＦＥ膜を３２７℃以上に加熱した後除冷し、その結晶化度が８０％以上になるように熱処理し、次いで２５〜２６０℃の温度において延伸倍率１.５〜４倍に一軸延伸することを特徴とするＰＴＦＥ多孔体の製造方法が開示されている。
【０００４】
ところが、このような方法により製造されたＰＴＦＥ製多孔質膜は、孔を真円に近い形状に、しかも孔径を所定の大きさに製造することは難しいという問題点があった。また該多孔質膜の機械的強度も充分であるとは言えないという問題点もあった。
【０００５】
またＰＴＦＥ半焼結膜をその融点以下の温度で延伸することによって、ＰＴＦＥ多孔質膜を製造する方法も知られており、たとえば特公平６−８９１６５号公報に記載されている。この方法によれば、高気孔率のＰＴＦＥ多孔質膜を製造しうるが、ＰＴＦＥを半焼結状態とするための熱処理条件の範囲が狭く、このような半焼結状態のＰＴＦＥ膜を製造することが容易でないという問題点があった。
【０００６】
【発明の目的】
本発明は、上記のような従来技術における問題点を解決しようとするものであって、真円形に近い孔を有し、しかも機械的強度、透ガス量、透水量に優れたＰＴＦＥ製多孔質膜の製造方法を提供することを目的としている。
【０００７】
【発明の概要】
本発明に係るＰＴＦＥ製多孔質膜の製造方法は、ＰＴＦＥ製膜と、数平均分子量が５００〜１万である低分子量ＰＴＦＥとを、低分子量ＰＴＦＥの融点以上の温度で接触させ、次いでこのＰＴＦＥ製膜をＰＴＦＥの融点以下の温度で１.３〜６.５倍に一軸または二軸延伸することを特徴としている。
【０００８】
本発明では、ＰＴＦＥ製膜と数平均分子量が５００〜１万である低分子量ＰＴＦＥとの接触は、たとえばＰＴＦＥ膜上に該低分子量ＰＴＦＥ粉末を付着させて行うか、あるいはＰＴＦＥ膜を溶融状態の該低分子量ＰＴＦＥ中に浸漬することによって行うことができる。
【０００９】
【発明の具体的説明】
以下本発明に係るＰＴＦＥ製多孔質膜の製造方法について説明する。
本発明では、まず、ＰＴＦＥ製膜と、低分子量ＰＴＦＥとを、低分子量ＰＴＦＥの融点（ＰＴＦＥの融点は分子量により異なる）以上の温度で接触させる。
【００１０】
ＰＴＦＥ製膜としては、ＰＴＦＥ製フィルム、ＰＴＦＥ製薄肉チューブなどが用いられる。このＰＴＦＥ製膜の膜厚は１０〜５００μｍ程度であることが好ましい。
【００１１】
このようなＰＴＦＥ製膜としては、たとえば、乳化重合法によって得られたＰＴＦＥファインパウダーと液状潤滑剤との配合物を圧縮予備成形した後、これを押出または圧延あるいはこの両者を含む方法によってフィルム状としたものでもよい。また懸濁重合法によって得られたＰＴＦＥモールディングパウダーを圧縮成形して円筒状の予備成形品を作成し、次いでこの予備成形品をＰＴＦＥの融点（３２７℃）以上の温度で焼成した後、これを切削してフィルム状としたものでもよい。また複数枚のＰＴＦＥ製膜を熱融着させて得られたものであってもよい。
【００１２】
このようなＰＴＦＥの数平均分子量は、２００万〜２０００万、好ましくは２００万〜８００万程度である。
このようなＰＴＦＥ製膜を、低分子量ＰＴＦＥと、低分子量ＰＴＦＥの融点以上の温度で接触させる。
【００１３】
この操作は、具体的には、たとえば以下のような方法で行われる。
イ）ＰＴＦＥ膜上に、低分子量ＰＴＦＥ粉末をまぶすようにして付着させ、次いで低分子量ＰＴＦＥの融点以上の温度に加熱した後冷却する。この際の加熱温度は、１００〜４００℃、好ましくは２５０〜３８０℃、さらに好ましくは３００〜３８０℃程度であることが望ましい。
【００１４】
加熱時間は、加熱温度によって大きく変化するが、通常５〜３６００秒、好ましくは数秒〜２０分程度であることが望ましい。
ロ）まず低分子量ＰＴＦＥ粉末を、エタノール、エチレングリコールなどの有機溶媒あるいは水などに分散させて分散液を調製する。次いでこの分散液をＰＴＦＥ膜上に塗布あるいは噴霧して、ＰＴＦＥ膜上に低分子量ＰＴＦＥ粉末を付着させ、分散媒を除去した後、低分子量ＰＴＦＥの融点以上の温度に加熱した後冷却する。加熱温度および加熱時間は、上記と同様である。
【００１５】
ハ）まず低分子量ＰＴＦＥ粉末を加熱して溶融させる。次いでこの溶融状態にある低分子量ＰＴＦＥ中に、ＰＴＦＥ膜を浸漬して、ＰＴＦＥ膜と低分子量ＰＴＦＥとを接触させ、ＰＴＦＥの融点以上の温度に加熱した後冷却する。あるいはＰＴＦＥ膜上に溶融状態にある低分子量ＰＴＦＥを塗布または噴霧してＰＴＦＥ膜と低分子量ＰＴＦＥとを接触させ、低分子量ＰＴＦＥの融点以上の温度に加熱した後冷却する。加熱温度および加熱時間は、上記と同様である。
【００１６】
このようにしてＰＴＦＥ膜と低分子量ＰＴＦＥとを、低分子量ＰＴＦＥの融点以上の温度で接触させた後冷却し、このＰＴＦＥ膜をＰＴＦＥの融点以下の温度で１.３〜６.５倍に一軸または二軸延伸すると、ＰＴＦＥ製多孔質膜が得られる。
【００１７】
この延伸温度は１９〜３２０℃、好ましくは５０〜２９０℃程度であることが望ましい。
ＰＴＦＥ膜の延伸倍率は１.３〜６.５倍であることが好ましく、この延伸倍率が６.５倍を超えると、膜にピンホールが発生したり、延伸時に膜が破断したりする恐があり、一方延伸倍率が１.３倍未満であると、所望の微細孔が得られないことがある。
【００１８】
このような延伸は一軸または二軸方向好ましくは二軸方向に行われる。ＰＴＦＥ膜に二軸延伸を行うことによって、得られるＰＴＦＥ多孔質膜の孔が真円に近づくという効果が認められる。
【００１９】
本明細書において、低分子量ＰＴＦＥとは、数平均分子量１００万以下、好ましくは５００〜１万、さらに好ましくは５００〜２０００程度のＰＴＦＥを意味する。このような低分子量ＰＴＦＥは、たとえばセントラル硝子（株）より商品名セフラルルーブとして販売されている。
【００２０】
本発明では、ＰＴＦＥ膜と低分子量ＰＴＦＥとを、低分子量ＰＴＦＥの融点以上の温度で接触させた後に、このＰＴＦＥ膜をＰＴＦＥの融点以下の温度で１.３〜６.５倍に一軸または二軸延伸してＰＴＦＥ製多孔質膜を製造すると、ＰＴＦＥ膜と低分子量ＰＴＦＥとを低分子量ＰＴＦＥの融点以上の温度で接触させないでＰＴＦＥ製多孔質膜を製造した場合と比較して、透水量、透ガス量が高く、機械的強度にも優れたＰＴＦＥ製多孔質膜が得られる。この理由については定かではないが、ＰＴＦＥ膜と低分子量ＰＴＦＥとを低分子量ＰＴＦＥの融点以上の温度で接触させることにより、ＰＴＦＥ膜中に低分子量ＰＴＦＥが入りこみ、ＰＴＦＥ膜が膨潤し、このためＰＴＦＥ膜の延伸工程で真円に近い孔が形成され、しかも透水量、透ガス量、機械的強度に優れたＰＴＦＥ製多孔質膜が得られるのであろうと推測される。
【００２１】
【発明の効果】
本発明によれば、透水量、透ガス量、機械的強度に優れ、しかも真円形に近く比較的均一な孔を有するＰＴＦＥ製多孔質膜が得られる。
【００２２】
【実施例】
以下本発明を実施例により説明するが、本発明はこれら実施例に限定されるものではない。
【００２３】
【実施例１〜８】
懸濁重合法によって得られる平均粒子径２５μｍのＰＴＦＥモールディングパウダー（ポリフロンＭ−１２、ダイキン工業（株）製）を金型中で１５０kg／cm2の成形圧で予備成形した後、３６０℃で焼成してＰＴＦＥ成型品を作製した。この成型品を切削して膜厚２０μｍのＰＴＦＥ膜を作製した。
【００２４】
このようにして得られたフィルムを２枚重ねて５０％ロール圧延した後３６０℃で熱融着した後、冷却し、膜厚４０μｍのＰＴＦＥ膜を作製した。
このようにして得られた焼成されたＰＴＦＥ膜表面に、数平均分子量７００〜１５００の低分子量ＰＴＦＥ（セフラルルーブ−Ｖ、セントラル硝子（株）製）を１５重量％となるようにエタノール中に分散させた分散液を、スプレーガンで噴霧した後乾燥して２mg／cm2の量で低分子量ＰＴＦＥ粉末を塗布した。このフィルムを電気炉中で３００〜３６０℃の温度範囲で６０〜３００秒間熱処理した後、室温まで急冷してＰＴＦＥ膜を作製した。
【００２５】
熱処理温度および熱処理時間を表１に示す。
このＰＴＦＥ膜を７０℃の温度で２.０×２.０の延伸倍率で二軸延伸を行ってＰＴＦＥ多孔質膜を作成した。
【００２６】
【比較例１】
実施例１において、延伸前のＰＴＦＥ膜を低分子量ＰＴＦＥと接触させなかった以外は、実施例１と同様にして、ＰＴＦＥ製多孔質膜を作成した。
【００２７】
実施例１〜８および比較例１で得られたＰＴＦＥ製多孔質膜について、それぞれ気孔率透水量、Ｎ2ガス透過量、引張り強度、伸び率の測定を行い、さらに走査型電子顕微鏡による表面形態の観察を行った。
【００２８】
その結果を表１および表２に示す。
また図１に実施例４で得られたＰＴＦＥ製多孔質膜の電子顕微鏡写真を示すとともに、図２に比較例１で得られたＰＴＦＥ製多孔質膜の電子顕微鏡写真を示す。
【００２９】
表１より実施例１のＰＴＦＥ製多孔質膜は透水量および透ガス量に優れていることがわかる。
【００３０】
【表１】
【表２】
【実施例９】
乳化重合法によって得られる平均粒子径５５０μｍのＰＴＦＥファインパウダー（フルオンＣＤ−１、旭硝子（株）製）を液状潤滑剤と配合して圧縮予備成形した後、押出し成形によって膜状とし、次いで所定の温度で熱処理して液状潤滑剤を除去して膜厚５０μｍの未焼成ＰＴＦＥ膜を作製した。この未焼成ＰＴＦＥ膜を３６０℃で熱処理して焼成ＰＴＦＥ膜を得た。
【００３３】
この焼成ＰＴＦＥ膜表面に、数平均分子量７００〜１５００の低分子量ＰＴＦＥ（セフラルルーブ−Ｖ、セントラル硝子（株）製）を１５重量％の割合でエタノール中に分散させた分散液を、スプレーガンで噴霧した後乾燥して２mg／cm2の量で低分子量ＰＴＦＥ粉末を塗布した。このＰＴＦＥ膜を電気炉中で３６０℃の温度で６０秒間熱処理した後、室温まで急冷してＰＴＦＥ膜を作製した。
【００３４】
このＰＴＦＥ膜を７０℃の温度で２.０×２.０の延伸倍率で二軸延伸を行って膜厚３２μｍのＰＴＦＥ多孔質膜を得た。
【００３５】
【比較例２】
実施例２において、延伸前のＰＴＦＥ膜を低分子量ＰＴＦＥと接触させなかった以外は、実施例２と同様にして、ＰＴＦＥ製多孔質膜を作成した。
【００３６】
実施例２および比較例２で得られたＰＴＦＥ製多孔質膜について、それぞれ透水量、Ｎ2ガス透過量、引張り強度の測定を行い、さらに走査型電子顕微鏡による表面形態の観察を行った。
【００３７】
その結果を表２および表３に示す。
また図３に実施例９で得られたＰＴＦＥ製多孔質膜の電子顕微鏡写真を示すとともに、図４に比較例２で得られたＰＴＦＥ製多孔質膜の電子顕微鏡写真を示す。
【００３８】
表２および表３より実施例９のＰＴＦＥ製多孔質膜は透水量および透ガス量に優れていることがわかる。
【００３９】
【表３】
【表４】
【実施例１０〜１２】
懸濁重合法によって得られる平均粒子径２５μｍのＰＴＦＥモールディングパウダー（ポリフロンＭ−１２、ダイキン工業（株）製）を金型中で１５０kg／cm2の成形圧で予備成形したあと３６０℃で焼成してＰＴＦＥ成型品を作製した。この成型品を切削して膜厚４０〜６０μｍのフィルムを作製した。
【００４２】
このＰＴＦＥ膜表面に低分子量ＰＴＦＥ粉末をまぶし、電気炉中で３５０℃で２０分間熱処理した後冷却してＰＴＦＥ膜を得た。このＰＴＦＥ膜を二軸方向に逐次延伸してＰＴＦＥ製多孔質膜を得た。実施例１０〜１２の延伸条件を表４に示す。また表４に実施例１０で得られた多孔質膜の特性、図５にＳＥＭ写真を示す。
【００４３】
【表５】
【実施例１３】
乳化重合法によって得られる平均粒子径５５０μｍのＰＴＦＥファインパウダー（フルオンＣＤ−１、旭硝子（株）製）を液状潤滑剤と配合して圧縮予備成形した後、押出し成形によって膜状とし、次いで所定の温度で熱処理して液状潤滑剤を除去して膜厚５０μｍの未焼成ＰＴＦＥ膜を作製した。この未焼成ＰＴＦＥ膜を３６０℃で熱処理して焼成ＰＴＦＥ膜を得た。
【００４５】
この焼成ＰＴＦＥフィルムを、３２０℃の温度で融液化された低分子量ＰＴＦＥ中に１０分間浸漬した。得られたＰＴＦＥ膜を二軸方向に逐次延伸してＰＴＦＥ製多孔質膜を得た。得られたＰＴＦＥ製多孔質膜の特性を表５に示す。
【００４６】
【表６】
【図面の簡単な説明】
【図１】 実施例４のＰＴＦＥ製多孔質膜表面の電子顕微鏡写真
【図２】 比較例１のＰＴＦＥ製多孔質膜表面の電子顕微鏡写真
【図３】 実施例９のＰＴＦＥ製多孔質膜表面の電子顕微鏡写真
【図４】 比較例２のＰＴＦＥ製多孔質膜表面の電子顕微鏡写真
【図５】 実施例１２のＰＴＦＥ製多孔質膜表面のＳＥＭ写真[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a porous film made of polytetrafluoroethylene, and more specifically, made of polytetrafluoroethylene having excellent mechanical strength, gas permeation amount, water permeation amount, and having relatively uniform pores that are nearly circular The present invention relates to a method for producing a porous membrane.
[0002]
TECHNICAL BACKGROUND OF THE INVENTION
Polytetrafluoroethylene resin (hereinafter sometimes abbreviated as PTFE) has excellent chemical resistance, heat resistance, and mechanical properties, and is therefore used in various fields. For example, a porous membrane made of PTFE is widely used as a filter for a corrosive substance or a high-temperature substance by utilizing the above-described characteristics, and is also used as an electrolytic diaphragm, a fuel cell, or the like.
[0003]
Conventionally, in order to produce a porous membrane from PTFE resin, liquid lubricant is mixed with PTFE fine particles called fine powder having an average particle diameter of 0.1 to 0.4 μm obtained by emulsion polymerization of tetrafluoroethylene and compressed. A method of preforming, then forming into a film by a method including extrusion and / or rolling, removing the liquid lubricant, and then stretching the obtained PTFE film uniaxially or biaxially under normal heating conditions is employed. It was done. (See Japanese Patent Publication No. 42-13560, Japanese Patent Publication No. 49-118760, Japanese Patent Publication No. 51-40902, Japanese Patent Publication No. 51-18991)
Japanese Patent Publication No. 53-42794 discloses that a calcined PTFE film is heated to 327 ° C. or higher and then cooled, heat-treated so that its crystallinity becomes 80% or higher, and then a temperature of 25 to 260 ° C. Discloses a method for producing a porous PTFE material, which is uniaxially drawn at a draw ratio of 1.5 to 4 times.
[0004]
However, the porous PTFE membrane manufactured by such a method has a problem that it is difficult to manufacture the pores in a shape close to a perfect circle and the pore diameter to a predetermined size. There is also a problem that the mechanical strength of the porous membrane cannot be said to be sufficient.
[0005]
Also known is a method for producing a PTFE porous membrane by stretching a PTFE semi-sintered membrane at a temperature below its melting point, for example, described in JP-B-6-89165. According to this method, a porous PTFE membrane having a high porosity can be produced, but the range of heat treatment conditions for making PTFE into a semi-sintered state is narrow, and such a semi-sintered PTFE membrane can be produced. There was a problem that it was not easy.
[0006]
OBJECT OF THE INVENTION
The present invention is intended to solve the above-described problems in the prior art, and has a porous shape made of PTFE having holes close to a perfect circle and excellent in mechanical strength, gas permeability, and water permeability. It aims at providing the manufacturing method of a film | membrane.
[0007]
SUMMARY OF THE INVENTION
In the method for producing a porous PTFE membrane according to the present invention, a PTFE membrane is contacted with a low molecular weight PTFE having a number average molecular weight of 500 to 10,000 at a temperature equal to or higher than the melting point of the low molecular weight PTFE. The film formation is characterized by being uniaxially or biaxially stretched 1.3 to 6.5 times at a temperature not higher than the melting point of PTFE.
[0008]
In the present invention, PTFE film formation and the number average molecular weight of the low molecular weight PTFE which is a 500 to 10,000 contact, for example, whether carried out by attaching the low molecular weight PTFE powder on a PTFE film or PTFE film in a molten state it can be carried out by immersion in the low molecular weight in PTFE.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a method for producing a PTFE porous membrane according to the present invention will be described.
In the present invention, first, PTFE film formation and low molecular weight PTFE are brought into contact with each other at a temperature equal to or higher than the melting point of low molecular weight PTFE (the melting point of PTFE varies depending on the molecular weight).
[0010]
As the PTFE film, a PTFE film, a thin PTFE tube, or the like is used. The film thickness of this PTFE film is preferably about 10 to 500 μm.
[0011]
As such PTFE film formation, for example, after a pre-compression molding of a blend of PTFE fine powder obtained by an emulsion polymerization method and a liquid lubricant, it is extruded or rolled, or a film-like form by a method including both of them. It may be a thing. Also, a PTFE molding powder obtained by the suspension polymerization method is compression-molded to prepare a cylindrical preform, and then the preform is fired at a temperature equal to or higher than the melting point of PTFE (327 ° C.). It may be cut into a film. Further, it may be obtained by thermally fusing a plurality of PTFE films.
[0012]
The number average molecular weight of such PTFE is about 2 million to 20 million, preferably about 2 million to 8 million.
Such a PTFE film is brought into contact with the low molecular weight PTFE at a temperature equal to or higher than the melting point of the low molecular weight PTFE.
[0013]
Specifically, this operation is performed by the following method, for example.
B) A low molecular weight PTFE powder is deposited on the PTFE film by dusting, and then heated to a temperature equal to or higher than the melting point of the low molecular weight PTFE and then cooled. The heating temperature at this time is 100 to 400 ° C, preferably 250 to 380 ° C, more preferably about 300 to 380 ° C.
[0014]
The heating time varies greatly depending on the heating temperature, but it is usually 5 to 3600 seconds, preferably several seconds to 20 minutes.
B) First, a low molecular weight PTFE powder is dispersed in an organic solvent such as ethanol or ethylene glycol or water to prepare a dispersion. Next, this dispersion is applied or sprayed onto the PTFE membrane, the low molecular weight PTFE powder is adhered onto the PTFE membrane, the dispersion medium is removed, and then heated to a temperature equal to or higher than the melting point of the low molecular weight PTFE and then cooled. The heating temperature and the heating time are the same as described above.
[0015]
C) First, the low molecular weight PTFE powder is heated and melted. Next, the PTFE membrane is immersed in this low molecular weight PTFE in a molten state, the PTFE membrane and the low molecular weight PTFE are brought into contact with each other, heated to a temperature equal to or higher than the melting point of PTFE, and then cooled. Alternatively, a low molecular weight PTFE in a molten state is applied or sprayed on the PTFE film to bring the PTFE film into contact with the low molecular weight PTFE, heated to a temperature equal to or higher than the melting point of the low molecular weight PTFE, and then cooled. The heating temperature and the heating time are the same as described above.
[0016]
In this way, the PTFE membrane and the low molecular weight PTFE are brought into contact with each other at a temperature equal to or higher than the melting point of the low molecular weight PTFE and then cooled, and the PTFE membrane is uniaxially increased by 1.3 to 6.5 times at a temperature equal to or lower than the melting point of PTFE. Alternatively, biaxial stretching yields a PTFE porous membrane.
[0017]
The stretching temperature is 19 to 320 ° C, preferably about 50 to 290 ° C.
The stretching ratio of the PTFE membrane is preferably 1.3 to 6.5 times. If this stretching ratio exceeds 6.5 times, pinholes may be generated in the membrane or the membrane may be broken during stretching. On the other hand, if the draw ratio is less than 1.3 times, desired fine pores may not be obtained.
[0018]
Such stretching is performed uniaxially or biaxially, preferably biaxially. By biaxially stretching the PTFE membrane, an effect that the pores of the obtained PTFE porous membrane approach a perfect circle is recognized.
[0019]
In the present specification, the low molecular weight PTFE means PTFE having a number average molecular weight of 1 million or less, preferably 500 to 10,000, and more preferably about 500 to 2,000. Such low molecular weight PTFE is sold, for example, by Central Glass Co., Ltd. under the trade name Cefral Lube.
[0020]
In the present invention, after the PTFE membrane and the low molecular weight PTFE are brought into contact with each other at a temperature equal to or higher than the melting point of the low molecular weight PTFE, the PTFE membrane is uniaxially or biaxially 1.3 to 6.5 times at a temperature equal to or lower than the melting point of the PTFE. When a PTFE porous membrane is produced by axial stretching, the amount of water permeation is compared with the case where a PTFE porous membrane is produced without contacting the PTFE membrane and the low molecular weight PTFE at a temperature equal to or higher than the melting point of the low molecular weight PTFE. A porous PTFE membrane having a high gas permeability and excellent mechanical strength can be obtained. Although the reason for this is not clear, when the PTFE membrane and the low molecular weight PTFE are brought into contact with each other at a temperature equal to or higher than the melting point of the low molecular weight PTFE, the low molecular weight PTFE enters the PTFE membrane, and the PTFE membrane swells. It is presumed that a porous film made of PTFE that is formed with pores close to a perfect circle in the stretching process of the membrane and that has excellent water permeability, gas permeability, and mechanical strength will be obtained.
[0021]
【The invention's effect】
According to the present invention, it is possible to obtain a porous PTFE membrane having excellent water permeability, gas permeability, and mechanical strength, and having a relatively uniform hole that is nearly circular.
[0022]
【Example】
EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.
[0023]
Examples 1-8
After preforming the average PTFE molding powder of particle diameter 25 [mu] m (Polyflon M-12, manufactured by Daikin Industries Ltd.) molding pressure of 150 kg / cm 2 in a mold obtained by a suspension polymerization method, calcined at 360 ° C. Thus, a PTFE molded product was produced. This molded product was cut to prepare a PTFE film having a thickness of 20 μm.
[0024]
Two films thus obtained were stacked and 50% rolled and then heat-sealed at 360 ° C. and then cooled to produce a PTFE film having a thickness of 40 μm.
On the surface of the calcined PTFE film thus obtained, low molecular weight PTFE having a number average molecular weight of 700 to 1500 (cefural lube-V, manufactured by Central Glass Co., Ltd.) is dispersed in ethanol so as to be 15% by weight. The dispersion was sprayed with a spray gun and dried, and a low molecular weight PTFE powder was applied in an amount of 2 mg / cm 2 . This film was heat-treated in an electric furnace at a temperature range of 300 to 360 ° C. for 60 to 300 seconds, and then rapidly cooled to room temperature to prepare a PTFE film.
[0025]
Table 1 shows the heat treatment temperature and heat treatment time.
This PTFE membrane was biaxially stretched at a stretching ratio of 2.0 × 2.0 at a temperature of 70 ° C. to prepare a PTFE porous membrane.
[0026]
[Comparative Example 1]
In Example 1, a PTFE porous membrane was prepared in the same manner as in Example 1 except that the PTFE membrane before stretching was not brought into contact with the low molecular weight PTFE.
[0027]
About the porous film made from PTFE obtained in Examples 1-8 and Comparative Example 1, the porosity water permeability, N 2 gas permeation, tensile strength, and elongation were measured, respectively, and the surface morphology by a scanning electron microscope Was observed.
[0028]
The results are shown in Tables 1 and 2.
1 shows an electron micrograph of the PTFE porous membrane obtained in Example 4, and FIG. 2 shows an electron micrograph of the PTFE porous membrane obtained in Comparative Example 1.
[0029]
From Table 1, it can be seen that the porous PTFE membrane of Example 1 is excellent in water permeability and gas permeability.
[0030]
[Table 1]
[Table 2]
[Example 9]
PTFE fine powder (Fluon CD-1, manufactured by Asahi Glass Co., Ltd.) having an average particle diameter of 550 μm obtained by emulsion polymerization is blended with a liquid lubricant and subjected to compression pre-molding, and then formed into a film by extrusion molding, The liquid lubricant was removed by heat treatment at a temperature to produce an unsintered PTFE film having a thickness of 50 μm. This unfired PTFE film was heat-treated at 360 ° C. to obtain a fired PTFE film.
[0033]
A dispersion liquid in which a low molecular weight PTFE having a number average molecular weight of 700 to 1500 (cefural lube-V, manufactured by Central Glass Co., Ltd.) is dispersed in ethanol at a ratio of 15% by weight is sprayed on the surface of the sintered PTFE film with a spray gun. After drying, a low molecular weight PTFE powder was applied in an amount of 2 mg / cm 2 . This PTFE membrane was heat-treated at a temperature of 360 ° C. for 60 seconds in an electric furnace, and then rapidly cooled to room temperature to produce a PTFE membrane.
[0034]
The PTFE membrane was biaxially stretched at a stretching ratio of 2.0 × 2.0 at a temperature of 70 ° C. to obtain a PTFE porous membrane having a thickness of 32 μm.
[0035]
[Comparative Example 2]
In Example 2, a PTFE porous membrane was prepared in the same manner as in Example 2 except that the PTFE membrane before stretching was not brought into contact with the low molecular weight PTFE.
[0036]
The porous membranes made of PTFE obtained in Example 2 and Comparative Example 2 were measured for water permeability, N 2 gas permeability, and tensile strength, respectively, and surface morphology was observed with a scanning electron microscope.
[0037]
The results are shown in Tables 2 and 3.
3 shows an electron micrograph of the PTFE porous membrane obtained in Example 9, and FIG. 4 shows an electron micrograph of the PTFE porous membrane obtained in Comparative Example 2.
[0038]
From Table 2 and Table 3, it can be seen that the PTFE porous membrane of Example 9 is excellent in water permeability and gas permeability.
[0039]
[Table 3]
[Table 4]
Examples 10-12
PTFE molding powder (Polyflon M-12, manufactured by Daikin Industries, Ltd.) having an average particle size of 25 μm obtained by suspension polymerization is pre-molded in a mold at a molding pressure of 150 kg / cm 2 and then fired at 360 ° C. Thus, a PTFE molded product was produced. This molded product was cut to produce a film having a thickness of 40 to 60 μm.
[0042]
The PTFE membrane surface was coated with a low molecular weight PTFE powder, heat treated at 350 ° C. for 20 minutes in an electric furnace, and then cooled to obtain a PTFE membrane. The PTFE membrane was sequentially stretched in the biaxial direction to obtain a PTFE porous membrane. Table 4 shows the stretching conditions of Examples 10-12. Table 4 shows the characteristics of the porous membrane obtained in Example 10, and FIG. 5 shows an SEM photograph.
[0043]
[Table 5]
Example 13
PTFE fine powder (Fluon CD-1, manufactured by Asahi Glass Co., Ltd.) having an average particle diameter of 550 μm obtained by emulsion polymerization is blended with a liquid lubricant and subjected to compression pre-molding, and then formed into a film by extrusion molding, The liquid lubricant was removed by heat treatment at a temperature to produce an unsintered PTFE film having a thickness of 50 μm. This unfired PTFE film was heat-treated at 360 ° C. to obtain a fired PTFE film.
[0045]
This baked PTFE film was immersed in a low molecular weight PTFE melted at a temperature of 320 ° C. for 10 minutes. The obtained PTFE membrane was sequentially stretched in the biaxial direction to obtain a porous PTFE membrane. Table 5 shows the properties of the obtained porous PTFE membrane.
[0046]
[Table 6]
[Brief description of the drawings]
1 is an electron micrograph of the surface of a PTFE porous membrane of Example 4, FIG. 2 is an electron micrograph of the surface of a PTFE porous membrane of Comparative Example 1, and FIG. 3 is a surface of the PTFE porous membrane of Example 9. 4 is an electron micrograph of the surface of the porous PTFE membrane of Comparative Example 2. FIG. 5 is an SEM photo of the surface of the porous PTFE membrane of Example 12.
Claims (3)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP21127297A JP3914302B2 (en) | 1997-07-22 | 1997-07-22 | Method for producing porous film made of polytetrafluoroethylene |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP21127297A JP3914302B2 (en) | 1997-07-22 | 1997-07-22 | Method for producing porous film made of polytetrafluoroethylene |
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| Publication Number | Publication Date |
|---|---|
| JPH1135716A JPH1135716A (en) | 1999-02-09 |
| JP3914302B2 true JP3914302B2 (en) | 2007-05-16 |
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| JP21127297A Expired - Lifetime JP3914302B2 (en) | 1997-07-22 | 1997-07-22 | Method for producing porous film made of polytetrafluoroethylene |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US8795565B2 (en) * | 2006-02-21 | 2014-08-05 | Celgard Llc | Biaxially oriented microporous membrane |
| US20100203310A1 (en) | 2006-08-09 | 2010-08-12 | Sumitomo Electric Fine Polymer, Inc. | Fluororesin thin film, fluororesin composite, porous fluororesin composite, manufacturing methods thereof, and seperation membrane element |
| JP5470140B2 (en) | 2010-03-31 | 2014-04-16 | 富士フイルム株式会社 | Crystalline polymer microporous membrane and filter for filtration |
| JP5633793B2 (en) * | 2010-08-26 | 2014-12-03 | 旭硝子株式会社 | Method for producing stretched polytetrafluoroethylene film and stretched polytetrafluoroethylene film |
| JP5830782B2 (en) | 2012-01-27 | 2015-12-09 | 住友電工ファインポリマー株式会社 | Method for producing modified polytetrafluoroethylene microporous membrane and method for producing modified polytetrafluoroethylene porous resin membrane composite |
| JP2015200058A (en) * | 2014-04-04 | 2015-11-12 | 東洋紡株式会社 | electret |
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