JP3845067B2

JP3845067B2 - Method for measuring pore size of porous filter

Info

Publication number: JP3845067B2
Application number: JP2003080107A
Authority: JP
Inventors: 知典高橋
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 2003-03-24
Filing date: 2003-03-24
Publication date: 2006-11-15
Anticipated expiration: 2023-03-24
Also published as: WO2004086008A1; JP2004286635A

Description

【０００１】
【発明の属する技術分野】
本発明は、いわゆるバブルポイント法を応用した平均細孔径に関連する濾過体の評価方法を提供するものである。より詳しくは、セラミックス体等の細孔が３次元的に入り組んでいる濾過体において、実用上有益な平均細孔径に関連する濾過体の評価が可能な細孔径測定方法を提供するものである。
【０００２】
【従来の技術】
各種濾過体の平均細孔径評価は、その基本性能の評価として必須であり、従来より、バブルポイント法、水銀法、細菌濾過法等の各種評価方法が行われている。中でも、バブルポイント法は、測定が比較的簡易であることから、各種濾過体の品質管理等において広く用いられている。
【０００３】
ところで、当該バブルポイント法はＡＳＴＭＦ３１６−８６に記載されているが、各細孔に試験用液体を充填させた濾過体を加圧ガス流路に設置した際、濾過体の一の面で濾過体の各細孔中に充填された試験用液体にかかる加圧ガスの圧力が、濾過体の各細孔に充填させた試験用液体の表面張力による抵抗力を超えた際に、ガス−液界面が濾過体の細孔開口部まで進展してガスが透過することを利用するものである。そして、この方法における平均細孔径の計測は、上記加圧ガスを段階的に昇圧した際に、試験用液体を充填させない濾過体の透過ガス量に対する、試験用液体を充填させた濾過体の透過ガス量の割合が、全細孔を透過する透過流量に対する、各段階のガス圧に対応する細孔径以上の細孔を透過する透過流量の割合に一致する、と言う仮定を用いている（例えば非特許文献１参照）。
【０００４】
具体的には、試験用液体を充填させない濾過体（以下「乾性濾過体」という。）と、試験用液体を充填させた濾過体（以下「湿性濾過体」という。）とを、それぞれ各端部をシールした状態でホルダーに設置し、各濾過体の一の面に、加圧ガスを供給し、加圧ガスの圧力を段階的に昇圧させ、各ガス圧段階で各濾過体を透過するガス量を検出し、乾性濾過体を透過するガス流量に対する湿性濾過体を透過するガス流量の比が１／２となるガス圧に対応する細孔径を平均細孔径（ＭＦＰＤ）とみなし、下記数式（１）から求める。
【０００５】
【数３】
ＭＦＰＤ＝４ＢγＣＯＳθ／Ｐ …（１）
【０００６】
「上記数式（１）中、ＭＦＰＤは平均細孔径（μｍ）、θは濾過体の細孔に充填させた試験用液体の、濾過体を構成する材料に対する接触角（°）、γは濾過体の細孔に充填させた試験液体の表面張力（Ｎ／ｍ）、Ｂはキャピラリー定数（０．７１５）又は１、Ｐは乾性濾過体を透過するガス流量に対する湿性濾過体を透過するガス流量の比が１／２になるガス圧力（ＭＰａ）を示す。θは通常０度と近似しても良い。」
【０００７】
従来、この方法による平均細孔径の評価方法としては、各ガス圧段階において、一定時間のガス流量の変化量が特定数値以下となるまで、供給する気体のガス圧を保持し、その後、次のガス圧段階まで昇圧する工程を段階的に繰り返す方法が行われている。この従来の方法は、一定時間のガス流量の変化量が特定数値以下となった状態を、ガス流量が飽和した状態とみなし、飽和するまでガス圧を保持することで、各ガス圧力でガス−液界面が濾過体の細孔開口部まで充分進展するのを待つもので、ガスを透過させている湿性濾過体のガスの流通の経路が、乾性濾過体でガスの一部が透過する経路と同じであると言う仮定に基づく。
【０００８】
しかし、この従来の評価方法は、実際に評価対象となる濾過体の特性を全く考慮していなかったため、実際の製品に対する評価方法としては、必ずしも充分なものではなかった。
【０００９】
【非特許文献１】
「ＡＮＵＡＬＢＯＯＫＯＦＡＭＥＲＩＣＡＮＳＴＡＮＤＡＲＤＳ」ｖｏｌ．１１．０１、ＡＭＥＲＩＣＡＮＳＯＣＩＥＴＹＦＯＲＴＥＳＴＩＮＧＡＮＤＭＡＴＥＲＩＡＬＳ発行
【００１０】
【発明が解決しようとする課題】
本発明は、上述の問題に鑑みなされたもので、３次元的に入り組んだ細孔を有する濾過体について、平均細孔径の測定を、正確且つ高精度で行うことができ、しかも実使用時の濾過体の性能を反映した品質評価が可能な濾過体の細孔径測定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】
本発明者は、上述の課題を解決するべく鋭意研究した結果、従来の方法で適切な評価結果が得られなかった点に関し、以下の知見を得た。
【００１２】
即ち、図６（ａ）に示すように、実際に評価対象となる濾過体では、通常の濾過における被濾過流体は、細孔のつながりにより決まった分布で流通する。これに対し、図６（ｂ）に示すように、湿性濾過体にガスを低圧から順次流通させる場合には、大きい細孔を優先してガスが透過しはじめるため、通常の濾過とは異なる経路をたどる。殊に多孔質セラミックスにあっては、濾過体の流体流路が、複数の細孔の結合によって形成され、３次元的に複雑に入り組んで存在するため、湿性濾過体の部分的なガス透過は、乾性濾過体のガス透過の部分や、通常の濾過とは大きく異なる経路をたどり易い。
【００１３】
しかし、従来の評価方法では、乾性濾過体のガス透過や、実用時の被濾過流体の流路に対して、湿性濾過体の部分的なガス透過が、このように極めて様々な流路を経ることが、評価結果に大きな影響を与える点について全く考慮されていなかったため、正確性及び精度の点で充分なものではなく、また、各製品の実使用時の性能を評価する上でも充分なものでもないことがわかった。更に、以下に示す知見を得た。
【００１４】
▲１▼ 従来の評価方法では、ある圧力における一定時間での湿性濾過体のガス流量の変化量が特定数値以下となることで、いわゆるガス飽和状態とみなすことから、長い流路でガス−液界面が移動中にも拘らず、いわゆるガス透過の飽和とみなされる場合がある。このため、当該長い流路による透過ガスは、本来のガス圧段階以降のガス圧段階で検出され、これが誤差要因となっていた。
【００１５】
▲２▼ 従来の評価方法で、いわゆる飽和までガス圧を保持する場合、上記▲１▼から明らかなように、各ガス圧力段階での積み重ねによってガス−液界面が進展する。このため、従来の方法では、各ガス圧段階の制御機器や測定機器の精度不足による評価結果への影響が、積み重なって増幅され、これが評価結果の正確性、及び精度をより低減させる要因となっていた。
【００１６】
▲３▼ 乾性濾過体では、ガス透過はガス流速などによって決まるひとつの経路による。ある細孔から入ったガスの部分は常に特定の経路を通って透過する。従来の評価方法における湿性濾過体の測定では、いわゆる飽和までガス圧を保持するが、保持時間が長くなる場合、ガスが大きく回り込むなどして、基準となる乾性濾過体におけるガスの部分が透過する経路と、湿性濾過体でガスが透過する経路が異なってしまう。このため、従来の方法では、基準となる乾性濾過体との実質的評価対象に差を生じ、これが評価結果の正確性をより低減する要因となっていた。
【００１７】
▲４▼ 実使用時において、乾性濾過体のガスが通過する場合と同じように、ある細孔から入った被濾過流体の部分は特定の経路を通って透過する。このため、従来の方法では、実使用時の濾過体を透過する被濾過流体の経路と湿性濾過体を透過するガスの経路が異なり、この点においても、実質的評価対象について差を生じ、これが、濾過体の実使用時の性能を充分に反映しない要因となっていた。
【００１８】
本発明者は、以上の知見に基づき、更に検討を重ねたところ、濾過体の一の面に供給する気体のガス圧を、各ガス圧段階で、実際に濾過対象となる被濾過流体が濾過体を通過する時間を基準として、これに対する所定比率の保持時間でガス圧を保持して次のガス圧段階に移行させたところ、正確且つ高精度で実用上有用な平均細孔径の評価が可能となることを見出し、本発明を完成するに至った。
【００１９】
即ち、本発明は、乾燥状態の乾性濾過体、及び該乾性濾過体の細孔を試験用液体で充填した湿性濾過体について、各濾過体に、加圧ガスを供給し、加圧ガスの圧力を段階的に昇圧させ、各ガス圧段階で該各濾過体を透過するガス流量を検出し、次いで、下記数式（１）に基づき平均細孔径を求める多孔質濾過体の細孔径測定方法であって、下記数式（２）により求められる被濾過流体通過時間（Ｓ）が３秒未満の場合には（Ｓ）秒〜３０秒、被濾過流体通過時間（Ｓ）が３秒以上の場合には（Ｓ）秒〜（（Ｓ）×１０）秒の保持時間、一定圧力で湿性濾過体を保持した後、次のガス圧段階に昇圧させる保持−昇圧工程を含むことを特徴とする多孔質濾過体の細孔径測定方法を提供するものである。
【００２０】
【数４】
ＭＦＰＤ＝（４ＢγＣＯＳθ）／Ｐ …（１）
「上記数式（１）中、ＭＦＰＤは平均細孔径（μｍ）、θは濾過体の細孔に充填させた試験液体の濾過体を構成する材料に対する接触角（°）、γは濾過体の細孔に充填させた試験液体の表面張力（Ｎ／ｍ）、Ｂはキャピラリー定数（０．７１５）又は１、Ｐは乾性濾過体を透過するガス流量に対する湿性濾過体を透過するガス流量の比が１／２になるガス圧力（ＭＰａ）を示す。」
【００２１】
【数５】
（Ｓ）＝（Ｘ／Ｊ）×Ｖs／Ｖr …（２）
「上記数式（２）中、Ｘは濾過体の濾過方向における厚さ（ｍ）であり、Ｊは実用時の被濾過流体の線速度（ｍ／ｓ）であり、Ｖsは試験用液体の粘度（Ｐａ・ｓ）であり、Ｖrは被濾過流体の粘度（Ｐａ・ｓ）である。」
【００２２】
本発明において、前記保持−昇圧工程を、乾性濾過体を透過するガス流量に対する湿性濾過体を透過するガス流量の比（以下、このガス流量比を単にガス流量比と称する）が１／５〜１／２となる範囲において行うことが好ましく、この範囲の全ガス圧段階において行うことが更に好ましい。また、前記ガス流量の比が１／５〜１／２となる範囲における各ガス圧段階の保持時間を、前記ガス流量の比が１／５〜１／２となる範囲におけるガス圧段階の平均保持時間の±１０％以内とすることが好ましく、前記ガス流量の比が１／５〜１／２となる範囲における各保持時間を１秒〜１分とすることが更に好ましい。また、前記保持−昇圧工程において、一のガス圧段階から次のガス圧段階に昇圧させる昇圧値を、実用時の被濾過流体の線速度（Ｊ）で被濾過流体を透過させたときの膜差圧より大きな昇圧値とすることが好ましく、前記ガス流量の比が１／５〜１／２となる範囲における一のガス圧段階から次のガス圧段階に昇圧する各昇圧値を、前記ガス流量の比が１／５〜１／２となる範囲における平均昇圧値の±２０％以内とすることが更に好ましい。また、前記ガス流量の比が１／５〜１／２となる範囲における各昇圧値を０．０１〜０．０４ＭＰａとすることが好ましい。
【００２３】
【発明の実施の形態】
以下、本発明の実施の形態の一例を、図面に基づいて各工程毎に具体的に説明する。なお、図１は本発明の評価方法に、通常用いられる測定装置のフローを示すものであり、加圧ガス供給源１１と、当該加圧ガス供給源１１から導入されるガスの圧力を制御するレギュレータ１２と、当該レギュレータ１２で設定された圧力を測定する圧力センサ１６と、濾過体２を設置するホルダー１０と、濾過体に供給されるガス流量を測定する流量計１４とを備えている。また、図２は、濾過体２が、ホルダー１０に設置されている状態を示す断面図である。また、図３は、各濾過体（乾性濾過体、湿性濾過体）において検出される透過ガスの流量とガス圧との関係を示すグラフであり、グラフ中のＨは、湿性濾過体の透過ガス流量が乾性濾過体の透過ガス流量に対して１／２となるガス圧を示すものである。
【００２４】
本発明の平均細孔径評価方法は、まず、図１及び図２に示すように、乾燥状態の乾性濾過体２を、ホルダー１０にその端部をシール部材３を用いて、シールした状態で設置する。シール部材３はエポキシなどのポリマー、グレーズなどと、パッキン、Ｏリングなどとを組み合わせて用いる。ガス透過量測定後、同じ乾性濾過体２の細孔を試験用液体で充填した湿性濾過体２を、ホルダー１０にその端部を同様にシールした状態で設置し、ガス透過量を測定する。
【００２５】
本発明の評価対象たる濾過体２としては、多孔質体であることの他特に制限はなく、例えば、濾紙、有機樹脂性のフィルター、セラミックスフィルター等各種濾過体に適用することができる。もっとも、本発明の評価方法は、前述したように細孔が複雑に入り組んでいる濾過体に特に好ましく適用することができ、この点から、セラミックスフィルターへの適用が好ましい。また、多孔質の基材上に、細孔径と異なる１層以上の濾過膜を積層したセラミックスフィルターへの適用もできる。更に、図２には板状の濾過体を示したが、ホルダーを用意することでチューブ、モノリス等の形状の濾過体も測定できる。
【００２６】
本発明において、乾性濾過体２の細孔に充填させる試験用液体４としては、例えば、ＡＳＴＭＦ３１６−８６のＤ１１２９及びＤ１１９３に記載するような高純度の水、変性アルコール、ミネラルオイル、１，１，２−トリクロロ−１，２，２−トルオレート、あるいはフッ素系不活性液体（商品名：フロリナートＦＣ−４０、スリーエム社製フッ素系不活性液体）等が好ましい。
【００２７】
また、実際の使用において濾過対象となる被濾過流体としては、例えば、水、石油などを挙げることができる。
【００２８】
次に、本発明においては、乾性濾過体、湿性濾過体の一の面に段階的に昇圧した加圧ガスを供給するが、その際、湿性濾過体の透過ガス測定において、各ガス圧段階で、数式（２）により求められる被濾過流体通過時間（Ｓ）が３秒未満の場合には（Ｓ）秒〜３０秒、被濾過流体通過時間（Ｓ）が３秒以上の場合には（Ｓ）秒〜（Ｓ×１０）秒の保持時間、一定圧力で湿性濾過体を保持した後、次のガス圧段階に昇圧させる。各ガス圧段階において、保持時間をなるべく短くすることにより、試験対象たる乾性濾過体及び湿性濾過体間において、ガスが透過するそれぞれの経路がより近似することとなるからである。このため、正確且つ高精度の評価が可能となる。なお、被濾過流体通過時間（Ｓ）の１０倍以下の保持時間とすることにより、精度良く細孔径を測定することができるが、（Ｓ）が３秒未満と短い場合には、（Ｓ）の１０倍を超えても保持時間が３０秒以下であれば精度良く細孔径を測定することができる。
【００２９】
ここで数式（２）より求められる（Ｓ）は、実用時の被濾過流体の線速度（Ｊ）に依存するが、（Ｊ）は通常、該濾過体を用いた濾過装置の設計を行う際に設定され、その設計を考慮して濾過体が製造された時点で既知の値となっている。また、（Ｊ）は、所定の幅をもって設定される場合もあり、その際（Ｓ）も所定の幅を持つこととなるが、その場合は、上記（Ｓ）が３秒以上とは（Ｓ）の最大値が３秒以上、（Ｓ）が３秒未満とは（Ｓ）の最大値が３秒未満を意味する。そして、保持時間の上限は、（Ｓ）の最大値に近い方がより精度が出やすく、（Ｓ）の最大値の１０倍以下、更に２倍以下であることが好ましい。
【００３０】
また、保持時間が短すぎる場合は、長い流路でガス−液界面が移動中であるなど、昇圧段階で検出されるべきガス流量が検出されないため、得られる平均細孔径に関する評価が、本来の評価結果より小さい値となってしまう。従って保持時間は、（Ｓ）の値以上でなくてはならない。なお、（Ｓ）が所定の幅を持つ場合には、ここでの（Ｓ）も、最大値を意味する。また、保持時間が短すぎると装置の操作性、応答性の問題が出るため、保持時間は１秒以上、更には３秒、特に５秒以上であることが好ましい。
【００３１】
即ち、本発明の好ましい態様においては、各ガス圧段階において、保持時間を（Ｓ）より長いが、かつ、その中でなるべく短くすることにより、実際の濾過対象である被濾過流体が濾過体を通過する時間に近い時間、ガスの圧力を保持することとなる。このため、湿性濾過体中のガスの経路が、被濾過流体の部分がそれぞれ通過する経路とも近似し、濾過体の実使用時の性能を充分に反映した評価が可能となる。なお、被濾過流体と試験用液体とは粘度の違いにより、それぞれ膜内の通過時間とガス圧による排出の時間とが異なるため、（Ｓ）は被濾過流体と試験用液体との粘度の比で補正したものである。
【００３２】
本発明においては、乾性濾過体を透過するガス流量に対する湿性濾過体を透過するガス流量の比が１／５〜１／２となるガス圧段階において、上記のような保持時間を設定することが好ましく、更にこの範囲の全ガス圧段階において、上記のような保持時間を設定することが好ましい。これは、上記ガス流量の比が１／２となるところで平均粒子径が決定されるため、この地点に近いところ、特に湿性濾過体におけるガス流量が増加しはじめる地点からは正確な制御を行うことが好ましいからである。従って、上記ガス流量の比が１／５となるガス圧段階までは、各ガス圧段階におけるガス圧保持時間を上記のような設定から外れる範囲に設定しても良い。
【００３３】
また、上記ガス流量の比が１／５〜１／２の範囲のガス圧段階においては、正確且つ精密な評価を行うために各ガス圧段階におけるガス圧保持時間を、できるだけ均等にすることが好ましい。具体的には、上記ガス流量の比が１／５〜１／２となる範囲の各ガス圧段階における保持時間を上記ガス流量の比が１／５〜１／２となる範囲の全ガス圧段階における平均ガス圧保持時間の±１０％以内の範囲とすることが好ましい。
【００３４】
本発明においては、一のガス圧段階から次のガス圧段階への各昇圧値は、実用時の線速度（Ｊ）で被濾過流体を透過したときの膜差圧より大きく、これに近い方が好ましい。好ましくは膜差圧の１−１０倍が良い。昇圧値が小さすぎると、保持時間内にガス−液界面が移動しきらず、長すぎると細孔径の分解能がなくなるからである。なお、膜差圧に範囲がある場合には、最大の膜差圧より大きいことが好ましい。
【００３５】
また、上述と同様の理由から、ガス流量の比が１／５〜１／２となる範囲におけるガス圧段階で、更にはこの範囲における全ガス圧段階で昇圧値を上記のように制御することが好ましい。
【００３６】
また、本発明においては、ガス流量の比が１／５〜１／２となる範囲の各ガス圧段階においては、正確且つ精密な評価を行うために、当該各昇圧値についても、できるだけ均等にすることが好ましい。
【００３７】
具体的には、この範囲における各昇圧値を、この範囲の全ガス圧段階における平均昇圧値の±２０％以内の範囲とすることが好ましい。また、各圧力保持時間、昇圧幅を管理する範囲は、細孔径分布が広い場合には、更に低い圧力段階から行った方が好ましい。
【００３８】
なお、本発明においては、各ガス圧段階における前ガス圧段階に対する各昇圧値、及び各ガス圧段階における各ガス圧保持時間を上記のようにすれば、正確且つ高精度であるとともに、実際の性能を反映した評価を行うことができるが、充分大きい細孔の基材表面に、平均細孔径０．０５−２ミクロン、厚さ１０−３００ミクロン、実用時の被濾過流体の流速が１−１０ｍ／日のセラミックス製の濾過体であれば、測定装置の能力を考慮して、各ガス圧段階における前ガス圧段階に対する各昇圧値を、０．０１〜０．０４ＭＰａの範囲、前記各ガス圧段階における各ガス圧保持時間を、１秒〜１分の範囲から選択することができる。乾性濾過体を測定する場合の昇圧は、装置の操作時間・応答時間以上の保持時間であれば良い。
【００３９】
また、本発明において用いられる加圧ガスは、例えば、空気、アルゴン、窒素等の不活性ガスが好ましく、試験用液体へ溶解しにくいこと、評価条件、検出手段、コスト等を考慮して、適宜選択すれば良い。
【００４０】
次に、本発明においては、各ガス圧段階で各濾過体の透過ガス流量を検出し、数式（１）に基づき平均細孔径を求める。図３に示すように、乾性濾過体では、細孔中に加圧ガスの押圧対象が存しないことから、加圧ガスの圧力上昇にほぼ比例して検出されるガス流量が増大する（図中、実線で示す）。一方、湿性濾過体では、細孔中に加圧ガスの押圧対象である試験流体が存在しており、加圧ガスの圧力が、当該試験液体の表面張力による抵抗力に打ち勝つまでは、ガス−液界面が移動しない。従って、加圧初期段階では、加圧ガスの圧力が上昇しても、透過ガスが検出されず、加圧ガスの圧力が、ある一定の圧力に達すると透過ガス流量が増大しはじめ、最終的には乾性濾過体における透過ガス流量−ガス圧直線と重なる（図中、点線で示す）。そして、この透過ガス流量が増大しはじめてから最終的に乾性濾過体における透過ガス流量−ガス圧直線と重なるまでに各ガス圧で検出される透過ガス流量は、ガスの通路となる一連の各細孔の孔径分布に依存して変化する。湿性濾過体における透過ガス流量が、乾性濾過体における透過ガス流量に対して１／２となるガス圧Ｈを求め（図面中１点鎖線は、乾性濾過体の各ガス圧における透過ガス流量を１／２とした線を示す）、数式（１）に基づき当該ガス圧Ｈに相当する細孔径を平均細孔径とする。
【００４１】
【実施例】
以下、本発明を実施例により具体的に説明するが、本発明はこれら実施例によって何ら限定されるものではない。なお、各実施例及び比較例においては、以下に記載する試料、試験用液体及び被濾過流体を用いて濾過体の評価を行った。
【００４２】
（試料）
平均細孔径約１０μｍ、直径３０ｍｍ、厚さ３ｍｍの円盤状のアルミナ製基材に、平均細孔径約１μｍ、厚さ２００μｍのアルミナ製中間層、及び平均粒径０．５ミクロンのチタニアの等方的な粒子よりなる厚さ１５μｍのチタニア濾過層を、順に製膜、焼成したセラミックス製の濾過体を試料とした。
【００４３】
（評価の際の基準とする被濾過流体）
被濾過流体は水（粘度：１×１０^-6ｍ²／ｓ）で、浄水等の実用条件は１−５ｍ／日であり、そのときの膜差圧は、０．００２６−０．０１２８ＭＰａとなる。適する昇圧幅は０．０１２８ＭＰａ以上となる。
【００４４】
（試験用流体）
フロリナート（粘度：２．２×１０^-6ｍ²／ｓ、表面張力：１６ｄｙｎｅ／ｃｍ）を用いた。従って、数式（２）より求められる被濾過流体通過時間（Ｓ）は、０．６−２．９秒である。好ましい保持時間は３０秒以下である。
【００４５】
（実施例１〜６、比較例１〜４）
試験用液体を充填しない試料（乾性濾過体）を細孔径評価装置のホルダーに端部をグレーズとＯリングとでシールした状態で、加圧ガス供給側にチタニア層があるように、設置した。次いで、加圧ガス供給側に、加圧空気を供給した。２５−３０秒毎に０．０１７−０．０２１ＭＰａずつ昇圧し、ガス流量を測定した。
【００４６】
次に、上記試験用液体中に、上記試料を浸し、試料中の細孔に試験用液体を完全に充填した。次いで、試験用液体を完全に充填した試料（湿性濾過体）を、細孔径評価装置のホルダーに、端部を同様にシールした状態で設置した。
【００４７】
次いで、加圧ガス供給側に加圧空気を供給した。この際、実施例１〜６は、各ガス圧段階で、それぞれ１秒間、２秒間、４−６秒間、９−１１秒間、１８−２２秒間、２５−３０秒間、ガス圧を保持し、比較例１〜４は、各ガス圧段階で、それぞれ５５−６５秒間、２９０−３１０秒間、４７０−４９０秒間、５９０−６１０秒間、ガス圧を保持し、０．０１７−０．０２１ＭＰａずつ昇圧し、ガス流量を測定した。湿性濾過体のガス流量が、乾性濾過体のガス流量の１／２となるガス圧から、数式（１）に基づき、各試料の平均細孔径を求めた。
【００４８】
（評価）
保持時間が短い方が平均細孔径の測定結果が小さい。Ｓより長ければ、実用時の被濾過流体のある部分が透過する細孔のつながりの経路が長くても、湿性濾過体でその経路をガスが透過し、評価され、また、Ｓに近い方がより、乾性濾過体を透過するガスや実用時の被濾過流体のある部分が、透過し得ない過剰に長い経路は評価に含まれにくく、正確な評価となる。
【００４９】
（実施例７−２８、比較例５−２６）
実施例１と同じ濾過膜試料の湿性濾過体のガス透過測定において、供給した空気のガス圧を、３０秒間で透過ガス流量の変化が１２ｍＬ／分以下となることで飽和として、それまで保持した後、次のガス圧工程まで昇圧したこと以外は、実施例１と同様にして、２２個の異なる試料の平均細孔径を求め、比較例５−２６とした。平均細孔に相当する圧力は０．３５ＭＰａでの乾性濾過体のガス透過量は約１００００ｍＬ／分であった。実施例１−６の湿性濾過体のガス透過測定におけるガス圧保持時間を９−１１秒間として、２２個の異なる試料の平均細孔径を求め、実施例７−２８とした。
【００５０】
（評価）
図５に示すように、本発明の実施例６−２７では、平均細孔径が０．１３〜０．１５μｍ（標準偏差０．００７）の範囲となった。これに対して、いわゆるガス飽和状態となる時点までガス圧を保持した後、昇圧する比較例６−２７では、各ガス圧段階での保持時間が３０秒−２０分までばらつき、平均細孔径が０．１６〜０．２１μｍ（標準偏差０．０１１）とばらつき、図４に示した約１０分の保持時間よりも更に大きい平均細孔径となった。
【００５１】
【発明の効果】
以上説明したように、本発明によれば、３次元的に入り組んだ細孔を有する濾過体について、平均細孔径に関する評価を、正確且つ高精度で行うことができ、しかも実使用時の濾過体の性能を反映した品質評価が可能な濾過体の評価方法を提供することができる。
【図面の簡単な説明】
【図１】本発明の評価方法を実施するための装置の構成を、模式的に示す説明図である。
【図２】本発明の評価方法の一例において、ホルダーに濾過体が設置されている状態を模式的に示す断面図である。
【図３】各濾過体（乾性濾過体、湿性濾過体）において検出されるガスの流量とガス圧との関係を示すグラフである。
【図４】各実施例及び各比較例において求められた平均細孔径とガス圧保持時間との関係を示すグラフである。
【図５】実施例１及び比較例８の方法で２２個の資料を測定した際の平均細孔径の分布を示すグラフである。
【図６】セラミックス製の濾過体における細孔の存在状態を模式的に示す説明図である
【符号の説明】
１…加圧ガス、２…濾過体、３…シール部材、１０…ホルダー、１１…加圧ガス供給源、１２…レギュレータ、１４…流量計。[0001]
BACKGROUND OF THE INVENTION
The present invention provides a method for evaluating a filter body related to an average pore diameter by applying a so-called bubble point method. More specifically, the present invention provides a pore diameter measuring method capable of evaluating a filter body related to a practically useful average pore diameter in a filter body in which pores such as a ceramic body are three-dimensionally complicated.
[0002]
[Prior art]
Evaluation of the average pore diameter of various filter bodies is essential as an evaluation of the basic performance, and various evaluation methods such as a bubble point method, a mercury method, and a bacterial filtration method have been conventionally performed. Among these, the bubble point method is widely used in quality control and the like of various filter bodies because measurement is relatively simple.
[0003]
By the way, the bubble point method is described in ASTM F316-86, but when a filter body in which each pore is filled with a test liquid is installed in a pressurized gas flow path, filtration is performed on one surface of the filter body. When the pressure of the pressurized gas applied to the test liquid filled in each pore of the body exceeds the resistance force due to the surface tension of the test liquid filled in each pore of the filter body, the gas-liquid This utilizes the gas that permeates through the interface to the pore opening of the filter body. Then, the average pore diameter in this method is measured by the permeation of the filter medium filled with the test liquid with respect to the permeate gas amount of the filter medium not filled with the test liquid when the pressurized gas is stepped up in steps. It is assumed that the ratio of the gas amount matches the ratio of the permeation flow rate that permeates the pores having a diameter equal to or larger than the pore diameter corresponding to the gas pressure at each stage with respect to the permeation flow rate that permeates all pores (for example, Non-patent document 1).
[0004]
Specifically, a filter body that is not filled with the test liquid (hereinafter referred to as “dry filter body”) and a filter body that is filled with the test liquid (hereinafter referred to as “wet filter body”) are provided at each end. Installed in a holder with the part sealed, supply pressurized gas to one surface of each filter, step up the pressure of the pressurized gas, and pass through each filter at each gas pressure stage Detecting the gas volume, the gas flow rate through the wet filter body relative to the gas flow rate through the dry filter body Ratio A pore diameter corresponding to a gas pressure that is ½ is regarded as an average pore diameter (MFPD), and is obtained from the following mathematical formula (1).
[0005]
[Equation 3]
MFPD = 4BγCOSθ / P (1)
[0006]
“In the above formula (1), MFPD is the average pore diameter (μm), θ is the contact angle (°) of the test liquid with which the pores of the filter body are filled, and γ is the filter body The surface tension (N / m) of the test liquid filled in the pores of B, B is the capillary constant (0.715) or 1, P is the gas flow rate through the wet filter relative to the gas flow rate through the dry filter Ratio The gas pressure (MPa) which becomes 1/2 is shown. θ may be approximated to 0 degrees normally. "
[0007]
Conventionally, as an evaluation method of the average pore diameter by this method, in each gas pressure stage, the gas pressure of the gas to be supplied is maintained until the amount of change in the gas flow rate for a certain time becomes a specific numerical value or less, and then the following There is a method in which the step of increasing the pressure to the gas pressure step is repeated step by step. In this conventional method, a state in which the amount of change in the gas flow rate for a certain period of time is less than a specific value is regarded as a state in which the gas flow rate is saturated, and the gas pressure is maintained at each gas pressure by maintaining the gas pressure until saturation. Waiting for the liquid interface to sufficiently advance to the pore opening of the filter body, the flow path of the gas of the wet filter body through which the gas is permeated is the path through which part of the gas passes through the dry filter body Based on the assumption that they are the same.
[0008]
However, since this conventional evaluation method does not take into consideration the characteristics of the filter body that is actually an evaluation target, it is not always sufficient as an evaluation method for an actual product.
[0009]
[Non-Patent Document 1]
“ANUAL BOOK OF AMERICA STANDARDS” vol. 11.01, issued by AMERICA SOCIETY FOR TESTING AND MATERIALS
[0010]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned problems, and it is possible to accurately and highly accurately measure the average pore diameter of a filter body having three-dimensionally complicated pores, and in actual use. It is an object of the present invention to provide a method for measuring the pore size of a filter body capable of quality evaluation reflecting the performance of the filter body.
[0011]
[Means for Solving the Problems]
As a result of earnest research to solve the above-mentioned problems, the present inventor has obtained the following knowledge regarding the point that an appropriate evaluation result could not be obtained by the conventional method.
[0012]
That is, as shown in FIG. 6A, in a filter body that is actually an evaluation target, the fluid to be filtered in normal filtration circulates in a distribution determined by the connection of pores. On the other hand, as shown in FIG. 6 (b), when the gas is sequentially circulated from the low pressure to the wet filter body, the gas begins to permeate with priority given to the large pores. Follow. Particularly in the case of porous ceramics, the fluid flow passage of the filter body is formed by the combination of a plurality of pores, and is present in a complicated three-dimensional manner. It is easy to follow a gas permeation portion of the dry filter body and a path greatly different from normal filtration.
[0013]
However, in the conventional evaluation method, the gas permeation of the dry filter body and the partial gas permeation of the wet filter body through the flow path of the fluid to be filtered at the time of practical use pass through various channels as described above. However, it has not been considered at all in terms of accuracy and accuracy because it has not taken into consideration the points that have a significant effect on the evaluation results, and it is also sufficient for evaluating the performance of each product in actual use. But I knew it wasn't. Furthermore, the following knowledge was obtained.
[0014]
(1) In the conventional evaluation method, since the amount of change in the gas flow rate of the wet filter body for a certain time at a certain pressure is less than a specific value, it is regarded as a so-called gas saturation state. Even though the interface is moving, it may be regarded as so-called gas permeation saturation. For this reason, the permeated gas through the long flow path is detected in the gas pressure stage after the original gas pressure stage, which is an error factor.
[0015]
{Circle around (2)} When the gas pressure is maintained until the so-called saturation in the conventional evaluation method, as is clear from the above {circle around (1)}, the gas-liquid interface develops by stacking at each gas pressure stage. For this reason, in the conventional method, the influence on the evaluation results due to insufficient accuracy of the control equipment and measuring equipment at each gas pressure stage is accumulated and amplified, which becomes a factor that further reduces the accuracy and precision of the evaluation results. It was.
[0016]
(3) In the dry filter medium, the gas permeation is based on one path determined by the gas flow rate. The part of the gas that enters from a certain pore always permeates through a specific path. In the measurement of the wet filter in the conventional evaluation method, the gas pressure is maintained until so-called saturation. However, when the holding time becomes long, the gas in the reference dry filter passes through, for example, the gas largely wraps around. A path | route and the path | route which gas permeate | transmits with a wet filter body will differ. For this reason, in the conventional method, the difference in the substantial evaluation object with the dry filter medium used as a reference is caused, and this is a factor for further reducing the accuracy of the evaluation result.
[0017]
{Circle around (4)} In actual use, the portion of the fluid to be filtered that has entered from a certain pore permeates through a specific path in the same way as when the gas of the dry filter passes. For this reason, in the conventional method, the path of the fluid to be filtered that permeates the filter body in actual use and the path of the gas that permeates the wet filter body are different. This is a factor that does not sufficiently reflect the performance of the filter body during actual use.
[0018]
Based on the above knowledge, the present inventor has made further studies. As a result, the gas pressure of the gas supplied to one surface of the filter body is filtered at each gas pressure stage. Using the time to pass through the body as a reference, when the gas pressure is maintained at a predetermined retention time and then transferred to the next gas pressure stage, it is possible to evaluate the practically useful average pore diameter with high accuracy and accuracy. As a result, the present invention has been completed.
[0019]
That is, the present invention relates to a dry filter body in a dry state and a wet filter body in which pores of the dry filter body are filled with a test liquid. Is a method for measuring the pore size of a porous filter body, which detects the gas flow rate permeating each filter body at each gas pressure step and then obtains the average pore diameter based on the following formula (1). When the filtered fluid passage time (S) obtained by the following formula (2) is less than 3 seconds, (S) seconds to 30 seconds, and when the filtered fluid passage time (S) is 3 seconds or more, (S) Seconds ~ ((S) × 10) Provided is a method for measuring the pore size of a porous filter, characterized by including a holding-pressurizing step of holding the wet filter at a constant pressure for a holding time of seconds and then increasing the pressure to the next gas pressure stage. .
[0020]
[Expression 4]
MFPD = (4BγCOSθ) / P (1)
“In the above formula (1), MFPD is the average pore diameter (μm), θ is the contact angle (°) of the test liquid filled in the pores of the filter body with the material constituting the filter body, and γ is the fineness of the filter body. The surface tension (N / m) of the test liquid filled in the holes, B is the capillary constant (0.715) or 1, and P is the gas flow rate through the wet filter relative to the gas flow rate through the dry filter. Ratio The gas pressure (MPa) which becomes 1/2 is shown. "
[0021]
[Equation 5]
(S) = (X / J) × Vs / Vr (2)
“In the above formula (2), X is the thickness (m) in the filtration direction of the filter body, J is the linear velocity (m / s) of the fluid to be filtered in practical use, and Vs is the viscosity of the test liquid. (Pa · s) and Vr is the viscosity (Pa · s) of the fluid to be filtered. ”
[0022]
In the present invention, the holding-pressurizing step is performed by a ratio of a gas flow rate permeating the wet filter body to a gas flow rate permeating the dry filter body. (Hereinafter, this gas flow ratio is simply referred to as a gas flow ratio.) Is preferably in the range of 1/5 to 1/2, and more preferably in the total gas pressure stage in this range. In addition, the holding time of each gas pressure stage in the range where the ratio of the gas flow rate is 1/5 to 1/2 is the average of the gas pressure stage in the range where the ratio of the gas flow rate is 1/5 to 1/2. It is preferable to be within ± 10% of the holding time, and it is more preferable that each holding time in the range where the ratio of the gas flow rate is 1/5 to 1/2 is 1 second to 1 minute. Further, in the holding-pressurizing step, a membrane obtained when the fluid to be filtered is permeated at a linear velocity (J) of the fluid to be filtered at the practical time is used as the pressure increasing value that is increased from one gas pressure phase to the next gas pressure phase. It is preferable that the pressure increase value is larger than the differential pressure, and each pressure increase value to be increased from one gas pressure stage to the next gas pressure stage in the range where the ratio of the gas flow rate is 1/5 to 1/2 More preferably, it is within ± 20% of the average boost value in the range where the flow rate ratio is 1/5 to 1/2. Moreover, it is preferable that each pressure | voltage rise value in the range from which the ratio of the said gas flow rate becomes 1/5-1/2 is 0.01-0.04 MPa.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be specifically described for each step based on the drawings. FIG. 1 shows a flow of a measuring apparatus normally used in the evaluation method of the present invention, and controls the pressurized gas supply source 11 and the pressure of the gas introduced from the pressurized gas supply source 11. A regulator 12, a pressure sensor 16 for measuring the pressure set by the regulator 12, a holder 10 for installing the filter body 2, and a flow meter 14 for measuring a gas flow rate supplied to the filter body are provided. FIG. 2 is a cross-sectional view showing a state in which the filter body 2 is installed in the holder 10. FIG. 3 is a graph showing the relationship between the flow rate of the permeated gas detected in each filter body (dry filter body and wet filter body) and the gas pressure, and H in the graph is the permeate gas of the wet filter body. This shows a gas pressure at which the flow rate is ½ of the permeate gas flow rate of the dry filter body.
[0024]
In the average pore diameter evaluation method of the present invention, first, as shown in FIGS. 1 and 2, a dry filter body 2 in a dry state is installed in a holder 10 with its end sealed using a seal member 3. To do. The seal member 3 is formed by combining a polymer such as epoxy, glaze, etc., packing, O-ring, or the like. After measuring the gas permeation amount, the wet filter body 2 in which the pores of the same dry filter body 2 are filled with the test liquid is placed in the holder 10 with its end sealed in the same manner, and the gas permeation amount is measured.
[0025]
The filter body 2 to be evaluated in the present invention is not particularly limited except that it is a porous body, and can be applied to various filter bodies such as filter paper, organic resin filters, ceramic filters, and the like. However, the evaluation method of the present invention can be particularly preferably applied to a filter body in which the pores are complicated as described above, and from this point, application to a ceramic filter is preferable. Moreover, the present invention can be applied to a ceramic filter in which one or more filtration membranes different from the pore diameter are laminated on a porous substrate. Further, FIG. 2 shows a plate-shaped filter body, but a filter body having a shape such as a tube or a monolith can also be measured by preparing a holder.
[0026]
In the present invention, the test liquid 4 filled in the pores of the dry filter body 2 is, for example, high-purity water, denatured alcohol, mineral oil, 1, 1 as described in ASTM F316-86 D1129 and D1193. , 2-trichloro-1,2,2-toluorate, or a fluorine-based inert liquid (trade name: Fluorinert FC-40, a fluorine-based inert liquid manufactured by 3M) or the like is preferable.
[0027]
Moreover, as a to-be-filtered fluid used as filtration object in actual use, water, petroleum, etc. can be mentioned, for example.
[0028]
Next, in the present invention, a pressurized gas whose pressure is increased stepwise is supplied to one surface of the dry filter body and the wet filter body. At that time, in the measurement of the permeated gas of the wet filter body, at each gas pressure stage. When the fluid passage time (S) determined by Equation (2) is less than 3 seconds (S) seconds to 30 seconds, and when the fluid passage time (S) is 3 seconds or more (S) ) After holding the wet filter at a constant pressure for a holding time of seconds to (S × 10) seconds, the pressure is increased to the next gas pressure stage. This is because, in each gas pressure stage, by reducing the holding time as much as possible, each path through which the gas permeates between the dry filter body and the wet filter body to be tested becomes closer. For this reason, accurate and highly accurate evaluation becomes possible. The pore diameter can be accurately measured by setting the retention time to be 10 times or less of the fluid passage time (S), but when (S) is as short as less than 3 seconds, (S) If the retention time is 30 seconds or less, the pore diameter can be measured with high accuracy even when the ratio exceeds 10 times.
[0029]
Here, (S) obtained from Equation (2) depends on the linear velocity (J) of the fluid to be filtered in practical use, but (J) is usually used when designing a filtration device using the filter body. And is a known value when the filter body is manufactured in consideration of the design. In addition, (J) may be set with a predetermined width, and in this case, (S) also has a predetermined width. In this case, the above (S) is 3 seconds or more (S The maximum value of) is 3 seconds or more and (S) is less than 3 seconds means that the maximum value of (S) is less than 3 seconds. The upper limit of the retention time is more accurate when closer to the maximum value of (S), and is preferably 10 times or less, more preferably 2 times or less of the maximum value of (S).
[0030]
In addition, when the retention time is too short, the gas flow rate to be detected at the pressurization stage is not detected, for example, the gas-liquid interface is moving in a long flow path. The value is smaller than the evaluation result. Accordingly, the holding time must be equal to or greater than the value of (S). When (S) has a predetermined width, (S) here also means the maximum value. Further, if the holding time is too short, problems of operability and responsiveness of the apparatus appear, so that the holding time is preferably 1 second or longer, more preferably 3 seconds, especially 5 seconds or longer.
[0031]
That is, in a preferred embodiment of the present invention, in each gas pressure stage, the retention time is longer than (S), and by shortening the retention time as much as possible, the fluid to be filtered, which is the actual filtration target, is filtered. The gas pressure is maintained for a time close to the passing time. For this reason, the path of the gas in the wet filter body approximates the path through which the portion of the fluid to be filtered passes, and evaluation that sufficiently reflects the performance during actual use of the filter body becomes possible. Since the fluid to be filtered and the test liquid have different viscosities, the passage time in the membrane and the discharge time by the gas pressure are different from each other. Therefore, (S) is the ratio of the viscosity of the fluid to be filtered and the test liquid. It was corrected by.
[0032]
In the present invention, the gas flow rate permeating the wet filter body relative to the gas flow rate permeating the dry filter body is Ratio It is preferable to set the holding time as described above in the gas pressure stage of 1/5 to 1/2, and it is preferable to set the holding time as described above in the entire gas pressure stage in this range. this is, the above Since the average particle diameter is determined when the gas flow rate ratio becomes 1/2, it is preferable to perform accurate control near this point, particularly from the point where the gas flow rate in the wet filter begins to increase. is there. Therefore, the above Until the gas pressure stage at which the ratio of the gas flow rates becomes 1/5, the gas pressure holding time in each gas pressure stage may be set in a range outside the above setting.
[0033]
Also, the above In the gas pressure stage where the ratio of gas flow rates is in the range of 1/5 to 1/2, it is preferable to make the gas pressure holding time in each gas pressure stage as uniform as possible in order to perform an accurate and precise evaluation. In particular, the above Holding time at each gas pressure step in the range where the ratio of gas flow rate is 1/5 to 1/2 Above gas flow rate It is preferable that the ratio is within ± 10% of the average gas pressure holding time in all gas pressure steps in the range where the ratio is 1/5 to 1/2.
[0034]
In the present invention, each pressure increase value from one gas pressure stage to the next gas pressure stage is larger than the membrane differential pressure when passing through the fluid to be filtered at the linear velocity (J) at the time of practical use, and is closer to this. Is preferred. Preferably, 1-10 times the membrane differential pressure is good. This is because if the pressure increase value is too small, the gas-liquid interface does not move within the holding time, and if it is too long, the resolution of the pore diameter is lost. In addition, when there exists a range in a film differential pressure, it is preferable that it is larger than the maximum film differential pressure.
[0035]
For the same reason as described above, the boost value is controlled as described above at the gas pressure stage in the range where the gas flow ratio is 1/5 to 1/2, and further at the entire gas pressure stage in this range. Is preferred.
[0036]
Further, in the present invention, in each gas pressure stage where the ratio of gas flow rate is 1/5 to 1/2, in order to perform an accurate and precise evaluation, each boosted value is also as uniform as possible. It is preferable to do.
[0037]
Specifically, each boost value in this range is preferably within a range of ± 20% of the average boost value in all gas pressure stages in this range. Further, the range for managing each pressure holding time and the pressure increase width is preferably performed from a lower pressure step when the pore size distribution is wide.
[0038]
In the present invention, if each pressure value with respect to the previous gas pressure stage in each gas pressure stage and each gas pressure holding time in each gas pressure stage are as described above, it is accurate and highly accurate, Although the performance can be evaluated, the surface of the substrate having sufficiently large pores has an average pore diameter of 0.05-2 microns, a thickness of 10-300 microns, and the flow rate of the fluid to be filtered in practical use is 1- If the filter body is made of 10 m / day of ceramics, each pressure value relative to the previous gas pressure stage in each gas pressure stage is in the range of 0.01 to 0.04 MPa in consideration of the capability of the measuring device. Each gas pressure holding time in the pressure stage can be selected from the range of 1 second to 1 minute. The pressure increase in measuring the dry filter body may be a holding time that is equal to or longer than the operation time and response time of the apparatus.
[0039]
In addition, the pressurized gas used in the present invention is preferably an inert gas such as air, argon, nitrogen, etc., and is appropriately selected in consideration of being difficult to dissolve in a test liquid, evaluation conditions, detection means, cost, etc. Just choose.
[0040]
Next, in the present invention, the permeate gas flow rate of each filter body is detected at each gas pressure stage, and the average pore diameter is obtained based on Equation (1). As shown in FIG. 3, in the dry filter body, there is no object to be pressed with the pressurized gas in the pores, so that the detected gas flow rate increases almost in proportion to the pressure increase of the pressurized gas (in the figure). , Indicated by a solid line). On the other hand, in the wet filter body, there is a test fluid to be pressed by the pressurized gas in the pores, and until the pressure of the pressurized gas overcomes the resistance force due to the surface tension of the test liquid, the gas − The liquid interface does not move. Therefore, in the initial stage of pressurization, even if the pressure of the pressurized gas increases, the permeate gas is not detected, and when the pressure of the pressurized gas reaches a certain pressure, the permeate gas flow rate starts to increase. Overlaps with the permeate gas flow rate-gas pressure line in the dry filter body (indicated by a dotted line in the figure). The permeate gas flow rate detected at each gas pressure from when the permeate gas flow rate starts to increase until it finally overlaps with the permeate gas flow rate-gas pressure line in the dry filter medium is a series of fine gas passages. Varies depending on the pore size distribution. The gas pressure H at which the permeate gas flow rate in the wet filter is ½ of the permeate gas flow rate in the dry filter is obtained (the one-dot chain line in the drawing indicates the permeate gas flow rate at each gas pressure of the dry filter as 1 And the pore diameter corresponding to the gas pressure H is defined as the average pore diameter based on the formula (1).
[0041]
【Example】
EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. In each example and comparative example, the filter body was evaluated using the sample, the test liquid, and the fluid to be filtered described below.
[0042]
(sample)
An isotropy of an alumina intermediate layer having an average pore diameter of about 1 μm and a thickness of 200 μm, and titania having an average particle diameter of 0.5 μm on a disk-shaped alumina substrate having an average pore diameter of about 10 μm, a diameter of 30 mm, and a thickness of 3 mm A 15 μm thick titania filter layer made of typical particles was sequentially formed and fired, and a ceramic filter body was used as a sample.
[0043]
(Fluid to be filtered as standard for evaluation)
The fluid to be filtered is water (viscosity: 1 × 10 ^-6 m ² / S), the practical condition such as water purification is 1-5 m / day, and the membrane differential pressure at that time is 0.0026-0.0128 MPa. A suitable pressure increase width is 0.0128 MPa or more.
[0044]
(Test fluid)
Fluorinert (viscosity: 2.2 × 10 ^-6 m ² / S, surface tension: 16 dyne / cm). Therefore, the to-be-filtered fluid passage time (S) calculated | required from Numerical formula (2) is 0.6-2.9 second. A preferable holding time is 30 seconds or less.
[0045]
(Examples 1-6, Comparative Examples 1-4)
A sample (dry filter body) not filled with the test liquid was placed in a holder of a pore diameter evaluation apparatus with the end sealed with glaze and O-ring so that there was a titania layer on the pressurized gas supply side. Next, pressurized air was supplied to the pressurized gas supply side. The pressure was increased by 0.017-0.021 MPa every 25-30 seconds, and the gas flow rate was measured.
[0046]
Next, the sample was immersed in the test liquid, and the test liquid was completely filled in the pores in the sample. Next, the sample (wet filter) completely filled with the test liquid was placed in the holder of the pore diameter evaluation apparatus with the end sealed in the same manner.
[0047]
Next, pressurized air was supplied to the pressurized gas supply side. At this time, in Examples 1 to 6, the gas pressure was maintained for 1 second, 2 seconds, 4-6 seconds, 9-11 seconds, 18-22 seconds, and 25-30 seconds at each gas pressure stage. In Examples 1 to 4, gas pressure is maintained for 55 to 65 seconds, 290 to 310 seconds, 470 to 490 seconds, and 590 to 610 seconds, and the pressure is increased by 0.017 to 0.021 MPa at each gas pressure stage. The gas flow rate was measured. From the gas pressure at which the gas flow rate of the wet filter becomes 1/2 of the gas flow rate of the dry filter, the average pore diameter of each sample was determined based on Equation (1).
[0048]
(Evaluation)
The shorter the retention time, the smaller the average pore diameter measurement result. If the length is longer than S, gas is permeated through the wet filter body and evaluated even if the path of the pores through which a part of the fluid to be filtered in practical use permeates is long. Therefore, an excessively long path through which a portion of the gas that permeates the dry filter body and the fluid to be filtered at the time of practical use cannot be included in the evaluation, and the evaluation is accurate.
[0049]
(Example 7-28, Comparative Example 5-26)
In the gas permeation measurement of the wet filter body of the same filter membrane sample as in Example 1, the gas pressure of the supplied air was maintained as saturated by changing the permeate gas flow rate to 12 mL / min or less in 30 seconds. Thereafter, the average pore diameters of 22 different samples were determined in the same manner as in Example 1 except that the pressure was increased to the next gas pressure step, which was designated as Comparative Example 5-26. When the pressure corresponding to the average pore was 0.35 MPa, the gas permeation rate of the dry filter was about 10,000 mL / min. The average pore diameter of 22 different samples was determined by setting the gas pressure holding time in the gas permeation measurement of the wet filter of Example 1-6 to 9 to 11 seconds, and set as Examples 7 to 28.
[0050]
(Evaluation)
As shown in FIG. 5, in Example 6-27 of this invention, the average pore diameter became the range of 0.13-0.15 micrometer (standard deviation 0.007). On the other hand, in Comparative Example 6-27 in which the gas pressure is maintained until the so-called gas saturation state and then increased, the retention time at each gas pressure stage varies from 30 seconds to 20 minutes, and the average pore diameter is The variation was 0.16 to 0.21 μm (standard deviation 0.011), and the average pore diameter was larger than the retention time of about 10 minutes shown in FIG.
[0051]
【The invention's effect】
As described above, according to the present invention, the filter having three-dimensionally complicated pores can be accurately and highly accurately evaluated with respect to the average pore diameter, and the filter in actual use. It is possible to provide a method for evaluating a filter body capable of quality evaluation reflecting the performance of the filter.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram schematically showing the configuration of an apparatus for carrying out an evaluation method of the present invention.
FIG. 2 is a cross-sectional view schematically showing a state in which a filter body is installed in a holder in an example of the evaluation method of the present invention.
FIG. 3 is a graph showing the relationship between gas flow rate and gas pressure detected in each filter body (dry filter body, wet filter body).
FIG. 4 is a graph showing the relationship between the average pore diameter determined in each example and each comparative example and the gas pressure holding time.
5 is a graph showing a distribution of average pore diameters when 22 materials are measured by the method of Example 1 and Comparative Example 8. FIG.
FIG. 6 is an explanatory view schematically showing the existence state of pores in a ceramic filter body.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Pressurized gas, 2 ... Filter body, 3 ... Seal member, 10 ... Holder, 11 ... Pressurized gas supply source, 12 ... Regulator, 14 ... Flowmeter.

Claims

For a dry filter in a dry state and a wet filter in which pores of the dry filter are filled with a test liquid, a pressurized gas is supplied to each filter to increase the pressure of the pressurized gas stepwise. , Detecting the flow rate of gas passing through each filter at each gas pressure stage,
Next, a method for measuring the pore diameter of a porous filter body for obtaining an average pore diameter based on the following formula (1),
The filtered fluid passage time obtained by the following formula (2) , when ( S) is less than 3 seconds (S) seconds to 30 seconds, and when the filtered fluid passage time (S) is 3 seconds or more ( A porous filter comprising a holding-pressurizing step of holding a wet filter at a constant pressure for a holding time of S) seconds to ( (S) × 10) seconds, and then increasing the pressure to the next gas pressure stage. Pore diameter measurement method.

“In the above formula (1), MFPD is the average pore diameter (μm), θ is the contact angle (°) of the test liquid filled in the pores of the filter body with the material constituting the filter body, and γ is the fineness of the filter body. The surface tension (N / m) of the test liquid filled in the holes, B is the capillary constant (0.715) or 1, and P is the ratio of the gas flow rate through the wet filter to the gas flow rate through the dry filter. Indicates the gas pressure (MPa) to be halved. "

“In the above formula (2), X is the thickness (m) in the filtration direction of the filter body, J is the linear velocity (m / s) of the fluid to be filtered in practical use, and Vs is the viscosity of the test liquid. (Pa · s) and Vr is the viscosity (Pa · s) of the fluid to be filtered. ”

2. The porous filter body according to claim 1, wherein the holding-pressurizing step is performed in a range where a ratio of a gas flow rate permeating the wet filter body to a gas flow rate permeating the dry filter body is 1/5 to 1/2. Pore diameter measurement method.

The holding - claim 2 a boosting step is performed at a total gas pressure stage of the range ratio of gas flux through the wet filter body to the gas flow rate passing through the pre-Symbol dry filter body is 1 / 5-1 / 2 The method for measuring the pore diameter of the porous filter according to claim 1.

Retention time of each gas pressure stage, passes through the pre-Symbol dry filter body in the region where the ratio of gas flux through the wet filter body to the gas flow rate passing through the pre-Symbol dry filter body is 1 / 5-1 / 2 holes according to claim 2 or 3 ratio of gas flux through the wet filter body to the gas flow rate is within ± 10% of the average retention time of the gas pressure step in the range of 1 / 5-1 / 2 A method for measuring the pore diameter of a filter material.

According to claim 4, the ratio of gas flux through the wet filter body to the gas flow rate passing through the pre-Symbol dry filter body is 1 second to 1 minute each retention time in the range of 1 / 5-1 / 2 Method for measuring the pore diameter of a porous filter body.

In the holding-pressurizing step, the pressure difference to be boosted from one gas pressure stage to the next gas pressure stage is the membrane differential pressure when the filtered fluid is permeated at the linear velocity (J) of the filtered fluid in practical use. The method for measuring a pore diameter of a porous filter according to any one of claims 2 to 5, wherein the pressure increase value is larger.

Each booster which boosts from a gas pressure step in the range of the ratio of gas flux through the wet filter body to the gas flow rate passing through the pre-Symbol dry filter body is 1 / 5-1 / 2 to the next gas pressure stage claim values, the ratio of gas flux through the wet filter body to the gas flow rate passing through the pre-Symbol dry filter body is within ± 20% of the average boost value in the range of 1 / 5-1 / 2 6 The method for measuring the pore diameter of the porous filter according to claim 1.

7. the ratio of gas flux through the wet filter body to the gas flow rate passing through the pre-Symbol dry filter body is to 0.01~0.04MPa each boost value in the range of 1 / 5-1 / 2 The method for measuring the pore diameter of the porous filter according to claim 1.