JP4367678B2

JP4367678B2 - Ceramic filter

Info

Publication number: JP4367678B2
Application number: JP2000127157A
Authority: JP
Inventors: 忠典菰田
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 2000-04-27
Filing date: 2000-04-27
Publication date: 2009-11-18
Anticipated expiration: 2020-04-27
Also published as: JP2001300273A

Description

【０００１】
【発明の属する技術分野】
本発明はセラミック多孔体からなる基材の表面に、基材に比して平均細孔径が小さい濾過膜を形成したセラミックフィルタに関し、詳しくは高強度で、かつ、フィルタの構成部材にクラックが発生し難いセラミックフィルタに関する。
【０００２】
【従来の技術】
セラミックフィルタは、セラミック多孔体を利用したフィルタであり、物理的強度、耐久性、耐食性等に優れるため、例えば水処理や排ガス処理、或いは医薬・食品分野などの広範な分野において、液体やガス中の懸濁物質、細菌、粉塵等の除去に用いられている。
【０００３】
セラミックフィルタにおいては、セラミック多孔体をそのまま濾材として用いる場合もあるが、濾過性能、流体透過量（即ち処理能力）の双方を向上させるため、セラミック多孔体を基材（支持体）として、その表面にセラミックからなる濾過膜を形成することが一般的である。
例えば、濾過膜の平均細孔径を０．０１〜１．０μｍ程度と小さく構成して濾過性能を確保する一方、基材の平均細孔径を１〜数１００μｍ程度に大きく構成して、基材内部の流動抵抗を低下させ、流体透過量（即ち処理能力）を向上させることが行われている。
【０００４】
また、セラミックフィルタは、基材を濾過目的に応じて種々の形状に加工したものが用いられるが、基材を単一の貫通孔を有するチューブ状、或いは並行する多数の貫通孔を有するハニカム状（モノリス状も含む）としたものが汎用されている。チューブ状、或いはハニカム状基材の表面、例えば貫通孔の内周面に濾過膜を形成したフィルタは、ハウジング内に収容し、基材外周面側と貫通孔が開口する基材端面側とをＯ−リング等で気密的に隔離する構造とすることにより、クロスフロー型のフィルタとして利用されている。
【０００５】
クロスフロー型のフィルタによれば、気体、液体等の被処理流体を、基材の一方の端面側から貫通孔内に供給することにより、貫通孔内周面の濾過膜を透過した濾過流体が基材外周面側から回収する一方、濾過されなかった被処理流体については基材の他方の端面側から回収することが可能となる。
【０００６】
しかしながら、図１（ｂ）に示すように、単に基材１２端面近傍をＯ−リング１４で隔離するのみでは、濾過膜１３が形成されていない基材１２端面から被処理流体が基材１２内部に侵入してしまうため、目的とする濾過を行うことができず、また、既に濾過された濾過流体をも汚染することになる。
【０００７】
そこで、図１（ａ）に示すように、セラミック等からなるシール材５により、少なくとも基材２端部及び基材２端部近傍の濾過膜３を被覆した膜分離装置が提案されている（特開昭６１−８１０６号公報）。
このような構造は、基材２端面から被処理流体が侵入する事態を防止でき、被処理流体が必ず濾過膜３を透過するため、目的とする濾過を行うことができ、また、既に濾過された濾過流体の汚染も防止可能である点において有用である。
【０００８】
【発明が解決しようとする課題】
ところで、上記膜分離装置のように、基材、濾過膜、シール材という複数の部材で構成されるセラミックフィルタにおいては、各構成部材をその機能に適合する物理的、化学的特性の材質とするために、或いはコスト面での要請から、各々を異なる材質とすることを要求される場合も多い。しかしながら、このような場合において各構成部材の熱膨張係数が極端に異なると、相互に引張応力や圧縮応力が発生するため、各構成部材にクラックが発生したり、或いはフィルタの機械的強度が発現できないという問題があった。
【０００９】
また、基材は、主として粒径５〜２００μｍ程度の骨材と、骨材同士の結合を強化するための添加材である、粒径５μｍ未満の焼結助剤とから構成されるが、骨材と焼結助剤は異なる材質である場合が多い。
従って、基材の構成材料間においても、フィルタの構成部材間と同様にその熱膨張係数が極端に異なる場合には、相互に引張応力や圧縮応力が発生し、フィルタの強度が低下するという問題があった。
【００１０】
これらの問題点を解決するために、フィルタの各構成部材、或いは基材の構成材料を、可能な限り熱膨張係数が近い材質とする方法も考えられる。しかしながら、本発明者らが検討した結果、各構成部材間の、或いは基材の構成材料間の熱膨張係数を単に近づけるのみではこれらの事態を防止できないことが判明した。
【００１１】
本発明は、このような従来技術の問題点に鑑みてなされたものであって、本発明の目的とするところは、フィルタの各構成部材、或いは基材の構成材料を異なる材質とした場合においても、高強度で、かつ、フィルタの各構成部材にクラックが発生し難いセラミックフィルタを提供することにある。
【００１２】
【課題を解決するための手段】
本発明者らが上記従来技術の問題点について鋭意検討した結果、フィルタの構成部材間、或いは基材の構成材料間に所定の熱膨張係数差を与え、これらの間に内在応力を発生せしめることにより、上記問題点を解決できることを見出して本発明を完成した。
【００１３】
即ち、本発明によれば、単一の又は並行する多数の貫通孔を有する多孔体からなる基材と、当該基材の表面に形成される、基材に比して平均細孔径が小さい濾過膜と、少なくとも基材端部及び基材端部近傍の濾過膜を被覆するシール材と、を備えたセラミックフィルタであって、シール材を基材とは異なる材質により構成し、かつ、シール材の熱膨張係数と基材の熱膨張係数の熱膨張係数差が下記式（Ｉ）の範囲内となるように構成したことを特徴とするセラミックフィルタが提供される（以下「第１の発明」と記す。）。
０≦Ｋ _２ −Ｋ _１ ≦４：（Ｉ）
［Ｋ _１：シール材の熱膨張係数（×１０ ^−６／℃）、Ｋ _２：基材の熱膨張係数（×１０ ^−６／℃）］
【００１４】
第１の発明においては、シール材を濾過膜とは異なる材質により構成し、かつ、シール材の熱膨張係数と濾過膜の熱膨張係数の熱膨張係数差が下記式（ＩＩ）の範囲内となるように構成したものが好ましく、基材に含まれる焼結助剤を、基材を構成する骨材とは異なる材質により構成し、かつ、焼結助剤の熱膨張係数と骨材の熱膨張係数の熱膨張係数差が下記式（ＩＩＩ）の範囲内となるように構成したものが更に好ましい。
０≦Ｋ _３ −Ｋ _１ ≦３：（ＩＩ）
［Ｋ _１：シール材の熱膨張係数（×１０ ^−６／℃）、Ｋ _３：濾過膜の熱膨張係数（×１０ ^−６／℃）］
０≦Ｋ _５ −Ｋ _４ ≦３：（ＩＩＩ）
［Ｋ _４：焼結助剤の熱膨張係数（×１０ ^−６／℃）、Ｋ _５：骨材の熱膨張係数（×１０ ^−６／℃）］
【００１５】
また、本発明によれば、単一の又は並行する多数の貫通孔を有する多孔体からなる基材と、当該基材の表面に形成される、基材に比して平均細孔径が小さい濾過膜と、少なくとも基材端部及び基材端部近傍の濾過膜を被覆するシール材と、を備えたセラミックフィルタであって、シール材を濾過膜とは異なる材質により構成し、かつ、シール材の熱膨張係数と濾過膜の熱膨張係数の熱膨張係数差が上記式（ＩＩ）の範囲内となるように構成したことを特徴とするセラミックフィルタが提供される（以下「第２の発明」と記す。）。
【００１６】
第２の発明においては、基材に含まれる焼結助剤を骨材とは異なる材質により構成し、かつ、焼結助剤の熱膨張係数と基材を構成する骨材の熱膨張係数の熱膨張係数差が上記式（ＩＩＩ）の範囲内となるように構成したものが好ましい。
【００１７】
更に、本発明によれば、単一の又は並行する多数の貫通孔を有する多孔体からなる基材と、当該基材の表面に形成される、基材に比して平均細孔径が小さい濾過膜と、少なくとも基材端部及び基材端部近傍の濾過膜を被覆するシール材と、を備えたセラミックフィルタであって、基材に含まれる焼結助剤を、基材を構成する骨材とは異なる材質により構成し、かつ、焼結助剤の熱膨張係数と骨材の熱膨張係数の熱膨張係数差が上記式（ＩＩＩ）の範囲内となるように構成したことを特徴とするセラミックフィルタが提供される（以下「第３の発明」と記す。）。
【００１８】
【発明の実施の形態】
（１）フィルタの構成
本発明のセラミックフィルタは、少なくとも基材、濾過膜、及びシール材を構成部材として備える。
【００１９】
（１−１）基材
本発明にいう「基材」とは、濾過膜の支持体としての機能を有する部材であって、主として骨材と焼結助剤とから構成されるセラミックの多孔体である。
基材の形状としては、単一の貫通孔を有するチューブ状、或いは並行する多数の貫通孔を有するハニカム状（モノリス状も含む）のいずれかが用いられる。
【００２０】
骨材は、基材の主たる構成要素であって、平均粒径５〜２００μｍ程度のセラミック粒子からなる。骨材を含む坏土を成形し、焼結せしめることにより、骨材の粒径に応じた細孔を有する多孔体、即ち基材が形成される。
骨材の材質は、濾過の目的に適合するように適宜選択すればよいが、例えばアルミナ、ムライト、コージェライト、炭化珪素、陶磁器屑等を用いることができる。
【００２１】
焼結助剤は、骨材同士の結合を強化するための添加材であって、平均粒径５μｍ未満のセラミック粒子からなる。骨材とともに坏土に含有せしめることにより、骨材間の結合が強化され、強固な多孔体が形成される。
焼結助剤についても、その材質は特に限定されないが、例えばアルミナ、シリカ、ジルコニア、チタニア、ガラスフリット、長石、コージェライト等を用いることができる。通常は、骨材同士の結合強度を確保し、多孔体の細孔閉塞を防止するため、骨材及び焼結助剤の全質量に対し、１０〜３５質量％程度含有せしめる。
【００２２】
（１−２）濾過膜
本発明にいう「濾過膜」とは、基材に比して平均細孔径が小さい、薄膜状のセラミック多孔体であり、少なくとも１層、場合によっては２層以上形成して複層とする。通常、「濾過膜」とは、フィルタの濾過機能を確保するための部材を指すが、本発明にいう「濾過膜」には、濾過膜を複層とした場合における中間層（複数の層のうち、最上層以外の層）も包含される。
【００２３】
濾過膜は、基材を構成する骨材に比して平均粒径の小さい、０．１〜５μｍ程度のセラミック粒子を含むスラリーを基材表面に製膜した後、焼結せしめることにより形成する。濾過膜を形成する「基材の表面」には、基材の貫通孔内周面の他、場合によっては基材外周面も含まれる。前記セラミック粒子の材質は、基材を構成する骨材と同様のものを用いることができる。
【００２４】
（１−３）シール材
本発明にいう「シール材」とは、基材端面から被処理流体が基材内部に侵入することを防止するための部材であり、当該機能を確保するため少なくとも基材端部及び基材端部近傍の濾過膜を被覆することが必要である。
【００２５】
シール材は、例えばホウケイ酸ガラス、長石質ガラス等のガラス状物質（ガラスフリット等）からなる釉薬を基材端部及び基材端部近傍の濾過膜を被覆するように塗布した後、焼結せしめることにより、形成することができる。但し、濾過膜と同等以下の細孔径を有するものである限りにおいて、特に釉薬には限定されず、場合によっては濾過膜をシール材として用いることも可能である。
【００２６】
（２）本発明の実施態様
本発明は、上述のようなセラミックフィルタにおいて、フィルタの構成部材間、或いは基材の構成材料間に所定の熱膨張係数差を与え、これらの間に内在応力を発生せしめたものである。本発明のセラミックフィルタは、フィルタの各構成部材、或いは基材の構成材料を異なる材質とした場合においても、高強度で、かつ、フィルタの各構成部材にクラックが発生し難い。
以下、本発明のセラミックフィルタについて詳細に説明する。
【００２７】
（２−１）第１の発明
第１の発明は、シール材を基材とは異なる材質により構成し、かつ、シール材の熱膨張係数と基材の熱膨張係数の熱膨張係数差が下記式（Ｉ）の範囲内となるように構成したものである。
シール材−基材間に上記範囲内の熱膨張係数差を与えることにより、シール材側に圧縮応力、基材側に引張応力が発生するため、フィルタの各構成部材におけるクラックの発生が防止される。
０≦Ｋ _２ −Ｋ _１ ≦４：（Ｉ）
［Ｋ _１：シール材の熱膨張係数（×１０ ^−６／℃）、Ｋ _２：基材の熱膨張係数（×１０ ^−６／℃）］
【００２８】
熱膨張係数差Ｋ _２ −Ｋ _１が４を超える場合にはシール材に対して過大な圧縮応力が加わるため、図３に示すようなジグザグ状のクラックが発生する一方、熱膨張係数差Ｋ _２ −Ｋ _１が負の値の場合にはシール材に対して引張応力が加わるため、図４に示すような直線状のクラックが発生する。なお、シール材の熱膨張係数が基材の熱膨張係数に極めて近い場合でも基材の熱膨張係数より少しでも高いと（即ち、熱膨張係数差Ｋ _２ −Ｋ _１が負の値であると）、シール材のクラックを防止することができない点には留意すべきである。
【００２９】
（２−２）第２の発明
第２の発明は、第１の発明と同様の思想により、シール材を濾過膜とは異なる材質により構成し、かつ、シール材の熱膨張係数と濾過膜の熱膨張係数の熱膨張係数差が下記式（ＩＩ）の範囲内となるように構成したものである。
０≦Ｋ _３ −Ｋ _１ ≦３：（ＩＩ）
［Ｋ _１：シール材の熱膨張係数（×１０ ^−６／℃）、Ｋ _３：濾過膜の熱膨張係数（×１０ ^−６／℃）］
【００３０】
熱膨張係数差Ｋ _３ −Ｋ _１が３を超える場合にはシール材に対して過大な圧縮応力が加わるため、熱膨張係数差Ｋ _３ −Ｋ _１が負の値の場合にはシール材に対して引張応力が加わるため、いずれもシール材にクラックが発生する。また、シール材の熱膨張係数が濾過膜の熱膨張係数に極めて近い場合でも濾過膜の熱膨張係数より少しでも高いと（即ち、熱膨張係数差Ｋ _３ −Ｋ _１が負の値であると）、シール材のクラックを防止することができない点については第１の発明と同様である。
【００３１】
（２−３）第３の発明
第３の発明は、基材に含まれる焼結助剤を、基材を構成する骨材とは異なる材質により構成し、かつ、焼結助剤の熱膨張係数と骨材の熱膨張係数の熱膨張係数差が下記式（ＩＩＩ）の範囲内となるように構成したものである。第１及び第２の発明が、フィルタの構成部材間の熱膨張係数差に着目したものであるのに対し、第３の発明は基材の構成材料間の熱膨張係数差に着目したものである。
０≦Ｋ _５ −Ｋ _４ ≦３：（ＩＩＩ）
［Ｋ _４：焼結助剤の熱膨張係数（×１０ ^−６／℃）、Ｋ _５：骨材の熱膨張係数（×１０ ^−６／℃）］
【００３２】
具体的には、熱膨張係数差Ｋ _５ −Ｋ _４が３を超える場合には焼結助剤に対して圧縮応力が加わるため、熱膨張係数差Ｋ _５ −Ｋ _４が負の値の場合には焼結助剤に対して引張応力が加わるため、いずれの場合にも基材の強度が低下する。
【００３３】
（２−４）熱膨張係数差の算出
第１及び第２の発明における熱膨張係数差は、基材、濾過膜、シール材の各評価サンプルの線熱膨張量ΔＬ_１〜ΔＬ_３を測定し、下記式（１）〜（３）により規定される、各構成部材の熱膨張係数Ｋ_１〜Ｋ_３から算出する。
Ｋ_１＝（ΔＬ_１／ΔＴ_１）／Ｌ …（１）
Ｋ_２＝（ΔＬ_２／ΔＴ_１）／Ｌ …（２）
Ｋ_３＝（ΔＬ_３／ΔＴ_１）／Ｌ …（３）
（但し、Ｋ_１：シール材の熱膨張係数（×１０^−６／℃）、Ｋ_２：基材の熱膨張係数（×１０^−６／℃）、Ｋ_３：濾過膜の熱膨張係数（×１０^−６／℃）、ΔＬ_１：Ｔｓ_１からＴｔ_１の間のシール材サンプルの線熱膨張量（単位：ｍｍ）、ΔＬ_２：Ｔｓ_１からＴｔ_１の間の基材サンプルの線熱膨張量（単位：ｍｍ）、ΔＬ_３：Ｔｓ_１からＴｔ_１の間の濾過膜サンプルの線熱膨張量（単位：ｍｍ）、Ｌ：室温における各評価サンプルの長さ（単位：ｍｍ））
【００３４】
具体的には、評価サンプルとして、基材、濾過膜、シール材の単体焼結体を断面３ｍｍ×４ｍｍ、長さＬが２０ｍｍ（室温で測定）の四角柱状に加工したものを使用し、基準温度Ｔｓ₁からシール材の転移温度Ｔｔ₁の間の温度差ΔＴ₁における、各評価サンプルの線熱膨張量ΔＬ₁〜ΔＬ₃を、高精度二試料熱分析装置−ＴＭＡ標準形（商品名：理学電機社製）により、標準試料と評価サンプルとの伸びの差を差動トランスを用いて検出することにより測定する。
【００３５】
「基準温度Ｔｓ₁」は、評価サンプルの線熱膨張係数の変化が少ない温度に設定することが一般的である。従って、本発明の評価サンプルがセラミックであることを考慮して、上記式（１）〜（３）のいずれにおいても４０℃と規定する。
【００３６】
また、「シール材の転移温度Ｔｔ₁」は、上記の線熱膨張量測定において、図２に示すようにシール材サンプルがガラス状態から過冷却液体に転移することにより線熱膨張量が急速に立ち上がる温度と規定する。
図２（ｂ）は、クリストバライトのように結晶転移がある場合の例であり、転移温度Ｔｔ₁より低い温度域で線熱膨張量が凸の屈曲を示しているが、この場合でも同様に規定することができる。
なお、後述する「シール材の軟化点」とは、図２に示すようにシール材サンプルの線熱膨張量が極大値を示し、収縮に転ずる温度をいう。
【００３７】
第３の発明における熱膨張係数差も第１及び第２の発明と同様にして、焼結助剤、骨材の単体焼結体からなる評価サンプルの線熱膨張量ΔＬ_４〜ΔＬ_５を測定し、下記式（４），（５）により規定される、各構成材料の熱膨張係数Ｋ_４，Ｋ_５から算出する。
Ｋ_４＝（ΔＬ_４／ΔＴ_２）／Ｌ …（４）
Ｋ_５＝（ΔＬ_５／ΔＴ_２）／Ｌ …（５）
（但し、Ｋ_４：焼結助剤の熱膨張係数（×１０^−６／℃）、Ｋ_５：骨材の熱膨張係数（×１０^−６／℃）、ΔＬ_４：Ｔｓ_２からＴｔ_２の間の焼結助剤サンプルの線熱膨張量（単位：ｍｍ）、ΔＬ_５：Ｔｓ_２からＴｔ_２の間の骨材サンプルの線熱膨張量（単位：ｍｍ）、Ｌ：室温における各評価サンプルの長さ（単位：ｍｍ））
【００３８】
なお、「基準温度Ｔｓ_２」は、上記式（４），（５）のいずれにおいても４０℃とする。
また、「焼結助剤の転移温度Ｔｔ_２」は、上記の熱膨張量測定において、焼結助剤サンプルがガラス状態から過冷却液体に転移することにより線熱膨張量が急速に立ち上がる温度と規定する。但し、基材の焼成温度以下の温度域に上記転移温度が存在しない場合には、Ｔｔ_２は６５０℃であるものとして熱膨張係数を算出する。
【００３９】
（２−５）製造方法
本発明のフィルタは、上記の方法により予め測定した熱膨張係数に基づいて、所定の熱膨張係数差を有するフィルタの構成部材（シール材、基材、濾過膜）、或いは基材の構成材料（焼結助剤、骨材）の材質を選択することを除き、従来公知のセラミックフィルタの製造方法に準じて製造することが可能である。
【００４０】
例えば、まず、骨材、焼結助剤の他、分散媒、有機バインダ、必要により界面活性剤、可塑剤等を添加し、混練してなる坏土を、押出成形してなる成形体を乾燥・焼成して基材を製造し、次いで、セラミック粒子を水等の分散媒中に分散し、必要に応じ有機バインダ、ｐＨ調整剤、界面活性剤等を添加してなる製膜用スラリーを当該基材の貫通孔内周面に製膜し、乾燥・焼成して濾過膜を形成し、更に、基材端部にシール材であるガラス状物質からなる釉薬を塗布した後、乾燥・焼成する方法によりフィルタを得ることができる。
【００４１】
【実施例】
以下、本発明のフィルタを実施例により更に詳細に説明するが、本発明は下記の実施例により限定されるものではない。
【００４２】
実施例１〜３で使用した基材は、以下のように製造した。
基材を構成する骨材としては、平均粒径が３０〜１００μｍとなるように篩い分けしたアルミナ質研磨剤（アルミナ純度９５質量％、表中「アルミナ」と記す。）、或いはムライト質磁器（ムライト純度９５質量％、表中「ムライト」と記す。）の粉砕物のいずれかを使用した。
【００４３】
上記骨材に、焼結助材として平均粒径０．５〜５μｍの長石質ガラス（表中「長石質」と記す。）、コージェライト含有ガラス（表中「コージェライト」と記す。）、或いはホウ酸ガラス（表中「ホウ酸」と記す。）のいずれか一種、分散媒として水、有機バインダとしてメチルセルロースを添加し混練した坏土を押出成形し、押出成形体を得た。当該押出成形体を乾燥し、焼成することにより外径（Ｌｏ）３０ｍｍφ、内径（Ｌｉ）２２ｍｍφ、長さ２５０ｍｍのチューブ状の基材を得た。水銀圧入法により測定した基材の平均細孔径は５〜２０μｍであった。
【００４４】
実施例１においては、既述の基材の端部及び端部近傍を被覆するように、実施例２においては、上記基材の端部及び基材端部近傍の濾過膜を被覆するように、平均粒径０．５〜５μｍの長石質ガラス、コージェライト含有ガラス、或いはホウ酸ガラスのいずれか一種をシール材として塗布した後、当該シール材の軟化温度より１５０℃高い温度で焼成した。
クラックの有無は、焼成後において、染料水溶液に浸漬し、水洗した後、シール材表面を目視観察することにより評価した。
【００４５】
（実施例１）
実施例１では、各種のシール材及び基材を用い、シール材と基材に種々の熱膨張係数差を与えた場合の効果について評価した。その結果を表１及び図３〜４に示す。
【００４６】
【表１】

【００４７】
表１から明らかなように、シール材の熱膨張係数Ｋ _１と基材の熱膨張係数Ｋ _２の熱膨張係数差Ｋ _２ −Ｋ _１が０〜４（×１０ ^−６／℃）の範囲内の場合にはいずれもシール材にクラックが発生しなかった（実施例１−１〜１−５）。
【００４８】
一方、熱膨張係数差Ｋ _２ −Ｋ _１が４（×１０ ^−６／℃）を超える場合には、図３に示すようにシール材に圧縮応力によるジグザグ状のクラックが発生し（比較例１−１）、逆に熱膨張係数差Ｋ _２ −Ｋ _１が負の値をとる場合には、シール材に引張応力に起因するクラックが発生した（比較例１−２〜１−５）。この場合のクラックは、図４に示すような直線状のクラックであった（比較例１−３）。また、シール材の熱膨張係数が基材の熱膨張係数に極めて近くても熱膨張係数差Ｋ _２ −Ｋ _１が負の値をとる場合には、シール材のクラックを防止することができなかった（比較例１−２）。
【００４９】
（実施例２）
実施例２では、各種のシール材及び濾過膜を用い、シール材と濾過膜に種々の熱膨張係数差を与えた場合の効果について評価した。
【００５０】
実施例２においては、濾過膜を構成するセラミック粒子として平均粒径１〜３μｍのアルミナ、ムライト、コージェライトのいずれかを使用し、当該セラミック粒子に、分散媒として水、有機バインダとしてカルボキシメチルセルロースを添加し調製したスラリーを、既述の基材の内周面に従来公知の方法により製膜した後、乾燥し、焼成することにより、平均厚さ１５０μｍの濾過膜を形成した。ＡＳＴＭＦ３１６に記載のエアフロー法により測定した濾過膜の平均細孔径は０．８〜１μｍであった。
【００５１】
なお、実施例２においては、濾過膜上面及び基材上面の双方におけるシール材表面を目視観察することによりクラックの有無を評価した。その結果を表２に示す。
【００５２】
【表２】

【００５３】
表２から明らかなように、シール材の熱膨張係数Ｋ _１と基材の熱膨張係数Ｋ _２の熱膨張係数差Ｋ _２ −Ｋ _１が０〜４（×１０ ^−６／℃）の範囲内で、シール材の熱膨張係数Ｋ _１と濾過膜の熱膨張係数Ｋ _３との熱膨張係数差Ｋ _３ −Ｋ _１が０〜３（×１０ ^−６／℃）の範囲内の場合には濾過膜上面及び基材上面ともシール材にクラックが発生しなかった（実施例２−１〜２−５）。
【００５４】
一方、熱膨張係数差Ｋ _３ −Ｋ _１が３（×１０ ^−６／℃）を超える場合には、シール材に圧縮応力によるジグザグ状のクラックが発生し（比較例２−１）、逆に熱膨張係数差Ｋ _３ −Ｋ _１が負の値をとる場合には、シール材に引張応力に起因する直線状のクラックが発生した（比較例２−２〜２−５）。また、シール材の熱膨張係数が濾過膜の熱膨張係数に極めて近くても熱膨張係数差Ｋ _３ −Ｋ _１が負の値をとる場合には、シール材のクラックを防止することができなかった（比較例２−２）。
【００５５】
（実施例３）
実施例３では、各種の骨材及び焼結助剤を用い、骨材と焼結助剤に種々の熱膨張係数差を与えた場合の効果について評価した。
【００５６】
実施例３においては、まず、一端を封止し、かつ、他端を水圧ポンプに接続した不透水性のゴムチューブを、既述の方法により製造した基材の貫通孔に挿入する。次いで、水圧ポンプにより徐々に水圧を加えることにより、貫通孔内でゴムチューブを膨張させ、基材が破損した際の圧力計指示値Ｐを測定する。基材が破損すると、ゴムチューブが破れ、圧力計指示値が瞬間的に０に戻るので、その直前の圧力計指示値Ｐを用いて、下記式（６）から内圧破壊強度Ｄを算出し、基材（即ちフィルタ）の強度について評価した。
本実施例の基材は、外径Ｌｏが３０ｍｍ、内径Ｌｉが２２ｍｍであるので、内圧破壊強度Ｄは圧力計指示値Ｐを約３．３倍した値となる。
Ｄ＝Ｐ×（Ｌｏ²＋Ｌｉ²）／（Ｌｏ²−Ｌｉ²） …（６）
（但し、Ｄ：内圧破壊強度（ＭＰａ）、Ｐ：圧力計指示値（ＭＰａ）、Ｌｏ：基材外径（ｍｍ）、Ｌｉ：基材内径（ｍｍ））
【００５７】
本実施例においては、基材が破損した際の圧力計指示値Ｐが２ＭＰａ以上である場合にフィルタが高強度であると評価した。一般に、セラミックフィルタは、内圧０．２ＭＰａ程度の条件で濾過を行うが、濾過圧力の急激な変動があった場合（例えばウォーターハンマー現象等）の破損を防止するためには、１０倍の安全率、即ち、通常運転内圧である０．２ＭＰａの１０倍以上の圧力計指示値Ｐを有していることが好ましいからである。その結果を表３に示す。
【００５８】
【表３】

【００５９】
表３から明らかなように、焼結助剤の熱膨張係数Ｋ _４と骨材の熱膨張係数Ｋ _５の熱膨張係数差Ｋ _５ −Ｋ _４が０〜３（×１０ ^−６／℃）の範囲内の場合には、いずれも圧力計指示値Ｐが２ＭＰａ以上であり、フィルタが高強度であった（実施例３−１〜３−５）。
【００６０】
一方、熱膨張係数差Ｋ _５ −Ｋ _４が３（×１０ ^−６／℃）を超える場合（比較例３−１）、逆に熱膨張係数差Ｋ _５ −Ｋ _４が負の値をとる場合（比較例３−２〜３−３）のいずれの場合にも圧力計指示値Ｐは２ＭＰａ未満となり、フィルタの強度が低下した。
また、焼結助剤の熱膨張係数が骨材の熱膨張係数に極めて近くても熱膨張係数差Ｋ _５ −Ｋ _４が負の値をとる場合には、フィルタの強度が低下した（比較例３−２）。更に、焼結助剤の熱膨張係数が骨材の熱膨張係数と等しい場合（熱膨張係数差Ｋ _５ −Ｋ _４が０の場合）は、圧力計指示値Ｐは２ＭＰａ以上ではあるものの実施例中で最も低かった（実施例３−５）。
【００６１】
【発明の効果】
本発明は、フィルタの構成部材間（シール材、基材、濾過膜）、或いは基材の構成材料（焼結助剤、骨材）に所定の熱膨張係数差を与え、これらの間に内在応力を発生せしめたので、フィルタの構成部材間、基材の構成材料間に発生する引張応力や圧縮応力を低減することができる。
従って、本発明によれば、フィルタの構成部材、或いは基材の構成材料を異なる材質とした場合においても、高強度で、かつ、フィルタの各構成部材にクラックが発生し難いセラミックフィルタを提供することが可能となる。
【図面の簡単な説明】
【図１】ハウジングに装填されたフィルタの概略断面図であって、（ａ）はシール材を備えたフィルタ、（ｂ）はシール材を備えないフィルタを示す。
【図２】シール材の熱膨張曲線を示すグラフであって、（ａ）は通常の場合、（ｂ）は結晶転移がある場合を示す。
【図３】圧縮応力によりクラックを生じたセラミック材料（シール材）の表面組織を示す写真である。
【図４】引張応力によりクラックを生じたセラミック材料（シール材）の表面組織を示す写真である。
【符号の説明】
１…ハウジング、２…基材、３…濾過膜、４…Ｏ−リング、５…シール材、１１…ハウジング、１２…基材、１３…濾過膜、１４…Ｏ−リング。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ceramic filter in which a filter membrane having an average pore diameter smaller than that of a base material is formed on the surface of a base material made of a porous ceramic body. Specifically, the filter has high strength and cracks are generated in constituent members of the filter. It is related with the ceramic filter which is hard to do.
[0002]
[Prior art]
A ceramic filter is a filter using a ceramic porous body, and is excellent in physical strength, durability, corrosion resistance, and the like. For example, in a wide range of fields such as water treatment, exhaust gas treatment, and pharmaceutical / food fields, It is used to remove suspended matter, bacteria, dust, etc.
[0003]
In a ceramic filter, the ceramic porous body may be used as a filter medium as it is, but the surface of the ceramic porous body is used as a base material (support) in order to improve both the filtration performance and the fluid permeation amount (that is, the processing capacity). In general, a filter membrane made of ceramic is formed.
For example, the average pore diameter of the filtration membrane is configured to be as small as about 0.01 to 1.0 μm to ensure filtration performance, while the average pore diameter of the base material is configured to be as large as about 1 to several hundred μm, The flow resistance of the fluid is reduced, and the amount of fluid permeation (that is, processing capability) is improved.
[0004]
In addition, the ceramic filter is obtained by processing the base material into various shapes depending on the purpose of filtration, but the base material is in a tube shape having a single through hole or in a honeycomb shape having a large number of parallel through holes. What was made into a monolith form is also used widely. A filter in which a filtration membrane is formed on the surface of a tube-like or honeycomb-like substrate, for example, the inner peripheral surface of a through hole, is accommodated in the housing, and the outer peripheral surface side of the substrate and the end surface side of the substrate where the through holes are opened It is used as a cross flow type filter by adopting a structure in which it is hermetically isolated by an O-ring or the like.
[0005]
According to the cross flow type filter, by supplying a fluid to be treated such as gas or liquid into the through hole from one end surface side of the base material, the filtered fluid that has permeated the filtration membrane on the inner peripheral surface of the through hole is obtained. While being recovered from the outer peripheral surface side of the base material, the fluid to be treated that has not been filtered can be recovered from the other end surface side of the base material.
[0006]
However, as shown in FIG. 1B, by simply isolating the vicinity of the end surface of the base material 12 with the O-ring 14, the fluid to be treated is introduced into the base material 12 from the end surface of the base material 12 where the filtration membrane 13 is not formed. Therefore, the target filtration cannot be performed, and the filtered fluid that has already been filtered is contaminated.
[0007]
Therefore, as shown in FIG. 1 (a), a membrane separation device has been proposed in which a sealing material 5 made of ceramic or the like covers at least the base 2 end portion and the filtration membrane 3 in the vicinity of the base 2 end ( JP-A-61-8106).
Such a structure can prevent the fluid to be treated from entering from the end face of the base material 2, and the fluid to be treated always passes through the filtration membrane 3, so that the intended filtration can be performed and the fluid has already been filtered. Further, it is useful in that contamination of the filtered fluid can be prevented.
[0008]
[Problems to be solved by the invention]
By the way, in the ceramic filter composed of a plurality of members such as a base material, a filtration membrane, and a sealing material as in the above-mentioned membrane separation device, each constituent member is made of a material having physical and chemical characteristics suitable for its function. Therefore, there are many cases where it is required to use different materials for each because of cost requirements. However, in such a case, if the thermal expansion coefficients of the constituent members are extremely different, tensile stress and compressive stress are generated between the constituent members, so that cracks occur in the constituent members or the mechanical strength of the filter is expressed. There was a problem that I could not.
[0009]
The substrate is mainly composed of an aggregate having a particle size of about 5 to 200 μm and a sintering aid having a particle size of less than 5 μm, which is an additive for strengthening the bond between the aggregates. The material and the sintering aid are often different materials.
Therefore, even when the thermal expansion coefficients are extremely different between the constituent materials of the base material, as in the case of the constituent members of the filter, there is a problem that tensile strength and compressive stress are generated and the strength of the filter is reduced. was there.
[0010]
In order to solve these problems, a method in which each constituent member of the filter or the constituent material of the base material is made of a material having a thermal expansion coefficient as close as possible is conceivable. However, as a result of investigations by the present inventors, it has been found that these situations cannot be prevented simply by bringing the coefficients of thermal expansion between the constituent members or between the constituent materials of the substrate.
[0011]
The present invention has been made in view of such problems of the prior art, and the object of the present invention is to make each constituent member of the filter or the constituent material of the base material different from each other. Another object of the present invention is to provide a ceramic filter that has high strength and is less likely to cause cracks in the constituent members of the filter.
[0012]
[Means for Solving the Problems]
As a result of the present inventors diligently examining the problems of the prior art, a predetermined thermal expansion coefficient difference is given between the constituent members of the filter or between the constituent materials of the base material, and an internal stress is generated between them. Thus, the present invention was completed by finding that the above problems could be solved.
[0013]
  That is, according to the present invention, a base material composed of a porous body having a single or a large number of parallel through-holes, and a filtration formed on the surface of the base material and having an average pore diameter smaller than that of the base material. A ceramic filter comprising a membrane and a sealing material covering at least the base material end and the filtration membrane in the vicinity of the base material end, wherein the sealing material isIt is made of a material different from the base material, and the difference in thermal expansion coefficient between the thermal expansion coefficient of the sealing material and the thermal expansion coefficient of the base material is within the range of the following formula (I).A ceramic filter characterized by being configured is provided (hereinafter referred to as “first invention”).
  0 ≦ K ₂ -K ₁ ≦ 4: (I)
[K ₁ : Thermal expansion coefficient of sealing material (× 10 ^-6 / ° C), K ₂ : Thermal expansion coefficient of substrate (× 10 ^-6 / ℃)]
[0014]
  In the first invention, the sealing material is used.It is made of a material different from that of the filtration membrane, and the difference in thermal expansion coefficient between the thermal expansion coefficient of the sealing material and the thermal expansion coefficient of the filtration membrane is within the range of the following formula (II).What is configured is preferable, the sintering aid contained in the substrateIn addition, it is made of a material different from the aggregate constituting the base material, and the difference in thermal expansion coefficient between the thermal expansion coefficient of the sintering aid and the thermal expansion coefficient of the aggregate is within the range of the following formula (III) InWhat was comprised is still more preferable.
  0 ≦ K ₃ -K ₁ ≦ 3: (II)
[K ₁ : Thermal expansion coefficient of sealing material (× 10 ^-6 / ° C), K ₃ : Thermal expansion coefficient of filtration membrane (× 10 ^-6 / ℃)]
  0 ≦ K ₅ -K ₄ ≦ 3: (III)
[K ₄ : Thermal expansion coefficient of sintering aid (× 10 ^-6 / ° C), K ₅ : Thermal expansion coefficient of aggregate (× 10 ^-6 / ℃)]
[0015]
  In addition, according to the present invention, a base material composed of a porous body having a single or a large number of through-holes in parallel, and a filtration formed on the surface of the base material and having an average pore diameter smaller than that of the base material A ceramic filter comprising a membrane and a sealing material covering at least the base material end and the filtration membrane in the vicinity of the base material end, wherein the sealing material isIt is made of a material different from the filtration membrane, and the difference in thermal expansion coefficient between the thermal expansion coefficient of the sealing material and the thermal expansion coefficient of the filtration membrane is within the range of the above formula (II).A ceramic filter characterized by being configured is provided (hereinafter referred to as “second invention”).
[0016]
  In the second invention, the sintering aid contained in the substrate is added.It is made of a material different from the aggregate, and the difference in thermal expansion coefficient between the thermal expansion coefficient of the sintering aid and the thermal expansion coefficient of the aggregate constituting the base material is within the range of the above formula (III).What was comprised is preferable.
[0017]
  Furthermore, according to the present invention, a base material composed of a porous body having a single or a large number of through-holes in parallel, and filtration formed on the surface of the base material and having an average pore diameter smaller than that of the base material. A ceramic filter comprising a membrane and a sealing material that covers at least a base material end portion and a filter membrane in the vicinity of the base material end portion, and comprising a sintering aid contained in the base materialThe material is made of a material different from the aggregate constituting the base material, and the difference in thermal expansion coefficient between the thermal expansion coefficient of the sintering aid and the thermal expansion coefficient of the aggregate is within the range of the above formula (III). InA ceramic filter characterized by being configured is provided (hereinafter referred to as “third invention”).
[0018]
DETAILED DESCRIPTION OF THE INVENTION
(1) Filter configuration
The ceramic filter of the present invention includes at least a base material, a filtration membrane, and a sealing material as constituent members.
[0019]
(1-1)Base material
  The “base material” referred to in the present invention is a member having a function as a support for a filtration membrane, and is a ceramic porous body mainly composed of an aggregate and a sintering aid.
  As the shape of the substrate, either a tube shape having a single through hole or a honeycomb shape (including a monolith shape) having a large number of parallel through holes is used.
[0020]
The aggregate is a main component of the base material, and is composed of ceramic particles having an average particle size of about 5 to 200 μm. By molding and sintering the clay containing the aggregate, a porous body having pores corresponding to the particle size of the aggregate, that is, a base material is formed.
The material of the aggregate may be appropriately selected so as to suit the purpose of filtration. For example, alumina, mullite, cordierite, silicon carbide, ceramic scraps, or the like can be used.
[0021]
The sintering aid is an additive for reinforcing the bonding between aggregates, and is made of ceramic particles having an average particle size of less than 5 μm. By including it in the clay together with the aggregate, the bond between the aggregates is strengthened and a strong porous body is formed.
The material of the sintering aid is not particularly limited, and for example, alumina, silica, zirconia, titania, glass frit, feldspar, cordierite, and the like can be used. Usually, in order to ensure the bonding strength between the aggregates and prevent pore blockage of the porous body, about 10 to 35% by mass is contained with respect to the total mass of the aggregate and the sintering aid.
[0022]
(1-2)Filtration membrane
  The “filtration membrane” referred to in the present invention is a thin-film ceramic porous body having an average pore diameter smaller than that of the substrate, and is formed into at least one layer, or in some cases, two or more layers to form a multilayer. Usually, the “filtration membrane” refers to a member for ensuring the filtration function of the filter, but the “filtration membrane” referred to in the present invention is an intermediate layer (a plurality of layers) in the case where the filtration membrane is a multilayer. Of these, layers other than the uppermost layer) are also included.
[0023]
The filtration membrane is formed by forming a slurry containing ceramic particles having a mean particle size of about 0.1 to 5 μm, which has a smaller average particle size than the aggregate constituting the substrate, on the surface of the substrate and then sintering the slurry. . The “surface of the substrate” forming the filtration membrane includes the substrate outer peripheral surface as well as the through hole inner peripheral surface of the substrate. As the material of the ceramic particles, the same material as the aggregate constituting the base material can be used.
[0024]
(1-3)Sealing material
  The “sealing material” referred to in the present invention is a member for preventing the fluid to be treated from entering the inside of the base material from the end face of the base material, and at least the base material end portion and the base material end to ensure the function. It is necessary to cover the filtration membrane in the vicinity of the part.
[0025]
The sealing material is sintered after applying a glaze made of a glassy substance (glass frit, etc.) such as borosilicate glass or feldspar glass so as to cover the substrate end and the filtration membrane in the vicinity of the substrate end. It can be formed by caulking. However, as long as it has a pore diameter equal to or smaller than that of the filtration membrane, it is not particularly limited to the glaze, and in some cases, the filtration membrane can be used as a sealing material.
[0026]
(2) Embodiment of the present invention
In the ceramic filter as described above, a predetermined thermal expansion coefficient difference is given between the constituent members of the filter or between the constituent materials of the base material, and an internal stress is generated therebetween. The ceramic filter of the present invention is high in strength even when each constituent member of the filter or the constituent material of the base material is made of a different material, and cracks are hardly generated in each constituent member of the filter.
Hereinafter, the ceramic filter of the present invention will be described in detail.
[0027]
(2-1)1st invention
  The first invention uses a sealing material.It is made of a material different from the base material, and the difference in thermal expansion coefficient between the thermal expansion coefficient of the sealing material and the thermal expansion coefficient of the base material is within the range of the following formula (I).It is composed.
  By giving a difference in coefficient of thermal expansion within the above range between the sealing material and the base material, a compressive stress is generated on the sealing material side and a tensile stress is generated on the base material side. The
  0 ≦ K ₂ -K ₁ ≦ 4: (I)
[K ₁ : Thermal expansion coefficient of sealing material (× 10 ^-6 / ° C), K ₂ : Thermal expansion coefficient of substrate (× 10 ^-6 / ℃)]
[0028]
  Thermal expansion coefficient difference K ₂ -K ₁ Exceeds 4In this case, since excessive compressive stress is applied to the sealing material, a zigzag crack as shown in FIG. 3 occurs,Thermal expansion coefficient difference K ₂ -K ₁ Is negativeIn this case, since a tensile stress is applied to the sealing material, a linear crack as shown in FIG. 4 occurs. Note that even if the thermal expansion coefficient of the sealing material is very close to the thermal expansion coefficient of the base material,(That is, thermal expansion coefficient difference K ₂ -K ₁ Is negative)It should be noted that cracking of the sealing material cannot be prevented.
[0029]
(2-2)Second invention
  The second invention uses a sealing material based on the same idea as the first invention.It is made of a material different from that of the filtration membrane, and the difference in thermal expansion coefficient between the thermal expansion coefficient of the sealing material and the thermal expansion coefficient of the filtration membrane is within the range of the following formula (II).It is composed.
  0 ≦ K ₃ -K ₁ ≦ 3: (II)
[K ₁ : Thermal expansion coefficient of sealing material (× 10 ^-6 / ° C), K ₃ : Thermal expansion coefficient of filtration membrane (× 10 ^-6 / ℃)]
[0030]
  Thermal expansion coefficient difference K ₃ -K ₁ Exceeds 3In some cases, excessive compressive stress is applied to the sealing material.Thermal expansion coefficient difference K ₃ -K ₁ Is negativeIn some cases, a tensile stress is applied to the sealing material, so that cracks occur in the sealing material. Also, even if the thermal expansion coefficient of the sealing material is very close to the thermal expansion coefficient of the filtration membrane,(That is, thermal expansion coefficient difference K ₃ -K ₁ Is negative)The point that the crack of the sealing material cannot be prevented is the same as that of the first invention.
[0031]
(2-3)Third invention
  In the third invention, the sintering aid contained in the substrate is added.In addition, it is made of a material different from the aggregate constituting the base material, and the difference in thermal expansion coefficient between the thermal expansion coefficient of the sintering aid and the thermal expansion coefficient of the aggregate is within the range of the following formula (III) InIt is composed. Whereas the first and second inventions focus on the difference in thermal expansion coefficient between the constituent members of the filter, the third invention focuses on the difference in thermal expansion coefficient between the constituent materials of the base material. is there.
  0 ≦ K ₅ -K ₄ ≦ 3: (III)
[K ₄ : Thermal expansion coefficient of sintering aid (× 10 ^-6 / ° C), K ₅ : Thermal expansion coefficient of aggregate (× 10 ^-6 / ℃)]
[0032]
  In particular,Thermal expansion coefficient difference K ₅ -K ₄ Exceeds 3In some cases, compression stress is applied to the sintering aid,Thermal expansion coefficient difference K ₅ -K ₄ Is negativeIn this case, since tensile stress is applied to the sintering aid, the strength of the substrate is reduced in any case.
[0033]
(2-4)Calculation of thermal expansion coefficient difference
  The difference in thermal expansion coefficient between the first and second inventions is the linear thermal expansion amount ΔL of each evaluation sample of the base material, the filtration membrane, and the sealing material.₁~ ΔL₃Of each constituent member defined by the following formulas (1) to (3)Coefficient of thermal expansionK₁~ K₃Calculate from
  K₁= (ΔL₁/ ΔT₁) / L (1)
  K₂= (ΔL₂/ ΔT₁) / L (2)
  K₃= (ΔL₃/ ΔT₁) / L (3)
(However, K₁: Thermal expansion coefficient of sealing material (× 10^-6/ ° C), K₂: Thermal expansion coefficient of substrate (× 10^-6/ ° C), K₃: Thermal expansion coefficient of filtration membrane (× 10^-6/ ° C), ΔL₁: Ts₁To Tt₁Linear thermal expansion amount (unit: mm) of sealant sample between₂: Ts₁To Tt₁Amount of linear thermal expansion (unit: mm) of the substrate sample during the period, ΔL₃: Ts₁To Tt₁The linear thermal expansion of the filtration membrane sample between (unit: mm), L: length of each evaluation sample at room temperature (unit: mm))
[0034]
Specifically, as an evaluation sample, a base material, a filtration membrane, and a single sintered body of a sealing material processed into a square column shape having a cross section of 3 mm × 4 mm and a length L of 20 mm (measured at room temperature) are used as a reference. Temperature Ts₁To seal material transition temperature Tt₁Temperature difference ΔT between₁Of linear thermal expansion ΔL of each evaluation sample₁~ ΔL_ThreeIs measured by using a high-precision two-sample thermal analyzer-TMA standard type (trade name: manufactured by Rigaku Corporation) to detect the difference in elongation between the standard sample and the evaluation sample using a differential transformer.
[0035]
"Reference temperature Ts₁Is generally set to a temperature at which the change in the coefficient of linear thermal expansion of the evaluation sample is small. Therefore, considering that the evaluation sample of the present invention is ceramic, any one of the above formulas (1) to (3) is defined as 40 ° C.
[0036]
Also, “Transition temperature Tt of sealing material₁"Is defined as the temperature at which the linear thermal expansion amount rapidly rises when the sealing material sample transitions from the glass state to the supercooled liquid as shown in FIG. 2 in the measurement of the linear thermal expansion amount.
FIG. 2B shows an example in which there is a crystal transition like cristobalite, and the transition temperature Tt.₁Although the linear thermal expansion amount shows a convex bend in a lower temperature range, it can be similarly defined in this case.
The “softening point of the sealing material” to be described later refers to a temperature at which the linear thermal expansion amount of the sealing material sample shows a maximum value and starts to shrink as shown in FIG.
[0037]
  The difference in thermal expansion coefficient in the third invention is also the same as in the first and second inventions, and the linear thermal expansion amount ΔL of the evaluation sample consisting of a sintering aid and a single sintered body of aggregate.₄~ ΔL₅Of each constituent material defined by the following formulas (4) and (5)Coefficient of thermal expansionK₄, K₅Calculate from
  K₄= (ΔL₄/ ΔT₂) / L (4)
  K₅= (ΔL₅/ ΔT₂) / L (5)
(However, K₄: Sintering aidCoefficient of thermal expansion(× 10^-6/ ° C), K₅: AggregateCoefficient of thermal expansion(× 10^-6/ ° C), ΔL₄: Ts₂To Tt₂Of linear thermal expansion (unit: mm) of the sintering aid sample during₅: Ts₂To Tt₂Linear thermal expansion amount of aggregate sample during (unit: mm), L: length of each evaluation sample at room temperature (unit: mm))
[0038]
  In addition, “reference temperature Ts₂Is 40 ° C. in both of the above formulas (4) and (5).
  In addition, “transition temperature Tt of sintering aid”₂"Is defined as the temperature at which the linear thermal expansion amount rapidly rises when the sintering aid sample transitions from the glass state to the supercooled liquid in the measurement of the thermal expansion amount. However, if the above transition temperature does not exist in the temperature range below the firing temperature of the substrate, Tt₂Is assumed to be 650 ° CCoefficient of thermal expansionIs calculated.
[0039]
(2-5)Production method
  The filter of the present invention is based on the thermal expansion coefficient measured in advance by the above-described method, and the constituent member (sealant, base material, filtration membrane) of the filter having a predetermined difference in thermal expansion coefficient or the constituent material of the base material ( Except for selecting the material of the sintering aid and aggregate), it can be manufactured according to a conventionally known method for manufacturing a ceramic filter.
[0040]
For example, first, in addition to aggregates and sintering aids, a dispersion medium, an organic binder, if necessary, a surfactant, a plasticizer, and the like are added, and a kneaded clay is extruded, and then a molded body formed by extrusion molding is dried.・ Firing to produce a substrate, and then dispersing the ceramic particles in a dispersion medium such as water, and adding a slurry for film formation to which an organic binder, a pH adjuster, a surfactant and the like are added if necessary. Form a film on the inner peripheral surface of the through hole of the base material, dry and fire it to form a filtration membrane, and further apply a glaze made of a glassy material as a sealing material to the end of the base material, then dry and fire it A filter can be obtained by the method.
[0041]
【Example】
EXAMPLES Hereinafter, although the filter of this invention is demonstrated in detail by an Example, this invention is not limited by the following Example.
[0042]
The base material used in Examples 1 to 3 was produced as follows.
The aggregate constituting the base material is an alumina abrasive (95% by mass alumina purity, indicated as “alumina” in the table), or mullite porcelain (screened to have an average particle size of 30 to 100 μm). Any one of pulverized products having a mullite purity of 95% by mass and described as “mullite” in the table was used.
[0043]
To the above-mentioned aggregate, feldspar glass having an average particle size of 0.5 to 5 μm (referred to as “feldspar” in the table), cordierite-containing glass (referred to as “cordrite” in the table), as a sintering aid. Alternatively, any one of borate glasses (referred to as “boric acid” in the table), water as a dispersion medium, and kneaded clay added with methylcellulose as an organic binder were extruded to obtain an extruded molded body. The extruded molded body was dried and fired to obtain a tube-shaped substrate having an outer diameter (Lo) of 30 mmφ, an inner diameter (Li) of 22 mmφ, and a length of 250 mm. The average pore diameter of the base material measured by the mercury intrusion method was 5 to 20 μm.
[0044]
In Example 1, the end of the base material and the vicinity of the end are covered, and in Example 2, the end of the base and the filtration membrane near the end of the base are covered. After applying any one of feldspar glass having an average particle size of 0.5 to 5 μm, cordierite-containing glass, or borate glass as a sealing material, it was fired at a temperature 150 ° C. higher than the softening temperature of the sealing material.
The presence or absence of cracks was evaluated by visually observing the surface of the sealing material after immersing in an aqueous dye solution and washing with water.
[0045]
Example 1
In Example 1, various sealing materials and base materials were used, and the effects when various thermal expansion coefficient differences were given to the sealing materials and the base materials were evaluated. The results are shown in Table 1 and FIGS.
[0046]
[Table 1]

[0047]
As is clear from Table 1,Thermal expansion coefficient K of sealing material ₁ And base material thermal expansion coefficient K ₂ Thermal expansion coefficient difference K ₂ -K ₁ Is 0-4 (× 10 ^-6 / ° C)In any case, no crack was generated in the sealing material (Examples 1-1 to 1-5).
[0048]
on the other hand,Thermal expansion coefficient difference K ₂ -K ₁ Is 4 (× 10 ^-6 / ℃)In this case, as shown in FIG. 3, zigzag cracks due to compressive stress occur in the sealing material (Comparative Example 1-1).Thermal expansion coefficient difference K ₂ -K ₁ Takes a negative valueIn this case, cracks due to tensile stress occurred in the sealing material (Comparative Examples 1-2 to 1-5). The crack in this case was a linear crack as shown in FIG. 4 (Comparative Example 1-3). Even if the thermal expansion coefficient of the sealing material is very close to the thermal expansion coefficient of the substrate,Thermal expansion coefficient difference K ₂ -K ₁ Takes a negative valueIn such a case, cracking of the sealing material could not be prevented (Comparative Example 1-2).
[0049]
(Example 2)
In Example 2, various sealing materials and filtration membranes were used, and the effects when various thermal expansion coefficient differences were given to the sealing materials and the filtration membranes were evaluated.
[0050]
In Example 2, any one of alumina, mullite, and cordierite having an average particle diameter of 1 to 3 μm is used as the ceramic particles constituting the filtration membrane, and water is used as the dispersion medium, and carboxymethyl cellulose is used as the organic binder. The slurry prepared by addition was formed on the inner peripheral surface of the above-described base material by a conventionally known method, then dried and fired to form a filtration membrane having an average thickness of 150 μm. The average pore diameter of the filtration membrane measured by the air flow method described in ASTM F316 was 0.8 to 1 μm.
[0051]
In Example 2, the presence or absence of cracks was evaluated by visually observing the sealing material surface on both the upper surface of the filtration membrane and the upper surface of the base material. The results are shown in Table 2.
[0052]
[Table 2]

[0053]
As is clear from Table 2,Thermal expansion coefficient K of sealing material ₁ And base material thermal expansion coefficient K ₂ Thermal expansion coefficient difference K ₂ -K ₁ Is 0-4 (× 10 ^-6 / ° C), the thermal expansion coefficient K of the sealing material ₁ And the thermal expansion coefficient K of the filter membrane ₃ Difference in thermal expansion coefficient ₃ -K ₁ 0-3 (× 10 ^-6 / ° C)In that case, no crack was generated in the sealing material on both the upper surface of the filtration membrane and the upper surface of the base material (Examples 2-1 to 2-5).
[0054]
on the other hand,Thermal expansion coefficient difference K ₃ -K ₁ Is 3 (× 10 ^-6 / ℃)In this case, a zigzag crack due to the compressive stress occurs in the sealing material (Comparative Example 2-1).Thermal expansion coefficient difference K ₃ -K ₁ Takes a negative valueIn this case, a linear crack caused by tensile stress occurred in the sealing material (Comparative Examples 2-2 to 2-5). Even if the thermal expansion coefficient of the sealing material is very close to the thermal expansion coefficient of the filtration membrane,Thermal expansion coefficient difference K ₃ -K ₁ Takes a negative valueIn such a case, cracking of the sealing material could not be prevented (Comparative Example 2-2).
[0055]
(Example 3)
In Example 3, various aggregates and sintering aids were used, and the effects when various thermal expansion coefficient differences were given to the aggregate and the sintering aid were evaluated.
[0056]
In Example 3, first, an impermeable rubber tube having one end sealed and the other end connected to a hydraulic pump is inserted into the through hole of the base material manufactured by the method described above. Next, by gradually applying water pressure with a water pressure pump, the rubber tube is expanded in the through hole, and the pressure gauge instruction value P when the base material is damaged is measured. When the base material is broken, the rubber tube is torn and the pressure gauge indicated value instantaneously returns to 0, so that the internal pressure breaking strength D is calculated from the following formula (6) using the pressure gauge indicated value P immediately before that, The strength of the substrate (ie filter) was evaluated.
The base material of the present example has an outer diameter Lo of 30 mm and an inner diameter Li of 22 mm, so the internal pressure breaking strength D is a value obtained by multiplying the pressure gauge instruction value P by about 3.3.
D = P × (Lo²+ Li²) / (Lo²-Li²(6)
(However, D: Internal pressure fracture strength (MPa), P: Pressure gauge instruction value (MPa), Lo: Substrate outer diameter (mm), Li: Substrate inner diameter (mm))
[0057]
In this example, it was evaluated that the filter had high strength when the pressure gauge instruction value P when the base material was damaged was 2 MPa or more. In general, a ceramic filter performs filtration under an internal pressure of about 0.2 MPa, but in order to prevent breakage when there is a sudden change in the filtration pressure (for example, water hammer phenomenon), the safety factor is 10 times. That is, it is preferable to have a pressure gauge instruction value P that is 10 times or more of 0.2 MPa, which is the normal operating internal pressure. The results are shown in Table 3.
[0058]
[Table 3]

[0059]
  As is clear from Table 3,Thermal expansion coefficient K of sintering aid ₄ And thermal expansion coefficient K of aggregate ₅ Thermal expansion coefficient difference K ₅ -K ₄ 0-3 (× 10 ^-6 / ° C)In all cases, the pressure gauge instruction value P was 2 MPa or more, and the filter had high strength (Examples 3-1 to 3-5).
[0060]
  on the other hand,Thermal expansion coefficient difference K ₅ -K ₄ Is 3 (× 10 ^-6 / ℃)In case (Comparative Example 3-1), converselyThermal expansion coefficient difference K ₅ -K ₄ Takes a negative valueIn any case (Comparative Examples 3-2 to 3-3), the pressure gauge instruction value P was less than 2 MPa, and the strength of the filter was reduced.
  Even if the thermal expansion coefficient of the sintering aid is very close to the thermal expansion coefficient of the aggregate,Thermal expansion coefficient difference K ₅ -K ₄ Takes a negative valueIn this case, the strength of the filter was reduced (Comparative Example 3-2). Furthermore, when the thermal expansion coefficient of the sintering aid is equal to the thermal expansion coefficient of the aggregate(Thermal expansion coefficient difference K ₅ -K ₄ Is 0)Although the pressure gauge instruction value P was 2 MPa or more, it was the lowest among the examples (Example 3-5).
[0061]
【The invention's effect】
The present invention gives a predetermined difference in coefficient of thermal expansion between constituent members of the filter (sealant, base material, filtration membrane) or constituent materials of the base material (sintering aid, aggregate). Since the stress is generated, the tensile stress and the compressive stress generated between the constituent members of the filter and between the constituent materials of the base material can be reduced.
Therefore, according to the present invention, there is provided a ceramic filter that has high strength and is less likely to cause cracks in the constituent members of the filter even when the constituent members of the filter or the constituent materials of the base material are different materials. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a filter loaded in a housing, wherein (a) shows a filter with a sealing material, and (b) shows a filter without a sealing material.
FIG. 2 is a graph showing a thermal expansion curve of a sealing material, where (a) shows a normal case and (b) shows a case where there is a crystal transition.
FIG. 3 is a photograph showing the surface structure of a ceramic material (sealant) that has cracked due to compressive stress.
FIG. 4 is a photograph showing the surface structure of a ceramic material (sealant) that has cracked due to tensile stress.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Housing, 2 ... Base material, 3 ... Filtration membrane, 4 ... O-ring, 5 ... Sealing material, 11 ... Housing, 12 ... Base material, 13 ... Filtration membrane, 14 ... O-ring.

Claims

A base material comprising a porous body having a single or a large number of through-holes in parallel, a filtration membrane having a small average pore diameter as compared with the base material, formed on the surface of the base material, and at least an end portion of the base material And a sealing material that covers the filter membrane in the vicinity of the end of the substrate, and a ceramic filter comprising:
The sealing material is made of a material different from the base material, and
A ceramic filter characterized in that the difference in thermal expansion coefficient between the thermal expansion coefficient of the sealing material and the thermal expansion coefficient of the substrate is within the range of the following formula (I) .
0 ≦ K ₂ −K ₁ ≦ 4: (I)
[K ₁ : Thermal expansion coefficient of sealing material (× 10 ⁻⁶ / ° C.), K ₂ : Thermal expansion coefficient of base material (× 10 ⁻⁶ / ° C.)]

A base material comprising a porous body having a single or a large number of through-holes in parallel, a filtration membrane having a small average pore diameter as compared with the base material, formed on the surface of the base material, and at least an end portion of the base material And a sealing material that covers the filter membrane in the vicinity of the end of the substrate, and a ceramic filter comprising:
The sealing material is made of a material different from the filtration membrane, and
A ceramic filter characterized in that the difference in thermal expansion coefficient between the thermal expansion coefficient of the sealing material and the thermal expansion coefficient of the filtration membrane falls within the range of the following formula (II) .
0 ≦ K ₃ −K ₁ ≦ 3: (II)
[K ₁ : Thermal expansion coefficient of sealing material (× 10 ⁻⁶ / ° C.), K ₃ : Thermal expansion coefficient of filtration membrane (× 10 ⁻⁶ / ° C.)]

A base material comprising a porous body having a single or a large number of through-holes in parallel, a filtration membrane having a small average pore diameter as compared with the base material, formed on the surface of the base material, and at least an end portion of the base material And a sealing material that covers the filter membrane in the vicinity of the end of the substrate, and a ceramic filter comprising:
The sintering aid contained in the base material is composed of a material different from the aggregate constituting the base material, and
A ceramic filter characterized in that a difference in thermal expansion coefficient between the thermal expansion coefficient of the sintering aid and the thermal expansion coefficient of the aggregate is within the range of the following formula (III) .
0 ≦ K ₅ −K ₄ ≦ 3: (III)
[K ₄ : Thermal expansion coefficient of sintering aid (× 10 ⁻⁶ / ° C.), K ₅ : Thermal expansion coefficient of aggregate (× 10 ⁻⁶ / ° C.)]

The sealing material is made of a material different from the filtration membrane, and
The ceramic filter according to claim 1, wherein the difference in thermal expansion coefficient between the thermal expansion coefficient of the sealing material and the thermal expansion coefficient of the filtration membrane is within the range of the following formula (II) .
0 ≦ K ₃ −K ₁ ≦ 3: (II)
[K ₁ : Thermal expansion coefficient of sealing material (× 10 ⁻⁶ / ° C.), K ₃ : Thermal expansion coefficient of filtration membrane (× 10 ⁻⁶ / ° C.)]

The sintering aid contained in the base material is composed of a material different from the aggregate constituting the base material, and
5. The structure according to claim 1, wherein the difference in thermal expansion coefficient between the thermal expansion coefficient of the sintering aid and the thermal expansion coefficient of the aggregate is within the range of the following formula (III) . Ceramic filter.
0 ≦ K ₅ −K ₄ ≦ 3: (III)
[K ₄ : Thermal expansion coefficient of sintering aid (× 10 ⁻⁶ / ° C.), K ₅ : Thermal expansion coefficient of aggregate (× 10 ⁻⁶ / ° C.)]