JP3717111B2

JP3717111B2 - Ceramic honeycomb filter

Info

Publication number: JP3717111B2
Application number: JP2001331421A
Authority: JP
Inventors: 博久諏訪部; 靖彦大坪; 博舟橋; 誠辻田; 久貴通阪
Original assignee: Hino Motors Ltd; Hitachi Metals Ltd
Current assignee: Hino Motors Ltd; Hitachi Metals Ltd
Priority date: 2001-10-29
Filing date: 2001-10-29
Publication date: 2005-11-16
Anticipated expiration: 2021-10-29
Also published as: JP2003126629A

Description

【０００１】
【発明の属する技術分野】
本発明は、例えば、デイーゼルエンジンから排出される排気ガスから微粒子を取り除くセラミックハニカム構造体に関するものである。
【０００２】
【従来の技術】
地域環境や地球環境の保全面から、自動車などのエンジンから排出される排気ガスに含まれる有害物質の削減が求められ、特に最近は、デイーゼルエンジンからの排気ガス中に含まれる微粒子を除去するために、ハニカム構造体の所定の貫通孔端部を排気ガスの流入側または流出側で交互に目封止したハニカム構造体からなるセラミックハニカムフィルタが使用されている。
【０００３】
図１は、排気ガス中の微粒子、特に黒鉛微粒子を捕捉するセラミックハニカムフィルタの使用
例の一例を示す要部の模式断面概略図である。通常セラミックハニカムフィルタ１１の端面外周の形状は略円形状で、その外周壁１１ａとこの外周壁１１ａの内周側に各々直交する隔壁１１ｂにより形成された複数の流路１１ｃを有し、この流路１１ｃの両端部が交互に流入側封止材１ａ、流出側封止材１ｂで封止されている。このセラミックハニカムフィルタ１１は、図１に示すように金属製収納容器１２内に、支持部材１４を介して圧着把持され、また、支持部材１３を介して貫通孔方向に挟持され、収納されている。ここで、支持部材は一般に金属メッシュ或いはセラミックス製のマットで形成されるが、使用条件に応じて併用される。
このような構造のセラミックハニカムフィルタでの排気ガス浄化作用は以下の通り行われる。先ず、流入側排気ガス２ａは収納容器１２に収納されたセラミックハニカムフィルタ１１の流入側端面の開口している流路１１ｃから流入し、矢印で示すように、隔壁１１ｂを通過し流出側排気ガス２ｂとして排気される。流入側排気ガス２ａが隔壁１１ｂを通過する際に、流入側排気ガス２ａに含まれる微粒子は、隔壁１１ｂに捕捉され、浄化された排気ガスが流出側排気ガス２ｂとして、大気中に放出される。隔壁１１ｂに捕捉された微粒子は一定量以上になるとフィルタの目詰まりが発生するため、バーナーや電気ヒーターにより燃焼させ、フィルタの再生が行われる。
【０００４】
上述のセラミックハニカムフィルタを金属製収納容器内に収納するための支持部材からの締め付け圧力により生じる、セラミックハニカムフィルの欠けや割れの問題を解決するため、特公平１−４７２０６号公報では、支持部材が当接する位置のセラミックハニカムフィルタの外周縁部の流体通路を充填材で充填したり、開口端面部を充填材で充填することによって、強度を改善したセラミックハニカムフィルタが開示されている。また、特公昭６３−２８８７号公報では、開口端部における所定の位置の貫通孔を特定のセラミック材料で封止し、かつ外周壁近傍の開口端面の貫通孔を少なくとも一方の端面で封止する開口端面封止方法が開示されている。
【０００５】
一方、フィルタ再生の際に、金属製収納容器１２から微粒子の燃焼熱の放散を防ぎ、フィルタ再生を良好に行わせる目的で、実開昭６０−１５９８１３号公報、実開昭６２−１０５３２０号公報、実開昭６３−２８８２０号公報、実開昭６４−１２６１４号公報、特開平５−１１８２１１号公報には、外周部に存在する各流路の両端部を目封止材により目封じし、該流路を保温空間とする技術が開示されている。
【０００６】
【発明が解決しようとする課題】
しかしながら、上記従来の技術に開示されている開口端面封止方法では、以下に示すような問題点があった。
特公平１−４７２０６号公報では、支持部材が当接する位置のセラミックハニカムフィルタ外周縁部の流体通路を充填材で充填していることから、セラミックハニカムフィルタの外周縁部の熱伝導性が良好となるが、外周壁は支持部材を介して金属製容器と接触し冷却されやすい構造となっているため、排気ガス中の微粒子を燃焼させる際に、充填材、外周壁を介して燃焼熱が金属製容器へ伝わりやすく、フィルタ中心部と外周部の温度勾配が過度に大きくなって熱歪によりフィルタの割れを招いたり、外周部での微粒子の燃焼除去が不完全となり耐久性や実用性の観点から好ましくなかった。
また、特公昭６３−２８８７５号公報では、外周部強化のため外周壁近傍の開口端面を封止している目封止材の長さが、第４図によればハニカム構造体の全長の約１０％であり、また実施例でも全長１５２ｍｍのハニカム構造体に対して、目封止部の長さは１５〜２５ｍｍ(全長対比９．９％〜１６．４％)であり、封止部の長さが全長に対して相対的に長いことから、排気ガス中の微粒子を燃焼させる際の燃焼熱がこの封止部を介して金属製容器へ放散され易くなるため、フィルタ中心部と外周部の温度勾配が過度に大きくなって熱歪によりフィルタの割れを招いたり、外周部での微粒子の燃焼除去が不完全となり耐久性や実用性の観点から好ましくなかった。
また、実開昭６０−１５９８１３号公報、実開昭６２−１０５３２０号公報、実開昭６３−２８８２０号公報、実開昭６４−１２６１４号公報に記載されている外周部に存在する各流路の両端部を目封止材により目封じし、該流路を保温空間とする技術では、目封止材の長さについては何ら記載がないことから、特公昭６３−２８８７５公報と同様に、排気ガス中の微粒子を燃焼させる際の熱エネルギーが目封止部を介して金属製容器へ放散され易くなり、フィルタの割れを招いたり、外周部での微粒子の燃焼除去が不完全となる場合があった。また、外周近くで両端が目封止された流路の数については、何ら記載がないことから、フィルタ機能を有する流路が実質的に減少し、フィルタの圧力損失が上昇するため、エンジン性能が低下するという問題の発生することもあった。
また、特開平５−１１８２１１号公報に記載されている、両端を目封止された断熱部の断面積の全断面積に対する割合を示す栓詰率を１０〜２０％としたフィルタでは、確かにフィルタ外周部からの金属製容器への熱拡散を防止でき、微粒子を効率よく燃焼除去できるものの、栓詰率が１０〜２０％と高いことから、フィルタ機能を有する流路が実質的に減少し、フィルタの圧力損失が上昇するため、エンジン性能が低下するという問題があった。
以上のように従来の技術では、外周壁近傍における両端が目封止された流路の断熱特性を利用しているが、再生時の微粒子除去が高効率で行え、しかも低圧力損失という、二つの特性を両立させたフィルタを得ることは、困難であった。
【０００７】
本発明の目的は、上記課題に鑑みてなされたもので、再生時の微粒子除去が高効率で行え、低圧力損失の特性を有するセラミックハニカムフィルタを提供することにある。
【０００８】
【課題を解決するための手段】
本発明者らは、セラミックハニカムフィルタの外周壁近傍の流路の断熱性及び隔壁の微粒子捕集特性に注目し、鋭意検討した結果、上記課題が解決できるとの知見を得、本発明に想到した。
すなわち、本発明のセラミックハニカムフィルタは、セラミックハニカム構造体の所定の流路端部を目封止し、該流路を区画する多孔質の隔壁に排気ガスを通過せしめることにより、排気ガス中に含まれる微粒子を除去するセラミックハニカムフィルタにおいて、外周壁近傍の流路が両端部において目封止材で目封止され、前記目封止材のフィルタ端面からの長さがセラミックハニカムフィルタの全長の８．２％以下であり、且つ、前記両端が目封止されている流路は、ハニカムフィルタ端面の外周壁からハニカムフィルタ端面の中心に向かって、最大５×（隔壁ピッチ）の長さの範囲に存在する流路であることを特徴とする。
このとき、前記外周壁近傍の流路を両端部で目封止した目封止材の端面からの長さはセラミックハニカムフィルタの全長の３．３％以下であることが好適である。
また、前記両端が目封止されている外周壁近傍の流路は、ハニカムフィルタ端面の外周壁からハニカムフィルタ端面の中心に向かって、最大３×（隔壁ピッチ）の長さの範囲に存在する流路であることが好適である。また、前記セラミックハニカムフィルタの外周壁は、厚さが０．３〜２．０ｍｍであり、コージェライト粒子と、それらの間に存在するコロイダルシリカとから構成されていることが好適である。
【０００９】
【作用】
本発明における作用効果について説明する。
本発明のセラミックハニカムフィルタは、外周壁近傍の流路が両端部において目封止材で目封止され、前記目封止材の端面からの長さをセラミックハニカムフィルタの全長の８．２％以下、且つ、前記両端が目封止されている流路は、ハニカムフィルタ端面の外周壁からハニカムフィルタ端面の中心に向かって、最大５×（隔壁ピッチ）の長さの範囲に存在する流路としている。このため、フィルタ外周壁から金属製容器の熱放散がなく、捕集された微粒子を効率よく燃焼除去でき、フィルタ再生率に優れている。更に、フィルタの圧力損失を最小限に押さえることができ、エンジン性能の低下を招くこともない。すなわち、流路の両端部を目封止している目封止材の端面の長さをフィルタ全長の８．２％以下としていることから、微粒子燃焼時の燃焼熱の目封止材を介しての金属製容器へ放散が無視できる程度に押さえることが可能になる。ここで目封止材の端面の長さがフィルタ全長の８．２％を越えると、微粒子燃焼時の燃焼熱の目封止材を介しての金属製容器へ放散が無視できなくなり、捕集された微粒子をの燃え残りが生じ、フィルタ再生率が低下する。また、両端が目封止されている流路が、ハニカムフィルタ端面の外周壁からハニカムフィルタ端面の中心に向かって、最大５×（隔壁ピッチ）の長さの範囲に存在する流路としていることから、フィルタの圧力損失を最小限に押さえることができる。ここで両端が目封止されている流路が、ハニカムフィルタ端面の外周壁からハニカムフィルタ端面の中心に向かって、最大５×（隔壁ピッチ）の長さの範囲を越えると、相対的にフィルタ機能を有する隔壁の割合が少なくなることから、フィルタの圧力損失が上昇するため、エンジンの排圧が上昇し、エンジン性能の低下を招く。
【００１０】
さらに、外周壁近傍の流路を両端部で目封止した目封止材の端面からの長さがセラミックハニカムフィルタの全長の３．３％以下とすることにより、外周部近傍の流路が断熱空気層として働く効果が大きくなり、フィルタ外周壁から金属製容器の熱放散が更に少なくなり、捕集された微粒子を効率よく燃焼除去でき、フィルタ再生率が更に優れるようになる。
【００１１】
また、前記両端が目封止されている外周壁近傍の流路を、ハニカムフィルタ端面の外周壁からハニカムフィルタ端面の中心に向かって、最大３×（隔壁ピッチ）の範囲に存在する流路であるとすることにより、フィルタの圧力損失を更に低減できるため、エンジンの排圧が低下し、エンジン性能が更に向上する。
【００１２】
また、セラミックハニカムフィルタの外周壁が、厚さが０．３〜２．０ｍｍであり、コージェライト粒子と、それらの間に存在するコロイダルシリカとから構成されていることが好適であるのは、該外周壁において、両端面を目封止された外周壁近傍の流路の断熱効果がいっそう有効になるからである。外周壁の厚さは、厚い方が断熱性からは好ましいが、２．０ｍｍを越えると、フィルタに熱衝撃が加わった際に外周壁の割れが発生しやすなり、また０．３ｍｍ未満では、断熱効果は得られないことから、０．３〜２ｍｍの範囲が好ましい。また、外周壁がコージェライト粒子と、それらの間に存在するコロイダルシリカとから構成されていると、外周壁がコージェライトセラミックス単独で構成されている場合に比べて、外周壁内におけるコージェライトの連続性が損なわれるため、熱が伝わりにくく、外周壁での断熱効果が更に改善されるからである。ここで、コージェライト粒子を使用するのは、熱膨張係数が小さく、耐熱衝撃に有利なためであり、一般に５０μｍ以下の平均粒径を有する焼成粉末である。またコロイダルシリカを使用するのはコージェライト粒子を結合して耐熱性を有する外周壁を形成するためである。外周壁には上記コージェライト粒子とコロイダルシリカ以外にも、耐熱性や強度を損なわない範囲で、セラミックファイバー、水ガラス、アルミナセメント、コロイダルアルミナ等を適宜添加しても良い。
【００１３】
【００１４】
【発明の実施の形態】
以下、本発明を実施の形態により説明する。
図２に本発明によるセラミックハニカムフィルタの端面の模式図を示す。また、図３に本発明によるセラミックハニカムフィルタの流路方向の断面模式図を示す。仮想線１５は外周壁に対して端面中心に向かって２×（隔壁ピッチ）の長さだけ小さい輪郭を示し、仮想線１５と外周壁との間に存在する流路は両端で目封止されている。ここで、目封止材の流路への充填は、公知の技術、例えば、目封止材スラリーを準備した後、ハニカム構造体の流路における一端側の所定の開口端部を樹脂製マスクにより閉塞し、当該ハニカム構造体の一端側に所定の深さが得られるようにスラリーを浸積し、スラリーが乾燥した後に、樹脂製マスクを除去し、さらに目封止材の焼成を行うことにより行われる。
ここで本発明の実施の形態は図２乃至３の形状に限定されるものでなく、例えば、両端部で目封止された流路の目封止長さが、セラミックハニカムフィルタの全長の８．２％を越えない範囲で、且つ、前記両端が目封止されている流路は、ハニカムフィルタ端面の外周壁からハニカムフィルタ端面の中心に向かって、最大５×（隔壁ピッチ）の長さの範囲に存在する流路であれば、図４に示す他の発明例の形状でも、外周壁近傍で両端を目封止された流路が断熱空気層として働くため、フィルタ外周壁から金属製容器の熱放散がなく、捕集された微粒子を効率よく燃焼除去できると共に、フィルタの圧力損失を最小限に押さえることができるため、エンジン性能の低下を防ぐことができる。
【００１５】
また、本発明のセラミックハニカムフィルタを構成する材料としては、本発明が主としてディーゼルエンジンから排出される排ガスを対象とするため、耐熱性の良い材料を使用することが好ましい。このためコージェライト、ムライト、アルミナ、窒化珪素、炭化珪素、LAS等を主結晶相とするセラミック材料を用いることが好ましいが、中でもコージェライトを主結晶相とするセラミックハニカムフィルタは、安価で耐熱性に優れ、化学的にも安定なため最も好ましい。
【００１６】
また本発明のセラミックハニカムフィルタは従来技術で示したように交互再生方式に適用できるのは勿論のこと、貴金属触媒との組合せにより微粒子を連続的に燃焼させる、連続再生式のセラミックハニカムフィルタに適用できることは言うまでもない。
【００１７】
（実施例１）
コージェライト化原料を混合、混練し、公知の押出成形法によりハニカム構造体を成形した後、１４００℃で焼成を行い、外径２６７ｍｍ、長さ３０５ｍｍ、隔壁の厚さが０．３ｍｍ、隔壁のピッチが１．４７ｍｍ、外周壁の厚さが１．５ｍｍであるコージェライト質セラミックハニカム焼成体を得た。次いで、セラミックハニカム構造体の流路端部を交互に目封止がなされると共に、外周壁近傍の流路に対しては両端部が目封止されるように公知の技術により、コージェライト化原料からなる目封止材スラリーを充填した後、目封止材スラリーの乾燥、焼成を行い、各種コージェライト質セラミックハニカムフィルタを得た。この際、外周部近傍の両端を目封止された目封止材の各種長さ及び端面における各種範囲が得られるよう目封止スラリーの充填条件を調整した。これらのセラミックハニカムフィルタに対して、ディーゼルエンジンから排出される微粒子を捕捉させた後、微粒子を燃焼除去した後の質量再生率及び、圧力損失の評価を行った。結果を表１に示す。表１において、両端部目封止部の目封止長さ比とは、（外周壁近傍の流路を両端部で目封止した目封止材の端面からの長さ）×１００／（フィルタの全長）のことであり、本実施例ではフィルタ全長は３０５ｍｍである。また端面における両端目封止部の範囲とは、両端が目封止された流路の存在する範囲を、端面における外周壁からの中心に向かう長さで示したものである。
【００１８】
ここで質量再生率とは、（捕捉量−再生後の燃え残り量）×１００／（捕捉量）（％）のことを示す。試験結果は、質量再生率が８０％以上の場合を合格（○）とし、更に９０％以上の好ましい場合を（◎）とし、８０％未満の場合を不合格（×）で示した。
一方、圧力損失は、圧力損失テストスタンドにて、空気流量７．５Ｎｍ^３／ｍｉｎの時のハニカムフィルタ流入前と流出後の圧力損失で評価を行い、２５０ｍｍＡｑ以下の圧力損失であれば合格（○）とし、更に好ましい２００ｍｍＡｑ以下の場合は（◎）で、２５０ｍｍＡｑを超える圧力損失であれば不合格とし（×）で示した。そして、総合判定として、質量再生率、圧力損失のいずれも合格であるものを（○）、そのうち両者とも（◎）であるものを（◎）、いずれかに（×）があるものを（×）で評価した。
【００１９】
表１に示す結果のうち、試験ＮＯ．１〜５は、本発明例であり、外周部近傍の流路を両端部で目封止した目封止材の長さがセラミックハニカムフィルタ全長の８．２％以下であり、両端が目封止されている外周壁近傍の流路が、ハニカムフィルタ端面の外周壁から端面の中心に向かって最大５×（隔壁ピッチ）の範囲内にあることから、質量再生率、圧力損失とも（○）或いは（◎）で合格し、総合判定はいずれも合格であった。特に、試験ＮＯ．４は、外周部近傍の流路を両端部で目封止した目封止材の長さがセラミックハニカムフィルタ全長の３．３％以下であり、両端が目封止されている外周壁近傍の流路が、ハニカムフィルタ端面の外周壁から端面の中心に向かって最大３×（隔壁ピッチ）の範囲のより好ましい範囲であることから、質量再生率、圧力損失とも（◎）判定で、総合判定（◎）であった。試験ＮＯ．６〜８は、本発明の比較例であり、外周部近傍の流路を両端部で目封止した目封止材の長さがセラミックハニカムフィルタ全長の８．２％を超えていることから、微粒子燃焼時に、この目封止材を介しての燃焼熱の放散が大きくなり、質量再生率の判定が不合格（×）となり、総合判定は（×）であった。また、試験ＮＯ．９は本発明の比較例で、両端が目封止されている外周壁近傍の流路が、ハニカムフィルタ端面の外周壁から端面の中心に向かって最大５×（隔壁ピッチ）の範囲を超えた領域にも存在することから、外周壁近傍の両端を目封止された流路による断熱効果が大きくなり、質量再生率の判定は（◎）であったが、フィルタ機能を有する流路の数が実質的に減少することから、圧力損失の判定が不合格（×）となり、総合判定は不合格（×）であった。更に、試験ＮＯ．１０は、本発明の比較例で、外周壁近傍に両端部を目封止された流路のないフィルタの例であるが、外周壁近傍の流路による断熱効果が得られないため、質量再生率の判定が不合格（×）となり、総合判定は不合格（×）であった。
【００２０】
（実施例２）
実施例１と同様の方法により、コージェライト化原料を混合、混練し、公知の押出成形法によりハニカム構造体を成形した後、両端部の所定の流路に目封止を行い、１４００℃で焼成を行い、セラミックハニカム焼成体を得た。その後、この焼成体の周縁部を加工により除去し、加工後の外周面に、平均粒径１５μｍのコージェライト骨材１００質量部に対してコロイダルシリカを１０質量部加え、更にバインダー、水などを加えて調整したコージェライト質スラリーを塗布して外周壁を形成した。その後、外周壁の乾燥、焼成を行い、外径２６７ｍｍ、長さ３０５ｍｍ、隔壁の厚さが０．３ｍｍ、隔壁のピッチが１．４７ｍｍ、外周壁の厚さが１．５ｍｍである、表１の試験ＮＯ．１１、１２に示すコージェライト質セラミックハニカムフィルタを得た。これらに対して実施例１と同様の、質量再生率、圧力損失の評価を行った結果を、表１に示す。試験ＮＯ．１１、１２は、本発明例であり、外周部近傍の流路を両端部で目封止した目封止材の長さがセラミックハニカムフィルタ全長の８．２％以下であり、両端が目封止されている外周壁近傍の流路が、ハニカムフィルタ端面の外周壁から端面の中心に向かって最大５×（隔壁ピッチ）の範囲内にあることから、質量再生率、圧力損失とも（○）或いは（◎）で合格し、総合判定はいずれも合格であった。
【００２１】
【表１】

【００２２】
以上、本発明につき、実施の形態及び、実施例１〜２をもとに説明したが、本発明は上記発明例に限定されず、技術思想の範囲で応用可能である。例えば、セラミックハニカム構造体の外周形状は、円形でなくとも、楕円など他の形状にも適用可能である。
【００２３】
【発明の効果】
以上詳細に説明のとおり、本発明のセラミックハニカムフィルタは、フィルタの外周壁近傍に両端を目封止材で目封止した流路を設けており、しかもこの目封止材の長さ、端面における存在する範囲を詳細に規定しているため、フィルタ外周部からの放熱がほとんどなく、捕集された微粒子を効率よく燃焼除去でき、フィルタの再生特性が優れている。更に、フィルタの圧力損失を最小限に押さえることができ、エンジン性能の低下を防ぐことができる。
【図面の簡単な説明】
【図１】従来のセラミックハニカムフィルタの一例の断面模式図である。
【図２】本発明のセラミックハニカムフィルタの一例の端面の正面図である。
【図３】本発明のセラミックハニカムフィルタの一例の模式概略断面図である。
【図４】本発明のセラミックハニカムフィルタの他の例の模式概略断面図である。
【符号の説明】
１ａ流入側目封止材
１ｂ流出側目封止材
２ａ流入側排気ガス
２ｂ流出側排気ガス
１１セラミックハニカムフィルタ
１１ａ外周壁
１１ｂ隔壁
１１ｃ流路
１２収納容器
１３ａ、１３ｂ支持部材
１４支持部材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ceramic honeycomb structure for removing fine particles from exhaust gas discharged from, for example, a diesel engine.
[0002]
[Prior art]
In order to protect the local environment and the global environment, it is necessary to reduce harmful substances contained in exhaust gas emitted from engines such as automobiles. Recently, in order to remove particulates contained in exhaust gas from diesel engines. In addition, a ceramic honeycomb filter having a honeycomb structure in which predetermined end portions of through holes of the honeycomb structure are alternately plugged on the exhaust gas inflow side or the outflow side is used.
[0003]
FIG. 1 is a schematic cross-sectional schematic view of an essential part showing an example of use of a ceramic honeycomb filter that captures fine particles in exhaust gas, particularly graphite fine particles. Usually, the shape of the outer periphery of the end face of the ceramic honeycomb filter 11 is substantially circular, and has a plurality of flow paths 11c formed by the outer peripheral wall 11a and the partition walls 11b orthogonal to the inner peripheral side of the outer peripheral wall 11a. Both ends of the path 11c are alternately sealed with the inflow side sealing material 1a and the outflow side sealing material 1b. As shown in FIG. 1, the ceramic honeycomb filter 11 is crimped and held in a metal storage container 12 through a support member 14 and is sandwiched and stored in a through-hole direction through a support member 13. . Here, the support member is generally formed of a metal mesh or a ceramic mat, and is used in combination according to use conditions.
The exhaust gas purification action of the ceramic honeycomb filter having such a structure is performed as follows. First, the inflow side exhaust gas 2a flows in from the flow path 11c opened in the end surface of the inflow side of the ceramic honeycomb filter 11 housed in the storage container 12, passes through the partition wall 11b as shown by the arrow, and flows into the outflow side exhaust gas. Exhaust as 2b. When the inflow side exhaust gas 2a passes through the partition wall 11b, the particulates contained in the inflow side exhaust gas 2a are captured by the partition wall 11b, and the purified exhaust gas is released into the atmosphere as the outflow side exhaust gas 2b. . When the amount of the fine particles trapped in the partition wall 11b exceeds a certain amount, the filter is clogged. Therefore, the filter is regenerated by burning it with a burner or an electric heater.
[0004]
In order to solve the problem of chipping or cracking of the ceramic honeycomb fill caused by the tightening pressure from the support member for storing the ceramic honeycomb filter in the metal storage container, Japanese Patent Publication No. 1-47206 discloses a support member. There has been disclosed a ceramic honeycomb filter having improved strength by filling the fluid passage at the outer peripheral edge of the ceramic honeycomb filter at a position where the filter contacts with the filler, or filling the opening end face with the filler. In Japanese Patent Publication No. 63-2887, a through-hole at a predetermined position in the opening end is sealed with a specific ceramic material, and a through-hole in the opening end face near the outer peripheral wall is sealed with at least one end face. An opening end face sealing method is disclosed.
[0005]
On the other hand, for the purpose of preventing the release of the combustion heat of the fine particles from the metal container 12 during the filter regeneration, and performing the filter regeneration satisfactorily, Japanese Utility Model Laid-Open Nos. 60-159813 and 62-105320 are disclosed. In Japanese Utility Model Laid-Open No. 63-28820, Japanese Utility Model Laid-Open No. 64-12614, and Japanese Patent Laid-Open No. 5-118211, both ends of each flow path existing in the outer peripheral portion are plugged with a plugging material, A technique for making the flow path a heat insulation space is disclosed.
[0006]
[Problems to be solved by the invention]
However, the open end face sealing method disclosed in the above prior art has the following problems.
In Japanese Examined Patent Publication No. 1-44726, since the fluid passage in the outer peripheral edge of the ceramic honeycomb filter at the position where the support member abuts is filled with a filler, the thermal conductivity of the outer peripheral edge of the ceramic honeycomb filter is good. However, since the outer peripheral wall is in contact with the metal container via the support member and is easily cooled, when the particulates in the exhaust gas are burned, the combustion heat is transferred to the metal through the filler and the outer peripheral wall. From the viewpoint of durability and practicality, the temperature gradient between the filter center and the outer periphery becomes excessively large, causing the filter to crack due to thermal strain, and the removal of fine particles on the outer periphery is incompletely removed. It was not preferable.
Further, in Japanese Patent Publication No. 63-28875, the length of the plugging material sealing the opening end surface in the vicinity of the outer peripheral wall for reinforcing the outer peripheral portion is about the total length of the honeycomb structure according to FIG. 10%, and in the examples, the length of the plugged portion is 15 to 25 mm (9.9% to 16.4% compared to the full length) with respect to the honeycomb structure having a total length of 152 mm. Since the length is relatively long with respect to the overall length, the heat of combustion when the particulates in the exhaust gas are burned is easily dissipated to the metal container through this sealing portion, so that the filter center portion and the outer peripheral portion The temperature gradient becomes excessively large, causing cracking of the filter due to thermal distortion, and incomplete combustion removal of fine particles at the outer peripheral portion, which is not preferable from the viewpoint of durability and practicality.
Further, each flow path existing in the outer peripheral portion described in Japanese Utility Model Laid-Open No. 60-159913, Japanese Utility Model Laid-Open No. 62-105320, Japanese Utility Model Laid-Open No. 63-28820, Japanese Utility Model Laid-Open No. 64-12614. In the technology in which both end portions of the plug are plugged with a plugging material and the flow path is used as a heat retaining space, there is no description about the length of the plugging material, so as in Japanese Patent Publication No. 63-28875, When the heat energy when burning particulates in the exhaust gas is easily dissipated to the metal container via the plugging part, causing cracks in the filter or incomplete combustion removal of the particulates at the outer periphery was there. In addition, since there is no description about the number of the channels whose both ends are plugged near the outer periphery, the number of channels having a filter function is substantially reduced, and the pressure loss of the filter is increased. In some cases, the problem of decrease in the amount of the problem occurred.
In addition, in the filter described in JP-A-5-118211, a filter with a plugging rate of 10 to 20% indicating the ratio of the cross-sectional area of the heat insulating portion plugged at both ends to the total cross-sectional area is surely Although heat diffusion from the outer periphery of the filter to the metal container can be prevented and fine particles can be burned and removed efficiently, the plugging rate is as high as 10 to 20%. Since the pressure loss of the filter increases, there is a problem that the engine performance is deteriorated.
As described above, the conventional technique uses the heat insulating property of the flow path in which both ends in the vicinity of the outer peripheral wall are plugged. However, the particulate removal at the time of regeneration can be performed with high efficiency and low pressure loss. It has been difficult to obtain a filter having both characteristics.
[0007]
An object of the present invention is to provide a ceramic honeycomb filter that can efficiently remove fine particles during regeneration and has low pressure loss characteristics.
[0008]
[Means for Solving the Problems]
As a result of diligent investigations, the inventors have obtained the knowledge that the above problems can be solved, and arrived at the present invention, paying attention to the heat insulating properties of the flow path near the outer peripheral wall of the ceramic honeycomb filter and the particulate collection characteristics of the partition walls. did.
That is, the ceramic honeycomb filter of the present invention plugs the end of a predetermined flow path of the ceramic honeycomb structure and allows the exhaust gas to pass through the porous partition walls that define the flow path, thereby In the ceramic honeycomb filter for removing the contained fine particles, the flow path in the vicinity of the outer peripheral wall is plugged with plugging material at both ends, and the length of the plugging material from the filter end surface is equal to the total length of the ceramic honeycomb filter. The flow path which is 8.2% or less and whose both ends are plugged has a maximum length of 5 × (partition pitch) from the outer peripheral wall of the honeycomb filter end face toward the center of the honeycomb filter end face. It is a flow path existing in the range.
At this time, it is preferable that the length from the end face of the plugging material in which the flow path in the vicinity of the outer peripheral wall is plugged at both ends is 3.3% or less of the total length of the ceramic honeycomb filter.
Further, the flow path in the vicinity of the outer peripheral wall whose both ends are plugged exists in a range of a maximum length of 3 × (partition wall pitch) from the outer peripheral wall of the honeycomb filter end face toward the center of the honeycomb filter end face. A channel is preferred. The outer peripheral wall of the ceramic honeycomb filter has a thickness of 0.3 to 2.0 mm, and is preferably composed of cordierite particles and colloidal silica existing therebetween.
[0009]
[Action]
The effect in this invention is demonstrated.
In the ceramic honeycomb filter of the present invention, the flow path near the outer peripheral wall is plugged with plugging material at both ends, and the length from the end surface of the plugging material is 8.2% of the total length of the ceramic honeycomb filter. In the following, the flow path in which both ends are plugged is a flow path existing in a range of a maximum length of 5 × (partition wall pitch) from the outer peripheral wall of the honeycomb filter end face toward the center of the honeycomb filter end face. It is said. For this reason, there is no heat dissipation of the metal container from the filter outer peripheral wall, the collected fine particles can be efficiently burned and removed, and the filter regeneration rate is excellent. Furthermore, the pressure loss of the filter can be minimized, and the engine performance is not degraded. That is, since the length of the end face of the plugging material plugging the both ends of the flow path is 8.2% or less of the total length of the filter, the plugging material of the combustion heat at the time of particulate combustion is used. All metal containers can be suppressed to a level where radiation can be ignored. Here, if the length of the end face of the plugging material exceeds 8.2% of the total length of the filter, the diffusion of the combustion heat during the combustion of the fine particles to the metal container through the plugging material cannot be ignored and collected. Burnout of the generated fine particles occurs, and the filter regeneration rate decreases. Further, the flow path whose both ends are plugged is a flow path that exists within a maximum length of 5 × (partition wall pitch) from the outer peripheral wall of the honeycomb filter end face toward the center of the honeycomb filter end face. Therefore, the pressure loss of the filter can be minimized. When the flow path whose both ends are plugged exceeds the range of a maximum length of 5 × (partition wall pitch) from the outer peripheral wall of the honeycomb filter end face toward the center of the honeycomb filter end face, the filter is relatively Since the ratio of the partition having the function is reduced, the pressure loss of the filter is increased, so that the exhaust pressure of the engine is increased and the engine performance is deteriorated.
[0010]
Further, the length from the end face of the plugging material in which the channel near the outer peripheral wall is plugged at both ends is 3.3% or less of the total length of the ceramic honeycomb filter, so that the channel near the outer periphery is The effect of acting as an adiabatic air layer is increased, the heat dissipation of the metal container from the filter outer peripheral wall is further reduced, the collected fine particles can be efficiently burned and removed, and the filter regeneration rate is further improved.
[0011]
Further, the flow path in the vicinity of the outer peripheral wall whose both ends are plugged is a flow path existing in a range of 3 × (partition wall pitch) from the outer peripheral wall of the honeycomb filter end face toward the center of the honeycomb filter end face. As a result, the pressure loss of the filter can be further reduced, so that the exhaust pressure of the engine is lowered and the engine performance is further improved.
[0012]
In addition, it is preferable that the outer peripheral wall of the ceramic honeycomb filter has a thickness of 0.3 to 2.0 mm and is composed of cordierite particles and colloidal silica existing therebetween. This is because, in the outer peripheral wall, the heat insulating effect of the flow path in the vicinity of the outer peripheral wall whose both end faces are plugged is more effective. As for the thickness of the outer peripheral wall, it is preferable from the viewpoint of heat insulation, but if it exceeds 2.0 mm, the outer wall tends to crack when a thermal shock is applied to the filter, and if it is less than 0.3 mm, Since the heat insulation effect cannot be obtained, a range of 0.3 to 2 mm is preferable. Further, when the outer peripheral wall is composed of cordierite particles and colloidal silica existing between them, the cordierite in the outer peripheral wall is compared with the case where the outer peripheral wall is composed of cordierite ceramics alone. This is because the continuity is impaired, so that heat is not easily transmitted and the heat insulating effect on the outer peripheral wall is further improved. Here, cordierite particles are used because they have a small thermal expansion coefficient and are advantageous for thermal shock, and are generally fired powders having an average particle size of 50 μm or less. The colloidal silica is used because the outer peripheral wall having heat resistance is formed by bonding the cordierite particles. In addition to the cordierite particles and colloidal silica, ceramic fibers, water glass, alumina cement, colloidal alumina, and the like may be appropriately added to the outer peripheral wall as long as the heat resistance and strength are not impaired.
[0013]
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to embodiments.
FIG. 2 is a schematic view of the end face of the ceramic honeycomb filter according to the present invention. FIG. 3 is a schematic sectional view of the ceramic honeycomb filter according to the present invention in the flow path direction. The imaginary line 15 has a contour that is smaller by a length of 2 × (partition wall pitch) toward the center of the end surface than the outer peripheral wall, and the flow path existing between the imaginary line 15 and the outer peripheral wall is plugged at both ends. ing. Here, the plugging material is filled into the flow path by a known technique, for example, after preparing a plugging material slurry, a predetermined opening end on one end side in the flow path of the honeycomb structure is made of a resin mask. The slurry is immersed so as to obtain a predetermined depth on one end side of the honeycomb structure, and after the slurry is dried, the resin mask is removed, and the plugging material is fired. Is done.
Here, the embodiment of the present invention is not limited to the shape of FIGS. 2 to 3. For example, the plugged length of the flow path plugged at both ends is 8 of the total length of the ceramic honeycomb filter. The flow path in which both ends are plugged within a range not exceeding 2% is a maximum length of 5 × (partition wall pitch) from the outer peripheral wall of the honeycomb filter end face toward the center of the honeycomb filter end face. 4, even in the shape of another example of the invention shown in FIG. 4, since the flow path plugged at both ends near the outer peripheral wall works as a heat insulating air layer, the filter is made of metal from the outer peripheral wall. There is no heat dissipation of the container, and the collected fine particles can be burned and removed efficiently, and the pressure loss of the filter can be suppressed to the minimum, so that a decrease in engine performance can be prevented.
[0015]
Moreover, as a material which comprises the ceramic honeycomb filter of this invention, since this invention mainly targets the exhaust gas discharged | emitted from a diesel engine, it is preferable to use a material with good heat resistance. For this reason, it is preferable to use a ceramic material whose main crystal phase is cordierite, mullite, alumina, silicon nitride, silicon carbide, LAS, etc. Among them, ceramic honeycomb filters whose main crystal phase is cordierite are inexpensive and heat resistant. It is most preferable because it is excellent in chemical stability and chemically stable.
[0016]
In addition, the ceramic honeycomb filter of the present invention can be applied to an alternating regeneration system as shown in the prior art, as well as to a continuously regenerative ceramic honeycomb filter in which fine particles are continuously burned in combination with a noble metal catalyst. Needless to say, you can.
[0017]
(Example 1)
A cordierite-forming raw material is mixed and kneaded, and a honeycomb structure is formed by a known extrusion molding method, followed by firing at 1400 ° C., an outer diameter of 267 mm, a length of 305 mm, a partition wall thickness of 0.3 mm, A cordierite ceramic honeycomb fired body having a pitch of 1.47 mm and an outer peripheral wall thickness of 1.5 mm was obtained. Next, the ends of the channels of the ceramic honeycomb structure are alternately plugged, and the both ends of the channels near the outer peripheral wall are plugged by a known technique. After filling the plugging material slurry made of the raw material, the plugging material slurry was dried and fired to obtain various cordierite ceramic honeycomb filters. At this time, the filling conditions of the plugging slurry were adjusted so that various lengths of plugging materials plugged at both ends in the vicinity of the outer peripheral portion and various ranges at the end surfaces were obtained. These ceramic honeycomb filters were evaluated for mass regeneration rate and pressure loss after capturing fine particles discharged from a diesel engine and then burning and removing the fine particles. The results are shown in Table 1. In Table 1, the plugging length ratio of both end plugged portions is (the length from the end face of the plugging material in which the channel near the outer peripheral wall is plugged at both ends) × 100 / ( The total length of the filter is 305 mm in this embodiment. Further, the range of the both end plugged portions on the end face indicates the range where the flow path having both ends plugged exists by the length from the outer peripheral wall to the center of the end face.
[0018]
Here, the mass regeneration rate means (captured amount−burning residual amount after regeneration) × 100 / (captured amount) (%). As a result of the test, the case where the mass regeneration rate was 80% or more was determined to be acceptable (◯), the case where 90% or more was preferable was evaluated as (◎), and the case where it was less than 80% was indicated as rejected (×).
On the other hand, the pressure loss is evaluated by the pressure loss before and after the inflow of the honeycomb filter when the air flow rate is 7.5 Nm ³ / min at the pressure loss test stand. In the case of 200 mmAq or less, (◎), and a pressure loss exceeding 250 mmAq is rejected and indicated by (x). And as a comprehensive judgment, (○) indicates that both the mass regeneration rate and the pressure loss are acceptable, (◎) indicates that both are (◎), and (×) indicates that either has (×). ).
[0019]
Of the results shown in Table 1, test NO. 1 to 5 are examples of the present invention. The length of the plugging material obtained by plugging the flow path in the vicinity of the outer periphery at both ends is 8.2% or less of the total length of the ceramic honeycomb filter, and both ends are plugged. Since the flow path in the vicinity of the stopped outer peripheral wall is within a range of 5 × (partition wall pitch) from the outer peripheral wall of the end face of the honeycomb filter toward the center of the end face, both the mass regeneration rate and the pressure loss (◯) Or it passed by ((double-circle)) and all the comprehensive determinations were pass. In particular, test NO. 4, the length of the plugging material in which the flow path in the vicinity of the outer peripheral portion is plugged at both ends is 3.3% or less of the total length of the ceramic honeycomb filter, and the length in the vicinity of the outer peripheral wall in which both ends are plugged Since the flow path is a more preferable range of a maximum 3 × (partition wall pitch) from the outer peripheral wall of the end face of the honeycomb filter toward the center of the end face, both mass regeneration rate and pressure loss are judged by (（) judgment and comprehensive judgment (◎). Test NO. 6 to 8 are comparative examples of the present invention, and the length of the plugging material obtained by plugging the flow path in the vicinity of the outer peripheral portion at both ends exceeds 8.2% of the total length of the ceramic honeycomb filter. During the combustion of fine particles, the diffusion of the combustion heat through the plugging material was increased, the mass regeneration rate was judged to be unacceptable (x), and the overall judgment was (x). Test NO. 9 is a comparative example of the present invention, and the flow path in the vicinity of the outer peripheral wall plugged at both ends exceeded the range of 5 × (partition wall pitch) at the maximum from the outer peripheral wall of the end face of the honeycomb filter toward the center of the end face. Since it also exists in the region, the heat insulation effect due to the channels plugged at both ends in the vicinity of the outer peripheral wall is increased, and the mass regeneration rate was judged as (◎), but the number of channels having a filter function Was substantially reduced, the pressure loss judgment was rejected (x), and the comprehensive judgment was rejected (x). Furthermore, test NO. 10 is a comparative example of the present invention, which is an example of a filter having no flow path in which both end portions are plugged in the vicinity of the outer peripheral wall. However, since the heat insulating effect by the flow path in the vicinity of the outer peripheral wall cannot be obtained, The rate judgment was rejected (x), and the overall judgment was rejected (x).
[0020]
(Example 2)
The cordierite-forming raw materials are mixed and kneaded by the same method as in Example 1, and after forming a honeycomb structure by a known extrusion molding method, plugging is performed on predetermined flow paths at both ends, at 1400 ° C. Firing was performed to obtain a ceramic honeycomb fired body. Thereafter, the peripheral edge of the fired body is removed by processing, and 10 parts by weight of colloidal silica is added to 100 parts by weight of cordierite aggregate having an average particle size of 15 μm on the outer peripheral surface after processing, and further, binder, water, and the like are added. In addition, an adjusted cordierite slurry was applied to form an outer peripheral wall. Thereafter, the outer peripheral wall was dried and fired, the outer diameter was 267 mm, the length was 305 mm, the partition wall thickness was 0.3 mm, the partition wall pitch was 1.47 mm, and the outer wall thickness was 1.5 mm. Test NO. Cordierite ceramic honeycomb filters shown in Nos. 11 and 12 were obtained. Table 1 shows the results of evaluating the mass regeneration rate and pressure loss in the same manner as in Example 1. Test NO. 11 and 12 are examples of the present invention. The length of the plugging material obtained by plugging the flow path in the vicinity of the outer peripheral portion at both ends is 8.2% or less of the total length of the ceramic honeycomb filter, and both ends are plugged. Since the flow path in the vicinity of the stopped outer peripheral wall is within a range of 5 × (partition wall pitch) from the outer peripheral wall of the end face of the honeycomb filter toward the center of the end face, both the mass regeneration rate and the pressure loss (◯) Or it passed by ((double-circle)) and all the comprehensive determinations were pass.
[0021]
[Table 1]

[0022]
As mentioned above, although this invention was demonstrated based on embodiment and Examples 1-2, this invention is not limited to the said invention example, It can apply in the range of a technical idea. For example, the outer peripheral shape of the ceramic honeycomb structure can be applied to other shapes such as an ellipse as well as a circular shape.
[0023]
【The invention's effect】
As described above in detail, the ceramic honeycomb filter of the present invention is provided with a flow path having both ends plugged with plugging material in the vicinity of the outer peripheral wall of the filter, and the length and end face of the plugging material. Since the range existing in is defined in detail, there is almost no heat radiation from the outer periphery of the filter, and the collected particulates can be burned and removed efficiently, and the regeneration characteristics of the filter are excellent. Furthermore, the pressure loss of the filter can be suppressed to a minimum, and the engine performance can be prevented from deteriorating.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an example of a conventional ceramic honeycomb filter.
FIG. 2 is a front view of an end face of an example of the ceramic honeycomb filter of the present invention.
FIG. 3 is a schematic cross-sectional view of an example of a ceramic honeycomb filter of the present invention.
FIG. 4 is a schematic cross-sectional view of another example of the ceramic honeycomb filter of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1a Inflow side plugging material 1b Outflow side plugging material 2a Inflow side exhaust gas 2b Outflow side exhaust gas 11 Ceramic honeycomb filter 11a Outer peripheral wall 11b Partition wall 11c Channel 12

Storage container

13a, 13b Support member 14 Support member

Claims

In a ceramic honeycomb filter for removing fine particles contained in exhaust gas by plugging a predetermined flow path end of the ceramic honeycomb structure and allowing the exhaust gas to pass through a porous partition wall defining the flow path The flow path near the outer peripheral wall is plugged with plugging material at both ends, and the length of the plugging material from the filter end surface is 8.2% or less of the total length of the ceramic honeycomb filter, and The flow path in which both ends are plugged is a flow path that exists in a range of a maximum length of 5 × (partition wall pitch) from the outer peripheral wall of the honeycomb filter end face toward the center of the honeycomb filter end face. A featured ceramic honeycomb filter.

The length from the end surface of the plugging material in which the flow path near the outer peripheral wall is plugged at both ends is 3.3% or less of the total length of the ceramic honeycomb filter. Ceramic honeycomb filter.

The flow path in the vicinity of the outer peripheral wall that is plugged at both ends is a flow path that exists within a maximum length of 3 × (partition wall pitch) from the outer peripheral wall of the honeycomb filter end face toward the center of the honeycomb filter end face. The ceramic honeycomb filter according to claim 1 or 2, wherein:

The outer peripheral wall of the ceramic honeycomb filter has a thickness of 0.3 to 2.0 mm, from claim 1, characterized in that it is composed of a cordierite particles, and colloidal silica present between them 4. The ceramic honeycomb filter according to any one of 3 above.