JP2006016991A - Exhaust gas cleaning filter - Google Patents

Exhaust gas cleaning filter Download PDF

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JP2006016991A
JP2006016991A JP2004193323A JP2004193323A JP2006016991A JP 2006016991 A JP2006016991 A JP 2006016991A JP 2004193323 A JP2004193323 A JP 2004193323A JP 2004193323 A JP2004193323 A JP 2004193323A JP 2006016991 A JP2006016991 A JP 2006016991A
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cell
exhaust gas
pore diameter
cell partition
average pore
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JP4285342B2 (en
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Tatsuji Mizuno
達司 水野
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Toyota Motor Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To suppress an increase in back pressure and erosion of a filter by controlling deposition of PMs in the pore while efficiently collecting PMs. <P>SOLUTION: An average pore diameter of a cell partition in an outer periphery is set smaller than that of a cell partition in an inner periphery. Since PMs having a considerably large diameter with respect to the pore diameter never flow in the pore, a blockage of the opening of the pore can be prevented, thereby controlling the deposition of PMs. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

本発明は、ディーゼルエンジンの排気流路などに装着され、排ガス中の粒子状物質(PM)を捕集して排出を抑制する排ガス浄化フィルタに関する。   The present invention relates to an exhaust gas purification filter that is attached to an exhaust passage of a diesel engine or the like and collects particulate matter (PM) in exhaust gas to suppress emission.

ガソリンエンジンについては、排ガスの厳しい規制とそれに対処できる技術の進歩とにより、排ガス中の有害成分は確実に減少している。しかし、ディーゼルエンジンについては、有害成分がPMとして排出されるという特異な事情から、規制も技術の進歩もガソリンエンジンに比べて遅れている。   As for gasoline engines, toxic components in exhaust gas are steadily decreasing due to strict regulations on exhaust gas and technological advances that can cope with it. However, with regard to diesel engines, regulations and technological advances are delayed compared to gasoline engines due to the unique situation that harmful components are emitted as PM.

現在までに開発されているディーゼルエンジン用排ガス浄化装置としては、大きく分けてトラップ型の排ガス浄化装置と、オープン型の排ガス浄化装置とが知られている。このうちトラップ型の排ガス浄化装置としては、コーディエライトなどのセラミック製の目封じタイプのDPFが知られている。このDPFは、セラミックハニカム構造体の複数のセルが、排ガス下流端が目詰めされた流入側セルと、流入側セルに隣接し排ガス上流端が目詰めされた流出側セルと、からなる複数のセルをもつものであり、セル隔壁の細孔で排ガスを濾過してセル隔壁にPMを捕集することで排出を抑制するいわゆるウォールフロー型のものである。   2. Description of the Related Art As an exhaust gas purification device for a diesel engine that has been developed so far, a trap type exhaust gas purification device and an open type exhaust gas purification device are known. Among these, as a trap type exhaust gas purifying apparatus, a ceramic plugged DPF such as cordierite is known. In this DPF, a plurality of cells of the ceramic honeycomb structure are composed of an inflow side cell in which the exhaust gas downstream end is clogged and an outflow side cell adjacent to the inflow side cell and clogged in the exhaust gas upstream end. It has a cell, and is a so-called wall flow type that suppresses discharge by filtering exhaust gas through the pores of the cell partition and collecting PM in the cell partition.

しかしDPFでは、PMの堆積によって圧損が上昇するため、何らかの手段で堆積したPMを定期的に除去して再生する必要がある。そこで従来は、圧損が上昇した場合にバーナや電気ヒータ等で加熱して、あるいは高温の排ガスを供給して、堆積したPMを燃焼させることでDPFを再生することが行われている。しかしながらこの場合には、PMの堆積量が多いほど燃焼時の温度が上昇し、それによってDPFが溶損したり、熱応力によって破損やクラックが生じる場合があった。   However, in the DPF, the pressure loss increases due to the accumulation of PM. Therefore, it is necessary to periodically remove and regenerate PM accumulated by some means. Thus, conventionally, when the pressure loss increases, the DPF is regenerated by burning the accumulated PM by heating with a burner, an electric heater or the like, or by supplying high-temperature exhaust gas. However, in this case, as the amount of accumulated PM increases, the temperature at the time of combustion rises, which may cause the DPF to melt or break or crack due to thermal stress.

またDPFのセル隔壁にアルミナなどからコート層を形成し、そのコート層に白金族貴金属などを担持した触媒付きDPFが開発されている。この触媒付きDPFによれば、セル隔壁の細孔中に捕集されたPMが貴金属の触媒活性によって酸化燃焼するため、捕集と同時にあるいは捕集に連続して燃焼させることでDPFを再生することができる。そして触媒活性は比較的低温で生じること、及び捕集量が少ないうちに燃焼できることから、DPFに作用する熱応力が小さく破損が防止されるという利点がある。   In addition, a DPF with a catalyst in which a coating layer is formed from alumina or the like on the cell partition of the DPF and a platinum group noble metal or the like is supported on the coating layer has been developed. According to this catalyst-attached DPF, the PM collected in the pores of the cell partition wall is oxidized and burned by the catalytic activity of the noble metal, so that the DPF is regenerated by burning simultaneously with the collection or continuously with the collection. be able to. Since the catalytic activity occurs at a relatively low temperature and can be burned while the amount collected is small, there is an advantage that the thermal stress acting on the DPF is small and damage is prevented.

DPFにおいては、セル隔壁の細孔径より小さい粒径のPMは細孔内に捕集されるが、細孔径より大きな粒径のPMは細孔の開口に堆積し、所定量堆積すると開口を閉塞するため、細孔内におけるPMの捕集が困難となる。ところが排ガスの流速は、DPFの中心部ほど大きく外周部ほど小さい分布をもち、単位時間あたりに流れるPM量は内周部ほど多い分布を有している。さらに外周部は、放熱によって温度が低下しやすい。そのため触媒付きDPFの低温域での使用時には、粒径の大きなPMによって中心部の細孔の開口が早期に閉塞され、そうなると大部分のPMが外周部に流れるようになるため、外周部の細孔の開口も比較的早く閉塞されてしまう。そしてその表面にさらにPMが堆積し、PM堆積量が一定量を超えると背圧が上昇してエンジンが不調になったり、排ガス温度の上昇によって触媒が活性化温度以上となることで、堆積したPMが一気に燃焼して触媒付きDPFが損傷する場合があった。   In the DPF, PM having a particle size smaller than the pore size of the cell partition is collected in the pores, but PM having a particle size larger than the pore size is deposited at the pore opening, and when a predetermined amount is deposited, the opening is blocked. Therefore, it becomes difficult to collect PM in the pores. However, the flow rate of the exhaust gas has a distribution that is larger at the center of the DPF and smaller at the outer periphery, and the amount of PM flowing per unit time is larger at the inner periphery. Furthermore, the temperature of the outer peripheral portion tends to decrease due to heat dissipation. For this reason, when the DPF with catalyst is used in a low temperature region, the opening of the pores in the central part is blocked early due to the large particle size PM, and then most of the PM flows to the outer peripheral part, so that the outer peripheral part is narrow. The opening of the hole is also closed relatively quickly. Further, PM accumulates on the surface, and when the PM accumulation amount exceeds a certain amount, the back pressure rises and the engine malfunctions or the catalyst becomes accumulated due to the exhaust gas temperature rising above the activation temperature. In some cases, PM burned at once and the DPF with catalyst was damaged.

そこで特開2003−225540号公報には、排ガスの上流側から下流側に向かってセル隔壁の平均細孔径を大きなものから小さなものとなるように分布させた触媒付きDPFが提案されている。この触媒付きDPFでは、大きな径のPMほど上流側で捕集され、下流側の小さな径の細孔が大きな径のPMで閉塞されるような不具合がない。したがって細孔の閉塞が抑制され、背圧の上昇が抑制される。   Japanese Patent Laid-Open No. 2003-225540 proposes a DPF with a catalyst in which the average pore diameter of the cell partition wall is distributed from the largest to the smallest from the upstream side to the downstream side of the exhaust gas. In this DPF with a catalyst, PM having a larger diameter is collected on the upstream side, and there is no problem that the small-diameter pores on the downstream side are blocked by the larger-diameter PM. Therefore, blockage of the pores is suppressed, and an increase in back pressure is suppressed.

また特開平08−229412号公報には、実質的に二つの独立した細孔群からなる細孔を有するハニカム触媒が記載されている。しかしこの触媒は、細孔内のガス拡散性を調整することで脱硝活性を高めるものであり、細孔にPMを捕集するフィルタ触媒ではない。
特開平08−229412号 特開2003−225540号
Japanese Unexamined Patent Publication No. 08-229412 discloses a honeycomb catalyst having pores substantially consisting of two independent pore groups. However, this catalyst enhances the denitration activity by adjusting the gas diffusivity in the pores, and is not a filter catalyst that collects PM in the pores.
JP 08-229412 JP2003-225540

本発明は上記した事情に鑑みてなされたものであり、PMを効率よく捕集するとともに、細孔へのPMの堆積を抑制して背圧の上昇及びフィルタの溶損を抑制することを解決すべき課題とする。   The present invention has been made in view of the circumstances described above, and solves the problem of efficiently collecting PM and suppressing the accumulation of PM in the pores to suppress the increase in back pressure and the erosion of the filter. It should be a challenge.

上記課題を解決する本発明の排ガス浄化フィルタの特徴は、排ガス下流側で目詰めされた流入側セルと、流入側セルに隣接し排ガス上流側で目詰めされた流出側セルと、流入側セルと流出側セルを区画し多数の細孔を有する多孔質のセル隔壁と、をもつハニカム形状の排ガス浄化フィルタであって、外周部のセル隔壁の平均細孔径が内周部のセル隔壁の平均細孔径より小さいことにある。   The features of the exhaust gas purification filter of the present invention that solves the above-described problems include an inflow side cell that is clogged on the exhaust gas downstream side, an outflow side cell that is adjacent to the inflow side cell and clogged on the exhaust gas upstream side, and an inflow side cell And a porous cell partition wall having a large number of pores partitioning the outflow side cell, and having an average pore diameter of the outer peripheral cell partition wall average of the inner cell partition wall It is because it is smaller than the pore diameter.

セル隔壁の平均細孔径は、径方向の中心から外周表面に向かって小さくなる分布をもつように構成することが好ましい。   The average pore diameter of the cell partition walls is preferably configured to have a distribution that decreases from the radial center toward the outer peripheral surface.

またセル隔壁の細孔の表面には、多孔質酸化物と貴金属を含む触媒層をもつことが望ましく、セル隔壁の平均細孔径の分布は、触媒層の厚さによって制御されていることが好ましい。   The surface of the pores of the cell partition walls preferably has a catalyst layer containing a porous oxide and a noble metal, and the average pore diameter distribution of the cell partition walls is preferably controlled by the thickness of the catalyst layer. .

本発明の排ガス浄化フィルタによれば、外周部のセル隔壁の平均細孔径が内周部のセル隔壁の平均細孔径より小さいので、外周から内周までほぼ均一な細孔径分布をもつ従来のフィルタに比べてPM堆積時の背圧の上昇が抑制される。また熱応力による損傷やクラックの発生が抑制されるとともに、外周部におけるPMの燃え残りが抑制され、外周部のセル隔壁によるPMの捕集効率が向上するため、PM浄化率が向上する。   According to the exhaust gas purification filter of the present invention, since the average pore diameter of the cell partition at the outer peripheral portion is smaller than the average pore diameter of the cell partition at the inner peripheral portion, the conventional filter having a substantially uniform pore size distribution from the outer periphery to the inner periphery Compared with, increase in back pressure during PM deposition is suppressed. In addition, damage due to thermal stress and generation of cracks are suppressed, PM unburned residue at the outer periphery is suppressed, and PM collection efficiency by the cell partition walls at the outer periphery is improved, so that the PM purification rate is improved.

そしてセル隔壁の細孔の表面に多孔質酸化物と貴金属を含む触媒層をもつフィルタ触媒とすれば、局部的にPMが多く堆積するのが抑制されているため、PMの捕集と同時あるいは捕集直後に効率よくPMを酸化燃焼することができ、PMを連続して効率よく捕集・浄化することができる。   And if it is a filter catalyst having a catalyst layer containing a porous oxide and a noble metal on the surface of the pores of the cell partition walls, it is possible to suppress the accumulation of a large amount of PM locally. Immediately after collection, PM can be oxidized and burned efficiently, and PM can be collected and purified continuously and efficiently.

本発明の排ガス浄化フィルタでは、外周部のセル隔壁の平均細孔径が内周部のセル隔壁の平均細孔径より小さい。そのため、先ず内周部に多く流れるPMが内周部の細孔に捕集されるが、内周部の平均細孔径が大きいため粒径の大きなPMも細孔内部に捕集され、細孔の開口の閉塞が抑制される。また外周部には比較的小さな粒径のPMが流入し、それは外周部の平均細孔径が小さな細孔内部で捕集され、細孔の開口の閉塞が抑制される。したがってPMの堆積が抑制され、その結果、背圧の上昇が抑制される。   In the exhaust gas purification filter of the present invention, the average pore diameter of the cell partition at the outer periphery is smaller than the average pore diameter of the cell partition at the inner periphery. Therefore, PM that flows a lot in the inner peripheral part is first collected in the pores in the inner peripheral part, but because the average pore diameter in the inner peripheral part is large, PM with a large particle size is also collected in the pores. Blockage of the opening is suppressed. Further, PM having a relatively small particle size flows into the outer peripheral portion, and is trapped inside the pore having a small average pore diameter in the outer peripheral portion, thereby suppressing the clogging of the pore opening. Therefore, PM accumulation is suppressed, and as a result, an increase in back pressure is suppressed.

すなわち外周部のセル隔壁の平均細孔径を内周部のセル隔壁の平均細孔径より小さく構成することで、細孔径に対して非常に大きな径のPMが流入することがなく、細孔の開口の閉塞が生じず開口を覆うようにPMが堆積するのが抑制される。これにより圧損の上昇が抑制され、また局部的に多量のPMが堆積するのも抑制されるため、再生時の熱応力による損傷が防止される。   In other words, by configuring the average pore diameter of the outer peripheral cell partition wall to be smaller than the average pore diameter of the inner peripheral cell partition wall, PM having a very large diameter does not flow into the pore opening. It is suppressed that PM is deposited so as to cover the opening without blocking. As a result, an increase in pressure loss is suppressed, and the accumulation of a large amount of PM is also suppressed, thereby preventing damage due to thermal stress during regeneration.

本発明の排ガス浄化フィルタは、アルミナ、ジルコニア、セリア、チタニア、シリカ、シリカ−アルミナ、コージェライト、炭化ケイ素、窒化ケイ素などから形成することができる。中でも実績があり、嵩密度が低いコージェライトが特に好ましい。   The exhaust gas purification filter of the present invention can be formed from alumina, zirconia, ceria, titania, silica, silica-alumina, cordierite, silicon carbide, silicon nitride, or the like. Of these, cordierite, which has a proven record and has a low bulk density, is particularly preferred.

セル隔壁に細孔を形成するには、カーボン粉末、木粉、澱粉、樹脂粉末などの可燃物粉末などを混合したペーストからセル及びセル隔壁を押出成形などによって形成し、焼成時に可燃物粉末を焼失させることで細孔が形成される。そして可燃物粉末の粒径及び添加量を調整することで、表面空孔及び内部細孔の径の分布と開口面積を制御することができる。   In order to form pores in the cell partition walls, the cells and cell partition walls are formed by extrusion molding from a paste mixed with combustible powders such as carbon powder, wood powder, starch, resin powder, etc. By burning out, pores are formed. And by adjusting the particle size and addition amount of the combustible powder, the distribution of the surface vacancies and the diameter of the internal pores and the opening area can be controlled.

すなわち、外周部のセル隔壁の平均細孔径を内周部のセル隔壁の平均細孔径より小さくするには、ペースト中の可燃物粉末の粒径を調整し、平均粒子径の大きな可燃物粉末を含むペーストから内周部を形成するとともに、平均粒子径の小さな可燃物粉末を含むペーストから外周部を形成すればよい。あるいは実施例に示すように、外周部を形成するためのペーストと内周部を形成するためのペーストからそれぞれ独立したセルユニットを形成し、複数のセルユニットどうしを接合することで内周部及び外周部を形成することもできる。   That is, in order to make the average pore diameter of the cell partition in the outer peripheral portion smaller than the average pore diameter of the cell partition in the inner peripheral portion, the particle size of the combustible powder in the paste is adjusted, and a combustible powder having a large average particle size is used. While forming an inner peripheral part from the paste containing, an outer peripheral part should just be formed from the paste containing a combustible powder with a small average particle diameter. Alternatively, as shown in the embodiment, each of the cell units independent from the paste for forming the outer peripheral portion and the paste for forming the inner peripheral portion is formed, and the inner peripheral portion and the plurality of cell units are joined together. An outer periphery can also be formed.

外周部のセル隔壁の平均細孔径は、内周部のセル隔壁の平均細孔径より小さければよく、平均細孔径が内周部から外周部に向かって少なくとも二段階で小さくなるように平均細孔径を調整すればよい。三段階以上の複数段階で小さくなるように構成することがさらに好ましく、内周部から外周部に向かって連続的に平均細孔径が小さくなるように構成することもできる。   The average pore diameter of the outer peripheral cell partition may be smaller than the average pore diameter of the inner peripheral cell partition, and the average pore diameter may be reduced in at least two steps from the inner periphery to the outer periphery. Can be adjusted. It is more preferable to make it smaller in three or more stages, and it is also possible to make the average pore diameter continuously smaller from the inner periphery toward the outer periphery.

最外周部のセル隔壁は平均細孔径が10〜40μmの範囲であることが好ましく、最内周部(中心部)のセル隔壁は平均細孔径が70〜 100μmの範囲であることが好ましい。最外周部及び最内周部ともに、平均細孔径がこの範囲より小さいとPMが堆積しやすくなり、この範囲より大きくなるとPMのすり抜けが生じてPM浄化率が低下してしまう。   The outermost cell partition preferably has an average pore diameter in the range of 10 to 40 μm, and the innermost peripheral (center) cell partition preferably has an average pore diameter in the range of 70 to 100 μm. When the average pore diameter is smaller than this range in both the outermost peripheral portion and the innermost peripheral portion, PM is likely to be deposited, and if it exceeds this range, PM slips out and the PM purification rate decreases.

なお、本発明の排ガス浄化フィルタは、従来のものと同様に、排ガス下流側で目詰めされた流入側セルと、流入側セルに隣接し排ガス上流側で目詰めされた流出側セルとを有している。例えば、従来と同様にペースト注入機(ディスペンサ)などを用いて、上流側端面のセルに一舛ずつ交互に目詰めして流出側セルを形成し、下流側端面で上流側端面が目詰めされていないセルを目詰めすることで流入側セルを形成することができる。   The exhaust gas purification filter of the present invention has an inflow side cell clogged on the exhaust gas downstream side and an outflow side cell clogged on the exhaust gas upstream side adjacent to the inflow side cell, as in the conventional filter. is doing. For example, by using a paste injecting machine (dispenser) as in the past, the cells on the upstream end face are alternately clogged one by one to form the outflow side cells, and the upstream end face is clogged at the downstream end face. An inflow side cell can be formed by plugging cells that are not.

本発明の排ガス浄化フィルタは、流入側セルと流出側セルを区画するセル隔壁の細孔の表面に、多孔質酸化物と貴金属を含む触媒層を有することが好ましい。これによりフィルタ触媒とすることができる。触媒層に用いられる多孔質酸化物としては、アルミナ,ジルコニア,セリア,チタニアなどの酸化物あるいはこれらの複数種からなる複合酸化物などを用いることができる。   The exhaust gas purification filter of the present invention preferably has a catalyst layer containing a porous oxide and a noble metal on the surface of the pores of the cell partition wall that partitions the inflow side cell and the outflow side cell. Thereby, it can be set as a filter catalyst. As the porous oxide used in the catalyst layer, oxides such as alumina, zirconia, ceria, and titania, or composite oxides composed of a plurality of these can be used.

触媒層の形成量は、隔壁の細孔径にもよるが、厚さが1〜20μmの範囲、あるいはフィルタ体積1リットルあたり60〜 200gの範囲とすることが好ましい。触媒層の形成量がこの範囲より少なくなると、貴金属が高密度に担持されるため高温に晒されると貴金属の粒成長が生じて活性が低下する場合がある。また触媒層の形成量がこの範囲より多くなると、細孔の径及び開口面積が低下し圧損が増大してしまう。   The formation amount of the catalyst layer is preferably in the range of 1 to 20 μm, or in the range of 60 to 200 g per liter of filter volume, although it depends on the pore diameter of the partition walls. When the formation amount of the catalyst layer is less than this range, the noble metal is supported at a high density, so that when exposed to a high temperature, grain growth of the noble metal may occur and the activity may decrease. Moreover, when the formation amount of the catalyst layer is larger than this range, the pore diameter and the opening area are reduced, and the pressure loss is increased.

このフィルタ触媒においては、セル隔壁の平均細孔径は触媒層を形成した後の平均細孔径をいう。したがって、触媒層を形成する前のセル隔壁の平均細孔径を調整することで本発明の排ガス浄化フィルタを形成することも可能であるが、触媒層の形成量を調整することで平均細孔径を調整することもできる。この場合には、触媒層形成前のフィルタ基材の平均細孔径を全体で均一とすることが可能となるので、フィルタ基材の製造工数を大きく低減することができる。   In this filter catalyst, the average pore diameter of the cell partition wall means the average pore diameter after forming the catalyst layer. Therefore, it is possible to form the exhaust gas purification filter of the present invention by adjusting the average pore diameter of the cell partition wall before forming the catalyst layer, but by adjusting the formation amount of the catalyst layer, the average pore diameter can be reduced. It can also be adjusted. In this case, the average pore diameter of the filter base material before formation of the catalyst layer can be made uniform as a whole, so that the number of manufacturing steps of the filter base material can be greatly reduced.

触媒層を形成するには、多孔質酸化物粉末をアルミナゾルなどのバインダ成分及び水とともにスラリーとし、そのスラリーをセル隔壁に含浸させた後に焼成し、その後少なくとも貴金属を担持すればよい。スラリーをセル隔壁に含浸させるには通常の浸漬法を用いることができるが、エアブローあるいは吸引によって細孔内に入ったスラリーの余分なものを除去することが望ましい。   In order to form the catalyst layer, the porous oxide powder may be made into a slurry together with a binder component such as alumina sol and water, impregnated into the cell partition wall, fired, and then loaded with at least a noble metal. A normal dipping method can be used to impregnate the cell partition walls with the slurry, but it is desirable to remove excess slurry that has entered the pores by air blowing or suction.

そしてスラリーのコート量を調整することで、触媒層の形成量を調整することができる。つまり、全体で均一な細孔をもつフィルタ基材を用いて、外周部では多くコートし、内周部では少なくコートすれば、外周部のセル隔壁の平均細孔径を内周部のセル隔壁の平均細孔径より小さくすることができる。   And the formation amount of a catalyst layer can be adjusted by adjusting the coat amount of a slurry. In other words, if a filter substrate having uniform pores as a whole is used, and the outer peripheral part is coated more and the inner peripheral part is less coated, the average pore diameter of the outer peripheral cell partition is set to that of the inner peripheral part. It can be made smaller than the average pore diameter.

触媒層には少なくとも貴金属が担持されている。この貴金属としては、触媒反応によってPMの酸化を促進するものであれば用いることができるが、Pt、Rh、Pdなどの白金族の貴金属から選ばれた一種又は複数種を担持することが特に好ましい。貴金属の担持量は、フィルタ堆積1リットルあたり 0.5〜10gの範囲とすることが好ましい。担持量がこれより少ないと活性が低すぎて実用的でなく、この範囲より多く担持しても活性が飽和するとともにコストアップとなってしまう。   At least a noble metal is supported on the catalyst layer. The noble metal can be used as long as it promotes the oxidation of PM by a catalytic reaction, but it is particularly preferable to support one or more selected from platinum group noble metals such as Pt, Rh, and Pd. . The amount of noble metal supported is preferably in the range of 0.5 to 10 g per liter of filter deposition. If the loading amount is less than this, the activity is too low to be practical, and if the loading amount exceeds this range, the activity is saturated and the cost is increased.

また貴金属に加えて、Ba,Ca,Srなどのアルカリ土類金属、Na,K,Li,Csなどのアルカリ金属、あるいはLa,Nd,Sc,Yなどの希土類元素から選ばれるNOx 吸蔵材をさらに担持することが好ましい。NOx 吸蔵材を担持することでNOx 吸蔵放出能が発現され、NOx 浄化能が向上する。このNOx 吸蔵材の担持量は、フィルタ堆積1リットルあたり0.01〜2モルの範囲とすることが好ましい。担持量がこれより少ないとNOx 吸蔵放出能が発現されず、これより多く担持するとPtなどの貴金属を覆って酸化能が低下するようになる。 In addition to precious metals, NO x occlusion materials selected from alkaline earth metals such as Ba, Ca and Sr, alkali metals such as Na, K, Li and Cs, or rare earth elements such as La, Nd, Sc and Y Furthermore, it is preferable to carry. By supporting the NO x storage material, the NO x storage and release ability is expressed, and the NO x purification ability is improved. The amount of the NO x storage material supported is preferably in the range of 0.01 to 2 mol per liter of filter deposition. If the supported amount is less than this, the NO x storage / release ability is not expressed.

貴金属及びNOx 吸蔵材を担持するには、貴金属又はNOx 吸蔵元素の硝酸塩などを溶解した溶液を用い、吸着担持法、吸水担持法などによって多孔質酸化物層に担持すればよい。また多孔質酸化物粉末に予め貴金属を担持しておき、その触媒粉末を用いて触媒層を形成した後にNOx 吸蔵材を担持することもできる。 In order to support the noble metal and the NO x storage material, a solution in which nitrate of the noble metal or the NO x storage element is dissolved may be supported on the porous oxide layer by an adsorption support method, a water absorption support method, or the like. Alternatively, a noble metal may be supported on the porous oxide powder in advance, and the catalyst layer may be formed using the catalyst powder, and then the NO x storage material may be supported.

以下、実施例及び比較例により本発明を具体的に説明する。   Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

先ずアルミナ,タルク,カオリン,シリカからなるコージェライト組成の粉末に所定量の有機バインダと水及び所定粒径のカーボン粉末を混合したペーストを用い、複数のセル通路をもつ角筒形状に押出成形後、1300℃で焼成して、図1に示すように、断面20mm角の正方形、長さ 100mm、壁厚 300μmの成形品を形成した。次いで Al2O3粉末に予めPtが3重量%担持されたPt/ Al2O3触媒粉末をバインダとともにスラリー化し、セル隔壁の細孔中に充填した後、吸引して余分なスラリーを除去し、同様に焼成して、成形品1リットルあたり 100gのコート量で触媒層を形成し、小細孔セルユニット1を形成した。この小細孔セルユニット1には、1cm2 当たり 300個のセルが形成され、セル隔壁の平均細孔径は25μmである。 First, after extrusion molding into a rectangular tube shape with multiple cell passages, using a paste in which a predetermined amount of organic binder, water, and carbon powder with a predetermined particle size are mixed in a cordierite composition powder composed of alumina, talc, kaolin, and silica As shown in FIG. 1, a molded article having a square with a cross section of 20 mm square, a length of 100 mm and a wall thickness of 300 μm was formed. Then advance Pt 3 wt% supported Pt / Al 2 O 3 catalyst powder to Al 2 O 3 powder were slurried together with a binder, after filling into the pores of the cell partition walls, removing excess slurry was suction In the same manner, the catalyst layer was formed with a coating amount of 100 g per liter of the molded product, and the small pore cell unit 1 was formed. In this small pore cell unit 1, 300 cells are formed per 1 cm 2 , and the average pore diameter of the cell partition is 25 μm.

また、カーボン粉末の粒径をやや大きなものとしたこと以外は同様にして、図1に示すように、セル隔壁の平均細孔径が55μmであること以外は小細孔セルユニット1と同一形状の中細孔セルユニット2を形成した。   Similarly, the carbon powder has the same shape as the small pore cell unit 1 except that the average pore diameter of the cell partition is 55 μm as shown in FIG. Medium pore cell unit 2 was formed.

さらに、カーボン粉末の粒径をさらに大きなものとしたこと以外は同様にして、図1に示すように、セル隔壁の平均細孔径が85μmであること以外は小細孔セルユニット1及び中細孔セルユニット2と同一形状の大細孔セルユニット3を形成した。   Further, except that the particle size of the carbon powder is made larger, the small pore cell unit 1 and the medium pores except that the average pore diameter of the cell partition is 85 μm as shown in FIG. A large pore cell unit 3 having the same shape as the cell unit 2 was formed.

(実施例1)
図2に示すように、大細孔セルユニット3を縦2個、横2個となるように、セラミック製セグメント材(イビデン社製)を用いて貼り合わせ、その周囲に中細孔セルユニット2を一重に貼り合わせ、さらにその周囲に小細孔セルユニット1を一重に貼り合わせた。大細孔セルユニット3はセル隔壁を点線で示し、中細孔セルユニット2はやや太い実線で示し、小細孔セルユニット1は中細孔セルユニット2より細い実線で示している。そして目詰め用のスラリーを用い、所定長さのパイプをもつペースト注入機(ディスペンサ)を用いて、上流側端面のセルに一舛ずつ交互に目詰めして上流栓を形成し、下流側端面では上流栓をもたないセルを目詰めして下流栓を形成した。次いで1300℃で焼成して、図3の左側に示す形状とした後、外周を切削加工して円柱形状のフィルタとし、図3の右側に示すように、外筒4に収納して触媒コンバータ化した。
Example 1
As shown in FIG. 2, the large-pore cell unit 3 is bonded using a ceramic segment material (manufactured by Ibiden Co., Ltd.) so as to be two vertically long and two horizontally wide. Were bonded together, and the small-pore cell unit 1 was bonded together around it. The large pore cell unit 3 shows a cell partition by a dotted line, the medium pore cell unit 2 shows a slightly thick solid line, and the small pore cell unit 1 shows a solid line thinner than the medium pore cell unit 2. Then, using the slurry for plugging, using a paste injection machine (dispenser) having a pipe of a predetermined length, the cells on the upstream end face are alternately plugged one by one to form the upstream plug, and the downstream end face Then, a cell having no upstream plug was plugged to form a downstream plug. Next, after baking at 1300 ° C. to obtain the shape shown on the left side of FIG. 3, the outer periphery is cut into a cylindrical filter, which is housed in the outer cylinder 4 as shown on the right side of FIG. did.

この排ガス浄化フィルタでは、内周部のセル隔壁の平均細孔径が85μmであり、外周部のセル隔壁の平均細孔径が25μmであり、内周部と外周部の中間部のセル隔壁の平均細孔径は55μmである。また小細孔セルユニット1によるセル数は全セル数の43.5%であり、中細孔セルユニット2によるセル数は全セル数の42.4%であり、大細孔セルユニット3によるセル数は全セル数の14.1%である。   In this exhaust gas purifying filter, the average pore diameter of the inner peripheral cell partition is 85 μm, the average pore diameter of the outer peripheral cell partition is 25 μm, and the average fineness of the cell partition between the inner peripheral portion and the outer peripheral portion. The pore diameter is 55 μm. The number of cells by small pore cell unit 1 is 43.5% of the total number of cells, the number of cells by medium pore cell unit 2 is 42.4% of the total number of cells, and the number of cells by large pore cell unit 3 is all. This is 14.1% of the number of cells.

図4に、用いた各セルユニットの細孔分布を示す。本実施例の排ガス浄化フィルタにおけるセル隔壁の細孔分布は、この3つの分布を合計した分布となり、排ガス中のPMの粒度分布のピークよりやや大きな範囲をカバーしている。   FIG. 4 shows the pore distribution of each cell unit used. The pore distribution of the cell partition walls in the exhaust gas purification filter of the present example is a total distribution of these three distributions, and covers a range that is slightly larger than the peak of the particle size distribution of PM in the exhaust gas.

(実施例2)
図5に示すように、大細孔セルユニット3を縦2個、横2個となるように、実施例1と同様のセグメント材を用いて貼り合わせ、その周囲に小細孔セルユニット1を二重に貼り合わせた。そして上記した同種のスラリーを用い、所定長さのパイプをもつペースト注入機(ディスペンサ)を用いて、上流側端面のセルに一舛ずつ交互に目詰めして上流栓を形成し、下流側端面では上流栓をもたないセルを目詰めして下流栓を形成した。次いで1300℃で焼成して、図5の左側に示す形状とした後、外周を切削加工して円柱形状のフィルタとし、外筒4に収納して触媒コンバータ化した。
(Example 2)
As shown in FIG. 5, the large pore cell units 3 are bonded together using the same segment material as in Example 1 so that they are two vertically long and two horizontally wide. Double bonded. Then, using the same kind of slurry as described above, using a paste injection machine (dispenser) having a pipe of a predetermined length, the cells on the upstream end face are alternately packed one by one to form the upstream plug, and the downstream end face Then, a cell having no upstream plug was plugged to form a downstream plug. Next, after baking at 1300 ° C. to obtain the shape shown on the left side of FIG. 5, the outer periphery was cut into a cylindrical filter, which was housed in the outer cylinder 4 to form a catalytic converter.

この排ガス浄化フィルタでは、内周部のセル隔壁の平均細孔径が85μmであり、外周部のセル隔壁の平均細孔径が25μmである。また小細孔セルユニット1によるセル数は全セル数の85.9%であり、大細孔セルユニット3によるセル数は全セル数の14.1%である。   In this exhaust gas purification filter, the average pore diameter of the cell partition in the inner peripheral portion is 85 μm, and the average pore diameter of the cell partition in the outer peripheral portion is 25 μm. The number of cells by the small pore cell unit 1 is 85.9% of the total number of cells, and the number of cells by the large pore cell unit 3 is 14.1% of the total number of cells.

(実施例3)
大細孔セルユニット3を形成するための成形品(セル隔壁の平均細孔径 100μm)を用い、Pt/ Al2O3触媒粉末のコート量を成形品1リットルあたり 100g、 150g、 200gとしたものを用意した。セル隔壁の平均細孔径は、触媒層が 100g/L形成されたものが85μm、 150g/L形成されたものが55μm、 200g/L形成されたものが25μmであるので、これらはそれぞれ大細孔セルユニット3、中細孔セルユニット2及び小細孔セルユニット1に相当する。
Example 3
A molded product for forming the large pore cell unit 3 (average pore diameter of the cell partition wall 100 μm), and the coating amount of the Pt / Al 2 O 3 catalyst powder is 100 g, 150 g, 200 g per liter of the molded product Prepared. The average pore diameter of the cell partition walls is 85 μm for the catalyst layer formed of 100 g / L, 55 μm for the catalyst layer formed of 150 g / L, and 25 μm for the catalyst layer formed of 200 g / L. It corresponds to the cell unit 3, the medium pore cell unit 2 and the small pore cell unit 1.

これらのセルユニットを用い、実施例1と全く同様にして図3と同様の触媒コンバータを形成した。この排ガス浄化フィルタでは、内周部のセル隔壁の平均細孔径が85μmであり、外周部のセル隔壁の平均細孔径が25μmであり、内周部と外周部の中間部のセル隔壁の平均細孔径は55μmである。また触媒層が 200g/L形成された小細孔セルユニット1によるセル数は全セル数の43.5%であり、触媒層が 150g/L形成された中細孔セルユニット2によるセル数は全セル数の42.4%であり、触媒層が 100g/L形成された大細孔セルユニット3によるセル数は全セル数の14.1%である。   Using these cell units, the same catalytic converter as in FIG. 3 was formed in the same manner as in Example 1. In this exhaust gas purifying filter, the average pore diameter of the inner peripheral cell partition is 85 μm, the average pore diameter of the outer peripheral cell partition is 25 μm, and the average fineness of the cell partition between the inner peripheral portion and the outer peripheral portion. The pore diameter is 55 μm. The number of cells by the small pore cell unit 1 having a catalyst layer of 200 g / L is 43.5% of the total number of cells, and the number of cells by the medium pore cell unit 2 having a catalyst layer of 150 g / L is all cells. 42.4% of the number of cells, and the number of cells by the large pore cell unit 3 in which the catalyst layer was formed at 100 g / L was 14.1% of the total number of cells.

(比較例1)
小細孔セルユニット1のみを用い、実施例1と同様にして触媒コンバータを形成した。この排ガス浄化フィルタでは、内周部から外周部まで、全てのセル隔壁の平均細孔径が25μmである。
(Comparative Example 1)
Using only the small pore cell unit 1, a catalytic converter was formed in the same manner as in Example 1. In this exhaust gas purification filter, the average pore diameter of all the cell partition walls from the inner periphery to the outer periphery is 25 μm.

(比較例2)
大細孔セルユニット3のみを用い、実施例1と同様にして触媒コンバータを形成した。この排ガス浄化フィルタでは、内周部から外周部まで、全てのセル隔壁の平均細孔径が85μmである。
(Comparative Example 2)
Using only the large pore cell unit 3, a catalytic converter was formed in the same manner as in Example 1. In this exhaust gas purification filter, the average pore diameter of all cell partition walls is 85 μm from the inner periphery to the outer periphery.

<試験・評価>
それぞれの触媒コンバータを、2L直噴ディーゼルエンジンを搭載したエンジンベンチの排気系に取付け、実車11Lap 走行を模擬した条件で 100時間(5000km相当)運転した。運転終了直前のフィルタ前後の排ガス中のPM濃度を測定し、PM酸化率とした。また運転後触媒コンバータを取り外してフィルタの重量を測定し、運転前の重量との差からPM堆積量を算出した。結果を表1に示す。
<Test and evaluation>
Each catalytic converter was attached to the exhaust system of an engine bench equipped with a 2L direct-injection diesel engine, and operated for 100 hours (equivalent to 5000km) under the conditions of simulating actual 11Lap running. The PM concentration in the exhaust gas before and after the filter just before the end of the operation was measured and used as the PM oxidation rate. In addition, after the operation, the catalytic converter was removed, the weight of the filter was measured, and the PM deposition amount was calculated from the difference from the weight before the operation. The results are shown in Table 1.

Figure 2006016991
Figure 2006016991

各実施例のフィルタによれば、PM酸化率が高く、かつPM堆積量が少ないことがわかり、これは、平均細孔径を内周部で大きく外周部で小さくした効果であることが明らかである。   According to the filter of each example, it can be seen that the PM oxidation rate is high and the PM deposition amount is small, and this is an effect that the average pore diameter is increased at the inner peripheral portion and decreased at the outer peripheral portion. .

本発明の排ガス浄化フィルタは、ディーゼルエンジンの排気、ボイラーの排気など、PMを含む排ガス中で用いられる。そしてセル隔壁の細孔の表面に多孔質酸化物と貴金属を含む触媒層を形成すれば、PMを捕集と同時にあるいは捕集直後に燃焼除去できるので、特別な再生処理を不要とすることができ、特に有用である。   The exhaust gas purification filter of the present invention is used in exhaust gas containing PM, such as exhaust from a diesel engine and exhaust from a boiler. If a catalyst layer containing a porous oxide and a noble metal is formed on the surface of the pores of the cell partition walls, PM can be burned and removed at the same time or immediately after collection, so that no special regeneration treatment is required. And is particularly useful.

本発明の実施例で形成したセルユニットの斜視図である。It is a perspective view of the cell unit formed in the Example of this invention. 本発明の一実施例において、セルユニットどうしを接合する際の各セルユニットの配置状態を示す説明図である。In one Example of this invention, it is explanatory drawing which shows the arrangement | positioning state of each cell unit at the time of joining cell units. 本発明の一実施例のフィルタの端面を切削加工前後の状態で示す説明図である。It is explanatory drawing which shows the end surface of the filter of one Example of this invention in the state before and behind cutting. 本発明の一実施例のフィルタのセル隔壁の細孔分布をセルユニット毎に示すグラフである。It is a graph which shows the pore distribution of the cell partition wall of the filter of one Example of this invention for every cell unit. 本発明の第2の実施例のフィルタの端面を切削加工前後の状態で示す説明図である。It is explanatory drawing which shows the end surface of the filter of the 2nd Example of this invention in the state before and behind cutting.

符号の説明Explanation of symbols

1:小細孔セルユニット 2:中細孔セルユニット 3:大細孔セルユニット
4:外筒
1: Small pore cell unit 2: Medium pore cell unit 3: Large pore cell unit 4: Outer cylinder

Claims (4)

排ガス下流側で目詰めされた流入側セルと、該流入側セルに隣接し排ガス上流側で目詰めされた流出側セルと、該流入側セルと該流出側セルを区画し多数の細孔を有する多孔質のセル隔壁と、をもつハニカム形状の排ガス浄化フィルタであって、
外周部の該セル隔壁の平均細孔径が内周部の該セル隔壁の平均細孔径より小さいことを特徴とする排ガス浄化フィルタ。
An inflow side cell clogged on the exhaust gas downstream side, an outflow side cell adjacent to the inflow side cell and clogged on the exhaust gas upstream side, the inflow side cell and the outflow side cell are partitioned, and a large number of pores are formed. A honeycomb-shaped exhaust gas purification filter having a porous cell partition wall,
An exhaust gas purification filter, wherein an average pore diameter of the cell partition wall in the outer peripheral portion is smaller than an average pore diameter of the cell partition wall in the inner peripheral portion.
前記セル隔壁の平均細孔径は、径方向の中心から外周表面に向かって小さくなる分布をもつ請求項1に記載の排ガス浄化フィルタ。   The exhaust gas purification filter according to claim 1, wherein the average pore diameter of the cell partition wall has a distribution that decreases from the center in the radial direction toward the outer peripheral surface. 前記セル隔壁の細孔の表面には、多孔質酸化物と貴金属を含む触媒層をもつ請求項1又は請求項2に記載の排ガス浄化フィルタ。   The exhaust gas purification filter according to claim 1 or 2, wherein a catalyst layer containing a porous oxide and a noble metal is provided on the surface of the pores of the cell partition wall. 前記セル隔壁の平均細孔径の分布は、前記触媒層の厚さによって制御されている請求項3に記載の排ガス浄化フィルタ。   The exhaust gas purification filter according to claim 3, wherein the distribution of the average pore diameter of the cell partition walls is controlled by the thickness of the catalyst layer.
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Cited By (8)

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US7138003B2 (en) * 2003-03-10 2006-11-21 Ngk Insulators, Ltd Honeycomb structure
WO2008120802A1 (en) 2007-04-03 2008-10-09 Yanmar Co., Ltd. Black exhaust purification apparatus for diesel engine
JP2011522156A (en) * 2008-06-02 2011-07-28 アラントゥーム Filter media for aftertreatment of exhaust gas from internal combustion engines
JP2013530332A (en) * 2010-04-19 2013-07-25 ビー・エイ・エス・エフ、コーポレーション Gasoline engine exhaust treatment system with gasoline particulate filter
JP2015158197A (en) * 2014-01-27 2015-09-03 株式会社デンソー Exhaust gas purification filter and exhaust gas purification filter manufacturing method
CN107237670A (en) * 2016-03-28 2017-10-10 日本碍子株式会社 The manufacture method of honeycomb structured body and honeycomb structured body
JP2019136619A (en) * 2018-02-06 2019-08-22 日本碍子株式会社 Honeycomb filter
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Publication number Priority date Publication date Assignee Title
US7138003B2 (en) * 2003-03-10 2006-11-21 Ngk Insulators, Ltd Honeycomb structure
WO2008120802A1 (en) 2007-04-03 2008-10-09 Yanmar Co., Ltd. Black exhaust purification apparatus for diesel engine
US8327629B2 (en) 2007-04-03 2012-12-11 Yanmar Co., Ltd. Black exhaust purification apparatus for diesel engine
JP2011522156A (en) * 2008-06-02 2011-07-28 アラントゥーム Filter media for aftertreatment of exhaust gas from internal combustion engines
JP2017024000A (en) * 2010-04-19 2017-02-02 ビーエーエスエフ コーポレーション Gasoline engine emissions treatment systems having gasoline particulate filters
JP2013530332A (en) * 2010-04-19 2013-07-25 ビー・エイ・エス・エフ、コーポレーション Gasoline engine exhaust treatment system with gasoline particulate filter
JP2015158197A (en) * 2014-01-27 2015-09-03 株式会社デンソー Exhaust gas purification filter and exhaust gas purification filter manufacturing method
US10352211B2 (en) 2014-01-27 2019-07-16 Denso Corporation Exhaust gas purification filter and method of producing the same
CN107237670A (en) * 2016-03-28 2017-10-10 日本碍子株式会社 The manufacture method of honeycomb structured body and honeycomb structured body
CN107237670B (en) * 2016-03-28 2020-09-11 日本碍子株式会社 Honeycomb structure and method for manufacturing honeycomb structure
JP2019136619A (en) * 2018-02-06 2019-08-22 日本碍子株式会社 Honeycomb filter
CN112203741A (en) * 2018-05-31 2021-01-08 康宁股份有限公司 Honeycomb body with a multi-region honeycomb structure and coextrusion production method
US11666897B2 (en) * 2018-05-31 2023-06-06 Corning Incorporated Honeycomb bodies with multi-zoned honeycomb structures and co-extrusion manufacturing methods

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