HONEYCOMB STRUCTURED BODY

Abstract

A column-shaped porous honeycomb structured body forms a plurality of first flow passages that are opened on one end face and closed on the other end face and a plurality of second flow passages that are closed on the one end face and opened on the other end face. The honeycomb structured body comprises: central partition walls where sectional areas of each first flow passage and each second flow passage are individually constant in an axial direction; and other-end-side inclined partition walls where the sectional area of each first flow passage is shrank and the sectional area of each second flow passage is expanded from the central partition walls to the other end face. An axial-directional length of the other-end-side inclined partition wall is 4 mm or more.

Claims

1. A column-shaped porous honeycomb structured body which forms a plurality of first flow passages that are opened on one end face and closed on the other end face and a plurality of second flow passages that are closed on the one end face and opened on the other end face, the honeycomb structured body comprising; central partition walls where sectional areas of each first flow passage and each second flow passage are individually constant in an axial direction; and other-end-side inclined partition walls where the sectional area of each first flow passage is shrunk and the sectional area of each second flow passage is expanded from the central partition walls toward the other end face, wherein an axial-directional length of the other-end-side inclined partition wall is 4 mm or more.

2. The honeycomb structured body according to claim 1, wherein the axial-directional length of the other-end-side inclined partition wall is 20 mm or less.

3. The honeycomb structured body according to claim 1, further comprising one-end-side inclined partition walls where the sectional area of each first flow passage is expanded and the sectional area of each second flow passage is shrunk from the central partition walls toward the one end face.

4. The honeycomb structured body according to claim 1, wherein the one end face is an inlet side of gas and the other end face is an outlet side of the gas.

5. A honeycomb filter comprising: the honeycomb structured body according to claim 1: and a catalyst.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0013] FIG. 1 is a perspective view of a honeycomb filter 100 according to a first embodiment.

[0014] FIG. 2 is a cross-sectional view of central partition walls 10.sub.cent of a honeycomb structured body 10 taken along II-II in FIG. 1.

[0015] FIG. 3(a) is an expanded view of an end face of an inlet (one-end-side) end face 10E.sub.in in FIG. 1, and FIG. 3(b) is a cross-sectional view taken along b-b in FIG. 3(a).

[0016] FIG. 4(a) is an expanded view of an end face of an outlet (other-end-side) end face 10E.sub.out in FIG. 1, and FIG. 4(b) is a cross-sectional view taken along b˜b in FIG. 4(a)

[0017] FIG. 5 is a schematic diagram showing a method for producing a honeycomb filter according to the first embodiment.

DESCRIPTION OF EMBODIMENTS

[0018] A first embodiment of the present invention is described with reference to the drawings.

First Embodiment

[0019] A honeycomb filter 100 according to the embodiment includes a column-shaped porous honeycomb structured body 10 as shown in FIG. 1. The honeycomb structured body 10 has an inlet end face (one end face) 10E.sub.in and an outlet end face (the other end face) 10E.sub.out. The honeycomb structured body 10 forms a plurality of inlet flow passages (plurality of first flow passages) 70H.sub.in that are opened on the inlet, end face 10E.sub.in and closed on the outlet end face 10E.sub.out, and a plurality of outlet flow passages (plurality of second flow passages) 70H.sub.out that are closed on the inlet end face 10E.sub.in and opened on the outlet end face 10E.sub.out, and these flow passages extend in the axial direction of the honeycomb structured body 10. Moreover, the honeycomb structured body 10 has inlet-side inclined partition walls (one-end-side inclined partition walls) 10.sub.in having the inlet end face 10E.sub.in, outlet-side inclined partition walls (other-end-side inclined partition walls) 10.sub.out having the outlet end lace 10E.sub.out, and central partition walls 10.sub.cent between these.

[0020] The outer diameter of the honeycomb structured body 10 can be sets for example, to be 50 to 250 mm. The axial-directional length of the honeycomb structured body 10 can be set, for example, to be 50 to 300 mm.

[0021] FIG. 2 is a cross-section of the central partition walls 10.sub.cent of the honeycomb structured body 10. The central partition walls 10.sub.cent form many inlet flow passages 70H.sub.in and many outlet flow passages 70H.sub.out sectional areas of which are individually substantially constant along the axial direction. In the embodiment, the inlet flow passages 70H.sub.in and the outlet flow passages 70H.sub.out are regularly arranged in such a way that in the central partition walls 10.sub.cent, one inlet flow passage 70H.sub.in is adjacent to three other inlet flow passages 70H.sub.in and adjacent to three outlet flow passages 70H.sub.out. One outlet flow passage 70H.sub.out is adjacent to six inlet flow passages 70H.sub.in and not adjacent to the other outlet flow passages 70H.sub.out. Each flow passage Is adjacent to totally six flow passages respectively via the partition walls. In the central partition walls 10.sub.cent the sectional shapes of the inlet flow passages 70H.sub.in and the outlet flow passages 70H.sub.out are substantially hexagonal. The thickness of a portion W that separates two flow passages in the central partition wall 10.sub.cent can be set, for example, to be 0.10 to 0.35 mm. The density of the flow passages can be set, for example, to be 150 to 400 cpsi.

[0022] Next, referring to FIGS. 3(a) and FIG. 3(b), a structure of the inlet-side inclined partition walls (one-end-side inclined partition walls) 10.sub.in is shown. The inlet-side inclined partition wails 10.sub.in are inclined relative to the axis of the inlet flow passages 70H.sub.in and the outlet flow passages 70H.sub.out in such a way as to gradually expand the sectional areas of the inlet flow passages 70H.sub.in and to gradually shrink and close the sectional areas of the outlet flow passages 70H.sub.out as compared with the central partition walls 10.sub.cent, from the central partition walls 10.sub.cent toward the inlet end face 10E.sub.in. Specifically, the inlet-side inclined partition walls 10.sub.in gradually expand the sectional areas of the inlet flow passages 70H.sub.in which are substantially hexagonal in the central partition walls 10.sub.cent and make the sectional shapes triangular on the inlet end face 10E.sub.in, and make the sectional areas of the outlet flow passages 70H.sub.out 0 before reaching the inlet end face 10E.sub.in, from the central partition walls 10.sub.cent toward the inlet end face 10E.sub.in. On the inlet end face 10E.sub.in, the vertices of each triangle forming the expanded inlet flow passage 70H.sub.in reach the centers of the outlet flow passages 70H.sub.out, and in this way, the outlet flow passages 70H.sub.out are closed. In the inlet-side inclined partition walls 10.sub.in, the thickness of a plate-like portion separating two flow passages can be set, for example, to be 0.10 to 0.35 mm. This thickness can be a thickness within ±10% relative to the thickness of the partition wall in the central partition walls 10.sub.cent.

[0023] Next, referring to FIG. 4(a) and FIG. 4(b), a structure of the outlet-side inclined partition wails (other-end-side inclined partition walls) 10.sub.out is shown. The outlet-side inclined partition walls 10.sub.out are inclined relative to the axis of the inlet flow passages 70H.sub.in and the outlet flow passages 70H.sub.out in such a way as to gradually expand the sectional areas of the outlet flow passages 70H.sub.out and to gradually shrink and close the sectional areas of the inlet flow passages 70H.sub.in as compared with the central partition walls 10.sub.cent, from the central partition walls 10.sub.cent toward the outlet end face 10E.sub.out. Specifically, the outlet-side inclined partition walls 10.sub.out gradually expand the sectional areas of the outlet flow passages 70H.sub.out which are substantially hexagonal in the central partition walls 10.sub.cent into hexagons, side portions of each of the outlet flow passages 70H.sub.out becoming the corners of the hexagon, and make the sectional areas of the outlet flow passages 70H.sub.out 0 before reaching the outlet end face 10E.sub.out, from the central partition walls 10.sub.cent to the outlet end face 10E.sub.out. On the outlet end face 10E.sub.out, the vertices of each hexagon of the expanded outlet flow passage 70H.sub.out reach the vicinities of the centers of the inlet flow passages 70H.sub.in, and in this way, the inlet flow passages 70H.sub.in are closed. In the outlet-side inclined partition walls 10.sub.out, the thickness of a plate-like portion separating two flow passages can be set, for example, to be 0.10 to 0.8 mm. This thickness can set to be a thickness equivalent to (for example, not less than 0.9 times) the thickness of the partition wall in the central partition walls 10.sub.cent or not less than the thickness of the partition wall and its upper limit can be made large up to the length of opposite sides (see FIG. 2) out of the contour lines of substantial hexagons of two adjacent Met flow passages 70H.sub.in in the central partition walls 10.sub.cent.

[0024] An aperture ratio on the inlet end face 10E.sub.in can be made larger than an aperture ratio on the outlet end face 10E.sub.out.

[0025] In the embodiment, an axial-directional length H.sub.out of the outlet-side inclined partition wall 10.sub.out is 4 mm or more. The upper limit of H.sub.out does not specially exist but it can be set, for example, to be 20 mm or less. An axial-directional length H.sub.in of the inlet-side inclined partition wall 10.sub.in is not specially limited but it can be set, for example, to be 4 mm or more, and also, to be 20 mm or less.

[0026] Notably, the axial-directional, lengths H.sub.in and H.sub.out of the inclined partition walls can also have dispersions on the individual flow passages, and in such a case, the arithmetic mean of those only has to satisfy the aforementioned requirement.

[0027] The material of the honeycomb structured body 10 is porous ceramics, which have pores that gas can pass through, and on the other hand, that can capture particles such as soot. Examples of the ceramics include aluminum titanate, silicon carbide and cordierite. Aluminum titanate can contain magnesium, silicon and the like. The porosity of the partition wall of the honeycomb structured body 10 can be set, for example, to be 40 to 70%.

[0028] A catalyst may be supported on the surface of the honeycomb structured body 10. Examples of the catalyst include particles of at least one metal element selected from the group consisting of Pt, Pd, Rh, silver, vanadium, chromium, manganese, iron, cobalt, nickel and copper, or a zeolite catalyst. The particle diameter of the catalyst can be set, for example, to be 1 nm to 10 μm.

[0029] While the catalyst may be directly supported on the surface of the honeycomb structured body 10, it can also be held on a support held on the honeycomb structured body. The support sometimes functions as a co-catalyst.

[0030] Examples of the support include particles of oxides such as alumina, silica, magnesia, titania, zirconia, ceria, La.sub.2O.sub.3, BaO and zeolite, or composite oxides containing one or more of these. The particle diameter of the support can be set, for example, to be 0.1 to 100 μm.

[0031] Subsequently, operation of the honeycomb filter according to the embodiment is described. As compared with a honeycomb filter 100 in which flow passages are closed with plugs, the honeycomb filter 100 as above can have a lower initial pressure loss. Specifically, the effect of reducing a pressure loss by an end surface of the inlet flow passage 70H.sub.in being set to be an inclined surface by the outlet-side inclined partition wall 10.sub.out is high. In particular, since in the embodiment the axial-directional length H.sub.out of the outlet-side inclined partition wall 10.sub.out is 4 mm or more, the end surface is sufficiently inclined relative to the axis as compared with, the case where the end surface of the inlet flow passage 70H.sub.in is orthogonal to the axis of the flow passage as in conventional plug closing, and hence, sufficient reduction of the pressure loss is possible. Accordingly, an initial pressure loss of the honeycomb filter 100 can be suppressed.

[0032] Subsequently, a method for producing such a honeycomb filter is described. First, a ceramic raw material undergoes extrusion molding by an extrusion molding machine to produce a honeycomb compact having the same sectional shape as that of the central partition wails 10.sub.cent. This honeycomb compact has unclosed inlet flow passages 70H.sub.in and unclosed outlet flow passages 70H.sub.out in the state of these being penetrated.

[0033] The composition of the ceramic raw material only has to be one with which porous ceramics are given after firing it. For example, it can contain Hie ceramic raw material, an organic binder, a pore-forming agent, a solvent, and an additive which is added as needed.

[0034] The ceramic raw material is powder containing elements composing the ceramics. The binder can be an organic binder, and examples thereof include: celluloses such as methylcelluloses, carboxymethylcelluloses, hydroxyalkylmethylcelluloses and sodium carboxymethylcelluloses; alcohols such as polyvinyl alcohol); and lignin sulfonate salts. Examples of the additive include, for example, lubricants, plasticizers and dispersants.

[0035] Subsequently, as shown in FIG. 5, the inlet-side inclined partition walls 10in are formed on the inlet end face 10E.sub.of an obtained unfired honeycomb compact 100′. Specifically, a closing jig 400 having many triangular pyramidal projections 410a is prepared. Then, the closing jig 400 is moved in such a way that each projection 410a comes into the inlet flow passage 70H.sub.in. In this way, the partition walls of the inlet flow passage 70H.sub.in are deformed and the sectional area of the flow passage is expanded, and meanwhile, the sectional areas of the outlet flow passages 70H.sub.out are shrank. Then, finally, as shown in FIG. 3(a) and FIG. 3(b), the sectional shapes of the inlet flow passages 70H.sub.in become triangular, and the partition walls are completely crimped in the outlet flow passages 70H.sub.out and the outlet flow passages 70H.sub.out are sealed. Namely, the outlet flow passages 70H.sub.out are closed on the inlet end face 10E.sub.in. Notably, vibration or ultrasonic waves may be given to the closing jig 400.

[0036] Next, likewise, the outlet-side inclined partition walls 10.sub.out are formed on the outlet end face 10E.sub.out. Projections of a closing jig inserted into the outlet flow passages 70H.sub.out can be set to be hexagonal pyramidal. After that, alter drying as needed, the honeycomb compact 100′ both of whose end faces have been sealed is fired to obtain the honeycomb structured body.

[0037] Subsequently, the catalyst can be supported on the honeycomb structured body 10 as needed by a known method.

[0038] Notably, the present invention is not limited to the aforementioned embodiment but various modifications thereof are possible. For example, arrangements of the inlet flow passages and the outlet flow passages, that is, the numbers of flow passages adjacent to each flow passage are also not limited to those in the aforementioned embodiment. For example, each flow passage can be arranged in such a way that one inlet flow passage 70H.sub.in is adjacent to four other inlet flow passages 70H.sub.in and adjacent to two outlet flow passages 70H.sub.out and that one outlet flow passage 70H.sub.out is adjacent to six inlet flow passages 70H.sub.in and not adjacent to the other outlet flow passages 70H.sub.out. Notably, in the present specification, that “two flow passages are adjacent to each other” can mean that two flow passages are separated from each other via one partition wall in the thickness direction of the partition wall.

[0039] Moreover, any shapes of the inclined partition walls are sufficient as long as the sectional area of each inlet flow passage is shrunk and the sectional area of each outlet flow passage is expanded from the central partition walls toward the other end face, and detailed shapes can be properly modified in accordance with the sectional shape of each flow passage and the arrangement of the flow passages.

[0040] Moreover, the sectional shape of the flow passage is not specially limited to that in the aforementioned embodiment but a polygon such as a tetragon or an octagon, a circle, or the like is possible.

[0041] Moreover, while the honeycomb structured body 10 of the aforementioned embodiment has a structure having inlet inclined partition walls on the inlet side, implementation thereof is possible even with a structure in which the inlet flow passages are closed with plugs at the inlet end and which does not have the inlet-side inclined partition walls.

[0042] Furthermore, the external shape of the filter does not have to be a cylindrical body but may be, for example, a quadrangular prism.

EXAMPLES

Reference Example 1

[0043] A cordierite-made porous honeycomb structured body onto which a catalyst was not adhered and that had a structure as shown in FIG. 1 to FIG. 4 for the aforementioned embodiment was prepared. The outer diameter was 118.4 mm, the length was 113.4 mm, the cell density was 360 cpsi, the wall thickness was 10 mil (0.25 mm), the aperture ratio at the inlet end was 42%, the aperture ratio at the outlet end was 27%, the porosity of the partition walls was 58%, and the average pore diameter was 18 μm. The axial-directional length H.sub.in of the inlet-side inclined partition walls and the axial-directional length H.sub.out of the outlet-side inclined partition walls were set to be 2 to 3 mm (2.5 mm on average) and 2 to 3 mm (2.5 mm on average), respectively. A pressure loss when air at 600 Nm.sub.3/h was fed at room temperature was 5.80 kPa.

Reference Example 2

[0044] This was set to be the same as Reference Example 1 except that the axial-directional length H.sub.in of the inlet-side inclined partition walls was set to be 0, that is, the inlet side was closed with plugs. The pressure loss was 6.00 kPa.

Reference Example 3

[0045] This was set to be the same as Reference Example 1 except that the axial-directional length H.sub.out of the outlet-side Inclined partition walls was set to be 0, that is, the outlet side was closed with plugs. The pressure loss was 6.86 kPa.

Reference Example 4

[0046] This was set to be the same as Reference Example 1 except that the axial-directional length H.sub.in of the inlet-side inclined partition walls was set to be 0 and the axial-directional length H.sub.out of the outlet-side inclined partition walls, that is, both the inlet side and the outlet side were closed with plugs. The pressure loss was 7.67 kPa.

[0047] It is found from these experiments that to provide the inclined partition walls on the outlet side is more effective for reduction of a pressure loss than to provide the inclined partition walls on the inlet side.

Comparative Example 1

[0048] The cell density was changed from 360 cpsi to 250 cpsi. Due to the change of the cell density, the inlet-side aperture ratio became 43% from 42%, and the outlet-side aperture ratio became 30% from 27%. This was set to be the same as Reference Example 1 except the above. The pressure loss was 4.46 kPa.

[0049] This was set to be the same as Comparative Example 1 except that the axial-directional length H.sub.out of the outlet-side inclined partition walls was set to be 4 to 5 mm (4.5 mm on average). The pressure loss was 4.18 kPa.

[0050] Table 1 presents the results.

TABLE-US-00001 TABLE 1 Pressure Cell Wall Inlet-Side Outlet-Side Loss at Density Thickness Aperture Aperture Hin Hout 600 Nm.sup.3/h [cpsi] [mil] Ratio [%] Ratio [%] [mm] [mm] [kPa] Reference 360 10 42 27 2.5 mm 2.5 mm 5.80 Example 1 on on Average Average Reference 360 10 42 27 0 2.5 mm 6.00 Example 2 on Average Reference 360 10 42 27 2.5 mm 0 6.86 Example 3 on Average Reference 360 10 42 27 0 0 7.67 Example 4 Comparative 250 10 43 30 2.5 mm 2.5 mm 4.46 Example 1 on on Average Average Example 1 250 10 43 30 2.5 mm 4.5 mm 4.18 on on Average Average

REFERENCE SIGNS LIST

[0051] 70H.sub.in Inlet flow passage (first flow passage)

[0052] 70H.sub.out Outlet flow passage (second flow passage)

[0053] 10 Honeycomb structured body

[0054] 10.sub.cent Central partition wall

[0055] 10.sub.out Outlet-side inclined partition wall (other-end-side inclined partition wall)

[0056] 10.sub.in Inlet-side inclined partition wall (one-end-side inclined partition wall)

[0057] 10E.sub.in Inlet end face (one end face)

[0058] 10E.sub.out Outlet end face (the other end face)

[0059] 100 Honeycomb filter

[0060] W Portion separating two flow passages

[0061] H.sub.in Axial-directional length of the inlet-side inclined partition wall (one-end-side inclined partition wall)

[0062] H.sub.out Axial-directional length of fee outlet-side inclined partition wall (other-end-side inclined partition wall)

[0063] 400 Closing jig

[0064] 410a Projection