Honeycomb filter

Abstract

To provide a honeycomb filter having excellent trapping performance for trapping particulate matter contained in exhaust gas and excellent purification performance for purifying harmful components contained in the exhaust gas.SOLUTION: The honeycomb filter includes: a honeycomb structure 4 having a porous partition wall 1; and a plugging portion 5 disposed to seal any one end of a cell 2. The honeycomb structure 4 has, in the extending direction of the cell 2 of the honeycomb structure 4: an inflow side region 15 including a range of up to at least 30% of the total length L1 of the honeycomb structure 4 starting from an inflow end face 11 of the honeycomb structure 4; and an outflow side region 16 including a range of up to at least 20% of the total length L1 of the honeycomb structure 4 starting from an outflow end face 12 of the honeycomb structure 4. An average pore diameter of the partition wall 1 in the inflow side region 15 is 15 to 20 μm, and an average pore diameter of the partition wall 1 in the outflow side region 16 is 9 to 14 μm.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a honeycomb filter. More specifically, the present invention relates to a honeycomb filter having excellent collection performance for collecting particulate matter contained in exhaust gas and excellent purification performance for purifying harmful components contained in exhaust gas.

Background Art

[0002] In recent years, regulations regarding the removal of particulate matter contained in exhaust gas discharged from gasoline engines have become stricter worldwide, and honeycomb filters having a honeycomb structure are used as filters for removing particulate matter. Hereinafter, particulate matter may be referred to as "PM". PM is an abbreviation for "Particulate Matter".

[0003] For example, as a honeycomb filter, there can be mentioned one including a honeycomb structure having porous partition walls that partition and form a plurality of cells, and a plugging portion that plugs one end of the cells. Such a honeycomb filter has a structure in which the porous partition walls serve as a filter for removing PM. Specifically, exhaust gas containing PM is made to flow in from the inflow end face of the honeycomb filter, filtered by collecting PM with the porous partition walls, and then the purified exhaust gas is discharged from the outflow end face of the honeycomb filter. In this way, PM in the exhaust gas can be removed.

[0004] For the purpose of improving the purification performance of such a honeycomb filter, an exhaust gas purification catalyst is supported on the porous partition walls (see, for example, Patent Document 1). Examples of the exhaust gas purification catalyst include a platinum group element-containing catalyst composed of an exhaust gas purification catalyst containing a platinum group element. Hereinafter, the platinum group element-containing catalyst may be referred to as a "PGM catalyst". "PGM" is an abbreviation for "Platinum Group Metal". PGM includes ruthenium, rhodium, palladium, osmium, iridium, and platinum.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In recent years, a honeycomb filter in which a catalyst for purifying exhaust gas (hereinafter, also simply referred to as "catalyst") as described above is supported on a porous partition wall has had problems such as a decrease in the collection performance of the honeycomb filter and an increase in the pressure loss of the honeycomb filter. In addition, with the strengthening of exhaust gas regulations, further measures are required to further improve the exhaust gas purification performance of the honeycomb filter. For example, if more catalyst is supported by the porous partition wall, although the exhaust gas purification performance can be improved, the decrease in the collection performance of the honeycomb filter described above becomes more significant. For this reason, there is a demand for the development of a honeycomb filter that can improve the exhaust gas purification performance without increasing the catalyst loading amount and that also has excellent collection performance.

[0007] The present invention has been made in view of such problems of the prior art. According to the present invention, there is provided a honeycomb filter having excellent collection performance for collecting PM contained in exhaust gas and excellent purification performance for purifying harmful components contained in exhaust gas.

Means for Solving the Problems

[0008] According to the present invention, there is provided a honeycomb filter as shown below.

[0009] [1] A honeycomb structure having a porous partition wall disposed so as to surround a plurality of cells serving as fluid flow paths extending from an inflow end face to an outflow end face, and a plugging portion disposed so as to seal either one end of the cell on the inflow end face side or the outflow end face side. The eye-sealing portion is disposed at the end on the outflow end face side, and the cell with the inflow end face side opened is used as an inflow cell. The eye-sealing portion is disposed at the end on the inflow end face side, and the cell with the outflow end face side opened is used as an outflow cell. In the direction in which the cells of the honeycomb structure extend, the honeycomb structure has an inflow-side region starting from the inflow end face of the honeycomb structure and an outflow-side region starting from the outflow end face of the honeycomb structure. The length L2 in the extending direction of the cells in the inflow-side region starting from the inflow end face is in the range of 30% to 60% of the total length L1 of the honeycomb structure, and the length L3 in the extending direction of the cells in the outflow-side region starting from the outflow end face is in the range of 20% to 50% of the total length L1 of the honeycomb structure. Further, the honeycomb structure has an intermediate region between the inflow-side region and the outflow-side region in the extending direction of the cells. The average pore diameter of the partition walls in the inflow-side region is 9 to 14 μm, and the average pore diameter of the partition walls in the outflow-side region is 15 to 20 μm. The average pore diameter of the partition walls in the intermediate region does not belong to either the numerical range of 9 to 14 μm of the average pore diameter of the partition walls in the inflow-side region or the numerical range of 15 to 20 μm of the average pore diameter of the partition walls in the outflow-side region. A honeycomb filter.

[0010] [2] The honeycomb filter according to [1], wherein the porosity of the partition walls is 50 to 65%, and the thickness of the partition walls is 0.19 to 0.31 mm.

[0011] [3] The cell density of the honeycomb structure is 30 to 50 cells / cm 2 The honeycomb filter according to [1] or [2].

[0012] [4] The honeycomb filter further includes an exhaust gas purification catalyst supported on the partition walls constituting the honeycomb structure. The exhaust gas purification catalyst is supported at least on the surface of the partition walls in the inflow side region of the honeycomb structure, and is the honeycomb filter according to any one of [1] to [3] above.

[0013] [5] The honeycomb filter according to [4] above, wherein the exhaust gas purification catalyst contains a platinum group element-containing catalyst.

[0014] [6] The honeycomb filter according to [5] above, wherein the platinum group element-containing catalyst contains an oxide of at least one element among aluminum, zirconium, and cerium.

[0015] [7] The honeycomb filter according to any one of [4] to [6] above, wherein the loading amount of the exhaust gas purification catalyst per unit volume of the honeycomb structure is less than 50 g / L.

Advantages of the Invention

[0016] When the honeycomb filter of the present invention is used by supporting an exhaust gas purification catalyst on a porous partition wall, it has excellent collection performance for collecting PM contained in the exhaust gas and excellent purification performance for purifying harmful components contained in the exhaust gas. In particular, the honeycomb filter of the present invention can improve the purification performance without increasing the loading amount of the exhaust gas purification catalyst, and can also improve the collection performance.

[0017] That is, in the direction in which the cells of the honeycomb structure of the honeycomb filter of the present invention extend, starting from the inflow end face of the honeycomb structure, in a range of at least 30% with respect to the total length of the honeycomb structure, there is an inflow-side region having an average pore diameter of 9 to 14 μm. This inflow-side region is configured such that the average pore diameter of the partition walls becomes relatively small. When a catalyst for exhaust gas purification is supported, it is difficult for the catalyst for exhaust gas purification to penetrate into the pores formed in the partition walls. Therefore, when a catalyst for exhaust gas purification is supported on the honeycomb filter, in the above-described inflow-side region, the catalyst for exhaust gas purification is preferentially supported on the surface of the partition walls, and a catalyst layer in which the catalyst for exhaust gas purification is deposited is formed on the surface of the partition walls. In particular, as described above, in the inflow-side region, it is difficult for the catalyst for exhaust gas purification to penetrate into the pores formed in the partition walls. Therefore, even with a small catalyst loading amount, a catalyst layer having a sufficient thickness is formed on the surface of the partition walls. For this reason, in the inflow-side region, the contact between the catalyst layer on the surface of the partition walls and the exhaust gas increases, and the exhaust gas purification performance can be effectively improved. On the other hand, the honeycomb filter of the present invention has an outflow-side region having an average pore diameter of 15 to 20 μm in a range of at least 20% with respect to the total length of the honeycomb structure, starting from the outflow end face of the honeycomb structure, in the direction in which the cells of the honeycomb structure extend. When the amount of the catalyst for exhaust gas purification supported on the honeycomb filter is small, the catalyst loading amount in the outflow-side region will relatively decrease compared to the catalyst loading amount in the inflow-side region. Further, even when the catalyst for exhaust gas purification is supported, it is difficult for the catalyst for exhaust gas purification to penetrate into the pores formed in the partition walls, and in the outflow-side region, it is difficult to form a cake layer such as a catalyst layer. For this reason, the porous partition walls in the outflow-side region can effectively function as a filter medium for collecting PM, and excellent collection performance can be realized.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. Therefore, it should be understood that those obtained by appropriately changing and improving the following embodiments based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention also fall within the scope of the present invention.

[0020] (1) Honeycomb filter: The first embodiment of the honeycomb filter of the present invention is a honeycomb filter 100 as shown in Figs. 1 to 4. Here, Fig. 1 is a perspective view schematically showing the first embodiment of the honeycomb filter of the present invention. Fig. 2 is a plan view of the inflow end face side of the honeycomb filter shown in Fig. 1. Fig. 3 is a plan view of the outflow end face side of the honeycomb filter shown in Fig. 1. Fig. 4 is a cross-sectional view schematically showing the A-A' cross-section of Fig. 2.

[0021] As shown in Figs. 1 to 4, the honeycomb filter 100 of the present embodiment includes a honeycomb structure 4 and an end sealing portion 5. The honeycomb structure 4 has a porous partition wall 1 disposed so as to surround a plurality of cells 2 that serve as fluid flow paths extending from the inflow end face 11 to the outflow end face 12. The honeycomb structure 4 shown in Figs. 1 to 4 is configured in a cylindrical shape having the inflow end face 11 and the outflow end face 12 as both end faces, and further has an outer peripheral wall 3 on its outer peripheral side surface. That is, the outer peripheral wall 3 is disposed so as to surround the partition walls 1 arranged in a lattice pattern.

[0022] The eye seal portion 5 is arranged to seal one end of either the inflow end face 11 side or the outflow end face 12 side of the cell 2. Hereinafter, among the plurality of cells 2, the cell 2 in which the eye seal portion 5 is disposed at the end on the outflow end face 12 side and the inflow end face 11 side is open is referred to as the "inflow cell 2a". Further, among the plurality of cells 2, the cell 2 in which the eye seal portion 5 is disposed at the end on the inflow end face 11 side and the outflow end face 12 side is open is referred to as the "outflow cell 2b". In the honeycomb filter 100 of the present embodiment, it is preferable that the inflow cells 2a and the outflow cells 2b are alternately arranged with the partition wall 1 therebetween.

[0023] The honeycomb filter 100 is characterized in that the honeycomb structure 4 is configured as follows. The honeycomb structure 4 has an inflow side region 15 including a range of at least 30% with respect to the total length L1 of the honeycomb structure 4 starting from the inflow end face 11 of the honeycomb structure 4 in the extending direction of the cells 2 of the honeycomb structure 4. Further, the honeycomb structure 4 has an outflow side region 16 including a range of at least 20% with respect to the total length L1 of the honeycomb structure 4 starting from the outflow end face 12 of the honeycomb structure 4 in the extending direction of the cells 2 of the honeycomb structure 4. That is, as shown in FIG. 4, in the honeycomb structure 4, the length L2 in the extending direction of the cells 2 in the inflow side region 15 is at least 30% with respect to the total length L1 of the honeycomb structure 4, and the length L3 in the extending direction of the cells 2 in the outflow side region 16 is at least 20% with respect to the total length L1 of the honeycomb structure 4.

[0024] Hereinafter, the ratio (%) of the length of the inflow side region 15 starting from the inflow end face 11 of the honeycomb structure 4 to the total length L1 of the honeycomb structure 4 may be referred to as the "length range (%) from the inflow end face 11 of the inflow side region 15". Further, the ratio (%) of the length of the outflow side region 16 starting from the outflow end face 12 of the honeycomb structure 4 to the total length L1 of the honeycomb structure 4 may be referred to as the "length range (%) from the outflow end face 12 of the outflow side region 16".

[0025] In the honeycomb filter 100 of this embodiment, the average pore diameter of the partition wall 1 in the inflow side region 15 is 9 to 14 μm, and the average pore diameter of the partition wall 1 in the outflow side region 16 is 15 to 20 μm. That is, in the inflow side region 15 of the honeycomb structure 4 of the honeycomb filter 100, the average pore diameter of the partition wall 1 is relatively small, while in the outflow side region 16 of the honeycomb structure 4, the average pore diameter of the partition wall 1 is relatively large. The average pore diameter of the partition wall 1 in the inflow side region 15 and the outflow side region 16 of the honeycomb structure 4 is a value measured by the mercury intrusion method. The average pore diameter of the partition wall 1 can be measured, for example, using AutoPore 9500 (trade name) manufactured by Micromeritics.

[0026] When the honeycomb filter 100 is used with an exhaust gas purification catalyst supported on the porous partition wall 1, it has excellent collection performance for collecting PM contained in the exhaust gas and also excellent purification performance for purifying harmful components contained in the exhaust gas.

[0027] That is, when the honeycomb filter 100 is used with the exhaust gas purification catalyst supported on the porous partition wall 1, in the inflow side region 15 where the average pore diameter of the partition wall 1 is 9 to 14 μm, it is difficult for the exhaust gas purification catalyst to penetrate into the pores formed in the partition wall 1. Therefore, when the exhaust gas purification catalyst is supported on the honeycomb filter 100, in the inflow side region 15, the exhaust gas purification catalyst is preferentially supported on the surface of the partition wall 1, and a catalyst layer in which the exhaust gas purification catalyst is deposited is formed on the surface of the partition wall 1. In particular, as described above, in the inflow side region 15, it is difficult for the exhaust gas purification catalyst to penetrate into the pores formed in the partition wall 1. Therefore, even with a small catalyst loading amount, a catalyst layer with a sufficient thickness is formed on the surface of the partition wall 1. For this reason, in the inflow side region 15, the contact between the catalyst layer on the surface of the partition wall 1 and the exhaust gas increases, and the exhaust gas purification performance can be effectively improved. On the other hand, in the outflow side region 16 where the average pore diameter of the partition wall 1 is 15 to 20 μm, when the exhaust gas purification catalyst is supported, the catalyst loading amount thereof will relatively decrease compared to the catalyst loading amount in the inflow side region 15. Further, even if the exhaust gas purification catalyst is supported, the exhaust gas purification catalyst penetrates into the pores formed in the partition wall 1, and it is difficult to form a cake layer such as a catalyst layer in the outflow side region 16. Therefore, the porous partition wall 1 in the outflow side region 16 effectively functions as a filter medium for collecting PM, and excellent collection performance can be realized.

[0028] The method for confirming the inflow side region 15 and the outflow side region 16 of the honeycomb structure 4, and the method for measuring the average pore diameter of each partition wall 1 in the inflow side region 15 and the outflow side region 16 are as follows. First, starting from the inflow end face 11, five measurement points are determined at 1% intervals with respect to the total length L1 of the honeycomb structure 4. Then, from each of the above-described measurement points, a part of the partition wall 1 of the honeycomb structure 4 is cut out, and a measurement sample piece for measuring the average pore diameter is cut out respectively. As the measurement sample piece, for example, a rectangular parallelepiped having lengths of about 10 mm, about 10 mm, and about 10 mm in the longitudinal, transverse, and height directions, respectively, is used. Then, for each measurement sample piece, the average pore diameter (that is, the average pore diameter at 1% intervals with respect to the total length L1 of the honeycomb structure 4 starting from the inflow end face 11) is measured by the mercury intrusion method.

[0029] In the measurement of the average pore diameter described above, the range where the average pore diameter of the partition wall 1 is 9 to 14 μm starting from the inflow end face 11 is the "inflow side region 15". Further, the ratio of the length of the range where the average pore diameter of the partition wall 1 is 9 to 14 μm (that is, the inflow side region 15) starting from the inflow end face 11 to the total length L1 of the honeycomb structure 4 is the "length range (%) from the inflow end face 11 of the inflow side region 15".

[0030] Similarly, in the measurement of the average pore diameter described above, the range where the average pore diameter of the partition wall 1 is 15 to 20 μm starting from the outflow end face 12 is the "outflow side region 16". Further, the ratio of the length of the range where the average pore diameter of the partition wall 1 is 15 to 20 μm (that is, the outflow side region 16) starting from the outflow end face 12 to the total length L1 of the honeycomb structure 4 is the "length range (%) from the outflow end face 12 of the outflow side region 16".

[0031] In the honeycomb filter 100 of the present embodiment, the inflow side region 15 is in the range of at least 30% with respect to the total length L1 of the honeycomb structure 4 starting from the inflow end face 11. On the other hand, the outflow side region 16 is in the range of at least 20% with respect to the total length L1 of the honeycomb structure 4 starting from the outflow end face 12. For this reason, the honeycomb structure 4 may further have an "intermediate region 17" other than the inflow side region 15 and the outflow side region 16 in a part of the range of 30 to 80% in the direction of the extension of the cell 2 of the honeycomb structure 4 starting from the inflow end face 11 in the total length L1 direction of the honeycomb structure 4. The intermediate region 17 does not satisfy the respective numerical ranges of the average pore diameter of the partition wall 1 in the inflow side region 15 and the outflow side region 16, and is a region not included in any of the regions. Of course, the honeycomb structure 4 may not have the intermediate region 17 as described above, and the predetermined length range starting from the inflow end face 11 may be the inflow side region 15, and the remaining length range may all be the outflow side region 16.

[0032] In the honeycomb structure 4, it is preferable that the average pore diameter of the partition wall 1 in the intermediate region 17 exceeds 14 μm and is less than 15 μm. For example, when the average pore diameter of the honeycomb structure 4 is 9 to 14 μm in the range of 50% with respect to the total length L1 of the honeycomb structure 4 starting from the inflow end face 11, and 14 to 15 μm in the range of 50% to 70%, the above-mentioned 50% range becomes the inflow side region 15, and the range of 50% to 70% becomes the intermediate region 17. And, for example, when the average pore diameter in the remaining range of 70 to 100% with respect to the total length L1 of the honeycomb structure 4 starting from the inflow end face 11 is 15 to 20 μm, this remaining range (70 to 100% range) becomes the outflow side region 16.

[0033] As shown in FIG. 4, in the honeycomb structure 4, the length L2 in the extending direction of the cells 2 in the inflow side region 15 is at least 30% with respect to the total length L1 of the honeycomb structure 4, and is at most 80% with respect to the total length L1 of the honeycomb structure 4. The length L2 in the extending direction of the cells 2 in the inflow side region 15 is not particularly limited, but for example, it is preferably 30 to 60% with respect to the total length L1 of the honeycomb structure 4, and more preferably 30 to 50%.

[0034] Also, in the honeycomb structure 4, the length L3 in the extending direction of the cells 2 in the outflow side region 16 is at least 20% with respect to the total length L1 of the honeycomb structure 4, and is at most 70% with respect to the total length L1 of the honeycomb structure 4. The length L3 in the extending direction of the cells 2 in the outflow side region 16 is not particularly limited, but for example, it is preferably 20 to 40% with respect to the total length L1 of the honeycomb structure 4, and more preferably 20 to 30%.

[0035] In the honeycomb structure 4, the intermediate region 17 is an arbitrary component as described above, and the length L4 in the extending direction of the cells 2 in the intermediate region 17 is at most 50% with respect to the total length L1 of the honeycomb structure 4. The length L4 in the extending direction of the cells 2 in the intermediate region 17 can be appropriately set according to the length L2 in the extending direction of the cells 2 in the inflow side region 15 and the length L3 in the extending direction of the cells 2 in the outflow side region 16 described so far.

[0036] The average pore diameter of the partition wall 1 in the inflow side region 15 is 9 to 14 μm, preferably 9 to 13 μm, and more preferably 9 to 12 μm. Further, the average pore diameter of the partition wall 1 in the outflow side region 16 is 15 to 20 μm, preferably 15 to 19 μm, and more preferably 15 to 17 μm.

[0037] The porosity of the partition wall 1 of the honeycomb structure 4 is preferably 50 to 65%, more preferably 55 to 65%, and particularly preferably 60 to 65%. The porosity of the partition wall 1 is a value measured by the mercury intrusion method. The porosity of the partition wall 1 can be measured, for example, using an AutoPore 9500 (trade name) manufactured by Micromeritics. If the porosity of the partition wall 1 is less than 50%, the partition wall permeation resistance increases, which is not preferable in terms of the increase in pressure loss. If the porosity of the partition wall 1 exceeds 65%, the strength significantly decreases, which is not preferable.

[0038] For the honeycomb structure 4, the thickness of the partition wall 1 is preferably 0.19 to 0.31 mm, more preferably 0.22 to 0.31 mm, and particularly preferably 0.22 to 0.28 mm. The thickness of the partition wall 1 can be measured, for example, using a scanning electron microscope or a microscope. If the thickness of the partition wall 1 is less than 0.19 mm, sufficient strength may not be obtained. On the other hand, if the thickness of the partition wall 1 exceeds 0.31 mm, the pressure loss may increase when a catalyst is supported on the partition wall 1.

[0039] There is no particular limitation on the shape of the cells 2 formed in the honeycomb structure 4. For example, the shape of the cells 2 in a cross-section orthogonal to the extending direction of the cells 2 can include polygons, circles, ellipses, etc. Examples of polygons can include triangles, quadrilaterals, pentagons, hexagons, octagons, etc. Note that the shape of the cells 2 is preferably a triangle, quadrilateral, pentagon, hexagon, or octagon. Also, regarding the shape of the cells 2, the shapes of all the cells 2 may be the same or different. For example, although not shown in the figure, it may be a mixture of quadrilateral cells and octagonal cells. Further, regarding the size of the cells 2, the sizes of all the cells 2 may be the same or different. For example, although not shown in the figure, among a plurality of cells, the size of some cells may be increased and the size of other cells may be relatively decreased. In the present invention, a cell means a space surrounded by partition walls.

[0040] The cell density of the cells 2 partitioned and formed by the partition walls 1 is preferably 30 to 50 cells / cm 2 and more preferably 35 to 50 cells / cm 2 By configuring in this way, it can be suitably used as a filter for collecting PM in the exhaust gas discharged from an engine of an automobile or the like.

[0041] The outer peripheral wall 3 of the honeycomb structure 4 may be integrally formed with the partition wall 1 or may be an outer peripheral coat layer formed by coating an outer peripheral coating material so as to surround the partition wall 1. Although not shown in the figure, the outer peripheral coat layer can be provided on the outer peripheral side of the partition wall after, during manufacturing, removing the formed outer peripheral wall by a known method such as grinding after integrally forming the partition wall and the outer peripheral wall.

[0042] There is no particular limitation on the shape of the honeycomb structure 4. Examples of the shape of the honeycomb structure 4 include columnar shapes such as circular, elliptical, and polygonal shapes for the inflow end face 11 and the outflow end face 12.

[0043] The size of the honeycomb structure 4, for example, the length in the extending direction of the cells 2 of the honeycomb structure 4 (hereinafter also referred to as "total length L1"), and the size of the cross-section orthogonal to the extending direction of the cells 2 of the honeycomb structure 4 (hereinafter also referred to as "cross-sectional area") are not particularly limited. Each size may be appropriately selected so as to obtain optimal purification performance when the honeycomb filter 100 is used. The total length L1 of the honeycomb structure 4 is preferably 90 to 160 mm, and more preferably 120 to 140 mm. Further, the cross-sectional area of the honeycomb structure 4 is preferably 8000 to 16000 mm 2 and more preferably 10000 to 14000 mm 2 .

[0044] It is preferable that the material of the partition wall 1 contains at least one selected from the group consisting of cordierite, silicon carbide, silicon-silicon carbide composite material, mullite, alumina, aluminum titanate, silicon nitride, and silicon carbide-cordierite composite material. The material constituting the partition wall 1 is preferably a material containing 30% by mass or more of the materials listed in the above group, more preferably a material containing 40% by mass or more, and particularly preferably a material containing 50% by mass or more. In the honeycomb filter 100 of the present embodiment, cordierite is particularly preferable as the material constituting the partition wall 1.

[0045] The honeycomb structure 4 is preferably an integrally molded product made of the material constituting the partition wall 1 described above. That is, the honeycomb structure 4 in the honeycomb filter 100 is preferably not a product produced by connecting the inflow side region 15 and the outflow side region 16 which are separately produced, but an integrally molded product integrally molded using a predetermined molding material.

[0046] The honeycomb filter 100 may further include an exhaust gas purification catalyst (not shown) supported on the partition walls 1 constituting the honeycomb structure 4. And, it is preferable that the exhaust gas purification catalyst is supported at least on the surface of the partition wall 1 in the inflow side region 15 of the honeycomb structure 4. Here, "supported at least on the surface of the partition wall 1" means that the exhaust gas purification catalyst may be supported only on the surface of the partition wall 1, or may be supported on the surface of the partition wall 1 and inside the pores. "Supported only on the surface of the partition wall 1" means that in the thickness direction of the partition wall 1, the catalyst exists on the surface of the partition wall 1, and there is no exhaust gas purification catalyst between 0.1T (where T represents the thickness of the partition wall 1) and 1.0T from the surface of the partition wall 1 on the inflow cell 2a side of the partition wall 1 in the thickness direction of the partition wall 1. "Supported on the surface of the partition wall 1 and inside the pores" means that the catalyst exists on the surface of the partition wall 1, and in the thickness direction of the partition wall 1, the exhaust gas purification catalyst exists at least somewhere between 0.1T (where T represents the thickness of the partition wall 1) and 0.9T from the surface of the partition wall 1 on the inflow cell 2a side of the partition wall 1 in the thickness direction of the partition wall 1. On the other hand, in the outflow side region 16 of the honeycomb structure 4, it is preferable that the exhaust gas purification catalyst is not supported. Also, when the exhaust gas purification catalyst is supported in the outflow side region 16, it may be supported inside the pores formed in the partition wall 1. "Supported inside the pores of the partition wall 1" means that in the thickness direction of the partition wall 1, the exhaust gas purification catalyst exists at least somewhere between 0.1T (where T represents the thickness of the partition wall 1) and 0.9T from the surface of the partition wall 1 on the inflow cell 2a side of the partition wall 1 in the thickness direction of the partition wall 1. By configuring in this way, in the inflow side region 15, a catalyst layer in which the exhaust gas purification catalyst is deposited on the surface of the partition wall 1 is formed. In particular, in the inflow side region 15, since it is difficult for the exhaust gas purification catalyst to enter inside the pores formed in the partition wall 1, even with a small catalyst loading amount, a catalyst layer with a sufficient thickness is formed on the surface of the partition wall 1. For this reason, in the inflow side region 15, the contact between the catalyst layer on the surface of the partition wall 1 and the exhaust gas increases, and the exhaust gas purification performance can be effectively improved.In addition, the porous partition wall 1 in the outflow side region 16 effectively functions as a filter medium for collecting PM, and excellent collection performance can be realized.

[0047] As described above, in the honeycomb filter 100 further provided with a catalyst for purifying exhaust gas, it is preferable to make the supported form of the catalyst different between the inflow side region 15 and the outflow side region 16 having different average pore diameters. Since the average pore diameter of the partition wall 1 is different in the two regions of the inflow side region 15 and the outflow side region 16, for example, by using one type of catalyst-supporting slurry (for example, catalyst liquid), the supported form of the catalyst can be changed for each region. In particular, the supported form of the catalyst for a desired region can be easily changed by one catalyst-supporting step. Therefore, according to the honeycomb filter 100 of the present embodiment, the honeycomb filter 100 further provided with a catalyst for purifying exhaust gas as described above can be manufactured extremely easily.

[0048] In the inflow side region 15, as described above, as long as the catalyst is supported at least on the surface of the partition wall 1, a part of the catalyst may be supported inside the pores formed in the partition wall 1. However, in the inflow side region 15, when the catalyst is supported, it is difficult for the catalyst to penetrate inside the pores. Therefore, the catalyst is preferentially supported on the surface of the partition wall 1, and even with a small catalyst support amount, a catalyst layer with a sufficient thickness can be formed on the surface of the partition wall 1. Therefore, according to the honeycomb filter 100 of the present embodiment, the usage amount (in other words, the supported amount) of the catalyst for purifying exhaust gas can be reduced.

[0049] The exhaust gas purification catalyst supported on the partition wall 1 constituting the honeycomb structure 4 preferably contains a platinum group element-containing catalyst. The platinum group element-containing catalyst refers to an exhaust gas purification catalyst containing a platinum group element. The platinum group elements are ruthenium, rhodium, palladium, osmium, iridium, and platinum. Hereinafter, the platinum group elements may be referred to as "PGM". When the exhaust gas purification catalyst contains a platinum group element-containing catalyst, it has the effect of excellent purification performance for purifying harmful components contained in the exhaust gas. In the honeycomb filter 100 of the present embodiment, the exhaust gas purification catalyst supported on the partition wall 1 is preferably a substantially platinum group element-containing catalyst.

[0050] The platinum group element-containing catalyst preferably contains an oxide of at least one element among aluminum, zirconium, and cerium. The catalyst containing such an oxide preferably contains 1 to 3% by mass of platinum group elements based on the total mass of the catalyst. The composition of the platinum group element-containing catalyst can be measured, for example, by X-ray fluorescence analysis (XRF). Specifically, by detecting the fluorescence X-rays specific to each element generated by irradiating the sample with X-rays, the composition analysis of the platinum group element-containing catalyst can be performed.

[0051] There is no particular limitation on the loading amount of the exhaust gas purification catalyst per unit volume of the honeycomb structure 4. For example, it is preferably less than 50 g / L, more preferably 30 g / L or more and less than 50 g / L, and particularly preferably 40 g / L or more and less than 50 g / L. The loading amount of the exhaust gas purification catalyst is the mass (g) of the catalyst supported per 1 L of the volume of the honeycomb structure 4. Examples of the method for loading the exhaust gas purification catalyst include a method in which a catalyst solution containing a catalyst component is wash-coated on the honeycomb structure 4 and then heat-treated at a high temperature for baking.

[0052] (2) Method for manufacturing a honeycomb filter: There is no particular limitation on the method for manufacturing the honeycomb filter of the present invention, and for example, the following methods can be mentioned.

[0053] First, a plastic clay for producing the partition walls of the honeycomb structure is prepared. The clay for producing the partition walls of the honeycomb structure can be prepared by appropriately adding additives such as binders, pore formers, and water to the raw material powder for producing the suitable materials for the aforementioned partition walls. As the raw material powder, for example, powders of alumina, talc, kaolin, and silica can be used. Examples of the binder include methylcellulose and hydroxypropyl methylcellulose. In addition, examples of the additive include surfactants.

[0054] Next, by extruding the clay thus obtained, a columnar honeycomb formed body having partition walls that partition and form a plurality of cells and an outer peripheral wall disposed so as to surround the partition walls is produced. Next, the obtained honeycomb formed body is dried, for example, with microwaves and hot air.

[0055] Next, a plugging portion is formed on the dried honeycomb formed body. The method of forming the plugging portion can be carried out in accordance with a conventionally known method for manufacturing a honeycomb filter. For example, first, a mask is applied to the inflow end face of the honeycomb formed body so that the inflow cells are covered. Then, the end portion of the honeycomb formed body with the mask applied is immersed in a plugging slurry, and the plugging slurry is filled into the openings of the outflow cells that are not masked. Then, for the outflow end face of the honeycomb formed body as well, the plugging slurry is filled into the openings of the inflow cells in the same manner as above. Then, the honeycomb formed body with the plugging portion formed is further dried with a hot air dryer.

[0056] Next, the honeycomb formed body with the eye seal portion is fired to produce a honeycomb filter including a honeycomb structure and an eye seal portion disposed so as to seal one end of either the cells. The firing temperature and firing atmosphere when firing the honeycomb formed body vary depending on the raw materials used to produce the honeycomb formed body, and those skilled in the art can select the firing temperature and firing atmosphere optimal for the selected material.

[0057] Here, when manufacturing the honeycomb filter of the present invention, the average pore diameter of the partition walls of the obtained honeycomb structure is adjusted by the following steps. That is, the average pore diameter of the partition walls in the inflow side region of the obtained honeycomb structure is set to 9 to 14 μm, and the average pore diameter of the partition walls in the outflow side region is set to 15 to 20 μm. Specifically, when firing the honeycomb formed body to produce a honeycomb filter, the difference between the temperature inside the filter on the inflow end face side and the temperature inside the filter on the outflow end face side is set to 10°C or more. Thus, by providing a difference of a predetermined temperature or more in the honeycomb formed body between the inflow end face side and the outflow end face side during firing, the size of the average pore diameter of the partition walls constituting the honeycomb filter can be adjusted.

Example

[0058] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples in any way.

[0059] (Example 1) First, alumina, talc, kaolin, and silica raw materials for producing the partition walls of the honeycomb structure were prepared. To the prepared alumina, talc, kaolin, and silica raw materials, 2 parts by mass of a dispersion medium and 7 parts by mass of an organic binder were added respectively, and they were mixed and kneaded to prepare a clay. Water was used as the dispersion medium. Methyl cellulose was used as the organic binder. A surfactant was used as the dispersant.

[0060] Next, the clay was extruded using a die for producing a honeycomb formed body to obtain a honeycomb formed body having a cylindrical overall shape. The shape of the cells of the honeycomb formed body was square.

[0061] Next, the honeycomb formed body was dried with a microwave dryer and further completely dried with a hot air dryer. Then, both end faces of the honeycomb formed body were cut and adjusted to a predetermined dimension.

[0062] Next, a sealing portion was formed on the dried honeycomb formed body. Specifically, first, a mask was applied to the inflow end face of the honeycomb formed body so that the inflow cells were covered. Then, the end portion of the honeycomb formed body with the mask was immersed in a sealing slurry, and the sealing slurry was filled into the openings of the outflow cells not covered with the mask. Then, regarding the outflow end face of the honeycomb formed body as well, the sealing slurry was filled into the openings of the inflow cells in the same manner as above. Then, the honeycomb formed body with the sealing portion formed was further dried with a hot air dryer.

[0063] Next, the dried honeycomb formed body was degreased and fired to produce the honeycomb filter of Example 1. In Example 1, in the firing step, by adjusting the temperature distribution, the size of the average pore diameter of the partition walls constituting the honeycomb filter was adjusted.

[0064] Next, a platinum group element-containing catalyst was supported on the partition walls of the honeycomb filter of Example 1 by the method shown below. First, a catalyst layer-forming slurry containing a powder of aluminum oxide supporting palladium as a platinum group element, ion-exchanged water, and a dispersant was prepared. Next, the catalyst layer-forming slurry was poured from the inflow end face of the honeycomb filter, and from the outflow end face, the poured catalyst layer-forming slurry was sucked at an appropriate suction amount so that the platinum group element-containing catalyst layer was coated on the partition walls. Then, the platinum group element-containing catalyst coated on the partition walls was fired at 500°C to support the platinum group element-containing catalyst on the partition walls of the honeycomb filter of Example 1. In Example 1, the platinum group element-containing catalyst was supported by the above method so that the supported amount of the platinum group element-containing catalyst per unit volume of the honeycomb structure was 40 g / L. The supported amount of the platinum group element-containing catalyst is shown in the column of "Supported amount of catalyst (g / L)" in Table 1.

[0065] The honeycomb filter of Example 1 was cylindrical with circular inlet and outlet end faces. Also, the length of the cells of the honeycomb filter in the extending direction was 127 mm. The diameter of the end face of the honeycomb filter was 118 mm. The honeycomb structure constituting the honeycomb filter had a partition wall thickness of 0.216 mm and a cell density of 46.5 cells / cm 2 It was. The partition walls of the honeycomb structure had a porosity of 63%. The cell density, partition wall thickness, and porosity are shown in Table 1.

[0066] Also, in the honeycomb filter of Example 1, in the range up to 40% of the total length of the honeycomb structure starting from the inlet end face of the honeycomb structure, the average pore diameter of the partition walls was 13 μm. Therefore, in the honeycomb filter of Example 1, the range up to 40% of the total length of the honeycomb structure starting from the inlet end face of the honeycomb structure was the inlet-side region where the average pore diameter of the partition walls was 9 to 14 μm. Also, in the honeycomb filter of Example 1, in the range up to 40% of the total length of the honeycomb structure starting from the outlet end face of the honeycomb structure, the average pore diameter of the partition walls was 20 μm. Therefore, in the honeycomb filter of Example 1, the range up to 40% of the total length of the honeycomb structure starting from the outlet end face of the honeycomb structure was the outlet-side region where the average pore diameter of the partition walls was 15 to 20 μm. Each result is shown in the columns of "Average Pore Diameter (μm)" and "Length Range from Inlet End Face (%)" in the "Inlet-Side Region", and "Average Pore Diameter (μm)" and "Length Range from Outlet End Face (%)" in the "Outlet-Side Region" of Table 1.

[0067]

Table 1

[0068] Regarding the honeycomb filter of Example 1, the "collection efficiency performance" and "exhaust gas purification performance" were evaluated by the following method. The results are shown in Table 2.

[0069] [Collection Efficiency Performance] First, an exhaust gas purification device was fabricated with the honeycomb filters of each example and comparative example used as the exhaust gas purification filter. The fabricated exhaust gas purification device was connected to the outlet side of the engine exhaust manifold of a 1.2L direct injection gasoline engine vehicle, and the number of soot particles contained in the gas discharged from the outlet of the exhaust gas purification device was measured by the PN measurement method. The "PN measurement method" refers to the measurement method proposed by the Particle Measurement Program (PMP) of the Expert Meeting on Exhaust Gas Energy of the World Forum for Harmonization of Vehicle Regulations (WP29) of the Economic Commission for Europe (ECE) of the United Nations (abbreviated as UN). Specifically, in the determination of the number of soot particles, the cumulative number of soot particles discharged after driving in the WLTC (Worldwide harmonized Light duty Test Cycle) mode was taken as the number of soot particles of the exhaust gas purification device to be judged, and the collection efficiency was measured. Regarding the collection efficiency measured as described above, when the value of the collection efficiency of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 was set to 100%, the values (%) of the collection efficiency of the exhaust gas purification devices using the honeycomb filters of each example and comparative example were determined. Then, based on the following evaluation criteria, the collection efficiency performance was evaluated. Evaluation "Excellent": When the value of the collection efficiency of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, if the value of the collection efficiency of the exhaust gas purification device using the honeycomb filter to be evaluated is 120% or more, the evaluation is "excellent". Evaluation "Good": When the value of the collection efficiency of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, if the value of the collection efficiency of the exhaust gas purification device using the honeycomb filter to be evaluated is 110% or more and less than 120%, the evaluation is "good". Evaluation "Fair": When the value of the collection efficiency of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, if the value of the collection efficiency of the exhaust gas purification device using the honeycomb filter to be evaluated is 100% or more and less than 110%, the evaluation is "fair". Evaluation "Not Pass": When the value of the collection efficiency of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, if the value of the collection efficiency of the exhaust gas purification device using the honeycomb filter to be evaluated is less than 100%, the evaluation is "Not Pass".

[0070] [Exhaust Gas Purification Performance] First, exhaust gas purification devices using the honeycomb filters of each Example and Comparative Example as exhaust gas purification filters were fabricated. The fabricated exhaust gas purification device was connected to the outlet side of the engine exhaust manifold of a 1.2L direct injection gasoline vehicle, and the NOx concentration contained in the gas discharged from the outlet of the exhaust gas purification device was measured to obtain the NOx purification rate. Regarding the NOx purification rate measured as described above, when the value of the NOx purification rate of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 was set to 100%, the values (%) of the NOx purification rates of the exhaust gas purification devices using the honeycomb filters of each Example and Comparative Example were obtained. Then, based on the following evaluation criteria, the exhaust gas purification performance was evaluated. Evaluation "Excellent": When the value of the NOx purification rate of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, if the value of the NOx purification rate of the exhaust gas purification device using the honeycomb filter to be evaluated is 120% or more, the evaluation is "Excellent". Evaluation "Good": When the value of the NOx purification rate of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, if the value of the NOx purification rate of the exhaust gas purification device using the honeycomb filter to be evaluated is 110% or more and less than 120%, the evaluation is "Good". Evaluation "Pass": When the value of the NOx purification rate of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, if the value of the NOx purification rate of the exhaust gas purification device using the honeycomb filter to be evaluated is 100% or more and less than 110%, the evaluation is "Pass". Evaluation "Not Pass": When the value of the NOx purification rate of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, if the value of the NOx purification rate of the exhaust gas purification device using the honeycomb filter to be evaluated is less than 100%, the evaluation is "Not Pass".

[0071]

Table 2

[0072] (Examples 2 - 9) A honeycomb filter was produced in the same manner as in Example 1, except that the cell density, the thickness of the partition walls, the porosity, and the configurations of the inflow - side region and the outflow - side region were changed as shown in Table 1. In Examples 2 - 9, for the configurations of the inflow - side region and the outflow - side region, when firing the honeycomb formed body, by making the difference between the temperature inside the filter on the inflow end face side and the temperature inside the filter on the outflow end face side 10°C or more, the average pore diameter (μm) of the partition walls and the length range (%) from each end face were adjusted. Then, for the honeycomb filters of Examples 2 - 9, a platinum - group - element - containing catalyst was supported in the same manner as in Example 1 so as to have the supported amount shown in the column of "Supported amount of catalyst (g / L)" in Table 1.

[0073] (Comparative Examples 1 - 4) A honeycomb filter was produced in the same manner as in Example 1, except that the cell density, the thickness of the partition walls, the porosity, and the configurations of the inflow - side region and the outflow - side region were changed as shown in Table 1. In Comparative Examples 2 - 4, for the configurations of the inflow - side region and the outflow - side region, in the firing process, by adjusting the temperature distribution, the average pore diameter (μm) of the partition walls and the length range (%) from each end face were adjusted. In Comparative Example 1, when firing the honeycomb formed body, by making the difference between the temperature inside the filter on the inflow end face side and the temperature inside the filter on the outflow end face side less than 10°C, the average pore diameter of the partition walls was made 19 μm in any range in the direction in which the cells of the honeycomb structure part extend. Then, for the honeycomb filters of Comparative Examples 1 - 4, a platinum - group - element - containing catalyst was supported in the same manner as in Example 1 so as to have the supported amount shown in the column of "Supported amount of catalyst (g / L)" in Table 1.

[0074] For the honeycomb filters of Examples 2 - 9 and Comparative Examples 1 - 4, the "collection efficiency performance" and the "exhaust gas purification performance" were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0075] (Results) It was confirmed that the honeycomb filters of Examples 1 to 9 exceeded the respective performances of the honeycomb filter of Comparative Example 1, which was used as a reference, in all evaluations of "collection efficiency performance" and "exhaust gas purification performance". Therefore, it was found that the honeycomb filters of Examples 1 to 9 were excellent in both collection performance and purification performance. In particular, the honeycomb filters of Examples 1 to 9 were capable of achieving excellent exhaust gas purification performance even when the supported amount of the catalyst was relatively small (for example, less than 50 g / L). On the other hand, the honeycomb filter of Comparative Example 2 was inferior in collection efficiency performance compared to the honeycomb filter of Comparative Example 1. It is considered that the average pore diameter in the outflow side region of the honeycomb filter of Comparative Example 2 was too large, and the partition wall in the outflow side region did not function sufficiently as a filter medium for collecting PM. On the other hand, the honeycomb filter of Comparative Example 3 was inferior in exhaust gas purification performance compared to the honeycomb filter of Comparative Example 1. In the honeycomb filter of Comparative Example 3, the average pore diameter in the inflow side region was too large, and the catalyst penetrated into the pores formed in the partition wall, and no catalyst layer formation that contributed to the improvement of exhaust gas purification performance was observed.

Industrial Applicability

[0076] The honeycomb filter of the present invention can be used as a filter for collecting particulate matter in exhaust gas.

Explanation of Signs

[0077] 1: Partition wall, 2: Cell, 2a: Inflow cell, 2b: Outflow cell, 3: Outer peripheral wall, 4: Honeycomb structure, 5: Plugging portion, 11: Inflow end face, 12: Outflow end face, 15: Inflow side region, 16: Outflow side region, 17: Intermediate region, 100: Honeycomb filter.

Claims

1. a honeycomb structure having porous partition walls arranged to surround a plurality of cells that serve as fluid flow paths extending from an inflow end face to an outflow end face; and a plugging portion arranged to plug either one of the inlet end surface side or the outlet end surface side of the cell, The plugging portion is disposed at an end portion on the outflow end face side, and the cell having an opening on the inflow end face side is defined as an inflow cell, The plugging portion is disposed at an end portion on the inflow end face side, and the cell having an open outflow end face side is defined as an outflow cell, The honeycomb structure has, in the cell extension direction of the honeycomb structure, an inlet side region starting from the inlet end face of the honeycomb structure and an outlet side region starting from the outlet end face of the honeycomb structure, a length L2 of the inlet side region starting from the inlet end face in the cell extension direction is in a range of 30 to 60% of a total length L1 of the honeycomb structure, and a length L3 of the outlet side region starting from the outlet end face in the cell extension direction is in a range of 20 to 50% of a total length L1 of the honeycomb structure, and further, the honeycomb structure has an intermediate region between the inlet side region and the outlet side region in the cell extension direction, a honeycomb filter, wherein the partition walls in the inlet side region have an average pore diameter of 9 to 14 μm and the partition walls in the outlet side region have an average pore diameter of 15 to 20 μm, and the partition walls in the intermediate region have an average pore diameter that does not fall within either the numerical range of the average pore diameter of the partition walls in the inlet side region, which is 9 to 14 μm, or the numerical range of the average pore diameter of the partition walls in the outlet side region, which is 15 to 20 μm.

2. The honeycomb filter according to claim 1, wherein the partition walls have a porosity of 50 to 65%, and a thickness of the partition walls is 0.19 to 0.31 mm.

3. The honeycomb structure has a cell density of 30 to 50 cells / cm ２ The honeycomb filter according to claim 1 or 2,

4. The honeycomb structure further includes an exhaust gas purifying catalyst supported on the partition walls, 4. The honeycomb filter according to claim 1, wherein the exhaust gas purifying catalyst is supported at least on the surface of the partition wall in the inlet side region of the honeycomb structure.

5. The honeycomb filter according to claim 4, wherein the exhaust gas purification catalyst comprises a platinum group element-containing catalyst.

6. The honeycomb filter according to claim 5 , wherein the platinum group element-containing catalyst contains an oxide of at least one of aluminum, zirconium, and cerium.

7. 7. The honeycomb filter according to claim 4, wherein the amount of the exhaust gas purifying catalyst supported per unit volume of the honeycomb structure is less than 50 g / L.

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