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, and more particularly to a honeycomb filter that has excellent performance in capturing particulate matter contained in exhaust gases and also excellent performance in purifying harmful components contained in exhaust gases. [Background technology]

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

[0003] For example, a honeycomb filter can include a honeycomb structure having porous partition walls that define a plurality of cells, and plugging portions that plug either end of the cells. Such a honeycomb filter is structured so that the porous partition walls function as a filter to remove PM. Specifically, exhaust gas containing PM is introduced into the inlet end face of the honeycomb filter, and the PM is filtered by being captured by the porous partition walls. The purified exhaust gas is then discharged from the outlet end face of the honeycomb filter. In this manner, PM can be removed from the exhaust gas.

[0004] In order to improve the purification performance of such honeycomb filters, an exhaust gas purification catalyst has been supported on the porous partition walls (see, for example, Patent Document 1). An example of the exhaust gas purification catalyst is a platinum group element-containing catalyst constituted by 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 documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-066536 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, honeycomb filters in which the above-mentioned exhaust gas purification catalyst (hereinafter simply referred to as "catalyst") is supported on the porous partition walls have had problems such as a decrease in the honeycomb filter's collection performance and an increase in the honeycomb filter's pressure loss. Furthermore, with the tightening of exhaust gas regulations, further measures are required to further improve the exhaust gas purification performance of honeycomb filters. For example, if a larger amount of catalyst is supported on the porous partition walls, the exhaust gas purification performance can be improved, but the above-mentioned decrease in the honeycomb filter's collection performance becomes more significant. Therefore, there is a demand for the development of a honeycomb filter that can improve exhaust gas purification performance without increasing the amount of catalyst supported and also has excellent collection performance.

[0007] The present invention has been made in view of the problems of the prior art. According to the present invention, a honeycomb filter is provided which has excellent performance in capturing PM contained in exhaust gas and excellent performance in purifying harmful components contained in exhaust gas. [Means for solving the problem]

[0008] According to the present invention, there is provided the following honeycomb filter.

[0009] [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; a plugging portion arranged to plug either one of the inlet end face side or the outlet end face side of the cell, The plugging portion is disposed at the end portion on the outflow end surface side, and the cell having an opening on the inflow end surface side is defined as an inflow cell, The plugged 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 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 in the cell extension direction of the honeycomb structure, wherein 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 wherein 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 average pore diameter of the partition walls in the inlet-side region is 9 to 14 μm and the average pore diameter of the partition walls in the outlet-side region is 15 to 20 μm, and the average pore diameter of the partition walls in the intermediate region does not fall within either the numerical range of the average pore diameter of the partition walls in the inlet-side region, 9 to 14 μm, or the numerical range of the average pore diameter of the partition walls in the outlet-side region, 15 to 20 μm.

[0010] [2] The honeycomb filter according to [1] above, 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 the above [1] or [2],

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

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

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

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

[0016] The honeycomb filter of the present invention, when used with an exhaust gas purification catalyst supported on the porous partition walls, exhibits excellent PM trapping performance in exhaust gas and excellent purification performance in purifying harmful components contained in exhaust gas. In particular, the honeycomb filter of the present invention can improve the purification performance and trapping performance without increasing the amount of exhaust gas purification catalyst supported.

[0017] That is, the honeycomb filter of the present invention has an inlet-side region with an average pore diameter of 9 to 14 μm in a range of at least 30% of the total length of the honeycomb structure, starting from the inlet end face of the honeycomb structure, in the cell extension direction of the honeycomb structure. This inlet-side region is configured so that the average pore diameter of the partition walls is relatively small, and when an exhaust gas purifying catalyst is loaded, the exhaust gas purifying catalyst is less likely to penetrate into the pores formed in the partition walls. Therefore, when an exhaust gas purifying catalyst is loaded on the honeycomb filter, the exhaust gas purifying catalyst is preferentially loaded on the surfaces of the partition walls in the inlet-side region, and a catalyst layer in which the exhaust gas purifying catalyst is deposited is formed on the surfaces of the partition walls. In particular, as described above, since the exhaust gas purifying catalyst is less likely to penetrate into the pores formed in the partition walls in the inlet-side region, a catalyst layer of sufficient thickness is formed on the surfaces of the partition walls even with a small amount of catalyst loaded. Therefore, in the inlet-side region, contact between the catalyst layer on the surface of the partition walls and the exhaust gas increases, effectively improving exhaust gas purification performance. Meanwhile, the honeycomb filter of the present invention has an outlet-side region with an average pore diameter of 15 to 20 μm, extending from the outlet end face of the honeycomb structure and covering at least 20% of the total length of the honeycomb structure in the cell extension direction of the honeycomb structure. When the amount of exhaust gas purification catalyst supported on the honeycomb filter is small, the amount of catalyst supported in the outlet-side region is relatively reduced compared to the amount of catalyst supported in the inlet-side region. Even if the exhaust gas purification catalyst is supported, the exhaust gas purification catalyst penetrates into the pores formed in the partition walls, making it difficult for a cake layer like a catalyst layer to form in the outlet-side region. Therefore, the porous partition walls in the outlet-side region effectively function as a filter material for capturing PM, achieving excellent collection performance. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a perspective view schematically showing a first embodiment of a honeycomb filter of the present invention. FIG. [Figure 2] FIG. 2 is a plan view of the inlet end face side of the honeycomb filter shown in FIG. [Figure 3]FIG. 2 is a plan view of the outflow end face side of the honeycomb filter shown in FIG. [Figure 4] FIG. 3 is a cross-sectional view schematically showing the AA' cross section of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0019] While the present invention will be described below with reference to exemplary embodiments, it should be understood that the present invention is not limited to the following exemplary embodiments. Therefore, it should be understood that modifications and improvements to the following exemplary embodiments, based on the ordinary knowledge of those skilled in the art, are also within the scope of the present invention, provided that they do not deviate from the spirit of the present invention.

[0020] (1) Honeycomb filter: A 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, a honeycomb filter 100 of this embodiment includes a honeycomb structure 4 and plugging portions 5. The honeycomb structure 4 has porous partition walls 1 arranged so as to surround a plurality of cells 2 that serve as fluid flow paths extending from an inflow end face 11 to an outflow end face 12. The honeycomb structure 4 shown in Figs. 1 to 4 is configured in a cylindrical shape with 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 arranged so as to surround the partition walls 1 arranged in a lattice pattern.

[0022] The plugging portions 5 are arranged so as to plug either one of the ends of the cells 2, on the inlet end face 11 side or the outlet end face 12 side. Hereinafter, among the plurality of cells 2, a cell 2 having a plugging portion 5 arranged at an end on the outlet end face 12 side and open on the inlet end face 11 side will be referred to as an "inlet cell 2a." Furthermore, among the plurality of cells 2, a cell 2 having a plugging portion 5 arranged at an end on the inlet end face 11 side and open on the outlet end face 12 side will be referred to as an "outlet cell 2b." In the honeycomb filter 100 of this embodiment, the inlet cells 2a and the outlet cells 2b are preferably arranged alternately 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 inlet-side region 15 that extends from the inlet end face 11 of the honeycomb structure 4 in the direction in which the cells 2 of the honeycomb structure 4 extend, and that covers a range of at least 30% of the total length L1 of the honeycomb structure 4. The honeycomb structure 4 also has an outlet-side region 16 that extends from the outlet end face 12 of the honeycomb structure 4 in the direction in which the cells 2 of the honeycomb structure 4 extend, and that covers a range of at least 20% of the total length L1 of the honeycomb structure 4. That is, as shown in FIG. 4 , in the honeycomb structure 4, the length L2 of the inlet-side region 15 in the direction in which the cells 2 extend is at least 30% of the total length L1 of the honeycomb structure 4, and the length L3 of the outlet-side region 16 in the direction in which the cells 2 extend is at least 20% of the total length L1 of the honeycomb structure 4.

[0024] Hereinafter, the ratio (%) of the length of the inlet-side region 15, starting from the inlet end face 11 of the honeycomb structure 4, to the entire length L1 of the honeycomb structure 4 may be referred to as the "length range (%) from the inlet end face 11 of the inlet-side region 15." Furthermore, the ratio (%) of the length of the outlet-side region 16, starting from the outlet end face 12 of the honeycomb structure 4, to the entire length L1 of the honeycomb structure 4 may be referred to as the "length range (%) from the outlet end face 12 of the outlet-side region 16."

[0025] In the honeycomb filter 100 of this embodiment, the average pore diameter of the partition walls 1 in the inlet-side region 15 is 9 to 14 μm, and the average pore diameter of the partition walls 1 in the outlet-side region 16 is 15 to 20 μm. That is, in the honeycomb filter 100, the average pore diameter of the partition walls 1 is relatively small in the inlet-side region 15 of the honeycomb structure 4, while the average pore diameter of the partition walls 1 is relatively large in the outlet-side region 16 of the honeycomb structure 4. The average pore diameters of the partition walls 1 in the inlet-side region 15 and the outlet-side region 16 of the honeycomb structure 4 are values ​​measured by mercury intrusion porosimetry. The average pore diameter of the partition walls 1 can be measured using, for example, an 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 walls 1, it has excellent collection performance for capturing PM contained in the exhaust gas, and also has excellent purification performance for purifying harmful components contained in the exhaust gas.

[0027] That is, when the honeycomb filter 100 is used with an exhaust gas purification catalyst loaded on the porous partition walls 1, the exhaust gas purification catalyst is less likely to penetrate into the pores formed in the partition walls 1 in the inlet-side region 15 where the average pore diameter of the partition walls 1 is 9 to 14 μm. Therefore, when the exhaust gas purification catalyst is loaded on the honeycomb filter 100, the exhaust gas purification catalyst is preferentially loaded on the surfaces of the partition walls 1 in the inlet-side region 15, and a catalyst layer in which the exhaust gas purification catalyst is deposited is formed on the surfaces of the partition walls 1. In particular, as described above, since the exhaust gas purification catalyst is less likely to penetrate into the pores formed in the partition walls 1 in the inlet-side region 15, a catalyst layer of sufficient thickness is formed on the surfaces of the partition walls 1 even with a small amount of catalyst loaded. Therefore, in the inlet-side region 15, there is more contact between the catalyst layer on the surfaces of the partition walls 1 and the exhaust gas, and the exhaust gas purification performance can be effectively improved. On the other hand, in the outlet-side region 16 where the average pore diameter of the partition walls 1 is 15 to 20 μm, when an exhaust gas purification catalyst is loaded, the amount of the catalyst loaded is relatively reduced compared to the amount of catalyst loaded in the inlet-side region 15. Even if the exhaust gas purification catalyst is loaded, the exhaust gas purification catalyst penetrates into the pores formed in the partition walls 1, and a cake layer such as a catalyst layer is unlikely to form in the outlet-side region 16. For this reason, the porous partition walls 1 in the outlet-side region 16 effectively function as a filter material for capturing PM, and excellent collection performance can be achieved.

[0028] The methods for checking the inlet-side region 15 and the outlet-side region 16 of the honeycomb structure 4 and for measuring the average pore diameters of the partition walls 1 in the inlet-side region 15 and the outlet-side region 16 are as follows. First, five measurement points are determined at 1% intervals along the entire length L1 of the honeycomb structure 4, starting from the inlet end face 11. Then, a portion of the partition wall 1 of the honeycomb structure 4 is cut out from each of the measurement points to obtain measurement sample pieces for measuring the average pore diameter. The measurement sample pieces are, for example, rectangular parallelepipeds with lengths of approximately 10 mm, approximately 10 mm, and approximately 10 mm in height. Then, the average pore diameters of the measurement sample pieces (i.e., the average pore diameters at 1% intervals along the entire length L1 of the honeycomb structure 4, starting from the inlet end face 11) are measured by mercury porosimetry.

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

[0030] Similarly, in the measurement of the average pore diameter described above, the range of the partition walls 1 where the average pore diameter is 15 to 20 μm from the outflow end face 12 as the starting point is the "outflow side region 16." Furthermore, the ratio of the length of the partition walls 1 where the average pore diameter is 15 to 20 μm from the outflow end face 12 as the starting point (i.e., the outflow side region 16) 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 this embodiment, the inlet-side region 15 extends from the inlet end face 11 to at least 30% of the total length L1 of the honeycomb structure 4. On the other hand, the outlet-side region 16 extends from the outlet end face 12 to at least 20% of the total length L1 of the honeycomb structure 4. Therefore, the honeycomb structure 4 may further have an "intermediate region 17" other than the inlet-side region 15 and the outlet-side region 16, in a part of a range of 30 to 80% in the direction of the total length L1 of the honeycomb structure 4, when the inlet end face 11 is taken as the starting point, in the extension direction of the cells 2 of the honeycomb structure 4. The intermediate region 17 does not satisfy the respective numerical ranges of the average pore diameter of the partition walls 1 in the inlet-side region 15 and the outlet-side region 16, and is a region that is not included in either region. Of course, the honeycomb structure 4 may not have the intermediate region 17 as described above, and a predetermined length range starting from the inlet end face 11 may be the inlet side region 15, and the remaining length range may be the outlet side region 16.

[0032] The intermediate region 17 of the honeycomb structure 4 preferably has an average pore diameter of the partition walls 1 in the intermediate region 17 that is greater than 14 μm and less than 15 μm. For example, if the average pore diameter of the honeycomb structure 4 is 9 to 14 μm in a range that is 50% of the total length L1 of the honeycomb structure 4, starting from the inflow end face 11, and is 14 to 15 μm in a range that is 50% to 70%, the above 50% range becomes the inflow-side region 15, and the range that is 50% to 70% becomes the intermediate region 17. Then, for example, if the average pore diameter is 15 to 20 μm in a range that is the remaining 70 to 100% of the total length L1 of the honeycomb structure 4, starting from the inflow end face 11, the remaining range (70 to 100%) becomes the outflow-side region 16.

[0033] 4, in the honeycomb structure 4, the length L2 in the extension direction of the cells 2 in the inlet side region 15 is at least 30% of the overall length L1 of the honeycomb structure 4, and is up to 80% of the overall length L1 of the honeycomb structure 4. The length L2 in the extension direction of the cells 2 in the inlet side region 15 is not particularly limited, but is preferably 30 to 60% of the overall length L1 of the honeycomb structure 4, for example, and more preferably 30 to 50%.

[0034] Furthermore, in the honeycomb structure 4, the length L3 in the extension direction of the cells 2 in the outlet side region 16 is at least 20% of the overall length L1 of the honeycomb structure 4, and is at most 70% of the overall length L1 of the honeycomb structure 4. The length L3 in the extension direction of the cells 2 in the outlet side region 16 is not particularly limited, but is preferably 20 to 40% of the overall 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 optional component as described above, and the length L4 of the intermediate region 17 in the direction in which the cells 2 extend is a maximum of 50% of the overall length L1 of the honeycomb structure 4. The length L4 of the intermediate region 17 in the direction in which the cells 2 extend can be set appropriately depending on the length L2 of the inlet-side region 15 in the direction in which the cells 2 extend and the length L3 of the outlet-side region 16 in the direction in which the cells 2 extend, as described above.

[0036] The average pore size of the partition walls 1 in the inlet side region 15 is 9 to 14 μm, preferably 9 to 13 μm, and more preferably 9 to 12 μm. The average pore size of the partition walls 1 in the outlet 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 walls 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 walls 1 is a value measured by mercury porosimetry. The porosity of the partition walls 1 can be measured using, for example, Autopore 9500 (trade name) manufactured by Micromeritics. If the porosity of the partition walls 1 is less than 50%, it is not preferable because the partition wall permeation resistance increases and the pressure loss increases. If the porosity of the partition walls 1 exceeds 65%, it is not preferable because the strength decreases significantly.

[0038] In the honeycomb structure 4, the thickness of the partition walls 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 walls 1 can be measured using, for example, a scanning electron microscope or a microscope. If the thickness of the partition walls 1 is less than 0.19 mm, sufficient strength may not be obtained. On the other hand, if the thickness of the partition walls 1 exceeds 0.31 mm, the pressure loss may increase when a catalyst is loaded on the partition walls 1.

[0039] The shape of the cells 2 formed in the honeycomb structure 4 is not particularly limited. For example, examples of the shape of the cells 2 in a cross section perpendicular to the extension direction of the cells 2 include polygons, circles, ellipses, etc. Examples of polygons include triangles, rectangles, pentagons, hexagons, and octagons. The shape of the cells 2 is preferably triangles, rectangles, pentagons, hexagons, or octagons. All the cells 2 may have the same shape or different shapes. For example, although not shown in the drawings, a mixture of rectangles and octagons may be used. All the cells 2 may have the same size or different sizes. For example, although not shown in the drawings, among a plurality of cells, some cells may be larger in size and the other cells may be smaller in size. In the present invention, a cell means a space surrounded by partition walls.

[0040] The cell density of the cells 2 partitioned by the partition walls 1 is 30 to 50 cells / cm 2 It is preferable that the density is 35 to 50 particles / cm 2 With this configuration, the filter can be suitably used as a filter for capturing PM in exhaust gas emitted from the engine of an automobile or the like.

[0041] The peripheral wall 3 of the honeycomb structure 4 may be configured integrally with the partition walls 1, or may be an peripheral coating layer formed by applying an peripheral coating material so as to surround the partition walls 1. Although not shown in the drawings, the peripheral coating layer can be provided on the outer periphery of the partition walls during production after the partition walls and the peripheral wall are integrally formed and the formed peripheral wall is removed by a known method such as grinding.

[0042] There is no particular limitation on the shape of the honeycomb structure 4. The honeycomb structure 4 may have an inflow end face 11 and an outflow end face 12 that are cylindrical, elliptical, polygonal, or the like.

[0043] There are no particular limitations on the size of the honeycomb structure 4, for example, the length in the direction in which the cells 2 of the honeycomb structure 4 extend (hereinafter also referred to as "total length L1") and the size of the cross section of the honeycomb structure 4 perpendicular to the direction in which the cells 2 extend (hereinafter also referred to as "cross-sectional area"). Each size may be appropriately selected so that optimal purification performance is obtained 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. The cross-sectional area of ​​the honeycomb structure 4 is 8000 to 16000 mm. 2 It is preferable that the thickness is 10,000 to 14,000 mm. 2 It is more preferable that:

[0044] The material of the partition walls 1 preferably 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 walls 1 is preferably a material containing 30 mass% or more of the material listed in the above group, more preferably a material containing 40 mass% or more, and particularly preferably a material containing 50 mass% or more. In the honeycomb filter 100 of the present embodiment, the material constituting the partition walls 1 is particularly preferably cordierite.

[0045] The honeycomb structure 4 is preferably an integrally molded product made of the material that constitutes the above-mentioned partition walls 1. That is, the honeycomb structure 4 in the honeycomb filter 100 is preferably not one in which the inlet side region 15 and the outlet side region 16 are separately manufactured and then joined together, but is preferably an integrally molded product that is integrally molded using a predetermined molding material.

[0046] The honeycomb filter 100 may further include an exhaust gas purifying catalyst (not shown) supported on the partition walls 1 constituting the honeycomb structure 4. The exhaust gas purifying catalyst is preferably supported on at least the surfaces of the partition walls 1 in the inlet-side region 15 of the honeycomb structure 4. Here, "supported on at least the surfaces of the partition walls 1" means that the exhaust gas purifying catalyst may be supported only on the surfaces of the partition walls 1, or may be supported on the surfaces of the partition walls 1 and inside the pores. "Supported only on the surfaces of the partition walls 1" means that the catalyst is present on the surfaces of the partition walls 1 in the thickness direction of the partition walls 1, and that the exhaust gas purifying catalyst is not present between the surface of the partition walls 1 on the inlet cell 2a side of the partition walls 1 and 1.0T in the thickness direction of the partition walls 1, starting from 0.1T (where T indicates the thickness of the partition walls 1) in the thickness direction of the partition walls 1. "Supported on the surface of the partition wall 1 and inside the pores" means that a catalyst is present on the surface of the partition wall 1, and that the exhaust gas purifying catalyst is present at least somewhere between the surface of the partition wall 1 on the inlet cell 2a side of the partition wall 1 and 0.9T in the thickness direction of the partition wall 1, starting from 0.1T (where T indicates the thickness of the partition wall 1) in the thickness direction of the partition wall 1. On the other hand, it is preferable that the exhaust gas purifying catalyst is not supported in the outlet-side region 16 of the honeycomb structure 4, and when the exhaust gas purifying catalyst is supported in the outlet-side region 16, the exhaust gas purifying catalyst may be supported inside the pores formed in the partition wall 1. "Supported inside the pores of the partition wall 1" means that the exhaust gas purifying catalyst is present at least somewhere between the surface of the partition wall 1 on the inlet cell 2a side of the partition wall 1 and 0.9T in the thickness direction of the partition wall 1, starting from 0.1T (where T indicates the thickness of the partition wall 1) in the thickness direction of the partition wall 1. With this configuration, a catalyst layer in which the exhaust gas purification catalyst is deposited on the surfaces of the partition walls 1 is formed in the inlet-side region 15. In particular, in the inlet-side region 15, the exhaust gas purification catalyst is unlikely to penetrate into the pores formed in the partition walls 1, so even with a small catalyst loading, a catalyst layer of sufficient thickness is formed on the surfaces of the partition walls 1. Therefore, in the inlet-side region 15, there is increased contact between the catalyst layer on the surfaces of the partition walls 1 and the exhaust gas, and the exhaust gas purification performance can be effectively improved.Furthermore, the porous partition walls 1 in the outlet side region 16 effectively function as a filter material for capturing PM, and excellent capturing performance can be achieved.

[0047] As described above, the honeycomb filter 100 further comprising an exhaust gas purification catalyst preferably has different catalyst loading forms in the inlet-side region 15 and the outlet-side region 16, which have different average pore diameters. In the honeycomb filter 100, the average pore diameters of the partition walls 1 are different in the two regions, the inlet-side region 15 and the outlet-side region 16. Therefore, for example, it is possible to change the catalyst loading form in each region using one type of catalyst loading slurry (e.g., catalyst liquid). In particular, it is possible to easily change the catalyst loading form in a desired region by performing a single catalyst loading step. Therefore, according to the honeycomb filter 100 of this embodiment, it is possible to extremely easily manufacture the honeycomb filter 100 further comprising the above-described exhaust gas purification catalyst.

[0048] In the inlet-side region 15, as described above, as long as the catalyst is loaded at least on the surfaces of the partition walls 1, a part of the catalyst may be loaded inside the pores formed in the partition walls 1. However, in the inlet-side region 15, when the catalyst is loaded, it is difficult for the catalyst to penetrate into the pores, so the catalyst is loaded preferentially on the surfaces of the partition walls 1, and even with a small amount of catalyst loaded, a catalyst layer of sufficient thickness can be formed on the surfaces of the partition walls 1. Therefore, according to the honeycomb filter 100 of the present embodiment, the amount of exhaust gas purification catalyst used (in other words, the loaded amount) can be reduced.

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

[0050] The platinum group element-containing catalyst preferably contains an oxide of at least one element selected from the group consisting of aluminum, zirconium, and cerium. A catalyst containing such an oxide preferably contains 1 to 3 mass% of a platinum group element relative to 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, the composition of the platinum group element-containing catalyst can be analyzed by detecting fluorescent X-rays specific to each element generated by irradiating a sample with X-rays.

[0051] There is no particular limitation on the amount of exhaust gas purifying catalyst carried per unit volume of the honeycomb structure 4, but it is preferably less than 50 g / L, more preferably 30 g / L or more but less than 50 g / L, and particularly preferably 40 g / L or more but less than 50 g / L. The amount of exhaust gas purifying catalyst carried is the mass (g) of catalyst carried per 1 L of volume of the honeycomb structure 4. Examples of methods for carrying the exhaust gas purifying catalyst include wash-coating the honeycomb structure 4 with a catalyst liquid containing catalyst components, followed by heat treatment at high temperature to bake it.

[0052] (2) Honeycomb filter manufacturing method: The method for producing the honeycomb filter of the present invention is not particularly limited, and examples thereof include the following methods.

[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 adding additives such as binders, pore formers, and water to the raw material powder for producing the above-mentioned suitable material for the partition walls. Examples of the raw material powder that can be used include powders of alumina, talc, kaolin, and silica. Examples of the binder include methylcellulose and hydroxypropyl methylcellulose. Examples of the additive include surfactants.

[0054] The thus obtained clay is then extruded to produce a columnar honeycomb formed body having partition walls that define a plurality of cells and an outer peripheral wall that surrounds the partition walls. The obtained honeycomb formed body is then dried, for example, by microwaves and hot air.

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

[0056] Next, the honeycomb formed body with the plugging portions formed thereon is fired to manufacture a honeycomb filter including a honeycomb structure and plugging portions arranged so as to plug either end of the cells. The firing temperature and firing atmosphere when firing the honeycomb formed body vary depending on the raw materials from which the honeycomb formed body is produced, and a person skilled in the art can select the firing temperature and firing atmosphere that are optimal for the selected materials.

[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 process. That is, the average pore diameter of the partition walls in the inlet 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 outlet side region is set to 15 to 20 μm. Specifically, when the honeycomb formed body is fired to produce the honeycomb filter, the difference in the filter internal temperature between the inlet end face side and the outlet end face side is set to 10°C or more. In this way, by providing a predetermined or greater temperature difference within the honeycomb formed body between the inlet end face side and the outlet end face side during firing, the average pore diameter of the partition walls constituting the honeycomb filter can be adjusted. [Example]

[0058] The present invention will be explained in more detail below with reference to 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. 2 parts by mass of a dispersion medium and 7 parts by mass of an organic binder were added to the prepared alumina, talc, kaolin, and silica raw materials, respectively, and the mixture was mixed and kneaded to prepare a clay. Water was used as the dispersion medium, methyl cellulose was used as the organic binder, and 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 an overall cylindrical shape. The shape of the cells of the honeycomb formed body was rectangular.

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

[0062] Next, plugging portions were formed on the dried honeycomb formed body. Specifically, first, a mask was applied to the inlet end face of the honeycomb formed body so that the inlet cells were covered. Thereafter, the end of the masked honeycomb formed body was immersed in plugging slurry, and the plugging slurry was filled into the openings of the outlet cells that were not masked. Thereafter, the plugging slurry was also filled into the openings of the inlet cells on the outlet end face of the honeycomb formed body in the same manner as above. Thereafter, the honeycomb formed body with the plugging portions formed thereon was further dried in 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, the average pore diameter of the partition walls constituting the honeycomb filter was adjusted by adjusting the temperature distribution in the firing process.

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

[0065] The honeycomb filter of Example 1 was cylindrical, with circular inlet and outlet end faces. The length of the honeycomb filter in the cell extension 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 The partition walls of the honeycomb structure had a porosity of 63%. Table 1 shows the cell density, the thickness of the partition walls, and the porosity.

[0066] Furthermore, in the honeycomb filter of Example 1, the average pore diameter of the partition walls was 13 μm in a range from the inlet end face of the honeycomb structure to 40% of the total length of the honeycomb structure. Therefore, in the honeycomb filter of Example 1, the average pore diameter of the partition walls was 9 to 14 μm in a range from the inlet end face of the honeycomb structure to 40% of the total length of the honeycomb structure. Furthermore, in the honeycomb filter of Example 1, the average pore diameter of the partition walls was 20 μm in a range from the outlet end face of the honeycomb structure to 40% of the total length of the honeycomb structure. Therefore, in the honeycomb filter of Example 1, the average pore diameter of the partition walls was 15 to 20 μm in a range from the outlet end face of the honeycomb structure to 40% of the total length of the honeycomb structure. The results are shown in Table 1 in the columns "Average pore diameter (μm)" and "Length range from the inlet end face (%)" in the "Inlet side region" and "Average pore diameter (μm)" and "Length range from the outlet end face (%)" in the "Outlet side region."

[0067] [Table 1]

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

[0069] [Collection efficiency performance] First, an exhaust gas purification device was fabricated using the honeycomb filters of each example and comparative example as an 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 emitted from the outlet of the exhaust gas purification device was measured using the PN measurement method. The "PN measurement method" refers to a measurement method proposed by the Particle Measurement Program (abbreviated as PMP) of the Group of Exhaust Gas Energy Experts (abbreviated as GRPE) of the World Forum for Harmonization of Vehicle Regulations (abbreviated as WP29) of the Economic Commission for Europe (abbreviated as ECE) of the United Nations (abbreviated as UN). Specifically, in determining the number of soot particles, the cumulative number of soot particles emitted after driving in the WLTC (Worldwide harmonized Light duty Test Cycle) mode was used as the number of soot particles in the exhaust gas purification device to be evaluated, and the collection efficiency was measured. Regarding the collection efficiency measured as described above, the collection efficiency values ​​(%) of the exhaust gas purification devices using the honeycomb filter of each Example and Comparative Example were calculated, assuming that the collection efficiency value of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 was 100%. Then, the collection efficiency performance was evaluated based on the following evaluation criteria. Evaluation "Excellent": If the collection efficiency of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, and the collection efficiency of the exhaust gas purification device using the honeycomb filter being evaluated is 120% or more, the evaluation is "Excellent". Evaluation "Good": If the collection efficiency of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, and the collection efficiency of the exhaust gas purification device using the honeycomb filter being evaluated is 110% or more and less than 120%, the evaluation is "Good". Evaluation: "Acceptable": If the collection efficiency of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is taken as 100%, and the collection efficiency of the exhaust gas purification device using the honeycomb filter being evaluated is 100% or more but less than 110%, the evaluation is "Acceptable". Evaluation: "Fail": If the collection efficiency of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is taken as 100%, and the collection efficiency of the exhaust gas purification device using the honeycomb filter being evaluated is less than 100%, the evaluation is "Fail".

[0070] [Exhaust gas purification performance] First, an exhaust gas purification device was fabricated using the honeycomb filters of each Example and Comparative Example as an 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 NOx concentration contained in the gas discharged from the outlet of the exhaust gas purification device was measured to determine the NOx purification rate. Regarding the NOx purification rate measured as described above, the NOx purification rate (%) of the exhaust gas purification device using the honeycomb filter of each Example and Comparative Example was calculated, assuming that the NOx purification rate of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 was 100%. Then, the exhaust gas purification performance was evaluated based on the following evaluation criteria. Evaluation "Excellent": If the NOx purification rate of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, and the NOx purification rate of the exhaust gas purification device using the honeycomb filter being evaluated is 120% or more, the evaluation is "Excellent". Evaluation "Good": If the NOx purification rate of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, and the NOx purification rate of the exhaust gas purification device using the honeycomb filter being evaluated is 110% or more and less than 120%, the evaluation is "Good". Evaluation: "Acceptable": If the NOx purification rate of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is taken as 100%, and the NOx purification rate of the exhaust gas purification device using the honeycomb filter being evaluated is 100% or more and less than 110%, the evaluation is "Acceptable". Evaluation: "Fail": If the NOx purification rate of the exhaust gas purification device using the honeycomb filter of Comparative Example 1 is set to 100%, and the NOx purification rate of the exhaust gas purification device using the honeycomb filter being evaluated is less than 100%, the evaluation is "Fail".

[0071] [Table 2]

[0072] Examples 2 to 9 Honeycomb filters were produced in the same manner as in Example 1, except that the cell density, partition wall thickness and porosity, and the configurations of the inlet-side region and the outlet-side region were changed as shown in Table 1. In Examples 2 to 9, the configurations of the inlet-side region and the outlet-side region were adjusted by adjusting the average pore diameter (μm) of the partition walls and the length range (%) from each end face by setting the difference in the filter internal temperature between the inlet end face side and the outlet end face side to 10°C or more when firing the honeycomb formed body. Then, a platinum group element-containing catalyst was loaded onto the honeycomb filters of Examples 2 to 9 in the same manner as in Example 1, so as to achieve the loading amount shown in the column of "Catalyst loading amount (g / L)" in Table 1.

[0073] (Comparative Examples 1 to 4) Honeycomb filters were produced in the same manner as in Example 1, except that the cell density, the thickness and porosity of the partition walls, and the configurations of the inlet-side region and the outlet-side region were changed as shown in Table 1. In Comparative Examples 2 to 4, the configurations of the inlet-side region and the outlet-side region were adjusted by adjusting the temperature distribution in the firing process to adjust the average pore diameter (μm) of the partition walls and the length range (%) from each end face. In Comparative Example 1, when firing the honeycomb formed body, the difference in the temperature inside the filter on the inlet end face side and the outlet end face side was set to less than 10°C, so that the average pore diameter of the partition walls in the cell extension direction of the honeycomb structure portion was 19 μm in any range. Then, platinum group element-containing catalysts were loaded on the honeycomb filters of Comparative Examples 1 to 4 in the amounts shown in the "Catalyst Loading Amount (g / L)" column in Table 1 by the same manner as in Example 1.

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

[0075] (result) It was confirmed that the honeycomb filters of Examples 1 to 9 exceeded the performance of the honeycomb filter of Comparative Example 1, which was used as the benchmark, 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 able to achieve excellent exhaust gas purification performance even when the catalyst loading 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 of the outlet side region of the honeycomb filter of Comparative Example 2 was too large, and the partition walls of the outlet side region did not function sufficiently as a filter material for capturing 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 inlet region was too large, causing the catalyst to penetrate into the pores formed in the partition walls, and no catalyst layer was formed that would contribute to improving exhaust gas purification performance. [Industrial Applicability]

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

[0077] 1: partition wall, 2: cell, 2a: inlet cell, 2b: outlet cell, 3: outer wall, 4: honeycomb structure, 5: plugging portion, 11: inlet end face, 12: outlet end face, 15: inlet side region, 16: outlet 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; a plugging portion arranged to plug either one of the inlet end face side or the outlet end face side of the cell, The plugging portion is disposed at the end portion on the outflow end surface side, and the cell having an opening on the inflow end surface side is defined as an inflow cell, The plugged 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 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 in the cell extension direction 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 the 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 the total length L1 of the honeycomb structure, and 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 average pore diameter of the partition walls in the inlet-side region is 9 to 14 μm, and the average pore diameter of the partition walls in the outlet-side region is 15 to 20 μm, and the average pore diameter of the partition walls in the intermediate region does not fall within either the numerical range of the average pore diameter of the partition walls in the inlet-side region, 9 to 14 μm, or the numerical range of the average pore diameter of the partition walls in the outlet-side region, 15 to 20 μm.

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

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

4. The honeycomb structure further includes an exhaust gas purification 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 walls in the inlet side region of the honeycomb structure.

5. The honeycomb filter according to claim 4, wherein the exhaust gas purification catalyst includes 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 element selected from the group consisting 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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