Honeycomb Filter

Abstract

To provide a honeycomb filter which can improve purification performance while suppressing an increase in pressure loss.SOLUTION: The honeycomb filter comprises: a columnar honeycomb structure 4 which has porous partitions 1 so arranged as to surround a plurality of cells 2 serving as liquid channels extending from an inflow end surface 11 to an outflow end surface 12; and porous sealing parts 5 arranged either one of an end part on the inflow end surface 11 side or an end part on the outflow end surface 12 side of the cells 2. The honeycomb filter has a thickness of the partition 1 of 152 to 254 μm, a cell density of the honeycomb structure 4 of 38.8 to 62.0 pieces / cm2, a pore size D50 with 50% of the total pore volume of 11 to 15 μm, in a pore size distribution of the partition 1 measured by the mercury press-in method, for a cumulative pore volume, a porosity of the partition 1 measured by the mercury press-in method of 60 to 75%, and a partition wet area ratio (A / S) that is a value obtained by dividing a pore wet area A formed in the porous partition 1 by a cross-sectional area S of the pore of 0.21 to 0.35 m2 / m2.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a honeycomb filter, and more particularly to a honeycomb filter that can improve purification performance while suppressing an increase in pressure loss. [Background technology]

[0002] As a means for reducing the amount of particulate matter contained in exhaust gas emitted from an internal combustion engine, a method of providing a particulate filter for the purpose of depositing and capturing particulate matter in an exhaust gas passage of the internal combustion engine is known (for example, Patent Document 1). In particular, in recent years, from the viewpoint of saving installation space, etc., studies have been conducted to provide a catalyst layer by applying a catalyst slurry to a particulate filter and baking it in order to simultaneously suppress the emission of particulate matter and remove harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx).

[0003] As a particulate filter for purifying exhaust gas, for example, a honeycomb filter using a honeycomb structure is known. The honeycomb structure has partition walls made of porous ceramics such as cordierite, and a plurality of cells are defined by the partition walls. The honeycomb filter is obtained by arranging plugging portions in the above-mentioned honeycomb structure so that openings on the inflow end face side and openings on the outflow end face side of a plurality of cells are alternately plugged. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-219319 Summary of the Invention [Problem to be solved by the invention]

[0005] In honeycomb filters provided with a catalyst layer, in order to improve the exhaust gas purification performance of the catalyst, it is useful to increase the surface area of ​​the porous partition walls (in other words, the porous support) on which the catalyst is supported and increase the frequency of contact between the catalyst and the exhaust gas. For example, one possible method for increasing the surface area of ​​the porous support constituting the partition walls is to increase the cell density of the honeycomb structure. However, an increase in cell density has the problem of inducing a significant increase in pressure loss. In particular, there is a demand for the development of honeycomb filters, such as gasoline particulate filters (GPFs), that can improve purification performance while suppressing an increase in pressure loss.

[0006] The present invention has been made in view of the problems of the conventional art. According to the present invention, a honeycomb filter is provided that can improve purification performance while suppressing an increase in pressure loss. [Means for solving the problem]

[0007] According to the present invention, there is provided the following honeycomb filter.

[0008] [1] A columnar 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 disposed at either an end portion on the inlet end face side or an end portion on the outlet end face side of the cell, The thickness of the partition wall is 152 to 254 μm, The cell density of the honeycomb structure is 38.8 to 62.0 cells / cm 2 and in a pore size distribution of the partition walls measured by mercury porosimetry, a pore size D50 at which a cumulative pore volume becomes 50% of a total pore volume is 11 to 15 μm, the porosity of the partition walls measured by mercury porosimetry is 60 to 75%, The partition wall wetted area ratio (A / S), which is the value obtained by dividing the wetted area A of the pores formed in the porous partition wall by the cross-sectional area S of the pores, is 0.21 to 0.35 m2 / m 2 That is the honeycomb filter.

[0009] [2] The honeycomb filter according to [1], wherein in the pore size distribution of the partition walls measured by mercury porosimetry, the pore size D10 at which the cumulative pore volume is 10% of the total pore volume is 5.5 to 7.5 μm.

[0010] [3] The honeycomb filter according to [1] or [2], wherein in the pore size distribution of the partition walls measured by mercury intrusion porosimetry, the pore size D90 at which the cumulative pore volume is 90% of the total pore volume is 35.0 μm or less. [Effects of the Invention]

[0011] The honeycomb filter of the present invention can improve purification performance while suppressing an increase in pressure loss. For example, when a catalyst layer is provided by coating a honeycomb filter with a catalyst slurry and firing the coated layer, the catalyst slurry is applied in a manner that allows it to penetrate into the porous partition walls that constitute the honeycomb structure. The honeycomb filter of the present invention has a partition wall wetted area ratio (A / S) of 0.21 to 0.35 m 2 / m 2 By setting the cell density of the honeycomb structure to 38.8 to 62.0 cells / cm, it is possible to increase the number of relatively small pores among the pores formed in the partition walls, and to increase the surface area in the partition walls onto which the catalyst is applied. Therefore, when a catalyst layer is provided on such a honeycomb filter, the frequency of contact between the exhaust gas and the catalyst increases, and the purification performance of the honeycomb filter can be improved. In addition, in the honeycomb filter of the present invention, the cell density of the honeycomb structure is set to 38.8 to 62.0 cells / cm. 2 Therefore, the honeycomb filter of the present invention can improve the purification performance more effectively while effectively suppressing an increase in pressure loss, compared to the conventional method of improving the purification performance by increasing the cell density. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view schematically showing one embodiment of a honeycomb filter of the present invention. [Figure 2] FIG. 2 is a plan view showing the inlet end face side of the honeycomb filter shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view schematically showing the AA' cross section of FIG. [Figure 4] FIG. 1 is a conceptual diagram of voxel data for determining the partition wall wetted area ratio (A / S). DETAILED DESCRIPTION OF THE INVENTION

[0013] 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.

[0014] (1) Honeycomb filter: One embodiment of the honeycomb filter of the present invention is a honeycomb filter 100 as shown in Figures 1 to 3. Here, Figure 1 is a perspective view schematically showing one embodiment of the honeycomb filter of the present invention. Figure 2 is a plan view showing the inlet end face side of the honeycomb filter shown in Figure 1. Figure 3 is a cross-sectional view schematically showing the A-A' cross section of Figure 2.

[0015] As shown in Figs. 1 to 3, a honeycomb filter 100 includes a honeycomb structure 4 and plugging portions 5. The honeycomb structure 4 is columnar and has porous partition walls 1 arranged 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. In the honeycomb filter 100, the honeycomb structure 4 is columnar and further has an outer peripheral wall 3 on its outer peripheral side surface. That is, the outer peripheral wall 3 is arranged to surround the partition walls 1 arranged in a lattice pattern.

[0016] The plugging portions 5 are arranged at the openings on the inlet end face 11 side or the outlet end face 12 side of each cell 2. In the honeycomb filter 100 shown in FIGS. 1 to 3, the plugging portions 5 are arranged at the openings on the inlet end face 11 side of predetermined cells 2 and at the openings on the outlet end face 12 side of the remaining cells 2. The cells 2 having the plugging portions 5 arranged at the openings on the outlet end face 12 side and opening on the inlet end face 11 side are referred to as inlet cells 2a. The cells 2 having the plugging portions 5 arranged at the openings on the inlet end face 11 side and opening on the outlet end face 12 side are referred to as outlet cells 2b. The inlet cells 2a and the outlet cells 2b are preferably arranged alternately with the partition wall 1 between them. As a result, it is preferable that a checkerboard pattern is formed on both end faces of the honeycomb filter 100 by the plugging portions 5 and the "openings of the cells 2."

[0017] The honeycomb filter 100 has particularly important characteristics in the honeycomb structure 4 and the configuration of the partition walls 1 that constitute the honeycomb structure 4. That is, the partition walls 1 that constitute the honeycomb structure 4 have a thickness of 152 to 254 μm. In addition, the cell density of the honeycomb structure 4 is 38.8 to 62.0 cells / cm. 2 In addition, in the pore size distribution of the partition walls 1 measured by mercury porosimetry, the pore size D50 at which the cumulative pore volume is 50% of the total pore volume is 11 to 15 μm, and the porosity of the partition walls 1 measured by mercury porosimetry is 60 to 75%. Furthermore, the partition wall wetted area ratio (A / S), which is the value obtained by dividing the wetted area A of the pores formed in the porous partition walls 1 by the cross-sectional area S of the pores, is 0.21 to 0.35 m 2 / m 2 Hereinafter, the minute holes formed in the porous partition walls 1 may be referred to as the "pores" or "fine holes" of the partition walls 1.

[0018] The honeycomb filter 100 configured in this manner can improve the purification performance while suppressing an increase in pressure loss. For example, when a catalyst layer is provided by coating the honeycomb filter 100 with a catalyst slurry and firing it, the catalyst slurry is applied in a manner that allows it to penetrate into the porous partition walls 1 that constitute the honeycomb structure 4. The honeycomb filter 100 has a partition wall wetted area ratio (A / S) of 0.21 to 0.35 m 2 / m 2 By doing so, it is possible to increase the number of pores with relatively small diameters among the pores of the partition walls 1, and to increase the surface area on which the catalyst is applied. Therefore, when a catalyst layer is provided on the honeycomb filter 100, the frequency of contact between the exhaust gas and the catalyst increases, and the purification performance of the honeycomb filter 100 can be improved. Furthermore, in the honeycomb filter 100, the cell density of the honeycomb structure 4 is set to 38.8 to 62.0 cells / cm 2 This range allows for improvement in purification performance without excessively increasing the cell density. Therefore, compared to conventional methods of improving purification performance by increasing the cell density, the honeycomb filter 100 can more effectively improve purification performance while effectively suppressing an increase in pressure loss. The honeycomb filter 100 of this embodiment will be described in more detail below.

[0019] The partition walls 1 constituting the honeycomb structure 4 have a thickness of 152 to 254 μm. By setting the thickness of the partition walls 1 within the above range, it is possible to achieve both ensuring the strength of the structure and suppressing an increase in pressure loss. For example, if the thickness of the partition walls 1 is less than 152 μm, this is not preferable in terms of a decrease in strength. If the thickness of the partition walls 1 exceeds 254 μm, this is not preferable because the pressure loss increases significantly. Although not particularly limited, the thickness of the partition walls 1 is preferably 203 to 254 μm, and more preferably 203 to 229 μm. The thickness of the partition walls 1 can be measured using, for example, a scanning electron microscope or a microscope.

[0020] In addition, the honeycomb structure 4 having the partition walls 1 as described above has a cell density of 38.8 to 62.0 cells / cm.2 By setting the cell density within the above range, it is possible to suppress an increase in pressure loss when ash (hereinafter also referred to as "ash") accumulates. For example, when the cell density is 38.8 cells / cm 2 If the cell density is less than 62.0 cells / cm, the geometric surface area (GSA) decreases, the thickness of the ash deposit layer increases, and the pressure loss increases significantly, which is not desirable. 2 If the cell density of the honeycomb structure 4 exceeds 43 to 54 cells / cm, the hydraulic diameter at the gas inlet end face becomes small, and the pressure loss increases sharply, which is not preferable. 2 It is preferable that the density is 45 to 48 particles / cm. 2 It is more preferable that:

[0021] In the pore size distribution of the partition walls 1 measured by mercury porosimetry, the pore size D50 at which the cumulative pore volume is 50% of the total pore volume is 11 to 15 μm. Hereinafter, in the pore size distribution of the partition walls 1, the pore size D50 at which the cumulative pore volume is 50% of the total pore volume may be simply referred to as "D50" in the pore size distribution of the partition walls 1. This "D50" is a value calculated by defining it as the pore size that gives half the total pore volume in the pore size distribution of the partition walls 1, and may also be referred to as the average pore size of the partition walls 1. If D50 is less than 11 μm, this is not preferable because the pressure loss after catalyst application may increase dramatically. If the pore size D50 exceeds 15 μm, this is not preferable because the collection performance decreases. Although not particularly limited, D50 is preferably 12 to 15 μm, and more preferably 13 to 15 μm.

[0022] The cumulative pore volume of the partition walls 1 is a value measured by mercury intrusion porosimetry. The cumulative pore volume of the partition walls 1 can be measured using, for example, an Autopore 9500 (trade name) manufactured by Micromeritics. The cumulative pore volume of the partition walls 1 can be measured by the following method. First, a test piece for measuring the cumulative pore volume is prepared by cutting out a portion of the partition walls 1 from the honeycomb filter 100. There are no particular restrictions on the size of the test piece, but it is preferably a rectangular parallelepiped with lengths of approximately 10 mm, approximately 10 mm, and approximately 20 mm in height, for example. There are no particular restrictions on the part of the partition walls 1 from which the test piece is cut out, but it is preferably prepared by cutting out the test piece from near the center in the axial direction of the honeycomb structure part. The obtained test piece is placed in a measurement cell of a measurement device, and the pressure inside the measurement cell is reduced. Next, mercury is introduced into the measurement cell. Next, the mercury introduced into the measurement cell is pressurized, and the volume of mercury forced into the pores present in the test piece is measured. As the pressure applied to the mercury increases, the mercury is forced from the larger pores to the smaller pores. Therefore, the relationship between the "pore size of the pores formed in the test piece" and the "cumulative pore volume" can be determined from the relationship between the "pressure applied to the mercury" and the "volume of mercury forced into the pores." As described above, when pressure is gradually applied to force mercury into the pores of a sample (test piece) in a sealed vacuum container using the mercury intrusion method, the applied pressure causes the mercury to penetrate the pores in the sample, from the larger pores to the smaller pores. The pore size and pore volume of the pores formed in the sample can be calculated from the pressure and the amount of mercury injected. Hereinafter, when pore diameters are designated as D1, D2, D3, etc., they are assumed to satisfy the relationship D1>D2>D3. Here, the average pore diameter D between each measurement point (for example, from D1 to D2) can be shown on the horizontal axis as "average pore diameter D = (D1 + D2) / 2." Furthermore, the log differential pore volume on the vertical axis can be calculated by dividing the increase in pore volume dV between each measurement point by the logarithmic difference in pore diameter (i.e., "log(D1) - log(D2)").

[0023] The porosity of the partition walls 1 measured by mercury intrusion porosimetry is 60 to 75%. If the porosity of the partition walls 1 is less than 60%, there is a possibility that the pressure loss during catalyst application increases dramatically, which is not preferable. If the porosity of the partition walls 1 exceeds 75%, it is not preferable in terms of a decrease in strength. Although not particularly limited, the porosity of the partition walls 1 is preferably 61 to 70%, and more preferably 62 to 66%. The porosity of the partition walls 1 can be measured using, for example, Autopore 9500 (trade name) manufactured by Micromeritics. The porosity can be measured by cutting out a part of the partition walls 1 from the honeycomb filter 100 as a test piece and using the test piece thus obtained.

[0024] Furthermore, the honeycomb filter 100 has a partition wall wetted area ratio (A / S) of 0.21 to 0.35 m 2 / m 2 The partition wall wetted area ratio (A / S) is the wetted area A (m 2 ) is the cross-sectional area of ​​the pore, S (m 2 ) divided by the wetted area of ​​the pores (A / S). 2 ) and cross-sectional area S(m 2) is calculated using three-dimensional voxel data 60 obtained by CT scanning the partition wall 1. Figure 4 is a conceptual diagram of the voxel data 60. First, the thickness direction of the partition wall 1 (see, for example, Figure 3) is defined as the X direction, and the axial direction of the cell 2 (for example, the up-and-down direction in Figure 3) is defined as the Y direction, with the XY plane being the imaging cross section. Next, a CT scan of the partition wall 1 is performed to capture multiple images of the imaging cross section shifted in the Z direction perpendicular to the X and Y directions, obtaining multiple image data. Based on this image data, voxel data 60 as shown in the upper part of Figure 4 is obtained. The resolution in each of the X, Y, and Z directions is 1.2 μm, and the resulting cube with a side length of 1.2 μm is the smallest unit, or voxel, of the three-dimensional voxel data 60. Note that although the image data of the imaging cross section obtained by the CT scan is planar data with no thickness in the Z direction, each imaging cross section is treated as having a thickness equal to the spacing (1.2 μm) between the imaging cross sections in the Z direction. That is, each two-dimensional pixel in the image data is treated as a cube (voxel) with a side length of 1.2 μm. The size of the voxel data 60 is a rectangular parallelepiped with an X direction of 300 μm (= 1.2 μm × 250 voxels), a Y direction of 480 μm (= 1.2 μm × 400 voxels), and a Z direction of 480 μm (= 1.2 μm × 400 voxels), as shown in the upper part of Figure 3. Each voxel's position is represented by X, Y, and Z coordinates (where a coordinate value of 1 corresponds to the side length of a voxel, 1.2 μm), and it is also distinguished as either a space voxel representing a space (pore) or an object voxel representing an object. The distinction between space voxels and object voxels is made using a binarization process using the modal method, as follows: The multiple image data actually obtained by a CT scan are intensity data for each X, Y, and Z coordinate. Based on this intensity data, an intensity histogram is created for all coordinates (all pixels of the multiple image data). The brightness value of the area between two peaks (valleys) appearing in the histogram is then set as a threshold value, and the brightness of each coordinate is binarized based on whether the brightness is greater than or less than the threshold value. This distinguishes the voxel at each coordinate from a space voxel or an object voxel. The middle section of Figure 4 shows a two-dimensional example of a state in which space voxels and object voxels have been distinguished. The bottom section of Figure 4 shows a two-dimensional enlarged view 64 of a portion of this.Such a CT scan can be performed using, for example, SMX-160CT-SV3 (product name) manufactured by Shimadzu Corporation. There are no particular restrictions on the position of the partition wall 1 where the CT scan is performed, but it is preferably the central part in the extension direction of the cells 2 of the honeycomb structure 4 (the axial direction of the cells 2 described above).

[0025] Next, using this voxel data 60, the cross-sectional area S' of the pore and the wetted area A' of the pore are calculated. The cross-sectional area S' of the pore is the area of ​​the range in which the "space voxels" shown in the middle and bottom rows of Figure 4 exist. Therefore, the cross-sectional area S' of the pore can be calculated as follows: Cross-sectional area S' = number of space voxels × 1.2 μm × 1.2 μm. The wetted area A' is calculated as the sum of the areas of the boundary surfaces between the space voxels and the object voxels in the voxel data 60. More specifically, it is derived as the wetted area A' = (number of boundary surfaces in the voxel data 60) × (area of ​​one boundary surface). The area of ​​one boundary surface is 1.44 μm 2 (=1.2 μm×1.2 μm). For example, in the enlarged view 64 shown in the bottom of FIG. 4, there are six boundary surfaces between the space voxel and the object voxel, so the total area of ​​the boundary surfaces in the enlarged view 64 is 6×1.44=8.64 μm 2 In this way, the wetted area A' is calculated. In the explanation so far, the unit of the cross-sectional area S' of the pore and the wetted area A' of the pore is "μm 2 " is explained as an example, but by converting the unit of the size (length) of the voxel data 60 into "m" as appropriate, the wetted area A (m 2 ) and the cross-sectional area of ​​the pores S (m 2 Then, the partition wall wetted area ratio (A / S) is calculated from the cross-sectional area S of the pores and the wetted area A.

[0026] In the honeycomb filter 100, the partition wall wet area ratio (A / S) is 0.21 m 2 / m 2If the partition wall wetted area ratio (A / S) is less than 0.35 m, the surface area in the partition wall 1 where the catalyst is applied (i.e., the wetted area in the partition wall 1) becomes small. Therefore, when a catalyst layer is provided on the honeycomb filter 100, it is difficult to increase the frequency of contact between the exhaust gas and the catalyst, and a sufficient improvement in purification performance cannot be expected. On the other hand, if the partition wall wetted area ratio (A / S) is less than 0.35 m, 2 / m 2 If the ratio exceeds 0.21 to 0.35 m, the pressure loss may increase after the catalyst is applied. 2 / m 2 For example, 0.23 to 0.30 m 2 / m 2 It is preferable that the thickness is 0.25 to 0.27 m. 2 / m 2 It is more preferable that:

[0027] Furthermore, in the honeycomb filter 100, in the pore size distribution of the partition walls 1 described above, the pore size D10 at which the cumulative pore volume is 10% of the total pore volume is preferably 5.5 to 7.5 μm. Hereinafter, the pore size D10 at which the cumulative pore volume is 10% of the total pore volume may be simply referred to as "D10" in the pore size distribution of the partition walls 1. A D10 of 5.5 to 7.5 μm is preferable in that an increase in pressure loss after catalyst application can be suppressed. Although not particularly limited, D10 is more preferably 6.0 to 7.0 μm.

[0028] Furthermore, in the honeycomb filter 100, the pore diameter D90 at which the cumulative pore volume is 90% of the total pore volume in the pore diameter distribution of the partition walls 1 is preferably 35.0 μm or less. Hereinafter, the pore diameter D90 at which the cumulative pore volume is 90% of the total pore volume may be simply referred to as "D90" in the pore diameter distribution of the partition walls 1. If D90 is 35.0 μm or less, it is preferable in that sufficient collection performance can be exhibited. Although not particularly limited, D90 is more preferably 27.0 to 35.0 μm, and particularly preferably 27.0 to 32.0 μm.

[0029] The shape of the cells 2 partitioned by the partition walls 1 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. Note that the shape of the cells 2 is preferably triangles, rectangles, pentagons, hexagons, or octagons. Furthermore, with regard to the shape of the cells 2, all the cells 2 may have the same shape or different shapes. For example, although not shown in the drawings, a mixture of rectangular cells and octagonal cells may be used. Furthermore, with regard to the size of the cells 2, 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, the size of some cells may be larger and the size of the other cells may be relatively smaller. Note that, in the present invention, a cell means a space surrounded by partition walls.

[0030] 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, circular, elliptical, polygonal, or the like.

[0031] There are no particular limitations on the size of the honeycomb structure 4, for example, the length from the inflow end face 11 to the outflow end face 12 and the size of the cross section perpendicular to the extension direction of the cells 2 of the honeycomb structure 4. When the honeycomb filter 100 is used as a filter for purifying exhaust gases, each size may be appropriately selected so as to obtain optimal purification performance.

[0032] There are no particular limitations on the material of the partition walls 1 constituting the honeycomb structure 4. For example, the material of the partition walls 1 preferably contains at least one selected from the group consisting of cordierite, silicon carbide, a silicon-silicon carbide composite material, a cordierite-silicon carbide composite material, silicon nitride, mullite, alumina, and aluminum titanate. In the honeycomb filter 100 of the present embodiment, a suitable example of the material of the partition walls 1 is a material containing at least one of cordierite, silicon carbide, and aluminum titanate.

[0033] There is no particular limitation on the material of the plugging portions 5. For example, the same material as the material of the partition walls 1 described above can be used.

[0034] In the honeycomb filter 100, a catalyst for purifying exhaust gas is preferably supported on the partition walls 1 that define the plurality of cells 2. Supporting a catalyst on the partition walls 1 means that the catalyst is coated on the surfaces of the partition walls 1 and on the inner walls of the pores formed in the partition walls 1. With this configuration, CO, NOx, HC, and the like in the exhaust gas can be converted into harmless substances through a catalytic reaction. In addition, the oxidation of PM such as collected soot can be promoted.

[0035] There is no particular limitation on the catalyst supported on the partition walls 1. For example, a catalyst containing a platinum group element, which contains an oxide of at least one element selected from aluminum, zirconium, and cerium, can be used.

[0036] (2) Honeycomb filter manufacturing method: The method for manufacturing the honeycomb filter of the present invention is not particularly limited, and examples thereof include the following methods. First, a plastic clay for manufacturing the honeycomb structure is prepared. The clay for manufacturing the honeycomb structure can be prepared by adding, as raw material powder, a material selected from the aforementioned suitable materials for the partition walls, as appropriate, additives such as binders, a pore-forming material, and water. When manufacturing the honeycomb filter of the present invention, the raw material powder for preparing the clay can be, for example, kaolin, talc, alumina, aluminum hydroxide, silica, etc., and these raw material powders can be prepared so as to have a chemical composition within the ranges of 42 to 56 mass% silica, 30 to 45 mass% alumina, and 12 to 16 mass% magnesia. Using kaolin, alumina, and aluminum hydroxide with an average particle size of 7 μm or less increases the number of small pores in the matrix and increases the wetted area of ​​the partition walls.

[0037] Next, the thus obtained clay is extrusion-molded to produce a columnar honeycomb molded body having partition walls that define a plurality of cells and an outer peripheral wall that surrounds the partition walls. In the extrusion molding, a die can be used that has slits on the extrusion surface of the clay that form the inverted shape of the honeycomb molded body to be molded.

[0038] The obtained honeycomb formed body is dried, for example, by microwaves and hot air, and the openings of the cells are plugged with the same material as that used to produce the honeycomb formed body, thereby producing plugging portions. After producing the plugging portions, the honeycomb formed body may be further dried.

[0039] Next, the honeycomb formed body with the plugged portions is fired to manufacture a honeycomb filter. The firing temperature and firing atmosphere vary depending on the raw materials, and a person skilled in the art can select the optimum firing temperature and firing atmosphere for the selected materials. [Example]

[0040] 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.

[0041] Example 1 To 100 parts by mass of the cordierite raw material, 2 parts by mass of a pore-forming material, 2 parts by mass of a dispersion medium, and 7 parts by mass of an organic binder were added, and the mixture was mixed and kneaded to prepare a clay. Alumina, aluminum hydroxide, kaolin, talc, and silica were used as the cordierite raw materials. Water was used as the dispersion medium. Methylcellulose was used as the organic binder. Dextrin was used as the dispersant. Aluminum hydroxide with an average particle size of 5 μm was used to prepare a clay for producing a honeycomb structure.

[0042] The resulting clay was then molded using an extrusion molding machine to produce a honeycomb molded body. The resulting honeycomb molded body was then dried using high-frequency dielectric heating and then further dried using a hot-air dryer. The cell shape of the honeycomb molded body was rectangular.

[0043] Next, plugging portions were formed on the dried honeycomb formed body. First, a mask was applied to the inflow end face of the honeycomb formed body. Next, the masked end (the end on the inflow end face side) was immersed in plugging slurry, and the plugging slurry was filled into the openings of the unmasked cells (outflow cells). In this way, plugging portions were formed on the inflow end face side of the honeycomb formed body. Then, plugging portions were also formed on the inflow cells on the outflow end face of the dried honeycomb formed body in the same manner.

[0044] Next, the honeycomb formed body with the plugged portions formed thereon 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. Next, the dried honeycomb formed body was degreased and fired to produce the honeycomb filter of Example 1.

[0045] The honeycomb filter of Example 1 had an end face diameter of 132.6 mm, a length in the cell extension direction of 127.3 mm, a partition wall thickness of 210.8 μm, and a cell density of 46.8 cells / cm 2 The thickness values ​​of the partition walls are shown in Table 1.

[0046] For the honeycomb filter of Example 1, the "porosity (%)", "D50 (μm)", "D10 (μm)" and "D90 (μm)" of the partition walls were measured by the following methods. In addition, the "partition wall wetted area ratio" of the partition walls was determined by the following method. The results are shown in Table 1.

[0047] [Porosity (%), D50 (μm), D10 (μm) and D90 (μm)] The porosity (%), D50 (μm), D10 (μm), and D90 (μm) of the partition walls were measured using an Autopore 9500 (trade name) manufactured by Micromeritics. The values ​​of D50 (μm), D10 (μm), and D90 (μm) were determined by confirming the pore sizes (μm) at which the cumulative pore volume accounted for 50%, 10%, and 90% of the total pore volume in the pore size distribution of the partition walls. In these measurements, a portion of the partition wall was cut out from the honeycomb filter to prepare a test piece, and measurements were performed using the obtained test piece. The test piece was a rectangular parallelepiped with lengths of approximately 10 mm, approximately 10 mm, and approximately 20 mm in height. The test piece was taken near the center of the honeycomb structure in the axial direction.

[0048] [Partition wall wetted area ratio] By performing a CT scan on the partition walls of the honeycomb structure using the method described above, three-dimensional voxel data 60 as shown in Fig. 4 was obtained. Then, using the obtained three-dimensional voxel data 60, the partition wall wetted area ratio was calculated according to the method described above.

[0049] [Table 1]

[0050] The honeycomb filter of Example 1 was evaluated for pressure loss, purification performance, and collection performance by the following methods. The results are shown in Table 1.

[0051] (pressure loss) Using a large wind tunnel tester, gas at 25°C was blown at 10 Nm 3 / min, and the pressure at the inlet end face side and the outlet end face side of the honeycomb filter was measured. The pressure difference between the inlet end face side and the outlet end face side was calculated to determine the pressure loss (kPa) of the honeycomb filter. The increase rate (%) of the pressure loss of the honeycomb filter of each example relative to the pressure loss value of the honeycomb filter of Comparative Example 1 was then determined. In evaluating the pressure loss, the honeycomb filters of each example were evaluated based on the following evaluation criteria. Evaluation "Good": If the increase rate (%) of pressure loss is less than 10%, the evaluation is "Good". Evaluation: "Fail": If the pressure loss increase rate (%) is 10% or more, the evaluation is "Fail."

[0052] (Purification performance) A honeycomb filter carrying 100 g / L of three-way catalyst was mounted under the floor of a vehicle with an engine displacement of 1500 cc, and a bench test was performed in the RTS95 cycle driving mode to determine the NOx purification rate (%) of the honeycomb filter. The NOx purification rate (%) of the honeycomb filter of each example was compared with the value of the NOx purification rate (%) of the honeycomb filter of Comparative Example 1 to evaluate the purification performance. Specifically, the honeycomb filter of each example was evaluated for purification performance based on the following evaluation criteria. Evaluation "Excellent": When the NOx purification rate (%) is improved by 1.0% or more compared to the NOx purification rate (%) of the honeycomb filter of Comparative Example 1, the evaluation is "Excellent". Evaluation "Good": When the NOx purification rate (%) is improved by 0.5% or more but less than 1.0% compared to the NOx purification rate (%) of the honeycomb filter of Comparative Example 1, the evaluation is "Good". Evaluation "Fail": When the NOx purification rate (%) is improved by less than 0.5% compared to the NOx purification rate (%) of the honeycomb filter of Comparative Example 1, the evaluation is "Fail".

[0053] (Collection performance) The honeycomb filter was mounted under the floor of a vehicle with an engine displacement of 1500cc, and a bench test was performed in the RTS95 cycle running mode, with exhaust gas containing PM being passed through the honeycomb filter. The number of PM in the exhaust gas before it entered the honeycomb filter and the number of PM in the exhaust gas flowing out of the honeycomb filter were measured to determine the collection efficiency (%) of the honeycomb filter. The honeycomb filters of each example were evaluated for collection performance based on the following evaluation criteria. Evaluation "Good": When the collection efficiency (%) is 70% or more, the evaluation is "Good". Evaluation: "Fair": If the collection efficiency (%) is 65% or more and less than 70%, the evaluation is "Fair". Evaluation "Fail": If the collection efficiency (%) is less than 65%, the evaluation is "Fail".

[0054] Examples 2 to 4 In Examples 2 to 4, the configuration of the honeycomb structure was changed as shown in "Partition wall characteristics" in Table 1. In Examples 2 and 4, the honeycomb structure was manufactured by adding a pore-forming material with a smaller particle size to the raw material powder. In Example 3, the honeycomb structure was manufactured by adding a pore-forming material with a larger particle size to the raw material powder.

[0055] (Comparative Example 1) In Comparative Example 1, the configuration of the honeycomb structure was changed as shown in "Partition wall characteristics" in Table 1. In Comparative Example 1, a honeycomb structure was produced in which the small pore volume was reduced by adjusting the particle diameter of the pore-forming material and the amount of the pore-forming material added.

[0056] The honeycomb filters of Examples 2 to 4 were also evaluated for pressure loss, purification performance, and collection performance in the same manner as in Example 1. The results are shown in Table 1. The honeycomb filter of Comparative Example 1 served as the evaluation standard for pressure loss and purification performance.

[0057] (result) The honeycomb filters of Examples 1 to 4 exhibited superior results in the evaluation of pressure loss and purification performance to the honeycomb filter of Comparative Example 1, which was the evaluation standard. In particular, the honeycomb filter of Example 4 exhibited superior results in the evaluation of pressure loss and purification performance to the honeycomb filter of Comparative Example 1, which was the evaluation standard. 2 / m 2 The honeycomb filters of Examples 1 and 3 had similar partition wall wetted area ratios, but a detailed comparison of the collection performance revealed that the honeycomb filter of Example 1 had better collection performance. The honeycomb filter of Example 1 had a smaller D90 value than the honeycomb filter of Example 3, which is presumed to be due to an improvement in collection performance. [Industrial Applicability]

[0058] The honeycomb filter of the present invention can be used as a filter for collecting particulate matter in exhaust gases. [Explanation of symbols]

[0059] 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, 60: voxel data, 64: enlarged view, 100: honeycomb filter.

Claims

[Claim 1] a columnar 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 disposed at either an end portion on the inlet end face side or an end portion on the outlet end face side of the cell, the thickness of the partition wall is 152 to 254 μm, The cell density of the honeycomb structure is 38.8 to 62.0 cells / cm ２ and In a pore size distribution of the partition walls measured by mercury intrusion porosimetry, a pore size D50 at which a cumulative pore volume becomes 50% of a total pore volume is 11 to 15 μm, In the pore size distribution of the partition walls, a pore size D10 at which a cumulative pore volume corresponds to 10% of a total pore volume is 6.0 to 7.0 μm, In the pore size distribution of the partition walls, a pore size D90 at which a cumulative pore volume accounts for 90% of a total pore volume is 27.0 to 35.0 μm, the porosity of the partition walls measured by mercury porosimetry is 60 to 75%, The thickness direction of the partition wall is the X direction, the extension direction of the cell is the Y direction, and the XY plane is the photographed cross section, and the photographed cross section is photographed while being shifted in the Z direction perpendicular to the X and Y directions. By CT scanning the partition wall, three-dimensional voxel data is obtained in which a cube having a side length of 1.2 μm in the resolution in the X direction, the Y direction, and the Z direction is used as the minimum unit voxel. Each voxel is determined to be a space voxel representing a space or an object voxel representing an object according to the brightness value of each voxel. A cross-sectional area S of a pore is calculated based on the area occupied by the space voxel in the photographed cross section. A wetted area A of the pore is calculated based on the area of ​​the boundary surface obtained by multiplying the length of the boundary line between the space voxel and the object voxel in the photographed cross section by the length of the resolution in the Z direction, 1.2 μm. When the wetted area A of the pore is calculated based on the area of ​​the boundary surface obtained by multiplying the length of the boundary line between the space voxel and the object voxel in the photographed cross section by the length of the resolution in the Z direction, a partition wall wetted area ratio (A / S) obtained by dividing the wetted area A of the pore by the cross-sectional area S of the pore is 0.21 to 0.35 m ２ / m ２ That is the honeycomb filter.

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