Honeycomb filter

Abstract

To provide a honeycomb filter that can suppress pressure loss and performance variation in collection efficiency.SOLUTION: There is provided a porous partition wall 1 which is so arranged as to surround a plurality of cells 2. A thickness of the partition wall 1 is 152 to 305 μm. A porosity of the partition wall 1 is 35% or more and 70% or less. An average pore diameter of the partition wall 1 is 7 μm or more and 24 μm or less. A porous body constituting the partition wall 1 has a communication pore 31 which opens on a surface of the partition wall 1 and communicates with the pore in the partition wall 1. The communication pore 31 has a narrow part 35 in which a diameter of the communication hole 31 partially narrows in the partition wall 1, and in a virtual single pore 32 in which the communication pore 31 is virtually divided by the narrow part 35, an average value of a ratio (X / Y) of a minimum width X (μm) to a maximum width Y (μm) passing a center of gravity O of the virtual single pore 32 is 0.51 or more and 1.00 or less.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a honeycomb filter, and more particularly to a honeycomb filter capable of suppressing variations in performance in terms of pressure loss and collection efficiency. [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). Hereinafter, particulate matter contained in exhaust gas may be referred to as "PM." "PM" is an abbreviation for "particulate matter."

[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] By installing a honeycomb filter as a particulate filter in the exhaust system of an automobile, the honeycomb filter can capture PM contained in exhaust gases emitted from the engine, thereby reducing PM emissions. However, installing a honeycomb filter in the exhaust system increases pressure loss within the exhaust system piping, which can lead to a decrease in vehicle fuel efficiency. For this reason, there is a demand for the development of a honeycomb filter that can suppress increases in pressure loss while maintaining collection performance. This demand is particularly strong for honeycomb filters such as gasoline particulate filters (GPFs) and diesel particulate filters (DPFs).

[0006] The trapping performance and pressure drop performance of gasoline particulate filters (GPFs) and diesel particulate filters (DPFs) can be significantly affected by the state of the pores of the porous body that constitutes the partition walls of the honeycomb filter. Conventionally, the state of the pores of a porous body has been evaluated based on characteristics such as porosity and average pore diameter. However, when the shape of the pores in the porous body is nonuniform, the state of the pores cannot be fully understood using the conventional evaluation methods described above. For this reason, even honeycomb filters that are evaluated as having similar levels of trapping performance and pressure drop performance when measured under the same conditions are prone to variations, and may not be able to achieve stable 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 that can suppress variations in performance such as pressure loss and collection efficiency. [Means for solving the problem]

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

[0009] [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 305 μm, the porosity of the partition walls is 35% or more and 70% or less, the partition walls have an average pore diameter of 7 μm or more and 24 μm or less, the porous body constituting the partition walls has communicating pores that open to the partition wall surfaces and communicate with pores inside the partition walls, the communicating pores having narrowed portions in the partition walls where the diameters of the communicating pores are partially narrowed, A honeycomb filter, wherein, in virtual single pores obtained by virtually dividing the communicating pores by the narrow portions, when the minimum width passing through the center of gravity of each virtual single pore is X (μm) and the maximum width passing through the center of gravity of each virtual single pore is Y (μm), the average value of the ratio (X / Y) of the minimum width X to the maximum width Y of the virtual single pore is 0.51 or more and 1.00 or less.

[0010] [2] The honeycomb filter according to [1], wherein the standard deviation of the ratio (X / Y) of the minimum width X to the maximum width Y of the virtual single pore is 0.2 or less.

[0011] [3] A honeycomb filter according to [1] or [2], wherein the average equivalent diameter of the equal-area circle of the imaginary pore dividing plane that virtually divides the communicating pores into each imaginary single pore at the narrow portion is 8.8 to 30 μm.

[0012] [4] The porosity of the partition walls is 45% or more, The honeycomb filter according to [1] or [2] above, wherein the partition walls are made of a porous body containing cordierite as a main component.

[0013] [5] The honeycomb filter according to [4], wherein an average value of the ratio (X / Y) of the minimum width X to the maximum width Y of the virtual single pore is 0.80 or more and 1.00 or less.

[0014] [6] The honeycomb filter according to [4], wherein the partition walls have an average pore size of 10 μm or less.

[0015] [7] The honeycomb filter according to [1] or [2], wherein the partition walls are made of a porous body containing silicon carbide as a main component.

[0016] [8] The honeycomb filter according to [4], wherein an average value of the ratio (X / Y) of the minimum width X to the maximum width Y of the virtual single pore is 0.58 or more and 1.00 or less.

[0017] [9] The honeycomb filter according to [7], wherein the average equivalent diameter of the equal-area circle of the imaginary pore dividing plane that virtually divides the communicating pores into each imaginary single pore at the narrow portion is 9 to 30 μm. [Effects of the Invention]

[0018] The honeycomb filter of the present invention can suppress variations in pressure loss and collection efficiency, and therefore, in particular in gasoline particulate filters (GPFs) and diesel particulate filters (DPFs), the performance variations in pressure loss and collection efficiency can be suppressed, and stable performance can be ensured. [Brief explanation of the drawings]

[0019] [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 used to determine the minimum width X (μm) and maximum width Y (μm) of a hypothetical single pore. [Figure 5] FIG. 2 is a conceptual diagram showing interconnected pores of a porous body. [Figure 6]6 is a conceptual diagram for explaining the minimum width X and maximum width Y of a virtual single pore in the communicating pores shown in FIG. 5. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] 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.

[0021] (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.

[0022] 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.

[0023] 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."

[0024] In the honeycomb filter 100, the material of the partition walls 1 of the honeycomb structure 4 is not particularly limited, and examples thereof include cordierite, silicon carbide, and silicon-silicon carbide composite materials. For example, the partition walls 1 of the honeycomb structure 4 may be made of a porous body containing cordierite as a main component, or may be made of a porous body containing silicon carbide or a silicon-silicon carbide composite material as a main component. Although not particularly limited, in the honeycomb filter 100, the partition walls 1 of the honeycomb structure 4 are preferably made of a porous body containing cordierite as a main component or a porous body containing silicon carbide as a main component. It is more preferable that the partition walls 1 are made of cordierite or silicon carbide, excluding components that are inevitably contained.

[0025] The honeycomb filter 100 has a thickness of the partition walls 1 of 152 to 305 μm. By setting the thickness of the partition walls 1 within the above range, it is possible to effectively suppress an increase in pressure loss while ensuring sufficient collection efficiency as an exhaust gas purification filter. Furthermore, by setting the thickness of the partition walls 1 within the above range, it is possible to ensure the structural strength of the honeycomb filter 100. 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 collection efficiency and a decrease in mechanical strength. If the thickness of the partition walls 1 exceeds 305 μm, this is not preferable because the pressure loss increases significantly. Although not particularly limited, the thickness of the partition walls 1 is preferably 165 to 305 μm, and more preferably 208 to 305 μm. The thickness of the partition walls 1 can be measured using, for example, a scanning electron microscope or a microscope.

[0026] In the honeycomb filter 100, the porosity of the cell walls 1 is 35% or more and 70% or less. The porosity of the cell walls 1 is a value measured by mercury intrusion porosimetry, and can be measured using, for example, an Autopore 9500 (trade name) manufactured by Micromeritics. The porosity can be measured using a test piece obtained by cutting out a part of the cell walls 1 from the honeycomb filter 100. The porosity of the cell walls 1 is not particularly limited as long as it is 35% or more and 70% or less, but is preferably 35% or more and 67% or less, and more preferably 35% or more and 65% or less. If the porosity of the cell walls 1 is less than 35%, this is not preferable because the pressure loss increases. On the other hand, if the porosity of the cell walls 1 exceeds 70%, this is not preferable because the structural strength of the honeycomb filter 100 decreases. When the partition walls 1 of the honeycomb structure 4 are made of a porous body containing cordierite as a main component, the porosity of the partition walls 1 is preferably 45% or more and 70% or less.

[0027] In the honeycomb filter 100, the average pore diameter of the partition walls 1 is 7 μm or more and 24 μm or less. The average pore diameter of the partition walls 1 is a value measured by mercury intrusion porosimetry, and can be measured using, for example, an Autopore 9500 (trade name) manufactured by Micromeritics. The average pore diameter can be measured by cutting out a part of the partition walls 1 from the honeycomb filter 100 to form a test piece, and using the test piece thus obtained. If the average pore diameter of the partition walls 1 is less than 7 μm, this is not preferable because the pressure loss increases. On the other hand, if the average pore diameter of the partition walls 1 exceeds 24 μm, this is not preferable because the collection performance deteriorates. Here, when the partition walls 1 of the honeycomb structure 4 are made of a porous body containing cordierite as a main component, the average pore diameter of the partition walls is preferably 10 μm or less.

[0028] The porous body constituting the partition wall 1 has communicating pores that are open to the surface of the partition wall 1 and communicate with pores inside the partition wall 1. For example, as shown in FIGS. 5 and 6 , the porous body constituting the partition wall 1 has communicating pores 31 formed by multiple pores formed inside the partition wall 1 that are connected to each other. These communicating pores 31 serve as fine flow paths through which a fluid passes through the partition wall 1. The communicating pores 31 are preferably formed in the partition wall 1 that separates the inflow cells 2a and the outflow cells 2b, as shown in FIG. 3 , so as to communicate one surface of the partition wall 1 that separates the inflow cells 2a with the other surface of the partition wall 1 that separates the outflow cells 2b. Note that although the communicating pores 31 are drawn as if they are closed on both sides of the paper in FIGS. 5 and 6 , the communicating pores 31 are formed so as to be three-dimensionally continuous within the partition wall 1.

[0029] As shown in FIGS. 5 and 6 , the communicating pore 31 has narrowed portions 35 in the partition wall 1 where the diameter of the communicating pore 31 is partially narrowed. Here, the individual portions obtained by virtually dividing the communicating pore 31 by the narrowed portions 35 are referred to as imaginary single pores 32 (32a, 32b, 32c, 32d). Here, the minimum width passing through the center of gravity O of each imaginary single pore 32 (32a, 32b, 32c, 32d) is referred to as X (μm), and the maximum width passing through the center of gravity O of each imaginary single pore 32 (32a, 32b, 32c, 32d) is referred to as Y (μm). Hereinafter, the above-mentioned minimum width may be referred to as "minimum width X (μm)" and the maximum width may be referred to as "maximum width Y (μm)." In the honeycomb filter 100 of this embodiment (see FIG. 1, the same applies hereinafter), the average ratio (X / Y) of the minimum width X (μm) to the maximum width Y (μm) of this virtual single pore 32 is 0.51 or more and 1.00 or less. Note that although FIGS. 5 and 6 two-dimensionally illustrate how the communicating pores 31 are virtually divided into virtual single pores 32 by the narrow portions 35, as will be described later, the virtual division of the communicating pores 31 is performed three-dimensionally using a three-dimensional model.

[0030] The average value of X / Y described above is an index of the sphericity of the virtual single pore 32. The closer the average value of X / Y is to 1.00, the closer the pore shape of the virtual single pore 32 is to a perfect sphere. Here, the communicating pore 31 is formed by connecting a plurality of pores in the porous body, and the junctions where the plurality of pores are connected to form the communicating pore 31 correspond to the narrow portions 35 described above. Therefore, by setting the average value of X / Y within the above numerical range, the pore shapes of the porous body constituting the partition wall 1 can be made as close to a perfect sphere as possible. Furthermore, by making the shapes of the individual pores closer to a perfect sphere, the widths of the narrow portions 35 (hereinafter sometimes referred to as the "neck diameters" of the communicating pores 31) become more uniform regardless of how the pores are connected to each other, and the number of locations where the diameter of the communicating pore 31 becomes extremely narrow is reduced. Therefore, it is possible to appropriately secure fine flow paths within the partition wall 1, effectively suppress an increase in pressure loss, and appropriately maintain the filtering performance of the filter. On the other hand, if the average value of X / Y is less than 0.51, the pore shape of the virtual single pore 32 becomes closer to an ellipsoid than a perfect sphere. Therefore, when a plurality of pores are connected to each other to form the communicating pores 31, the neck diameter of the communicating pores 31 is likely to be extremely narrow or wide. In particular, if the neck diameter of the communicating pores 31 becomes extremely narrow, the microchannels in the partition wall 1 are likely to be clogged, which is likely to result in an increase in pressure loss. Conversely, if the neck diameter of the communicating pores 31 becomes extremely wide, this may result in a deterioration in the filtering efficiency. Therefore, by setting the average value of X / Y to 0.51 or more and 1.00 or less, the shape of each pore forming the communicating pores 31 becomes closer to a perfect sphere, and thus the variations in pressure loss and filtering efficiency can be effectively suppressed.

[0031] The minimum width X (μm) and maximum width Y (μm) of the virtual single pore 32 obtained by virtually dividing the communicating pore 31 by the narrow portions 35 can be determined by the following method. The minimum width X (μm) and maximum width Y (μm) of the virtual single pore 32 obtained by virtually dividing the communicating pore 31 by the narrow portions 35 are calculated using three-dimensional voxel data 60 (see FIG. 4) obtained by performing a CT scan on the partition wall 1. FIG. 4 is a conceptual diagram of voxel data used to determine the minimum width X (μm) and maximum width Y (μm) of the virtual single pore. First, the thickness direction of the partition wall 1 (see FIG. 3, for example) is defined as the X direction, and the axial direction of the cell 2 (for example, the up-and-down direction in FIG. 3) is defined as the Y direction, and the XY plane is defined as the photographed cross section. Next, a CT scan of the partition wall 1 is performed so that the photographed cross section is photographed multiple times while being shifted in the Z direction perpendicular to the XY direction, thereby obtaining multiple image data. Based on this image data, voxel data 60 as shown in FIG. 4 is obtained. The resolution in each of the X, Y, and Z directions is set to 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 while the image data of the cross section obtained by a CT scan is planar data with no thickness in the Z direction, each cross section is treated as having a thickness equal to the spacing between the cross sections in the Z direction (1.2 μm). In other words, 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 set to a rectangular parallelepiped with a side length of 300 μm (= 1.2 μm × 250 voxels) in the X direction, 480 μm (= 1.2 μm × 400 voxels) in the Y direction, and 480 μm (= 1.2 μm × 400 voxels) in the Z direction, as shown in Figure 4. The position of each voxel is expressed by X, Y, and Z coordinates (where the coordinate value 1 corresponds to 1.2 μm, the length of one side of the voxel), and each voxel is 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 as follows using binarization processing using the mode method. The multiple image data actually obtained by a CT scan are brightness data for each X, Y, and Z coordinate. Based on this brightness data, a brightness histogram is created for all coordinates (all pixels of the multiple image data).Then, the brightness value of the portion between two peaks (valleys) appearing in the histogram is set as a threshold value, and the brightness of each coordinate is binarized based on whether the brightness for each coordinate is greater than or less than the threshold value. This distinguishes whether the voxel at each coordinate is a space voxel or an object voxel. Such a CT scan can be performed using, for example, an 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 center portion in the extension direction of the cells 2 of the honeycomb structure 4 (the axial direction of the cells 2 described above).

[0032] Next, this voxel data 60 is used to model the internal structure of the partition wall 1 (for example, the shape of the communicating pores 31 in the partition wall 1) as shown in Figures 4 and 5. Then, an algorithm for separating contacting objects, known as the "Watershed algorithm," is applied to the internal structure of the partition wall 1 modeled in this way to first identify narrow portions 35 where the diameters of the communicating pores 31 are partially narrowed. Furthermore, for the identified narrow portions 35, a virtual pore division surface 33 that virtually divides the communicating pores 31 into virtual single pores 32 is obtained, and the area of ​​the virtual pore division surface 33 is calculated. The equivalent diameter of an equal-area circle of the virtual pore division surface 33 thus obtained is defined as the length equivalent to the width of the narrow portion 35. In other words, hereinafter, the "width of the narrow portion 35" refers to the "equivalent diameter of an equal-area circle of the virtual pore division surface 33 of the narrow portion 35."

[0033] Furthermore, the minimum widths X1, X2, X3, and X4 (μm) and maximum widths Y1, Y2, Y3, and Y4 (μm) passing through each of the centers of gravity O1 to O4 are calculated for each of the virtual single pores 32a, 32b, 32c, and 32d obtained by virtually dividing the communicating pore 31 by the narrow portion 35. The calculation of these minimum widths X1, X2, X3, and X4 (μm) and maximum widths Y1, Y2, Y3, and Y4 (μm) is performed within a program that executes the Watershed algorithm described above.

[0034] Next, the ratios of the minimum widths X1, X2, X3, and X4 (μm) to the maximum widths Y1, Y2, Y3, and Y4 (μm) are calculated for each of the virtual single pores 32a, 32b, 32c, and 32d. For example, in FIG. 5, "X1 / Y1" for the virtual single pore 32a, "X2 / Y2" for the virtual single pore 32b, "X3 / Y3" for the virtual single pore 32c, and "X4 / Y4" for the virtual single pore 32d are calculated. Then, the "X / Y" values ​​for the virtual single pores 32 observed within the analysis range (480 μm × 480 μm × 300 μm) are individually calculated, and the average of the calculated "X / Y" values ​​is calculated. The average "X / Y" value is preferably calculated by, for example, calculating the "X / Y" values ​​for 2,500 or more virtual single pores 32 using the analysis described above and averaging them. That is, the number of samples (in other words, the number of samples) used to calculate the average value of "X / Y" is preferably 2500 or more. If the number of samples used to calculate the average value is 2500 or more, it will be a statistically significant number of samples.

[0035] Here, when the partition walls 1 of the honeycomb structure 4 are formed of a porous material containing cordierite as a main component, the average value of the ratio (X / Y) of the minimum width X to the maximum width Y of the imaginary single pore 32 is preferably 0.80 or more and 1.00 or less. By configuring in this manner, the pore shape of the imaginary single pore 32 becomes closer to a perfect sphere, and performance variations in pressure loss and collection efficiency can be more effectively suppressed. The theoretical upper limit of the average value of X / Y is 1.00 when the minimum width X (μm) and the maximum width Y (μm) are the same value in all the imaginary single pores 32, but a practically preferable upper limit of the average value of X / Y can be 0.90. It is more preferable that the average value of the ratio (X / Y) of the minimum width X to the maximum width Y of the imaginary single pore 32 is 0.80 or more and 0.90 or less. On the other hand, when the partition walls 1 of the honeycomb structure 4 are made of a porous material containing silicon carbide as a main component, it is preferable that the average ratio (X / Y) of the minimum width X to the maximum width Y of the virtual single pore 32 is 0.58 or more and 1.00 or less.

[0036] The standard deviation of the ratio (X / Y) of the minimum width X to the maximum width Y of the imaginary single pore 32 is preferably 0.2 or less. The standard deviation of X / Y is preferably a value obtained by calculating the average of the "X / Y" values ​​of 2500 or more imaginary single pores 32 obtained by the analysis described above. That is, the number of specimens (in other words, the number of samples) for calculating the average value of "X / Y" is preferably 2500 or more.

[0037] The average value of the equivalent circle diameter of the imaginary pore dividing surface 33, which virtually divides the communicating pore 31 into imaginary single pores 32a, 32b, 32c, and 32d at the narrow portions 35, is preferably 98.8 to 30 μm. By configuring in this manner, it is possible to more effectively suppress performance variations in pressure loss and collection efficiency. In particular, when the partition walls 1 of the honeycomb structure 4 are made of a porous body containing silicon carbide as a main component, the average value of the equivalent circle diameter of the imaginary pore dividing surface 33 is preferably 9 to 30 μm.

[0038] There is no particular limitation on the cell density of the honeycomb structure 4. For example, the cell density of the honeycomb structure 4 is 31 to 62 cells / cm. 2 It is preferable that the density is 43 to 50 particles / cm 2 With this configuration, it is possible to effectively suppress an increase in pressure loss while maintaining the collection performance of the honeycomb filter 100.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] There is no particular limitation on the material of the plugging portions 5. For example, the plugging portions 5 may be made of the same material as the material of the partition walls 1 described above, or may be made of a material different from the material of the partition walls 1.

[0043] 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.

[0044] 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.

[0045] (2) Honeycomb filter manufacturing method: The method for manufacturing the honeycomb filter of the present invention is not particularly limited. For example, in the case of a honeycomb filter whose partition walls are composed of a porous material containing cordierite as a main component, the following method can be used. First, a plastic clay for manufacturing the honeycomb structure is prepared. For example, kaolin, talc, alumina, aluminum hydroxide, silica, etc. can be used as raw material powders for preparing the clay. These raw material powders can be prepared so that the chemical composition falls within the range of 42 to 56 mass% silica, 30 to 45 mass% alumina, and 12 to 16 mass% magnesia. The pore-forming material can be a mixture of a spherical pore-forming material and a non-spherical pore-forming material in a predetermined blend ratio. By using a spherical pore-forming material with an average particle size of 10 to 25 μm, a clay can be obtained that can be used to manufacture a porous body containing many pores of approximately spherical size. The average particle size refers to the median diameter (D50) measured using a laser diffraction / scattering particle size distribution analyzer.

[0046] Furthermore, starch-based (particularly wheat-derived) pore-forming materials are effective as the spherical pore-forming materials used in the method for manufacturing the honeycomb filter of the present invention. Conventionally, pore-forming materials used in the manufacture of ordinary honeycomb filters have difficulty maintaining their spherical shape due to swelling characteristics during molding and water absorption. On the other hand, starch-based pore-forming materials, such as those derived from wheat, can mitigate this effect. Furthermore, it is preferable that the pore-forming material used in the method for manufacturing the honeycomb filter of the present invention has an average ratio of the minimum minor axis to the maximum major axis (minimum minor axis / maximum major axis) of 0.5 or more.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The above has been explained using a cordierite honeycomb filter as an example, but a honeycomb filter in which the partition walls are composed of a porous body containing silicon carbide as the main component can also be manufactured by adding a similar pore-forming material, dispersion medium, and organic binder to silicon carbide powder (silicon carbide) to prepare a clay, and then subjecting the clay to a similar treatment. [Example]

[0051] 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.

[0052] 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 dispersing medium, and 7 parts by mass of an organic binder were added, mixed, and kneaded to prepare a clay. The cordierite raw materials used were alumina, aluminum hydroxide, kaolin, talc, and silica. Water was used as the dispersing medium. Methylcellulose was used as the organic binder. Dextrin was used as the dispersing agent. The pore-forming material was a mixture of spherical and non-spherical pore-forming materials in a predetermined blend ratio. The spherical pore-forming material in particular had an average particle size of 15 μm and an average ratio of the minimum minor axis to the maximum major axis of 0.5 or more. The average particle size was the median diameter (D50) measured using a laser diffraction / scattering particle size distribution analyzer.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] The honeycomb filter of Example 1 had an end face diameter of 118.4 mm, a length in the cell extension direction of 152.4 mm, a partition wall thickness of 210.8 μm, and a cell density of 47.3 cells / cm 2 The partition wall thickness and cell density values ​​are shown in Table 1. In Example 1, 10 honeycomb filters of the same lot were produced by the method described above. Hereinafter, a plurality of honeycomb filters (10 in Example 1) produced by the same method using the same raw materials as in Example 1 above may be referred to as "products of the same lot."

[0057] For the honeycomb filter of Example 1, the "porosity (%)" and "average pore diameter (μm)" of the partition walls were measured by the following method. The results are shown in Table 1. Furthermore, by the method described above, the minimum width X (μm) and maximum width Y (μm) of each imaginary single pore obtained by virtually dividing the continuous pores of the porous body constituting the partition walls by narrow portions were determined. Then, the ratio (X / Y) of the minimum width X (μm) to the maximum width Y (μm) of each imaginary single pore was determined, and the average value was calculated. The results are shown in the column "Average value of X / Y" in Table 1. Furthermore, by the method described above, the equivalent diameter of a circle of equal area of ​​a virtual pore division plane that virtually divides the continuous pores into each virtual single pore was determined, and the average value was calculated. The results are shown in the column "Average equivalent diameter of a circle of equal area of ​​a virtual pore division plane (μm)" in Table 1. The number of virtual single pores used to calculate each of the above average values ​​was 2,842. The value is shown in the column of "Number of virtual single pores" in Table 1.

[0058] [Porosity (%) and average pore diameter (μm)] The porosity (%) and average pore diameter (μm) of the partition walls were measured using an Autopore 9500 (trade name) manufactured by Micromeritics. In these measurements, a part of the partition wall was cut out from the honeycomb filter to form a test piece, and the measurements were carried out using the obtained test piece. The test piece was a rectangular parallelepiped with length, width, and height of approximately 10 mm, approximately 10 mm, and approximately 20 mm, respectively. The test piece was taken from near the center in the axial direction of the honeycomb structure.

[0059] [Table 1]

[0060] The honeycomb filter of Example 1 was evaluated for collection efficiency and pressure loss by the following methods. The results are shown in Table 1.

[0061] [Collection efficiency] A honeycomb filter was installed under the floor of a 1500cc vehicle, and a bench test was conducted in the RTS95 cycle. Exhaust gas containing PM was passed through the honeycomb filter. The number of PM particles in the exhaust gas before it entered the honeycomb filter and the number of PM particles in the exhaust gas flowing out of the honeycomb filter were measured to determine the honeycomb filter's collection efficiency (%). The collection efficiency (%) was measured for 10 honeycomb filters from the same lot, and the average collection efficiency (%), as well as the maximum and minimum collection efficiencies (%) of the 10 filters from the same lot were determined. Furthermore, the percentage change (%) from the average was calculated for the 10 filters from the same lot that showed the maximum and minimum collection efficiencies (%). The percentage change (%) from the average was calculated by dividing the difference between the maximum or minimum value and the average by the average and multiplying the result by 100. The maximum and minimum values ​​of the "rate of change (%) from the average value" of the filtering efficiency (%) were compared, and the value showing the larger rate of change (%) (hereinafter also referred to as the "maximum rate of change") was evaluated for filtering efficiency. In the evaluation of filtering efficiency, a maximum rate of change of filtering efficiency (%) of less than 5.0% was considered to be pass, and a maximum rate of change of more than 5.0% was considered to be fail.

[0062] [Pressure loss] Using a large wind tunnel tester, gas at 25°C was blown over a distance of 10 m 3 Air was introduced at a flow rate of 1 / min, and the pressure at the inlet end and outlet end of the honeycomb filter was measured. The pressure difference between the inlet end and outlet end was calculated to determine the pressure loss (kPa) of the honeycomb filter. The pressure loss (kPa) was measured for each of 10 honeycomb filters from the same lot, and the average pressure loss (kPa) and the maximum and minimum pressure losses (kPa) of the 10 filters from the same lot were determined. Furthermore, the percentage change (%) from the average was calculated for the maximum and minimum pressure losses (kPa) of the 10 filters from the same lot. The percentage change (%) from the average was calculated by dividing the difference by the average and multiplying the result by 100. The maximum and minimum values ​​of the "percent change (%) from the average" of the pressure loss (kPa) were compared, and the filter with the larger percentage change (%) (hereinafter also referred to as the "maximum percentage change") was selected for evaluation of pressure loss. In the evaluation of pressure loss, a maximum rate of change in pressure loss (kPa) of less than 4.0% was judged as pass, and a rate of change exceeding 4.0% was judged as fail.

[0063] Examples 2 to 10 In Examples 2 to 10, the configuration of the honeycomb structure was changed as shown in Table 1. In Examples 2 to 10, the mixing ratio of the spherical pore-forming material and the non-spherical pore-forming material was adjusted to fabricate honeycomb structures having the configurations of Examples 2 to 10 shown in Table 1. Here, Examples 2 to 8 have almost the same end face diameters and cell extension direction lengths as Example 1, and Examples 1 and 2 to 8 are gasoline particulate filters (GPFs). On the other hand, Examples 9 and 10 are diesel particulate filters (DPFs) and have different dimensions from Example 1. Specifically, Example 9 has an end face diameter of 266.7 mm and a cell extension direction length of 127 mm, while Example 10 has an end face diameter of 304.8 mm and a cell extension direction length of 203.2 mm.

[0064] (Comparative Example 1) In Comparative Example 1, the configuration of the honeycomb structure was changed as shown in Table 1. In Comparative Example 1, the honeycomb structure was produced using a crushed pore-forming material, kaolin, alumina, and aluminum hydroxide. In Comparative Example 1, the diameter of the end face and the length in the cell extension direction were almost the same as in Example 1.

[0065] The honeycomb filters of Examples 2 to 8 and Comparative Example 1 were also evaluated for collection efficiency and pressure loss in the same manner as in Example 1. The results are shown in Table 1. For Examples 9 and 10, the size of the honeycomb filters was larger than those of Examples 1 to 8 and Comparative Example 1, so the measurement conditions were changed. Specifically, the measurement of collection efficiency was changed to a bench test with an engine displacement of 6700 cc and a WHTC cycle driving mode. The pressure loss was measured with a gas flow rate of 20 m 3 / min. The other measurement conditions were the same, and the evaluation method was also the same. The results of Examples 9 and 10 are also shown in Table 1.

[0066] (result) The honeycomb filters of Examples 1 to 10 were evaluated as passing, satisfying the evaluation criteria for both filtering efficiency and pressure loss. That is, the honeycomb filters of Examples 1 to 10 had small variations in pressure loss and filtering efficiency among the 10 honeycomb filters produced in the same lot. On the other hand, the honeycomb filter of Comparative Example 1 had large variations in pressure loss and filtering efficiency among the 10 honeycomb filters produced in the same lot. Furthermore, among Examples 1 to 10, Example 8, which had an average ratio (X / Y) of 0.80 or more, and Examples 9 and 10, which had an average pore size of the partition walls of 10 μm or less, had a maximum variation in filtering efficiency of 1.3% or less, and thus had extremely small variations in filtering efficiency compared to Examples 1 to 7, which did not satisfy any of these requirements.

[0067] Example 11 To 100 parts by mass of ceramic raw material (a mixture of silicon carbide powder and metal Si powder in a mass ratio of 80:20), 15 parts by mass of a pore-forming material, 0.1 parts by mass of a dispersing medium, and 7 parts by mass of an organic binder were added, mixed, and kneaded to prepare a clay. Water was used as the dispersing medium. Methylcellulose was used as the organic binder. Dextrin was used as the dispersing agent. The pore-forming material was a mixture of spherical and non-spherical pore-forming materials in a predetermined ratio. The spherical pore-forming material in particular had an average particle size of 30 μm and an average ratio of the minimum minor axis to the maximum major axis of 0.5 or greater. The average particle size was the median diameter (D50) measured using a laser diffraction / scattering particle size distribution analyzer.

[0068] 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.

[0069] 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.

[0070] 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 11.

[0071] The honeycomb filter of Example 11 had an end face diameter of 143.8 mm, a length in the cell extension direction of 177.8 mm, a partition wall thickness of 235.5 μm, and a cell density of 45.0 cells / cm 2 The partition wall thickness and cell density values ​​are shown in Table 2. For Example 11, 10 honeycomb filters of the same lot were produced in the same manner as in Example 1.

[0072] For the honeycomb filter of Example 11, the partition wall porosity (%), average pore diameter (μm), average value of the ratio (X / Y), and average value of the equivalent circle diameter of the virtual pore division plane were determined in the same manner as in Example 1. Each value is shown in Table 2. Here, the number of virtual single pores was 3,448, which is also shown in Table 2.

[0073] [Table 2]

[0074] The honeycomb filter of Example 11 was evaluated for collection efficiency and pressure loss by the following methods. The results are shown in Table 2.

[0075] [Collection efficiency] The honeycomb filter was installed under the floor of a vehicle equipped with a 3500cc diesel engine, and a bench test was performed in the WLTC cycle driving 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 10 honeycomb filters from the same lot. The maximum rate of change in collection efficiency (%) was then determined using the same method as in Example 1, and a maximum rate of change of less than 5.0% was deemed acceptable, while a rate of change of more than 5.0% was deemed unacceptable.

[0076] [Pressure loss] Using a large wind tunnel tester, gas at 25°C was blown over a distance of 10 m 3Air was introduced into the honeycomb filter at a flow rate of 1.5 / min, and the pressure at the inlet end face side and the outlet end face side of the honeycomb filter were 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 10 honeycomb filters from the same lot. The maximum rate of change in pressure loss (kPa) was then determined in the same manner as in Example 1, and a maximum rate of change of less than 4.0% was determined as pass, and a rate of change of more than 4.0% was determined as fail.

[0077] Examples 12 to 16 In Examples 12 to 16, the configuration of the honeycomb structure was changed as shown in Table 2. In Examples 12 to 16, the mixing ratio of the spherical pore-forming material and the non-spherical pore-forming material was adjusted to produce honeycomb structures having the configurations of Examples 12 to 16 as shown in Table 2. Here, the above-mentioned Examples 11 and 12 to 16 are diesel particulate filters (DPF).

[0078] (Comparative Example 2) In Comparative Example 2, the configuration of the honeycomb structure was changed from that of Example 11 as shown in Table 2. In Comparative Example 2, the honeycomb structure was manufactured using a crushed pore-forming material.

[0079] The honeycomb filters of Examples 12 to 16 and Comparative Example 2 were also evaluated for collection efficiency and pressure loss in the same manner as in Example 11. Table 2 shows the results.

[0080] (result) The honeycomb filters of Examples 11 to 16 were evaluated as passing in terms of filtering efficiency and pressure loss, satisfying the evaluation criteria. That is, the honeycomb filters of Examples 11 to 16 had small variations in pressure loss and filtering efficiency among the ten honeycomb filters produced in the same lot. On the other hand, the honeycomb filters of Comparative Example 2 had large variations in pressure loss and filtering efficiency among the ten honeycomb filters produced in the same lot. Furthermore, among Examples 11 to 16, Examples 13 to 16, which had an average ratio (X / Y) of 0.58 or more, had a maximum variation in filtering efficiency of 3.3% or less, and had extremely small variations in filtering efficiency compared to Examples 11 and 12, which did not satisfy this requirement. [Industrial Applicability]

[0081] The honeycomb filter of the present invention can be used as a filter for collecting particulate matter in exhaust gases. [Explanation of symbols]

[0082] 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, 31: interconnected pores, 32, 32a, 32b, 32c, 32d: virtual single pore, 33: virtual pore division surface, 35: narrow portion, 60: voxel data, 100: honeycomb filter, O1, O2, O3, O4: center of gravity, X, X1, X2, X3, X4: minimum width, Y, Y1, Y2, Y3, Y4: maximum width.

Claims

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 305 μm, the porosity of the partition walls is 35% or more and 70% or less, the partition walls have an average pore diameter of 7 μm or more and 24 μm or less, the porous body constituting the partition walls has communicating pores that open to the partition wall surfaces and communicate with pores inside the partition walls, the communicating pores having narrowed portions in the partition walls where the diameters of the communicating pores are partially narrowed, In the honeycomb filter, when the minimum width passing through the center of gravity of each virtual single pore is X (μm) and the maximum width passing through the center of gravity of each virtual single pore is Y (μm), the average value of the ratio (X / Y) of the minimum width X to the maximum width Y of the virtual single pore is 0.51 or more and 1.00 or less.

2. The honeycomb filter according to claim 1, wherein a standard deviation of a ratio (X / Y) of the minimum width X to the maximum width Y of the imaginary single pore is 0.2 or less.

3. The honeycomb filter according to claim 1 or 2, wherein the average equivalent diameter of the equal area circle of the imaginary pore dividing plane that virtually divides the communicating pores into each imaginary single pore at the narrow portion is 8.8 to 30 μm.

4. the porosity of the partition walls is 45% or more, The honeycomb filter according to claim 1 or 2, wherein the partition walls are made of a porous body containing cordierite as a main component.

5. The honeycomb filter according to claim 4, wherein an average value of a ratio (X / Y) of the minimum width X to the maximum width Y of the imaginary single pore is 0.80 or more and 1.00 or less.

6. The honeycomb filter according to claim 4, wherein the partition walls have an average pore size of 10 µm or less.

7. The honeycomb filter according to claim 1 or 2, wherein the partition walls are made of a porous body containing silicon carbide as a main component.

8. The honeycomb filter according to claim 7, wherein an average value of a ratio (X / Y) of the minimum width X to the maximum width Y of the imaginary single pore is 0.58 or more and 1.00 or less.

9. The honeycomb filter according to claim 7, wherein the average equivalent diameter of the equal-area circle of the imaginary pore dividing plane that virtually divides the communicating pores into each imaginary single pore at the narrow portion is 9 to 30 μm.

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