Honeycomb filter

Abstract

The utility model provides a honeycomb filter which can restrain pressure loss and performance deviation of trapping efficiency. The honeycomb filter is provided with: a columnar honeycomb structure having porous partition walls and sealing parts, the thickness of the partition walls being 152-305 [mu] m, the porosity of the partition walls being 35%-70%, and the average pore diameter of the partition walls being 7 [mu] m-24 [mu] m; a porous body constituting a partition wall has communicating pores that open in the surface of the partition wall and communicate with pores inside the partition wall, the communicating pores having a narrow portion in which the diameter of the communicating pores in the partition wall is locally narrowed, and a virtual single pore formed by virtually dividing the communicating pores by the narrow portion, when the minimum width passing through the center of gravity of each imaginary single pore is X and the maximum width passing through the center of gravity of each imaginary single pore is Y, the average value of X / Y, which is the ratio of the minimum width X to the maximum width Y of each imaginary single pore, is 0.51-1.00 (where X and Y are in [mu] m).

Description

TECHNICAL FIELD

[0001] The utility model relates to honeycomb filter. More in detail, relate to the honeycomb filter that can inhibit pressure loss and the performance deviation of trapping efficiency. BACKGROUND

[0002] As a means for reducing the emission 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 accumulating particulate matter in the exhaust passage of the internal combustion engine and trapping it is known (for example, Patent Literature 1). Hereinafter, the particulate matter contained in the exhaust gas will be sometimes referred to as "PM". "PM" is an abbreviation of "particulate matter".

[0003] As a particulate filter for exhaust gas purification, for example, a honeycomb filter using a honeycomb structure is known. The honeycomb structure has a partition wall composed of a porous ceramic such as cordierite, and a plurality of cells are formed by the partition wall. The honeycomb filter is provided with a plugged portion that alternately plugs the opening portions on the inflow end surface side and the opening portions on the outflow end surface side of the plurality of cells with respect to the above-described honeycomb structure.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Laid-Open No. 2002-219319 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] By providing a honeycomb filter as a particulate filter in the exhaust system of an automobile, it is possible to trap PM contained in exhaust gas emitted from the engine using the honeycomb filter, and reduce the emission amount of PM. However, if the honeycomb filter is provided in the exhaust system, there is a problem that the pressure loss in the exhaust system piping increases, leading to deterioration of the fuel consumption of the vehicle. Therefore, it is desirable to develop a honeycomb filter that can suppress the increase in pressure loss while maintaining trapping performance. In particular, such a desire is more strongly present in honeycomb filters typified by gasoline particulate filters (GPFs) and diesel particulate filters (DPFs).

[0009] Here, the trapping performance and the pressure loss performance of a gasoline particulate filter (GPF), a diesel particulate filter (DPF) are sometimes greatly affected by the state of the pores of a porous body constituting the partition walls of a honeycomb filter. In the past, the state of the pores of a porous body has been evaluated based on characteristics such as porosity and average pore diameter, but in the case where the shape of the pores of a porous body is not uniform, the state of the pores cannot sometimes be sufficiently grasped in the past evaluation described above. Therefore, for example, even if honeycomb filters that are evaluated to be equivalent are judged to be equivalent by measurement under the same conditions, the above trapping performance and pressure loss performance can easily deviate, and stable performance can not be exhibited.

[0010] The present utility model is completed in view of the problem of such prior art. According to the present utility model, a honeycomb filter capable of inhibiting performance deviation of pressure loss and trapping efficiency is provided.

[0011] Solution for solving the problem

[0012] According to the present utility model, the following honeycomb filter is provided.

[0013] [1] A honeycomb filter characterized by comprising:

[0014] A columnar honeycomb structure body having partition walls of a porous body arranged so as to surround a plurality of cells, the plurality of cells becoming flow paths of fluid extending from an inflow end surface to an outflow end surface; and

[0015] A plugged portion provided at either one of an end portion on the inflow end surface side of the cell and an end portion on the outflow end surface side,

[0016] The thickness of the partition wall is 152 to 305 μm,

[0017] The porosity of the partition wall is 35% or more and 70% or less,

[0018] The average pore diameter of the partition wall is 7 μm or more and 24 μm or less,

[0019] A porous body constituting the partition wall has a communication pore opening on the surface of the partition wall and communicating with the pores inside the partition wall, the communication pore having a narrow portion in which the diameter of the communication pore locally narrows inside the partition wall,

[0020] In a hypothetical single pore hypothetically divided from the communication pore, in a case where the minimum width passing through the center of gravity of each hypothetical single pore is set to X and the maximum width passing through the center of gravity of each hypothetical single pore is set to Y, the average value of the ratio X / Y of the minimum width X to the maximum width Y of the hypothetical single pore is 0.51 or more and 1.00 or less.

[0021] The units for X and Y are μm.

[0022] [2] According to the honeycomb filter described in [1], the standard deviation of the ratio of the minimum width X of the imaginary single pore to the maximum width Y, i.e., X / Y, is 0.2 or less.

[0023] [3] According to the honeycomb filter described in [1] or [2], the average value of the equivalent diameter of the circle of equal area of ​​the imaginary pore dividing surface that imaginarily divides the connected pores by the narrow portion according to each imaginary single pore is 8.8 to 30 μm.

[0024] [4] According to the honeycomb filter described in [1] or [2], the characteristic is that the porosity of the partition is 45% or more, and the partition is composed of a porous body containing cordierite as the main component.

[0025] [5] According to the honeycomb filter described in [4], the average value of the ratio of the minimum width X to the maximum width Y of the imaginary single pore, i.e., X / Y, is 0.80 or more and 1.00 or less.

[0026] [6] According to the honeycomb filter described in [4], the average pore size of the partition wall is less than 10 μm.

[0027] [7] The honeycomb filter described in [1] or [2] is characterized in that the partition wall is composed of a porous body containing silicon carbide as the main component.

[0028] [8] According to the honeycomb filter described in [7], the average value of the ratio of the minimum width X to the maximum width Y of the imaginary single pore, i.e., X / Y, is 0.58 or more and 1.00 or less.

[0029] [9] According to the honeycomb filter described in [7], the average value of the equivalent diameter of the circle of equal area of ​​the imaginary pore dividing surface that imaginarily divides the connected pores by the narrow portion according to each imaginary single pore is 9 μm to 30 μm.

[0030] Utility Model Effect

[0031] The honeycomb filter of this invention can suppress pressure loss and performance deviations in collection efficiency. Therefore, especially in gasoline particulate filters (GPF) and diesel particulate filters (DPF), it can suppress pressure loss and performance deviations in collection efficiency, ensuring stable performance. Attached Figure Description

[0032] Figure 1 This is a perspective view schematically illustrating one embodiment of the honeycomb filter of this utility model.

[0033] Figure 2 It means Figure 1 The top view of the inflow end face of the shown cellular filter.

[0034] Figure 3 It is a schematic representation Figure 2 A sectional view of section A-A'.

[0035] Figure 4 This is a conceptual diagram of the voxel data used to determine the minimum width X (μm) and maximum width Y (μm) of a hypothetical single pore.

[0036] Figure 5 It is a conceptual diagram that schematically represents the interconnected pores of a porous material.

[0037] Figure 6 It is used for explanation Figure 5 A conceptual diagram showing the minimum width X and maximum width Y of a hypothetical single aperture in a connected micro-aperture. Detailed Implementation

[0038] The embodiments of this utility model will be described below, but this utility model is not limited to the following embodiments. Therefore, it should be understood that appropriate changes, modifications, etc., to the following embodiments based on ordinary knowledge of those skilled in the art, without departing from the spirit of this utility model, also fall within the scope of this utility model.

[0039] (1) Honeycomb filter:

[0040] One embodiment of the honeycomb filter of this utility model is as follows: Figures 1-3 The shown is a cellular filter 100. Here, Figure 1 This is a perspective view schematically illustrating one embodiment of the honeycomb filter of this utility model. Figure 2 It means Figure 1 The top view of the inflow end face of the shown cellular filter. Figure 3 It is a schematic representation Figure 2 A sectional view of section A-A'.

[0041] like Figures 1-3As shown, the honeycomb filter 100 includes a honeycomb structure 4 and a sealing portion 5. The honeycomb structure 4 is a columnar honeycomb structure with porous partitions 1 arranged to surround multiple compartments 2, which form a flow path for fluid extending from the inflow end face 11 to the outflow end face 12. In the honeycomb filter 100, the honeycomb structure 4 is columnar and has an outer peripheral wall 3 on its outer peripheral side. That is, the outer peripheral wall 3 is arranged to surround the partitions 1 arranged in a grid pattern.

[0042] The sealing portion 5 is provided at the opening on the inflow end face 11 or the outflow end face 12 side of each compartment 2. Figures 1-3 In the shown honeycomb filter 100, sealing portions 5 are respectively provided at the openings of the predetermined compartment 2 at the inflow end face 11 side and at the openings of the remaining compartment 2 at the outflow end face 12 side. The compartment 2 with the sealing portion 5 at the opening on the outflow end face 12 side and the opening on the inflow end face 11 side is designated as the inflow compartment 2a. The compartment 2 with the sealing portion 5 at the opening on the inflow end face 11 side and the opening on the outflow end face 12 side is designated as the outflow compartment 2b. The inflow compartment 2a and the outflow compartment 2b are preferably arranged alternately with a partition wall 1 between them. Furthermore, it is preferable to form a checkered pattern on both ends of the honeycomb filter 100 using the sealing portions 5 and the openings of the compartment 2.

[0043] There are no particular limitations on the material of the partition 1 of the honeycomb structure 4 in the honeycomb filter 100, and examples include cordierite, silicon carbide, and silicon-silicon carbide composite materials. For example, the partition 1 of the honeycomb structure 4 can be composed of a porous material containing cordierite as the main component, or it can be composed of a porous material containing silicon carbide or a silicon-silicon carbide composite material as the main component. Although there are no particular limitations, it is preferable that the partition 1 of the honeycomb structure 4 in the honeycomb filter 100 is composed of a porous material containing cordierite as the main component or a porous material containing silicon carbide as the main component. It is more preferable that the partition 1 is composed of cordierite or silicon carbide except for components that are unavoidably contained therein.

[0044] The thickness of the septum 1 in the honeycomb filter 100 is 152–305 μm. By setting the thickness of the septum 1 within the above-mentioned range, sufficient collection efficiency as an exhaust gas purification filter can be ensured, and the increase in pressure loss can be effectively suppressed. Furthermore, by setting the thickness of the septum 1 within the above-mentioned range, the structural strength of the honeycomb filter 100 can also be ensured. For example, if the thickness of the septum 1 is less than 152 μm, it is not preferable from the viewpoint of reduced collection efficiency and reduced mechanical strength. If the thickness of the septum 1 exceeds 305 μm, the pressure loss increases significantly, which is also not preferable. Although not particularly limited, the thickness of the septum 1 is preferably 165–305 μm, more preferably 208–305 μm. The thickness of the septum 1 can be measured, for example, using a scanning electron microscope or a microscope.

[0045] The porosity of the septum 1 of the honeycomb filter 100 is 35% or more and 70% or less. The porosity of the septum 1 is determined by mercury intrusion porosimetry, for example, using an Autopore 9500 (trade name) manufactured by Micromeritics. The porosity can be measured by cutting a portion of the septum 1 from the honeycomb filter 100 as a test piece. There is no particular limitation as long as the porosity of the septum 1 is 35% or more and 70% or less, preferably 35% or more and 67% or less, and more preferably 35% or more and 65% or less. If the porosity of the septum 1 is less than 35%, it is not preferred from the viewpoint of increased pressure loss. On the other hand, if the porosity of the septum 1 exceeds 70%, the structural strength of the honeycomb filter 100 decreases, which is not preferred. Furthermore, when the septum 1 of the honeycomb structure 4 is composed of a porous body containing cordierite as the main component, the porosity of the septum 1 is preferably 45% or more and 70% or less.

[0046] The average pore size of the septum 1 in the honeycomb filter 100 is 7 μm or more and 24 μm or less. The average pore size of the septum 1 is determined by mercury porosimetry, for example, using an Autopore 9500 (trade name) manufactured by Micromeritics. The average pore size can be determined by cutting a portion of the septum 1 from the honeycomb filter 100 as a test piece. If the average pore size of the septum 1 is less than 7 μm, it is not preferable from the viewpoint of increased pressure loss. On the other hand, if the average pore size of the septum 1 exceeds 24 μm, it is not preferable from the viewpoint of decreased collection performance. Here, when the septum 1 of the honeycomb structure 4 is composed of a porous body containing cordierite as the main component, the average pore size of the septum is preferably 10 μm or less.

[0047] The porous material constituting the partition 1 has communicating pores that open on the surface of the partition 1 and communicate with the fine pores inside the partition 1. For example, as Figure 5 and Figure 6 As shown, the porous body constituting the partition 1 has interconnected micropores 31 formed by multiple interconnected micropores formed inside the partition 1. These interconnected micropores 31 serve as fine flow paths for fluid to pass through the partition 1. The interconnected micropores 31 are preferably formed such that, as shown... Figure 3 In the partition wall 1 shown, which divides the inflow compartment 2a and the outflow compartment 2b, one surface on the side dividing the inflow compartment 2a is connected to the other surface on the side dividing the outflow compartment 2b. Furthermore, in Figure 5 and Figure 6 In the figure, the connecting aperture 31 is drawn in a way that the left and right sides are closed on the paper, but the connecting aperture 31 is formed in a way that it is three-dimensionally continuous within the partition wall 1.

[0048] like Figure 5 and Figure 6 As shown, the connecting pore 31 has a narrow portion 35 within the partition wall 1 where the diameter of the connecting pore 31 is locally narrowed. Here, each portion formed by imaginarily dividing the connecting pore 31 by the narrow portion 35 is designated as an imaginary single pore 32 (32a, 32b, 32c, 32d). Here, the minimum width of the centroid O of each imaginary single pore 32 (32a, 32b, 32c, 32d) is designated as X (μm), and the maximum width of the centroid O of each imaginary single pore 32 (32a, 32b, 32c, 32d) is designated as Y (μm). Hereinafter, the minimum width will sometimes be referred to as "minimum width X (μm)" and the maximum width as "maximum width Y (μm)". The honeycomb filter 100 of this embodiment (see Figure 1 The average value of the ratio (X / Y) of the minimum width X (μm) to the maximum width Y (μm) of the hypothetical single aperture 32 is 0.51 or more and 1.00 or less. Furthermore, in Figure 5 and Figure 6 The two-dimensional map illustrates the case where the connecting aperture 31 is hypothetically divided into hypothetical single apertures 32 by the narrow portion 35, but as described later, the connecting aperture 31 is hypothetically divided in three dimensions using a three-dimensional model.

[0049] The average X / Y ratio mentioned above serves as an indicator of the sphericity of the hypothetical single pore 32. The closer the average X / Y ratio is to 1.00, the closer the pore shape of the hypothetical single pore 32 is to a perfect sphere. Here, the connecting pore 31 is formed by connecting multiple pores in the porous body, and the junction when multiple pores are connected to form the connecting pore 31 corresponds to the aforementioned narrow portion 35. Therefore, by setting the average X / Y ratio to the aforementioned range, the pore shape of the porous body constituting the partition wall 1 can be made as close to a perfect sphere as possible. Moreover, by making the shape of each pore close to a perfect sphere, regardless of the connection method between the pores, the width of the narrow portion 35 (hereinafter, sometimes referred to as the "neck diameter" of the connecting pore 31) becomes a more uniform width, and the portion where the diameter of the connecting pore 31 becomes extremely narrow is reduced. Therefore, the micro-flow path within the partition wall 1 can be properly ensured, the increase in pressure loss can be effectively suppressed, and the collection performance as a filter can be properly maintained. On the other hand, if the average value of X / Y is less than 0.51, then the shape of the pore 32 of a single pore is closer to an ellipsoid than a sphere. When multiple pores are connected to form a connecting pore 31, the neck diameter of the connecting pore 31 is more likely to become extremely narrow or wide. In particular, when the neck diameter of the connecting pore 31 becomes extremely narrow, the micro-flow paths within the partition wall 1 are easily blocked, leading to an increase in pressure loss. Conversely, when the neck diameter of the connecting pore 31 becomes extremely wide, it can sometimes lead to a deterioration in collection efficiency. Therefore, by setting the average value of X / Y to 0.51 or higher and 1.00 or lower, the shape of each pore forming the connecting pore 31 is made close to a sphere, thereby extremely effectively suppressing performance deviations in pressure loss and collection efficiency.

[0050] The minimum width X (μm) and maximum width Y (μm) of the imaginary single aperture 32 formed by imaginary dividing the connecting aperture 31 using the narrow portion 35 can be determined using the following method. The minimum width X (μm) and maximum width Y (μm) of the imaginary single aperture 32 formed by imaginary dividing the connecting aperture 31 using the narrow portion 35 are obtained using three-dimensional voxel data 60 (refer to) obtained by CT scanning of the septum 1. Figure 4 ) to calculate. Figure 4 This is a conceptual diagram of the voxel data used to determine the minimum width X (μm) and maximum width Y (μm) of a hypothetical single pore. First, the partition 1 (e.g., refer to...) Figure 3 The thickness direction of compartment 2 is set as the X direction, and the axial direction of compartment 2 (e.g.) is set as the X direction. Figure 3 The vertical direction is set as the Y direction, and the XY plane is set as the imaging section. Then, multiple CT scans of the diaphragm 1 are performed by offsetting the imaging section in the Z direction (perpendicular to the XY direction) to obtain multiple image data. Based on this image data, [the following is a separate, unrelated sentence:] Figure 4Such voxel data 60. The resolution in each of the X, Y, and Z directions is set to 1.2 μm, and the resulting cube with one side of 1.2 μm becomes the smallest unit of the three-dimensional voxel data 60, namely the voxel. Furthermore, the image data of the imaging sections obtained through CT scans are data of a plane without thickness in the Z direction, but each imaging section is treated as data with a thickness of 1.2 μm in the Z direction interval of the imaging section. That is, each pixel of the two-dimensional image data is treated as a cube (voxel) with one side of 1.2 μm. For example... Figure 4 As shown, the voxel data 60 is a cuboid with dimensions 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. Each voxel is represented by its X, Y, and Z coordinates (the value of 1 corresponds to the length of one side of the voxel, i.e., 1.2 μm), and a distinction is made between spatial voxels representing space (a small aperture) and object voxels representing an object. The distinction between spatial and object voxels is achieved through binarization using a pattern-based method as follows: The multiple image data obtained from CT scans 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 from multiple image data). Then, the brightness value between two peaks (troughs) in the histogram is set as a threshold, and for each coordinate, the brightness is binarized based on whether the brightness is greater than or less than the threshold. Thus, it is possible to distinguish whether the voxels for each coordinate are spatial voxels or object voxels. It should be noted that such CT scans can be performed, for example, using the Shimadzu SMX-160CT-SV3 (trade name). There are no particular restrictions on the location of the partition 1 used for the CT scan, but it is preferably located in the central portion of the extending direction (axial direction of the aforementioned partition 2) of the cell 2 of the honeycomb structure 4.

[0051] Next, using voxel data 60, as follows Figure 4 and Figure 5 The internal structure of the partition 1 shown is modeled (e.g., the shape and state of the connecting aperture 31 within the partition 1). Furthermore, for this modeled internal structure of the partition 1, an algorithm such as the "Watershed algorithm" that separates contacting objects is applied. First, a narrow section 35 where the diameter of the connecting aperture 31 locally narrows is determined. Then, for the determined narrow section 35, an imaginary vent dividing surface 33 that imaginarily divides the connecting aperture 31 into imaginary single apertures 32 is calculated, and the area of ​​this imaginary vent dividing surface 33 is determined. The equivalent diameter of the circle of equal area of ​​the imaginary vent dividing surface 33 thus calculated is set to a length equivalent to the width of the narrow section 35. That is, hereinafter, "the width of the narrow section 35" refers to "the equivalent diameter of the circle of equal area of ​​the imaginary vent dividing surface 33 of the narrow section 35".

[0052] Furthermore, for each imaginary single aperture 32a, 32b, 32c, 32d obtained by imaginarily dividing the connecting aperture 31 with the narrow portion 35, the minimum widths X1, X2, X3, X4 (μm) and maximum widths Y1, Y2, Y3, Y4 (μm) passing through each centroid O1 to O4 are calculated. The calculation of such minimum widths X1, X2, X3, X4 (μm) and maximum widths Y1, Y2, Y3, Y4 (μm) is performed within the program that executes the Watershed algorithm described above.

[0053] Next, for each of the hypothetical single apertures 32a, 32b, 32c, and 32d, 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 example, in... Figure 5 In this process, the "X1 / Y1" of the imaginary single pore 32a, the "X2 / Y2" of the imaginary single pore 32b, the "X3 / Y3" of the imaginary single pore 32c, and the "X4 / Y4" of the imaginary single pore 32d are calculated. Then, the values ​​of "X / Y" of the imaginary single pore 32 observed within the analytical range (480μm×480μm×300μm) are calculated, and the average value of the calculated "X / Y" is calculated. The average value of "X / Y" is preferably obtained by calculating the average of more than 2500 values ​​of "X / Y" of the imaginary single pore 32 obtained through the previously described analytical method. That is, the sample size (in other words, the number of samples) for which the average value of "X / Y" is calculated is preferably more than 2500. If the sample size for which the average value is calculated is more than 2500, it becomes a statistically significant sample size.

[0054] Here, when the partition 1 of the honeycomb structure 4 is composed of a porous material containing cordierite as the 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. With this configuration, the pore shape of the imaginary single pore 32 is closer to a perfect sphere, which can more effectively suppress pressure loss and performance deviations in collection efficiency. 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) of each of the imaginary single pores 32 are the same, but as a practically preferred upper limit of the average value of X / Y, 0.90 can be listed. It is further preferred 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 1 of the honeycomb structure 4 is composed of a porous body containing silicon carbide as the main component, the average value of the ratio (X / Y) of the minimum width X to the maximum width Y of the hypothetical single pore 32 is preferably 0.58 or more and 1.00 or less.

[0055] Preferably, the standard deviation of the ratio (X / Y) of the minimum width X to the maximum width Y of the imaginary single aperture 32 is 0.2 or less. The standard deviation of X / Y is preferably obtained by calculating the average of the X / Y values ​​of at least 2500 imaginary single apertures 32 obtained through the previously described analysis. That is, the number of samples (in other words, the number of specimens) for which the average X / Y value is obtained is preferably 2500 or more.

[0056] The average value of the equivalent circular diameter of the imaginary pore dividing surface 33, which is imaginarily divided by the narrow portion 35 according to each imaginary single pore 32a, 32b, 32c, 32d, of the interconnecting pore 31, is preferably 8.8 to 30 μm. This configuration allows for more effective suppression of pressure loss and performance deviations in trapping efficiency. In particular, when the partition 1 of the honeycomb structure 4 is composed of a porous body containing silicon carbide as the main component, the average value of the equivalent circular diameter of the aforementioned imaginary pore dividing surface 33 is preferably 9 μm to 30 μm.

[0057] There are no particular restrictions on the cell density of the honeycomb structure 4. For example, the preferred cell density of the honeycomb structure 4 is 31 to 62 cells / cm². 2 More preferably 43-50 per cm 2 This configuration maintains the collection performance of the cellular filter 100 and effectively suppresses the increase in pressure loss.

[0058] The shape of the compartments 2 divided by the partition 1 is not particularly limited. For example, the shape of the compartment 2 in a cross-section orthogonal to the direction in which the compartment 2 extends can be polygonal, circular, elliptical, etc. As a polygon, examples include triangles, quadrilaterals, pentagons, hexagons, octagons, etc. Furthermore, the shape of the compartment 2 is preferably triangular, quadrilateral, pentagonal, hexagonal, or octagonal. Regarding the shape of the compartments 2, all compartments 2 can have the same shape or different shapes. For example, although the illustration is omitted, a combination of quadrilateral and octagonal compartments is possible. Regarding the size of the compartments 2, all compartments 2 can have the same size or different sizes. For example, although the illustration is omitted, the size of some of the multiple compartments can be increased while the size of the other compartments is relatively decreased. It should be noted that in this invention, a compartment refers to a space enclosed by a partition.

[0059] There are no particular restrictions on the shape of the honeycomb structure 4. Examples of shapes for the honeycomb structure 4 include circular, elliptical, polygonal, and other columnar shapes for the inflow end face 11 and the outflow end face 12.

[0060] There are no particular restrictions on the size of the honeycomb structure 4, such as its length from the inflow end face 11 to the outflow end face 12, and the size of the cross-section of the honeycomb structure 4 that is orthogonal to the direction in which the compartment 2 extends. When using the honeycomb filter 100 as a filter for exhaust gas purification, the sizes can be appropriately selected in a way that yields the best purification performance.

[0061] There are no particular restrictions on the material of the sealing part 5. For example, it can be the same material as the material of the partition 1, or it can be a different material from the material of the partition 1.

[0062] The honeycomb filter 100 preferably has a catalyst for purifying exhaust gas supported on the partition walls 1 that divide the filter into multiple compartments 2. Supporting the catalyst on the partition walls 1 means coating the surface of the partition walls 1 and the inner walls of the pores formed in the partition walls 1 with the catalyst. With this configuration, CO, NOx, HC, and other substances in the exhaust gas can be converted into harmless substances through a catalytic reaction. Furthermore, it can promote the oxidation of PM such as particulate matter captured from coal.

[0063] There are no particular limitations on the catalyst supported on partition 1. For example, catalysts containing platinum group elements, which contain oxides of at least one of aluminum, zirconium, and cerium, can be listed.

[0064] (2) Manufacturing method of honeycomb filter:

[0065] There are no particular limitations on the method for manufacturing the honeycomb filter of this invention. For example, in the case of a honeycomb filter whose partitions are composed of a porous material containing cordierite as the main component, the following method can be listed. First, a plastic adobe for making the honeycomb structure is prepared. As raw material powders for preparing the adobe, kaolin, talc, alumina, aluminum hydroxide, silica, etc., can be used, and these raw material powders can be prepared to have a chemical composition in the range of 42-56% by mass of silica, 30-45% by mass of alumina, and 12-16% by mass of magnesium oxide. Regarding the pore-forming material, a material composed of spherical and non-spherical pore-forming materials mixed in a predetermined mixing ratio can be used. By using a material with an average particle size of 10 μm to 25 μm as the spherical pore-forming material, a adobe that can be made into a porous material containing a large number of fine pores of this size that are close to spherical. The average particle size refers to the median particle size (D50) measured using a laser diffraction / scattering particle size distribution measuring device.

[0066] Furthermore, starch-based (especially wheat-derived) pore-forming materials are effective as the pore-forming material for the spheres used in the method of manufacturing the honeycomb filter of this invention. Conventionally, pore-forming materials used in the manufacture of ordinary honeycomb filters have difficulty maintaining their spherical shape due to their swelling characteristics during molding and water absorption. On the other hand, using starch-based pore-forming materials such as wheat can mitigate this effect. Additionally, as the pore-forming material used in the method of manufacturing the honeycomb filter of this invention, for example, it is preferable that the average value of the ratio of the minimum short diameter to the maximum long diameter (minimum short diameter / maximum long diameter) is 0.5 or higher.

[0067] Next, the resulting adobe is extruded to produce a columnar honeycomb structure, which has partitions that divide the adobe into multiple compartments and an outer peripheral wall arranged around the partitions. In the extrusion molding, a die with slits that form the reverse shape of the honeycomb structure on the extrusion surface of the adobe can be used as the die.

[0068] The resulting honeycomb molded body is dried, for example, using microwaves and hot air. The openings of the compartments are then sealed with the same material used to make the honeycomb molded body, thereby creating sealed sections. After creating the sealed sections, the honeycomb molded body can be further dried.

[0069] Next, the honeycomb molded body with sealed pores is fired to manufacture a honeycomb filter. The firing temperature and firing atmosphere vary depending on the raw materials, and those skilled in the art can select the firing temperature and firing atmosphere most suitable for the selected materials.

[0070] The above explanation uses a cordierite honeycomb filter as an example. However, in the case of a honeycomb filter whose sidewall is composed of a porous material containing silicon carbide as the main component, it can also be manufactured by performing the same treatment on a clay brick prepared by adding the same pore-forming material, dispersion medium, and organic binder to silicon carbide powder (silicon carbide).

[0071] Example

[0072] The present invention will be described in more detail below through embodiments, but the present invention is not limited to these embodiments in any way.

[0073] (Example 1)

[0074] To prepare clay bricks, 2 parts by mass of pore-forming material, 2 parts by mass of dispersion medium, and 7 parts by mass of organic binder were added to 100 parts by mass of cordierite raw material, followed by mixing and kneading. The cordierite raw material used included alumina, aluminum hydroxide, kaolin, talc, and silica. Water was used as the dispersion medium. Methylcellulose was used as the organic binder. Dextrin was used as the dispersant. The pore-forming material was a mixture of spherical and non-spherical pore-forming materials in a predetermined blending ratio. Specifically, for the spherical pore-forming material, a material with 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 higher was used. The average particle size was the median particle size (D50) measured using a laser diffraction / scattering particle size distribution measuring device.

[0075] Next, the obtained adobe bricks are shaped using an extrusion molding machine to create honeycomb molded bodies. Following this, the honeycomb molded bodies are dried using high-frequency induction heating, and then further dried using a hot air dryer. The compartments in the honeycomb molded bodies are quadrilateral in shape.

[0076] Next, sealing portions are formed on the dried honeycomb molded body. First, a mask is applied to the inflow end face of the honeycomb molded body. Then, the masked end (the end on the inflow end face side) is immersed in sealing slurry, and the openings of the unmasked compartments (outflow compartments) are filled with sealing slurry. In this way, sealing portions are formed on the inflow end face side of the honeycomb molded body. Then, sealing portions are also formed on the inflow compartments on the outflow end face of the dried honeycomb molded body in the same way.

[0077] Next, the honeycomb molded body with sealed pores is dried using a microwave dryer, and then further dried completely using a hot air dryer. The two ends of the honeycomb molded body are then cut off and adjusted to a predetermined size. Next, the dried honeycomb molded body is degreased and fired to manufacture the honeycomb filter of Example 1.

[0078] The honeycomb filter in Example 1 has an end face diameter of 118.4 mm and a cell length of 152.4 mm. Additionally, the cell wall thickness is 210.8 μm, and the cell density is 47.3 cells / cm². 2 The thickness of the partition walls and the values ​​of the cell density are shown in Table 1. In Example 1, 10 honeycomb filters of the same batch were manufactured using the method described above. Hereinafter, multiple (10 in Example 1) honeycomb filters manufactured using the same raw materials and the same method as described in Example 1 above will sometimes be referred to as "the same batch of products".

[0079] For the honeycomb filter of Example 1, the "porosity (%)" and "average pore diameter (μm)" of the partition wall were measured using the following method. The results are shown in Table 1. Furthermore, using the method described previously, the minimum width X (μm) and maximum width Y (μm) of each imaginary single pore, formed by imaginary division of the porous material constituting the partition wall into narrow sections, were calculated. Then, the ratio (X / Y) of the minimum width X (μm) to the maximum width Y (μm) of each imaginary single pore was calculated, and its average value was determined. The result is shown in the "Average Value of X / Y" column of Table 1. Furthermore, using the method described previously, the equivalent diameter of the imaginary pore dividing surface, which imaginaryly divides the connecting pores into each imaginary single pore, was calculated, and its average value was determined. The result is shown in the "Average Equivalent Diameter of Imaginary Pore Dividing Surface (μm)" column of Table 1. The number of imaginary single pores used in the calculation of the above average values ​​was 2842. The value is indicated in the "Number of Imaginary Single Pores" column of Table 1.

[0080] [Porosity (%) and average pore size (μm)]

[0081] The porosity (%) and average pore size (μm) of the septum were measured using an Autopore 9500 (trade name) manufactured by Micromeritics. For these measurements, a portion of the septum was cut from the honeycomb filter to form a test piece, which was then used for the measurements. The test piece was a cuboid with lengths of approximately 10 mm, widths of approximately 10 mm, and heights of approximately 20 mm. The sampling location for the test piece was set near the axial center of the honeycomb structure.

[0082] [Table 1]

[0083]

[0084] For the cellular filter of Example 1, the collection efficiency and pressure loss were evaluated using the following method. The results are shown in Table 1.

[0085] [Capture Efficiency]

[0086] A honeycomb filter was installed under the floor of a 1500cc vehicle, and a bench test was conducted in RTS95 cycle driving mode, allowing exhaust gas containing PM to flow through the honeycomb filter. The capture efficiency (%) of the honeycomb filter was determined by measuring the number of PM in the exhaust gas before it entered the filter and the number of PM in the exhaust gas exiting the filter. The capture efficiency (%) was measured for 10 honeycomb filters from the same batch, and the average, maximum, and minimum capture efficiencies (%) of the 10 honeycomb filters from the same batch were calculated. Furthermore, for the honeycomb filters representing the maximum and minimum capture efficiencies (%) among the 10 honeycomb filters from the same batch, the rate of change (%) relative to the average was calculated. The rate of change (%) relative to the average was obtained by dividing the difference between the maximum or minimum value and the average value, multiplying the result by 100. Then, the magnitudes of the "rate of change (%) relative to the average" of the maximum and minimum capture efficiency (%) are compared, and the cell filter showing the larger value of the rate of change (%) (hereinafter also referred to as the "maximum rate of change") is selected as the evaluation object of capture efficiency. In the evaluation of capture efficiency, cases where the maximum rate of change of capture efficiency (%) is less than 5.0% are set as qualified, and cases where it exceeds 5.0% are set as unqualified.

[0087] [Pressure Loss]

[0088] Using a large wind tunnel testing machine, gas at 25°C was driven at a speed of 10m. 3 The pressure at the inflow and outflow sides of the honeycomb filter was measured at a flow rate of / minute. The pressure loss (kPa) of the honeycomb filter was then calculated by determining the pressure difference between the inflow and outflow sides. For the pressure loss (kPa) measurement, 10 honeycomb filters from the same batch were measured separately, and the average pressure loss (kPa) and the maximum and minimum pressure loss (kPa) of the 10 honeycomb filters from the same batch were calculated. Furthermore, for the honeycomb filters from the same batch that showed the maximum and minimum pressure loss (kPa), the rate of change (%) relative to the average was calculated. The rate of change (%) relative to the average was obtained by dividing the difference between the maximum or minimum value and the average, multiplying the result by 100. Then, the magnitude of the "rate of change (%) relative to the average" for the maximum and minimum pressure loss (kPa) was compared, and the honeycomb filter showing the larger value (hereinafter referred to as the "maximum rate of change") was selected as the evaluation object for pressure loss. In the evaluation of pressure loss, a maximum change rate of less than 4.0% in pressure loss (kPa) is considered acceptable, while a change rate exceeding 4.0% is considered unacceptable.

[0089] (Examples 2 to 10)

[0090] In Examples 2 through 10, the structure of the honeycomb structure was modified as shown in Table 1. Furthermore, in Examples 2 through 10, the mixing ratio of the pore-forming material of the spheres and the pore-forming material of the non-spheres was adjusted to fabricate the honeycomb structure as shown in Table 1 for Examples 2 through 10. Here, the diameter of the end face and the length in the direction of the compartment extension in Examples 2 through 8 are approximately the same as in Example 1. These Examples 1 and 2 through 8 are gasoline particulate filters (GPF). On the other hand, Examples 9 and 10 are diesel particulate filters (DPF), with dimensions different from Example 1. Specifically, in Example 9, the diameter of the end face is 266.7 mm and the length in the direction of the compartment extension is 127 mm; on the other hand, in Example 10, the diameter of the end face is 304.8 mm and the length in the direction of the compartment extension is 203.2 mm.

[0091] (Comparative Example 1)

[0092] In Comparative Example 1, the structure of the honeycomb structure was modified as shown in Table 1. Furthermore, in Comparative Example 1, a fragmented pore-forming material and kaolin, alumina, and aluminum hydroxide were used to fabricate the honeycomb structure. Additionally, the diameter of the end faces and the length of the compartments in the direction of extension in Comparative Example 1 were approximately the same as in Example 1.

[0093] For the honeycomb filters of Examples 2-8 and Comparative Example 1, the collection efficiency and pressure loss were evaluated using the same method as in Example 1. The results are shown in Table 1. Regarding Examples 9 and 10, the size of the honeycomb filters was larger than that of Examples 1-8 and Comparative Example 1, therefore the measurement conditions were changed. Specifically, the collection efficiency was measured using a bench test with an exhaust displacement of 6700cc and a WHTC cycle driving mode. The pressure loss was measured by changing the gas flow rate to 20m³ / h. 3 / minute. All other measurement conditions and evaluation methods were the same. The results of Examples 9 and 10 are also shown in Table 1.

[0094] (result)

[0095] The honeycomb filters of Examples 1 to 10 all met the evaluation criteria for trapping efficiency and pressure loss, and were therefore rated as qualified. That is, for the ten honeycomb filters in the same batch, the performance deviations in pressure loss and trapping efficiency of the honeycomb filters of Examples 1 to 10 were small. On the other hand, the honeycomb filter of Comparative Example 1 showed greater performance deviations in pressure loss and trapping efficiency for the ten honeycomb filters in the same batch. Furthermore, among Examples 1 to 10, the maximum variation in trapping efficiency of Example 8 (with an average ratio (X / Y) of 0.80 or higher), or Example 9 (with an average pore size of 10 μm or less), and Example 10 (with an average pore size of 10 μm or less) was less than 1.3%, showing extremely small performance deviations in trapping efficiency compared to Examples 1 to 7, which did not meet these requirements.

[0096] (Example 11)

[0097] To 100 parts by mass of a ceramic raw material consisting of silicon carbide powder (silicon carbide) and metallic 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 dispersion medium, and 7 parts by mass of an organic binder were added, followed by mixing and kneading to prepare a clay body. Water was used as the dispersion medium. Methylcellulose was used as the organic binder. Dextrin was used as the dispersant. The pore-forming material was a mixture of spherical and non-spherical pore-forming materials in a predetermined blending ratio. Specifically, for the spherical pore-forming material, a material with 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 higher was used. The average particle size was the median particle size (D50) measured using a laser diffraction / scattering particle size distribution measuring device.

[0098] Next, the obtained adobe bricks are shaped using an extrusion molding machine to create honeycomb molded bodies. Following this, the honeycomb molded bodies are dried using high-frequency induction heating, and then further dried using a hot air dryer. The compartments in the honeycomb molded bodies are quadrilateral in shape.

[0099] Next, sealing portions are formed on the dried honeycomb molded body. First, a mask is applied to the inflow end face of the honeycomb molded body. Then, the masked end (the end on the inflow end face side) is immersed in sealing slurry, and the openings of the unmasked compartments (outflow compartments) are filled with sealing slurry. In this way, sealing portions are formed on the inflow end face side of the honeycomb molded body. Then, sealing portions are also formed on the inflow compartments on the outflow end face of the dried honeycomb molded body in the same way.

[0100] Next, the honeycomb molded body with sealed pores is dried using a microwave dryer, and then further dried completely using a hot air dryer. The two ends of the honeycomb molded body are then cut off and adjusted to a predetermined size. Next, the dried honeycomb molded body is degreased and fired to manufacture the honeycomb filter of Example 11.

[0101] The honeycomb filter of Example 11 has an end face diameter of 143.8 mm and a cell length of 177.8 mm. Additionally, the cell wall thickness is 235.5 μm, and the cell density is 45.0 cells / cm². 2 The thickness of the partition walls and the values ​​of the compartment density are shown in Table 2. For this Example 11, 10 honeycomb filters of the same batch of products were manufactured in the same manner as in Example 1.

[0102] For the honeycomb filter of Example 11, the average porosity (%), average pore diameter (μm), average ratio (X / Y), and average equivalent diameter of the imaginary pore segmentation surface of the partition wall were calculated using the same method as in Example 1. Table 2 shows these values. The number of imaginary individual pores is 3448, as also shown in Table 2.

[0103] [Table 2]

[0104]

[0105] For the cellular filter of Example 11, the collection efficiency and pressure loss were evaluated using the following method. The results are shown in Table 2.

[0106] [Capture Efficiency]

[0107] A honeycomb filter was installed under the floor of a vehicle equipped with a 3500cc diesel engine, and a bench test was conducted under WLTC driving mode, allowing exhaust gas containing PM to flow into the honeycomb filter. The PM count in the exhaust gas before and after the flow into the honeycomb filter was measured to determine the capture efficiency (%) of 10 honeycomb filters from the same batch. Then, the maximum rate of change of the capture efficiency (%) was determined using the same method as in Example 1. A maximum rate of change less than 5.0% was considered acceptable, while a rate exceeding 5.0% was considered unacceptable.

[0108] [Pressure Loss]

[0109] Using a large wind tunnel testing machine, gas at 25°C was driven at a speed of 10m. 3A flow rate of / minute was used to measure the pressure at the inflow and outflow sides of the honeycomb filter. Then, by calculating the pressure difference between the inflow and outflow sides, the pressure loss (kPa) of 10 honeycomb filters from the same batch was determined. The maximum rate of change of pressure loss (kPa) was then calculated using the same method as in Example 1. A maximum rate of change less than 4.0% was considered acceptable, while a rate exceeding 4.0% was considered unacceptable.

[0110] (Examples 12 to 16)

[0111] In Examples 12 to 16, the structure of the honeycomb structure was modified as shown in Table 2. Furthermore, in Examples 12 to 16, the mixing ratio of the pore-forming material for the spheres and the pore-forming material for the non-spheres was adjusted to fabricate the honeycomb structure in the manner shown in Table 2 for Examples 12 to 16. Here, Examples 11 and 12 to 16 described above are diesel particulate filters (DPFs).

[0112] (Comparative Example 2)

[0113] In Comparative Example 2, as shown in Table 2, the structure of the honeycomb structure was changed from that in Example 11. Furthermore, in Comparative Example 2, a fragmented pore-forming material was used to fabricate the honeycomb structure.

[0114] For the cellular filters of Examples 12 to 16 and Comparative Example 2, the collection efficiency and pressure loss were evaluated using the same method as in Example 11. The results are shown in Table 2.

[0115] (result)

[0116] The cellular filters of Examples 11 to 16 all met the evaluation criteria for both collection efficiency and pressure loss, and were therefore rated as qualified. That is, for 10 cellular filters from the same batch, the performance deviations in pressure loss and collection efficiency of the cellular filters of Examples 11 to 16 were small. On the other hand, for 10 cellular filters from the same batch, the cellular filter of Comparative Example 2 showed greater performance deviations in pressure loss and collection efficiency. Furthermore, among Examples 11 to 16, the maximum variation in collection efficiency of Examples 13 to 16, which had an average ratio (X / Y) of 0.58 or higher, was less than 3.3%, showing extremely low performance deviations in collection efficiency compared to Examples 11 and 12, which did not meet this requirement.

[0117] Industrial utilization potential

[0118] The honeycomb filter of this invention can be used as a filter to capture particulate matter in exhaust gas.

[0119] Symbol Explanation

[0120] 1—Block; 2—Compartment; 2a—Inflow compartment; 2b—Outflow compartment; 3—Outer peripheral wall; 4—Honeycomb structure; 5—Sealing section; 11—Inflow end face; 12—Outflow end face; 31—Connecting pore; 32, 32a, 32b, 32c, 32d—Imaginary single pore; 33—Imaginary pore dividing surface; 35—Narrow section; 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 honeycomb filter, characterized in that, have: A columnar honeycomb structure having porous partitions arranged to surround multiple compartments, which form a flow path for fluid extending from the inflow end face to the outflow end face. as well as A sealing portion, which is disposed on either the end face of the compartment on the inflow end face side or the end face of the compartment on the outflow end face side. The thickness of the partition wall is 152–305 μm. The porosity of the partition wall is greater than 35% and less than 70%. The average pore size of the partition wall is greater than 7 μm and less than 24 μm. The porous material constituting the partition has a communicating pore that opens on the surface of the partition and communicates with the fine pores inside the partition. This communicating pore has a narrow portion within the partition where the diameter of the communicating pore locally narrows. In an imaginary single aperture formed by imaginary dividing the connecting apertures using the narrow portion, if the minimum width passing through the centroid of each imaginary single aperture is defined as X, and the maximum width passing through the centroid of each imaginary single aperture is defined as Y, then the average value of the ratio of the minimum width X to the maximum width Y of the imaginary single aperture, i.e., X / Y, is 0.51 or more and 1.00 or less. The units for X and Y are μm.

2. The honeycomb filter according to claim 1, characterized in that, The standard deviation of the ratio of the minimum width X to the maximum width Y of the hypothetical single aperture, i.e., X / Y, is less than 0.

2.

3. The honeycomb filter according to claim 1 or 2, characterized in that, The average equivalent diameter of the circular segments of the imaginary pores that are imaginary to divide the connected pores by the narrow portion according to each imaginary single pore is 8.8 to 30 μm.

4. The honeycomb filter according to claim 1 or 2, characterized in that, The porosity of the partition wall is 45% or more. The partition is composed of a porous material containing cordierite as the main component.

5. The honeycomb filter according to claim 4, characterized in that, The average value of the ratio of the minimum width X to the maximum width Y of the hypothetical single aperture, i.e., X / Y, is greater than 0.80 and less than 1.

00.

6. The honeycomb filter according to claim 4, characterized in that, The average pore size of the partition wall is less than 10 μm.

7. The honeycomb filter according to claim 1 or 2, characterized in that, The partition is composed of a porous material containing silicon carbide as the main component.

8. The honeycomb filter according to claim 7, characterized in that, The average value of the ratio of the minimum width X to the maximum width Y of the hypothetical single aperture, i.e., X / Y, is greater than 0.58 and less than 1.

00.

9. The honeycomb filter according to claim 7, characterized in that, The average equivalent diameter of the circle of equal area of ​​the imaginary pore dividing surface that is used to imaginaryly divide the connected pores by the narrow portion according to each imaginary single pore is 9 μm to 30 μm.

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