Honeycomb Filter

Abstract

To provide a honeycomb filter which is excellent in erosion resistance and thermal shock resistance.SOLUTION: The honeycomb filter includes: a pillar-shaped honeycomb structure 4 having a porous partition wall 1 arranged to surround a plurality of cells 2, and a cellular plugging part 5 arranged at either one end of the cells 2; wherein an average plugging length L1(Ave) at a center 15 of an end face of the honeycomb structure 4 is 5 mm or more and 10 mm or less, an average plugging length L2(Ave) at an outer periphery 16 outside the center 15 is 2 mm or more and 5 mm or less, a difference ΔL between the average plugging length L1(Ave) and the average plugging length L2(Ave) is 2 to 6 mm, the ratio of an average radius R of the center 15 to a circular equivalent radius D of an end face 11 of the honeycomb structure 4 (R / D) is 0.2 to 0.5, in an electron microscopic image of the plugging part 5, the plugging part 5 is composed of a plurality of particles, and the average circular equivalent diameter of individual particles comprising the plugging part 5 is 3 to 5 μm, and the particle density of the plugging part 5 is 750-1250 particles / mm2.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a honeycomb filter, and more particularly to a honeycomb filter having excellent erosion resistance and thermal shock resistance. [Background technology]

[0002] Conventionally, a honeycomb filter using a honeycomb structure has been known as a filter for collecting particulate matter in exhaust gas discharged from an internal combustion engine such as an automobile engine, or as a device for purifying toxic gas components such as CO, HC, and NOx (see Patent Document 1). The honeycomb structure has partition walls made of porous ceramics such as cordierite, and a plurality of cells are partitioned by the partition walls. The honeycomb filter is obtained by disposing plugging portions so that the openings on the inflow end face side and the openings on the outflow end face side of a plurality of cells are alternately plugged with respect to the above-mentioned honeycomb structure. That is, the honeycomb filter has a structure in which inflow cells that are open on the inflow end face side and plugged on the outflow end face side, and outflow cells that are plugged on the inflow end face side and open on the outflow end face side are alternately arranged with the partition walls sandwiched therebetween. In the honeycomb filter, the porous partition walls serve as a filter for collecting particulate matter in exhaust gas. Hereinafter, the particulate matter contained in exhaust gas may be referred to as "PM". "PM" stands for "particulate matter." [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-163286 A Summary of the Invention [Problem to be solved by the invention]

[0004] One type of damage that honeycomb filters can sustain during use is erosion. Erosion is a phenomenon in which foreign matter such as welding spatter or engine wear powder travels through the air current and collides with the honeycomb filter, causing wear at the inlet end face of the honeycomb filter. As a countermeasure against this type of erosion, measures such as increasing the length of the plugging parts disposed on the end faces of the honeycomb filter and decreasing the porosity of the plugging parts have been considered.

[0005] However, when the length of the plugged portions is increased or the porosity of the plugged portions is decreased in order to improve the resistance to erosion, the heat capacity of the honeycomb filter increases, which causes a problem of deterioration of the light-off performance. Note that the light-off performance refers to the temperature characteristic at which the purification performance of the exhaust gas purification catalyst supported on the honeycomb filter is expressed.

[0006] In addition, during use of a honeycomb filter, PM such as soot accumulates on the partition walls that define the cells that serve as the exhaust gas flow paths, which may cause the flow paths to be blocked and fuel efficiency to deteriorate. For this reason, the honeycomb filter may be periodically regenerated to burn and remove PM accumulated on the partition walls. By performing such a regeneration process on the honeycomb filter, the flow paths are cleared and the deterioration of fuel efficiency can be improved. In order to improve fuel efficiency, it is desirable to extend the interval between regeneration processes, but there is a limit to how long the interval can be extended because of the thermal shock that occurs during the regeneration process. In particular, as described above, if the length of the plugging portion is increased as a measure against erosion, the effect of thermal expansion of the plugging portion during the regeneration process increases, and the thermal shock resistance of the honeycomb filter may decrease.

[0007] As described above, in conventional honeycomb filters, improvement of erosion resistance and improvement of thermal shock resistance are in a trade-off relationship, and it is very difficult to simultaneously achieve both. For this reason, there is a demand for the development of a honeycomb filter that is excellent in erosion resistance and can withstand a larger thermal shock.

[0008] The present invention has been made in consideration of the problems associated with the conventional techniques, and provides a honeycomb filter having excellent erosion resistance and thermal shock resistance. [Means for solving the problem]

[0009] According to the present invention, there is provided a honeycomb filter as described below.

[0010] [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 plurality of plugging portions are provided at either one of the end portion on the inlet end surface side or the end portion on the outlet end surface side of the cell, The porosity of the plugging portion is 40 to 60%, a central plugging portion having a plugging length L of 5 mm or more in the cell extension direction is disposed on a central portion side of the end portion on the inflow end face side or the end portion on the outflow end face side of the honeycomb structure, and a peripheral plugging portion having a plugging length L of less than 5 mm is disposed on a peripheral portion side on the outer side of the central portion at the end portion, The average plugging length L1, which is the average value of the plugging length L in the central portion (Ave) is 5mm or more and 10mm or less, Average plugging length L2, which is the average value of the plugging length L in the outer periphery (Ave) is 2mm or more and less than 5mm, The average plugging length L1 in the central portion (Ave) and the average plugging length L2 in the outer periphery (Ave) The difference ΔL is 2 to 6 mm. a ratio (R / D) of an average radius R of the central portion to a circle-equivalent radius D of the end face of the honeycomb structure is 0.2 to 0.5; In an electron microscope image of the plugged portion, the plugged portion is composed of a plurality of particles, the average circle equivalent diameter of each of the particles is 3 to 5 μm, and the particle density of the plugged portion is 750 to 1250 particles / mm 2That is, a honeycomb filter.

[0011] [2] The honeycomb filter according to the above [1], wherein the partition walls have a porosity of 60 to 70%.

[0012] [3] The honeycomb filter according to the above [1] or [2], wherein the partition walls have a thickness of 0.1 to 0.3 mm. Effect of the Invention

[0013] The honeycomb filter of the present invention has the effect of being excellent in erosion resistance and thermal shock resistance. [Brief description of the drawings]

[0014] [Figure 1] 1 is a perspective view showing a schematic view of one embodiment of a honeycomb filter of the present invention. [Diagram 2] FIG. 2 is a plan view showing the inlet end face side of the honeycomb filter shown in FIG. [Diagram 3] FIG. 2 is a plan view showing the outflow end face side of the honeycomb filter shown in FIG. [Figure 4] FIG. 3 is a cross-sectional view showing a schematic cross section taken along line AA' of FIG. [Diagram 5] FIG. 4 is an explanatory diagram for explaining a method for measuring the plugging length of plugged portions, and is a schematic diagram showing the inflow end face side of a honeycomb filter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The following describes the embodiments of the present invention, but the present invention is not limited to the following embodiments. Therefore, it should be understood that the scope of the present invention includes any modifications and improvements to the following embodiments based on the ordinary knowledge of a person skilled in the art without departing from the spirit of the present invention.

[0016] (1) Honeycomb filter: One embodiment of the honeycomb filter of the present invention is a honeycomb filter 100 as shown in Fig. 1 to Fig. 4. Here, Fig. 1 is a perspective view that typically shows one embodiment of the honeycomb filter of the present invention. Fig. 2 is a plan view showing the inflow end face side of the honeycomb filter shown in Fig. 1, and Fig. 3 is a plan view showing the outflow end face side of the honeycomb filter shown in Fig. 1. Fig. 4 is a cross-sectional view that typically shows the A-A' cross section of Fig. 2.

[0017] As shown in Figs. 1 to 4, the honeycomb filter 100 of this embodiment includes a honeycomb structure 4 and plugging portions 5. The honeycomb structure 4 is columnar and has porous partition walls 1 arranged so as to surround a plurality of cells 2 that serve as fluid flow paths extending from one end face 11 to the other 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 so as to surround the partition walls 1 arranged in a lattice pattern. Hereinafter, one end face 11 of the honeycomb structure 4 and the honeycomb filter 100 may be referred to as, for example, the "inflow end face 11". In addition, the other end face 12, which is the other end face of the honeycomb structure 4 and the honeycomb filter 100, may be referred to as, for example, the "outflow end face 12".

[0018] The plugging portions 5 are disposed at the openings on the inflow end face 11 side or the outflow end face 12 side of each cell 2. In the honeycomb filter 100 shown in Figs. 1 to 4, the plugging portions 5 are disposed at the openings on the inflow end face 11 side of a predetermined cell 2 and the openings on the outflow end face 12 side of the remaining cells 2. The plugging portions 5 are disposed at the openings on the outflow end face 12 side, and the cells 2 that are open on the inflow end face 11 side are referred to as inflow cells 2a. The plugging portions 5 are disposed at the openings on the inflow end face 11 side, and the cells 2 that are open on the outflow end face 12 side are referred to as outflow cells 2b. The inflow cells 2a and the outflow cells 2b are preferably disposed alternately with the partition wall 1 between them. As a result, it is preferable that a checkered pattern is formed on both end faces of the honeycomb filter 100 by the plugging portions 5 and the "openings of the cells 2".

[0019] The honeycomb structure 4, in a cross section perpendicular to the extension direction of the cells 2, includes a central portion 15 including the center of gravity O of the cross section, and a peripheral portion 16 located outside this central portion 15. For example, as shown in Fig. 2 and Fig. 3, a certain range including the center of gravity O of the cross section of the honeycomb structure 4 and extending from the center of gravity O to the outer periphery is the "central portion 15," and a range toward the outer periphery from this central portion 15 is the "peripheral portion 16."

[0020] The honeycomb filter 100 of this embodiment has particularly important characteristics in terms of the value of the porosity of the plugging portion 5 and the configuration of the plugging portion 5 in the central portion 15 and the peripheral portion 16 described above. That is, in the honeycomb filter 100 of this embodiment, the porosity of the plugging portion 5 is 40 to 60%. In addition, a central plugging portion 5a having a plugging length L1 of 5 mm or more in the extension direction of the cells 2 is disposed as the plugging portion 5 on the central portion 15 side of the end portion on the inflow end face 11 side or the end portion on the outflow end face 12 side of the honeycomb structure 4. In addition, a peripheral plugging portion 5b having a plugging length L2 of less than 5 mm in the extension direction of the cells 2 is disposed as the plugging portion 5 on the peripheral portion 16 side on the outer side of the central portion 15 at the end portion of the honeycomb structure 4 described above. Hereinafter, the length L of the plugging portion 5 in the extension direction of the cells 2 as described above may be simply referred to as the "plugging length L" of the plugging portion 5. Also, the plugging length L of the central plugging portion 5a may be referred to as "plugging length L1," and the plugging length L of the peripheral plugging portion 5b may be referred to as "plugging length L2." That is, the central plugging portion 5a is a plugging portion 5 having a plugging length L1 of 5 mm or more, and the peripheral plugging portion 5b is a plugging portion 5 having a plugging length L2 of less than 5 mm.

[0021] The central portion 15 has an average plugging length L1 which is the average value of the plugging lengths L of the plugging portions 5 present in the central portion 15. (Ave) On the other hand, the outer peripheral portion 16 has an average plugging length L2 (Ave) The average plugging length L1 in the central portion 15 is 2 mm or more and less than 5 mm. (Ave) and the average plugging length L2 in the outer periphery 16 (Ave) The difference ΔL between these is 2 to 6 mm.

[0022] Furthermore, in the honeycomb filter 100 of this embodiment, the ratio (R / D) of the average radius R of the central portion 15 to the circle-equivalent radius D of the end face of the honeycomb structure 4 is 0.2 to 0.5. The circle-equivalent radius D of the end face of the honeycomb structure 4 can be calculated as the square root of the area A of the end face of the honeycomb structure 4 divided by the circular constant π (i.e., D=√(A / π)).

[0023] Furthermore, the plugging portion 5 consisting of the central plugging portion 5a and the peripheral plugging portion 5b has the following configuration regarding its microstructure: That is, in an electron microscope image of the plugging portion 5, the plugging portion 5 is composed of a plurality of particles, the average value of the circle equivalent diameter of each particle is 3 to 5 μm, and the particle density of the plugging portion 5 is 750 to 1250 particles / mm 2 It is.

[0024] The honeycomb filter 100 of the present embodiment configured as above has the effects of being excellent in erosion resistance and thermal shock resistance.

[0025] As described above, in the honeycomb filter 100 of this embodiment, the central plugging portion 5a having a relatively long plugging length is disposed in the central portion 15 at the end of each end face side of the honeycomb structure 4. Since the central portion 15 of the honeycomb structure 4 generates more heat during regeneration treatment than the outer peripheral portion 16 outside the central portion 15, the thermal shock resistance of the honeycomb filter 100 is improved by disposing the central plugging portion 5a having a long plugging length and a relatively large volume in the central portion 15. Furthermore, since erosion is more likely to occur in the central portion 15 of the honeycomb structure 4 than in the outer peripheral portion 16, the erosion resistance is also improved by the central plugging portion 5a having a long plugging length. On the other hand, the outer peripheral plugging portion 5b having a relatively short plugging length generates less thermal stress, so by disposing such an outer peripheral plugging portion 5b in the outer peripheral portion 16, damage such as cracks is less likely to occur on the outer peripheral portion 16 side of the honeycomb structure 4. For example, the occurrence of cracks on the end face on the outer peripheral portion 16 side of the honeycomb structure 4 and cracks on the outer peripheral wall 3 of the honeycomb structure 4 (for example, the outer peripheral coating layer described later) can be effectively suppressed.

[0026] For example, the average plugging length L1 in the central portion 15 (Ave) and the average plugging length L2 in the outer periphery 16 (Ave) However, if the values ​​are outside the above-mentioned ranges, the effects described above may not be sufficiently exhibited. (Ave) and average plugging length L2 (Ave)The same applies when the difference ΔL between the center and the center 15 is outside the above-mentioned numerical range. In order to effectively realize each of the effects described above, it is also important that the ratio (R / D) of the average radius R of the center 15 to the circle-equivalent radius D of the end face of the honeycomb structure 4 is 0.2 to 0.5. Hereinafter, the ratio (R / D) of the average radius R of the center 15 to the circle-equivalent radius D of the end face of the honeycomb structure 4 may be referred to as the "average radius ratio (R / D) of the center 15". When the average radius ratio (R / D) of the center 15 is less than 0.2, the number of the center plugging portions 5a is too small, and sufficient thermal shock resistance and erosion resistance may not be obtained. On the other hand, when the average radius ratio (R / D) of the center 15 is more than 0.5, the number of the peripheral plugging portions 5b is too small, and sufficient effect of suppressing the occurrence of cracks may not be obtained.

[0027] Furthermore, in the honeycomb filter 100 of this embodiment, the porosity of the plugging portions 5 is 40 to 60%, and the plugging portions 5 have a relatively dense structure. By setting the porosity of the plugging portions 5 to 40 to 60%, the erosion resistance is improved. Note that if the porosity of the plugging portions 5 is less than 40%, this is not preferable because the thermal stress generated in the plugging portions 5 may become large.

[0028] Furthermore, the plugging portion 5 is a porous body having a microstructure composed of a plurality of particles in the electron microscope image. In particular, the plugging portion 5 is composed of a plurality of particles in the electron microscope image, and the particle density is 750 to 1250 particles / mm 2The plugging portion 5 has an average circle-equivalent diameter of each particle constituting the plugging portion 5 of 3 to 5 μm. The term "average circle-equivalent diameter of each particle" refers to the arithmetic mean obtained by dividing the sum of the circle-equivalent diameters of each particle by the number of particles. By configuring in this way, the gaps between the particles constituting the plugging portion 5 become cushions, mitigating thermal expansion during the regeneration process, and effectively suppressing the occurrence of cracks on the end face of the honeycomb structure 4 and the outer peripheral wall 3 side. For example, the plugging portion 5 composed of such a plurality of particles is preferably an unfired body in which the plurality of particles are not sintered. The unfired plugging portion 5 of such an unfired body does not shrink during firing, so that the residual stress during the manufacturing process is smaller than that of a fired body. The plugging portion 5 having such a small residual stress is less likely to cause cracks on the end face of the honeycomb structure 4 and the outer peripheral wall 3 side.

[0029] The porosity and the above-mentioned microstructure of the plugging portion 5 can be measured by the following method.

[0030] First, a measurement sample is cut out from the plugged portion 5 to be measured. Specifically, an area of ​​15 mm x 15 mm in length and width centered on the center of gravity of the end face 11 of the honeycomb structure 4 is cut out from the end face 11 to 15 mm in the depth direction to obtain a cubic measurement sample with one side of 15 mm. The plugged portion 5 included in such a measurement sample is the measurement target.

[0031] Next, the plugging portion 5 present on the cut surface of the obtained measurement sample is imaged using a scanning electron microscope (hereinafter also referred to as "SEM") to obtain an SEM image with a magnification of 100 times. "SEM" is an abbreviation of "Scanning Electron Microscope". The SEM image is an image in which one pixel is 0.992 μm in length × 0.992 μm in width. As the scanning electron microscope, for example, a scanning electron microscope "Model: S-3400N" manufactured by Hitachi High-Tech Corporation can be used. The SEM image thus obtained is subjected to image analysis using two-dimensional image analysis software (WinROOF (product name) manufactured by Mitani Shoji Co., Ltd.). The conditions for the image analysis are thresholds of 0.000 and 35.000, and transparency of 127. For the analysis mode of WinROOF (product name), after "black and white inversion", the analysis item of "shape characteristics" is selected.

[0032] In this manner, it is possible to calculate the particle area and particle density of the particles constituting the plugging portion 5 in the SEM image. In addition, the area of ​​the void portion other than the particles in the SEM image is calculated, and the area ratio of the void portion in the SEM image is calculated, thereby calculating the porosity of the plugging portion 5. The analysis of the plugging portion 5 using the SEM image is performed on SEM images of five fields of view, and the average of the analysis results of three fields of view excluding the maximum and minimum values ​​of the measurement results is calculated.

[0033] The plugging length of the plugged portion 5 can be measured by the following method. That is, the plugging length L1 of the central plugged portion 5a and the plugging length L2 of the peripheral plugged portion 5b, as well as the average plugging length L1 in the central portion 15 and the peripheral portion 16, which have been described so far, (Ave) and average plugging length L2 (Ave)are values ​​measured by the following measurement method. Here, Fig. 5 is an explanatory diagram for explaining a method for measuring the plugging length of the plugged portion 5 (see Fig. 2, the same applies below), and is a schematic diagram showing the inflow end face 11 side of the honeycomb filter 100. In Fig. 5, the partition walls 1 (see Fig. 2) and the cells 2 (see Fig. 2) on the inflow end face 11 of the honeycomb filter 100 are omitted. In the following description, the "inflow end face 11" of the honeycomb filter 100 may be simply referred to as the "end face 11" of the honeycomb filter 100.

[0034] When measuring the plugging length of the plugged portion (see FIG. 2), the plugging length is measured in a cross direction starting from the center of gravity O of the end face 11 of the honeycomb filter 100 as shown in FIG. 5. Here, the "center of gravity O" of the end face 11 of the honeycomb filter 100 refers to the center of gravity in a geometric sense of the end face 11 (in other words, the geometric center). A more specific method for measuring the plugging length is as follows. First, the measurement points are set in a total of 40 points in four directions, 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock directions, by dividing the radial direction from the center of gravity O of the end face 11 to the outer periphery into 10 equal parts. In FIG. 5, the 10 measurement points in each radial direction are indicated by numbers in circles from 1 to 10. In addition, the measurement point of the center of gravity O (i.e., the measurement point of the circled number 1 in FIG. 5) is assumed to overlap as a measurement point in each radial direction. At each of the 40 measurement points set in this way, the plugging length of the plugged portion 5 (see FIG. 2) is measured. The plugging length can be measured, for example, by inserting a rod whose length is known and longer than the entire length of the honeycomb filter 100 into the cell 2 (see FIG. 2) and measuring the difference between the length of the rod exposed from the honeycomb filter 100 and the length of the rod itself. When the end face 11 of the honeycomb filter 100 has a circular shape, the four directions of the 12 o'clock direction, the 3 o'clock direction, the 6 o'clock direction, and the 9 o'clock direction can be any cross direction starting from the center of gravity O. When the end face 11 of the honeycomb filter 100 has a shape other than a circular shape, the two axes of the cross direction are specified as follows. First, the longest axis among the axes passing through the center of gravity O of the end face 11 of the honeycomb filter 100 is defined as the first axis. Hereinafter, this longest axis is defined as the "long axis". Then, the axis passing through the center of gravity O of the end face 11 and perpendicular to the long axis is defined as the second axis. Hereinafter, this second axis is defined as the "short axis".

[0035] As described above, the plugging length is measured at 40 points (37 points when the overlapping center of gravity O is considered as one point), and then the boundary between the central portion 15 (see FIG. 2) and the outer peripheral portion 16 (see FIG. 2) of the end face 11 where the plugging length is measured is determined using the measurement results of the plugging length. Specifically, the radial lengths at which the plugging length finally satisfies 5 mm, counting from the center of gravity O, in each radial direction of the end face 11 are respectively r3, r6, r9, and r12. Note that r3 is the radial length at which the plugging length finally satisfies 5 mm, counting from the center of gravity O, at the measurement point in the 3 o'clock direction. r6, r9, and r12 are the radial lengths at which the plugging length finally satisfies 5 mm, counting from the center of gravity O, in the 6 o'clock direction, 9 o'clock direction, and 12 o'clock direction. The arithmetic mean of r3, r6, r9, and r12 thus obtained is determined as the average radius R of the central portion 15 (see FIG. 2).

[0036] When the end face 11 of the honeycomb filter 100 has a circular shape, the area inside the determined average radius R (i.e., the area toward the center of gravity O of the end face 11) is defined as the central portion 15 (see Figure 2), and the area outside of that is defined as the outer periphery 16 (see Figure 2).

[0037] In addition, when the shape of the end face 11 of the honeycomb filter 100 is not circular, first, the center of gravity O of the end face 11 is set to 0%, and the nine measurement points in the radial direction of each axis are sequentially set to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% measurement points toward the outside. Then, in each radial direction of the end face 11, the above-mentioned percentage values ​​are obtained at the measurement points (i.e., the measurement points corresponding to the above-mentioned r3, r6, r9, and r12) where the plugging length finally satisfies 5 mm, counting from the center of gravity O, and the arithmetic mean is obtained. For example, when r3 is 50%, r6 is 40%, r9 is 60%, and r12 is 40%, the arithmetic mean of the percentage values ​​is (50%+40%+60%+40%) / 4=47.5%. The arithmetic mean of the percentage values ​​thus obtained is set as the similarity ratio of the central portion 15 (see FIG. 2) when the end face 11 of the honeycomb filter 100 is set as 100%. That is, the central portion 15 (see FIG. 2) is specified so that the center of gravity O of the end face 11 of the honeycomb filter 100 is its center of gravity, and the similarity ratio with the end face 11 is 100:47.5. Therefore, the inside of the shape with the similarity ratio with the end face 11 of 100:47.5 (i.e., the side of the center of gravity O in the end face 11) is set as the central portion 15 (see FIG. 2), and the outside of that is set as the outer periphery portion 16 (see FIG. 2). Note that the method of specifying the central portion 15 described so far is for the case where the shape of the end face 11 is other than circular, but it can also be applied to the case where the shape of the end face 11 is circular by fitting the major axis and minor axis specified in the case where the shape is other than circular to any cross-direction axis in the case where the shape is circular.

[0038] And the average plugging length L1 (Ave) and average plugging length L2 (Ave) can be calculated by determining the arithmetic mean of the plugging lengths measured at the measurement points included in each range after defining the central portion 15 (see FIG. 2) and the peripheral portion 16 (see FIG. 2) as described above. The average radius ratio (R / D) of the central portion 15 (see FIG. 2) can also be calculated from the average radius R determined as described above and the circle-equivalent radius D of the end face 11.

[0039] In the honeycomb filter 100 as shown in Fig. 1 to Fig. 4, the porosity of the plugging portions 5 may be 40 to 60%, and is preferably, for example, 45 to 55%, and more preferably 47 to 53%. Although not particularly limited, the porosity of the plugging portions 5 is preferably a lower value than the porosity of the partition walls 1. By configuring in this way, it is possible to obtain excellent erosion resistance.

[0040] Average plugging length L1 in the central portion 15 (Ave) The average plugging length L2 in the outer circumferential portion 16 may be 5 mm or more and 10 mm or less, but is preferably 7 mm or more and 10 mm or less, and more preferably 9 mm or more and 10 mm or less. (Ave) It is sufficient that the thickness is 2 mm or more and less than 5 mm, but for example, it is preferably 2 mm or more and less than 4 mm, and more preferably 2 mm or more and less than 3 mm.

[0041] Average plugging length L1 (Ave) and average plugging length L2 (Ave) The difference ΔL between the above values ​​may be from 2 to 6 mm, but is preferably from 3 to 6 mm, and more preferably from 4 to 5 mm.

[0042] The ratio (R / D) of the average radius R of the central portion 15 may be from 0.2 to 0.5, preferably from 0.3 to 0.5, and more preferably from 0.4 to 0.5.

[0043] The microstructure of the plugged portion 5 in the electron microscope image has been described above. For example, the average particle area of ​​the particles constituting the plugged portion 5 is 2 to 5 μm 2 It is preferable that the thickness is 2 to 4 μm. 2 It is more preferable that the particle density of the particles constituting the plugging portion 5 is 800 to 1200 particles / mm 2 It is preferable that the number of particles is 900 to 1100 / mm 2As described above, the particles constituting the plugging portion 5 have an average equivalent circle diameter of 3 to 5 μm. The equivalent circle diameter of each particle is calculated by calculating the area S of each particle in the microstructural analysis of the electron microscope image described above, and calculating the equivalent circle diameter (μm) of each particle=√{4×(area S of particle (μm 2 )) / π}.

[0044] The porosity of the partition walls 1 of the honeycomb structure 4 is preferably 60 to 70%, more preferably 62 to 68%, and particularly preferably 64 to 66%. The porosity of the partition walls 1 is a value measured by mercury intrusion porosimetry. The porosity of the partition walls 1 can be measured, for example, using Autopore 9500 (product name) manufactured by Micromeritics. If the porosity of the partition walls 1 is less than 60%, it is not preferable in terms of pressure loss. If the porosity of the partition walls 1 is more than 70%, it is not preferable in terms of soot collection efficiency.

[0045] In the honeycomb structure 4, the thickness of the partition walls 1 is preferably 0.1 to 0.3 mm, and more preferably 0.1 to 0.2 mm. The thickness of the partition walls 1 can be measured, for example, using a profile projector. If the thickness of the partition walls 1 is less than 0.1 mm, sufficient strength may not be obtained. On the other hand, if the thickness of the partition walls 1 exceeds 0.3 mm, the pressure loss may increase.

[0046] There is no particular limitation on the shape of the cells 2 formed in the honeycomb structure 4. For example, examples of the shape of the cells 2 in a cross section perpendicular to the extension direction of the cells 2 include polygonal, circular, and elliptical shapes. Examples of polygonal shapes include triangular, rectangular, pentagonal, hexagonal, and octagonal shapes. The shape of the cells 2 is preferably triangular, rectangular, pentagonal, hexagonal, or octagonal. Regarding 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 figure, a mixture of rectangular cells and octagonal cells may be used. Regarding 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 figure, the size of some of the cells may be large and the size of the other cells may be relatively small. In the present invention, the cell 2 means a space surrounded by the partition wall 1.

[0047] The cell density of the cells 2 partitioned by the partition walls 1 is 42 to 51 cells / cm 2 is preferably 44 to 49 pieces / cm 2 With this configuration, the filter can be suitably used as a filter for collecting PM in exhaust gas discharged from an engine of an automobile or the like.

[0048] The peripheral wall 3 of the honeycomb structure 4 may be integrally formed with the partition walls 1, or may be an peripheral coating layer formed by applying an peripheral coating material so as to surround the partition walls 1. Although not shown in the drawings, the peripheral coating layer can be provided on the outer periphery of the partition walls after the partition walls and the peripheral wall are integrally formed during production, and then the formed peripheral wall is removed by a known method such as grinding.

[0049] There is no particular limitation on the shape of the honeycomb structure 4. The honeycomb structure 4 may have an inflow end face 11 and an outflow end face 12 that are cylindrical, circular, elliptical, polygonal, or the like.

[0050] There is no particular limitation on the size of the honeycomb structure 4, for example, the length in the extension direction of the cells 2 of the honeycomb structure 4 (hereinafter also referred to as the "total length") and the size of the cross section perpendicular to the extension direction of the cells 2 of the honeycomb structure 4 (hereinafter also referred to as the "cross-sectional area"). Each size may be appropriately selected so that the honeycomb filter 100 can obtain optimal purification performance when used.

[0051] There is no particular limitation on the material of the partition wall 1. For example, the material of the partition wall 1 preferably contains at least one selected from the group consisting of silicon carbide, cordierite, a silicon-silicon carbide composite material, a cordierite-silicon carbide composite material, silicon nitride, mullite, alumina, and aluminum titanate.

[0052] The material of the plugging portion 5 is not particularly limited, but is preferably ceramics from the viewpoint of strength and heat resistance. The ceramic is preferably ceramics containing at least one selected from the group consisting of cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon-silicon carbide composite material, silicon nitride, zirconia, spinel, indialite, sapphirine, corundum, and titania. These ceramics may contain one type alone or two or more types simultaneously. The plugging portion is preferably formed of a material containing 50 mass% or more of these ceramics in total, and more preferably formed of a material containing 80 mass% or more.

[0053] (2) Manufacturing method of honeycomb filter: The method for producing the honeycomb filter of the present invention is not particularly limited, and for example, the following method can be mentioned.

[0054] First, a plastic clay for producing the partition walls of the honeycomb structure is prepared. The clay for producing the partition walls of the honeycomb structure can be prepared by adding additives such as binders, pore formers, and water to the raw material powder for producing the above-mentioned suitable material for the partition walls. For example, powders of alumina, talc, kaolin, and silica can be used as the raw material powder. For example, methylcellulose, hydroxypropyl methylcellulose, and the like can be used as the binder. In addition, for example, a surfactant can be used as the additive.

[0055] Next, the thus obtained clay is extruded to produce a columnar honeycomb formed body having partition walls that define a plurality of cells and an outer peripheral wall disposed so as to surround the partition walls. Next, the obtained honeycomb formed body is dried, for example, by microwaves and hot air.

[0056] Next, the obtained honeycomb formed body is fired to produce a honeycomb structure, which is a honeycomb filter precursor before the plugging portions are provided. Note that the firing temperature and firing atmosphere when firing the honeycomb formed body vary depending on the raw materials used to produce the honeycomb formed body, and a person skilled in the art can select the firing temperature and firing atmosphere that are optimal for the selected materials.

[0057] Next, plugging portions are formed in the obtained honeycomb structure. The plugging portions can be formed by the following method. For example, first, a mask is applied to the inflow end face of the honeycomb structure so that the inflow cells are covered. Then, a plugging material is imprinted on the masked end face of the honeycomb structure, and the plugging material is filled into the openings of the outflow cells where the mask is not applied. Then, the plugging material is filled into the openings of the inflow cells on the outflow end face of the honeycomb structure in the same manner as above. When imprinting the plugging material on the end face of the honeycomb structure, first, a certain amount of plugging material is imprinted on the entire area of ​​the end face of the honeycomb structure. Then, a mask is further applied to the openings of the cells where the mask is not applied (i.e., the cells where the above-mentioned certain amount of plugging material is imprinted) in the outer periphery of the end face, so that all the cells in the outer periphery are covered with the mask. Then, a certain amount of plugging material is further imprinted only on the cells at the center of the end portion, so that the plugging length of the peripheral plugging portions at the outer periphery is relatively short, and the plugging length of the central plugging portions at the center is relatively long. Then, the honeycomb structure with the plugged portions formed thereon is further dried in a hot air dryer. In this manner, the honeycomb filter of the present invention can be manufactured. In particular, when manufacturing the honeycomb filter of the present invention, it is preferable to fire the honeycomb formed body before forming the plugging portions, and to form the plugging portions on the honeycomb structure obtained by firing. Then, it is preferable that the formed plugging portions are not fired again, and are left unfired.

[0058] It is preferable to use a plugging material for forming the plugged portion that is prepared to have the microstructure of the plugged portion described above. For example, the plugging material may contain 0.1 to 0.5 parts by mass of a thickener, 0.2 to 1.0 parts by mass of a binder, 7 to 15 parts by mass of a pore former, and 30 to 50 parts by mass of water, relative to 100 parts by mass of a ceramic raw material. It is also preferable to use a plugging material that is prepared so that the average value of the circle-equivalent diameter of each particle of the ceramic raw material is 3 to 5 μm. Here, the average value of the circle-equivalent diameter of each particle of the ceramic raw material is determined by calculating the circle-equivalent diameter of each particle from the particle area obtained by WinRoof (product name) and calculating the arithmetic mean of the obtained circle-equivalent diameters. EXAMPLES

[0059] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0060] Example 1 10 parts by mass of the cordierite raw material, 10 parts by mass of the pore former, 4 parts by mass of the dispersion medium, and 4 parts by mass of the organic binder were added to 100 parts by mass of the cordierite raw material, and mixed and kneaded to prepare a clay. Alumina, aluminum hydroxide, kaolin, talc, and silica were used as the cordierite raw material. Water was used as the dispersion medium. Methylcellulose was used as the organic binder. Dextrin was used as the dispersant. A water-absorbing polymer with an average particle diameter of 5 μm was used as the pore former. In this embodiment, the average particle diameter of each raw material is the particle diameter (D50) at 50% of the integrated value in the particle size distribution obtained by the laser diffraction and scattering method.

[0061] Next, the clay was extruded using a die for producing a honeycomb formed body to obtain a honeycomb formed body having an overall cylindrical shape. The shape of the cells of the honeycomb formed body was rectangular.

[0062] Next, the honeycomb molded body was dried in a microwave dryer and further completely dried in a hot air dryer, and then both end faces of the honeycomb molded body were cut to a predetermined size. Thereafter, the honeycomb molded body was degreased and fired to obtain a honeycomb structure.

[0063] Next, a plugging material for forming plugged portions was prepared. After that, plugging portions were formed at the openings of the predetermined cells on the inflow end face side of the honeycomb structure and the openings of the remaining cells on the outflow end face side using the plugging material. For the plugging material, talc, alumina, aluminum hydroxide, kaolin, and crystalline silica were used. The plugging material was prepared by adding a binder, a thickener, and a dispersant to the above-mentioned raw materials. Methyl cellulose and hydroxyethyl methyl cellulose were used as the binder. Polyethylene oxide was used as the thickener. Polyalcohol was used as the dispersant. Acrylic resin was used as the pore-forming material. The plugging material was filled by imprinting it into the end of the honeycomb structure as follows. First, a mask was applied to the inflow end face of the honeycomb structure so that the inflow cells were covered, and then the plugging material was imprinted over the entire area of ​​the end of the honeycomb structure where the mask was applied, and the plugging material was filled into the openings of the cells where the mask was not applied. Then, a mask was applied to the openings of the cells that were not masked at the outer periphery of the end on the inflow end face side of the honeycomb structure, so that all the cells at the outer periphery were covered with the mask. Then, a certain amount of plugging material was further imprinted only on the cells at the center of the end, so that the filling length of the plugging material at the outer periphery was relatively short and the filling length of the plugging material at the center was relatively long. Then, the plugging material was filled into the openings of the specified cells on the outflow end face side of the honeycomb structure in the same manner.

[0064] The honeycomb filter of Example 1 had a cylindrical shape with a length of 127 mm in the cell extension direction. This honeycomb filter had an inflow end face and an outflow end face with a circular shape, and the radius of the inflow end face and the outflow end face (corresponding to the circle equivalent radius D) was 66 mm. The honeycomb filter had a partition wall thickness of 0.21 mm, a partition wall porosity of 65%, and a cell density of 43 cells / cm. 2The results are shown in Table 1. The porosity of the partition walls was measured using Autopore 9500 (product name) manufactured by Micromeritics.

[0065] [Table 1]

[0066] In addition, an electron microscope image (SEM image) of the plugged portions of the honeycomb filter of Example 1 was obtained, and the microstructure of the plugged portions was analyzed by the method described above. The obtained results are shown in Table 1. The honeycomb filter of Example 1 had a porosity of 51% in the plugged portions, and the particle density of the particles constituting the plugged portions was 883 particles / mm 2 In addition, the average circle equivalent diameter of each particle constituting the plugging portion was 4 μm.

[0067] Furthermore, for the honeycomb filter of Example 1, the plugging length of the plugged portion described above as shown in FIG. 5 was measured, and the average plugging length L1 (Ave) , average plugging length L2 in the outer periphery (Ave) , and the difference ΔL in plugging length were obtained. In addition, the average radius R of the central part was obtained from the measurement results of the plugging length of the plugged portion, and the ratio (R / D) of the average radius R of the central part to the radius D of the end face of the honeycomb structure was calculated. The results are shown in Table 1. In addition, in the column "Whether fired or not" of "Plugged portion" in Table 1, whether or not the plugged portion was fired during production is recorded as the configuration of the plugged portion of the honeycomb filter produced in this example. In this column, "Unfired" indicates that the plugged portion was not fired during production, and the honeycomb filter was produced by only drying. On the other hand, in this column, "Fired" indicates that the honeycomb filter was produced by firing the plugged portion during production.

[0068] The honeycomb filter of Example 1 was evaluated for "erosion resistance" and "thermal shock resistance" by the following methods. The results are shown in Table 2.

[0069] [Table 2]

[0070] [Erosion resistance] First, the honeycomb filter was canned (stored) in a can body, and the canned honeycomb filter was placed in a gas burner tester. Next, SiC abrasive grains were collided with the inlet end face of the honeycomb filter by the gas burner tester. The conditions for colliding the abrasive grains were as follows. The amount of abrasive grains input was 10 g. The temperature of the gas flowing into the honeycomb filter was 700°C. The flow rate of the gas flowing into the honeycomb filter was 120 m / sec. The test time was 10 minutes, during which the abrasive grains were input little by little. After that, the honeycomb filter was taken out, and the taken-out honeycomb filter was photographed by a tomography (CT), and the depth of the honeycomb filter shaved by the collision of the abrasive grains (erosion depth (mm)) was calculated. In this erosion amount measurement test, abrasive grains with an average particle size of 50 μm were used. The "erosion resistance" of the honeycomb filter was evaluated according to the following evaluation criteria. In Examples 1 to 4 and Comparative Examples 1 to 3, the reference honeycomb filter is Comparative Example 1. The term "perforated plugging" refers to a state in which the plugging portions are scraped off by erosion and at least a part of the plugging portions penetrates in the gas flow direction. Evaluation "OK": When "plugging penetration due to erosion" does not occur in the honeycomb filter to be evaluated, the evaluation is rated as "OK". Evaluation "NG": When "plugging penetration due to erosion" occurs in the honeycomb filter to be evaluated, the evaluation is given as "NG".

[0071] [Thermal shock resistance] First, a predetermined amount of soot was generated under constant operating conditions on an engine bench equipped with a 1.4L gasoline engine, and the generated soot was deposited on the surface of the partition walls of the honeycomb filters of each Example and Comparative Example. Next, a regeneration process was performed by post-injection, the inlet gas temperature of the honeycomb filter was increased, and when the pressure loss before and after the honeycomb filter began to decrease, the post-injection was turned off and the engine was switched to an idle state. The predetermined amount of soot deposition before the regeneration process was gradually increased, and the above operation was repeated until cracks occurred in the honeycomb filter. The amount of soot deposition at which cracks occurred in the honeycomb filter was defined as the "soot deposition limit amount" for each honeycomb filter. The "soot deposition limit amount" of the honeycomb filter was evaluated according to the following evaluation criteria. In Examples 1 to 4 and Comparative Examples 1 to 3, the reference honeycomb filter was defined as Comparative Example 1. Evaluation "Excellent": If the "soot accumulation limit" of the standard honeycomb filter is set to 100%, and the "soot accumulation limit" of the honeycomb filter being evaluated is 130% or more, the filter is rated "Excellent". Rating "Good": If the "soot accumulation limit" of the reference honeycomb filter is set to 100%, and the "soot accumulation limit" of the honeycomb filter being evaluated is 120% or more and less than 130%, the filter is rated "Good". Rating "Fair": If the "soot accumulation limit" of the reference honeycomb filter is set to 100%, and the "soot accumulation limit" of the honeycomb filter being evaluated is greater than or equal to 100% and less than 120%, the rating is "Fair". Rating "Fail": If the "soot accumulation limit" of the standard honeycomb filter is set to 100%, and the "soot accumulation limit" of the honeycomb filter being evaluated is less than 100%, the rating is "Fail".

[0072] (Examples 2 to 4 and Comparative Examples 1 to 3) The configuration of the honeycomb filter was changed as shown in Table 1, and honeycomb filters of Examples 2 to 4 and Comparative Examples 1 to 3 were manufactured. The honeycomb filters of Examples 2 to 4 and Comparative Examples 1 to 3 were mainly produced in the same manner as the honeycomb filter of Example 1, except for the following changes during production. In Example 2, in preparation of the plugging material, the average particle size of talc was increased as shown in Table 1, the amount of the pore-forming material was reduced, and the temperature of the preliminary firing was lowered. In Example 3, in preparation of the plugging material, the average particle size of talc was reduced as shown in Table 1, the amount of the pore-forming material was reduced, the temperature of the preliminary firing was lowered, and the amount of the plugging material rubbed in was increased so that the plugging material penetrated for a long period of time. In Example 4, in preparation of the plugging material, the average particle size of talc was made small as shown in Table 1, the amount of the pore-forming material was reduced, and the temperature of the preliminary firing was lowered. In Comparative Example 1, in preparation of the plugging material, the average particle size of talc was reduced as shown in Table 1, the amount of the pore-forming material was increased, and the temperature of the preliminary firing was lowered. In Comparative Example 2, in preparing the plugging material, the average particle size of talc was reduced and the amount of the pore-forming material was reduced so as to be as shown in Table 1, and the plugging material was filled into the openings of each cell, and then the filled plugging material was fired to form plugged portions. In Comparative Example 3, in preparing the plugging material, the amount of the pore-forming material was reduced as shown in Table 1, the temperature of the pre-firing was lowered, and the plugging material was imprinted on the outer periphery without using a mask to be added later so that the plugging material had a uniform length.

[0073] The honeycomb filters of Examples 2 to 4 and Comparative Examples 1 to 3 were also subjected to the above-mentioned respective evaluations in the same manner as in Example 1. The respective results are shown in Table 2.

[0074] (result) The honeycomb filters of Examples 1 to 4 obtained good results in the evaluations of erosion resistance and thermal shock resistance. On the other hand, the honeycomb filter of Comparative Example 1 exhibited a relatively high porosity of 65% in the plugged portions, and the evaluation result of the erosion resistance was "NG." The honeycomb filter of Comparative Example 2 has a particle density of 498 particles / mm in the microstructure of the plugging portion. 2 and the average circle equivalent diameter of the individual particles constituting the plugging portions was 10 μm. The honeycomb filter of Comparative Example 2 had a thermal shock resistance evaluation result that was inferior to the honeycomb filters of Examples 1 to 4. That is, it is presumed that the honeycomb filter of Comparative Example 2 has fired plugging portions, and the particles contained in the plugging material are strongly bonded to each other by firing, resulting in a relatively large thermal expansion coefficient of the plugging portions. For this reason, it is considered that the honeycomb filter of Comparative Example 2 has large thermal stress generated in the plugging portions, and is more likely to cause cracks in the evaluation of thermal shock resistance. The honeycomb filter of Comparative Example 3 had no difference in plugging length between the center and the outer periphery of the end face, and the plugging length was uniform (4 mm) over the entire end face. The honeycomb filter of Comparative Example 3 was inferior in the evaluation results of erosion resistance to the honeycomb filters of Examples 1 to 4. [Industrial Applicability]

[0075] The honeycomb filter of the present invention can be used as a filter for collecting particulate matter in exhaust gas. [Explanation of symbols]

[0076] 1: partition wall, 2: cell, 2a: inlet cell, 2b: outlet cell, 3: outer peripheral wall, 4: honeycomb structure, 5: plugged portion, 5a: central plugged portion, 5b: peripheral plugged portion, 11: end face (inlet end face), 12: end face (outlet end face), 15: central portion, 16: outer peripheral portion, 100: honeycomb filter, D: circle equivalent radius (circle equivalent radius of end face of honeycomb structure), L, L1, L2: plugging length, R: average radius (average radius of central portion).

Claims

1. a cylindrical honeycomb structure having porous partition walls arranged to surround a plurality of cells that serve as fluid flow paths extending from an inflow end surface to an outflow end surface; A plurality of plugging portions are provided at either one of the end portion on the inlet end surface side or the end portion on the outlet end surface side of the cell, The porosity of the plugging portion is 40 to 60%, a central plugging portion having a plugging length L of 5 mm or more in the cell extension direction is disposed on a central portion side of the end portion on the inflow end face side or the end portion on the outflow end face side of the honeycomb structure, and a peripheral plugging portion having a plugging length L of less than 5 mm is disposed on a peripheral portion side on the outer side of the central portion at the end portion, an average plugging length L1 (Ave) which is an average value of the plugging lengths L in the central portion is 5 mm or more and 10 mm or less; An average plugging length L2 (Ave) which is an average value of the plugging lengths L in the outer circumferential portion is 2 mm or more and less than 5 mm, a difference ΔL between the average plugging length L1 (Ave) in the central portion and the average plugging length L2 (Ave) in the outer circumferential portion is 2 to 6 mm, a ratio (R / D) of an average radius R of the central portion to a circle-equivalent radius D of the inflow end face and the outflow end face of the honeycomb structure is 0.2 to 0.5; In an electron microscope image of the plugged portion, the plugged portion is composed of a plurality of particles, the average circle equivalent diameter of each particle is 3 to 5 μm, and the particle density of the plugged portion is 750 to 1250 particles / mm ２ That is, a honeycomb filter.

2. The honeycomb filter according to claim 1, wherein the partition walls have a porosity of 60 to 70%.

3. The honeycomb filter according to claim 1 or 2, wherein the partition walls have a thickness of 0.1 to 0.3 mm.

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