Honeycomb Filter

Abstract

To provide a honeycomb filter which has low pressure loss and can achieve, excellent purification performance when carrying an exhaust gas purification catalyst.SOLUTION: A honeycomb filter comprises: a columnar honeycomb structure 4 having a porous partition wall 1 arranged so as to surround a plurality of cells 2; a porous opening sealing part 5 provided on any one end of the cell 2. The honeycomb structure 4 comprises in a cross section orthogonal to a direction where the cells 2 extend: a center part 15 including a centroid O of the cross section; and an outer peripheral part 16 provided outside of the center part 15. A thickness T1 of the partition wall 1 on the center part 15 is 0.17-0.32 mm, and a thickness T2 of the partition wall 1 on the outer peripheral part 16 is 70-90% of the thickness T1 of the partition wall 1 on the center part 15. The outer peripheral part 16 is in a range of 6-12% to a radius r from the centroid O of the cross section to an outer peripheral edge, with the outer peripheral edge of the cross section as an original point.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a honeycomb filter, and more particularly to a honeycomb filter that has low pressure loss and can achieve excellent purification performance when carrying an exhaust gas purification catalyst. [Background technology]

[0002] Conventionally, honeycomb filters using a honeycomb structure have been known as filters for capturing particulate matter in exhaust gases emitted from internal combustion engines such as automobile engines, or as devices 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 these partition walls define a plurality of cells. A honeycomb filter is a honeycomb structure in which plugging portions are provided so that openings on the inflow end faces and openings on the outflow end faces of a plurality of cells are alternately plugged. That is, the honeycomb filter has a structure in which inflow cells that are open on the inflow end face and plugged on the outflow end face, and outflow cells that are plugged on the inflow end face and open on the outflow end face are alternately arranged with the partition walls sandwiched between them. In the honeycomb filter, the porous partition walls function as a filter for capturing particulate matter in exhaust gases. Hereinafter, particulate matter contained in exhaust gases may be referred to as "PM." "PM" stands for "particulate matter."

[0003] Exhaust gas purification using a honeycomb filter is performed as follows. First, the honeycomb filter is positioned so that its inlet end face is located upstream of the exhaust system from which the exhaust gas is discharged. The exhaust gas flows into the inlet cells from the inlet end face of the honeycomb filter. The exhaust gas that flows into the inlet cells then passes through the porous partition walls, flows into the outlet cells, and is discharged from the outlet end face of the honeycomb filter. As the exhaust gas passes through the porous partition walls, PM and other substances in the exhaust gas are captured and removed. In addition, such honeycomb filters may support an oxidation catalyst for promoting the oxidation (combustion) of PM, or an exhaust gas purification catalyst for purifying harmful components such as NOx. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-149510 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there was a problem in that the placement of honeycomb filters to capture and remove PM generated from automobile engines resulted in high pressure loss.

[0006] Furthermore, when PM is continuously removed from exhaust gas using a honeycomb filter, PM accumulates inside the honeycomb filter, increasing the pressure loss of the honeycomb filter. Therefore, in purification devices using honeycomb filters, PM accumulated inside the honeycomb filter is burned automatically or manually to prevent excessive pressure loss in the honeycomb filter. Hereinafter, the operation of burning PM accumulated inside the honeycomb filter may be referred to as the "regeneration operation" of the honeycomb filter. During the regeneration operation of a honeycomb filter, the PM accumulated inside the honeycomb filter is forcibly burned, causing the inside of the honeycomb filter to reach a high temperature. Therefore, there was a concern that if the heat capacity of the honeycomb filter was too small, the heat generated during the regeneration operation would damage the honeycomb filter.

[0007] One possible method for reducing the pressure loss of a honeycomb filter is to reduce the thickness of the partition walls. Meanwhile, one possible method for increasing the heat capacity of a honeycomb filter is to increase the thickness of the partition walls. However, reducing the thickness of the partition walls reduces the thickness of the partition walls that function as filtering material, resulting in a problem of reduced PM collection performance. Meanwhile, increasing the thickness of the partition walls increases the pressure loss of the honeycomb filter, and when various catalysts, such as exhaust gas purification catalysts, are supported, the increased weight inhibits early catalyst activation, making it difficult to achieve sufficient purification performance through the catalytic reaction.

[0008] The present invention has been made in view of the problems of the prior art. According to the present invention, there is provided a honeycomb filter that has low pressure loss and can achieve excellent purification performance when an exhaust gas purification catalyst is supported thereon. [Means for solving the problem]

[0009] According to the present invention, there is provided the following honeycomb filter.

[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 porous plugging portion disposed at either an end portion on the inflow end face side or an end portion on the outflow end face side of the cell, The honeycomb structure includes, in a cross section perpendicular to the cell extension direction, a central portion including a center of gravity O of the cross section, and a peripheral portion located outside the central portion, The thickness T1 of the partition wall at the central portion is 0.17 to 0.32 mm, a thickness T2 of the partition wall in the outer peripheral portion is 70 to 90% of a thickness T1 of the partition wall in the central portion, The honeycomb filter has a diameter of 6 to 12% of the radius r from the center of gravity O of the cross section to the outer peripheral edge, starting from the outer peripheral edge of the cross section.

[0011] [2] The cell density of the honeycomb structure is 30 to 63 cells / cm 2 The honeycomb filter according to [1] above,

[0012] [3] The honeycomb filter according to the above [1] or [2], wherein the porosity of the partition walls is 45 to 65%. [Effects of the Invention]

[0013] The honeycomb filter of the present invention has the effect of having low pressure loss and being able to achieve excellent purification performance when carrying an exhaust gas purification catalyst. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view schematically showing one embodiment of a honeycomb filter of the present invention. [Figure 2] FIG. 2 is a plan view showing the inlet end face side of the honeycomb filter shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view schematically showing the AA' cross section of FIG. [Figure 4]3 is an enlarged plan view of the area enclosed by the dashed line indicated by P in FIG. 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] While the present invention will be described below with reference to exemplary embodiments, it should be understood that the present invention is not limited to the following exemplary embodiments. Therefore, it should be understood that modifications and improvements to the following exemplary embodiments, based on the ordinary knowledge of those skilled in the art, are also within the scope of the present invention, provided that they do not deviate from the spirit of the present invention.

[0016] (1) Honeycomb filter: One embodiment of the honeycomb filter of the present invention is a honeycomb filter 100 as shown in Figs. 1 to 4. Here, Fig. 1 is a perspective view schematically showing one embodiment of the honeycomb filter of the present invention. Fig. 2 is a plan view showing the inlet end face side of the honeycomb filter shown in Fig. 1. Fig. 3 is a cross-sectional view schematically showing the A-A' cross section of Fig. 2. Fig. 4 is an enlarged plan view of the area surrounded by the dashed line indicated by P in Fig. 2.

[0017] As shown in Figs. 1 to 4, a honeycomb filter 100 of this embodiment includes a honeycomb structure 4 and plugging portions 5. The honeycomb structure 4 is columnar and has porous partition walls 1 arranged to surround a plurality of cells 2 that serve as fluid flow paths extending from an inflow end face 11 to an outflow end face 12. In the honeycomb filter 100, the honeycomb structure 4 is columnar and further has an outer peripheral wall 3 on its outer peripheral side surface. That is, the outer peripheral wall 3 is arranged to surround the partition walls 1 arranged in a lattice pattern.

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

[0019] The honeycomb structure 4 includes, in a cross section perpendicular to the extension direction of the cells 2, 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 Figs. 2 and 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 on the outer periphery side of this central portion 15 is the "peripheral portion 16."

[0020] The honeycomb filter 100 of this embodiment has a particularly important characteristic in the configuration of the partition walls 1 in the central portion 15 and the outer peripheral portion 16. That is, in the honeycomb filter 100 of this embodiment, the thickness T1 of the partition walls 1 in the central portion 15 is 0.17 to 0.32 mm, and the thickness T2 of the partition walls 1 in the outer peripheral portion 16 is 70 to 90% of the thickness T1 of the partition walls 1 in the central portion 15. The outer peripheral portion 16 has a radius r ranging from the center of gravity O of the cross section of the honeycomb structure 4 to the outer peripheral edge as the starting point. This configuration achieves low pressure loss and excellent purification performance when an exhaust gas purification catalyst is supported. That is, by making the thickness T2 of the partition walls 1 in the outer peripheral portion 16 thinner than the thickness T1 of the partition walls 1 in the central portion 15, the weight of the honeycomb filter 100 is reduced, and excellent purification performance can be achieved when an exhaust gas purification catalyst is supported. Furthermore, by reducing the thickness T2 of the partition walls 1 in the outer peripheral portion 16, the opening ratio of the cells 2 in the honeycomb filter 100 increases, and a reduction in pressure loss can also be expected. 1 By setting the particle size to 0.17 to 0.32 mm, it is possible to effectively suppress a decrease in the PM collection performance.

[0021] The thickness T1 of the partition walls 1 in the central portion 15 and the thickness T2 of the partition walls 1 in the outer peripheral portion 16 can be measured using, for example, a scanning electron microscope or a microscope. When measuring the thicknesses T1 and T2 of the partition walls 1, if the shape of the cells 2 is polygonal, the thickness of the partition walls 1 is measured at a position corresponding to the midpoint of one side of the polygon. Specifically, the thickness T1 of the partition walls 1 in the central portion 15 can be determined by the following method. First, in a cross section of the honeycomb structure 4 perpendicular to the extension direction of the cells 2, starting from the outer peripheral edge of the cross section, the thickness of the partition walls 1 in a range of 50 to 100% of the radius r from the center of gravity O of the cross section to the outer peripheral edge is measured at a total of 10 points at 5% intervals of the radius r. The average value of the thicknesses of the partition walls 1 measured at 10 points in this manner is defined as the "thickness T1 of the partition walls 1 in the central portion 15." Next, the boundary between the central portion 15 and the outer peripheral portion 16 is defined as follows. First, the thickness of the partition walls 1 is measured at 1% of the radius r from the outer peripheral edge of the cross section of the honeycomb structure 4, and the measurement point (measurement position) immediately before the point where the thickness of the partition walls 1 first exceeds 90% of the thickness T1 is defined as the "boundary between the central portion 15 and the outer peripheral portion 16." After the boundary between the central portion 15 and the outer peripheral portion 16 is defined in this manner, the thickness of the partition walls 1 in the outer peripheral portion 16 is measured again at 1% of the radius r from the outer peripheral edge of the cross section, and the average value is defined as the "thickness T2 of the partition walls 1 in the outer peripheral portion 16." Hereinafter, the partition walls 1 in the outer peripheral portion 16 may be referred to as the "outer peripheral partition wall 1b." Furthermore, the partition walls 1 in the central portion 15 may be referred to as the "central partition wall 1a." It is preferable that the thickness T2 of the outer peripheral partition wall 1b is a substantially constant thickness within the outer peripheral portion 16. It is also preferable that the thickness T1 of the central partition wall 1a is a substantially constant thickness within the central portion 15. For example, the thickness T2 of the outer peripheral partition wall 1b is preferably within ±0.012 mm in the outer peripheral portion 16. Furthermore, the thickness T1 of the central partition wall 1a is preferably within ±0.012 mm in the central portion 15.

[0022] The thickness T1 of the central partition wall 1a may be 0.17 to 0.32 mm, and is preferably 0.20 to 0.30 mm, and more preferably 0.20 to 0.28 mm. For example, if the thickness T1 of the central partition wall 1a is too thin, the PM collection performance may decrease. On the other hand, if the thickness T1 of the central partition wall 1a is too thick, the pressure loss increases.

[0023] The thickness T2 of the peripheral partition wall 1b may be 70 to 90% of the thickness T1 of the central partition wall 1a, but is preferably 73 to 90%, and more preferably 75 to 90%. If the thickness T2 of the peripheral partition wall 1b is less than 70% of the thickness T1 of the central partition wall 1a, the thickness T1 of the central partition wall 1a becomes thin, which reduces the contact area with the catalyst when the exhaust gas passes through the partition wall 1, and therefore an improvement in purification performance cannot be expected. On the other hand, if the thickness T2 of the peripheral partition wall 1b exceeds 90% of the thickness T1 of the central partition wall 1a, the weight of the honeycomb filter 100 does not decrease sufficiently, and a sufficient improvement in purification performance cannot be expected. Furthermore, the opening ratio of the cells 2 in the honeycomb filter 100 decreases, and the pressure loss also increases.

[0024] The outer peripheral portion 16 is in the range of 6 to 12% of the radius r from the center of gravity O of the cross section to the outer peripheral edge, starting from the outer peripheral edge of the cross section of the honeycomb structure 4. If the range of the outer peripheral portion 16 is outside the above numerical range, it becomes difficult to achieve both low pressure loss and high purification performance. Here, the "center of gravity O" of the cross section of the honeycomb structure 4 refers to the center of gravity in the geometric sense of the cross section (in other words, the geometric center).

[0025] The cell density of the honeycomb structure 4 is 30 to 63 cells / cm 2 It is preferable that the density is 30 to 62 particles / cm. 2 More preferably, the density is 31 to 62 particles / cm. 2It is particularly preferable that the cell density is 100 or less. By configuring the honeycomb filter 100 in this manner, the honeycomb filter 100 can be suitably used as a filter for purifying exhaust gas emitted from an automobile engine. If the cell density is too low, the pressure loss may increase. On the other hand, if the cell density is too high, the purification performance may decrease.

[0026] The porosity of the partition walls 1 is preferably 45 to 65%, more preferably 46 to 63%, and particularly preferably 46 to 61%. With this configuration, the honeycomb filter 100 can be suitably used as a filter for purifying exhaust gas emitted from an automobile engine. The porosity of the partition walls 1 is a value measured by mercury porosimetry. The porosity of the partition walls 1 can be measured using, for example, an Autopore 9500 (trade name) manufactured by Micromeritics. The porosity of the partition walls 1 can be measured using a sample piece obtained by cutting out a part of the partition walls 1 from the honeycomb structure 4. It is preferable that the porosity of the partition walls 1 is a constant value throughout the entire honeycomb structure 4.

[0027] The shape of the cells 2 partitioned by the partition walls 1 is not particularly limited. For example, the shape of the cells 2 in a cross section perpendicular to the extension direction of the cells 2 can be a polygon. Examples of polygons include a triangle, a square, a pentagon, a hexagon, and an octagon. The shape of the cells 2 is preferably a triangle, a square, a pentagon, a hexagon, or an octagon, and more preferably a square or an octagon.

[0028] The peripheral wall 3 of the honeycomb structure 4 may be configured integrally with the partition walls 1, or may be a peripheral coating layer formed by applying a peripheral coating material to the outer peripheral side of the partition walls 1. For example, although not shown in the drawings, the peripheral coating layer can be provided on the outer peripheral side 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.

[0029] There is no particular limitation on the shape of the honeycomb structure 4. The honeycomb structure 4 may have an inflow end face 11 and an outflow end face 12 that are cylindrical, elliptical, polygonal, or the like.

[0030] There are no particular limitations on the size of the honeycomb structure 4, for example, the length from the inflow end face 11 to the outflow end face 12 and the size of the cross section perpendicular to the extension direction of the cells 2 of the honeycomb structure 4. When the honeycomb filter 100 is used as a filter for purifying exhaust gases, each size may be appropriately selected so as to obtain optimal purification performance.

[0031] The material of the partition walls 1 is not particularly limited. For example, the material of the partition walls 1 can be a material containing 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. The material constituting the partition walls 1 is preferably a material containing 90 mass% or more of the materials listed in the above group, more preferably a material containing 92 mass% or more, and particularly preferably a material containing 95 mass% or more. The silicon-silicon carbide composite material is a composite material formed using silicon carbide as an aggregate and silicon as a binder. The cordierite-silicon carbide composite material is a composite material formed using silicon carbide as an aggregate and cordierite as a binder.

[0032] The material of the plugging portions 5 is preferably a material that is considered to be preferable as the material of the partition walls 1. The material of the plugging portions 5 and the material of the partition walls 1 may be the same material or different materials.

[0033] In the honeycomb filter 100, a catalyst for purifying exhaust gas is preferably supported on the partition walls 1 that define the plurality of cells 2. Supporting a catalyst on the partition walls 1 means that the catalyst is coated on the surfaces of the partition walls 1 and the inner walls of the pores formed in the partition walls 1. This configuration makes it possible to convert CO, NOx, HC, and other substances in the exhaust gas into harmless substances through a catalytic reaction. It also promotes the oxidation of PM, such as collected soot. In the honeycomb filter 100 of this embodiment, it is particularly preferable that the catalyst is supported inside the pores of the porous partition walls 1. This configuration makes it possible to achieve both improved collection performance and reduced pressure loss after catalyst loading when a low catalyst amount is used. Furthermore, since the gas flow becomes uniform after catalyst loading, improved purification performance can also be expected.

[0034] There is no particular limitation on the catalyst supported on the partition walls 1. For example, a catalyst containing a platinum group element, which contains an oxide of at least one element selected from aluminum, zirconium, and cerium, can be used.

[0035] (2) Honeycomb filter manufacturing method: The method for manufacturing the honeycomb filter of the present invention is not particularly limited, and examples thereof include the following method. First, a plastic clay for manufacturing the honeycomb structure is prepared. The clay for manufacturing the honeycomb structure can be prepared by adding, as raw material powder, a material selected from the above-mentioned suitable materials for the partition walls, as appropriate, additives such as a binder, a pore-forming material, and water.

[0036] Next, the thus obtained clay is extrusion-molded to produce a columnar honeycomb molded body having partition walls that define a plurality of cells and an outer peripheral wall that is disposed to surround the partition walls. In the extrusion molding, a die having slits on the extrusion surface of the clay that form the inverted shape of the honeycomb molded body to be molded can be used as the extrusion die. In particular, it is preferable to use a die having slits so that the thickness T1 of the central partition walls 1a is 0.17 to 0.32 mm and the thickness T2 of the outer peripheral partition walls 1b is 70 to 90% of the thickness T1 of the central partition walls 1a. Next, the obtained honeycomb molded body is dried, for example, by microwaves and hot air.

[0037] Next, plugging portions are arranged in the openings of the cells of the dried honeycomb formed body. Specifically, for example, first, a plugging material containing raw materials for forming the plugging portions is prepared. Next, a mask is applied to the inlet end face of the honeycomb formed body so that the inlet cells are covered. Next, the previously prepared plugging material is filled into the openings of the outlet cells that are not covered with a mask on the inlet end face side of the honeycomb formed body. Thereafter, the plugging material is filled into the openings of the inlet cells on the outlet end face of the honeycomb formed body using the same method as above.

[0038] Next, the honeycomb formed body having the plugged portions disposed in either one of the openings of the cells is fired to produce a honeycomb filter. The firing temperature and firing atmosphere vary depending on the raw materials, and a person skilled in the art can select the optimum firing temperature and firing atmosphere for the selected materials. [Example]

[0039] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0040] Example 1 To 100 parts by mass of the cordierite raw material, 2 parts by mass of a pore-forming material, 2 parts by mass of a dispersing medium, and 7 parts by mass of an organic binder were added, mixed, and kneaded to prepare a clay. Alumina, aluminum hydroxide, kaolin, talc, and silica were used as the cordierite raw materials. Water was used as the dispersing medium. Methylcellulose was used as the organic binder. Dextrin was used as the dispersing agent. A water-absorbing polymer with an average particle diameter of 20 μm was used as the pore-forming material. In this example, the average particle diameter of each raw material refers to the particle diameter (D50) at 50% of the integrated value in the particle size distribution determined by laser diffraction and scattering.

[0041] Next, the clay was extruded using a die for producing a honeycomb formed body to obtain a honeycomb formed body having a cylindrical overall shape. The shape of the cells of the honeycomb formed body was rectangular.

[0042] Next, the honeycomb formed body was dried in a microwave dryer and further completely dried in a hot air dryer, after which both end faces of the honeycomb formed body were cut and adjusted to a predetermined size.

[0043] Next, a plugging material for forming plugging portions was prepared. After that, plugging portions were formed using the plugging material at the openings of predetermined cells on the inflow end face side of the dried honeycomb formed body and at the openings of the remaining cells on the outflow end face side.

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

[0045] The honeycomb filter of Example 1 had a cylindrical shape with circular inlet and outlet end faces. The diameters of the inlet and outlet end faces were 267 mm. The length of the honeycomb filter in the cell extension direction was 178 mm. The honeycomb filter of Example 1 had a central partition wall thickness T1 of 0.26 mm and a peripheral partition wall thickness T2 of 0.19 mm. The thicknesses of each partition wall are shown in Table 1. The "central partition wall thickness T1" and the "peripheral partition wall thickness T2" were measured according to the measurement method described above. The ratio of the peripheral partition wall thickness T2 to the central partition wall thickness T1 (i.e., T2 / T1 × 100%) was 73%. The results are shown in the "Partition wall thickness ratio (T2 / T1 × 100%)" column in Table 1. The outer peripheral portion where the thickness T2 of the outer peripheral partition wall was 0.19 mm was in a range of 11% of the radius r from the center of gravity O of the cross section of the honeycomb structure to the outer peripheral edge, starting from the outer peripheral edge of the cross section. The results are shown in the column "Existence range of outer peripheral portion relative to radius r" in Table 1.

[0046] In addition, the honeycomb filter of Example 1 has a porosity of 52% in the partition walls constituting the honeycomb structure, and a cell density of 47 cells / cm. 2 The results are shown in Table 1. The rate is The measurement was carried out using Autopore 9500 (trade name) manufactured by Micromeritics.

[0047] [Table 1]

[0048] The honeycomb filter of Example 1 was evaluated for "pressure loss" and "purification performance" by the following methods. Table 1 shows the results.

[0049] [Pressure loss] From the inlet end of the honeycomb filter, the flow rate is 20 Nm 3 / min, and the differential pressure between the inlet end face and the outlet end face of the honeycomb filter was measured. The measured differential pressure was taken as the pressure loss of the honeycomb filter, and the honeycomb filters of each Example and Comparative Example were evaluated based on the following evaluation criteria. In the following evaluation criteria, the "pressure loss ratio (%)" refers to the ratio (%) of the pressure loss of each honeycomb filter when the pressure loss value of the honeycomb filter of Comparative Example 1 is taken as 100%. Evaluation "Excellent": A pressure loss ratio (%) of 80% or less is evaluated as "Excellent." Evaluation "Good": A pressure loss ratio (%) exceeding 80% and not exceeding 90% is evaluated as "Good". Evaluation: "Acceptable": The pressure loss ratio (%) is rated as "acceptable" if it is greater than 90% and less than or equal to 100%. Evaluation: "Fail": If the pressure loss ratio (%) exceeds 100%, it is rated as "Fail."

[0050] [Purification performance] First, a test gas containing NOx was passed through the honeycomb filter. The amount of NOx in the gas discharged from the honeycomb filter was then analyzed using a gas analyzer. The temperature of the test gas flowing into the honeycomb filter was set to 200°C. The temperature of the honeycomb filter and the test gas was adjusted using a heater. An infrared imaging furnace was used as the heater. The test gas used was a mixture of nitrogen with 5% by volume of carbon dioxide, 14% by volume of oxygen, 350 ppm (volume basis) of nitric oxide, 350 ppm (volume basis) of ammonia, and 10% by volume of water. Regarding this test gas, a mixed gas containing water and other gases was prepared separately, and these were mixed in the piping when the test was performed. The gas analyzer used was a "MEXA9100EGR (trade name)" manufactured by HORIBA. The space velocity when the test gas flowed into the honeycomb filter was 100,000 (hr). -1) The NOx purification rate of the honeycomb filter was measured from the amount of NOx in the test gas and the amount of NOx in the gas discharged from the honeycomb filter. The purification performance ratio (%) of each honeycomb filter was then calculated, and the honeycomb filters of each Example and Comparative Example were evaluated based on the following evaluation criteria. In the following evaluation criteria, the "purification performance ratio (%)" refers to the ratio (%) of the NOx purification rate of each honeycomb filter when the value of the NOx purification rate of the honeycomb filter of Comparative Example 1 is taken as 100%. Evaluation "Excellent": A purification performance ratio (%) of 110% or more is considered "Excellent." Evaluation "Good": A purification performance ratio (%) of 105% or more and less than 110% is evaluated as "Good". Evaluation "Fair": A purification performance ratio (%) of 100% or more and less than 105% is evaluated as "Fair". Evaluation "Fail": The purification performance ratio (%) is less than 100%.

[0051] (Examples 2 to 6 and Comparative Examples 1 to 6) Honeycomb filters were produced in the same manner as the honeycomb filter of Example 1, except that the configuration of the honeycomb filter was changed as shown in Table 1.

[0052] The honeycomb filters of Examples 2 to 6 and Comparative Examples 1 to 6 were also evaluated for "pressure loss" and "purification performance" in the same manner as in Example 1. Table 1 shows the results.

[0053] (result) It was confirmed that the honeycomb filters of Examples 1 to 6 exceeded the performance of the honeycomb filter of Comparative Example 1, which was used as the standard, in the evaluation of pressure loss and purification performance.

[0054] The honeycomb filter of Comparative Example 2 had a partition wall thickness ratio of 92%, and the difference in thickness between the central partition wall and the peripheral partition wall was very small. Furthermore, the honeycomb filter of Comparative Example 2 also had a very narrow peripheral portion existing in an area of ​​5%. The honeycomb filter of Comparative Example 2 was evaluated as "unacceptable" in both pressure loss and purification performance.

[0055] The honeycomb filter of Comparative Example 3 had an extremely wide range of peripheral portions, 13%. The honeycomb filter of Comparative Example 3 was evaluated as "unacceptable" in terms of purification performance.

[0056] The honeycomb filter of Comparative Example 4 had a partition wall thickness ratio of 69%, and the difference in thickness between the central partition wall and the peripheral partition wall was very large. The honeycomb filter of Comparative Example 4 was evaluated as "unacceptable" in terms of purification performance.

[0057] The honeycomb filter of Comparative Example 5 had a central partition wall thickness T1 of 0.33 mm, which was too thick, and therefore the evaluation result of the pressure loss was "unacceptable."

[0058] In the honeycomb filter of Comparative Example 6, the area in which the outer periphery is present is as very narrow as 5%. 6 The honeycomb filter No. 1 was evaluated as "unacceptable" in terms of pressure loss. [Industrial Applicability]

[0059] The honeycomb filter of the present invention can be used as a filter for collecting particulate matter in exhaust gases. [Explanation of symbols]

[0060] 1: partition wall, 1a: central partition wall, 1b: peripheral partition wall, 2: cell, 2a: inlet cell, 2b: outlet cell, 3: peripheral wall, 4: honeycomb structure, 5: plugging portion, 11: inlet end face, 12: outlet end face, 15: central portion, 16: peripheral portion, 100: honeycomb filter, T1: thickness (thickness of central partition wall), T2: Thickness (Thickness of peripheral bulkhead).

Claims

[Claim 1] a columnar honeycomb structure having porous partition walls arranged to surround a plurality of cells that serve as fluid flow paths extending from an inflow end face to an outflow end face; a porous plugging portion disposed at either an end portion on the inflow end face side or an end portion on the outflow end face side of the cell, The honeycomb structure includes, in a cross section perpendicular to the cell extension direction, a central portion including a center of gravity O of the cross section, and a peripheral portion located outside the central portion, a thickness T1 of the partition wall at the central portion is 0.20 to 0.28 mm; a thickness T2 of the partition wall at the outer periphery is 73 to 90% of a thickness T1 of the partition wall at the central portion, the outer peripheral portion has a radius r ranging from the center of gravity O of the cross section to the outer peripheral edge as a starting point, and the radius r ranging from the center of gravity O of the cross section to the outer peripheral edge is in a range of 6 to 12%; The honeycomb structure has a cell density of 31 to 38 cells / cm 2 ; A honeycomb filter, wherein the partition walls have a porosity of 52 to 60%.

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