HONEYCOMB FILTER

Abstract

Honeycomb filter (100, 200), comprising: a columnar honeycomb structure (10) having provided porous partition walls (1) surrounding a plurality of cells serving as fluid passageways extending from an inflow end face (11) to an outflow end face (12); and porous sealing sections (5) provided either at the ends on the side of the inflow face (11) of the cells or at the ends on the side of the outflow face (12) of the cells, wherein the sealing sections (5) consist of a porous material, the honeycomb structure (10) has a central region (15) containing a center of gravity in a cross section orthogonal to a direction in which the cells extend, and a peripheral region (16) on a peripheral side farther from the central region (15), and an S2 / S1 denoting a ratio of an area S2 of the peripheral region (16) with respect to an area S1 of the central region (15) ranging from 0.1 to 0.5, the porosity P1 of a central sealing portion (5a), which is the sealing portion (5) present in the central region (15), is higher than the porosity P2 of a peripheral sealing portion (5b), which is the sealing portion (5) present in the peripheral region (16), and the porosity P1 of the central sealing section (5a) ranges from 76% to 85% and the porosity P2 of the peripheral sealing section (5b) ranges from 60% to 75%, wherein the honeycomb filter (100, 200) further comprises a plurality of the center sealing portions (5a) and the peripheral sealing portions (5b) arranged from a center toward a circumference in a radial direction of the cross section of the honeycomb structure (10), wherein the center sealing portions (5a) and the peripheral sealing portions (5b) are configured such that each porosity of the center sealing portions (5a) and the peripheral sealing portions (5b) arranged in the order in the circumferential direction decreases gradually from the center sealing portions (5a) provided closer to a center in the radial direction of the cross section.

Description

The present application is an application based on JP 2019-066 133 filed on 29.3.2019 in the Japanese Patent Office, the entire contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTIONField of the InventionThe present invention relates to a honeycomb filter. More particularly, the present invention relates to a honeycomb filter which can improve exhaust gas purifying performance and which has high isostatic strength when loaded with an exhaust gas purifying catalyst.DESCRIPTION OF THE RELATED ARTHeretofore, as a filter configured to trap particulate matter in exhaust gas discharged from an internal combustion engine such as a diesel engine or an apparatus configured to purify toxic gas components such as CO, HC and NOx, a honeycomb filter using a honeycomb structure has been known (see Patent Documents 1 to 4). The honeycomb structure has partition walls formed of a porous ceramic such as cordierite or silicon carbide, and includes a plurality of cells defined by the partition walls. In the honeycomb filter, the above honeycomb structure is provided with sealing portions that alternately seal the open ends on the inflow end face side of the plurality of cells and the open ends on the outflow end face side thereof. In other words, the honeycomb filter has a structure in which the inflow cells having the inflow end face side open and the outflow end face side sealed and the outflow cells having the inflow end face side sealed and the outflow end face side open are alternately arranged with the partition walls interposed therebetween. Further, in the honeycomb filter, the porous partition walls of the honeycomb structure function as filters that trap the particulates in an exhaust gas. Hereinafter, the particulate matter contained in an exhaust gas may be referred to as "PM". "PM" is an abbreviation for "particulate matter".In recent years, a honeycomb filter for purifying an exhaust gas discharged from an engine of an automobile or the like has been required to achieve a decrease in pressure loss mainly for improving the performance of fuel economy of automobiles. As one of the measures for reducing the pressure loss as compared with the conventional partition wall, investigations have been carried out on "thinner walls" to reduce the thickness of the partition walls of a honeycomb structure and "higher porosity" to further increase the porosity of the partition walls.[Patent Document 1] JP 2015-164 712 A[Patent Document 2] JP 2010-221189 A[Patent Document 3] JP 2013-212 49 A[Patent Document 4] International Publication WO 2007 / 094 499 A1SUMMARY OF THE INVENTIONConventional honeycomb filters have presented a problem in that it is difficult to obtain satisfactory exhaust gas purifying performance when the honeycomb filters are loaded with an exhaust gas purifying catalyst. In recent years, for example, there has been a demand for improving the purification performance of honeycomb filters for purifying exhaust gases discharged from engines of automobiles to meet the exhaust regulations expanded each year due to the perception of environmental problems. In order to respond to the demand, for example, it has been necessary to promptly activate a catalyst loaded in a honeycomb filter by increasing the temperature rise speed of the catalyst. Consequently, there have been demands for developing a honeycomb filter that can provide satisfactory exhaust gas purifying performance immediately.Further, the honeycomb filters are required to have improved isostatic strength. For example, when a honeycomb filter is used as a filter for purifying an exhaust gas, the honeycomb filter is sometimes used by being accommodated in a shell body such as a metal shell. The accommodation of a honeycomb filter in a case body such as a metal case may be referred to as a mono-case. In the case of packaging a honeycomb filter, the honeycomb filter is held in a packaging body by applying a surface pressure to the circumferential surface of the honeycomb filter through the intermediary of a holding material such as a mat. When such a canning is carried out, the honeycomb filter is damaged by the surface pressure of compression in some cases, and there have been requirements for developing a honeycomb filter having high isostatic strength.The present invention has been made in view of the above-described problems of the prior art. The present invention provides a honeycomb filter which can improve exhaust gas purifying performance and which has high isostatic strength when loaded with an exhaust gas purifying catalyst.According to the present invention, a honeycomb filter described below is provided.[1] A honeycomb filter comprising:a pillar-shaped honeycomb structure having porous partition walls provided surrounding a plurality of cells serving as fluid passage passages extending from an inflow end face to an outflow end face; andporous sealing portions provided either at the ends on the inflow end face side of the cells or at the ends on the outflow end face side of the cells,wherein the sealing portions are made of a porous material,the honeycomb structure has a center region including a center of gravity in a cross section orthogonal to a direction in which the cells extend and a peripheral region on a peripheral side farther from the center region, and an S 2 / S 1 indicating a ratio of an area S 2 of the peripheral region with respect to an area S 1 of the center region extending from 0.1 to 0.5,the porosity P1 of a middle seal portion, which is the seal portion present in the middle region, is higher than the porosity P2 of a circumferential seal portion, which is the seal portion present in the circumferential region, andThe porosity P1 of the central sealing portion extends from 76% to 85%, and the porosity P2 of the peripheral sealing portion extends from 60% to 75%. The honeycomb filter further includes a plurality of the center sealing portions and the circumferential sealing portions arranged from a center toward a circumference in a radial direction of the cross section of the honeycomb structure, wherein the center sealing portions and the circumferential sealing portions are configured such that each porosity of the center sealing portions and the circumferential sealing portions arranged in the order toward the circumference decreases stepwise from the center sealing portions provided closer to a center in the radial direction of the cross section.[3] The honeycomb filter described in the above [1], wherein a cell structure of the honeycomb structure is the same in the center area and the peripheral area.[4] The honeycomb filter described in any one of the above [1] to [2], wherein the porosity of the partition walls extends from 52% to 66%.[5] The honeycomb filter described in any one of the above [1] to [3], wherein the value of the porosity P2 of the circumferential sealing portions in the direction in which the cells extend remains constant.The honeycomb filter according to the present invention provides an effect that enables the exhaust gas purification performance to be improved, and also has high isostatic strength when the honeycomb filter is loaded with an exhaust gas purification catalyst. The honeycomb filter according to the present invention is particularly effective as a honeycomb filter provided with a honeycomb structure having higher porosity. More specifically, the porosity P 1 of the center sealing portions is higher than the porosity P 2 of the circumferential sealing portions, so that the temperature of a center region including the center sealing portions having a relatively higher porosity immediately rises, thus making it possible to promptly activate the exhaust gas purification catalyst. Further, the circumferential seal portions having relatively low porosity enable isostatic strength to be increased. Consequently, damage or the like to the honeycomb filter can be effectively suppressed even when a high surface pressure of compression is applied when the honeycomb filter is shot into a shell body such as a metal shell.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a perspective view schematically showing an embodiment of a honeycomb filter according to the present invention; FIG. 2 is a plan view showing the inflow end face side of the honeycomb filter shown in FIG. 1 ; FIG. 3 is a plan view showing the outflow end face side of the honeycomb filter shown in FIG. 1 ; FIG. 4 is a sectional view schematically showing the cross section taken along A-A' of FIG. 2; and FIG. 5 is a sectional view schematically showing another embodiment of the honeycomb filter according to the present invention.DESCRIPTION OF THE PREFERRED EMBODIMENTSHereinafter, the embodiments of the present invention will be described; however, the present invention is not limited to the following embodiments. It should therefore be appreciated that those optionally produced by adding modifications, improvements, and the like to the following embodiments based on the general knowledge of a person skilled in the art without departing from the spirit of the present invention are also covered by the scope of the present invention.(1) Honeycomb FilterAn embodiment of the honeycomb filter according to the present invention is a honeycomb filter 100 shown in Figs. 1 to 4. FIG. 1 is a perspective view schematically showing the embodiment of the honeycomb filter according to the present invention. FIG. 2 is a plan view of the inflow end face side of the honeycomb filter shown in FIG. 1. FIG. 3 is a plan view of the outflow end face side of the honeycomb filter shown in FIG. 1. FIG. 4 is a sectional view schematically showing a cross section taken along A-A' of FIG. 2.As shown in FIGS. 1 to 4, the honeycomb filter 100 includes a honeycomb structure 10 and the sealing portions 5. the honeycomb structure 10 has the arranged porous partition walls 1 surrounding a plurality of cells 2 serving as fluid passage passages extending from an inflow end face 11 to an outflow end face 12. The honeycomb structure 10 is a columnar structure having the inflow end face 11 and the outflow end face 12 as their both end faces. In the honeycomb filter 100 of the present embodiment, the honeycomb structure 10 further includes a provided circumferential wall 3 enclosing the partition walls 1 on the circumferential side surface thereof.The seal portions 5 are provided either at the ends on the inflow end face 11 side of the cells 2 or at the ends on the outflow end face 12 side of the cells 2 to seal the open ends of the cells 2. The seal portions 5 are porous substances (i.e., porous bodies) made of a porous material. In the honeycomb filter 100 shown in FIGS. 1 to 4, the predetermined cells 2 having the seal portions 5 provided at the ends on the inflow end face 11 side and the remaining cells 2 having the seal portions 5 provided at the ends on the outflow end face 12 side are alternately arranged with the partition walls 1 interposed therebetween. In the following description, the cells 2 having the seal portions 5 provided at the ends on the inflow end face 11 side may be referred to as "the outflow cells 2 b". The cells 2 having the seal portions 5 provided at the ends on the outflow end face 12 side may be referred to as "the inflow cells 2 a".In the honeycomb filter 100, the honeycomb structure 10 has a center portion 15 including the center of gravity in a cross section orthogonal to the extending direction of the cells 2, and a peripheral portion 16 located on the circumferential side with respect to the center portion 15. Hereinafter, "the cross section orthogonal to the extending direction of the cells 2 of the honeycomb structure 10" may be simply referred to as "the cross section of the honeycomb structure 10". Further, "the center of gravity" of the cross section of the honeycomb structure 10 refers to the center of gravity of the cross section in a geometric sense (in other words, the geometric center point). In the honeycomb filter 100, the ratio of an area S 2 of the circumferential region 16 with respect to an area S 1 of the center region 15, that is, S 2 / S 1, extends from 0.1 to 0.5.The honeycomb filter 100 is configured such that the porosity P 1 of the center sealing portions 5 awhich are the sealing portions 5 present in the center region 15 is higher than the porosity P 2 of the circumferential sealing portions 5 bwhich are the sealing portions 5 present in the circumferential region 16. With this configuration, the honeycomb filter 100 provides an effect that enables the exhaust gas purification performance to be improved, and also has high isostatic strength when loaded with an exhaust gas purification catalyst. The honeycomb filter 100 is effectively used particularly in the honeycomb filter 100 provided with the honeycomb structure 10 having higher porosity. More specifically, the porosity P 1 of the middle seal portions 5 ais higher than the porosity P 2 of the circumferential seal portions 5 b, so that the temperature of the middle region 15 containing the middle seal portions 5 awith the relatively higher porosity immediately rises, thus making it possible to promptly activate the exhaust gas purification catalyst. Further, the circumferential sealing portions 5 bhaving the relatively lower porosity enable isostatic strength to be improved. Consequently, damage or the like to the honeycomb filter 100 can be effectively suppressed even when a high surface pressure of compression is applied when the honeycomb filter 100 is embedded in a shell body such as a metal case.When the honeycomb filter 100 is configured such that the porosity P 1 of the center sealing portions 5 aprovided in the center region 15 is equal to or less than the porosity P 2 of the circumferential sealing portions 5 bprovided in the circumferential region 16, the above effect is not obtained. Hereinafter, the middle seal portions 5 aprovided in the middle portion 15 may be simply referred to as "the middle seal portions 5 aof the middle portion 15". Further, the peripheral sealing portions 5 bprovided in the peripheral region 16 may be referred to as "the peripheral sealing portions 5 bof the peripheral region 16".There is no particular limitation on the shape of the center portion 15 in that the center portion 15 is a portion including the center of gravity of the cross section of the honeycomb structure 10. The center region 15 is the region where the center seal portions 5 aare located, which are the seal portions 5 having a porosity ranging from 76% to 85%. Further, the peripheral region 16 is a region where the peripheral sealing portions 5 b, which are the sealing portions 5 having a porosity ranging from 60% to 75%, are located. For example, the center portion 15 may have the center of gravity at the same position as that of the honeycomb structure 10, and may be shaped similarly to or differently from the circumferential shape of the honeycomb structure 10. Forming the center portion 15 similar to the circumferential shape of the honeycomb structure 10 causes the above effects to be further exhibited effectively.The porosity of the sealing portions 5 can be measured as described below. A cell equivalent portion including a sealing portion 5 and the partition walls 1 around the sealing portion 5 is cut out from the honeycomb filter 100 and processed to remove the partition walls 1 around the sealing portion 5. Thereafter, the mass of the sealing portion 5 is measured, and the porosity is calculated based on the measured mass and the true density of a sealing material constituting the sealing portion 5. When the porosity of the plugging portion 5 is measured, the porosity of all the plugging portions 5 provided at the ends of the cells 2 of the honeycomb structure 10 is to be measured.By measuring the porosity of the sealing portions 5 as described above, the central region 15 and the peripheral region 16 can be defined. More specifically, the region where the center sealing portions 5 aare located, which are the sealing portions 5 having a porosity ranging from 76% to 85%, may be defined as the center region 15. Further, the region where the circumferential sealing portions 5 b, which are the sealing portions 5 having a porosity ranging from 60% to 75%, are located may be defined as the circumferential region 16. In the honeycomb filter 100 of the present embodiment, the seal portions 5 that seal the open ends of the cells 2 are preferably either the center seal portions 5 athat have a porosity ranging from 76% to 85% or the circumferential seal portions 5 bthat have a porosity ranging from 60% to 75%.The porosity P 1 of the center seal portions 5 aextends from 76% to 85%, preferably extends from 77% to 85%, and more preferably extends from 80% to 85%. It is not preferable in terms of cleaning performance after catalyst coating that the porosity P 1 of the center sealing portions 5 ais below 76%. It is not preferable that the porosity P 1 of the middle seal portions 5 aexceeds 85% in view of thermal shock resistance and wear or scraping (erosion) of the seal portions and the like attributable to the foreign matters coming together with exhaust gas flow.The porosity P 2 of the circumferential sealing portions 5 bextends from 60% to 75%, preferably extends from 60% to 70%, and more preferably extends from 60% to 65%. It is not preferable in terms of thermal shock resistance that the porosity P 2 of the circumferential sealing portions 5 bis below 60%. It is not preferable in terms of isostatic strength, which is the strength of the filter itself, that the porosity P2 of the circumferential sealing portions 5b exceeds 75 %.It is not preferable that the area ratio (S 2 / S 1), which is the ratio of the area S 2 of the peripheral region 16 with respect to the area S 1 of the central region 15, is less than 0.1 because the peripheral region 16 is too small, making it difficult to exhibit the above effect. On the other hand, it is not preferable that the area ratio (S 2 / S 1) exceeds 0.5 because the center portion 15 is too small, making it difficult to exhibit the above effect. The area ratio (S 2 / S 1) preferably ranges from 0.1 to 0.5, and more preferably ranges from 0.15 to 0.45.The honeycomb filter 100 has a plurality of center sealing portions 5 aand circumferential sealing portions 5 bdisposed from the center in the radial direction of the cross section of the honeycomb structure 10 toward the circumference. The honeycomb filter 100 is configured such that the value of the porosity P 1 of the center sealing portions 5 aprovided in the center region 15 is substantially constant and the value of the porosity P 2 of the circumferential sealing portions 5 bprovided in the circumferential region 16 is substantially constant. However, the value of the porosity P 1 of the center sealing portions 5 ain the center region 15 may vary within the center region 15. Further, the value of the porosity P 2 of the circumferential sealing portions 5 bin the circumferential region 16 may vary within the circumferential region 16. As in a honeycomb filter 200 shown in FIG. 5, for example, the center sealing portions 5 aand the circumferential sealing portions 5 bmay be configured as described below. The center sealing portions 5 aand the circumferential sealing portions 5 bmay be configured such that the porosity of the center sealing portions 5 aand the porosity of the circumferential sealing portions 5 barranged in the order toward the circumference gradually decrease from the center sealing portions 5 aprovided closer to the center in the radial direction of the cross section. In other words, the honeycomb filter 200 shown in FIG. 5 is configured such that the porosity of each of the sealing portions 5 gradually decreases as the distance of the sealing portions 5 from the center of the cross section of the honeycomb structure 10 increases toward the periphery. The honeycomb filter 200 shown in FIG. 5 is preferable in terms of thermal shock resistance and erosion resistance. FIG. 5 is a sectional view schematically showing another embodiment of the honeycomb filter according to the present invention. In the honeycomb filter 200 shown in FIG. 5, the same constituent elements as those of the honeycomb filter 100 shown in FIGS. 1 to 4 are assigned the same reference numerals, and detailed descriptions thereof are omitted.In addition, in the honeycomb filter 200 shown in FIG. 5, the porosity P 1 of the center seal portions 5 aextends from 76% to 85%, while the porosity P 2 of the circumferential seal portions 5 bextends from 60% to 75%.The area S 1 of the center region 15 and the area S 2 of the peripheral region 16 of the honeycomb filter 100 shown in FIGS. 1 to 4 can be determined according to the following method, for example. First, the porosity of each of the sealing portions 5 on the inflow end face 11 side and on the outflow end face 12 side of the honeycomb filter 100 is calculated from the mass thereof according to the above method, identifying the boundary between the center sealing portions 5a and the circumferential sealing portions 5b. The boundary between the center sealing portions 5 aand the circumferential sealing portions 5 bmakes the boundary between the center region 15 and the circumferential region 16 in a plane orthogonal to the extending direction of the cells 2 of the honeycomb structure 10. Further, the area S 2 is calculated based on the difference between the area of the plane orthogonal to the extending direction of the cells 2 of the honeycomb structure 10 and the area S 1.There is no particular limitation on the length of the cell 2 in the extending direction of each of the seal portions 5. the length in the extending direction of the cell 2 of each of the seal portions 5 preferably extends from 3 mm to 9 mm, for example, and more preferably extends from 3 mm to 7 mm. It is not preferable that the length of the sealing portions 5 be less than 3 mm because the sealing portions 5 sometimes slightly decrease if the inflow end face 11 of the honeycomb filter 100 is dent or split. It is also not preferable that the length of the seal portions 5 exceeds 9 mm because the area through which a gas passes decreases, resulting in an increase in pressure loss.In the sealing portions 5 including the middle sealing portions 5 aand the circumferential sealing portions 5 b, preferably, the value of the porosity in the extending direction of the cell 2 is substantially constant for each of the sealing portions 5. More specifically, each of the seal portions 5 is preferably made of a porous material having substantially the same porosity as a whole, instead of locally increasing or decreasing the porosity by, for example, applying a glaze or the like to the surface on the inflow end face 11 side or the outflow end face 12 side.In the honeycomb structure 10, the porosity P 3 of the partition walls 1 preferably extends from 52% to 66%, and more preferably from 55% to 63%. The honeycomb filter 100 exhibits another marked effect when the honeycomb structure 10 having high porosity is used, wherein the porosity P 3 of the partition walls 1 extends from 55% to 63%. The porosity P 3 of the partition walls 1 denotes a value measured by the mercury pressing method. The porosity P 3 of the partition walls 1 can be measured using, for example, AutoPore 9500 (trade name) of Micromeritics. A part of the partition walls 1 is cut out from the honeycomb structure 10 to obtain a test piece, and the measurement of the porosity P 3 of the partition walls 1 can be performed using the test piece obtained as described above. The porosity P 3 of the partition walls 1 preferably has a constant value throughout the honeycomb structure 10. The absolute value of the difference between a maximum value and a minimum value of the porosity P 3 of the partition walls 1 is, for example, preferably 5% or less.In the honeycomb structure 10, the thickness of the partition walls 1 preferably extends from 0.15 mm to 0.30 mm, and more preferably from 0.15 mm to 0.25 mm, and particularly preferably from 0.20 mm to 0.25 mm. The thickness of the partition walls 1 can be measured using, for example, a scanning electron microscope or a microscope. If the thickness of the partition walls 1 is below 0.15 mm, sufficient strength cannot be obtained. On the other hand, when the thickness of the partition walls 1 exceeds 0.30 mm, the pressure loss of the honeycomb filter 100 may increase.There is no particular limitation on the shapes of the cells 2 defined by the partition walls 1. The shapes of the cells 2 in the cross section orthogonal to the extending direction of the cells 2 may be, for example, polygonal, circular, elliptic, or the like. A polygonal shape may be triangular, quadrangular, pentagonal, hexagonal, octagonal, or the like. The shapes of the cells 2 are preferably triangular, quadrangular, pentagonal, hexagonal or octagonal. Regarding the shapes of the cells 2, all the cells 2 may have the same shape or different shapes. For example, quadrangular cells and octagonal cells may be mixed, although not shown. Further, as for the sizes of the cells 2, all the cells 2 may have the same size or different sizes. Among the plurality of cells, for example, some cells may be larger and some other cells may be relatively smaller, although not shown. In the present invention, the term "cells" means the spaces surrounded by the partition walls.In the honeycomb filter 100, the cell structure of the honeycomb structure 10 is preferably the same in the center region 15 and the peripheral region 16. This configuration causes a gas to flow smoothly, so that the configuration is preferable in terms of pressure loss. The cell structure means the structure of the cells 2 in the honeycomb structure 10 including the thickness of the partition walls, the shapes of the cells 2, the cell density, and the like.In the honeycomb structure 10, the cell density of the cells 2 defined by the partition walls 1 preferably extends from 27 to 51 cells / cm 2 and more preferably from 31 to 47 cells / cm 2. This configuration makes it possible to suppress an increase in pressure loss while maintaining the PM trapping performance of the honeycomb filter 100.The circumferential wall 3 of the honeycomb structure 10 may be configured integrally with the partition walls 1, or may be a circumferential coating layer formed by applying a circumferential coating material enclosing the partition walls 1. The circumferential coating layer may be provided on the circumferential side of the partition walls after the partition walls and the circumferential wall are integrally formed, and then the formed circumferential wall is removed by a publicly known method such as grinding in a manufacturing process, although not shown.The honeycomb structure 10 may be pillar-shaped, and the shapes of the inflow end face 11 and the outflow end face 12 may be circular, elliptical, polygonal, or the like.There is no particular limitation on the size of the honeycomb structure 10, for example, the length from the inflow end face 11 to the outflow end face 12 and the size of the cross section orthogonal to the extending direction of the cells 2 of the honeycomb structure 10. Each size may be appropriately selected so that an optimum purification performance is obtained when the honeycomb filter 100 is used as a filter for purifying an exhaust gas. The length from the inflow end face 11 to the outflow end face 12 of the honeycomb structure 10 preferably extends from 90 mm to 160 mm, for example, and more preferably extends from 120 mm to 140 mm. Further, the area of the cross section orthogonal to the extending direction of the cells 2 of the honeycomb structure 10 preferably extends from 100 cm 2 to 180 cm 2 and more preferably from 110 cm 2 and 150 cm 2.The material of the partition walls 1 preferably includes, for example, at least one material selected from a group including silicon carbide, cordierite, a silicon-silicon carbide composite material, a cordierite-silicon carbide composite material, silicon nitride, mullite, alumina, and aluminum titanate.There is also no particular limitation on the material of the seal portions 5, for example, the same material as the above-described material of the partition walls 1 may be used. In the sealing portions 5, moreover, the material of the middle sealing portions 5 aand the material of the circumferential sealing portions 5 bmay be different or the same.(2) Manufacturing Method of Honeycomb FilterThere is no particular limitation on the method for manufacturing the honeycomb filter according to the present invention, and for example, the following method may be used. First, a plastic kneaded material for manufacturing the honeycomb structure is prepared. The kneaded material for manufacturing the honeycomb structure can be prepared by adding an additive such as a binder, a pore former, and optionally water to a material selected from the above suitable materials of the partition walls as raw material powders.Subsequently, the kneaded material obtained as described above is subjected to extrusion, to thereby obtain a pillar-shaped honeycomb formed body having the partition walls defining a plurality of cells and a provided circumferential wall surrounding the partition walls. Then, the obtained honeycomb formed article is dried by, for example, microwave and hot air.Then, sealing portions are provided at the open ends of the cells of the dried honeycomb formed body. More specifically, for example, first, a sealing material containing a raw material for forming the sealing portions is prepared. Then, a mask is provided on the inflow end face of the honeycomb formed body to cover the inflow cells. Next, the sealing material that has been prepared is filled in the open ends of the outflow cells that are not provided with the mask on the inflow end side of the honeycomb formed body. Thereafter, the sealing material for the outflow end face of the honeycomb formed body is also filled in the open ends of the inflow cells by the same method described above.In manufacturing the honeycomb filter according to the present invention, two types of sealing materials, namely, a center sealing material for forming the center sealing portions and a circumferential sealing material for forming the circumferential sealing portions, are prepared to provide the sealing portions. For the center sealing material, the ratio of a pore-forming raw material (e.g., a pore former) is set to be high to set the porosity P 1 of the center sealing portions to be relatively higher. Further, for the circumferential sealing material, the ratio of a pore-forming raw material (e.g., a pore former) is set low to set the porosity P 2 of the circumferential sealing portions to be relatively lower. Then, the two types of sealing materials are properly used to seal the open ends of the cells in a predetermined range. More specifically, the center sealing material is used to fill the open ends of the cells in a region which will be the center region in the honeycomb formed body, while the circumferential sealing material is used to fill the open ends of the cells in a region which will be the circumferential region in the honeycomb formed body.Then, the honeycomb formed body is fired with the sealing portions provided at the open ends of one side of the cells to produce the honeycomb filter according to the present invention. The firing temperature and the firing atmosphere vary according to a material, and a skilled artisan can select a firing temperature and a firing atmosphere that are most suitable for a selected material.(Examples)The following describes the present invention further specifically by Examples; however, the present invention is by no means limited by the Examples.(Example 1)Ten parts by mass of a pore former, 20 parts by mass of a dispersing medium, and 1 part by mass of an organic binder were added to 100 parts by mass of a cordierite forming raw material and mixed, thereby kneading the mixture to produce a kneaded material. As the starting material forming cordierite, alumina, aluminum hydroxide, kaolin, talc and silica were used. As the dispersing medium, water was used. As the organic binder, methyl cellulose was used. As the dispersant, dextrin was used. As the pore former, coke having an average particle diameter of 15 μm was used.Subsequently, the kneaded material was subjected to extrusion using an extruding die for producing honeycomb formed bodies, thereby obtaining a honeycomb formed body whose entire shape was a round pillar shape. The shape of the cells of the honeycomb formed body was quadrangular.Subsequently, the honeycomb formed body was dried by a microwave dryer and further dried by a hot air dryer to completely dry the honeycomb formed body. Thereafter, both end faces of the honeycomb formed body were cut to predetermined dimensions.Subsequently, the sealing materials were prepared to form the sealing portions. In Example 1, the two types of sealing materials, namely, the center sealing material for forming the center sealing portions and the peripheral sealing material for forming the peripheral sealing portions were prepared. For the center sealing material, in preparing the sealing material, the proportion of the pore-forming raw material was set to be relatively higher as compared with the peripheral sealing material. For the peripheral sealing material, in producing the sealing material, the proportion of the pore-forming raw material was set to be relatively smaller as compared with the center sealing material.Subsequently, using the above two types of sealing materials, the center sealing portions and the circumferential sealing portions were formed at the open ends of the cells on the inflow end face side of the dried honeycomb formed body. More specifically, a mask was first provided on the inflow end face of the honeycomb formed body to cover the inflow cells. Then, either the center sealing material or the circumferential sealing material was filled in the open ends of the outflow cells not provided with the mask, thereby forming the center sealing portions and the circumferential sealing portions. More specifically, the open ends of the cells in the area which will be the center area were filled with the medium sealing material, while the open ends of the cells in the area which will be the peripheral area were filled with the peripheral sealing material.Subsequently, the outflow end face of the honeycomb formed body was further provided with a mask to cover the outflow cells. Then, either the middle sealing material or the circumferential sealing material was filled in the open ends of the inflow cells not provided with the mask, thereby forming the middle sealing portions and the circumferential sealing portions.Subsequently, the honeycomb formed body in which the seal portions were formed was degreased and fired, thereby producing the honeycomb filter of Example 1.The honeycomb filter of Example 1 was round in a pillar shape, and the shapes of its inflow end face and its outflow end face were circular. The diameters of the inflow end face and the outflow end face were 118 mm. Further, the length of the cells of the honeycomb filter in the extending direction was 127 mm. In the honeycomb filter of Example 1, the thickness of the partition walls was 0.22 mm, the porosity P 3 of the partition walls was 55%, and the cell density was 31 cells / cm 2. Table 1 shows the thickness of the partition walls, the porosity P 3 of the partition walls, and the cell density of the honeycomb filter. The porosity P3 of the partition walls was measured using AutoPore 9500 (trade name) of Micromeritics.The honeycomb filter of Example 1 was configured such that the porosity P 1 of the center seal portions which were the seal portions present in the center region was higher than the porosity P 2 of the circumferential seal portions which were the seal portions present in the circumferential region. The porosity P1 of the center seal portions ranged from 79% to 81%, while the porosity P2 of the perimeter seal portions ranged from 64% to 66%. The porosity P1 of the middle seal portions and the porosity P2 of the circumferential seal portions were calculated as follows. After processing to remove only the sealing portions, the masses of the sealing portions were measured, and the porosity P1 and the porosity P2 were calculated from the measured masses and the true density of the sealing materials. In the honeycomb filter of Example 1, the area ratio, which is the ratio of the area S 2 of the peripheral portion with respect to the area S 1 of the center portion (S 2 / S 1), was 0.19, and the results are shown in the column "area ratio between the center portion and the peripheral portion (S 2 / S 1)" of Table 1. In Table 1, the columns of "porosity P1 (max.)(%)" and "porosity P1 (min.)(%)" of the "center sealing portion" show the maximum and minimum values obtained when the porosity P1 differs in the center sealing portions of the center portion. Further, in Table 1, the columns of "porosity P2(max.)(%)" and "porosity P2(min.)(%)" of the "circumferential sealing portion" show the maximum value and the minimum value obtained when the porosity P2 differs in the circumferential sealing portions of the circumferential portion. If the porosity of the center seal portions and the porosity of the circumferential seal portions are constant in the regions, then the values in the gaps are the same. (Table 1) (Table 1)Example 10,2255310,1981796664Example 20,2258310,2985837371Example 30,2263470,4177766462Example 40,2261470,1780786160Example 50,2160470,4177766563Example 60,2464470,3282807270Comparative Example 10,236247-84828482Comparative Example 20,225431-76747674Comparative Example 30,226347-81798179Comparative Example 40,2261470,5280786160On the honeycomb filter of Example 1, the "evaluation of exhaust gas purifying performance" and the "evaluation of isostatic strength" were carried out according to the following method. Table 2 shows the results.(Evaluation of Exhaust Gas Purification Performance)First, exhaust gas purifiers were produced using the honeycomb filters of Examples as the filters for purifying an exhaust gas. Each of the manufactured exhaust gas purifiers was connected to an outlet side of an engine exhaust manifold of an automobile with a direct injection type 1,2-I gasoline engine, and the concentration of NOx contained in the gas discharged through the outlet port of the exhaust gas purifier was measured to determine the NOx purification rate. Based on the value of the NOx purification rate in each measurement, the exhaust gas purification performance was evaluated according to the following evaluation standard. The column "NOx purification rate ratio (%)" of Table 2 shows the value of the NOx purification rate (%) of the exhaust gas purifier using the honeycomb filter of each example when the value of the NOx purification rate of the exhaust gas purifier using the honeycomb filter of Comparative Example 1 is defined as 100%.Evaluation "excellent": When the ratio of the NOx purification rate is 105% or more, the evaluation result is referred to as "excellent".Evaluation "good": When the ratio of the NOx purification rate is 102 % or more and less than 105%, the evaluation result is referred to as "good".Rating "acceptable": If the ratio of the NOx purification rate exceeds 100% and is below 102%, then the rating result is referred to as "acceptable".Evaluation "Failed": When the ratio of the NOx purification rate is 100% or less, the evaluation result is referred to as "Failed".(Evaluation of isostatic strength)The isostatic strength (MPa) of the honeycomb filter of each Example and each Comparative Example was measured according to the isostatic breaking strength measurement method specified by JASO Standard M505-87, which is the automobile standard issued by the Society of Automotive Engineers of Japan, Inc. Table 2 shows the measured isostatic strength (MPa) values. Further, the isostatic strength ratios of the honeycomb filters when the isostatic strength value of the honeycomb filter of Comparative Example 1 is defined as 100% are given in the column of "isostatic strength ratio (%)" of Table 2. Regarding the isostatic strength evaluation, the honeycomb filter of each example was evaluated according to the following evaluation standard.Evaluation "excellent": When the value of the ratio of isostatic strengths is 120% or more, the evaluation result is referred to as "excellent".Evaluation "good": When the value of the ratio of isostatic strengths is 110 % or more and is below 120 %, the evaluation result is referred to as "good".Rating "acceptable": If the value of the ratio of isostatic strengths exceeds 100% and is below 110%, then the rating result is referred to as "acceptable".Evaluation "Failed": When the value of the ratio of isostatic strengths is 100% or less, the evaluation result is referred to as "Failed".(Examples 2 to 6)The honeycomb filters were produced according to the same method as that used for the honeycomb filter of Example 1, except that the configurations of the honeycomb filters were changed as shown in Table 1. In Examples 2 to 6, the porosity P 1 of the center sealing portions and the porosity P 2 of the peripheral sealing portions were changed by changing the amount of a foamable resin when a sealing material was produced.(Comparative Examples 1 to 4)The honeycomb filters were produced according to the same method as that used for the honeycomb filter of Example 1, except that the configurations of the honeycomb filters were changed as shown in Table 1. In Comparative Examples 1 to 4, the porosity P1 of the center sealing portions and the porosity P2 of the peripheral sealing portions were changed by changing the amount of a foamable resin when a sealing material was produced.Further, on the honeycomb filters of Examples 2 to 6 and Comparative Examples 1 to 4, "evaluation of exhaust gas purifying performance" and "evaluation of isostatic strength" were carried out according to the same method as that used for Example 1. Table 2 shows the results. (Table 2) (Table 2)Example 1102139good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good 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excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellentExample 2108121excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent 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acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptablegood good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good 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acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptableExample 6101117acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptable acceptablegood good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good good goodComparative Example 1100100ReferenceReferenceComparative Example 299130Failedexcellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellentComparative Example 310587excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellentFailedComparative Example 499126Failedexcellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent excellent(Results)The evaluation results verified that the isostatic strength and the exhaust gas purifying performance of the honeycomb filters of Examples 1 to 6 were higher than those of the honeycomb filter of Comparative Example 1 which was the reference. It was thus found that the honeycomb filters of Examples 1 to 6 exhibited higher cleaning performance as compared with the conventional honeycomb filters while maintaining the required isostatic strength. Regarding the honeycomb filter of Comparative Example 4, the area ratio between the center region and the peripheral region (S 2 / S 1) exceeded 0.5 with the ratio of the NOx purification rate (%) being low, and therefore the evaluation result of the exhaust gas purification performance was "failed".Industrial applicabilityThe honeycomb filter according to the present invention can be used as a filter for trapping particulate matter in an exhaust gas.Description of the Reference Numerals

[0068] 1: Partition wall; 2: cell; 2a: inflow cell; 2b: outflow cell; 3: circumferential wall; 5: sealing portion; 5a: middle sealing portion; 5b: circumferential sealing portion; 10: honeycomb structure; 11: inflow end face; 12: outflow end face; 15: middle portion; 16: circumferential portion; and 100, 200: honeycomb filter.

Claims

A honeycomb filter (100, 200) comprising: a pillar-shaped honeycomb structure (10) having provided porous partition walls (1) surrounding a plurality of cells serving as fluid passage channels extending from an inflow end face (11) to an outflow end face (12); and porous sealing portions (5) provided at either ends on the inflow end face (11) side of the cells or ends on the outflow end face (12) side of the cells, wherein the sealing portions (5) are made of a porous material, the honeycomb structure (10) has a center region (15) including a center of gravity in a cross section orthogonal to a direction in which the cells extend and a circumferential region (16) on a circumferential side further from the center region (15), and has an S 2 / S 1, indicating a ratio of an area S2 of the peripheral region (16) with respect to an area S1 of the central region (15) extending from 0.1 to 0.5, the porosity P1 of a center sealing portion (5a) which is the sealing portion (5) present in the central region (15) is higher than the porosity P2 of a peripheral sealing portion (5b) which is the sealing portion (5) present in the peripheral region (16), and the porosity P1 of the center sealing portion (5a) extends from 76% to 85%, and the porosity P2 of the peripheral sealing portion (5b) extends from 60% to 75%, wherein the honeycomb filter (100, 200) further comprises a plurality of the center sealing portions (5a) and the peripheral sealing portions (5b), which are arranged from a center toward a periphery in a radial direction of the cross section of the honeycomb structure (10), wherein the center sealing portions (5a) and the periphery sealing portions (5b) are configured such that each porosity of the center sealing portions (5a) and the periphery sealing portions (5b) arranged in the order toward the periphery gradually decreases from the center sealing portions (5a) provided closer to a center in the radial direction of the cross section.The honeycomb filter (100, 200) according to claim 1, wherein a cell structure of the honeycomb structure (10) is the same in the central region (15) and the peripheral region (16).The honeycomb filter (100, 200) according to any one of claims 1 to 2, wherein the porosity of the partition walls (1) extends from 52% to 66%.The honeycomb filter (100, 200) according to any one of claims 1 to 3, wherein the value of the porosity P2 of the circumferential sealing portions (5b) in the direction in which the cells extend remains constant.

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