Honeycomb filter

Abstract

Provided is a honeycomb filter excellent in regeneration efficiency during continuous regeneration and capable of suppressing an increase in pressure loss due to accumulation of ash. The present invention comprises: a columnar honeycomb structure part 4 having a porous partition wall 1 arranged so as to surround a plurality of cells 2; and a sealing part 5 arranged so as to seal either one of an end part on the inflow end face 11 side or an end part on the outflow end face 12 side of the cells. The cross-sectional shape of an inflow cell 2a is an octagonal shape or a quadrangular shape, and the cross-sectional shape of an outflow cell 2b is a quadrangular shape. The cell density of the honeycomb structure part 4 is 49-70 cells / cm2, and the thickness of the partition wall 1 is 0.152 mm or more. The opening diameter L1 of the inflow cell 2a is 1.16-1.40 mm. The opening diameter L2 of the outflow cell 2b is 0.82 to 1.08 mm. The ratio (L1 / L2) of the opening diameter L1 to the opening diameter L2 is 1.30 to 1.53.

Description

Honeycomb Filter

[0001] The present invention relates to a honeycomb filter, and more particularly to a honeycomb filter that has excellent regeneration efficiency during continuous regeneration in which particulate matter trapped on partition walls is burned and removed, and that can suppress an increase in pressure loss due to ash accumulation.

[0002] Internal combustion engines are used as a power source in various industries. However, the exhaust gases emitted by internal combustion engines when burning fuel contain particulate matter such as soot and ash. Hereinafter, particulate matter will be referred to as "PM." "PM" is an abbreviation for "Particulate Matter." Regulations regarding the removal of harmful substances such as PM emitted from diesel engines are becoming stricter worldwide, and the installation of aftertreatment systems to purify them is required.

[0003] In particular, a filter for removing PM emitted from a diesel engine is sometimes called a diesel particulate filter. Hereinafter, the diesel particulate filter may be referred to as a "DPF." For example, a honeycomb filter using a honeycomb structure is known as such a DPF (see, for example, Patent Documents 1 and 2).

[0004] Exhaust gas purification using a honeycomb filter is performed as follows. First, the honeycomb filter is placed 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 has flowed 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.

[0005] When PM in exhaust gas is continuously removed using a DPF, PM such as soot accumulates in the DPF, reducing purification efficiency and increasing pressure loss in the DPF. Therefore, for example, in purification devices using DPFs, a "regeneration process" is performed to burn the PM such as soot accumulated in the DPF. Burning the soot when a large amount of soot has accumulated in the DPF can cause the temperature inside the DPF to rise, which can lead to damage to the DPF. For this reason, it is important to efficiently burn the soot (in other words, to perform the regeneration process).

[0006] Japanese Patent Application Laid-Open No. 2004-000896

[0007] DPF regeneration processes include, for example, "forced regeneration" and "continuous regeneration" as described below. "Forced regeneration" involves intentionally injecting fuel into the DPF to raise the gas temperature inside the DPF and forcibly burning the soot accumulated inside the DPF. In contrast, "continuous regeneration" involves converting NO in the exhaust gas into NO using an oxidation catalyst. ２ Some systems use a catalyst such as a fluorine-containing compound (FCC) to continuously burn the soot accumulated in the DPF, using it as an oxidizer. Continuous regeneration involves loading the DPF with an oxidation catalyst for purifying exhaust gas, allowing for continuous regeneration through the action of the catalyst. As mentioned above, forced regeneration uses fuel to burn the soot, which can lead to a deterioration in fuel economy. Continuous regeneration requires the application of a relatively expensive precious metal as a catalyst.

[0008] Due to recent tightening of regulations, fuel economy improvement is receiving more attention than ever before. For this reason, in the regeneration process of DPF, attention is being paid to continuous regeneration rather than forced regeneration, which leads to a deterioration of fuel economy, and improvements in regeneration efficiency during continuous regeneration are expected. However, it is not clear which aspects of the DPF need to be improved to improve regeneration efficiency during continuous regeneration, and the current situation is that improvements to the catalyst side are relied upon.

[0009] Furthermore, when the soot accumulated in the DPF is burned, ash is generated as unburned residues such as calcium (Ca). When such ash accumulates in the DPF, the pressure loss of the DPF increases, leading to a problem of reduced fuel efficiency. For example, conventionally, measures such as thinning the partition walls have been taken to suppress the increase in pressure loss due to ash accumulation. However, from the viewpoint of strength and heat capacity associated with thinning the walls, it is not realistic to pursue thinning alone. Therefore, there is a strong demand for the development of technology that suppresses the increase in pressure loss due to ash accumulation using methods other than thinning the walls.

[0010] The present invention has been made in view of the problems of the prior art, and provides a honeycomb filter that has excellent regeneration efficiency during continuous regeneration and is capable of suppressing an increase in pressure loss due to ash accumulation.

[0011] According to the present invention, there is provided the following honeycomb filter.

[0012] [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, and plugging portions arranged to plug either an end of the cells on the inflow end face side or the outflow end face side, wherein the plugging portions are arranged on the end of the outflow end face side, and the cells that are open on the inflow end face side are inflow cells, and the plugging portions are arranged on the end of the inflow end face side, and the cells that are open on the outflow end face side are outflow cells, and in a cross section of the honeycomb structure that is perpendicular to the direction in which the cells extend, the inflow cells have an octagonal or quadrangular cross section, and the outflow cells have a quadrangular cross section, except for the cells arranged on the outermost periphery of the honeycomb structure, and the honeycomb structure has a cell density of 49 to 70 cells / cm. ２ a thickness of the partition walls is 0.152 mm or more, an opening diameter L1 of the inlet cells is 1.16 to 1.40 mm, an opening diameter L2 of the outlet cells is 0.82 to 1.08 mm, and a ratio (L1 / L2) of the opening diameter L1 to the opening diameter L2 is 1.30 to 1.53.

[0013] [2] The geometric surface area of ​​the inflow cell is 1.23 to 1.50 mm ２ / mm ３ The honeycomb filter according to [1] above.

[0014] [3] The honeycomb filter according to the above [1] or [2], wherein the porosity of the partition walls is 35 to 65%.

[0015] [4] The honeycomb filter according to any one of [1] to [3] above, which is used as a diesel particulate filter.

[0016] The honeycomb filter of the present invention has excellent regeneration efficiency during continuous regeneration in which PM such as soot is removed by burning, and can effectively suppress an increase in pressure loss due to ash accumulation.

[0017] Fig. 2 is a perspective view seen from the inflow end face side, schematically showing one embodiment of a honeycomb filter of the present invention. Fig. 3 is a plan view seen from the inflow end face side of the honeycomb filter shown in Fig. 1. Fig. 4 is a plan view seen from the outflow end face side of the honeycomb filter shown in Fig. 1. Fig. 5 is a cross-sectional view schematically showing the AA' cross section of Fig. 2. Fig. 6 is an enlarged plan view showing a part of the inflow end face of the honeycomb filter shown in Fig. 2.

[0018] 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.

[0019] (1) Honeycomb filter: One embodiment of the honeycomb filter of the present invention is a honeycomb filter 100 as shown in Figs. 1 to 5. Here, Fig. 1 is a perspective view seen from the inflow end face side, schematically showing one embodiment of the honeycomb filter of the present invention. Fig. 2 is a plan view seen from the inflow end face side of the honeycomb filter shown in Fig. 1, and Fig. 3 is a plan view seen from the outflow end face side of the honeycomb filter shown in Fig. 1. Fig. 4 is a cross-sectional view schematically showing the A-A' cross section of Fig. 2. Fig. 5 is an enlarged plan view showing a part of the inflow end face of the honeycomb filter shown in Fig. 2.

[0020] As shown in Figures 1 to 5, the honeycomb filter 100 includes a honeycomb structure 4 and plugging portions 5. The honeycomb structure 4 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. The honeycomb structure 4 is a columnar structure having the inflow end face 11 and the outflow end face 12 as both end faces. In the present invention, the cell 2 means a space surrounded by the partition walls 1. The honeycomb structure 4 constituting the honeycomb filter 100 further has an outer peripheral wall 3 arranged on its outer peripheral side surface so as to surround the partition walls 1.

[0021] The plugging portions 5 are disposed at either the end of the cell 2 on the inlet end face 11 side or the end of the cell 2 on the outlet end face 12 side, and plug the openings of the cell 2. The plugging portions 5 are porous (i.e., porous bodies) made of a porous material. In the honeycomb filter 100 shown in FIGS. 1 to 5 , predetermined cells 2 each having a plugging portion 5 (inlet end face-side plugging portion 5a) disposed at the end of the inlet end face 11 side and the remaining cells 2 each having a plugging portion 5 (outlet end face-side plugging portion 5b) disposed at the end of the outlet end face 12 side are alternately arranged across the partition wall 1. Hereinafter, the cell 2 each having a plugging portion 5 disposed at the end of the inlet end face 11 side may be referred to as an "outlet cell 2b." The cell 2 each having a plugging portion 5 disposed at the end of the outlet end face 12 side may be referred to as an "inlet cell 2a."

[0022] In the honeycomb filter 100, in a cross section perpendicular to the extension direction of the cells 2 of the honeycomb structure 4, the cross-sectional shape of the inflow cells 2a is octagonal or quadrangular, and the cross-sectional shape of the outflow cells 2b is quadrangular, except for the cells 2 arranged on the outermost periphery of the honeycomb structure 4. Hereinafter, a cell 2 whose periphery is surrounded only by partition walls 1 may be referred to as a "complete cell." On the other hand, when a peripheral wall 3 is arranged on the outer peripheral side surface of the honeycomb structure 4, the cell 2 arranged on the outermost periphery of the honeycomb structure 4 (hereinafter simply referred to as the "outermost cell 2") is a cell 2 surrounded by the partition walls 1 and the outer peripheral wall 3. A part of the periphery of such an outermost cell 2 is partitioned by the outer peripheral wall 3, and the cell 2 is an incomplete cell 2 in which a part of the complete cell is missing. Such cells 2 whose peripheries are surrounded by the partition walls 1 and the outer peripheral wall 3 are sometimes called "incomplete cells," and such incomplete cells are not included in the cells 2 that constitute the inflow cells 2a and outflow cells 2b described above. Therefore, unless otherwise specified, when simply referring to "inflow cells 2a" and "outflow cells 2b," they refer to the "inflow cells 2a" and "outflow cells 2b," which are complete cells.

[0023] The honeycomb filter 100 of this embodiment has particularly important characteristics in the cell density of the honeycomb structure 4, the thickness of the partition walls 1, and the configuration of the inlet cells 2a and the outlet cells 2b. That is, first, the honeycomb structure 4 has a cell density of the cells 2 defined by the partition walls 1 of 49 to 70 cells / cm. ２ The thickness of the partition walls 1 constituting the honeycomb structure 4 is 0.152 mm or more. The upper limit of the thickness of the partition walls 1 is determined by the cell density of the honeycomb structure 4 and the opening diameter L1 of the inlet cells 2a and the opening diameter L2 of the outlet cells 2b, which will be described later.

[0024] In the honeycomb filter 100 of this embodiment, the opening diameter L1 of the inflow cells 2a is 1.16 to 1.40 mm, and the opening diameter L2 of the outflow cells 2b is 0.82 to 1.08 mm. The ratio (L1 / L2) of the opening diameter L1 of the inflow cells 2a to the opening diameter L2 of the outflow cells 2b is 1.30 to 1.53. Hereinafter, the "ratio (L1 / L2) of the opening diameter L1 of the inflow cells 2a to the opening diameter L2 of the outflow cells 2b" may be referred to as the "opening diameter ratio (L1 / L2)" of the outflow cells 2b and the inflow cells 2a.

[0025] The honeycomb filter 100 configured as described above has excellent regeneration efficiency during continuous regeneration in which PM such as soot is burned and removed, and can effectively suppress an increase in pressure loss due to ash accumulation. In particular, by setting the opening diameter ratio (L1 / L2) of the outflow cells 2b to the inflow cells 2a within the above-mentioned numerical range, the honeycomb filter 100 can improve the regeneration efficiency during continuous regeneration and effectively suppress an increase in pressure loss due to ash accumulation. For example, in continuous regeneration, soot and NO are burned on an oxidation catalyst (hereinafter also simply referred to as "catalyst") supported on the partition walls 1. ２ The soot is burned by the reaction of the two. Therefore, by adjusting the opening diameter L1 and the opening diameter L2 so as to achieve the above-mentioned opening diameter ratio (L1 / L2), the geometric surface area of ​​the inlet cell 2a is relatively increased. By configuring in this way, the contact between the catalyst and the soot is increased, and the regeneration efficiency during continuous regeneration can be improved. In addition, the oxidation catalyst carried on the DPF burns NOx emitted from the engine. ｘ (e.g., NO) to NO ２ In this case too, the oxidation function of the oxidation catalyst can be increased by increasing the geometric surface area of ​​the inflow cell 2a. ２ This promotes the production of β-glucan, which contributes to improving regeneration efficiency.

[0026] Furthermore, the increase in pressure loss due to ash accumulation is caused by ash accumulating on the inner wall surfaces of the inlet cells 2a and on the ends on the outflow end face 12 side, narrowing the flow path through which the exhaust gas flowing into the inlet cells 2a can pass. Therefore, by setting the cell density of the honeycomb structure 4 and the geometric surface area of ​​the inlet cells 2a to appropriate values, the amount of ash accumulated per inlet cell 2a and the thickness of the ash accumulation can be reduced, and the increase in pressure loss caused by ash accumulation can be effectively suppressed. Each component of the honeycomb filter 100 of this embodiment will be described in more detail below.

[0027] The cell density of the honeycomb structure 4 is 49 to 70 cells / cm ２ The cell density is 49 cells / cm ２ If the cell density is less than 70 cells / cm, both the opening diameter L1 of the inlet cell and the opening diameter L2 of the outlet cell will be large, making it difficult to sufficiently improve the regeneration efficiency during continuous regeneration. ２ If the cell density exceeds 50 to 70 cells / cm, for example, when the opening diameter L1 of the inlet cells is forcibly increased, the cell structure of the honeycomb structure 4 becomes distorted, and the isostatic strength of the honeycomb filter 100 decreases. ２ is preferably 50 to 69 particles / cm ２ More preferably, the density is 52 to 68 particles / cm ２ It is particularly preferred that:

[0028] The thickness of the partition walls 1 is 0.152 mm or more. If the thickness of the partition walls 1 is less than 0.152 mm, the isostatic strength of the honeycomb filter 100 will decrease. As described above, the upper limit of the thickness of the partition walls 1 is determined by the cell density of the honeycomb structure 4 and the opening diameter L1 of the inlet cells 2a and the opening diameter L2 of the outlet cells 2b. For example, the thickness of the partition walls 1 is preferably 0.152 to 0.198 mm, more preferably 0.173 to 0.196 mm, and particularly preferably 0.178 to 0.193 mm. The thickness of the partition walls 1 can be measured using, for example, a scanning electron microscope or a microscope.

[0029] The opening diameter L1 of the inlet cell 2a is 1.16 to 1.40 mm, and the opening diameter L2 of the outflow cell 2b is 0.82 to 1.08 mm. The opening diameter ratio (L1 / L2) between the outflow cell 2b and the inflow cell 2a is 1.30 to 1.53. If the opening diameter L1 of the inlet cell 2a is less than 1.16 mm, the opening diameter L1 of the inlet cell 2a is too small, resulting in an increase in pressure loss during ash deposition. On the other hand, if the opening diameter L1 of the inlet cell 2a exceeds 1.40 mm, a cell structure satisfying the above-mentioned opening diameter ratio (L1 / L2) will be distorted and will have reduced isostatic strength. Furthermore, even if the opening diameter L2 of the outflow cell 2b is outside the above-mentioned numerical range, the above-mentioned problems may occur if the cell structure satisfies the numerical range of the opening diameter L1 and opening diameter ratio (L1 / L2) of the inlet cell 2a.

[0030] The opening diameter L1 of the inlet cell 2a may be 1.16 to 1.40 mm, preferably 1.17 to 1.39 mm. The opening diameter L2 of the outlet cell 2b may be 0.82 to 1.08 mm, preferably 0.83 to 1.08 mm. The opening diameter ratio (L1 / L2) of the outlet cell 2b to the inlet cell 2a may be 1.30 to 1.53, preferably 1.32 to 1.49.

[0031] In addition, in a cross section perpendicular to the extension direction of the cells 2 of the honeycomb structure 4, the cross-sectional shape of the inflow cells 2a is octagonal or quadrangular, and the cross-sectional shape of the outflow cells 2b is quadrangular, except for the cells 2 arranged at the outermost periphery of the honeycomb structure 4. Hereinafter, for example, the "cross-sectional shape of the cells 2" in a cross section perpendicular to the extension direction of the cells 2 of the honeycomb structure 4 may be referred to as the "cross-sectional shape of the cells 2" or simply as the "shape of the cells 2." With respect to the cross-sectional shape of the inflow cells 2a, "octagonal" includes an octagon, a shape in which at least one corner of the octagon is curved, and a shape in which at least one corner of the octagon is linearly chamfered. Similarly, with respect to the cross-sectional shapes of the inflow cells 2a and the outflow cells 2b, "quadrangle" includes a square, a shape in which at least one corner of the square is curved, and a shape in which at least one corner of the square is linearly chamfered.

[0032] The honeycomb structure 4 preferably has a repeating unit in which inlet cells 2a having an octagonal or rectangular cross-sectional shape and outlet cells 2b having a rectangular cross-sectional shape are alternately arranged in a lattice pattern with partition walls 1 sandwiched therebetween. The cross-sectional shape of the outlet cells 2b is preferably a square. The cross-sectional shape of the inlet cells 2a is preferably an octagon with chamfered corners or a square. For example, as shown in FIG. 5 , in a cell structure in which a plurality of cells 2 are arranged in the left-right and up-down directions of the paper surface of FIG. 5 , it is preferable that the inlet cells 2a and the outlet cells 2b are alternately arranged with partition walls 1 sandwiched therebetween in the cell arrangement in each direction. In the honeycomb filter 100, the inlet cells 2a preferably have a single cross-sectional shape in which the opening diameter L1 is 1.16 to 1.40 mm, and the outlet cells 2b preferably have a single cross-sectional shape in which the opening diameter L2 is 0.82 to 1.08 mm.

[0033] The opening diameter L1 of the inflow cell 2a is a value measured by the following method. In the opening shape of the inflow cell 2a, the distance between two opposing sides of the four sides adjacent to the outflow cell 2b across the partition wall 1 is defined as the "opening diameter L1 of the inflow cell 2a." The opening diameter L2 of the outflow cell 2b is defined as the distance between two opposing sides of the four sides of the quadrangle in the opening shape of the outflow cell 2b. The opening diameters L1 and L2 can be measured using, for example, a scanning electron microscope or a microscope.

[0034] The honeycomb filter 100 has an inflow cell 2a with a geometric surface area of ​​1.23 to 1.50 mm ２ / mm ３ It is preferable that the thickness is 1.25 to 1.49 mm. ２ / mm ３ More preferably, it is 1.27 to 1.48 mm ２ / mm ３ Here, the geometric surface area of ​​the inflow cell 2a refers to the geometric surface area of ​​the partition wall 1 disposed so as to surround the inflow cell 2a. The "geometric surface area" of the inflow cell 2a is the total internal surface area (S: unit mm２ ) is the total volume of the honeycomb structure 4 (V: unit mm ３ ) (S / V: unit mm ２ / mm ３ ) The total internal surface area (S) of the inflow cells 2a is the sum of the surface areas of the partition walls 1 arranged so as to surround the inflow cells 2a (however, the surface area of ​​the range where the outlet end face side plugging portions 5b are arranged is excluded). The geometric surface area is sometimes referred to as, for example, "GSA" or "geometric surface area GSA". GSA is an abbreviation for "Geometric Surface Area". When the geometric surface area of ​​the inflow cells 2a is 1.23 mm ２ / mm ３ If the geometric surface area of ​​the inlet cell 2a is less than 1.50 mm, sufficient improvement in regeneration efficiency during continuous regeneration may not be expected. ２ / mm ３ If the cell structure of the honeycomb structure 4 becomes distorted, the isostatic strength of the honeycomb filter 100 may decrease.

[0035] The porosity of the partition walls 1 is not particularly limited, but is preferably 35 to 65%, and more preferably 40 to 60%, for example. 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 can be measured using a test piece obtained by cutting out a part of the partition walls 1 from the honeycomb structure 4. By setting the porosity of the partition walls 1 to be in the above-mentioned numerical range, the honeycomb filter 100 can be particularly suitably used as a filter for purifying exhaust gas, in particular, as a diesel particulate filter (DPF).

[0036] The material of the partition walls 1 is not particularly limited. For example, examples of the material of the partition walls 1 include 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 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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. With this configuration, CO, NOx, HC, and the like in exhaust gas can be converted into harmless substances by catalytic reaction.

[0041] 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 the group consisting of aluminum, zirconium, and cerium, can be used.

[0042] (2) Manufacturing method of honeycomb filter: The method for manufacturing the honeycomb filter of the present invention is not particularly limited, and examples thereof include the following methods. First, a plastic clay for manufacturing the honeycomb filter is prepared. The clay for manufacturing the honeycomb filter 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.

[0043] Next, the thus obtained clay is extrusion-molded to produce a columnar honeycomb molded body having partition walls that define a plurality of cells and an outer peripheral wall that surrounds the partition walls. In the extrusion molding, a die 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, when manufacturing the honeycomb filter of the present invention, it is preferable to use an extrusion die having slits for forming inlet cells and outlet cells with predetermined opening diameters in the honeycomb molded body to be extruded. Next, the obtained honeycomb molded body is dried, for example, by microwaves and hot air.

[0044] 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.

[0045] Next, the honeycomb formed body having the plugging 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.

[0046] 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.

[0047] Example 1 Two parts by mass of a pore-forming material, one part by mass of a dispersion medium, and six parts by mass of an organic binder were added to 100 parts by mass of a cordierite-forming raw material, and the mixture was mixed and kneaded to prepare a clay. Methylcellulose was used as the organic binder. Potassium laurate was used as the dispersant. A water-absorbing polymer with an average particle size of 20 μm was used as the pore-forming material.

[0048] Next, the clay was extruded using a die for producing a honeycomb formed body to obtain a honeycomb formed body having an overall cylindrical shape. The cell shapes of the honeycomb formed body were octagonal and quadrangular, and such octagonal and quadrangular cells were arranged alternately with partition walls sandwiched between them.

[0049] 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.

[0050] Next, a plugging material for forming plugging portions was prepared. Specifically, water, a binder, and the like were added to the ceramic raw material to prepare a slurry plugging material. Thereafter, plugging portions were formed using the plugging material in the openings of predetermined cells on the inflow end face side of the dried honeycomb formed body and in the openings of the remaining cells on the outflow end face side. The plugging portions were formed so that cells with an octagonal cell shape became inflow cells and cells with a square cell shape became outflow cells.

[0051] Next, the honeycomb formed body with the plugged portions formed thereon was degreased and fired to manufacture the honeycomb filter of Example 1.

[0052] The honeycomb filter of Example 1 had an end face diameter of 228.6 mm, a length in the cell extension direction of 184.2 mm, a partition wall thickness of 0.185 mm, and a cell density of 52 cells / cm. ２ The results of the partition wall thickness and cell density are shown in Table 1. The porosity of the partition walls of the honeycomb filter of Example 1 was 58%. The porosity of the partition walls was measured using Autopore 9500 (trade name) manufactured by Micromeritics.

[0053] The opening diameter L1 of the inlet cells and the opening diameter L2 of the outflow cells were measured for the honeycomb filter of Example 1. The results are shown in Table 1. In Table 1, the ratio of the opening diameter L1 of the inlet cells to the opening diameter L2 of the outflow cells is shown in the column "Opening diameter ratio (L1 / L2)". In addition, the honeycomb filter of Example 1 has a geometric surface area of ​​the inlet cells of 1.27 mm ２ / mm ３ It was.

[0054]

[0055] The honeycomb filter of Example 1 was subjected to measurements of the regeneration efficiency (%) during continuous regeneration and the isostatic strength (MPa) by the following methods. Furthermore, the pressure loss during ash deposition (hereinafter referred to as "pressure loss evaluation during ash deposition") was also evaluated by the following method. The results are shown in Table 2.

[0056] [Regeneration Efficiency (%) During Continuous Regeneration] First, an oxidation catalyst was loaded onto the partition walls of a honeycomb filter. The catalyst loading was 10 g / L. Next, 3 g / L of soot was deposited on the partition walls of the honeycomb filter loaded with the catalyst. A total of 23 g of soot was deposited within the honeycomb filter. In this state, another honeycomb structure (catalyst carrier) loaded with an oxidation catalyst was installed upstream of the honeycomb filter. High-temperature exhaust gas was then passed through the upstream side of the upstream honeycomb structure, and the exhaust gas that had passed through the upstream honeycomb structure was vented through the inlet end of the honeycomb filter to perform continuous regeneration of the filter. The exhaust gas was emitted from a 6.7 L diesel engine. The regeneration conditions were a gas temperature of 350°C at the inlet end and a gas venting time of 60 minutes. Thereafter, the honeycomb filter was removed from the device that had performed continuous regeneration, and the amount of soot remaining in the honeycomb filter was measured. The percentage (%) of the ratio obtained by dividing the mass of soot reduced by continuous regeneration by the mass of soot initially deposited was determined as the regeneration efficiency (%) during continuous regeneration. When the regeneration efficiency (%) during continuous regeneration thus determined exceeded the regeneration efficiency (50.8%) of the honeycomb filter of Comparative Example 1 described below, the filter was deemed to have passed, and when it was lower, the filter was deemed to have failed.

[0057] [Evaluation of Pressure Loss During Ash Deposition] First, the pressure loss of the honeycomb filter was measured, and the measured pressure loss was defined as "initial pressure loss (kPa)". Next, the pressure loss was measured in a state in which a predetermined amount of soot and ash was deposited on the partition walls of the honeycomb filter, and the measured pressure loss was defined as "pressure loss during ash deposition (kPa)". When measuring the pressure loss during ash deposition, the amount of soot deposition was 3 g / L, and the amount of ash deposition was 60 g / L. Here, the amount of soot and ash deposition refers to the amount (g) of soot and ash deposition per unit volume (1 L) of the honeycomb filter. Then, the value obtained by subtracting the "initial pressure loss (kPa)" from the "pressure loss during ash deposition (kPa)" was defined as the "pressure loss increase ΔP (kPa)" of the honeycomb filter to be evaluated. Furthermore, the pressure loss increase ΔP of the honeycomb filter of Comparative Example 1 described later was used as a reference (base), and the pressure loss increase rate (%) of the pressure loss evaluation during ash deposition was calculated using the following formula (1). In the following formula (1), the pressure loss increase ΔP (kPa) of the honeycomb filter of Comparative Example 1 serving as the reference was defined as the "reference pressure loss increase ΔP ０ " and the pressure loss increase ΔP (kPa) of the honeycomb filter to be evaluated is defined as "target pressure loss increase ΔP １ In the evaluation of pressure loss during ash accumulation, the honeycomb filter was judged to have failed if the pressure loss increase ΔP was larger than that of the honeycomb filter of Comparative Example 1, which served as the reference, and the pressure loss increase rate (%) showed a positive value. Pressure loss increase rate (%) = (target pressure loss increase ΔP １ - Reference pressure loss increase ΔP ０ ) × Reference pressure loss increase ΔP ０ ×100% (1)

[0058] [Isostatic Strength (MPa)] The measurement of isostatic strength was performed based on the isostatic fracture strength test specified in M505-87 of the automobile standard (JASO standard) issued by the Society of Automotive Engineers of Japan. The isostatic fracture strength test is a test in which a honeycomb filter is placed in a cylindrical rubber container, covered with an aluminum plate, and isostatically compressed in water. The isostatic strength measured by the isostatic fracture strength test is indicated by the pressurized pressure value (MPa) at which the honeycomb filter breaks. An isostatic strength of 1.0 MPa or more was considered to be pass, and an isostatic strength of less than 1.0 MPa was considered to be fail.

[0059]

[0060] Examples 2 to 14 and Comparative Examples 1 to 4 Honeycomb filters were produced in the same manner as in Example 1, except that the configuration of the honeycomb filter was changed as shown in Table 1.

[0061] For the honeycomb filters of Examples 2 to 14 and Comparative Examples 1 to 4, the regeneration efficiency (%) during continuous regeneration and the isostatic strength (MPa) were measured and the pressure loss during ash deposition was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0062] (Results) The honeycomb filters of Examples 1 to 14 showed good measurement results for both the regeneration efficiency (%) during continuous regeneration and the isostatic strength (MPa). Furthermore, in the evaluation of pressure loss during ash accumulation, the honeycomb filters of Examples 1 to 14 showed a smaller pressure loss increase ΔP than the honeycomb filter of Comparative Example 1, which served as the reference, and the pressure loss increase rate (%) showed a negative value.

[0063] On the other hand, in the honeycomb filter of Comparative Example 2, by reducing the thickness of the partition walls, it was possible to improve the regeneration efficiency (%) during continuous regeneration and reduce the pressure loss due to ash accumulation. However, because the thickness of the partition walls was made too thin, the isostatic strength was significantly reduced.

[0064] The honeycomb filter of Comparative Example 3 had a small opening diameter L1 of the inlet cells and also a small opening diameter ratio (L1 / L2) of 1.26. Therefore, in the evaluation of pressure loss during ash accumulation, the honeycomb filter of Comparative Example 3 had ash accumulated in the honeycomb filter, which blocked the inlet cells at the middle section rather than the rear section in the overall length direction, and the effective volume of the honeycomb filter was reduced, resulting in a larger pressure loss increase ΔP than the honeycomb filter of Comparative Example 1.

[0065] The honeycomb filter of Comparative Example 4 has an increased cell density of 71 cells / cm ２ At such a cell density, if an attempt is made to secure a constant opening diameter L1 of the inlet cells and increase the geometric surface area of ​​the inlet cells, the opening diameter L2 of the outflow cells must be reduced, which results in a distorted cell structure of the honeycomb structure and a deterioration in isostatic strength.

[0066] The honeycomb filter of the present invention can be used as a filter for removing PM emitted from a diesel engine.

[0067] 1: partition wall, 2: cell, 2a: inlet cell, 2b: outlet cell, 3: outer peripheral wall, 4: honeycomb structure, 5: plugging portion, 5a: inlet end face side plugging portion, 5b: outlet end face side plugging portion, 11: inlet end face, 12: outlet end face, 100: honeycomb filter, L1: opening diameter of inlet cell, L2: opening diameter of outlet cell.

Claims

1. A columnar honeycomb structure having a porous partition wall arranged so as to surround a plurality of cells serving as fluid flow paths extending from an inflow end face to an outflow end face, and a plugging portion arranged so as to seal either one end of the cells on the inflow end face side or the outflow end face side. The plugging portion is arranged at the end on the outflow end face side, and the cell having the inflow end face side open is defined as an inflow cell. The plugging portion is arranged at the end on the inflow end face side, and the cell having the outflow end face side open is defined as an outflow cell. In a cross-section orthogonal to the extending direction of the cells of the honeycomb structure, except for the cells arranged on the outermost periphery of the honeycomb structure, the cross-sectional shape of the inflow cells is octagonal or square, and the cross-sectional shape of the outflow cells is square. The cell density of the honeycomb structure is 49 to 70 cells / cm ２ and The thickness of the partition wall is 0.152 to 0.198 mm. The opening diameter L1 of the inflow cells is 1.16 to 1.40 mm. The opening diameter L2 of the outflow cells is 0.82 to 1.08 mm. A honeycomb filter in which the ratio (L1 / L2) of the opening diameter L1 to the opening diameter L2 is 1.30 to 1.

53.

2. The geometric surface area of the inflow cell is 1.23 to 1.50 mm ２ / mm ３ The honeycomb filter according to claim 1, wherein the geometric surface area is as described above.

3. The honeycomb filter according to claim 1 or 2, wherein the porosity of the partition wall is 35 to 65%.

4. The honeycomb filter according to claim 1 or 2, which is used as a diesel particulate filter.