Honeycomb filter

Abstract

To provide a honeycomb filter capable of reducing leakage of PM small in particle size in the case that an amount of catalyst carried is small.SOLUTION: A honeycomb filter includes: a porous cell partition wall sectioning and forming a plurality of cells to be a flow passage of exhaust gas; an exhaust gas introduction cell whose end surface on the exhaust gas entrance is opened and whose end surface on the exhaust gas exit is sealed; and an exhaust gas discharge cell whose end surface on the exhaust gas exit side is opened and whose end surface on the exhaust gas entrance side is sealed. The cell partition wall is composed of porous bodies of silicon carbide and, on the surface of the cell partition wall, 5 to 15g catalyst per honeycomb filter 1L is carried, and a maximum surface pore diameter to be the largest pore present on the surface of the cell partition wall is 45 μm or less.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a honeycomb filter. [Background technology]

[0002] Exhaust gases emitted from internal combustion engines such as diesel engines contain particulate matter (hereinafter referred to as PM), such as soot, and in recent years, the harm that this PM poses to the environment and human body has become a problem. Furthermore, because exhaust gases also contain harmful gas components such as CO, HC, and NOx, there are concerns about the impact that these harmful gas components have on the environment and human body.

[0003] Therefore, various honeycomb-structured filters (honeycomb filters) made of porous ceramics such as cordierite and silicon carbide have been proposed as exhaust gas purification devices that are connected to internal combustion engines to capture PM in exhaust gases and purify harmful gas components in exhaust gases, such as CO, HC, or NOx.

[0004] In recent years, due to stricter exhaust gas regulations, honeycomb filters are required to have high PM collection performance. PN standards (Particle Number standards) have also been established as an item in exhaust gas regulations, making it necessary to reduce the number of particles in exhaust gas. In order to meet the PN standards, it is necessary to reduce the leakage of small particles.

[0005] Honeycomb filters also carry catalysts to purify gas components and promote the combustion of PM. Precious metals are used as catalysts, but there is a demand for reducing the amount of catalyst carried in order to reduce costs and the amount of precious metals used, which are valuable resources.

[0006] Patent Document 1 discloses a method for improving initial PM leakage by specifying the area of ​​open pores on the surface of the filter wall and the average number of open pores. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2009-517207 Summary of the Invention [Problem to be solved by the invention]

[0008] In the method described in Patent Document 1, when the amount of catalyst loaded is reduced in response to a demand for a reduced amount of catalyst, if there are large pores in the surface layer of the filter wall, areas where the catalyst cannot be loaded are created in the pores, resulting in a problem of PM leakage.

[0009] The inventors investigated the cause of PM leakage and surmised that when the catalyst loading amount is small and there are large pores on the surface of the cell partition walls, the catalyst may not be sufficiently loaded in these large pores, resulting in gaps in the catalyst coating, which may result in small amounts of PM leaking through the gaps in the catalyst coating.

[0010] The present invention has been made in view of the above-mentioned problems, and has an object to provide a honeycomb filter that can reduce leakage of PM with a small particle size when the amount of catalyst carried is small. [Means for solving the problem]

[0011] The honeycomb filter of the present invention is a honeycomb filter comprising porous cell partition walls that define a plurality of cells that serve as exhaust gas flow paths, exhaust gas introduction cells that are open at their end faces on the exhaust gas inlet side and sealed at their end faces on the exhaust gas outlet side, and exhaust gas discharge cells that are open at their end faces on the exhaust gas outlet side and sealed at their end faces on the exhaust gas inlet side, wherein the cell partition walls are made of a porous silicon carbide body, 5 to 15 g of catalyst is supported on the surface of the cell partition walls per 1 L of honeycomb filter, and the maximum surface pore diameter, which is the diameter of the largest pore present on the surface of the cell partition walls, is 45 μm or less.

[0012] The honeycomb filter of the present invention is a honeycomb filter with a small catalyst loading amount of 5 to 15 g per liter. The present inventors have found that when the catalyst loading is small, PM leakage is likely to occur if large pores with a surface pore diameter exceeding 45 μm are present on the surface of the cell partition walls, and have also found that setting the maximum surface pore diameter of the cell partition walls to 45 μm or less is effective in preventing PM leakage. In the honeycomb filter of the present invention, there are no large pores with a maximum surface pore diameter exceeding 45 μm on the surface of the cell partition walls, so no gaps are formed between the coated catalyst particles, preventing leakage of PM with small particle diameters. Therefore, with the configuration of the present invention, it is possible to provide a honeycomb filter that can reduce leakage of PM with a small particle size.

[0013] In the honeycomb filter of the present invention, the maximum surface pore diameter is preferably 20 μm or more. If the maximum surface pore diameter is too small, the pressure loss may increase, and therefore, it is preferable that the pores present on the surface of the cell partition walls have an appropriate maximum surface pore diameter.

[0014] In the honeycomb filter of the present invention, the porosity of the cell walls is preferably 35 to 55%. In the honeycomb filter of the present invention, the cell partition walls preferably have an average pore diameter of 5 to 20 μm. In the honeycomb filter of the present invention, the thickness of the cell partition walls is preferably 0.10 to 0.46 mm.

[0015] It is preferable that the porosity of the cell walls, the average pore diameter of the cell walls, and the thickness of the cell walls are within the above ranges from the viewpoints of pressure loss and PM capture efficiency. The porosity of the cell walls, the average pore diameter of the cell walls, and the thickness of the cell walls can be determined in any combination within the above-mentioned ranges. [Brief explanation of the drawings]

[0016] [Figure 1]FIG. 1 is a perspective view schematically showing an example of a honeycomb filter. [Figure 2] FIG. 2 is a perspective view schematically showing an example of a honeycomb fired body. [Figure 3] FIG. 3 is a cross-sectional view of the honeycomb fired body shown in FIG. 2 taken along line AA. [Figure 4] FIG. 4 is a perspective view schematically showing another example of a honeycomb fired body. [Figure 5] FIG. 5 shows an example of a binarized SEM image of a cell partition wall used to measure the maximum surface pore diameter. [Figure 6] FIG. 6 shows an SEM image and a binarized image of a cross section of a cell partition wall in the honeycomb filters according to each of the Examples and Comparative Examples. [Figure 7] FIG. 7 is a schematic diagram of a PM collection efficiency measuring device.

[0017] (Detailed Description of the Invention) The honeycomb filter of the present invention will be described below. The honeycomb filter of the present invention is a honeycomb filter comprising porous cell partition walls that define a plurality of cells that serve as exhaust gas flow paths, exhaust gas introduction cells that are open at their end faces on the exhaust gas inlet side and sealed at their end faces on the exhaust gas outlet side, and exhaust gas discharge cells that are open at their end faces on the exhaust gas outlet side and sealed at their end faces on the exhaust gas inlet side, wherein the cell partition walls are made of a porous silicon carbide body, 5 to 15 g of catalyst is supported on the surface of the cell partition walls per 1 L of honeycomb filter, and the maximum surface pore diameter, which is the diameter of the largest pore present on the surface of the cell partition walls, is 45 μm or less.

[0018] FIG. 1 is a perspective view schematically showing an example of a honeycomb filter. FIG. 2 is a perspective view schematically showing an example of a honeycomb fired body. FIG. 3 is a cross-sectional view of the honeycomb fired body shown in FIG. 2 taken along line AA.

[0019] In the honeycomb filter 20 shown in Fig. 1, a plurality of honeycomb fired bodies 10 are bound together via adhesive layers 15 to form a ceramic block 18, and an outer peripheral coating layer 16 for preventing exhaust gas leakage is formed on the outer periphery of this ceramic block 18. The outer peripheral coating layer 16 may be formed as needed.

[0020] In the honeycomb filter 20, a plurality of honeycomb fired bodies 10 are bound together via adhesive layers 15. Therefore, even if stress occurs in one honeycomb fired body 10, the stress is alleviated by the adhesive layers 15 and is less likely to be transmitted to the other honeycomb fired bodies 10. In other words, the stress occurring in the honeycomb filter 20 can be alleviated. As a result, damage to the honeycomb filter 20 can be prevented.

[0021] The adhesive layer 15 is formed by applying and drying an adhesive paste containing an inorganic binder and inorganic particles. The adhesive layer 15 may further contain inorganic fibers and / or whiskers. The thickness of the adhesive layer 15 is preferably 0.5 to 2.0 mm.

[0022] The outer coating layer 16 serves to mechanically protect the internal cells, and therefore the honeycomb filter 20 has excellent mechanical properties such as compressive strength. The material of the outer circumferential coating layer 16 is preferably the same as the material of the adhesive layer 15. The thickness of the outer circumferential coating layer 16 is preferably 0.1 to 3.0 mm.

[0023] Although the honeycomb fired body 10 has a quadrangular prism shape, the corners of the end faces are chamfered to form curved shapes as shown in Fig. 2, thereby preventing thermal stress from concentrating on the corners and causing damage such as cracks. The corners may also be chamfered to form straight shapes.

[0024] The honeycomb fired body 10 shown in FIG. 2 includes porous cell partition walls 13 that define a plurality of cells that serve as exhaust gas flow paths, and has an end face 10a on the exhaust gas inlet side and an end face 10b on the exhaust gas outlet side. The cells separated by the cell partitions 13 comprise an exhaust gas introduction cell 11 having an open end face 10a on the exhaust gas inlet side and a sealed end face 10b on the exhaust gas outlet side, and an exhaust gas discharge cell 12 having an open end face 10b on the exhaust gas outlet side and a sealed end face 10a on the exhaust gas inlet side.

[0025] The end face of either the exhaust gas inlet cell or the exhaust gas discharge cell is plugged with a plugging material 14 . The plugging material 14 is preferably made of the same material as the honeycomb fired body 10 .

[0026] The cell partition walls 13 of the honeycomb fired body 10 are made of a porous body of silicon carbide (SiC). The cell partition walls being made of silicon carbide means that the main component of the cell partition walls is silicon carbide, but does not mean that the cell partition walls are made only of silicon carbide. For example, it includes a composite of silicon carbide and metal silicon, silicon-containing silicon carbide, and silicon carbide bonded with metal silicon.

[0027] In the honeycomb filter 20, the cross-sectional shape of the exhaust gas inlet cells 11 and the exhaust gas discharge cells 12 in the direction perpendicular to the longitudinal direction is the same for each cell from the end face on the exhaust gas inlet side to the end face on the exhaust gas outlet side, excluding the plugged portions.

[0028] In the honeycomb fired body 10 shown in FIG. 2, the cross-sectional shape of the exhaust gas introduction cells 11 and the cross-sectional shape of the exhaust gas discharge cells 12 are the same square shape, and these are arranged alternately in a checkerboard pattern.

[0029] The number of cells per unit area in the cross section of the honeycomb fired body is 31 to 93 cells / cm 2 (200~600 pieces / inch 2 ) is preferred.

[0030] Here, a case where exhaust gas flows into the honeycomb fired body 10 and PM is captured will be described with reference to FIG. As shown in Fig. 3, exhaust gas G (in Fig. 3, exhaust gas is indicated by G and the flow of exhaust gas is indicated by arrows) that flows into the exhaust gas introduction cell 11 passes through a cell partition wall 13 that separates the exhaust gas emission cell 12 and the exhaust gas introduction cell 11, and then flows out of the exhaust gas emission cell 12. When the exhaust gas G passes through the cell partition wall 13, PM and the like in the exhaust gas are captured, so the cell partition wall 13 functions as a filter.

[0031] The thickness of the cell partition walls is preferably 0.10 to 0.46 mm. The porosity of the cell partition walls is preferably 35 to 55%. The average pore size of the cell partition walls is preferably 5 to 20 μm. The "porosity" and "average pore diameter" of the cell partition walls can be determined by mercury intrusion porosimetry, which is performed under the following measurement conditions: contact angle of 130°, surface tension of 485 mN / m.

[0032] In the honeycomb filter of the present invention, 5 to 15 g of catalyst is supported on the surfaces of the cell partition walls per 1 L of the honeycomb filter. This catalyst carrying amount is in a small range as a catalyst carrying amount for a honeycomb filter.

[0033] The catalyst is not particularly limited as long as it can treat exhaust gas, and examples thereof include catalysts made of noble metals such as platinum, palladium, and rhodium. These catalysts may be used alone or in combination of two or more. When these catalysts are supported, toxic exhaust gases such as CO and HC can be suitably purified.

[0034] These catalysts are used after being supported on a catalyst support layer such as γ-alumina and formed on the cell partition walls together with the catalyst support layer. The amount of catalyst supported using a catalyst support layer is the sum of the weight of the catalyst support layer and the weight of the catalyst. The material for forming the catalyst support layer is preferably a material with a large specific surface area that can support the catalyst in a highly dispersed manner, and examples thereof include oxide ceramics such as alumina, titania, zirconia, ceria, and silica. These materials may be used alone or in combination of two or more.

[0035] FIG. 4 is a perspective view schematically showing another example of a honeycomb fired body. As the honeycomb fired body provided in the honeycomb filter 20, a honeycomb fired body 10' shown in FIG. 4 can also be used. The honeycomb fired body 10' shown in Figure 4 has porous cell partitions 13 that define multiple cells that serve as exhaust gas flow paths, and is composed of exhaust gas introduction cells (cells indicated by symbols 11A and 11B) that have open end faces 10a on the exhaust gas inlet side and plugged end faces 10b on the exhaust gas outlet side, and exhaust gas discharge cells 12 that have open end faces 10b on the exhaust gas outlet side and plugged end faces 10a on the exhaust gas inlet side.

[0036] The exhaust gas introduction cells are of two types: a first exhaust gas introduction cell and a second exhaust gas introduction cell having a larger cross-sectional area in a cross section perpendicular to the longitudinal direction of the cell than the first exhaust gas introduction cell. In a cross section perpendicular to the longitudinal direction of the cells, it is preferable that the exhaust gas discharge cell is octagonal, the first exhaust gas introduction cell is quadrangular, and the second exhaust gas introduction cell is octagonal.

[0037] As shown in FIG. 4, in the honeycomb fired body 10′, a first exhaust gas introduction cell 11A having a square cross section and a second exhaust gas introduction cell 11B having an octagonal cross section are adjacent to the entire periphery of an exhaust gas discharge cell 12 having an octagonal cross section. In addition, an outer peripheral wall 17 is formed on the outer periphery of this honeycomb fired body 10'.

[0038] In the honeycomb filter of the present invention, the maximum surface pore diameter, which is the diameter of the largest pore present on the surface of the cell partition wall, is 45 μm or less. The maximum surface pore diameter of the cell partition walls will be described.

[0039] FIG. 5 shows an example of a binarized SEM image of a cell partition wall used to measure the maximum surface pore diameter. To obtain a binary image, a scanning electron microscope (SEM) is used to photograph the cross section of the cell partition wall 13. A honeycomb filter without catalyst is used for the measurement. A honeycomb filter with catalyst can be used for the measurement after the catalyst is removed. As the SEM, an electron microscope (for example, FE-SEM: high-resolution field emission scanning electron microscope S-4800 manufactured by Hitachi High-Technologies Corporation) can be used. The magnification is preferably 100 to 400 times.

[0040] Next, as shown in Fig. 5, the SEM image of the cell partition wall 13 is binarized into pore portions 31 and material portions 32. The method of binarization is not particularly limited, but for example, the image analysis processing software "Image J" can be used.

[0041] In the binarized image, pores 31 are shown in black and material parts 32 are shown in white. The dimensions of all pores 31 on the surface of the cell partition wall are measured. In the cell wall shown in FIG. 5, the area indicated by the double arrow W1 on the upper surface and the area indicated by the double arrow W2 on the lower surface correspond to the widest pores on each surface of the cell partition wall. These dimensions are the maximum surface pore diameter on each surface of the cell partition wall. The maximum surface pore diameter of the cell partition wall is the longer of the maximum surface pore diameters on each surface of the cell partition wall (the dimension indicated by the double arrow W1 and the dimension indicated by the double arrow W2). In the cell wall shown in FIG. 5, the dimension indicated by the double arrow W2 is the maximum surface pore diameter of the cell partition wall.

[0042] In the honeycomb filter of the present invention, there are no large pores with a maximum surface pore size exceeding 45 μm on the surface of the cell partition walls, which means that there are no large pores on the surface of the cell partition walls that are prone to leaking small particle diameter PM, and the variation in surface pore size is small. If there are no large pores on the surface of the cell partition walls, no gaps will be formed between the coated catalyst particles, preventing leakage of PM with small particle diameters.

[0043] The maximum surface pore diameter of the cell partition walls is preferably 20 μm or more. If the maximum surface pore diameter is too small, the pressure loss may increase, and therefore, it is preferable that the pores present on the surface of the cell partition walls have an appropriate maximum surface pore diameter.

[0044] Figure 1 illustrates a so-called aggregated honeycomb filter formed by aggregating multiple honeycomb fired bodies as the honeycomb filter, but the honeycomb filter of the present invention may also be a so-called integrated honeycomb filter consisting of a single honeycomb fired body.

[0045] An example of the method for producing the honeycomb filter of the present invention will be described below.

[0046] (1) A molding step is carried out in which a wet mixture containing silicon carbide powder and a binder is extrusion-molded to produce a honeycomb molded body. Specifically, first, a wet mixture for manufacturing a honeycomb molded body is prepared by mixing silicon carbide coarse powder having an average particle size of 5 to 20 μm, silicon carbide fine powder having an average particle size of 0.1 to 2.0 μm, an organic binder, a liquid plasticizer, a lubricant, and water. In this case, it is preferable to use coarse silicon carbide powder having an average particle size of 11 to 15 μm. By using coarse silicon carbide powder of such a size, it is possible to prevent large pores with a maximum surface pore diameter exceeding 45 μm from being present on the surface of the cell partition walls in the honeycomb fired body produced in the subsequent steps.

[0047] If necessary, a pore-forming agent such as balloons, which are minute hollow spheres made of oxide ceramic, spherical acrylic particles, graphite, etc. may be added to the above-mentioned wet mixture. The balloons are not particularly limited, and examples thereof include alumina balloons, glass microballoons, shirasu balloons, fly ash balloons (FA balloons), mullite balloons, etc. Among these, alumina balloons are preferred.

[0048] Subsequently, the wet mixture is put into an extrusion molding machine and extrusion-molded to produce a honeycomb molded body of a predetermined shape. At this time, a mold is used to produce a honeycomb formed body having a cross-sectional shape with the cell structure (cell shape and cell arrangement) shown in FIG. 2 or FIG.

[0049] (2) The honeycomb formed body is cut to a predetermined length and dried using a microwave dryer, hot air dryer, dielectric dryer, reduced pressure dryer, vacuum dryer, freeze dryer, etc., and then a plugging process is carried out in which a plugging material paste that serves as a plugging material is filled into predetermined cells to plug the cells. Here, the above-mentioned wet mixture can be used as the plug material paste.

[0050] (3) The honeycomb formed body is heated to 300 to 650°C in a degreasing furnace to perform a degreasing process to remove organic matter from the honeycomb formed body, and then the degreasing honeycomb formed body is transported to a firing furnace and subjected to a firing process in which it is heated to 2000 to 2200°C to produce a honeycomb fired body as shown in Figure 2 or Figure 4. The plugging material paste filled into the ends of the cells is fired by heating to become plugging materials. Furthermore, the conditions for the cutting step, drying step, plugging step, degreasing step and firing step may be the same as those conventionally used for producing honeycomb fired bodies.

[0051] (4) A bonding step is performed in which a plurality of honeycomb fired bodies are stacked on a support table with an adhesive paste interposed therebetween and bonded together to produce a honeycomb aggregate in which a plurality of honeycomb fired bodies are stacked together. The adhesive paste used may be made of, for example, an inorganic binder, an organic binder, and inorganic particles, and may further contain inorganic fibers and / or whiskers.

[0052] (5) Next, the honeycomb aggregate is heated to heat and solidify the adhesive paste to form an adhesive layer, and a ceramic block in the shape of a square pillar is produced. The conditions for heating and solidifying the adhesive paste may be the same as those conventionally used for producing honeycomb filters.

[0053] (6) A cutting process is carried out to cut the ceramic block. Specifically, the outer periphery of a ceramic block is cut using a diamond cutter to produce a ceramic block whose outer periphery is machined into a substantially cylindrical shape.

[0054] (7) A peripheral coating layer forming step is carried out in which a peripheral coating material paste is applied to the peripheral surface of the substantially cylindrical ceramic block, and then dried and solidified to form a peripheral coating layer. The outer periphery coating paste may be the adhesive paste described above, although a paste having a different composition from the adhesive paste may also be used as the outer periphery coating paste. The outer peripheral coating layer does not necessarily have to be provided, but may be provided as needed. By providing the outer periphery coating layer, the outer shape of the ceramic block can be adjusted to form a cylindrical honeycomb filter. Through the above steps, a honeycomb filter including a honeycomb fired body can be manufactured.

[0055] In the above process, a honeycomb filter of a predetermined shape is manufactured by performing a cutting process, but in the process of manufacturing a honeycomb fired body, honeycomb fired bodies of multiple shapes each having an outer peripheral wall around the entire periphery may be manufactured, and these honeycomb fired bodies of multiple shapes may be combined via an adhesive layer to form a predetermined shape such as a cylinder. In this case, the cutting process can be omitted.

[0056] A catalyst is supported on the honeycomb fired body or honeycomb filter. As a method for supporting a catalyst, a honeycomb fired body or a honeycomb filter is immersed in a slurry containing a material such as γ-alumina that will become the catalyst supporting layer, and then the honeycomb fired body or the honeycomb filter is pulled out and heated to form a catalyst supporting layer. Thereafter, the honeycomb fired body or the honeycomb filter is immersed in a solution containing a catalyst such as a precious metal, and then the honeycomb fired body or the honeycomb filter is pulled out and heated.

[0057] When the honeycomb filter has an outer peripheral coating layer, the catalyst may be supported on the honeycomb fired body before the outer peripheral coating layer is formed, or the catalyst may be supported on the honeycomb fired body or honeycomb filter after the outer peripheral coating layer has been formed.

[0058] In the honeycomb filter manufacturing method of the present invention, the amount of catalyst supported is adjusted to 5 to 15 g / L per 1 L of honeycomb filter.

[0059] The present specification discloses the following:

[0060] The present disclosure (1) provides a honeycomb filter including: porous cell partition walls that partition and form a plurality of cells that serve as exhaust gas flow paths; exhaust gas introduction cells that have an open end face on the exhaust gas inlet side and a sealed end face on the exhaust gas outlet side; and exhaust gas discharge cells that have an open end face on the exhaust gas outlet side and a sealed end face on the exhaust gas inlet side, the cell partition walls are made of a porous silicon carbide body, 5 to 15 g of catalyst is supported on the surface of the cell partition walls per 1 L of the honeycomb filter, In the honeycomb filter, the maximum surface pore diameter, which is the diameter of the largest pore present on the surface of the cell partition walls, is 45 μm or less.

[0061] The present disclosure (2) is the honeycomb filter according to the present disclosure (1), wherein the maximum surface pore diameter is 20 μm or more.

[0062] The present disclosure (3) is the honeycomb filter according to the present disclosure (1) or (2), wherein the porosity of the cell partition walls is 35 to 55%.

[0063] The present disclosure (4) is the honeycomb filter according to any one of the present disclosures (1) to (3), wherein the cell partition walls have an average pore diameter of 5 to 20 μm.

[0064] The present disclosure (5) is the honeycomb filter according to any one of the present disclosures (1) to (4), wherein the thickness of the cell partition walls is 0.10 to 0.46 mm.

[0065] (Example) EXAMPLES Hereinafter, examples will be given that more specifically disclose embodiments of the present invention, but the present invention is not limited to these examples.

[0066] Example 1 54.6% by weight of coarse silicon carbide powder having an average particle size of 11 μm and 23.4% by weight of fine silicon carbide powder having an average particle size of 0.5 μm were mixed, and 4.4 parts by weight of an organic binder (methyl cellulose), 2.6 parts by weight of a lubricant (UNILUBE manufactured by NOF Corporation), 1.2 parts by weight of glycerin, and 13.8 parts by weight of water were added to the resulting mixture and kneaded to obtain a wet mixture, which was then extruded and molded. In this step, a raw honeycomb formed body with unplugged cells was produced, which had the same shape as the honeycomb fired body 10' shown in FIG.

[0067] Next, the raw honeycomb formed body was dried using a microwave dryer to produce a dried honeycomb formed body. After that, the cells of the dried honeycomb formed body were filled with a plugging material paste to be a plugging material, thereby plugging the cells.

[0068] Next, the dried honeycomb formed body was subjected to a degreasing treatment at 400°C, and then a firing step was carried out under the conditions of 2200°C for 3 hours in an argon atmosphere at normal pressure. In this way, the honeycomb fired body according to Example 1 was produced. The obtained honeycomb fired body according to Example 1 had a size of 36 mm×36 mm×177.8 mm, an average pore diameter of the cell partition walls of 9 μm, and a porosity of 38%. The cell partition thickness is 0.16 mm, and the cell density is 300 cells / inch 2 It was.

[0069] The finished honeycomb fired bodies were bundled together using an adhesive paste made from a mixture of SiC particles, silica sol, and alumina fibers, the outer periphery was processed, and a coating layer made from the same material as the adhesive paste was applied to the outer periphery to produce a cylindrical honeycomb filter measuring φ330.2 mm x 177.8 mm.

[0070] Next, the honeycomb filter was immersed in a slurry containing platinum-loaded gamma-alumina with an average particle size of 2 μm as an oxidation catalyst, dried at 120°C, and heat-treated at 450°C, thereby loading the catalyst onto the cell partition walls of the honeycomb filter in an amount of 15 g / L.

[0071] Example 2 A honeycomb filter was produced in the same manner as in Example 1, except that a coarse silicon carbide powder having an average particle size of 15 μm was used and the firing temperature of the honeycomb formed body was set to 2150°C.

[0072] (Comparative Example) A honeycomb filter was produced in the same manner as in Example 1, except that a coarse silicon carbide powder having an average particle size of 24 μm was used and the firing temperature of the honeycomb formed body was set to 2100°C.

[0073] (Measurement of maximum surface pore diameter) The honeycomb filters according to each of the Examples and Comparative Examples were cut in a direction perpendicular to the longitudinal direction, and the cross sections of the cell partition walls were photographed at a magnification of 200 times using an electron microscope (for example, FE-SEM: high-resolution field emission scanning electron microscope S-4800 manufactured by Hitachi High-Technologies Corporation) to obtain SEM images. For the measurement, honeycomb filters before loading the catalyst were used. Next, each SEM image was binarized using the image analysis processing software "Image J." FIG. 6 shows an SEM image and a binarized image of a cross section of a cell partition wall in each of the honeycomb filters according to the examples and comparative examples. The binarized image of Example 1 is the same as the binarized image shown in FIG.

[0074] The maximum surface pore diameter on the surface of the cell partition wall was measured from the binarized image, and the results were as follows: Example 1: 24 μm Example 2: 42 μm Comparative example: 103μm

[0075] (PM collection efficiency measurement) The PM collection efficiency was measured using a PM collection efficiency measuring device. FIG. 7 is a schematic diagram of a PM collection efficiency measuring device. In the PM collection efficiency measuring device 40 shown in FIG. 7, a gas inlet side 53 of an exhaust gas purification device 50 is arranged in an exhaust gas pipe 42 of a 12.8 L common rail diesel engine 41. In the exhaust gas purification device 50, an oxidation catalyst (Diesel Oxidation Catalyst DOC) 60 is disposed on the upstream side of the exhaust gas flow path, and a honeycomb filter 20 is disposed on the downstream side. The DOC 60 and the honeycomb filter 20 are placed in a casing 80 with a holding seal material 71 and a holding seal material 72 wrapped around them, respectively. A predetermined space is provided between the DOC 60 and the honeycomb filter 20 .

[0076] Furthermore, the PM collection efficiency measuring device 40 is equipped with a sampler 43 that samples the exhaust gas before it flows through the honeycomb filter 20, a sampler 44 that samples the exhaust gas after it flows through the honeycomb filter 20, a diluter 45 that dilutes the exhaust gas sampled by the sampler 43 or 44, and a PM counter 46 (TSI, agglomerated particle counter 3022A-S) that measures the amount of particulates contained in the diluted exhaust gas, and is configured as a scanning mobility particle sizer (SMPS). The PM collection efficiency was measured using a diesel engine with a high PM content in the exhaust gas, in order to shorten the measurement time and enable accurate measurement.

[0077] Before measuring the PM trapping efficiency, the engine 41 was operated to deposit 2 g / L of PM on the honeycomb filter 20 . The engine 41 was operated in WHTC mode six times with an EGR rate of 30%, and the exhaust gas from the engine 41 was passed through the honeycomb filter 20 on which PM had accumulated. At this time, the total number of PM particles after passing through the honeycomb filter 20 was calculated.

[0078] The measurement results for the total number of PM particles were as follows: Example 1: 9.1 x 10 10 pieces Example 2: 8.9 x 10 10 pieces Comparative example: 12.0 x 10 10 pieces

[0079] The honeycomb filters of Examples 1 and 2 had a maximum surface pore diameter of 45 μm or less, and the total number of PM particles after passing through the honeycomb filters was small. In other words, the honeycomb filters had excellent collection efficiency. On the other hand, the honeycomb filter of the comparative example had a large maximum surface pore diameter of 103 μm, and therefore the total number of PM particles after passing through the honeycomb filter was large, resulting in poor collection efficiency. [Explanation of symbols]

[0080] 10, 10´ honeycomb fired body 10a End face on the exhaust gas inlet side 10b End face on the exhaust gas outlet side 11 Exhaust gas introduction cell 11A First exhaust gas introduction cell 11B First exhaust gas introduction cell 12 Exhaust Gas Emission Cell 13 Cell partition 14 Plugging material 15 Adhesive layer 16 Periphery coating layer 17 Peripheral wall 18 Ceramic Block 20 Honeycomb filter 31 Pore 32 Materials Department 40 Collection efficiency measuring device 41 Engine 42 Exhaust gas pipe 43, 44 Sampler 45 Diluter 46 PM Counter 50 Exhaust gas purification equipment 53 Gas inlet side 60 DOC 71, 72 Retention seal material 80 Casing

Claims

1. A honeycomb filter comprising: porous cell partition walls that partition and form a plurality of cells that serve as exhaust gas flow paths; exhaust gas introduction cells that have an open end face on the exhaust gas inlet side and a sealed end face on the exhaust gas outlet side; and exhaust gas discharge cells that have an open end face on the exhaust gas outlet side and a sealed end face on the exhaust gas inlet side, the cell partition walls are made of a porous silicon carbide body, 5 to 15 g of catalyst is supported on the surfaces of the cell partition walls per 1 L of the honeycomb filter, A honeycomb filter, wherein a maximum surface pore diameter, which is the diameter of the largest pore present on the surface of the cell partition walls, is 45 μm or less.

2. The honeycomb filter according to claim 1, wherein the maximum surface pore diameter is 20 μm or more.

3. 3. The honeycomb filter according to claim 1, wherein the porosity of the cell partition walls is 35 to 55%.

4. 3. The honeycomb filter according to claim 1, wherein the cell partition walls have an average pore diameter of 5 to 20 μm.

5. 3. The honeycomb filter according to claim 1, wherein the cell partition walls have a thickness of 0.10 to 0.46 mm.

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