Honeycomb filter

Abstract

To provide a honeycomb filter capable of reducing a leak of PM.SOLUTION: The present invention relates to a honeycomb filter that comprises a porous cell partition wall 13 which has a plurality of cells, forming a flow passage of an exhaust gas, sectioned and formed, an exhaust gas introduction cell which has an exhaust gas intake-side end face opened and an exhaust gas outlet-side end face sealed, and an exhaust gas discharge cell which has an exhaust gas outlet-side end face opened and an exhaust gas intake-side end face sealed, wherein the cell partition wall is a sintered body of silicon carbide particles formed by sintering a plurality of silicon carbide particles, and when the sintered body is divided into a plurality of segments 34 by drawing a sectioning line 33 so as to section parts deriving from respective silicon carbide particles to be sintered in an image obtained by photographing a cross section of the cell partition wall and binarizing pore parts and material parts, the unit sectioning line length which is a value obtained by dividing the total (μm) of lengths of sectioning lines in the image by the total (mm2) of area of the material parts in the image is 17000 μm / mm2 or less.SELECTED DRAWING: Figure 5C

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] Patent Document 1 discloses that PM collection efficiency is improved by depositing PM at an early stage on the surface of the cell partition walls that capture PM in a honeycomb filter to form a cake layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-150220 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-167366 Summary of the Invention [Problem to be solved by the invention]

[0007] In the method described in Patent Document 1, deep filtration occurs, in which PM is trapped inside the partition walls. The deep-filtered PM is then decomposed as the temperature of the honeycomb filter rises, breaking down into smaller particles that leak out toward the outflow cells.

[0008] Patent Document 2 discloses that deep filtration is prevented by providing a surface layer containing the same material as the cell partition walls on the cell partition walls that capture PM in a honeycomb filter. However, since the process of providing the surface layer requires time and cost, there has been a demand for a method that can reduce leakage of PM using a method different from the method disclosed in Patent Document 2.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a honeycomb filter that can reduce leakage of PM. [Means for solving the problem]

[0010] The honeycomb filter of the present invention is 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 inlet 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, wherein the cell partition walls are sintered bodies of silicon carbide particles formed by sintering a plurality of silicon carbide particles, and a cross section of the cell partition walls is photographed, and in an image in which pore portions and material portions are binarized, dividing lines are drawn to divide portions originating from the silicon carbide particles before sintering, and when the sintered body is divided into a plurality of segments, the total length (μm) of the dividing lines in the image is calculated based on the total area (mm 2 ) The unit division line length is 17000 μm / mm 2Below is a honeycomb filter.

[0011] The length of the dividing line in the above definition indicates the length of the portion where silicon carbide particles are bonded together. A long dividing line indicates that the silicon carbide particles are well bonded together and that the thermal conductivity between the silicon carbide particles is high. The unit dividing line length is a parameter that indicates the degree of bonding of the silicon carbide particles (material portion) present in the cell partition walls, standardized by dividing the total length of the dividing lines in the image by the area of ​​the material portion in the image. Unit division line length is 17000μm / mm 2 The fact that the thermal conductivity is equal to or less than this value means that an upper limit is set for the thermal conductivity of the cell partition walls, and the cell partition walls having low thermal conductivity are specified. If the thermal conductivity of the cell partition walls is low, the surface of the cell partition walls that come into contact with high-temperature exhaust gas during honeycomb filter regeneration tends to become locally hot. This allows the PM that has been deep-filtered to be burned before it can leak out, preventing the leakage of PM. That is, the honeycomb filter of the present invention does not require the provision of a special layer as in the technique of Patent Document 2, but has a structure that makes PM more easily combustable in the cell partition walls, thereby providing a honeycomb filter that can reduce leakage of PM.

[0012] In the honeycomb filter of the present invention, the unit dividing line length is 13000 μm / mm 2 It is preferable that this is equal to or greater than this. A short unit dividing line length means that there are fewer bonding sites between silicon carbide particles. 2 If the thickness is more than this, contact between silicon carbide particles is sufficiently ensured, which is preferable from the viewpoint of strength of the cell partition walls.

[0013] 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 μm.

[0014] 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]

[0015] [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 5A] FIG. 5A is an example of an SEM image of a cross section of a cell partition wall. [Figure 5B] FIG. 5B is an example of a binarized SEM image of the cross section of the cell partition wall shown in FIG. 5A. [Figure 5C] FIG. 5C is an example of a division line drawn for the binarized image shown in FIG. 5B. [Figure 6A] FIG. 6A is an example of an SEM image of a cross section of a cell partition wall of a honeycomb filter according to Comparative Example 1. FIG. [Figure 6B] FIG. 6B is an example of a binarized SEM image of the cross section of the cell partition wall shown in FIG. 6A. [Figure 6C] FIG. 6C is an example of a depiction of a dividing line for the binarized image shown in FIG. 6B. [Figure 7] FIG. 7 is a schematic diagram of a PM collection efficiency measuring device.

[0016] (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 including porous cell partition walls that partition and form a plurality of cells that serve as exhaust gas flow paths, exhaust gas inlet 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, wherein the cell partition walls are sintered bodies of silicon carbide particles formed by sintering a plurality of silicon carbide particles, and a cross section of the cell partition walls is photographed, and in an image in which pore portions and material portions are binarized, dividing lines are drawn to divide portions originating from the silicon carbide particles before sintering, and when the sintered body is divided into a plurality of segments, the total length (μm) of the dividing lines in the image is calculated based on the total area (mm 2 ) The unit division line length is 17000 μm / mm 2 Below is a honeycomb filter.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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 .

[0025] The cell partition walls 13 of the honeycomb fired body 10 are sintered bodies of silicon carbide particles, which are formed by sintering a plurality of silicon carbide particles. The cell partition walls 13 are made of porous 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] It is preferable that a catalyst is carried on the surface of the cell partition walls. The catalyst is not particularly limited as long as it can treat exhaust gas, and examples thereof include catalysts made of precious metals such as platinum, palladium, and rhodium, zeolite, titania, vanadium oxide, etc. The zeolite may be a CHA-type zeolite, and the zeolite may be ion-exchanged with Cu or the like. These catalysts may be used alone or in combination of two or more. When these catalysts are supported, toxic exhaust gases such as CO, HC, and NOx can be suitably purified.

[0032] Alternatively, a catalyst support layer made of γ-alumina or the like may be formed on the cell partition walls, and then the catalyst may be supported on the catalyst support layer. 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.

[0033] 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.

[0034] 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.

[0035] 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'.

[0036] In the honeycomb filter of the present invention, a cross section of the cell partition wall is photographed, and in the image in which the pore portion and the material portion are binarized, dividing lines are drawn to divide the portions originating from the silicon carbide particles before sintering. When the sintered body is divided into a plurality of segments, the total length (μm) of the dividing lines in the image is calculated based on the total area (mm 2 ) The unit division line length is 17000 μm / mm 2 The following is the result. The unit section line length will be explained.

[0037] FIG. 5A is an example of an SEM image of a cross section of a cell partition wall. FIG. 5B is an example of a binarized SEM image of the cross section of the cell partition wall shown in FIG. 5A. FIG. 5C is an example of a division line drawn for the binarized image shown in FIG. 5B.

[0038] To obtain a binarized image of the cell partition wall, a cross section of the cell partition wall 13 is photographed using a scanning electron microscope (SEM), as shown in FIG. 5A. 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.

[0039] Next, as shown in Fig. 5B, the SEM image of the cell partition wall 13 is binarized into pore portions 31 and material portions 32. The method for binarization is not particularly limited, and for example, the image analysis processing software "Image J" can be used. In the binarized image, pores 31 are shown in white and material parts 32 are shown in black.

[0040] As shown in Fig. 5C, in the binarized image, division lines 33 are drawn to separate portions of material portion 32 that originate from each of the silicon carbide particles before sintering, and the bonded silicon carbide particles are separated into a plurality of segments 34. Division lines 33 are thin lines that separate material portion 32 into a plurality of segments 34 in Fig. 5C.

[0041] In this specification, "separating the portions originating from each silicon carbide particle before sintering" means separating the boundaries where silicon carbide particles are bonded by sintering, and this can be done by the "watershed processing" of the image analysis processing software "Image J." In the actual honeycomb fired body 10, since the silicon carbide particles are sintered together, it is not possible to observe any lines that represent boundaries. In other words, the above-mentioned "division" means division by boundaries calculated by software.

[0042] Next, the length of the demarcation lines in the image depicting the demarcation lines is measured. At the same time, the area of ​​the material part in the same image is measured. Then, the total length (μm) of the demarcation lines in the image is calculated as the total area (mm 2 ) is the unit division line length. The total area of ​​the material in the image (mm 2 ) is measured using the area of ​​the material in the image before the delineation of the sectioning lines (Figure 5B).

[0043] The unit dividing line length is measured in three images of the cell partition wall, and the average value of the unit dividing line lengths is taken as the unit dividing line length of the cell partition wall.

[0044] The length of the dividing line corresponds to the length of the bonded portion of the silicon carbide particles. A short dividing line means that the silicon carbide particles are not bonded well, which means that the thermal conductivity between the silicon carbide particles is low and the thermal conductivity of the cell partition walls is low. The total length of the dividing lines in the image is then divided by the area of ​​the material part in the image and normalized to provide an index showing the degree of bonding of silicon carbide particles under conditions where the amount of material part (silicon carbide particles) present is uniform.

[0045] In the honeycomb filter of the present invention, the unit dividing line length is 17000 μm / mm 2 This means that an upper limit is set for the thermal conductivity of the cell partition walls, and cell partition walls with low thermal conductivity are specified. If the thermal conductivity of the cell partition walls is low, the surface of the cell partition walls that come into contact with high-temperature exhaust gas during honeycomb filter regeneration tends to become locally hot. This allows the PM that has been deep-filtered to be burned before it can leak out, preventing the leakage of PM. That is, the honeycomb filter of the present invention does not require the provision of a special layer as in the technique of Patent Document 2, but has a structure that makes PM more easily combustable in the cell partition walls, thereby providing a honeycomb filter that can reduce leakage of PM.

[0046] The unit dividing line length is 13000 μm / mm 2 It is preferable that this is equal to or greater than this. A short unit dividing line length means that there are fewer bonding sites between silicon carbide particles. 2 If the thickness is more than this, contact between silicon carbide particles is sufficiently ensured, which is preferable from the viewpoint of strength of the cell partition walls.

[0047] 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.

[0048] An example of the method for producing the honeycomb filter of the present invention will be described below.

[0049] (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 16 to 40 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. By using silicon carbide coarse powder of such a size, the unit dividing line length can be made 17000 μm / mm in the cell partition walls of the honeycomb fired body produced in the subsequent process. 2 It can be as follows:

[0050] 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.

[0051] 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.

[0052] (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.

[0053] (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.

[0054] (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.

[0055] (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.

[0056] (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.

[0057] (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 adhesive paste described above can be used as the outer periphery coating paste, although a paste having a different composition from the adhesive paste described above 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.

[0058] 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.

[0059] A catalyst may be supported on the honeycomb fired body or honeycomb filter. Examples of a method for supporting a catalyst include a method in which a honeycomb fired body or a honeycomb filter is immersed in a solution containing a catalyst such as a precious metal, and then pulled out and heated. When a catalyst support layer is used for supporting the catalyst, the honeycomb fired body or honeycomb filter is immersed in a slurry containing a material such as γ-alumina that will become the catalyst support layer, and then the honeycomb fired body or honeycomb filter is pulled out and heated to form the catalyst support layer. Thereafter, the honeycomb fired body or honeycomb filter can be immersed in a solution containing a catalyst such as a precious metal, and then the honeycomb fired body or honeycomb filter is pulled out and heated to form the catalyst support layer.

[0060] 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.

[0061] The present specification discloses the following:

[0062] 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 sintered bodies of silicon carbide particles formed by sintering a plurality of silicon carbide particles, A cross section of the cell partition wall is photographed, and in the image in which the pore portion and the material portion are binarized, When dividing lines are drawn to divide the portions originating from each of the silicon carbide particles before sintering, and the sintered body is divided into a plurality of segments, the total length (μm) of the dividing lines in the image is calculated based on the total area (mm 2 ) The unit division line length is 17000 μm / mm 2 Below is a honeycomb filter.

[0063] In the present disclosure (2), the unit dividing line length is 13000 μm / mm 2 The above is the honeycomb filter according to the present disclosure (1).

[0064] 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%.

[0065] 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.

[0066] 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.

[0067] (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.

[0068] Example 1 54.6% by weight of coarse silicon carbide powder having an average particle size of 24 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.

[0069] 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.

[0070] Next, the dried honeycomb formed body was subjected to a degreasing treatment at 400°C, and then a firing process was carried out under the conditions of 2100°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 34.3 mm×34.3 mm×150.5 mm, an average pore diameter of the cell partition walls of 9 μm, and a porosity of 38%. The cell partition thickness is 0.17 mm, and the cell density is 300 cells / inch 2 It was.

[0071] 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 φ143.8 mm x 150.5 mm.

[0072] (Comparative Example 1) 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.

[0073] (Measurement of unit division line length) The honeycomb filters according to Example 1 and Comparative Example 1 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 (FE-SEM: high-resolution field emission scanning electron microscope S-4800 manufactured by Hitachi High-Technologies Corporation) to obtain SEM images. Next, each SEM image was binarized using the image analysis processing software "Image J." Furthermore, a division line was drawn on the binarized image. 5A, 5B, and 5C are an SEM image, a binarized image, and an image depicting the division lines of the honeycomb filter according to Example 1. FIG. 6A, 6B, and 6C are an SEM image, a binarized image, and an image depicting division lines of the honeycomb filter according to Comparative Example 1. FIG.

[0074] The unit dividing line lengths were measured at three locations on the cell partition walls of the honeycomb filters of Example 1 and Comparative Example 1. The results are shown in Table 1.

[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, a gas inlet side 53 of an exhaust gas purification device 50 is arranged in an exhaust gas pipe 42 of a 1.6 L common rail diesel engine 41. An exhaust pipe that discharges exhaust gas that has passed through the exhaust gas purification device 50 to the outside is connected to a gas outlet side 54 of the exhaust gas purification device 50. The exhaust gas purification device 50 comprises a honeycomb filter 20, a casing 80 that houses the honeycomb filter 20, and a holding seal material 71 that is disposed between the honeycomb filter 20 and the casing 80 and holds the honeycomb filter 20 within the casing 80.

[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 measurement of PM collection performance was carried out using a diesel engine whose exhaust gas contains a large amount of PM, in order to shorten the measurement time and enable accurate measurement.

[0077] Engine speed: 3100 min -1 The engine was then operated at a torque of 50 Nm for 4.5 hours, and 5 g / L of particulate matter was collected. -1 The regeneration treatment was carried out by burning particulate matter (PM) by setting the temperature of the gas flowing into the honeycomb filter at 450°C under a torque of 190 Nm. 1 cm of diluted exhaust gas after passing through the honeycomb filter 20 2.5 minutes after the start of regeneration 3 The total number of PM particles per unit (total number of particles during regeneration) was calculated. The measurement results of the PM particle count are shown in Table 1.

[0078] [Table 1]

[0079] The honeycomb filter of Example 1 has a unit dividing line length of 15027 μm / mm 2 The total number of PM particles after passing through the honeycomb filter was small, which means that the honeycomb filter has excellent collection efficiency. On the other hand, the honeycomb filter of Comparative Example 1 has a unit dividing line length of 18272 μm / mm 2 Because of this large size, the total number of PM particles that passed 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 Second 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 33 Division Line 34 silicon carbide particle segments 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 54 Gas outlet side 71 Retaining 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 sintered bodies of silicon carbide particles formed by sintering a plurality of silicon carbide particles, A cross section of the cell partition wall is photographed, and in the image in which the pore portion and the material portion are binarized, When dividing lines are drawn to divide the portions originating from each of the silicon carbide particles before sintering, and the sintered body is divided into a plurality of segments, the total length (μm) of the dividing lines in the image is calculated based on the total area (mm ２ The unit dividing line length, which is the value divided by 17000 μm / mm ２ Below is a honeycomb filter.

2. The unit dividing line length is 13000 μm / mm ２ The honeycomb filter according to claim 1, wherein:

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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