Pillar honeycomb structure filter and manufacturing method thereof

Abstract

To provide a columnar honeycomb structure filter with improved PM collecting performance.SOLUTION: In a columnar honeycomb structure filter, a plurality of first cells which extend from an inlet side bottom surface to an outlet side bottom surface and have a sealing part at the outlet side bottom surface, and in which the inlet side bottom surface is opened and a plurality of second cells which extend from the inlet side bottom surface to the outlet side bottom surface and have the sealing part at the inlet side bottom surface, and in which the outlet side bottom surface is opened are provided, and the plurality of the first cells and the plurality of the second cells are alternately arranged to be adjacent to each other with a porous partition wall in between. On a surface of each of the first cells, a porous film constituted of a plurality of particles is formed. In obtaining a frequency distribution between the particles by observing the porous film at a cross section in parallel to a film thickness direction and measuring a distance between the particles which is a distance in a direction perpendicular to a film thickness direction between the adjacent particles for the plurality of the particles, the distance (D90) between the particles of an accumulated ratio of 90% is 12.0 μm or less.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a columnar honeycomb structure filter and a method for manufacturing the columnar honeycomb structure filter. [Background technology]

[0002] Exhaust gas emitted from internal combustion engines such as diesel and gasoline engines contains particulate matter (PM) such as soot. Soot is harmful to the human body, so its emission is regulated. Currently, in order to comply with exhaust gas regulations, filters such as DPFs and GPFs are widely used, which filter out soot and other PM by passing exhaust gas through porous partition walls.

[0003] A known filter for capturing PM is a wall-flow type columnar honeycomb structure filter that includes a plurality of first cells extending in the height direction from the inlet side bottom surface to the outlet side bottom surface, with the inlet side bottom surface being open and the outlet side bottom surface being plugged, and a plurality of second cells that are arranged adjacent to the first cells with partition walls in between, extending in the height direction from the inlet side bottom surface to the outlet side bottom surface, with plugged portions on the inlet side bottom surface and the outlet side bottom surface being open.

[0004] In recent years, with the strengthening of exhaust gas regulations, stricter PM emission standards (PN regulations: particle matter number regulations) have been introduced, and filters are required to have high PM capture performance (high PN capture efficiency). Therefore, it has been proposed to form a layer for capturing PM (hereinafter also referred to as a "porous membrane" or "capture layer") on the surface of the cells (Patent Documents 1 to 3). By forming a porous membrane, it is possible to capture PM while reducing pressure loss. A known method for forming a porous membrane is to supply an aerosol containing ceramic particles toward the bottom surface on the inlet side of a columnar honeycomb structure, allow the particles to adhere to the surface of the first cells, and then perform a heat treatment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-154272 [Patent Document 2] Japanese Patent Publication No. 2021-154274 [Patent Document 3] Japanese Patent Publication No. 2022-157612 Summary of the Invention [Problem to be solved by the invention]

[0006] Forming a porous membrane on the cell surface is considered to be effective in improving the PM trapping performance of a columnar honeycomb structure filter. However, although various methods for manufacturing porous membranes have been studied, the influence of the structure of the porous membrane itself on PM trapping performance has not been fully elucidated. For example, the influence of the membrane thickness and the particle size of the raw material particles before the membrane formation process on PM trapping performance has only been confirmed. Patent Document 3 mentions the average pore size of the porous membrane, but there is still room for improvement in PM trapping performance.

[0007] In view of the above circumstances, an object of the present invention is to provide a columnar honeycomb structure filter having improved PM trapping performance in one embodiment, and to provide a method for manufacturing such a columnar honeycomb structure filter in another embodiment. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems and have found that the interparticle distance contained in a porous membrane is closely related to PM capture performance, and that controlling the interparticle distance at which the cumulative ratio reaches 90% (D90) is particularly effective in improving PM capture performance. The present invention was completed based on this finding and is exemplified below.

[0009] [Aspect 1] A columnar honeycomb structure filter comprising: a plurality of first cells extending from an inlet side bottom surface to an outlet side bottom surface, having an open inlet side bottom surface and plugging portions on the outlet side bottom surface; and a plurality of second cells extending from the inlet side bottom surface to the outlet side bottom surface, having plugging portions on the inlet side bottom surface and having an open outlet side bottom surface, wherein the plurality of first cells and the plurality of second cells are alternately arranged adjacent to each other with porous partition walls interposed therebetween, A porous membrane made up of multiple particles is formed on the surface of each first cell. The porous membrane is observed in a cross section parallel to the film thickness direction, and the inter-particle distances between adjacent particles in a direction perpendicular to the film thickness direction are measured for the plurality of particles. When the frequency distribution of the inter-particle distances is calculated, the inter-particle distance (D90) at a cumulative ratio of 90% is 12.0 μm or less. Pillar honeycomb structure filter. [Aspect 2] 2. The columnar honeycomb structure filter according to embodiment 1, wherein the inter-particle distance (D90) at which the cumulative ratio is 90% is 11.0 μm or less. [Aspect 3] A columnar honeycomb structure filter according to aspect 1 or 2, wherein the porous membrane is observed at a cross section parallel to the film thickness direction, and the inter-particle distance, which is the distance between adjacent particles in a direction perpendicular to the film thickness direction, is measured for the plurality of particles, and the frequency distribution of the inter-particle distances is calculated, and the average inter-particle distance is 5.3 μm or less. [Aspect 4] 4. The columnar honeycomb structure filter according to embodiment 3, wherein the average interparticle distance is 5.0 μm or less. [Aspect 5] A columnar honeycomb structure filter according to any one of aspects 1 to 4, wherein the porous membrane is observed at a cross section parallel to the film thickness direction, and the inter-particle distance, which is the distance between adjacent particles in a direction perpendicular to the film thickness direction, is measured for the plurality of particles, and the frequency distribution of the inter-particle distances is calculated, and the standard deviation of the inter-particle distances is 3.6 μm or less. [Aspect 6] 6. The pillar-shaped honeycomb structure filter according to embodiment 5, wherein the standard deviation of the interparticle distances is 3.4 μm or less. [Aspect 7] 7. The pillar-shaped honeycomb structure filter according to any one of aspects 1 to 6, wherein the porous film has an average thickness of 2 to 40 μm. [Aspect 8] 8. The pillar-shaped honeycomb structure filter according to any one of aspects 1 to 7, wherein the porous film is mainly made of silicon carbide, alumina, silica, cordierite, or mullite. [Aspect 9] preparing a pillar-shaped honeycomb structure comprising a plurality of first cells extending from an inlet-side bottom surface to an outlet-side bottom surface, the inlet-side bottom surface being open and having plugging portions on the outlet-side bottom surface, and a plurality of second cells extending from the inlet-side bottom surface to the outlet-side bottom surface, the inlet-side bottom surface being open and having plugging portions on the inlet-side bottom surface, the outlet-side bottom surface being open, the plurality of first cells and the plurality of second cells being alternately arranged adjacent to each other with porous partition walls interposed therebetween; a step of spraying an aerosol containing ceramic particles from a nozzle of an aerosol generator toward the inlet-side bottom surface from a direction perpendicular to the inlet-side bottom surface, while applying a suction force to the outlet-side bottom surface to suck the sprayed aerosol from the inlet-side bottom surface, thereby adhering the ceramic particles to the surface of the first cell; a step of baking the ceramic particles attached to the surface of the first cell to form a porous film composed of a plurality of particles on the surface of the first cell; Including, The aerosol generator has a BET specific surface area of ​​3.5 m 2 / g or more of the ceramic particles, and the ceramic particles are supplied from the container to the nozzle. A method for manufacturing a columnar honeycomb structure filter. [Aspect 10] The container has a BET specific surface area of ​​4.0 m 2 10. A method for producing a columnar honeycomb structure filter according to embodiment 9, wherein the ceramic particles are contained in an amount of 1000 / g or more. [Aspect 11] The aerosol generator includes a drive gas flow path for flowing a pressurized drive gas, a supply port provided midway along the drive gas flow path and capable of sucking the ceramic particles from the container into the drive gas flow path from the outer periphery of the drive gas flow path, and a nozzle attached to the tip of the drive gas flow path and capable of spraying an aerosol. A method for producing the pillar-shaped honeycomb structure filter according to aspect 9 or 10. [Aspect 12] A method for manufacturing a columnar honeycomb structure filter according to any one of aspects 9 to 11, wherein the storage section stores the ceramic particles having a median diameter (D50) of 0.5 to 3.0 μm in a volume-based cumulative particle size distribution measured by a laser diffraction / scattering method. [Aspect 13] A method for manufacturing a columnar honeycomb structure filter according to any one of aspects 9 to 12, wherein the baking treatment includes holding the columnar honeycomb structure having the ceramic particles adhered to the surface of the first cell in a heating furnace having an atmosphere temperature of 1100 to 1300°C for 1.5 to 4 hours. [Effects of the Invention]

[0010] According to the pillar-shaped honeycomb structure filter of one embodiment of the present invention, it is possible to provide a pillar-shaped honeycomb structure filter with improved PM trapping performance. In addition, since the relationship between the interparticle distance contained in the porous film of a pillar-shaped honeycomb structure filter and the PM trapping performance has been clarified, it is possible to accelerate the development of pillar-shaped honeycomb structure filters by using this relationship as the basis for performance evaluation. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view schematically showing an example of a columnar honeycomb structure filter. [Figure 2] 1 is a schematic cross-sectional view of an example of a columnar honeycomb structure filter, observed from a cross section parallel to the cell extension direction. [Figure 3] FIG. 2 is a schematic enlarged partial view of the columnar honeycomb structure filter when observed from a cross section perpendicular to the cell extension direction. [Figure 4] FIG. 1 is a diagram schematically illustrating an example of the structure of an aerosol generator. [Figure 5] FIG. 2 is a schematic diagram illustrating an example of the configuration of a particle adhering device. [Figure 6] This is an example of an SEM image of a porous membrane observed at a cross section parallel to the membrane thickness direction. [Figure 7] 1 is a graph showing the relationship between interparticle distance (D90) and collection performance. [Figure 8] FIG. 2 is a schematic diagram of a cross section of a columnar honeycomb structure filter cut out for determining the average thickness of the porous membrane. DETAILED DESCRIPTION OF THE INVENTION

[0012] Next, embodiments of the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes and improvements may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0013] <1. Pillar honeycomb structure filter> A columnar honeycomb structure filter according to one embodiment of the present invention will be described. The columnar honeycomb structure filter can be used as a DPF (Diesel Particulate Filter) or a GPF (Gasoline Particulate Filter) that collects soot and is attached to an exhaust gas line from a combustion device, typically an engine, mounted on a vehicle. The columnar honeycomb structure filter according to the present invention can be installed, for example, in an exhaust pipe.

[0014] 1 and 2 are a schematic perspective view and a cross-sectional view, respectively, of a pillar-shaped honeycomb structure filter 100. The pillar-shaped honeycomb structure filter 100 includes an outer peripheral side wall 102, a plurality of first cells 108 disposed on the inner peripheral side of the outer peripheral side wall 102, extending parallel to each other from an inlet-side bottom surface 104 to an outlet-side bottom surface 106, opening at the inlet-side bottom surface 104 and having plugging portions 109 at the outlet-side bottom surface 106, and a plurality of second cells 110 disposed on the inner peripheral side of the outer peripheral side wall 102, extending parallel to each other from the inlet-side bottom surface 104 to the outlet-side bottom surface 106, having plugging portions 109 at the inlet-side bottom surface 104 and opening at the outlet-side bottom surface 106. In this columnar honeycomb structure filter 100, the first cells 108 and the second cells 110 are arranged alternately adjacent to each other with porous partition walls 112 sandwiched therebetween, so that the inlet side bottom surface 104 and the outlet side bottom surface 106 each have a honeycomb shape.

[0015] When exhaust gas containing particulate matter (PM) such as soot is supplied to the upstream inlet-side bottom surface 104 of the columnar honeycomb structure filter 100, the exhaust gas is introduced into the first cells 108 and travels downstream within the first cells 108. Because the first cells 108 have plugging portions 109 on the downstream outlet-side bottom surface 106, the exhaust gas passes through porous partition walls 112 that separate the first cells 108 from the second cells 110 and flows into the second cells 110. Since the particulate matter cannot pass through the partition walls 112, it is captured and deposited within the first cells 108. After the particulate matter is removed, the clean exhaust gas that has flowed into the second cells 110 travels downstream within the second cells 110 and flows out from the downstream outlet-side bottom surface 106.

[0016] 3 shows a schematic enlarged partial view of the columnar honeycomb structure filter 100 when observed at a cross section perpendicular to the extending direction of the cells 108 and 110. A porous film 114 is formed on the surface of each first cell 108 of the columnar honeycomb structure filter 100 (the same as the surface of the partition walls 112 that define the first cells 108).

[0017] The porous membrane 114 is composed of multiple particles. The multiple particles that make up the porous membrane 114 are bonded to each other in a three-dimensional structure. When the porous membrane 114 is observed in a cross section parallel to the film thickness direction, the inter-particle distance, which is the distance between adjacent particles in a direction perpendicular to the film thickness direction, is measured for the multiple particles that make up the porous membrane 114, and the frequency distribution of the inter-particle distances is calculated, the PM collection performance tends to improve as the inter-particle distance (D90) at which the cumulative ratio reaches 90% becomes shorter. While controlling the average inter-particle distance, as described below, is also meaningful, controlling the inter-particle distance (D90) is more effective in improving PM collection performance because gas flows more easily through large pores such as D90.

[0018] Specifically, the interparticle distance (D90) is preferably 12.0 μm or less, more preferably 11.0 μm or less, even more preferably 10.0 μm or less, even more preferably 9.0 μm or less, and even more preferably 8.0 μm or less. While there is no particular lower limit for the interparticle distance (D90), from the viewpoint of suppressing pressure loss and saturating the improvement effect of PM trapping performance, D90 is preferably 0.5 μm or more, more preferably 0.75 μm or more, even more preferably 1.0 μm or more, even more preferably 1.5 μm or more, and even more preferably 2.0 μm or more. Therefore, the interparticle distance (D90) is, for example, preferably 0.5 to 12.0 μm, more preferably 0.75 to 11.0 μm, more preferably 1.0 to 10.0 μm, more preferably 1.5 to 9.0 μm, and even more preferably 2.0 to 8.0 μm.

[0019] When the porous membrane 114 is observed at a cross section parallel to the film thickness direction, the inter-particle distance, which is the distance between adjacent particles in a direction perpendicular to the film thickness direction, is measured for the multiple particles that make up the porous membrane 114, and the frequency distribution of the inter-particle distances is calculated, it is found that a shorter (arithmetic) average value of the inter-particle distances is also desirable in terms of improving PM collection performance.

[0020] Specifically, the average interparticle distance is preferably 5.3 μm or less, more preferably 5.0 μm or less, even more preferably 4.5 μm or less, and even more preferably 4.0 μm or less. While there is no particular lower limit for the average interparticle distance, from the viewpoint of suppressing pressure loss and saturating the effect of improving PM trapping performance, the average interparticle distance is preferably 0.25 μm or more, more preferably 0.5 μm or more, even more preferably 0.75 μm or more, and even more preferably 1.0 μm or more. Therefore, the average interparticle distance is, for example, preferably 0.25 to 5.3 μm, more preferably 0.5 to 5.0 μm, even more preferably 0.75 to 4.5 μm, and even more preferably 1.0 to 4.0 μm.

[0021] When the porous membrane 114 is observed at a cross section parallel to the film thickness direction, the inter-particle distance, which is the distance between adjacent particles in a direction perpendicular to the film thickness direction, is measured for the multiple particles that make up the porous membrane 114, and the frequency distribution of the inter-particle distances is calculated, it is desirable that the standard deviation of the inter-particle distances is also small in order to improve PM collection performance.

[0022] Specifically, the standard deviation of the interparticle distance is preferably 3.6 μm or less, more preferably 3.4 μm or less, and even more preferably 3.2 μm or less. There is no particular lower limit for the standard deviation of the interparticle distance, and it may be 0, but from the viewpoint of ease of production, the standard deviation of the interparticle distance is preferably 0.5 μm or more, and more preferably 0.7 μm or more. Therefore, the standard deviation of the interparticle distance is, for example, preferably 0.5 to 3.6 μm, more preferably 0.5 to 3.4 μm, and even more preferably 0.7 to 3.2 μm.

[0023] The porous membrane 114 is observed at a cross section parallel to the film thickness direction, and the interparticle distance, which is the distance between adjacent particles in the direction perpendicular to the film thickness direction, is measured for the multiple particles that make up the porous membrane 114 as follows: Samples (size = 10 mm × 10 mm × 10 mm) are taken from near the central axis (radial center) near the bottom surface on the inlet side of the columnar honeycomb structure filter, near the central axis near the bottom surface on the outlet side, and near the central axis near the center in the height direction (length direction of the cells).

[0024] Next, a cross section of the porous film of each sample parallel to the film thickness direction is observed using an electron microscope (SEM) at a magnification of 1000. Next, image analysis software is used to binarize the SEM image into void and solid portions.

[0025] The porous membrane is divided into three regions: near the boundary with the partition wall, near the outer surface, and near the center of the thickness. In each region, a straight line (70 μm long and 0.5 μm wide on the scale on the SME image) is drawn perpendicular to the film thickness direction. The length of each line segment (= interparticle distance) that these lines cross is measured, and the frequency distribution is calculated.

[0026] In this case, the straight lines are drawn in the region near the boundary with the partition walls so as not to include the partition wall portion. Furthermore, the outer surface is not necessarily flat and may have irregularities, but the straight lines are drawn in the region near the outer surface so as not to include spaces due to the irregularities that form the outer surface. Furthermore, the three straight lines are drawn at equal intervals. Figure 6 shows the three straight lines together with an example of a cross-sectional SEM image of the porous membrane of Example 1.

[0027] In this way, the frequency distribution of the interparticle distances was determined for each of the three samples, and three parameters, namely, the interparticle distance (D90), the average value of the interparticle distances, and the standard deviation of the interparticle distances, were calculated for each sample. The average value of each parameter was then calculated from the results of the three samples, and used as the measurement value for the columnar honeycomb structure filter.

[0028] The lower limit of the average membrane thickness of the porous membrane is preferably 2 μm or more, more preferably 4 μm or more, and even more preferably 6 μm or more, from the viewpoint of improving PM trapping performance. The upper limit of the average membrane thickness of the porous membrane is preferably 40 μm or less, more preferably 35 μm or less, and even more preferably 30 μm or less, from the viewpoint of suppressing an increase in pressure loss. Therefore, the average membrane thickness of the porous membrane is, for example, preferably 2 to 40 μm, more preferably 4 to 35 μm, and even more preferably 6 to 30 μm.

[0029] The average thickness of the porous membrane is measured by the following method. The direction in which the first cells of the columnar honeycomb structure filter extend is taken as the direction in which the coordinate axes extend, with the coordinate value of the inlet side bottom surface being 0 and the coordinate value of the outlet side bottom surface being X. The average thickness of the porous membrane is measured in five fields of view at six locations, A1, A2, A3, B1, B2, and B3, and the overall average value of these is taken as the thickness of the columnar honeycomb structure. filter The average thickness of the porous film is defined as the average thickness of the porous film. A1: The center of the cross section of the columnar honeycomb structure filter in the coordinate range of 0.1X to 0.3X, which is perpendicular to the extending direction of the first cell. B1: The outer periphery of the cross section of the columnar honeycomb structure filter in the coordinate range of 0.1X to 0.3X, which is perpendicular to the extending direction of the first cells. A2: The center of the cross section of the columnar honeycomb structure filter in the coordinate range of 0.4X to 0.6X, which is perpendicular to the extending direction of the first cell. B2: The outer periphery of the cross section of the columnar honeycomb structure filter in the coordinate range of 0.4X to 0.6X, which is perpendicular to the extending direction of the first cells. A3: The center of the cross section of the columnar honeycomb structure filter in the coordinate range of 0.7X to 0.9X, which is perpendicular to the extending direction of the first cell. B3: The outer periphery of the cross section of the columnar honeycomb structure filter in the coordinate range of 0.7X to 0.9X, which is perpendicular to the extending direction of the first cells.

[0030] The central and peripheral regions of the columnar honeycomb structure filter when measuring the average thickness of the porous membrane are determined as follows. When the columnar honeycomb structure filter is observed from a cross section perpendicular to the extension direction of the first cells, a line segment is drawn from the center of gravity of the cross section to the outer surface of the outer peripheral side wall, and the extension direction of the line segment is set to the extension direction of the coordinate axes, with the coordinate value of the center of gravity set to 0 and the coordinate value of the outer surface of the outer peripheral side wall set to R. In this case, on the line segment, the range of coordinate values ​​0 to 0.2R is the central region, and the range of coordinate values ​​0.7R to 0.9R is the outer region. By drawing many such line segments on the cross section and aggregating the central and peripheral regions on each line segment, the ranges of the central and peripheral regions on the cross section can be obtained.

[0031] The average thickness of the porous membrane at each of the points A1, A2, A3, B1, B2, and B3 is measured by the following method. A cross section parallel to the extension direction of the first cells and parallel to a line segment extending from the outer surface of the outer side wall toward the center of gravity is cut from the point (center or outer periphery) where the average thickness of the porous membrane of the columnar honeycomb structure filter is to be determined. The cross section is observed using a 3D shape measuring device (e.g., Keyence VR-3200) at a magnification of 25x and with an observation field of view of 12.5 mm (width) × 9.5 mm (length). The horizontal direction of the observation field is parallel to the extension direction of the first cells.

[0032] FIG. 8 shows a schematic diagram of the cut cross section. By observing the cross section, the first cells 108 on which the porous membrane is formed and the second cells 110 on which the porous membrane is not formed are identified. Next, the three first cells 108 adjacent to each other at the position closest to the center on the cross section are identified. Furthermore, the central regions 110a (reference planes) of the two second cells 110 sandwiched between the three first cells 108 adjacent to each other at the position closest to the center on the cross section are identified, and leveling is performed using image processing software (e.g., software included with Keyence's 3D shape measuring instrument VR-3200) so that the reference plane is as horizontal as possible based on the profiles of both regions. After leveling, the two second cells 11 are aligned. 0'sFor the central region 110a, an area is designated and the average height H2 of that area is measured. After leveling, an area is designated for the central regions 108a of the three first cells 108, and the average height H1 of that area is measured. The difference between the average height H1 and the average height H2 in one field of view is defined as the average thickness of the porous film in that field of view. Note that the central regions 108a and 110a refer to the central regions when the distance between the pair of partition walls 112 that separate each cell is divided into thirds.

[0033] The average thickness of the porous film in any five fields of view is determined for each of the points A1, A2, A3, B1, B2, and B3, and these are defined as the average thickness of the porous film at each of the points A1, A2, A3, B1, B2, and B3. The overall average value is defined as the average thickness of the porous film of the columnar honeycomb structure filter.

[0034] The porous film can be made of ceramics. For example, the porous film can contain one or more ceramics selected from cordierite, silicon carbide (SiC), talc, mica, mullite, cerium, aluminum titanate, alumina, silicon nitride, sialon, zirconium phosphate, zirconia, titania, and silica. The main component of the porous film is preferably silicon carbide, alumina, silica, cordierite, or mullite. Among these, the main component of the porous film is preferably silicon carbide, since the presence of a surface oxide film (SiO) provides a porous film that is strongly bonded to each other and is difficult to peel. The main component of the porous film refers to a component that accounts for 50% or more by mass of the porous film. SiC preferably accounts for 50% or more by mass, more preferably 70% or more by mass, and even more preferably 90% or more by mass of the porous film. The shape of the ceramic constituting the porous film is not particularly limited, but examples include granular and fibrous forms.

[0035] The materials constituting the partition walls and outer peripheral side walls of the columnar honeycomb structure filter include, but are not limited to, porous ceramics. Examples of ceramics include cordierite, mullite, zirconium phosphate, aluminum titanate, silicon carbide (SiC), silicon-silicon carbide composites (e.g., Si-bonded SiC), cordierite-silicon carbide composites, zirconia, spinel, indialite, sapphirine, corundum, titania, and silicon nitride. These ceramics may be used alone or in combination.

[0036] The columnar honeycomb structure filter may support a PM combustion catalyst that assists in the combustion of PM such as soot, an oxidation catalyst (DOC), an SCR catalyst and an NSR catalyst for removing nitrogen oxides (NOx), and a three-way catalyst that can simultaneously remove hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx).The columnar honeycomb structure filter according to this embodiment may also support various catalysts.

[0037] The bottom shape of the columnar honeycomb structure filter is not limited, and may be, for example, a round shape such as a circle, an ellipse, a racetrack shape, or an oval shape, or a polygonal shape such as a triangle or a rectangle. The columnar honeycomb structure filter 100 in Fig. 1 has a circular bottom shape and is cylindrical as a whole.

[0038] There is no particular limitation on the height of the columnar honeycomb structure filter (the length from the bottom surface on the inlet side to the bottom surface on the outlet side) and it may be set appropriately depending on the application and required performance. There is also no particular limitation on the relationship between the height of the columnar honeycomb structure filter and the maximum diameter of each bottom surface (the maximum length of the diameters passing through the center of gravity of each bottom surface of the columnar honeycomb structure filter). Therefore, the height of the columnar honeycomb structure filter may be longer than the maximum diameter of each bottom surface, or the height of the columnar honeycomb structure filter may be shorter than the maximum diameter of each bottom surface.

[0039] Although there is no limitation on the shape of the cells in a cross section perpendicular to the cell extension direction, a quadrangle, a hexagon, an octagon, or a combination thereof is preferred. Among these, a square and a hexagon are preferred. By using such a cell shape, it is possible to reduce the pressure loss when a fluid flows through the columnar honeycomb structure filter.

[0040] The columnar honeycomb structure filter can be provided as an integrally molded product. Alternatively, the columnar honeycomb structure filter can be provided as a segment assembly, which is formed by joining together a plurality of columnar honeycomb structure filter segments, each having an outer peripheral side wall. Providing the columnar honeycomb structure filter as a segment assembly can enhance thermal shock resistance.

[0041] The lower limit of the porosity of the partition walls is preferably 40% or more, more preferably 44% or more, and even more preferably 48% or more, from the viewpoint of keeping the pressure loss of exhaust gas low. Furthermore, the upper limit of the porosity of the partition walls is preferably 75% or less, more preferably 70% or less, and even more preferably 65% ​​or less, from the viewpoint of ensuring the strength of the columnar honeycomb structure filter. Therefore, the porosity of the partition walls is, for example, preferably 40 to 75%, more preferably 44 to 70%, and even more preferably 48 to 65%.

[0042] The porosity of the partition walls is measured by the following method. Samples (size = 10 mm × 10 mm × 10 mm) are collected from the vicinity of the central axis (radial center) near the bottom surface on the inlet side of the columnar honeycomb structure filter, the vicinity of the central axis near the bottom surface on the outlet side, and the vicinity of the central axis near the center in the height direction (length direction of the cells). Next, the partition wall cross section of each sample (size per field of view: 150 μm × 150 μm) is photographed at 1000 times magnification using an SEM (scanning electron microscope), and binarized into void and solid areas using image analysis software. Next, the area ratio of the void area in the field of view is calculated, and the average value of this ratio is calculated to obtain the porosity (%) of the partition walls of the sample. The average porosity of the three samples is then calculated and used as the measured value for the columnar honeycomb structure filter.

[0043] From the viewpoint of suppressing pressure loss, the upper limit of the average thickness of the partition walls in the columnar honeycomb structure filter is preferably 0.37 mm or less, more preferably 0.35 mm or less, and even more preferably 0.33 mm or less. However, from the viewpoint of ensuring the strength of the columnar honeycomb structure filter, the lower limit of the average thickness of the partition walls is preferably 0.10 mm or more, more preferably 0.13 mm or more, and even more preferably 0.15 mm or more. Therefore, for example, the average thickness of the partition walls in the columnar honeycomb structure filter is preferably 0.10 to 0.37 mm, more preferably 0.13 to 0.35 mm, and even more preferably 0.15 to 0.33 mm.

[0044] In this specification, the thickness of a partition wall refers to the length of a line segment that crosses a partition wall when the line segment connects the centers of gravity of adjacent cells in a cross section perpendicular to the extension direction of the cells. The average thickness of partition walls refers to the average value of the thicknesses of all partition walls.

[0045] The cell density (the number of cells per unit cross-sectional area perpendicular to the cell extension direction) is not particularly limited, but is, for example, 6 to 2000 cells / square inch (0.9 to 311 cells / cm 2 ), more preferably 50 to 1000 cells / square inch (7.8 to 155 cells / cm 2), and particularly preferably 100 to 400 cells / square inch (15.5 to 62.0 cells / cm 2 ) can be used.

[0046] The columnar honeycomb structure filter can be provided as an integrally molded product. Alternatively, the columnar honeycomb structure filter can be provided as a segment assembly, which is formed by joining together a plurality of columnar honeycomb structure filter segments, each having an outer peripheral side wall. Providing the columnar honeycomb structure filter as a segment assembly can enhance thermal shock resistance.

[0047] <2. Manufacturing method of columnar honeycomb structure filter> A method for manufacturing a columnar honeycomb structure filter is described below by way of example. First, a raw material composition containing ceramic raw materials, a dispersion medium, a pore-forming material, and a binder is kneaded to form a clay, and then the clay is extruded to form a desired columnar honeycomb molded body. Additives such as a dispersant can be blended into the raw material composition as needed. During extrusion molding, a die having the desired overall shape, cell shape, partition wall thickness, cell density, etc. can be used.

[0048] After drying the columnar honeycomb formed body, plugging portions are formed at predetermined positions on both bottom surfaces of the columnar honeycomb formed body, and the plugging portions are then dried to obtain a columnar honeycomb formed body with plugging portions. The columnar honeycomb formed body is then degreased and fired to obtain a columnar honeycomb structure. A porous film is then formed on the surfaces of the first cells of the columnar honeycomb structure to obtain a columnar honeycomb structure filter.

[0049] The ceramic raw material remains after firing and is the raw material for the portion that constitutes the skeleton of the honeycomb structure as ceramic. As the ceramic raw material, raw materials that can form the above-mentioned ceramics after firing can be used. The ceramic raw material can be provided, for example, in the form of powder. Examples of the ceramic raw material include raw materials for obtaining ceramics such as cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon nitride, zirconia, spinel, indialite, sapphirine, corundum, and titania. Specific examples include, but are not limited to, silica, talc, alumina, kaolin, serpentine, pyroferrite, brucite, boehmite, mullite, magnesite, and aluminum hydroxide. The ceramic raw material may be used singly or in combination of two or more types.

[0050] In the case of filter applications such as DPF and GPF, cordierite can be suitably used as the ceramic. In this case, a cordierite-forming raw material can be used as the ceramic raw material. The cordierite-forming raw material is a raw material that becomes cordierite when fired. The cordierite-forming raw material preferably has a chemical composition of 30 to 45 mass% alumina (Al2O3) (including aluminum hydroxide converted to alumina), 11 to 17 mass% magnesia (MgO), and 42 to 57 mass% silica (SiO2).

[0051] Examples of the dispersion medium include water and a mixed solvent of water and an organic solvent such as alcohol, with water being particularly preferred.

[0052] The pore-forming material is not particularly limited as long as it forms pores after firing, and examples thereof include wheat flour, starch, foamed resin, water-absorbent resin, porous silica, carbon (e.g., graphite), ceramic balloons, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic, and phenol. One type of pore-forming material may be used alone, or two or more types may be used in combination. From the viewpoint of increasing the porosity of the fired body, the content of the pore-forming material is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of the ceramic raw material. From the viewpoint of ensuring the strength of the fired body, the content of the pore-forming material is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less, per 100 parts by mass of the ceramic raw material.

[0053] Examples of binders include organic binders such as methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. It is particularly preferable to use a combination of methyl cellulose and hydroxypropyl methyl cellulose. Furthermore, from the viewpoint of increasing the strength of the honeycomb formed body, the binder content is preferably 4 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 6 parts by mass or more, per 100 parts by mass of the ceramic raw materials. From the viewpoint of suppressing cracks due to abnormal heat generation during the firing process, the binder content is preferably 9 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 7 parts by mass or less, per 100 parts by mass of the ceramic raw materials. One type of binder may be used alone, or two or more types may be used in combination.

[0054] The dispersant may be ethylene glycol, dextrin, fatty acid soap, polyether polyol, etc. One type of dispersant may be used alone, or two or more types may be used in combination. The content of the dispersant is preferably 0 to 2 parts by mass per 100 parts by mass of the ceramic raw material.

[0055] The method for plugging the bottom surface of the columnar honeycomb formed body is not particularly limited, and known methods can be used. The material for the plugging portions is not particularly limited, but ceramics are preferred from the viewpoints of strength and heat resistance. The ceramic is preferably a ceramic material containing at least one selected from the group consisting of cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon nitride, zirconia, spinel, indialite, sapphirine, corundum, and titania. It is even more preferred that the plugging portions have the same material composition as the main body of the honeycomb formed body, as this allows the expansion coefficients during firing to be the same, leading to improved durability.

[0056] After drying the honeycomb formed body, degreasing and firing are performed to manufacture a columnar honeycomb structure. The conditions for the drying, degreasing and firing processes may be well known conditions depending on the material composition of the honeycomb formed body, and no particular explanation is required, but examples of specific conditions are given below.

[0057] In the drying step, a conventionally known drying method can be used, for example, hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, freeze drying, etc. Among them, a drying method that combines hot air drying with microwave drying or dielectric drying is preferred, since it can dry the entire molded body quickly and uniformly.

[0058] When forming plugging portions, it is preferable to form plugging portions on both bottom surfaces of the dried honeycomb formed body and then dry the plugging portions. The plugging portions are formed at predetermined positions so that a plurality of first cells extending from the inlet-side bottom surface to the outlet-side bottom surface, having an open inlet-side bottom surface and a plugging portion on the outlet-side bottom surface, and a plurality of second cells extending from the inlet-side bottom surface to the outlet-side bottom surface, having a plugging portion on the inlet-side bottom surface and an open outlet-side bottom surface, are alternately arranged adjacent to each other with the porous partition wall interposed therebetween.

[0059] Next, the degreasing process will be described. The combustion temperature of the binder is about 200°C, and the combustion temperature of the pore-forming material is about 300 to 1000°C. Therefore, the degreasing process can be carried out by heating the honeycomb formed body to a temperature in the range of about 200 to 1000°C. The heating time is not particularly limited, but is usually about 10 to 100 hours. The honeycomb formed body after the degreasing process is called a calcined body.

[0060] The firing step depends on the material composition of the honeycomb formed body, but can be carried out, for example, by heating the calcined body to 1350 to 1600°C and holding it for 3 to 10 hours. In this way, a pillar-shaped honeycomb structure is produced, which includes a plurality of first cells extending from the inlet-side bottom face to the outlet-side bottom face, which are open at the inlet-side bottom face and have plugging portions at the outlet-side bottom face, and a plurality of second cells extending from the inlet-side bottom face to the outlet-side bottom face, which have plugging portions at the inlet-side bottom face and are open at the outlet-side bottom face, and in which the plurality of first cells and the plurality of second cells are alternately arranged adjacent to each other with porous partition walls sandwiched therebetween.

[0061] Next, a porous film is formed on the surfaces of the first cells of the columnar honeycomb structure that has undergone the firing process. First, a step is carried out in which an aerosol containing ceramic particles is sprayed from a direction perpendicular to the inlet-side bottom face of the columnar honeycomb structure toward the inlet-side bottom face, preferably toward the center of the inlet-side bottom face, while applying suction force to the outlet-side bottom face to suck the sprayed aerosol from the inlet-side bottom face, thereby adhering the ceramic particles to the surfaces of the first cells. Illustratively, the distance between the aerosol spray nozzle and the inlet-side bottom face can be 500 mm to 2000 mm.

[0062] The aerosol can be sprayed using an aerosol generator. In one embodiment, the aerosol generator has a container for containing ceramic particles, the ceramic particles are supplied from the container to a nozzle, and the aerosol is sprayed from the nozzle.

[0063] The particles that make up the porous membrane are arranged in a way that shortens the interparticle distance to form a dense porous membrane, with a BET specific surface area of ​​3.5m 2 It is preferable that ceramic particles of 1.0 m / g or more are contained in the container. Although it is not intended that the present invention be limited by theory, it is believed that if the BET specific surface area is large, the particles become bulky and are dispersed more uniformly when sprayed as an aerosol during film formation, thereby shortening the interparticle distance. The lower limit of the BET specific surface area of ​​the ceramic particles contained in the container is 4.0 m 2 / g or more is more preferable, and 6.0m 2 / g or more is more preferable, and 8.0m 2 / g or more is more preferable, and 10.0m 2 / g or more is more preferable, and 12.0m 2 / g or more is more preferable, and 14.0m 2 / g or more is more preferable, and 16.0m 2 Although there is no particular upper limit for the BET specific surface area of ​​the ceramic particles contained in the container, the upper limit is set to 100.0 m / g or more because the collection performance tends to saturate while the production cost increases. 2 / g or less, and 2 / g or less is more preferable, and 80.0m 2 Therefore, the BET specific surface area of ​​the ceramic particles contained in the container is, for example, 3.0 to 100.0 m 2 / g, and 4.0 to 90.0 m 2 / g, and more preferably 6.0 to 80.0 m 2 / g, and more preferably 8.0 to 80.0 m 2 / g, and more preferably 10.0 to 80.0 m 2 / g, and more preferably 12.0 to 80.0 m 2 / g, and more preferably 14.0 to 80.0 m 2 / g, and more preferably 16.0 to 80.0m 2 / g is even more preferred.

[0064] Methods for increasing the BET specific surface area of ​​ceramic particles include, for example, reducing the size of raw material particles, changing the pulverization method (from a jet mill to a ball mill), etc. Conversely, methods for decreasing the BET specific surface area of ​​ceramic particles include, for example, increasing the size of raw material particles.

[0065] The BET specific surface area of ​​the ceramic particles is measured in accordance with the BET single-point method in accordance with JIS Z8830:2013.

[0066] Furthermore, in order to shorten the interparticle distance and form a dense porous film, it is advantageous to control the particle size of the ceramic particles in addition to controlling the BET specific surface area. Specifically, the ceramic particles contained in the container preferably have an upper median diameter (D50) of 3.0 μm or less, more preferably 2.5 μm or less, and even more preferably 2.0 μm or less, in the volume-based cumulative particle size distribution measured by laser diffraction / scattering. Furthermore, the lower limit of the median diameter (D50) is preferably 0.5 μm or more, more preferably 0.7 μm or more, and even more preferably 0.9 μm or more. Therefore, the median diameter (D50) is preferably, for example, 0.5 to 3.0 μm, more preferably 0.7 to 2.5 μm, and even more preferably 0.9 to 2.0 μm.

[0067] The ceramic particles used are the same as those used to form the porous film. For example, ceramic particles containing one or more selected from cordierite, silicon carbide (SiC), talc, mica, mullite, cerium, aluminum titanate, alumina, silicon nitride, sialon, zirconium phosphate, zirconia, titania, and silica can be used. The main component of the ceramic particles is preferably silicon carbide, alumina, silica, cordierite, or mullite. The main component of the ceramic particles refers to a component that accounts for 50% or more by mass of the ceramic particles. Preferably, SiC accounts for 50% or more by mass of the ceramic particles, more preferably 70% or more by mass, and even more preferably 90% or more by mass.

[0068] Ceramic particles contained in the container may aggregate over time. Fine ceramic particles are particularly prone to aggregation. Therefore, it is preferable to loosen the aggregates before injecting the ceramic particles from the nozzle of the aerosol generator. Therefore, the aerosol generator preferably includes a drive gas flow path for supplying a pressurized drive gas, a supply port located midway through the drive gas flow path and capable of drawing ceramic particles from the container toward the inside of the drive gas flow path from the outer periphery of the drive gas flow path, and a nozzle attached to the end of the drive gas flow path and capable of injecting the aerosol. When ceramic particles are supplied from the outer periphery of the drive gas flow path toward the inside of the drive gas flow path, the drive gas effectively disintegrates the ceramic particles, enabling ceramic particles with reduced aggregation to be injected from the nozzle of the aerosol generator. In one embodiment, the supply port can be configured to introduce ceramic particles into the drive gas flow path from a direction substantially perpendicular to the flow direction of the drive gas through the drive gas flow path.

[0069] (aerosol generator) FIG. 4 shows a schematic example of the configuration of an aerosol generator 400 suitable for spraying ceramic particles with reduced aggregation. The aerosol generator 400 is a drive gas flow path 407 for flowing a pressurized drive gas; a supply port 407i provided in the driving gas flow path 407 and capable of sucking ceramic particles 402 from the outer periphery of the driving gas flow path 407 toward the inside of the driving gas flow path 407; a nozzle 401 attached to the tip of the driving gas flow path 407 and capable of injecting an aerosol; a flow path 403 for sucking and transporting ceramic particles 402, the flow path 403 having an outlet 403e communicating with the supply port 407i; a container 409 for containing ceramic particles 402 and supplying the ceramic particles 402 to a flow path 403 for suction and transport; It has.

[0070] The container 409 may be, for example, a funnel. Ceramic particles having a predetermined BET specific surface area are contained in the container 409. The ceramic particles 402 contained in the container 409 are transported by suction from an outlet 409e at the bottom of the container 409 through the flow path 403 to the outlet 403e by the suction force of the drive gas flow path 407, and then introduced into the drive gas flow path 407 through the supply port 407i. At this time, ambient gas (typically air) sucked through the inlet 409i of the container 409 is also introduced into the drive gas flow path 407 along with the ceramic particles 402 through the flow path 403. In the illustrated aerosol generator 400, the outlet 403e and the supply port 407i are common. In the illustrated aerosol generator 400, the ceramic particles 402 are introduced into the drive gas flow path 407 from a direction approximately perpendicular to the flow direction of the drive gas flowing through the drive gas flow path 407.

[0071] Ceramic particles 402 supplied into drive gas flow channel 407 collide with the drive gas flowing through drive gas flow channel 407, and are crushed and mixed to form an aerosol, which is then sprayed from nozzle 401. Nozzle 401 is preferably installed at a position and oriented so that the aerosol is sprayed in a direction perpendicular to the inlet-side bottom surface of the columnar honeycomb structure. More preferably, nozzle 401 is installed at a position and oriented so that the aerosol is sprayed in a direction perpendicular to the inlet-side bottom surface toward the center of the inlet-side bottom surface.

[0072] The ceramic particles 402 are preferably supplied to the container 409 using, but not limited to, a powder quantitative feeder 411 such as a screw feeder or a belt conveyor. The ceramic particles 402 discharged from the powder quantitative feeder 411 can fall into the container 409 by gravity.

[0073] In a preferred embodiment, the drive gas flow path 407 includes a venturi section 407v with a narrowed flow path, and the supply port 407i is located downstream of the most narrowed point of the venturi section 407v. The venturi section 407v in the drive gas flow path 407 increases the velocity of the drive gas passing through the venturi section 407v, allowing the drive gas to collide with the ceramic particles 402 supplied downstream of the venturi section 407v at a higher velocity, thereby improving the disintegration force. To enhance the disintegration force of the drive gas, the supply port 407i is preferably located downstream of and adjacent to the most narrowed point of the venturi section 407v. This configuration can be achieved, for example, by connecting the drive gas flow path 407 and the suction-transport flow path 403 using a venturi ejector 410.

[0074] From the viewpoint of increasing the crushing force of ceramic particles, the lower limit of the flow velocity of the driving gas immediately before passing through the venturi section 407v is preferably 13 m / s or more, more preferably 20 m / s or more, and even more preferably 26 m / s or more. There is no particular upper limit to the flow velocity of the driving gas immediately before passing through the venturi section 407v, but it is usually 50 m / s or less, typically 40 m / s or less.

[0075] From the viewpoint of increasing the disintegration force, the lower limit of the ratio of the flow path cross-sectional area immediately before the venturi section to the flow path cross-sectional area of ​​the venturi section is preferably 8 or more, and more preferably 16 or more. There is no particular upper limit to the ratio of the flow path cross-sectional area immediately before the venturi section to the flow path cross-sectional area of ​​the venturi section, but if it is too large, the pressure loss in the venturi section increases, so it is preferably 64 or less, and more preferably 32 or less. Here, the flow path cross-sectional area of ​​the venturi section means the flow path cross-sectional area at the narrowest point in the venturi section. Furthermore, the flow path cross-sectional area immediately before the venturi section means the flow path cross-sectional area immediately before the flow path narrows upstream of the venturi section.

[0076] By using the venturi ejector 410, for example, when the drive gas is flowed through the drive gas flow path 407, a large suction force can be applied to the flow path 403 for suction and transport, and the flow path 403 for suction and transport can be prevented from being clogged with the ceramic particles 402. The venturi ejector 410 is also effective as a means for removing the ceramic particles 402 when the flow path 403 for suction and transport is clogged with the ceramic particles 402.

[0077] The flow rate of the aerosol sprayed from the nozzle 401 can be controlled by using a compressed gas such as pressure-adjusted compressed air as the driving gas. Dry air (e.g., with a dew point of 10°C or less) is preferably used as the driving gas to suppress aggregation of the ceramic particles. In this specification, the "dew point" refers to a value measured using a polymer-type capacitance dew point meter conforming to JIS Z8806:2001.

[0078] (Particle attachment device) FIG. 5 shows a schematic configuration example of a particle attachment device 510 suitable for carrying out the step of attaching ceramic particles to the surfaces of the first cells of the pillar-shaped honeycomb structure. The particle deposition device 510 includes: a holder 514 for holding the columnar honeycomb structure 500; a blower 512 for applying suction force to the outlet side bottom surface 506 of the columnar honeycomb structure 500; an aerosol generator 511 for spraying an aerosol containing ceramic particles toward the inlet side bottom surface 504 in a direction perpendicular to the inlet side bottom surface 504 to cause the ceramic particles to adhere to the surface of the first cell; a chamber 513 provided between the nozzle 511a of the aerosol generator 511 and the inlet-side bottom surface 504 for guiding the aerosol through its interior; Equipped with.

[0079] The holder 514 is configured so as to hold the columnar honeycomb structure 500 at a position facing the nozzle 511a of the aerosol generator 511 with the inlet-side bottom surface 504 of the columnar honeycomb structure 500 exposed. For example, the holder 514 may have a chuck mechanism 514b for gripping the outer peripheral side wall 502. There are no particular limitations on the chuck mechanism, but a balloon chuck is an example. The holder 514 may also have a housing 514a for rectifying the aerosol that has passed through the columnar honeycomb structure 500 in one direction without diffusing.

[0080] Sidewall 513d of chamber 513 can be formed in a tubular shape, such as a cylindrical or rectangular tube. Chamber 513 has surface 513a facing inlet-side bottom surface 504. Surface 513a facing inlet-side bottom surface 504 has insertion port 513b for nozzle 511a of aerosol generator 511. With this configuration, aerosol sprayed from aerosol generator 511 can be directly introduced into chamber 513. Typically, downstream end 513e of sidewall 513d of chamber 513 is connected to holder 514, and this facing surface 513a is provided at upstream end 513f, which is opposite downstream end 513e of sidewall 513d of chamber 513.

[0081] Openings 513c for taking in ambient gas can be provided in sidewall 513d and / or surface 513a facing inlet-side bottom surface 504. This makes it possible to adjust the flow rate of gas flowing into chamber 513 according to the suction force from blower 512. However, as shown in Figure 5, it is preferable that openings 513c for taking in ambient gas are not provided in sidewall 513d of chamber 513, and that ambient gas flowing into chamber 513 is taken in only through openings 513c provided in surface 513a facing inlet-side bottom surface 504.

[0082] Taking in ambient gas only from surface 513a facing inlet-side bottom surface 504 has the advantage that the ambient gas flows in in the same direction as the flow of the sprayed aerosol, eliminating any disturbances to the aerosol and stabilizing the aerosol. Conversely, having openings 513c in sidewall 513d of chamber 513 is disadvantageous because the ambient gas flowing in from these openings is likely to cause disturbances and destabilize the flow of the aerosol. Therefore, in a preferred embodiment, surface 513a facing inlet-side bottom surface 504 has one or more openings 513c for taking in ambient gas into chamber 513, and no openings for taking in ambient gas into chamber 513 exist other than on surface 513a.

[0083] The opposing surface 513a of the chamber 513 may have a concentric closing portion 518 centered on the insertion port 513b. In this case, one or more openings 513c for introducing ambient gas into the chamber 513 are provided on the outer periphery of the closing portion 518. There are no particular limitations on the method for forming the closing portion 518, but in one embodiment, a disk-shaped plate having an insertion port 513b for the nozzle 511a can be used.

[0084] The provision of the closing portion 518 prevents ambient gas from flowing in from the vicinity of the nozzle 511a of the aerosol generator 511. On the other hand, ambient gas flows in from the vicinity of the side wall 513d of the chamber 513. This allows the aerosol sprayed from the nozzle 511a to be drawn into the ambient gas flowing in from the opening 513c and flowing near the side wall 513d, which advantageously makes it easier for the aerosol to spread uniformly in a direction perpendicular to the direction of the aerosol flow. The closing portion 518 can close, for example, 50 to 87% of the area of ​​the opposing surface (inner surface) 513a of the chamber 513, and can typically close 70 to 80%. Here, the area of ​​the opposing surface (inner surface) 513a includes the area of ​​the insertion opening 513b and the opening 513c in addition to the non-opening portion.

[0085] A punched plate and / or nonwoven fabric may be used on the opposing surface 513a of the chamber 513. Furthermore, a filter 513g may be installed in the opening 513c since there is a possibility that aggregated powder, honeycomb fragments, and dust may be caught in the opening 513c.

[0086] When the cross-sectional area of ​​the flow path of the aerosol flowing through chamber 513 is larger than the size of inlet-side bottom surface 504, tapered portion 513h may be provided at downstream end 513e of side wall 513d so that the cross-sectional area of ​​the flow path gradually decreases toward inlet-side bottom surface 504. It is preferable that the outline of the flow path cross section formed by tapered portion 513h at downstream end 513e of side wall 513d matches the outer circumferential outline of inlet-side bottom surface 504. By providing tapered portion 513h, ceramic particles are more likely to be sucked into inlet-side bottom surface 504.

[0087] The distance L from the outlet of the nozzle 511a to the inlet side bottom surface 504 of the columnar honeycomb structure 500 is preferably designed in accordance with the area A of the inlet side bottom surface 504 of the columnar honeycomb structure 500. Specifically, the area A (mm 2 ) increases, it is preferable to increase the distance L (mm) because this makes it easier for the aerosol to spread uniformly in the direction perpendicular to the direction of the aerosol flow.

[0088] The aerosol sprayed from the aerosol generator 511 passes through the inside of the chamber 513 by the suction force of the blower 512, and is then sucked into the first cells of the columnar honeycomb structure 500 from the inlet side bottom surface 504 of the columnar honeycomb structure 500 held by the holder 514. The ceramic particles in the aerosol sucked into the first cells adhere to the surfaces of the first cells.

[0089] The housing 514a of the holder 514 has an exhaust port 514e downstream of the outlet-side bottom surface 506 of the columnar honeycomb structure 500. The exhaust port 514e is connected to an exhaust pipe 515, and a blower 512 is provided downstream of the exhaust port 514e. Therefore, when the aerosol from which the ceramic particles have been removed is discharged from the outlet-side bottom surface 506 of the columnar honeycomb structure 500, it passes through the exhaust pipe 515 and is then exhausted through the blower 512. A flow meter 516 is provided in the exhaust pipe 515, so that the gas flow rate measured by the flow meter 516 can be monitored, and the strength of the blower 512 can be controlled according to the required gas flow rate.

[0090] From the viewpoint of increasing the film thickness stability of the ceramic particles adhered to the surface of the first cell, in the process of adhering the ceramic particles to the surface of the first cell, the average flow velocity of the aerosol flowing within chamber 513 is preferably 0.5 m / s to 3.0 m / s, and more preferably 1.0 to 2.0 m / s.

[0091] From the viewpoint of improving the film thickness stability of the ceramic particles adhered to the surface of the first cells, the lower limit of the average flow velocity of the aerosol flowing through the columnar honeycomb structure in the process of adhering the ceramic particles to the surface of the first cells is preferably 5 m / s or more, more preferably 8 m / s or more. Furthermore, in order to maintain a high porosity of the porous film, the upper limit of the average flow velocity of the aerosol flowing through the columnar honeycomb structure is preferably 20 m / s or less, more preferably 15 m / s or less.

[0092] As the process of adhering ceramic particles to the surfaces of the first cells continues, the pressure loss between the inlet-side bottom surface and the outlet-side bottom surface of the columnar honeycomb structure increases as the amount of ceramic particles attached increases. Therefore, by determining the relationship between the amount of ceramic particles attached and the pressure loss in advance, the end point of the process of adhering ceramic particles to the surfaces of the first cells can be determined based on the pressure loss. Therefore, the particle attachment device 510 can be equipped with a differential pressure gauge 550 to measure the pressure loss between the inlet-side bottom surface 504 and the outlet-side bottom surface 506 of the columnar honeycomb structure 500, and the end point of the process can be determined based on the value of the differential pressure gauge.

[0093] A laser diffraction particle size distribution measuring device 519 may be installed inside the chamber 513. By installing the laser diffraction particle size distribution measuring device 519, it is possible to measure in real time the particle size distribution of the ceramic particles in the aerosol sprayed from the aerosol generator 511. This makes it possible to monitor whether ceramic particles having the desired particle size distribution are being supplied to the columnar honeycomb structure.

[0094] When the process of adhering ceramic particles to the surface of the first cell is carried out, ceramic particles are adhered to the inlet side bottom surface 504 of the columnar honeycomb structure 500, so it is preferable to smooth the inlet side bottom surface with a tool such as a scraper while suctioning and removing the ceramic particles using a vacuum or the like.

[0095] (baking process) Thereafter, the ceramic particles adhered to the surfaces of the first cells are baked to form a porous film composed of a plurality of particles on the surfaces of the first cells. In one embodiment, the baking process includes holding the columnar honeycomb structure having the ceramic particles adhered to the surfaces of the first cells in a heating furnace with an internal atmosphere temperature of 1100 to 1300°C for 1.5 to 4 hours. Baking at 1100°C or higher has the advantage of adhering the partition walls and the film material to each other. Baking at 1300°C or lower has the advantage of preventing the film from becoming non-uniform due to excessive oxidation. A longer holding time tends to increase the interparticle distance between the plurality of particles constituting the porous film, so it is advantageous to set it to 4 hours or less. On the other hand, a holding time that is too short tends to cause the porous film to peel off, so it is advantageous to set it to 1.5 hours or more.

[0096] In the baking process, in order to increase the production rate, the average temperature increase rate from room temperature (25°C) to the maximum temperature is preferably 100°C / Hr or more. Furthermore, in order to suppress the occurrence of cracks, the average temperature increase rate from room temperature (25°C) to the maximum temperature is preferably 200°C / Hr or less. Furthermore, in order to suppress the occurrence of cracks and reduce the burden on the kiln materials, the average temperature decrease rate from the maximum temperature to room temperature (25°C) is preferably 200°C / Hr or less. Furthermore, in order to increase the production rate, the average temperature decrease rate from the maximum temperature to room temperature (25°C) is preferably 100°C / Hr or more.

[0097] In a preferred embodiment, the baking treatment includes holding the columnar honeycomb structure having ceramic particles adhered to the surfaces of the first cells for 1.5 to 4 hours in a heating furnace having an internal atmosphere temperature of 1100 to 1200° C. In a more preferred embodiment, the baking treatment includes holding the columnar honeycomb structure having ceramic particles adhered to the surfaces of the first cells for 1.5 to 2.5 hours, and even more preferably for 2 to 2.5 hours, in a heating furnace having an internal atmosphere temperature of 1200° C.

[0098] The baking treatment can be performed, for example, by placing the columnar honeycomb structure with the ceramic particles attached in an electric furnace or gas furnace. The heat treatment bonds the ceramic particles together and bakes them onto the partition walls in the first cells, forming a porous film on the surface of the first cells. When the heat treatment is performed under oxygen-containing conditions, such as in air, a surface oxide film is formed on the ceramic particle surface, promoting bonding between the ceramic particles. This results in a porous film that is difficult to peel off. [Example]

[0099] The following examples are provided to provide a better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

[0100] Example 1 (1) Manufacturing of pillar honeycomb structure To 100 parts by mass of the cordierite raw material, 3 parts by mass of a pore-forming material, 55 parts by mass of a dispersion medium, 6 parts by mass of an organic binder, and 1 part by mass of a dispersant were added, mixed, and kneaded to prepare a clay. The cordierite raw materials used were alumina, aluminum hydroxide, kaolin, talc, and silica. Water was used as the dispersion medium, a water-absorbent polymer was used as the pore-forming material, hydroxypropyl methylcellulose was used as the organic binder, and a fatty acid soap was used as the dispersant.

[0101] The clay was placed in an extrusion molding machine and extruded through a die of a predetermined shape to obtain a cylindrical honeycomb molded body. The obtained honeycomb molded body was then subjected to dielectric drying and hot air drying, and then both bottom surfaces were cut to the predetermined dimensions to obtain a dried honeycomb body.

[0102] The obtained dried honeycomb body was plugged with cordierite so that the first cells and the second cells were alternately arranged adjacent to each other, and then heated and degreased at about 200°C in an air atmosphere, and further fired at 1420°C for 5 hours in an air atmosphere to obtain a columnar honeycomb structure. The columnar honeycomb structures were manufactured in the number required for the following tests.

[0103] The specifications of the pillar-shaped honeycomb structure are as follows: Overall shape: cylindrical, diameter 132mm x height 120mm Cell shape in cross section perpendicular to the flow direction: square Cell density (number of cells per unit cross-sectional area): 200 cpsi Bulkhead thickness: 8 mil (0.2 mm) (nominal value based on base specifications)

[0104] (2) Adhesion of ceramic particles to the columnar honeycomb structure Using a particle attachment device configured as shown in Figure 5, an aerosol containing ceramic particles was sprayed toward the center of the inlet side bottom surface of the columnar honeycomb structure fabricated above in a direction perpendicular to the inlet side bottom surface, thereby attaching the ceramic particles to the surfaces of the first cells. The specifications and operating conditions of the particle attachment device are as follows. Chamber Shape: Cylindrical Inner diameter: 300mm Length: 600mm Ambient gas: Air Opening position for taking in ambient gas: Only on the surface facing the bottom of the inlet side of the columnar honeycomb structure Filter installation in opening: Yes Aerosol generator nozzle position: Center of the opposing surface Structure of the opposing surface: Punching plate (An insertion hole was provided in the center of the punched plate for inserting the nozzle of the aerosol generator. A disk-shaped plate with a diameter of 150 mm was fixed to the center of the insertion hole to form a closed section.) Distance L from the nozzle outlet of the aerosol generator to the bottom of the inlet side of the columnar honeycomb structure: 600 mm Aerosol generator: In-house manufactured product with the structure shown in Figure 4 Type: Continuous aerosol generator Connection method for the drive gas flow path and the flow path for suction transport: Venturi ejector The location of the ceramic particle supply port: downstream of the most narrowed part of the venturi section and adjacent to that part Method of feeding ceramic particles into the container: Screw feeder Type of container: Funnel Type of ceramic particles stored in the storage section: SiC particles (commercially available) BET specific surface area of ​​ceramic particles to be placed in the container: See Table 1 (Measuring device: Mauntech Macsorb (registered trademark) HM model-1200 Measurement method: BET single point method (JIS Z8830:2013) Gas used: Nitrogen Pretreatment: Degas the sample under vacuum at 110°C for 2 hours. Sample measurement amount: 1g (Calculation method: The sample is placed in an adsorption cell, and the cell is evacuated while being heated to remove gas molecules adsorbed to the sample surface, and the sample's weight is then measured. Nitrogen gas is then flowed into the adsorption cell with the sample sealed inside. As a result, nitrogen adsorbs to the sample surface, and by further increasing the flow rate of nitrogen gas, the gas molecules form multiple layers on the sample surface. A graph is then created that plots the above process as a function of pressure, and the amount of gas molecules adsorbed only on the sample surface is calculated from the resulting graph using the BET adsorption isotherm. Since the adsorption area of ​​the nitrogen molecules is known in advance, the surface area of ​​the sample can be calculated based on the amount of gas molecules adsorbed.) Volumetric particle size distribution of ceramic particles contained in the container (measured by laser diffraction / scattering method): Median diameter (D50): See Table 1 Drive gas: Compressed dry air (dew point below 10°C) Ambient gas drawn in: Air Flow velocity of the drive gas just before it passes through the venturi: 26 m / s (measured by Anemomaster) Ratio of the cross-sectional area of ​​the flow passage just before the venturi section to the cross-sectional area of ​​the flow passage at the venturi section = 1:0.028 Average flow rate of aerosol sprayed from the nozzle: 120 L / min (measured by a flow meter) Aerosol generator nozzle inner diameter: 12 mm Operating conditions Blower suction flow rate: 4000 L / min Average flow velocity of aerosol in the chamber: 1 m / s (measured by Anemomaster) Average flow velocity of aerosols flowing through the columnar honeycomb structure: Approximately 7 m / s (calculated by flow rate / cell opening area)

[0105] (3) Baking process The inlet-side bottom surface of the thus-obtained columnar honeycomb structure, to which the ceramic particles had adhered, was smoothed with a scraper, while the ceramic particles adhering to the inlet-side bottom surface were removed by vacuum suction. The columnar honeycomb structure was then placed in an electric furnace and baked in an air atmosphere under the baking temperature and holding time conditions listed in Table 1, thereby forming a porous film on the surface of the first cells, thereby obtaining a columnar honeycomb structure filter. During the baking process, the average heating rate from room temperature (25°C) to the maximum temperature was 150°C / hr, and the average cooling rate from the maximum temperature to room temperature (25°C) was 150°C / hr. The columnar honeycomb structure filters were fabricated in the number required to perform the following characteristic evaluations.

[0106] <Examples 2 to 8 and Comparative Examples 1 to 4> A columnar honeycomb structure filter was manufactured under the same conditions as in Example 1, except that the BET specific surface area and median diameter (D50) of the ceramic particles contained in the container of the aerosol generator were changed to the conditions shown in Table 1, and the baking treatment was changed to the conditions shown in Table 1. In addition, the average thickness of the porous film was set to 15 μm in all test examples by keeping the aerosol flow rate and spraying time constant. All of the ceramic particles used were commercially available products.

[0107] <Partition wall porosity> The porosity of the partition walls of the columnar honeycomb structure filters according to Examples 1 to 8 and Comparative Examples 1 to 4 obtained by the above manufacturing method was measured based on SEM images using the above-mentioned measurement method, and was found to be 59% for all test examples. The device used for the measurement was an FE-SEM (model: ULTRA55 (manufactured by ZEISS)). The image analysis software used was HALCON version 11.0.5 from Links Corporation. The results are shown in Table 1.

[0108] <Porous membrane properties> (1) Average film thickness The average thickness of the porous membrane of the columnar honeycomb structure filters according to Examples 1 to 8 and Comparative Examples 1 to 4 obtained by the above manufacturing method was measured according to the above-mentioned measuring method, and it was 15 μm in all test examples. The 3D shape measuring machine used for the measurement was VR-3200 manufactured by Keyence Corporation. (2) Interparticle distance For the multiple particles constituting the porous membrane of the columnar honeycomb structure filters according to Examples 1 to 8 and Comparative Examples 1 to 4 obtained by the above manufacturing method, the frequency distribution of the interparticle distance, which is the distance between adjacent particles in the direction perpendicular to the membrane thickness direction, was obtained based on SEM images using the measurement method described above, and the interparticle distance (D90), average interparticle distance (Ave.), and standard deviation of the interparticle distance (σ) were calculated. The measurement was performed using an FE-SEM (model: ULTRA55 (manufactured by ZEISS)). The image analysis software used was HALCON version 11.0.5 from Links Corporation. The results are shown in Table 1.

[0109] <Filter performance> (1) PM collection test The pillar-shaped honeycomb structure filters according to Examples 1 to 8 and Comparative Examples 1 to 4 obtained by the above manufacturing method were subjected to the following PM collection test. DEHS (bis(2-ethylhexyl)sebacate) particles with a particle diameter of about 100 to 1000 nm sprayed from an aerosol generator was collected. LAerosol containing oil particles such as )) particles was supplied to a prismatic honeycomb filter at a flow rate of 500 to 10,000 L / min for 30 seconds to capture PM in the prismatic honeycomb filter. The PN (number of emitted particles) in the exhaust gas was measured at the inlet side (upstream side in the gas flow direction) and outlet side (downstream side in the gas flow direction) of the prismatic honeycomb filter using a PN counter. The collection efficiency was calculated using the formula: (number of particles at the inlet side - number of particles at the outlet side) / number of particles at the inlet side x 100 (%). The results are shown in Table 1. Also, a graph showing the relationship between interparticle distance (D90) and collection performance is shown in FIG.

[0110] [Table 1] [Explanation of symbols]

[0111] 100: Pillar honeycomb structure filter 102: Outer wall 104: Bottom of the inlet 106: Outlet side bottom surface 108: First cell 109: Plugging part 110: Second cell 112: Bulkhead 114: Porous membrane 400: Aerosol generator 401: Nozzle 402: Ceramic particles 403: Flow path 403e :Exit 407: Drive gas flow path 407i: Supply port 407v: Venturi section 409: Storage unit 409e :Exit 409i :Entrance 410: Venturi ejector 411: Powder quantitative feeder 500: Pillar honeycomb structure 502: Peripheral side wall 504: Bottom of the inlet 506: Outlet side bottom surface 510: Particle attachment device 511: Aerosol generator 511a: Nozzle 512: Blower 513: Chamber 513a: Opposing surfaces 513b: Insertion port 513c :Aperture 513d: Side wall 513e: Downstream end 513f: upstream end 513g: Filter 513h: Tapered section 514: Holder 514a: Housing 514b: Chuck mechanism 514e: Exhaust port 515: Exhaust pipe 516:Flowmeter 518: Closed part 519: Laser diffraction particle size distribution analyzer 550: Differential pressure gauge

Claims

1. A columnar honeycomb structure filter comprising: a plurality of first cells extending from an inlet side bottom surface to an outlet side bottom surface, having an open inlet side bottom surface and plugging portions at the outlet side bottom surface; and a plurality of second cells extending from the inlet side bottom surface to the outlet side bottom surface, having plugging portions at the inlet side bottom surface and having an open outlet side bottom surface, wherein the plurality of first cells and the plurality of second cells are alternately arranged adjacent to each other with porous partition walls interposed therebetween, a porous film made up of a plurality of particles is formed on a surface of each of the first cells; The porous film contains SiC at a content of 50 mass % or more, The porous membrane is observed at a cross section parallel to the film thickness direction, and the inter-particle distances between adjacent particles in a direction perpendicular to the film thickness direction are measured for the plurality of particles. When the frequency distribution of the inter-particle distances is calculated, the inter-particle distance (D90) at a cumulative ratio of 90% is 12.0 μm or less. Pillar honeycomb structure filter.

2. 2. The columnar honeycomb structure filter according to claim 1, wherein the interparticle distance (D90) at which the cumulative ratio is 90% is 11.0 μm or less.

3. The porous membrane is observed at a cross section parallel to the film thickness direction, and the inter-particle distance, which is the distance between adjacent particles in a direction perpendicular to the film thickness direction, is measured for the plurality of particles, and the frequency distribution of the inter-particle distances is calculated, and the average inter-particle distance is found to be 5.3 μm or less.

4. 4. The columnar honeycomb structure filter according to claim 3, wherein the average interparticle distance is 5.0 μm or less.

5. The porous membrane is observed at a cross section parallel to the film thickness direction, and the inter-particle distance between adjacent particles, which is the distance perpendicular to the film thickness direction, is measured for the plurality of particles, and the frequency distribution of the inter-particle distances is calculated, and the standard deviation of the inter-particle distances is found to be 3.6 μm or less.

6. 6. The columnar honeycomb structure filter according to claim 5, wherein the standard deviation of the interparticle distances is 3.4 μm or less.

7. 3. The pillar-shaped honeycomb structure filter according to claim 1, wherein the porous film has an average thickness of 2 to 40 μm.

8. a step of preparing a pillar-shaped honeycomb structure comprising: a plurality of first cells extending from an inlet-side bottom surface to an outlet-side bottom surface, the inlet-side bottom surface being open and having plugging portions on the outlet-side bottom surface; and a plurality of second cells extending from the inlet-side bottom surface to the outlet-side bottom surface, the inlet-side bottom surface being open and having plugging portions on the inlet-side bottom surface; and a plurality of first cells and a plurality of second cells being alternately arranged adjacent to each other with porous partition walls interposed therebetween; a step of spraying an aerosol containing ceramic particles from a nozzle of an aerosol generator toward the inlet-side bottom surface from a direction perpendicular to the inlet-side bottom surface, while applying a suction force to the outlet-side bottom surface to suck the sprayed aerosol from the inlet-side bottom surface, thereby adhering the ceramic particles to the surface of the first cell; a step of baking the ceramic particles attached to the surface of the first cell to form a porous film composed of a plurality of particles on the surface of the first cell; Including, the ceramic particles contain SiC, and the porous film contains SiC at a content of 50 mass% or more; The aerosol generator has a BET specific surface area of ​​3.5 m 2 / g or more of the ceramic particles, and the ceramic particles are supplied from the container to the nozzle. A method for manufacturing a columnar honeycomb structure filter.

9. The storage section has a BET specific surface area of ​​4.0 m 2 9. The method for manufacturing a columnar honeycomb structure filter according to claim 8, wherein the ceramic particles are contained in an amount of 1 / g or more.

10. The aerosol generator includes a drive gas flow path for flowing a pressurized drive gas, a supply port provided midway along the drive gas flow path and capable of sucking the ceramic particles from the container into the drive gas flow path from the outer periphery of the drive gas flow path, and a nozzle attached to the tip of the drive gas flow path and capable of spraying an aerosol. A method for manufacturing the columnar honeycomb structure filter according to claim 8 or 9.

11. A method for manufacturing a columnar honeycomb structure filter as described in claim 8 or 9, wherein the storage section stores ceramic particles having a median diameter (D50) of 0.5 to 3.0 μm in a volume-based cumulative particle size distribution measured by a laser diffraction / scattering method.

12. A method for manufacturing a columnar honeycomb structure filter as described in claim 8 or 9, wherein the baking treatment includes holding the columnar honeycomb structure having the ceramic particles adhered to the surface of the first cell in a heating furnace having an atmosphere temperature of 1100 to 1300°C for 1.5 to 4 hours.

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