Honeycomb filter

Abstract

Provided is a honeycomb filter in which peeling of a collection layer from a partition wall is inhibited. This honeycomb filter comprises: a honeycomb structure 4 having a porous partition wall 1 disposed so as to surround a plurality of cells 2; and a plug section 5 disposed so as to seal one end of the cell 2. The honeycomb structure 4 also has, on the inner surface side of the partition wall 1 that surrounds an inflow cell 2a, a collection layer 14 for collecting the particulate matter in an exhaust gas. The collection layer 14 is a porous layer in which a plurality of non-oxide particles are bonded via an oxide. The thickness of the oxide that bonds adjacent non-oxide particles to each other is at least 0.077 µm, and, letting R (µm) be the average particle diameter of the non-oxide particles constituting the collection layer 14 and letting T (µm) be the thickness of the oxide, the relationship R ≤ 1.0609e^(4.7057 × T) is satisfied.

Description

[Technical Field]

[0001] The present invention relates to a honeycomb filter. More specifically, it relates to a honeycomb filter in which a collection layer for collecting particulate matter is disposed on the surface of a porous partition wall. [Background technology]

[0002] In recent years, regulations concerning the removal of particulate matter contained in exhaust gases emitted from gasoline engines have become stricter worldwide, and honeycomb filters, which have a honeycomb structure, are used as filters to remove particulate matter. Hereafter, particulate matter will be referred to as "PM." PM is an abbreviation for "Particulate Matter."

[0003] For example, a honeycomb filter can be described as having a honeycomb structure with porous partitions that divide multiple cells, and a sealing portion that seals one end of either cell. In such a honeycomb filter, the porous partitions act as filters that remove PM. Specifically, exhaust gas containing PM is introduced into the honeycomb filter from the inlet end, filtered by capturing the PM with the porous partitions, and then the purified exhaust gas is discharged from the outlet end of the honeycomb filter. In this way, PM can be removed from the exhaust gas.

[0004] Conventionally, techniques have been proposed to improve the collection performance of honeycomb filters, such as thickening the partitions of the honeycomb structure or reducing the size of the pores formed in the partitions. However, when collection performance is improved using the above techniques, PM (e.g., soot) tends to clog the pores formed in the partitions, leading to a problem of increased pressure loss in the honeycomb filter. In other words, the above techniques are not effective solutions because the effect of improving collection performance and the effect of suppressing the increase in pressure loss are inversely related.

[0005] For these reasons, a honeycomb filter has been proposed in which a collection layer for collecting PM is provided on the surface of the partition walls of the honeycomb structure (see, for example, Patent Document 1). For example, the collection layer is composed of a porous membrane with an average pore diameter smaller than the average pore diameter of the partition walls. With such a honeycomb filter, PM can be deposited on the surface of the collection layer, thereby suppressing a sharp increase in pressure loss due to clogging of PM in the pores of the partition walls and improving the collection efficiency when collecting PM. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2012-206061 [Overview of the project] [Problems that the invention aims to solve]

[0007] As described above, honeycomb filters, which have a collection layer on the surface of the partition walls, are constructed by forming a film of fine powder on a honeycomb filter precursor that serves as the substrate, thereby forming a dense film (i.e., a collection layer) on the surface of the partition walls. The main methods for forming the film include, for example, filtering a solution containing the film material through the honeycomb filter precursor, and drawing an aerosol containing the film material into the honeycomb filter precursor. In addition to the same material as the substrate, inorganic compounds such as metal oxides and metal carbides are used as the film material. Processes for bonding the film material to the substrate include sintering by heat treatment or oxide film formation.

[0008] Conventionally, in the technology for forming collection layers, heat treatment has been performed to bond the aforementioned membrane materials, but the conditions that must be met to withstand various loads after installation in an automobile have not been specified. For example, Patent Document 1 above is characterized in that the melting point of the bonding part of the membrane material is at least equal to or greater than that of the membrane material, but the structure of the bonding part is not specified. When a honeycomb filter is installed and used in an automobile, it is subjected to loads that include stress such as vibration and thermal shock in addition to temperature, and if the bonding part of the membrane material is formed only on a minute surface, there is a concern that the structure of the collection layer may be destroyed, even if the bonding part has a high melting point. For example, the collection layer may peel off from the partition wall when subjected to loads that include stress such as vibration and thermal shock.

[0009] This invention has been made in view of the problems of the prior art. According to this invention, a honeycomb filter is provided in which the collection layer is less likely to peel off from the partition wall even when subjected to stress such as vibration or thermal shock. [Means for solving the problem]

[0010] According to the present invention, a honeycomb filter as shown below is provided.

[0011] [1] A honeycomb structure having porous partition walls arranged to surround a plurality of cells that form fluid channels extending from an inlet end face to an outlet end face, The cell comprises an eye sealing portion arranged to seal either the inlet end face side or the outlet end face side of the cell, The cell in which the sealing portion is provided at the end on the outflow end face side and the inflow end face side is open is designated as an inflow cell. The cell in which the sealing portion is provided at the end on the inlet end face side and the outlet end face side is open is designated as an outlet cell. The honeycomb structure further includes a collection layer on the inner surface side of the partition wall surrounding the inflow cell for collecting particulate matter in the exhaust gas. The honeycomb filter wherein the collection layer is a porous layer in which a plurality of non-oxide particles are joined via an oxide, the thickness of the oxide joining adjacent non-oxide particles is 0.077 μm or more, and when the average particle size of the non-oxide particles constituting the collection layer is R (μm) and the thickness of the oxide is T (μm), the relationship R ≤ 1.0609e^(4.7057 × T) is satisfied.

[0012] [2] The honeycomb filter according to [1], wherein the oxide constituting the collection layer is arranged to cover the surface of the non-oxide particles.

[0013] [3] The honeycomb filter according to [1] or [2], wherein the non-oxide particles are silicon carbide particles. [Effects of the Invention]

[0014] The honeycomb filter of the present invention is a honeycomb filter equipped with a collection layer for collecting particulate matter in exhaust gas on the inner surface side of the partition wall surrounding the inlet cell, and has excellent collection performance. The collection layer is a porous layer in which multiple non-oxide particles are bonded together via an oxide, and the thickness of the oxide bonding adjacent non-oxide particles is 0.077 μm or more. Furthermore, when the average particle size of the non-oxide particles constituting the collection layer is R (μm) and the thickness of the oxide is T (μm), the relationship R ≤ 1.0609e^(4.7057 × T) is satisfied. For this reason, the honeycomb filter of the present invention is resistant to damage of the collection layer even when subjected to stress such as vibration or thermal shock, and can effectively suppress the peeling of the collection layer from the partition wall. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic perspective view showing one embodiment of the honeycomb filter of the present invention. [Figure 2] Figure 1 is a plan view of the inlet end face of the honeycomb filter. [Figure 3] Figure 1 is a plan view of the outlet end face of the honeycomb filter shown. [Figure 4]It is a cross-sectional view schematically showing the A-A' cross-section of FIG. 2. [Figure 5] It is a cross-sectional view schematically showing the cross-section of the partition wall. [Figure 6] It is an enlarged cross-sectional view of the collection layer in the range indicated by the symbol P in FIG. 5. [Figure 7] It is a schematic plan view for explaining the configuration of a vibration testing machine for performing a peel test of the collection layer.

Mode for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. Therefore, it should be understood that within the scope not departing from the gist of the present invention, those obtained by appropriately changing and improving the following embodiments based on the ordinary knowledge of those skilled in the art also fall within the scope of the present invention.

[0017] (1) Honeycomb filter: An embodiment of the honeycomb filter of the present invention is the honeycomb filter 100 as shown in FIGS. 1 to 4. Here, FIG. 1 is a perspective view schematically showing one embodiment of the honeycomb filter of the present invention. FIG. 2 is a plan view of the inflow end face side of the honeycomb filter shown in FIG. 1. FIG. 3 is a plan view of the outflow end face side of the honeycomb filter shown in FIG. 1. FIG. 4 is a cross-sectional view schematically showing the A-A' cross-section of FIG. 2.

[0018] As shown in FIGS. 1 to 4, the honeycomb filter 100 of the present embodiment includes a honeycomb structure 4 and an end sealing portion 5. The honeycomb structure 4 has a porous partition wall 1 disposed so as to surround a plurality of cells 2 that serve as fluid flow paths extending from the inflow end face 11 to the outflow end face 12. The honeycomb structure 4 shown in FIGS. 1 to 4 is configured in a cylindrical shape having the inflow end face 11 and the outflow end face 12 as both end faces, and further has an outer peripheral wall 3 on its outer peripheral side surface. That is, the outer peripheral wall 3 is disposed so as to surround the partition wall 1 arranged in a lattice pattern.

[0019] The sealing portion 5 is positioned to seal either the inlet end face 11 side or the outlet end face 12 side of the cell 2. Hereinafter, among the multiple cells 2, a cell 2 in which the sealing portion 5 is disposed at the end on the outlet end face 12 side and the inlet end face 11 side is open will be referred to as "inlet cell 2a". Similarly, among the multiple cells 2, a cell 2 in which the sealing portion 5 is disposed at the end on the inlet end face 11 side and the outlet end face 12 side is open will be referred to as "outlet cell 2b". In the honeycomb filter 100 of this embodiment, it is preferable that the inlet cells 2a and outlet cells 2b are arranged alternately with the partition wall 1 in between.

[0020] The honeycomb filter 100 is characterized in that the honeycomb structure 4 is configured as follows. Specifically, as shown in Figures 5 and 6, the honeycomb structure 4 further has a collection layer 14 on the inner surface side of the partition wall 1 surrounding the inlet cell 2a for collecting particulate matter (hereinafter also referred to as "PM") in the exhaust gas. The collection layer 14 is a porous layer in which a plurality of non-oxide particles 15 are joined together via an oxide 16. Furthermore, the thickness T of the oxide 16 that joins adjacent non-oxide particles 15 in this collection layer 14 is 0.077 μm or more. Moreover, when the average particle size of the non-oxide particles constituting the collection layer 14 is R (μm) and the thickness of the oxide 16 is T (μm), the relationship R ≤ 1.0609e^(4.7057 × T) is satisfied. Hereafter, the relationship expressed as "R ≤ 1.0609e^(4.7057 × T)" will be referred to as "Relationship (1)". The left side of Relationship (1) represents the average particle size R (μm) of the non-oxide particles. On the other hand, in the right side of Relationship (1), e represents Napier's number, which is the base of the natural logarithm. The right side of Relationship (1) is the value obtained by multiplying Napier's number (e), whose exponent is "the value obtained by multiplying the thickness T (μm) of oxide 16 by 4.7057", by 1.0609. Here, Figure 5 is a schematic cross-sectional view showing the cross-section of the partition wall. In Figure 5, the symbol 7 indicates a pore formed in partition wall 1. Figure 6 is an enlarged cross-sectional view of the collection layer in the range indicated by the symbol P in Figure 5.

[0021] Because the collection layer 14 is a porous layer composed of non-oxide particles 15 and oxide 16 as described above, the collection layer 14 is less likely to break even when subjected to stress such as vibration or thermal shock, and peeling of the collection layer 14 from the partition wall 1 can be effectively suppressed. In particular, if the thickness T of the oxide 16 is less than 0.077 μm, the bonding portion that holds the non-oxide particles 15 together becomes narrower, and the bonds between the non-oxide particles 15 become easily broken. Similarly, even if the thickness T of the oxide 16 is 0.077 μm or more, if the above relation (1) is not satisfied, the bonding portion that holds the non-oxide particles 15 together becomes narrower, and the bonds between the non-oxide particles 15 become easily broken. For example, if the average particle size R (μm) of the non-oxide particles is small, the lower limit of the allowable thickness T μm of the oxide 16 also becomes small. And as the average particle size R (μm) of the non-oxide particles increases, the lower limit of the allowable thickness T μm of the oxide 16 also increases.

[0022] The thickness T of the oxide 16 joining adjacent non-oxide particles 15 is 0.077 μm or more, and should be configured to satisfy the above-described relation (1). There are no particular limitations, but for example, when the average particle size R of the non-oxide particles is about 2.2 to 3.0 μm, the thickness of the oxide 16 is preferably 0.155 to 0.230 μm, and more preferably 0.155 to 0.167 μm. For example, if the thickness of the oxide 16 becomes extremely thick, cracks may form in the layer made of oxide 16 joining the non-oxide particles 15 (hereinafter also referred to as the "oxide layer"), and the joining (bonding) between the non-oxide particles 15 may break easily. For this reason, although there are no particular limitations, an upper limit of 0.230 μm can be given for the thickness of the oxide 16.

[0023] There are no particular restrictions on the average particle size R (μm) of the non-oxide particles 15 that constitute the collection layer 14. For example, the average particle size R (μm) of the non-oxide particles 15 is preferably 0.4 to 2.4 μm, and more preferably 0.9 to 2.4 μm. The average particle size R (μm) of the non-oxide particles 15 can be determined by the following method.

[0024] First, a portion of the partition wall 1 and the collection layer 14 is cut out as a test specimen from the honeycomb structure 4 that constitutes the honeycomb filter 100 as shown in Figures 1 to 3. The position from which the test specimen is cut out is between the central cross-section in the direction in which the cells 2 of the honeycomb filter 100 extend (i.e., the flow direction) and the outlet end face 12 (excluding the area where the sealing portion 5 on the outlet end face 12 side is provided).

[0025] Next, the cut specimen is cut in a direction perpendicular to the direction in which cell 2 extends, and the cut surface is polished. The cut surface is polished using mechanical polishing.

[0026] Next, the polished cross-section is imaged using a scanning electron microscope (hereinafter also referred to as "SEM") to obtain an SEM image. "SEM" is an abbreviation for "Scanning Electron Microscope". The imaging conditions are: magnification: 200x, file format: TIF, width: 1280 pixels, height: 960 pixels. SEM images are acquired for four fields. These four fields may be imaged at four different points on a single specimen, or four specimens may be prepared and imaged for each specimen. The SEM images of the four fields will hereinafter also be referred to as "four levels".

[0027] Next, among the non-oxide particles 15 constituting the collection layer 14 displayed in the SEM image, only those non-oxide particles 15 present on the substrate septum 1 are binarized. That is, non-oxide particles 15 present inside the pores of the septum 1, and non-oxide particles 15 present across the portion where the septum 1 is located, are not included in the binarization analysis. For example, if the septum 1 displayed in the SEM image is located at the bottom of the image, a line segment is virtually drawn at the boundary corresponding to the surface of the septum 1, and only the non-oxide particles 15 above that line segment are included in the binarization analysis. This allows for a more accurate calculation of the average particle size R (μm) of the non-oxide particles 15. The binarization process is performed using the image analysis software "Winroof 2018 (Mitani Corporation) (product name)" manufactured by Mitani Corporation. The analysis item for binarization is selected as "Equivalent Circle Diameter" to calculate the average particle size R (μm) of the non-oxide particles 15.

[0028] Furthermore, the thickness T (μm) of the oxide 16 constituting the collection layer 14 can be measured as follows. First, a portion of the partition wall 1 and the collection layer 14 is cut out as a test piece from the honeycomb structure 4 constituting the honeycomb filter 100 as shown in Figures 1 to 3. The position from which the test piece is cut out is between the central cross-section in the direction in which the cells 2 of the honeycomb filter 100 extend (i.e., the flow direction) and the outlet end face 12 (excluding the area where the sealing portion 5 on the outlet end face 12 side is provided).

[0029] Next, the cut specimen is cut in a direction perpendicular to the direction in which cell 2 extends, and the cut surface is polished. The cut surface is polished by mechanical polishing followed by ion polishing.

[0030] Next, the polished cross-section is imaged using a field emission scanning electron microscope (hereinafter also referred to as "FE-SEM") to obtain an SEM image at a magnification of 6000x. "FE-SEM" is an abbreviation for "Field Emission Scanning Electron Microscope". The imaging conditions are set to an acceleration voltage of 1.5kV. SEM images are acquired for four fields. These four fields may be imaged at four different points on a single specimen, or four specimens may be prepared and imaged for each specimen. The SEM images of the four fields will hereinafter also be referred to as "four levels".

[0031] Next, the components of the collection layer 14, as shown in the SEM image, are subjected to qualitative analysis by EDS analysis to confirm whether the components are oxides or non-oxides.

[0032] Next, an image analysis of the collection layer 14 in the obtained SEM image is performed. For the image analysis, the top three particles (non-oxide particles 15) with the largest cross-sectional area among the particles constituting the collection layer 14 in the SEM image are selected as the target particles for measurement. Then, the thickness T of the oxide 16 binding the non-oxide particles 15 is measured at five points on the outer circumference of the target particles. nThe following measurement is performed. Five measurement points on the outer circumference of the particle to be measured are determined so as to be evenly distributed over the outer circumference. The boundary between the surface of the non-oxide particle 15 and the oxide 16 is identified by a white area near the outer circumference of the particle to be measured in the SEM image. The thickness is measured by measuring the distance between two points: the outer circumference of the particle to be measured and the boundary. Image analysis is performed using "Image J" (product name) from the National Institutes of Health (NIH). The phenomenon of the boundary between the surface of the non-oxide particle 15 and the oxide 16 appearing white is presumed to be due to the effect of electron beam charge-up (charging phenomenon). That is, the SEM image used for image analysis is a secondary electron image and is affected by electron beam charge-up (charging phenomenon). Charge-up refers to the phenomenon in which, when measuring a sample containing an insulator, the insulator becomes charged, making it impossible to obtain appropriate results. Between the non-oxide particle 15 and the oxide 16, a slight insulating state occurs due to the difference in conductivity between the two, causing charging, and thus it appears white due to charge-up. Since the conductivity of the non-oxide particles 15 and the oxide particles 16 are fundamentally different, the boundary can be distinguished by the intensity of the image.

[0033] In the image analysis at each level, the thickness T of the oxide 16 was measured at 7 points for each of the three target particles. n The following measurements are taken. Then, of the seven measured points, the maximum and minimum values ​​are excluded, and the remaining five points are used as the measured values ​​for the three target particles mentioned above. The average value of these five points (a total of 15 points) is calculated. The average values ​​of the four levels are then further averaged to calculate the final measured thickness T of oxide 16. Therefore, the final measured thickness T (μm) of oxide 16 is calculated from the thickness T of a total of 60 oxide 16 points. n This will be the average value.

[0034] The oxide 16 constituting the collection layer 14 constitutes the bonding portion responsible for holding the non-oxide particles 15 together. The oxide 16 only needs to bond the non-oxide particles 15, which serve as aggregate in the collection layer 14, together. However, it is preferable that the oxide 16 is arranged so as to cover the surface of the non-oxide particles 15. By configuring it in this way, the bonds between the non-oxide particles 15 can be made stronger, the collection layer 14 becomes less prone to damage, and the peeling of the collection layer 14 from the partition wall 1 can be suppressed very effectively.

[0035] There are no particular restrictions on the type of oxide 16 that binds the non-oxide particles 15, but it is preferable that the oxide has a melting point of 1200°C or higher. Examples include silicon oxide, cerium oxide, titanium oxide, and zirconium oxide. In the honeycomb filter 100 of this embodiment, it is preferable that the oxide 16 is silicon oxide.

[0036] The particles constituting the collection layer 14 may be non-oxide particles (non-oxide particles 15). Examples of components constituting the non-oxide particles 15 include silicon carbide, cerium, titanium, and zirconium. In the honeycomb filter 100 of this embodiment, it is preferable that the non-oxide particles 15 are silicon carbide particles. By using silicon carbide particles for the non-oxide particles 15, oxides 16 that form bonding portions between the non-oxide particles 15 can be easily formed by sintering the non-oxide particles 15 together and then heat-treating the sintered non-oxide particles 15 under predetermined conditions in an oxidizing atmosphere. That is, when the sintered portion of the non-oxide particles 15 is oxidized, that sintered portion becomes silicon oxide (SiO2), and a collection layer 14 consisting of a porous layer in which multiple non-oxide particles 15 are joined via oxides 16 can be easily manufactured. In addition to silicon carbide, cerium, titanium, and zirconium also become oxides of their respective components when the sintered portion of the non-oxide particles 15 is oxidized.

[0037] Preferably, the collection layer 14 is disposed only on the inner surface of the partition wall 1 surrounding the inlet cell 2a. If the collection layer 14 is disposed on surfaces other than the inner surface of the partition wall 1 surrounding the inlet cell 2a, the pressure loss of the honeycomb filter 100 may increase.

[0038] It is preferable that the average pore diameter of the collection layer 14 is smaller than the average pore diameter of the partition wall 1. With this configuration, PM contained in the exhaust gas can be effectively collected by the collection layer 14, which is disposed on the inner surface side of the partition wall 1 surrounding the inflow cell 2a.

[0039] The average pore size of the collection layer 14 is preferably 2 to 9 μm, more preferably 2 to 7 μm, and particularly preferably 3 to 5 μm. There are no particular restrictions on the average particle size R (μm) of the non-oxide particles 15 that constitute the collection layer 14. For example, the average particle size R (μm) of the non-oxide particles 15 is preferably 2.4 μm or less. By setting the average particle size R (μm) of the non-oxide particles 15 to 2.4 μm or less, the bonds between the non-oxide particles 15 can be made stronger, making the collection layer 14 less susceptible to damage, and effectively suppressing the peeling of the collection layer 14 from the partition wall 1.

[0040] The porosity of the collection layer 14 is preferably 55-90%, more preferably 55-85%, and particularly preferably 60-85%. If the porosity of the collection layer 14 is less than 55%, the pressure loss may increase. On the other hand, if the porosity of the collection layer 14 exceeds 90%, the collection efficiency may deteriorate.

[0041] The porosity and average pore size of the collection layer 14 can be measured by the following method. First, a cross-sectional view of the collection layer 14 is observed using a scanning electron microscope (SEM) and an SEM image is obtained. The SEM image is observed at a magnification of 200x. Next, the acquired SEM image is analyzed to binarize the solid portion of the collection layer 14 and the void portion within the collection layer 14. The percentage of the ratio of the void portion in the collection layer 14 to the total area of ​​the solid portion and void portion of the collection layer 14 is then calculated, and this value is taken as the porosity of the collection layer 14. Separately, the voids between each particle size in the SEM image are binarized, and their size is directly measured using a scale. The pore size in the collection layer 14 is then calculated from the measured value. The average value of the calculated pore sizes is taken as the average pore size of the collection layer 14.

[0042] The thickness of the collection layer 14 is preferably 10 to 60 μm, more preferably 20 to 50 μm, and particularly preferably 20 to 40 μm. If the thickness of the collection layer 14 is less than 10 μm, it is undesirable because the potential for improvement in collection efficiency may be low. On the other hand, if the thickness of the collection layer 14 exceeds 60 μm, it is undesirable because the improvement in collection efficiency may plateau and the pressure loss may increase.

[0043] The thickness of the collection layer 14 can be measured by the following method. First, six intersection points are determined from a cross section parallel to the partition wall 1, passing through the central axis in the direction in which the cells 2 of the honeycomb filter 100 extend. These six intersection points are the points where three straight lines that divide the above cross section into four equal parts in the direction in which the cells 2 extend intersect with two straight lines that divide the above cross section into three equal parts perpendicular to the direction in which the cells 2 extend. Then, a test piece containing an area of ​​20 mm (vertical) x 20 mm (horizontal) is cut out parallel to the above cross section, with each intersection point as the center. The thickness of the test piece (i.e., the depth parallel to the above cross section) can be determined arbitrarily. An arbitrary pair of adjacent inlet cells 2a and outlet cells 2b are selected from the above test piece, and the average value of the surface height of each cell 2 (specifically, the surface height of each cell 2 in the direction perpendicular to the partition wall 1) is measured using a 3D shape measuring machine within a range of approximately 8 mm in the direction in which the cells 2 extend. Next, the difference in surface height between the inflow cell 2a and the outflow cell 2b is calculated, and this is taken as the thickness of the collection layer 14.

[0044] The average pore diameter of the partition wall 1 is preferably 7 to 19 μm, more preferably 7 to 12 μm, and particularly preferably 7 to 9 μm. The average pore diameter of the partition wall 1 is a value measured by the mercury intrusion method. The average pore diameter of the partition wall 1 can be measured, for example, using the Autopore 9500 (trade name) manufactured by Micromeritics. If the average pore diameter of the partition wall 1 is less than 7 μm, it is undesirable because the permeation resistance of the partition wall 1 increases, which may increase the pressure loss. If the average pore diameter of the partition wall 1 exceeds 19 μm, it is undesirable in terms of moldability when forming the collection layer 14.

[0045] The porosity of the partition walls 1 of the honeycomb structure 4 is preferably 48-65%, more preferably 55-60%, and particularly preferably 55-59%. The porosity of the partition walls 1 is a value measured by the mercury intrusion method. The porosity of the partition walls 1 can be measured, for example, using the Autopore 9500 (product name) manufactured by Micromeritics. If the porosity of the partition walls 1 is less than 48%, it is undesirable because the permeation resistance of the partition walls 1 increases, and the pressure loss increases. If the porosity of the partition walls 1 exceeds 65%, it is undesirable because the strength may decrease significantly.

[0046] The honeycomb structure 4 preferably has a partition wall 1 thickness of 0.152 to 0.305 mm, more preferably 0.190 to 0.267 mm, and particularly preferably 0.190 to 0.241 mm. The thickness of the partition wall 1 can be measured, for example, using a profile projector. If the thickness of the partition wall 1 is less than 0.152 mm, sufficient strength may not be obtained. On the other hand, if the thickness of the partition wall 1 exceeds 0.305 mm, the pressure loss may increase when the collection layer 14 is placed on the surface of the partition wall 1.

[0047] There are no particular restrictions on the shape of the cells 2 formed in the honeycomb structure 4. For example, the shape of the cell 2 in a cross section perpendicular to the direction in which the cell 2 extends can be a polygon, a circle, an ellipse, etc. Examples of polygons include triangles, squares, pentagons, hexagons, octagons, etc. It is preferable that the shape of the cell 2 be a triangle, a square, a pentagon, a hexagon, or an octagon. Furthermore, all cells 2 may have the same shape or different shapes. For example, although not shown in the illustration, there may be a mixture of square cells and octagonal cells. Furthermore, all cells 2 may have the same size or different sizes. For example, although not shown in the illustration, the size of some cells may be made larger and the size of other cells may be made relatively smaller. In this invention, cell 2 refers to the space surrounded by the partition wall 1.

[0048] The cell density of cell 2, which is partitioned by partition wall 1, is 31-62 cells / cm³. 2 Preferably, the number is 31-55 per cm. 2 It is even more preferable that this is the case. By configuring it in this way, it can be suitably used as a filter for capturing PM in exhaust gas emitted from engines of automobiles and the like.

[0049] The outer periphery wall 3 of the honeycomb structure 4 may be integrally formed with the partition wall 1, or it may be an outer periphery coating layer formed by coating the outer periphery coating material so as to surround the partition wall 1. Although not shown in the figures, the outer periphery coating layer can be provided on the outer periphery side of the partition wall after the partition wall and the outer periphery wall have been integrally formed during manufacturing, and the formed outer periphery wall has been removed by a known method such as grinding.

[0050] There are no particular restrictions on the shape of the honeycomb structure 4. Examples of the shape of the honeycomb structure 4 include columnar shapes such as circular, elliptical, or polygonal, for the inlet end face 11 and outlet end face 12.

[0051] There are no particular restrictions on the size of the honeycomb structure 4, for example, the length in the direction in which the cells 2 of the honeycomb structure 4 extend (hereinafter also referred to as "total length") or the size of the cross-section perpendicular to the direction in which the cells 2 of the honeycomb structure 4 extend (hereinafter also referred to as "cross-sectional area"). Each size should be appropriately selected to obtain optimal purification performance when using the honeycomb filter 100. The total length of the honeycomb structure 4 is preferably 90 to 160 mm, and more preferably 120 to 140 mm. The cross-sectional area of ​​the honeycomb structure 4 is preferably 8000 to 16000 mm². 2 Preferably, it is 10,000 to 14,000 mm. 2 It is even more preferable that this be the case.

[0052] It is preferable that the material of the partition wall 1 includes at least one selected from the group consisting of cordierite, silicon carbide, silicon-silicon carbide composite materials, mullite, alumina, aluminum titanate, silicon nitride, and silicon carbide-cordierite composite materials. The material constituting the partition wall 1 is preferably a material containing 30% by mass or more of the materials listed in the above group, more preferably 40% by mass or more, and particularly preferably 50% by mass or more. In the honeycomb filter 100 of this embodiment, cordierite is particularly preferred as the material constituting the partition wall 1.

[0053] (2) Method for manufacturing a honeycomb filter: There are no particular limitations on the method for manufacturing the honeycomb filter of the present invention, and examples include the following methods.

[0054] First, a plastic clay material for creating the partitions of the honeycomb structure is prepared. This clay material can be prepared by adding appropriate additives such as binders, pore-forming materials, and water to the raw material powder used to create the suitable partition material mentioned above. Examples of raw material powders include alumina, talc, kaolin, and silica powder. Examples of binders include methylcellulose and hydroxypropyl methylcellulose. Examples of additives include surfactants.

[0055] Next, the clay obtained in this way is extruded to produce a columnar honeycomb molded body having partition walls that divide multiple cells, and outer walls arranged to surround these partition walls. Then, the obtained honeycomb molded body is dried, for example, with microwaves and hot air.

[0056] Next, a seal portion is formed on the dried honeycomb molded body. The method for forming the seal portion can be carried out in accordance with conventionally known methods for manufacturing honeycomb filters. For example, first, a mask is applied to the inlet end face of the honeycomb molded body so that the inlet cells are covered. Then, a seal slurry is applied to the masked end of the honeycomb molded body, and the seal slurry is filled into the openings of the outlet cells that are not masked. After that, the seal slurry is also filled into the openings of the inlet cells on the outlet end face of the honeycomb molded body in the same manner as above. Finally, the honeycomb molded body with the seal portion formed is further dried in a hot air dryer.

[0057] Next, a honeycomb filter precursor is produced by firing the honeycomb molded body with the sealed portion formed therein, before the collection layer is installed. The firing temperature and atmosphere when firing the honeycomb molded body will vary depending on the raw materials used to produce the honeycomb molded body, and a person skilled in the art can select the optimal firing temperature and atmosphere for the selected material.

[0058] Next, non-oxide particles are prepared to create a collection layer. These non-oxide particles are then introduced into the cells of the honeycomb filter precursor, causing them to adhere to the surface of the septums of the honeycomb filter precursor. The method for introducing the non-oxide particles into the cells of the honeycomb filter precursor is not particularly limited, but one method is to disperse the non-oxide particles in a gas to form an aerosol, and then introduce the aerosol into the cells. Silicon carbide particles are a preferred example of non-oxide particles. There are no particular restrictions on the average particle size of the silicon carbide particles, but it is preferable that the average particle size is, for example, 0.4 to 2.4 μm.

[0059] As described above, non-oxide particles are attached to the inner surface of the partition wall surrounding the inlet cell of the honeycomb filter precursor to form a film. Then, the formed non-oxide particles are oxidized (heat-treated) at 600°C or higher in an atmospheric environment to bond the non-oxide particles together. With this configuration, the parts that bond the non-oxide particles together become oxide, and a collection layer consisting of a porous layer in which multiple non-oxide particles are bonded via oxide is formed on the inner surface of the partition wall surrounding the inlet cell of the honeycomb filter precursor. For example, when silicon carbide particles are used to form the film, the parts that bond the silicon carbide particles together become silicon oxide (SiO2), and a collection layer consisting of a porous layer in which multiple non-oxide particles are bonded via oxide can be easily produced. There are no particular restrictions on the temperature and time for oxidizing (heat-treating) the formed non-oxide particles, but it is preferable to continue the oxidation until the thickness of the parts that bond the silicon carbide particles together (silicon oxide) is 0.077 μm or more and the above-mentioned relational equation (1) is satisfied. For example, the oxidation temperature is preferably 800 to 1400°C, and the oxidation time is preferably 1 to 4 hours. The oxidation temperature and oxidation time mentioned above are heat treatment conditions that affect the thickness of the oxide bonding the non-oxide particles together. However, even if either the oxidation temperature or oxidation time satisfies the above numerical range, it does not necessarily mean that the oxide thickness will be above a certain level. It is preferable to appropriately select heat treatment conditions that result in an oxide thickness above a certain level while adjusting the oxidation temperature and oxidation time within the above numerical range. Furthermore, the amount of oxide produced can also be determined from the mass increase before and after oxidation (heat treatment). For example, when silicon carbide particles are used as non-oxide particles, if the mass increase after heat treatment is 20% or more relative to the mass of the raw material particles used, the thickness of the silicon oxide bonding site can be set to 0.077 μm or more, and the above-mentioned relational equation (1) can be satisfied. For example, although not particularly limited, if the average particle size R of the non-oxide particles is about 2.2 to 3.0 μm, the thickness of the silicon oxide can be set to 0.155 μm or more. Oxidation of the formed non-oxide particles can be carried out, for example, by introducing the honeycomb filter precursor into an electric furnace, or by heating the non-oxide particles attached to the inner surface of the partition wall with a gas burner.As described above, the honeycomb filter of the present invention can be manufactured. [Examples]

[0060] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0061] (Example 1) First, alumina, talc, kaolin, and silica raw materials were prepared to create the partitions of the honeycomb structure. Two parts by mass of a dispersion medium and seven parts by mass of an organic binder were added to the prepared alumina, talc, kaolin, and silica raw materials, and the mixture was kneaded to prepare the clay. Water was used as the dispersion medium. Methylcellulose was used as the organic binder. A surfactant was used as the dispersant.

[0062] Next, the clay was extruded using a die for honeycomb molding to obtain a honeycomb mold with an overall cylindrical shape. The cells of the honeycomb mold were made square.

[0063] Next, the honeycomb molded body was dried in a microwave dryer, and then completely dried in a hot air dryer. After that, both ends of the honeycomb molded body were cut to the specified dimensions.

[0064] Next, a seal was formed on the dried honeycomb molded body. Specifically, first, a mask was applied to the inlet end face of the honeycomb molded body so that the inlet cells were covered. Then, the seal slurry was rubbed into the masked end of the honeycomb molded body, and the seal slurry was filled into the openings of the outlet cells that were not masked. Subsequently, the seal slurry was filled into the openings of the inlet cells on the outlet end face of the honeycomb molded body in the same manner as above. After that, the honeycomb molded body with the seal formed was further dried in a hot air dryer.

[0065] Next, the dried honeycomb molded body was degreased and fired to produce a honeycomb filter precursor before the collection layer was installed.

[0066] Next, a collection layer was fabricated on the inner surface of the partition surrounding the inlet cell of the honeycomb filter precursor using the following method. Specifically, silicon carbide particles with an average particle size (median diameter) of 2.4 μm were prepared first. Next, the prepared silicon carbide particles were dispersed in a gas to form an aerosol, and this aerosol was introduced into the inlet cell. In this way, a film of silicon carbide particles was formed on the inner surface of the partition surrounding the inlet cell. The specific film formation conditions for the silicon carbide particles are as follows. • Aerosol generator: PALAS RBG2000 • Rotating body: Rotating brush • Non-oxide particles to be contained in the container: Silicon carbide particles (SiC particles) Median diameter (D50): 2.4 μm D10: 1.1 μm D90: 4.5 μm (Based on the volume-based cumulative particle size distribution measured by laser diffraction and scattering methods) • Mass of non-oxide particles sprayed: 6.0g • Medium gas: Compressed dry air (dew point below 10°C) • Ambient gas: air • Average flow velocity of aerosols flowing into the honeycomb filter precursor: 3 m / s • Laser diffraction particle size distribution analyzer: MALVERN Incitex spray • Operating time: 20 seconds • Aerosol generator nozzle inner diameter: 8mm • Distance from the nozzle tip of the aerosol generator to the inlet end face of the honeycomb filter precursor: 1000 mm • Aerosol ejection velocity: 20 m / s

[0067] Next, the honeycomb filter precursor, on which silicon carbide particles were deposited, was placed in an electric furnace and heat-treated at 1200°C under an atmospheric environment. The heat treatment was maintained at 1200°C for 2.2 hours. This heat treatment formed a collection layer on the inner surface of the partition wall surrounding the inlet cell, in which the silicon carbide particles were bonded together by silicon oxide. As a result of the above heat treatment, some of the particles (silicon carbide particles) used as raw material for the collection layer were oxidized, and the mass after heat treatment increased by 20% compared to the mass of the raw material used. This 20% mass increase due to heat treatment was caused by oxidation progressing from the surface side of the silicon carbide particles, resulting in the formation of oxides (silicon oxide) on the surface side of the silicon carbide particles and at the sites where the silicon carbide particles bond together. The thickness of the oxide at the sites where the silicon carbide particles bond together was measured using the method described above, and the thickness of the oxide was found to be 0.155 μm. The results are shown in Table 1. The honeycomb filter prepared in the manner described above was designated as the honeycomb filter of Example 1.

[0068] The honeycomb filter in Example 1 had a cylindrical shape with circular inlet and outlet ends. The length of the honeycomb filter cells in the direction of extension was 120 mm. The diameter of the end face of the honeycomb filter was 132 mm. The porosity of the partitions of the honeycomb structure was 60%. The average pore size of the partitions was 12 μm. The porosity and average pore size of the partitions were measured using an Autopore 9500 (product name) manufactured by Micromeritics. The results are shown in Table 1. The honeycomb structure constituting the honeycomb filter had a partition thickness of 0.216 mm and a cell density of 31 cells / cm³. 2 That was the case.

[0069] [Table 1]

[0070] The honeycomb filter of Example 1 was subjected to a delamination test of the collection layer using the following method. The results are shown in Table 1.

[0071] [Peel test (peel test of the collection layer)] First, the honeycomb filter 100 to be tested was mounted on the sample mounting part 41 of the vibration tester 20 as shown in FIG. 7, and a peeling test of the collection layer was conducted. FIG. 7 is a schematic plan view for explaining the configuration of the vibration tester for conducting the peeling test of the collection layer. As shown in FIG. 7, the vibration tester 20 includes a burner part 21 and a vibration part 31. The burner part 21 has a combustion chamber 24 in which a main burner 22 and a pilot burner 23 are arranged. The main burner 22 and the pilot burner 23 are burners that use liquefied petroleum gas (LPG) as fuel, and pilot air is supplied to the pilot burner 23 in addition to the fuel. Combustion air for burning the fuel and cooling air for cooling the honeycomb filter 100 at the time of combustion stop are supplied to the combustion chamber 24. The vibration part 31 is disposed below the sample mounting part 41 for mounting the honeycomb filter 100, and gives vertical vibration to the sample mounting part 41. The sample mounting part 41 is configured such that heated air heated by the burner part 21 flows while giving vibration from the vibration part 31 to the honeycomb filter 100 mounted inside. In the peeling test, a cycle test was conducted in which heated air heated by the burner and cooling air for cooling were alternately and repeatedly flowed under the following conditions while applying vibration with a vibration frequency of 150 Hz and a gravitational acceleration of 40 g to the honeycomb filter 100 by the vibration part 31. The inlet temperature of the heated air flowing into the honeycomb filter 100 was 900 ° C, and the flow rate was 2.0 Nm 3The setting was / min. After flowing this heated air for 5 minutes, the combustion of the main burner 22 and pilot burner 23 was stopped, and cooling air was flowed for 5 minutes. The peel test was performed by repeating this process of alternating heated air and cooling air 75 times. After the peel test, the honeycomb filter 100 was removed from the sample mounting section 41, and the mass of the honeycomb filter 100 (mass decrease) before and after the test was measured. A test is considered successful if the mass decrease after the test is less than 3% of the collection layer mass, and the decrease in collection efficiency after the test is less than the measurement variation (2σ) calculated from the results of 30 or more repeated measurements of the honeycomb filter before the test under those measurement conditions. In such cases, "OK" is written in Table 1. On the other hand, a test is considered unsuccessful if the mass decrease after the test is 3% or more of the collection layer mass, and the decrease in collection efficiency after the test is greater than or equal to the measurement variation (2σ) calculated from the results of 30 or more repeated measurements of the honeycomb filter before the test under those measurement conditions. In cases of failure, "NG" is indicated in Table 1.

[0072] (Examples 2-13, Comparative Examples 1-3) Honeycomb filters for Examples 2-13 and Comparative Examples 1-3 were fabricated by changing the honeycomb structure configuration and the composition and manufacturing method of the collection layer as shown in Tables 1 and 2. In Examples 2-5 and Comparative Example 3, the heat treatment of the collection layer was performed by heating the honeycomb filter precursor, which had silicon carbide particles formed into a film, using a gas burner. The honeycomb filters of Examples 2-13 and Comparative Examples 1-3 were also subjected to a peel test of the collection layer in the same manner as in Example 1. The results are shown in Tables 1 and 2. Examples 1-13 satisfy the previously described relation (1): R ≤ 1.0609e^(4.7057 × T). On the other hand, Comparative Examples 1-3 do not satisfy the above-mentioned relation (1).

[0073] [Table 2]

[0074] (result) The honeycomb filters of Examples 1 to 13 had an oxide thickness T of 0.077 μm or more and satisfied the above relational equation (1). In the peeling test of the collection layer, no peeling of the collection layer was observed, resulting in an OK (pass) result. On the other hand, even though the honeycomb filters of Comparative Examples 1 to 3 had an oxide thickness T of 0.077 μm or more, they did not satisfy relational equation (1): R ≤ 1.0609e^(4.7057 × T), and peeling of the collection layer was observed in the peeling test of the collection layer. [Industrial applicability]

[0075] The honeycomb filter of the present invention can be used as a filter for collecting particulate matter in exhaust gas. [Explanation of Symbols]

[0076] 1: Partition wall, 2: Cell, 2a: Inlet cell, 2b: Outlet cell, 3: Outer wall, 4: Honeycomb structure, 5: Seal section, 7: Pore, 11: Inlet end face, 12: Outlet end face, 14: Collection layer, 155: Non-oxide particles, 16: Oxides, 20: Vibration tester, 21: Burner section, 22: Main burner, 23: Pilot burner, 24: Combustion chamber, 31: Vibration section, 41: Sample mounting section, 100: Honeycomb filter.

Claims

1. A honeycomb structure having porous partition walls arranged to surround multiple cells that form fluid channels extending from the inlet end face to the outlet end face, The cell comprises an eye sealing portion arranged to seal either the inlet end face side or the outlet end face side of the cell, The cell in which the sealing portion is provided at the end on the outflow end face side and the inflow end face side is open is designated as an inflow cell. The cell in which the sealing portion is provided at the end on the inlet end face side and the outlet end face side is open is designated as an outlet cell. The honeycomb structure further includes a collection layer on the inner surface side of the partition wall surrounding the inflow cell for collecting particulate matter in the exhaust gas. The collection layer is a porous layer in which a plurality of non-oxide particles are joined via an oxide, the thickness of the oxide joining adjacent non-oxide particles is 0.077 μm or more, and when the average particle size of the non-oxide particles constituting the collection layer is R (μm) and the thickness of the oxide is T (μm), the relationship R ≤ 1.0609 e^(4.7057 × T) is satisfied, wherein the honeycomb filter.

2. The honeycomb filter according to claim 1, wherein the oxide constituting the collection layer is arranged to cover the surface of the non-oxide particles.

3. The honeycomb filter according to claim 1 or 2, wherein the non-oxide particles are silicon carbide particles.

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