ceramic filter

Abstract

Ceramic filter with a columnar honeycomb structure (100) comprising an outer circumferential side wall (102); a plurality of first cells (108) arranged on an inner circumferential side of the outer circumferential side wall (102), extending from a first end face (104) to a second end face (106), open at the first end face (104) and having closure sections (109) at the second end face (106); and a plurality of second cells (110) arranged on the inner circumferential side of the outer circumferential side wall (102), extending from the first end face (104) to the second end face (106), having closure sections (109) at the first end face (104) and being open at the second end face (106), wherein the plurality of first cells (108) and the plurality of second cells (110) are arranged alternately next to each other, with porous partitions (112) arranged between them;where, when viewing a plurality of pores of a surface of the partitions (112) with a laser microscope and plotting the equivalent circle diameter (µm) of each pore on the X-axis and the pore depth (µm) of each pore on the Y-axis on a two-dimensional coordinate system, the slope of the regression line (y / x) obtained by a least squares method in a range of 20 ≤ x ≤ 40 is 0 to 0.20, the average value of the pore depth of the plurality of pores is 2.5 µm to 5.0 µm, and the number density of the plurality of pores is 600 / mm; 2 up to 2450 / mm 2 amounts.

Description

AREA OF INVENTION

[0001] The present invention relates to a ceramic filter with a columnar honeycomb structure. BACKGROUND OF THE INVENTION

[0002] Solid particles (hereinafter referred to as PM) in the exhaust gas of an internal combustion engine, such as a diesel or gasoline engine, contain soot. Soot is harmful to the human body, and its emission is regulated. To comply with emissions regulations, filters such as DPFs and GPFs are currently widely used. These filters direct the exhaust gas through air-permeable, fine-pored baffles to filter out PMs such as soot.

[0003] A columnar honeycomb structure of the wall-flow type is known as a filter for collecting PM, comprising a plurality of first cells extending vertically from a first end face to a second end face, open at the first end face and having closure sections at the second end face, and a plurality of second cells arranged adjacent to the first cells with partitions between them, extending from the first end face to the second end face, having closure sections at the first end face and being open at the second end face.

[0004] In recent years, stricter emission standards have been introduced and the level of regulation has been tightened. Accordingly, a high PM removal efficiency is required, while at the same time a low pressure drop must be maintained. Therefore, there is a need for an exhaust filter that can achieve both requirements simultaneously. The following technologies are currently known for achieving both high PM removal efficiency and low pressure drop.

[0005] Patent publication 1 (Japanese patent application publication no. 2019-2298) discloses an exhaust gas purification filter, characterized in that, in a pore path length distribution of partitions for cell division, represented by a frequency histogram for each 10 µm pore path length of the partitions, a cumulative frequency, which is the maximum value obtained by adding the frequencies of a total of three adjacent classes including the maximum peak frequency, is 58% or more. Furthermore, this publication describes that the pore path length distribution is measured using image data analyzed three-dimensionally by means of a CT scan.

[0006] Patent literature 2 (Japanese patent application publication no. 2010-138770) discloses a ceramic filter, characterized in that, when the defect planes of the partitions of the ceramic filter are imaged at predetermined intervals by X-ray CT scan, for each defect plane obtained, a pore that exists across a plurality of defect planes and extends from one surface to the other surface of a partition is called a connection pore, and the number of connection pores for each defect plane is measured in order to calculate the total number of connection pores, the number of connection pores per unit volume being 7.5 × 10 4 Pores / mm 3 or more.

[0007] Patent literature 3 (WO 2011 / 102487) discloses a ceramic honeycomb structure with partitions in which: (a) the porosity is between 55 and 80%, (b) the mean pore diameter D50, measured using a mercury injection method, is 5 to 27 µm, (c) the opening area ratio of the pores open to the surface is 20% or more, (d) the area-related mean opening diameter d50 is 10 to 45 µm when the pores open towards the surface are represented by an equivalent circle diameter, (e) the pore density of pores open towards the surface with an equivalent circle diameter of 10 µm or more and less than 40 µm 350 cells / mm² 2 or more (f) the maximum value of the slope of a curve showing the cumulative pore volume in relation to the pore diameter is 1.6 or more when the pore distribution is measured by the mercury injection method, and (g) the ratio D50 / d50 of the mean pore diameter D50 to the mean opening diameter d50 is 0.65 or less.

[0008] Patent literature 4 (Japanese patent application publication no. 2005-095884) discloses a ceramic honeycomb structure characterized in that the porosity of the partitions is 55 to 75%, the average pore diameter Da on the surface of the partitions is 5 to 30 µm, the pore area fraction Sa on the surface of the partitions is 10 to 30%, and when viewed from a cross-sectional area perpendicular to the surface of the partitions, the average value La of the opening length of the surface of the plurality of pores open to the surface of the partitions and the average value Lb of the width of the plurality of pores at a depth La from the surface of the partitions on the cross-sectional area have a relationship of 1.1 < Lb / La < 5.

[0009] This literature describes how the mean pore diameter Da and the area ratio Sa on the surface of the partitions are determined using an image analyzer from images of five fields of view (100x magnification, image field 1.1 mm × 0.8 mm) obtained by SEM examination of the partition surface. It further describes how the average value La of the opening length and the average value Lb of the pore width are determined using an image analyzer from images of five fields of view (100x magnification, image field 1.1 mm × 0.8 mm) obtained by SEM examination of the partition cross-section.

[0010] EP 2 070 576 A1 discloses a ceramic honeycomb structure characterized in that it has a large number of flow paths surrounded by porous cell walls, the cell walls having a porosity of 55 to 70%, an average pore diameter of 10 to 40 µm, a concave area ratio CR (projected area ratio of sections lower than an average surface) of 0.32 to 0.6 and an average concave depth H (average depth of sections lower than the average surface) of 0.02 to 0.1 mm. LIST OF LITERATURES Patent Literature [Patent Literature 1] Japanese Patent Application Publication No. 2019-2298 [Patent Literature 2] Japanese Patent Application Publication No. 2010-138770 [Patent literature 3] WO 2011 / 102487 [Patent Literature 4] Japanese patent application publication no. 2005-095884 SUMMARY OF THE INVENTION

[0011] As described above, attempts were made to control various partition wall parameters, such as pore path length, porosity, pore diameter, and opening ratio, to obtain a filter that achieves both high PM removal efficiency and low pressure drop. Furthermore, these parameters were evaluated to identify the partition wall structure using X-ray CT scanning, electron microscopy, or mercury injection. However, when developing a filter that achieves both high PM removal efficiency and low pressure drop at a high level, characterizing the partition wall structure based on X-ray CT scanning, electron microscopy, or mercury injection is not always the optimal method. There is still room for improvement in filter performance.

[0012] In view of the above circumstances, the object of an embodiment of the present invention is to provide a ceramic filter with a column-shaped honeycomb structure that achieves both high PM separation efficiency and low pressure loss by improving the structure of the partitions from a perspective that has not been considered previously.

[0013] As a result of careful studies aimed at solving the aforementioned problems, the present inventors have determined that an approach to viewing and analyzing the surface of partitions using a laser microscope is advantageous for characterizing the partition structure. Furthermore, it is advantageous that the equivalent circular diameter of the surface pore, the pore depth, and the pore number density meet predetermined conditions to achieve both high PM deposition efficiency and low pressure drop. The present invention was developed based on the above findings and is described below by way of example. [1] Ceramic filter with a columnar honeycomb structure comprising an outer circumferential sidewall; a plurality of first cells arranged on an inner circumferential sidewall of the outer circumferential sidewall, extending from a first end face to a second end face, open at the first end face and having closure sections at the second end face; and a plurality of second cells arranged on the inner circumferential sidewall of the outer circumferential sidewall, extending from the first end face to the second end face, having closure sections at the first end face and being open at the second end face, wherein the plurality of first cells and the plurality of second cells are arranged alternately side by side, with porous partitions arranged between them; Where, when viewing a multitude of pores of a surface of the partitions with a laser microscope and plotting the equivalent circle diameter (µm) of each pore on the x-axis and the pore depth (µm) of each pore on the y-axis on a two-dimensional coordinate system, the slope of the regression line (y / x), obtained by a least squares method in a range of 20 ≤ x ≤ 40, is 0 to 0.20, the average value of the pore depth of the multitude of pores is 2.5 µm to 5.0 µm, and the number density of the multitude of pores is 600 / mm² 2 up to 2450 / mm 2 amounts. [2] Filter according to [1], where the slope of the regression line (y / x) is 0.08 to 0.20. [3] Filter according to [1] or [2], wherein the average value of the equivalent circular diameter of the plurality of pores is 7.5 µm to 14.0 µm. [4] Filter according to one of [1] to [3], wherein the porosity of the partitions is 52% to 65%. [5] Filter according to one of [1] to [4], wherein the average pore diameter of the partitions is 6.5 µm to 20 µm.

[0014] According to one embodiment of the present invention, it is possible to provide a ceramic filter with a column-shaped honeycomb structure that can achieve both a high PM separation efficiency and a low pressure loss. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a perspective view that schematically shows a columnar honeycomb structure of the wall flow type. Fig. Figure 2 is a schematic cross-sectional view of a columnar honeycomb structure of the wall flow type when viewed from a direction orthogonal to the direction in which the cells extend. Fig. Figure 3 is a schematic view showing the direction when viewing the surface of a partition with a laser microscope. DETAILED DESCRIPTION OF THE INVENTION

[0015] Embodiments of the present invention are described in detail below with reference to the drawings. It is understood that the present invention is not limited to the following embodiments, and any modification, improvement, or the like of the design can be made in a suitable manner based on the common knowledge of those skilled in the field, without departing from the core of the present invention. Furthermore, the ratio of the thicknesses of the individual components in the figures differs from the actual ratio, and the thin parts are also shown enlarged to make the structure easier to understand; the actual ratio of the thicknesses is not represented as it is. (1. Filter)

[0016] In one embodiment, a filter according to the present invention is provided as a columnar honeycomb structure of the wall-flow type, and it can be used as a DPF (diesel particulate filter) and GPF (gasoline particulate filter) that is installed in an exhaust line of a combustion device, typically an engine mounted in a vehicle, and captures soot. The filter according to the present invention can, for example, be installed in an exhaust pipe.

[0017] Fig. 1 and Fig.Figure 2 shows a schematic perspective view and a cross-sectional view of a columnar honeycomb structure (100) of the wall-flow type. The columnar honeycomb structure (100) comprises an outer circumferential side wall (102); a plurality of first cells (108) arranged on an inner circumferential side of the outer circumferential side wall (102), extending from a first end face (104) to a second end face (106), open at the first end face (104) and having closure sections (109) at the second end face (106); and a plurality of second cells (110) arranged on the inner circumferential side of the outer circumferential side wall (102), extending from the first end face (104) to the second end face (106), having closure sections (109) at the first end face (104) and being open at the second end face (106).In this columnar honeycomb structure (100), the multitude of first cells (108) and the multitude of second cells (110) are arranged alternately next to each other, with porous partitions (112) arranged between them.

[0018] When the exhaust gas, which contains particulate matter (PMs) such as soot, is fed to the first end face (104) on the upstream side of the columnar honeycomb structure (100), the exhaust gas is introduced into the first cells (108) and moves downstream within them. Since the first cells (108) have closure sections (109) on the second end face (106) on the downstream side, the exhaust gas passes through the porous partitions (112) that separate the first cells (108) from the second cells (110) and flows into the second cells (110). Because the particulate matter cannot pass through the partitions (112), it is collected and deposited in the first cells (108). After the solids have been removed, the purified exhaust gas that has flowed into the second cells (110) flows downstream in the second cells (110) and flows out of the second end face (106) on the downstream side.

[0019] Examples of the ceramics forming the columnar honeycomb structure according to the present embodiment include, but are not limited to, porous ceramics. Examples of ceramics include cordierite, mullite, zirconium phosphate, aluminum titanate, silicon carbide, silicon-silicon carbide composites (e.g., Si-bonded SiC), cordierite-silicon carbide composites, zirconium dioxide, spinel, indialite, sapphirine, corundum, titanium dioxide, silicon nitride, and the like. Furthermore, these ceramics may consist of one type alone or two or more types simultaneously.

[0020] In the columnar honeycomb structure according to the present embodiment, the porous partitions exhibit a characteristic three-dimensional structure. This characteristic three-dimensional structure can be identified by examining the surface of the partitions with a laser microscope. In particular, in one embodiment of the columnar honeycomb structure, when a plurality of pores are viewed from the surface of the partitions with a laser microscope and the equivalent circular diameter (µm) of each pore is plotted on the x-axis and the pore depth (µm) of each pore is plotted on the y-axis on a two-dimensional coordinate system, the slope of a regression line (y / x) obtained by a least squares method in a range of 20 ≤ x ≤ 40 is 0 to 0.20, the average pore depth of the plurality of pores is 2.5 µm to 5.0 µm, and the number density of the plurality of pores is 600 / mm². 2 up to 2450 / mm2 .

[0021] When examining the surface of the partitions with a laser microscope, pores of varying sizes can be observed. However, if the determined slope of the regression line (y / x) is 0 to 0.20 in the range of the equivalent circle diameter from 20 µm to 40 µm, this indicates that the pore depth does not increase significantly, even as the pore diameter increases. This suggests that there are many pores near the surface. The slope of the regression line (y / x) is preferably 0 to 0.18, more preferably 0 to 0.15, and even more preferably 0 to 0.10, and can typically be adjusted to 0.08 to 0.20. The range of the equivalent circular diameter of the pores, for which the slope of the regression line is determined, is set to 20 µm to 40 µm, since the coarse pores in this range have a large influence on the PM deposition performance.

[0022] The above regression line is calculated based on the measurement results for 10 or more samples obtained by taking a large number of arbitrary samples of the partitions from the columnar honeycomb structure.

[0023] In this description, the surface examination of the partitions is carried out using a laser microscope under the following conditions. Designation of measuring instrument: Shape analysis laser microscope (KEYENCE VK-X250 / 260) or a product with equivalent performance Analysis software: Multi-file analysis application (VK-1HXM) or software with equivalent performance Lens magnification: 10x Sample size: 20 mm x 20 mm x 10 mm Number of measurements: 10 times with different fields of view for one sample Measurement mode: Surface shape Measurement size per field of view: Standard (1024 pixels x 768 pixels) Measurement quality: high accuracy Measurement duration: 2 minutes Leveling process: A process is performed to determine a square area of ​​1000 µm × 1000 µm and to define the plane (reference plane) to be used as a measurement reference. All height data is rotated so that the defined reference plane is horizontal and offset vertically so that the height of the reference plane becomes 0. Position of the reference plane: -3 µm (offset so that the position at a depth of 3 µm has a height of 0). Ignore micro-areas: yes Number of pixels in the micro-area: ≥ 6 pixels (surface irregularities below 6 pixels are not recognized as pores). Viewing direction: Viewing from the direction perpendicular to the surface of a partition (see Fig. 3).

[0024] For the equivalent circular diameter of each pore, when considering the surface of the partitions under the above-mentioned conditions, the opening area of ​​each pore to be measured is measured in relation to the area in which the leveling process was carried out, and the diameter of a circle with the same area is calculated.

[0025] To determine the pore depth of each pore, when examining the surface of the partitions under the conditions mentioned above, the depth of the area forming each pore to be measured is measured by irradiation with a linear short-wave laser and measuring the depth of a point for each pixel, and the average is calculated.

[0026] From the perspective that the solids collected in the partitions should not penetrate deeply into them, the upper limit of the average pore depth of the plurality of pores is preferably 5.0 µm or less, more preferably 4.5 µm or less, and even more preferably 4.0 µm or less. Furthermore, from the perspective of improving the separation efficiency of the solids, the lower limit of the average pore depth of the plurality of pores is preferably 2.5 µm or more, more preferably 3.0 µm or more, and even more preferably 3.5 µm or more. The average pore depth is calculated based on the measurement results for 10 or more samples obtained by taking a plurality of arbitrary samples from the partitions within the columnar honeycomb structure.

[0027] From the perspective of PM deposition, the upper limit of the number density of the plurality of pores is preferably 2450 pores / mm².2 or less, and preferably 1400 pores / mm² 2 or less. From the perspective of pressure loss, the lower limit of the number density of the multitude of pores is preferably 600 pores / mm². 2 or more, preferably 700 pores / mm 2 or more, and preferably 800 pores / mm 2 or more.

[0028] The pore number density is determined by dividing the number of pores observed when examining the surface of the partitions under the conditions described above by the area of ​​the measurement. The pore number density is calculated based on the measurement results for 10 or more samples obtained by taking a large number of arbitrary samples from the partitions within the columnar honeycomb structure.

[0029] Although the present invention is not intended to be limited by any theory, the solids collected in the partitions can be prevented from penetrating deeply into them if the partitions have the aforementioned three-dimensional structure. Furthermore, the partitions have pores with a sufficient number density to collect solids. Therefore, it is expected that the pressure drop can be kept low while simultaneously achieving a high PM separation efficiency.

[0030] From the perspective of pressure drop, the lower limit of the average value of the equivalent circular diameter of the plurality of pores is preferably 6.5 µm or more, more preferably 7.0 µm or more, and even more preferably 7.5 µm or more. Furthermore, from the perspective of PM deposition, the upper limit of the average value of the equivalent circular diameter of the plurality of pores is preferably 18.0 µm or less, more preferably 16.0 µm or less, and even more preferably 14.0 µm or less. Therefore, in a preferred embodiment, the average value of the equivalent circular diameter of the plurality of pores can, for example, be in the range of 7.5 to 14.0 µm. The average value of the equivalent circular diameter of the pores is calculated based on the measurement results for 10 or more samples obtained by taking a plurality of arbitrary samples of the partitions from the columnar honeycomb structure.

[0031] The porosity of the partitions is preferably 52% or more, more preferably 58% or more, and even more preferably 65% ​​or more, when measured using a mercury injection method according to JIS R1655:2003 with a mercury porosimeter. If the porosity of the partitions is within the aforementioned range, it is possible to suppress a drop in the filter's pressure loss. Furthermore, the porosity of the partitions is preferably 65% ​​or less, more preferably 58% or less, and even more preferably 52% or less. If the porosity of the partitions is within the aforementioned range, the strength can be improved and damage during canning can be prevented. Therefore, in a preferred embodiment, the porosity of the partitions can be, for example, in the range of 52% to 65%.

[0032] The upper limit of the average pore diameter of the partitions is preferably 20 µm or less, more preferably 18 µm or less, and even more preferably 16 µm or less when measured using a mercury injection method according to JIS R1655:2003 with a mercury porosimeter. When the average pore diameter of the partitions is within the aforementioned range, the solids separation efficiency is significantly improved. Furthermore, the lower limit of the average pore diameter of the partitions, from the perspective of pressure drop, is preferably 6.5 µm or more, more preferably 8.0 µm or more, and even more preferably 9.0 µm or more when measured using a mercury injection method according to JIS R1655:2003 with a mercury porosimeter.

[0033] The mercury injection method is a procedure in which isostatic pressure is applied to a sample immersed in mercury under vacuum. Mercury is then intruded into the sample while the pressure is gradually increased, and the pore size distribution is calculated from the pressure and the volume of mercury entering the pores. As the pressure is gradually increased, mercury penetrates the pores, starting with those of larger diameter, thus increasing the cumulative volume of mercury. Finally, when all pores are filled with mercury, the cumulative volume reaches an equilibrium value.

[0034] The cumulative volume at this time is the total pore volume (cm³). 3 / g), and the pore diameter at the point when 50% of the total pore volume is permeated with mercury is defined as the average pore diameter. Furthermore, the porosity is calculated from the volume of mercury that has penetrated the pores. For the average pore diameter and porosity of the partitions, a large number of randomly selected partition samples are taken from the columnar honeycomb structure, and the average of the measurement results for 10 or more samples is used as the measured value.

[0035] From the perspective of increasing the strength and separation efficiency of the filter, the lower limit of the partition thickness is preferably 6 mil or more, more preferably 8 mil or more, and even more preferably 12 mil or more. From the perspective of suppressing the pressure drop of the filter, the upper limit of the partition thickness is preferably 12 mil or less, more preferably 8 mil or less, and even more preferably 6 mil or less. The partition thickness refers to the length at which a line segment intersects the partition when the centroids of adjacent cells are connected by the line segment in a cross-section orthogonal to the direction of extension of the cells. Furthermore, 1 mil is 1 / 1000 inch or 0.0254 mm.

[0036] A catalyst that supports PM combustion can be applied to the surface of the partitions or within the partition walls. The catalyst can include, for example, precious metals (Pt, Pd, Rh, and the like), alkali metals (Li, Na, K, Cs, and the like), alkaline earth metals (Ca, Ba, Sr, and the like), rare earth metals (Ce, Sm, Gd, Nd, Y, Zr, Ca, La, Pr, and the like), transition metals (Mn, Fe, Co, Ni, Cu, Zn, Sc, Ti, V, Cr, and the like), and similar materials.

[0037] The shape of the end faces of the columnar honeycomb structure is not limited, but it can be, for example, a round shape such as a circle, an elliptical shape, a racetrack shape, and an oval shape, a polygonal shape such as a triangle, and a quadrilateral shape. The columnar honeycomb structure (100) shown in the figures has circular end faces and is cylindrical as a whole.

[0038] The shape of the cells in cross-section perpendicular to the flow direction of the cells is not limited, but is preferably a square, a hexagon, an octagon, or a combination thereof. A square and a hexagon are particularly preferred. Forming the cells in this way reduces the pressure loss when liquid flows through the columnar honeycomb structure.

[0039] The cell density (number of cells per unit cross-sectional area) is also not particularly limited, but can range, for example, from 6 to 2000 cells / square inch (0.9 to 311 cells / cm²). 2 ), preferably 50 to 1000 cells / square inch (7.8 to 155 cells / cm²) 2 ), particularly preferably 100 to 400 cells / square inch (15.5 to 62.0 cells / cm²). 2 ). (2. Method for manufacturing the filter)

[0040] An exemplary process for producing the columnar honeycomb structure according to the present invention is described below. First, a raw material composition consisting of a ceramic raw material, a dispersion medium, a pore-forming agent, and a binder is kneaded into a green body. The green body is then extruded into the desired columnar honeycomb shape. Additives such as a dispersing agent can be added to the raw material composition as required. During extrusion, a die with the desired overall shape, cell shape, septum thickness, cell density, and the like can be used.

[0041] After the columnar honeycomb mold has dried, closure sections are formed on both end faces of the columnar honeycomb mold, and then these closure sections are dried to obtain a columnar honeycomb mold with closure sections. The columnar honeycomb mold is then degreased and fired to produce a fired columnar honeycomb structure.

[0042] A ceramic raw material can be used that, after firing, can form the aforementioned ceramics. The ceramic raw material can be provided, for example, in powder form. Examples of ceramic raw materials include cordierite, mullite, zirconium, aluminum titanate, silicon carbide, silicon nitride, zirconium dioxide, spinel, indialite, sapphirine, corundum, and titanium dioxide. Examples include, but are not limited to, silicon dioxide, talc, aluminum oxide, kaolin, serpentine, pyroferrite, bluesite, boehmite, mullite, magnesite, and aluminum hydroxide. A single type of ceramic raw material or a combination of two or more types can be used.

[0043] For filter applications such as DPFs and GPFs, cordierite can be used as a preferred ceramic material. In this case, a cordierite-forming raw material can be used as the ceramic material. A cordierite-forming raw material is a material that forms cordierite upon firing. It is desirable that the cordierite-forming raw material has a chemical composition of aluminum oxide (Al₂O₃) (including the amount of aluminum hydroxide that is converted to aluminum oxide): 30 to 45% by mass, magnesium oxide (MgO): 11 to 17% by mass, and silicon dioxide (SiO₂): 42 to 57% by mass.

[0044] Furthermore, it is advantageous to include porous silicon dioxide as a ceramic raw material. Porous silicon dioxide has the property of readily forming pores on its surface because it retains its shape until the late stages of firing, and this helps to reduce the slope (y / x) of the regression line described above. Therefore, the porous silicon dioxide preferably comprises 7.0 parts by mass or more, more preferably 15.0 parts by mass or more, and even more preferably 20.0 parts by mass or more in 100 parts by mass of the ceramic raw material. However, if the proportion of porous silicon dioxide in the ceramic raw material is too high, it becomes necessary to extend the firing time for the cordierite-forming reaction, which is costly. Therefore, the porous silicon dioxide preferably comprises 35.0 parts by mass or less, more preferably 30.0 parts by mass or less and even more preferably 25.0 parts by mass or less in 100 parts by mass of the ceramic raw material.Porous silicon dioxide plays a role as a pore-forming agent, but since it also forms the filter as a ceramic after firing, it is treated as a ceramic raw material in this description.

[0045] In one embodiment, the porous silicon dioxide is provided in powder form. In this case, the lower limit of the mean diameter (D50), when a volume-based cumulative particle size distribution of the porous silicon dioxide is obtained by a laser diffraction / scattering method, is preferably 5.0 µm or more, and more preferably 10.0 µm or more. The upper limit of the mean diameter (D50) is preferably 40.0 µm or less, and more preferably 30.0 µm or less, to prevent a reduction in PM deposition efficiency due to an increase in pore size.

[0046] Examples of the dispersion medium are water or a mixed solvent of water and an organic solvent such as alcohol, with water being particularly suitable.

[0047] The pore-forming agent is not particularly limited as long as it forms pores after firing, and examples include wheat flour, starch, foamed resin, water-absorbing resin, acrylic resin, carbon (e.g., graphite), ceramic balloon, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic, phenol, and the like. A single type of pore-forming agent may be used alone, or two or more types may be used in combination. The pore-forming agent content 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, based on 100 parts by mass of the ceramic raw material, with the aim of increasing the porosity of the fired body.The pore-forming agent content 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, based on 100 parts by mass of the ceramic raw material, from the point of view of ensuring the strength of the fired body.

[0048] Examples of binders include organic binders such as methylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, polyvinyl alcohol, and the like. The use of methylcellulose and hydroxypropylmethylcellulose in combination is particularly suitable. Furthermore, 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, based on 100 parts by mass of the ceramic raw material, with the aim of increasing the strength of the honeycomb-shaped body. 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, based on 100 parts by mass of the ceramic raw material, with the aim of suppressing the occurrence of cracks due to abnormal heat generation during the firing process.One type of binder can be used alone, or two or more types can be used in combination.

[0049] Suitable dispersing agents include ethylene glycol, dextrin, fatty acid soap, polyether polyol, and the like. A single dispersing agent or a combination of two or more may be used. The dispersing agent content is preferably 0 to 2 parts by weight per 100 parts by weight of the ceramic raw material.

[0050] The method for sealing the end faces of the columnar honeycomb mold is not particularly limited, and a known method may be used. The material of the sealing section is not particularly limited, but ceramic is preferred from the point of view of strength and heat resistance. The ceramic is preferably a ceramic material comprising at least one selected from the group consisting of cordierite, mullite, zirconium, aluminum titanate, silicon carbide, silicon nitride, zirconium dioxide, spinel, indialite, sapphirine, corundum, and titanium dioxide. It is even more preferred that the sealing section have the same material composition as the main body section of the honeycomb mold, because the coefficient of thermal expansion at the time of firing can be set to the same value, and durability can be improved.

[0051] A columnar honeycomb structure can be produced by drying the honeycomb mold and subsequently degreasing and firing it. Known conditions, corresponding to the material composition of the honeycomb mold, can be used as the drying, degreasing, and firing steps, and although no further explanation is required, specific examples of these conditions are given below.

[0052] In the drying step, conventionally known drying methods such as hot gas drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, and freeze-drying can be used. Among these, a drying process that combines hot gas drying with microwave drying or dielectric drying is preferable because the entire molded part can be dried quickly and uniformly. When forming the closure sections, these sections can be created on both end faces of the dried honeycomb molded part, and then dried to obtain a dried honeycomb molded part.

[0053] The next step is the degreasing process. The combustion temperature of the binder is approximately 200 °C, while the combustion temperature of the pore-forming agent is approximately 300 to 1000 °C. Therefore, the degreasing step can be carried out by heating the honeycomb mold body to a temperature of approximately 200 to 1000 °C. The heating time is not strictly limited but is typically about 10 to 100 hours. After the degreasing step, the honeycomb mold body is referred to as a calcined body.

[0054] The firing step depends on the material composition of the honeycomb mold, but can be carried out, for example, by heating the calcined body to 1350 to 1600 °C and holding the temperature for 3 to 10 hours. EXAMPLES

[0055] Examples are given below to better understand the present invention and its advantages, but the present invention is not limited to these examples. <Herstellung einer säulenförmigen Wabenstruktur>

[0056] According to the experiment number, the main raw materials (ceramic raw materials) and auxiliary raw materials with the particle diameters shown in Tables 1-1, 1-2, and 1-3 were mixed in a dispersion medium according to the mixing ratios shown in Tables 1-1, 1-2, and 1-3, and kneaded to produce green bodies. The particle diameter of each raw material represents the mean diameter (D50) when the cumulative particle size distribution was determined by volume using a laser diffraction / scattering method with an LA-950 instrument available from HORIBA. Water was used as the dispersion medium, acrylic resin as the organic pore-forming agent, hydroxypropyl methylcellulose as the binder, and fatty acid soap as the dispersant. Talc A and Talc B were the same material but had different particle sizes.Porous silicon dioxide A, porous silicon dioxide B, and porous silicon dioxide C were the same material but had different particle sizes. Organic pore-forming agent A and organic pore-forming agent B were the same material but had different particle sizes.

[0057] Each of the green bodies was loaded into an extrusion press and formed by extrusion to obtain a cylindrical honeycomb shape using a die with a predetermined shape. After the resulting honeycomb shape underwent dielectric drying and hot air drying, both end faces were trimmed to predetermined dimensions, resulting in a dried honeycomb shape.

[0058] The specifications of the dried honeycomb mold were as follows: Overall shape: a cylindrical shape with a diameter of 70 mm × a height of 100 mm. Cell shape in cross-section perpendicular to the flow direction of the cells: square. Cell density (number of cells per unit cross-sectional area): 300 cells / inch. 2 Partition wall thickness: 9 mil (229 µm) (nominal value based on nozzle specifications)

[0059] Each of the resulting dried honeycomb bodies was sealed with a cordierite-forming slurry, so that the first and second cells were arranged alternately next to each other. Then, after degreasing by heating at approximately 200 °C to 1000 °C in an air atmosphere and further firing at 1420 °C to 1440 °C for 5 hours in an air atmosphere, a columnar honeycomb structure was obtained according to each test example. A number of columnar honeycomb structures according to each test example were produced as needed to evaluate various characteristics. <Analyse der Trennwandstruktur mit dem Lasermikroskop>

[0060] Ten random samples were taken from the resulting columnar honeycomb structure, and the surface of the partitions was examined using a shape analysis laser microscope (KEYENCE VK-X250 / 260). Features (1) to (4) were measured according to the previously described measurement conditions. The results are presented in Table 1-1, Table 1-2, and Table 1-3. (1) The slope of the regression line (y / x) obtained by the least squares method in the range of 20 ≤ x ≤ 40 when the equivalent circle diameter (µm) of each pore is plotted on the x-axis and the pore depth (µm) of each pore is plotted on the y-axis in a two-dimensional coordinate system. (2) The average value of the pore depth of the multitude of pores. (3) The number density of the multitude of pores. (4) The average value of the equivalent circle diameter of the plurality of pores. <Analyse der Trennwandstruktur mit dem Quecksilbereinpressverfahren>

[0061] Ten random samples were taken from the resulting columnar honeycomb structure and their porosity and average pore diameter were measured using a mercury porosimeter (Autopore 9505 model, available from Micrometrics) under the previously described measurement conditions. The results are presented in Tables 1-1, 1-2, and 1-3. <Leistungsbewertung als Filter>

[0062] A rectangular parallelepiped sample measuring 36 mm × 36 mm × 100 mm L was cut from each of the obtained columnar honeycomb structures. A specific quantity of carbon black was introduced into the sample at a flow rate of 2 m / sec, and the PM deposition efficiency and pressure drop were evaluated under the condition that 1 g / L of carbon black was deposited in 2 to 3 hours. The results are presented in Table 1-1, Table 1-2, and Table 1-3.

[0063] The separation efficiency was divided into the following categories. ◯ (Circle): Equivalent to or better than the benchmark target △ (Triangle): Performance decline of 30% or less compared to the benchmark. × (cross): Performance decline of more than 30% compared to the benchmark.

[0064] The pressure loss power was divided into the following categories. ◯ (Circle): Equivalent to or better than the benchmark target △ (Triangle): Performance decline of 30% or less compared to the benchmark. × (cross): Performance decline of more than 30% compared to the benchmark.

[0065] The comparison targets were defined as Example 1 for Nos. 1 to 3, Example 4 for Nos. 4 to 8, Example 9 for Nos. 9 to 10 and Example 11 for Nos. 11 to 12. Table 1-1 Nr. 1 2 3 Raw material Particle diameter Example Comparative example Comparative example Main raw material Talc A 25,0µm - 40.0 mass parts 40.0 mass parts Talc B 15,0µm 40.0 mass parts - - kaolin 5,0µm 19.0 mass parts 19.0 mass parts 19.0 mass parts silicon dioxide 20,0µm 7.25 mass parts 12.5 mass parts 12.5 mass parts Aluminum dioxide 5,0µm 13.5 mass parts 13.5 mass parts 13.5 mass parts Aluminum hydroxide 5,0µm 13.0 mass parts 15.0 mass parts 15.0 mass parts Porous silicon dioxide A 15,0µm - - - Porous silicon dioxide B 20,0µm 7.25 mass parts - - Porous silicon dioxideC 40,0µm - - - Auxiliary raw material Organic Pore Former A 20,0µm 0.5 parts by mass 1.0 mass parts 0.5 parts by mass Organic Pore Former B 40,0µm - - 2.0 mass parts binder - 5.0 mass parts 5.0 mass parts 5.0 mass parts Dispersing agent - 0.5 parts by mass 0.5 parts by mass 0.5 parts by mass Features Porosity (%) 53,5 53,6 53,5 Average pore diameter (µm) 9,2 9,8 13,7 Anzahldichte der Poren (Poren / mm 2 ) 1000 900 600 Average value of the equivalent circle diameter (µm) 10,5 9,8 13,7 Average pore depth (µm) 2,7 3,6 3,6 Increase in pore depth / equivalent circle diameter (y / x) 0,18 0,27 0,35 Performance PN separation - △ (-10%) × (-43%) Pressure loss - × (-34%) ◯ Comparison target Comparison with Example 1 Table 1-2 Nr. 4 5 6 7 8 Raw material Particle diameter Example Example Comparative example Example Comparative example Main raw material Talc A 25,0µm - - 40.0 mass parts - - Talc B 15,0µm 40.0 mass parts 40.0 mass parts - 40.0 mass parts 40.0 mass parts kaolin 5,0µm 18.5 mass parts 18.5 mass parts 19.0 mass parts - 19.0 mass parts silicon dioxide 20,0µm - - 12.5 mass parts 12.5 mass parts 13.5 mass parts Aluminum dioxide 5,0µm 13.5 mass parts 13.5 mass parts 13.5 mass parts 13.5 mass parts 13.5 mass parts Aluminum hydroxide 5,0µm 13.5 mass parts 13.5 mass parts 15.0 mass parts 14.0 mass parts 14.0 mass parts Porous silicon dioxide A 15,0µm - 14.5 mass parts - - - Porous silicon dioxide B 20,0µm 14.5 mass parts - - 20.0 mass parts - Porous silicon dioxide C 40,0µm - - - - - Auxiliary raw material Organic Pore Former A 20,0µm 1.0 mass parts 1.0 mass parts 0.5 parts by mass 1.0 mass parts 0.5 parts by mass Organic Pore Former B 40,0µm - - 5.0 mass parts 5.0 mass parts binder - 5.0 mass parts 5.0 mass parts 5.0 mass parts 5.0 mass parts 5.0 mass parts Dispersing agent - 0.5 parts by mass 0.5 parts by mass 0.5 parts by mass 0.5 parts by mass 0.5 parts by mass Features Porosity (%) 57,5 56,5 56,7 60,2 58,4 Average pore diameter (µm) 9,5 6,5 13,7 10,1 9,5 Pore ​​density (pores / mm²) 2 ) 1130 2450 550 1250 890 Average value of the equivalent circle diameter (µm) 9,6 7,6 13,2 10,9 9,7 Average pore depth (µm) 3,2 3,0 3,7 2,6 2,8 Increase in pore depth / equivalent circle diameter (y / x) 0,13 0,09 0,28 0,08 0,24 Performance PN separation - ◯ × (-34%) ◯ △ (-18%) Pressure loss - △ (-13%) ◯ △ (-6%) × (-38%) Comparison target Comparison with example 4 Table 1-3 Nr. 9 10 11 12 Raw material Particle diameter Example Comparative example Example Comparative example Main raw material Talc A 25,0µm 40.0 mass parts 40.0 mass parts - - Talc B 15,0µm - - 40.0 mass parts 40.0 mass parts kaolin 5,0µm 19.5 mass parts 19.0 mass parts 19.0 mass parts 19.0 mass parts silicon dioxide 20.0 µm - 13.0 mass parts - 13.0 mass parts Aluminum dioxide 5,0µm 13.5 mass parts 13.5 mass parts 13.5 mass parts 13.5 mass parts Aluminum hydroxide 5,0µm 13.5 mass parts 14.5 mass parts 14.0 mass parts 14.5 mass parts Porous silicon dioxide A 15,0µm - - - - Porous silicon dioxide B 20,0µm - - - - Porous silicon dioxide C 40,0µm 13.5 mass parts - 13.5 mass parts - Auxiliary raw material Organic Pore Former A 20,0µm 1.0 mass parts 0.5 parts by mass 1.0 mass parts 0.5 parts by mass Organic Pore Former B 40,0µm - 10.0 mass parts - 10.0 mass parts binder - 5.0 mass parts 5.0 mass parts 5.0 mass parts 5.0 mass parts Dispersing agent - 0.5 parts by mass 0.5 parts by mass 0.5 parts by mass 0.5 parts by mass Features Porosity (%) 64,0 64,3 65,3 65,0 Average pore diameter (µm) 17,7 21,0 14,4 15,6 Pore ​​density (pores / mm²) 2 ) 600 520 700 550 Average value of the equivalent circle diameter (µm) 14,1 11,3 14,0 10,6 Average pore depth (µm) 4,9 3,4 4,5 2,5 Increase in pore depth / equivalent circle diameter (y / x) 0,10 0,51 0,20 0,32 Performance PN separation - × (-48%) - × (-39%) Pressure loss - × (-32%) - × (-48%) Comparison target Comparison with Example 9 Comparison target Comparison with Example 11 Description of the reference symbols 100 Columnar honeycomb structure 102 Outer perimeter side wall 104 First end surface 106 Second end surface 108 First cell 109 Closure section 110 Second cell 112 Partition wall

Claims

[1] Ceramic filter with a columnar honeycomb structure (100) comprising an outer circumferential side wall (102); a plurality of first cells (108) arranged on an inner circumferential side of the outer circumferential side wall (102), extending from a first end face (104) to a second end face (106), open at the first end face (104) and having closure sections (109) at the second end face (106); and a plurality of second cells (110) arranged on the inner circumferential side of the outer circumferential side wall (102), extending from the first end face (104) to the second end face (106), having closure sections (109) at the first end face (104) and being open at the second end face (106), wherein the plurality of first cells (108) and the plurality of second cells (110) are arranged alternately next to each other, with porous partitions (112) arranged between them;where, when viewing a plurality of pores of a surface of the partitions (112) with a laser microscope and plotting the equivalent circle diameter (µm) of each pore on the X-axis and the pore depth (µm) of each pore on the Y-axis on a two-dimensional coordinate system, the slope of the regression line (y / x) obtained by a least squares method in a range of 20 ≤ x ≤ 40 is 0 to 0.20, the average value of the pore depth of the plurality of pores is 2.5 µm to 5.0 µm, and the number density of the plurality of pores is 600 / mm; 2 up to 2450 / mm 2 amounts. [2] Filter according to claim 1, wherein the slope of the regression line (y / x) is 0.08 to 0.

20. [3] Filter according to claim 1 or 2, wherein the average value of the equivalent circular diameter of the plurality of pores is 7.5 µm to 14.0 µm. [4] Filter according to any one of claims 1 to 3, wherein the porosity of the partitions (112) is 52% to 65%. [5] Filter according to any one of claims 1 to 4, wherein the average pore diameter of the partitions (112) is 6.5 µm to 20 µm.

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