Porous composite

Abstract

Porous composite comprising: a porous base material; and a porous collecting layer formed on the base material, wherein the base material has a honeycomb structure whose interior is divided by a partition wall into a plurality of cells extending in a longitudinal direction, wherein the plurality of cells includes a plurality of first cells having one end closed in the longitudinal direction and a plurality of second cells having the other end closed in the longitudinal direction, the plurality of first cells and the plurality of second cells being arranged alternately, wherein the collecting layer is formed in film form on inner surfaces of the plurality of first cells and covers these inner surfaces of the plurality of first cells, wherein a total Sa, ie an arithmetic mean height Sa indicating a surface roughness of a surface of the collecting layer in the plurality of first cells, is greater than or equal to 0.1 µm and less than or equal to 12 µm, and wherein a total average thickness, ie an average thickness of the collection layer in the plurality of first cells, is greater than or equal to 10 µm and less than or equal to 40 µm, wherein a thickness of the collection layer is the distance between the surface of the collection layer and the inner surface of the first cell in the thickness direction.

Description

Technical field

[0001] The present invention relates to a porous composite. State of the art

[0002] Gases emitted from internal combustion engines, such as diesel engines, or various combustion devices contain particulate matter, such as soot. Therefore, vehicles and other devices with diesel engines are equipped with filters to collect particulate matter in exhaust gases. One of these filters uses a honeycomb structure, in which some cells made of a porous honeycomb base material have sealed portions at openings on their exhaust side, and the remaining cells have sealed portions at openings on their inlet side.

[0003] Recently, it has been proposed to collect particulates in the exhaust gas of a gasoline engine by using the above-mentioned honeycomb structure as a filter. For example, Japanese Patent Application Publication No. JP 2011-139975 A (Document 1) proposes a honeycomb structure that collects particulates contained in the exhaust gas of a direct-injection gasoline engine with high collection efficiency while suppressing an increase in pressure loss. Japanese Patent Application Publication No. JP 2011-147931 A (Document 2) proposes a technique for improving collection efficiency by forming a surface collection layer on the surface of the partition wall in the honeycomb structure.

[0004] At present, in the honeycomb structure used as the above filter, both further suppression of the increase in pressure loss and high collection efficiency of particles must be achieved.

[0005] JP 2011-189 246 A describes a honeycomb filter and its manufacturing process. Summary of the invention

[0006] The present invention relates to a porous composite according to claim 1 and it is an object of the present invention to reduce the pressure loss and increase the collection efficiency of particles.

[0007] The porous composite according to a preferred embodiment of the present invention comprises a porous base material and a collection layer formed on the base material. The base material has a honeycomb structure whose interior is divided by a partition wall into a plurality of cells extending in a longitudinal direction. The plurality of cells includes a plurality of first cells with one end closed in the longitudinal direction and a plurality of second cells with the other end closed in the longitudinal direction, wherein the plurality of first cells and the plurality of second cells are alternately arranged. The collection layer covers the inner surfaces of the plurality of first cells. A total Sa, that is, an arithmetic mean height Sa indicating a surface roughness of a surface of the collection layer in the plurality of first cells, is equal to or greater than 0.1 μm and equal to or less than 12 μm.A total average thickness, i.e., an average thickness of the collection layer in the plurality of first cells, is greater than or equal to 10 µm and less than or equal to 40 µm. The porous composite can reduce pressure loss and improve collection efficiency.

[0008] An outlet side height Sa, ie, an arithmetic mean height Sa of the surface of the collecting layer at end portions in the plurality of first cells, is preferably greater than or equal to 0.1 µm and less than or equal to 15 µm, the end portions being located on one side of one end in the longitudinal direction.

[0009] An average thickness of the outlet side, ie an average thickness of the collecting layer at the end portions in the plurality of first cells, is preferably greater than or equal to 35 µm and less than or equal to 50 µm.

[0010] The collection layer in the plurality of first cells preferably has an average pore diameter of greater than or equal to 0.1 µm and less than or equal to 20 µm.

[0011] The collection layer in the plurality of first cells preferably has a porosity of greater than or equal to 50% and less than or equal to 90%.

[0012] An aggregate of the collection layer in the plurality of first cells preferably has an average particle diameter of greater than or equal to 0.1 µm and less than or equal to 5 µm.

[0013] The collection layer in the plurality of first cells preferably contains at least one selected from silicon carbide, cordierite, mullite, alumina, silicon oxide, titanium oxide, zirconia, iron oxide and cerium oxide.

[0014] The collecting layer preferably does not exist in the plurality of second cells.

[0015] A primary material of the partition wall is preferably cordierite. The partition wall has an average pore diameter of greater than or equal to 5 µm and less than or equal to 30 µm. The partition wall has a porosity of greater than or equal to 30% and less than or equal to 70%.

[0016] The porous composite is preferably a gasoline particulate filter for collecting particulates in an exhaust gas emitted by a gasoline engine.

[0017] These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. Brief description of the drawings Fig. 1 is a plan view of a porous composite according to one embodiment; Fig. 2 is a sectional view of the porous composite; Fig.3 is a schematic diagram corresponding to an SEM image of a cross section of a collection layer and a base material; Fig. 4 is a schematic diagram corresponding to the SEM image of the cross section of the collection layer and the base material; Fig. 5 is a schematic diagram corresponding to the SEM image of the cross section of the collection layer and the base material; Fig. 6 is a view showing a sample; Fig. 7 is a view showing measurement areas on the sample; Fig. 8 is a view schematically showing a part of the sample; and Fig. Figure 9 is a flow chart of the preparation of the porous composite. Description of embodiments

[0018] Fig.Fig. 1 is a plan view illustrating a porous composite 1 according to an embodiment of the present invention in a simplified manner. The porous composite 1 is a tubular member that is long in one direction. Fig. 1 shows the end face on one side in the longitudinal direction of the porous composite 1. Fig. 2 is a sectional view of the porous composite 1. In Fig. 2 shows a partial cross-section along the longitudinal direction. The porous composite 1 is used, for example, as a gasoline particle filter (GPF) for collecting particulates such as soot in the exhaust gas emitted by a gasoline engine of a vehicle and the like.

[0019] The porous composite 1 comprises a porous base material 2 and a porous collection layer 3. In the Fig. 1 and Fig.2, the base material 2 is a member having a honeycomb structure. The base material 2 comprises a tubular outer wall 21 and a partition wall 22. The tubular outer wall 21 is a tubular portion extending in the longitudinal direction (ie, in Fig. 2 in the left-right direction). The tubular outer wall 21 has, for example, a generally round cross-sectional shape perpendicular to the longitudinal direction. This cross-sectional shape can be arbitrary, e.g., polygonal.

[0020] The partition wall 22 is a lattice-shaped portion provided in the tubular outer wall 21 and divides the interior into a plurality of cells 23. Each of the cells 23 is a space extending in the longitudinal direction. Each cell 23 has, for example, a generally square cross-sectional shape perpendicular to the longitudinal direction. This cross-sectional shape may be arbitrary, such as polygonal or circular. These cells 23 generally have the same cross-sectional shape. Alternatively, the cells 23 may include cells 23 having different cross-sectional shapes. The base material 2 is a cellular structure whose interior is divided into the cells 23 by the partition wall 22.

[0021] Both the tubular outer wall 21 and the partition wall 22 are porous sections. The tubular outer wall 21 and the partition wall 22 are made of, for example, ceramics. The main material of the tubular outer wall 21 and the partition wall 22 is preferably cordierite (2MgO·2Al2O3·5SiO2). The material of the tubular outer wall 21 and the partition wall 22 may be a ceramic other than cordierite, or may be a material other than ceramics.

[0022] The tubular outer wall 21 has a length of, for example, 50 mm to 300 mm in the longitudinal direction. The outer diameter of the tubular outer wall 21 is, for example, in the range of 50 mm to 300 mm. The thickness of the tubular outer wall 21 is, for example, greater than or equal to 30 micrometers (µm) and preferably greater than or equal to 50 µm. The thickness of the tubular outer wall 21 is also, for example, less than or equal to 1000 µm, preferably less than or equal to 500 µm, and more preferably less than or equal to 350 µm.

[0023] The length of the partition wall 22 in the longitudinal direction generally corresponds to that of the tubular outer wall 21. The thickness of the partition wall 22 is, for example, greater than or equal to 30 µm and preferably greater than or equal to 50 µm. The thickness of the partition wall 22 is also, for example, less than or equal to 1000 µm, preferably less than or equal to 500 µm and more preferably less than or equal to 350 µm. The porosity of the partition wall 22 is, for example, greater than or equal to 20% and preferably greater than or equal to 30%. The porosity of the partition wall 22 is also, for example, less than or equal to 80% and preferably less than or equal to 70%. The porosity can be measured, for example, using the Archimedes method using deionized water as the medium. The average pore diameter of the partition wall 22 is, for example, greater than or equal to 5 µm and preferably greater than or equal to 8 µm. The average pore diameter of the partition wall 22 is also, for example, less than or equal to 30 µm and preferably less than or equal to 25 µm.The mean pore diameter can be measured, for example, using mercury porosimetry (according to JIS R 1655).

[0024] A cell density of the base material 2 (ie the number of cells 23 per unit area of ​​a cross-section perpendicular to the longitudinal direction) is, for example, greater than or equal to 10 cells / cm 2 (per square centimeter), preferably greater than or equal to 20 cells / cm 2 and preferably greater than or equal to 30 cells / cm 2 . The cell density is, for example, less than or equal to 200 cells / cm 2 and preferably less than or equal to 150 cells / cm 2 . In the illustration in Fig. 1, the sizes of the cells 23 are larger than the actual sizes, and the number of cells 23 is smaller than the actual number. The sizes and number of cells 23 can be changed in several ways.

[0025] When the porous composite 1 is used as a GPF, a gas, e.g., an exhaust gas, flows through the interior of the porous composite 1, with one end side of the porous composite 1 in the longitudinal direction (ie, left side in Fig. 2) serves as an inlet and the other end as an outlet. Some of the cells 23 of the porous composite 1 each have a sealing part 24 at the end portion on the inlet side, and the remaining cells 23 each have a sealing part 24 at the end portion on the outlet side.

[0026] Fig. 1 is a representation of the inlet side of the porous composite 1. In Fig. 1, the sealing parts 24 on the inlet side are shown hatched to facilitate understanding of the drawing. In the Fig.1, the cells 23 which have the sealing parts 24 on the inlet side and the cells 23 which do not have the sealing parts 24 on the inlet side (ie the cells 23 which have the sealing parts 24 on the outlet side) are in Fig. 1 arranged alternately in the vertical and lateral directions.

[0027] In the following description, the cells 23 having the sealing parts 24 on the outlet side are referred to as "first cells 231," and the cells 23 having the sealing parts 24 on the inlet side are referred to as "second cells 232." In the case where it is not necessary to distinguish between the first cells 231 and the second cells 232, the cells 23 are collectively referred to as "cells 23" as described above. The cells 23 of the porous composite 1 include the first cells 231 with one end closed in the longitudinal direction and the second cells 232 with the other end closed in the longitudinal direction, with the first cells 231 and the second cells 232 being arranged alternately.

[0028] The collecting layer 3 is formed in film form on the surface of the base material 2. In the Fig.2, the collecting layer 3 is provided in the first cells 231 with the sealing parts 24 on the outlet side and covers the inner surfaces of the first cells 231 (ie, the surface of the partition wall 22). In Fig. 2, the collection layer 3 is shown by bold lines. The collection layer 3 also covers the inner surfaces of the sealing parts 24 on the outlet side in the first cells 231. However, the collection layer 3 does not exist in the second cells 232, which have the sealing parts 24 on the inlet side. In other words, the inner surfaces of the second cells 232 are exposed without being covered by the collection layer 3.

[0029] The collection layer 3 in the first cells 231 is made of, for example, ceramic. The collection layer 3 preferably contains at least one selected from silicon carbide, cordierite, mullite, alumina, silicon oxide, titanium oxide, zirconia, iron oxide, and cerium oxide as the main material. Note that the collection layer 3 may be made of any other ceramic or a material other than ceramic.

[0030] The average pore diameter of the collection layer 3 is preferably greater than or equal to 0.1 µm and less than or equal to 20 µm. The average pore diameter is more preferably greater than or equal to 4.1 µm and less than or equal to 20 µm and even more preferably greater than or equal to 4.1 µm and less than or equal to 6 µm. The porosity of the collection layer 3 is preferably greater than or equal to 50% and less than or equal to 90%. The porosity is more preferably greater than or equal to 70% and less than or equal to 78%. The average particle diameter of an aggregate forming the collection layer 3 is preferably greater than or equal to 0.1 µm and less than or equal to 5 µm. The average particle diameter is more preferably greater than or equal to 0.4 µm and less than or equal to 5 µm.

[0031] The average pore diameter and porosity of the collection layer 3 and the average particle diameter of the aggregate can be obtained using the following method. First, the porous composite 1 is processed with a cross-section polisher (CP) to expose a polished cross-section comprising the collection layer 3 and the base material 2. This polished cross-section is imaged with a scanning electron microscope (SEM) at a predetermined magnification (e.g., 1000x magnification) to obtain an SEM image. Fig. Figure 3 is a schematic diagram corresponding to the SEM image. This SEM image is then analyzed using image analysis software "Image-Pro Version 9.3.2" manufactured by Nippon Roper Co. Ltd., and the mean pore diameter and porosity of the collection layer 3 and the mean particle diameter of the aggregate can be obtained.

[0032] As shown in the schematic diagram from Fig. 4, in a region of the SEM image where the collection layer 3 exists, straight lines 91 extending parallel to the surface of the base material 2 are arranged in the direction orthogonal to the straight lines 91. One pixel of the SEM image corresponds to 0.1 µm × 0.1 µm. The width of each straight line 91 corresponds to one pixel of the SEM image, and the width in the region shown in Fig.4 is 0.1 μm. Next, in each region where bright parts (i.e., the aggregate of the collection layer 3) are connected to each other on the straight line 91 (hereinafter, the region is referred to as a "bright region"), the area is calculated. In addition, in each region where dark parts (i.e., pores of the collection layer 3) are connected to each other on the straight line 91 (hereinafter, the region is referred to as a "dark region"), the area is calculated. In the area calculation of the bright regions and the dark regions, an area with a width of 0.2 μm (i.e., an area with a width of two pixels) is extracted from each straight line 91. Specifically, each straight line 91 with a width of 0.1 μm is placed on the boundary line between two pixel rows adjacent to each other in the width direction (i.e., rows of a plurality of pixels arranged in a direction perpendicular to the width direction).All pixels overlapping a straight line 91 are subject to area calculation. The area of ​​each bright area and dark area is measured in units of 0.01 µm. 2 calculated and an area with an area of ​​less than 0.05 µm 2(i.e., an area with four pixels or less) is ignored as noise. Then, the arithmetic mean of the areas of the dark areas is obtained as the pore area extracted by the straight lines 91. The pore area is the integrated value of the pore diameter and the pore width (i.e., 0.2 μm corresponds to two pixels) defined by the straight line 91. Therefore, the mean pore diameter of the collection layer 3 is calculated by dividing the above-mentioned arithmetic mean of the areas of the dark areas by 0.2 μm (i.e., the pore width). The porosity of the collection layer 3 is obtained by dividing the total area of ​​the dark areas by the sum of the total area of ​​the light areas and the total area of ​​the dark areas.

[0033] As shown in the schematic view from Fig.5, a part of the collection layer 3 in the SEM image is cut out as a rectangular region 92, and the Feret diameter (JIS Z 8827-1) of each bright part (i.e., each aggregate particle) in the rectangular region 92 is measured. Specifically, when an aggregate particle is sandwiched between two parallel straight lines extending in a predetermined direction (e.g., left-right direction) in the rectangular region 92 so that the two straight lines circumscribe the aggregate particle, the Feret diameter is a distance between these two straight lines (i.e., the distance between the two straight lines in a direction perpendicular to the two straight lines). Then, the arithmetic mean of the Feret diameters of all the aggregate particles is obtained as the average particle diameter of the aggregate particles.

[0034] With respect to the entire surface area of ​​the collection layer 3, the arithmetic mean height Sa (hereinafter referred to as "total Sa") indicating the surface roughness of the surface is preferably greater than or equal to 0.1 μm and less than or equal to 12 μm. The total Sa is more preferably greater than or equal to 0.1 μm and less than or equal to 10 μm. In the surface of the collection layer 3, the arithmetic mean height Sa at the end portion on the outlet side where the gas flows out (hereinafter referred to as "outlet side Sa") is greater than or equal to 0.1 μm and less than or equal to 15 μm. The outlet side Sa is more preferably greater than or equal to 0.1 μm and less than or equal to 10 μm.

[0035] The average thickness across the collection layer 3 (hereinafter referred to as “total average thickness”) is preferably greater than or equal to 10 µm and less than or equal to 40 µm. The total average thickness is more preferably greater than or equal to 30 µm and less than or equal to 40 µm. The average thickness of the collection layer 3 at the above-mentioned end portion on the outlet side (hereinafter referred to as “average thickness of the outlet side”) is greater than or equal to 20 µm and less than or equal to 50 µm. The average thickness of the outlet side is more preferably greater than or equal to 35 µm and less than or equal to 50 µm. The average thickness of the outlet side is preferably greater than the total average thickness.

[0036] The arithmetic mean height Sa of the surface of the collection layer 3 and the mean thickness of the collection layer 3 are measured using a 3D shape measuring device. The porous composite 1 is cut into two planes parallel to the longitudinal direction to obtain a generally flat plate-shaped section as a sample sandwiched between the two cross sections. The two cross sections face each other, with a central axis of the porous composite 1 extending in the longitudinal direction, and at least one cross section includes the cells 23. The length of the sample in the longitudinal direction corresponds to the length of the porous composite 1 in the longitudinal direction. The width of the sample in the width direction corresponds to the diameter of the porous composite 1 (i.e., the outer diameter of the tubular outer wall 21).

[0037] Fig.6 is a view showing a main surface of the obtained sample 80 (i.e., the longitudinal section of the porous composite 1). As in Fig. 6, the cells 23 in the generally rectangular sample 80, which extend in the up-down direction in the drawing, are arranged in the left-right direction in the drawing. The up-down direction and the left-right direction in the drawing correspond to the longitudinal direction and the radial direction around the aforementioned central axis (ie, the width direction) in the porous composite 1, respectively. The lower side in the drawing corresponds to the aforementioned inlet side, and the upper side in the drawing corresponds to the aforementioned outlet side. Fig. 6 and Fig. 7, which will be described later, the hatched cells 23 are the cells 23 provided with the collecting layer 3.

[0038] As in Fig.7, nine measuring areas 811 to 813, 821 to 823 and 831 to 833 are then measured on the sample 80 in the longitudinal section of the porous composite 1 from Fig.6. Each of the measuring areas 811 to 813, 821 to 823, and 831 to 833 is a generally rectangular area having a pair of sides parallel to the longitudinal direction of the sample 80 and a pair of sides parallel to the width direction. The measuring areas 821 to 823 are arranged in this order in the up-down direction from the lower side (i.e., the inlet side) in the center of the measurement image in the width direction. The measuring areas 811 to 813 are arranged in this order in the up-down direction from the lower side on the right side of the measuring areas 821 to 823. The measuring areas 831 to 833 are arranged in this order in the up-down direction from the lower side on the left side of the measuring areas 821 to 823. The width of each of the measuring areas 811 to 813, 821 to 823 and 831 to 833 in the width direction corresponds to approximately 1 / 3 of the width of the sample 80.The length of each of the measuring areas 811 to 813, 821 to 823 and 831 to 833 in the longitudinal direction corresponds to approximately 20% of the total length of the sample 80 in the longitudinal direction (hereinafter simply referred to as “total length”).

[0039] The measuring areas 811, 821, and 831 are generally located at the same position in the longitudinal direction. The centers of the measuring areas 811, 821, and 831 in the longitudinal direction are located at a distance of approximately 20% of the total length of the sample 80 upwards from the bottom end of the sample 80. The measuring areas 812, 822, and 832 are generally located at the same position in the longitudinal direction. The centers of the measuring areas 812, 822, and 832 in the longitudinal direction are substantially in the center of the sample 80 in the longitudinal direction. The measuring areas 813, 823, and 833 are generally located at the same position in the longitudinal direction. The centers of the measuring areas 813, 823, and 833 in the longitudinal direction are located at a distance of approximately 20% of the total length of the sample 80 downwards from the top end of the sample 80.

[0040] Next, at an arbitrary point in the measurement area 821, the main surface of the sample 80 is imaged by a 3D shape measuring device (One-shot 3D measuring macroscope VR-3200, manufactured by Keyence Corporation) at a predetermined magnification (e.g., 25x magnification). Fig. Fig. 8 is a view schematically illustrating an image obtained by the 3D shape measuring device. In this image, three first cells 231 and two second cells 232 are arranged alternately in the width direction. Fig. 8, the collection layer 3 of each first cell 231 is shown hatched to facilitate understanding of the drawing. In Fig. 8, sections of the collecting layer 3 on the partition wall 22 are marked by thick lines.

[0041] Based on the Fig.8, the 3D shape measuring device calculates the arithmetic mean height Sa of the surface of the collection layer 3 in a first cell 231 in the image. Specifically, the arithmetic mean height Sa of the stripe region extending in the longitudinal direction in the center of the first cell 231 in the width direction is calculated. The calculated arithmetic mean height Sa is obtained as Sa of the collection layer 3 in the measurement region 821. The values ​​of Sa of the collection layer 3 obtained for corresponding first cells 231 in the Fig. 8 are generally the same. The values ​​of Sa of the collection layer 3 measured in the measurement area 821 by changing the imaging point in various ways using the 3D shape measuring device are generally the same. The same applies to the other measurement areas 811 to 813, 822 to 823, and 831 to 833.

[0042] After measuring the Sa of the collection layer 3 in the measuring area 821, the Sa of the collection layer 3 is measured in each of the measuring areas 822 to 823 using the same method. The Sa of the collection layer 3 is also measured in each of the measuring areas 811 to 813 using the same method. Then, the arithmetic mean of the values ​​of Sa of the collection layer 3 in the six measuring areas (i.e., measuring areas 811 to 813 and 821 to 823) is calculated, and this arithmetic mean is obtained as the aforementioned total Sa. The arithmetic mean of the values ​​of Sa of the collection layer 3 in the two measuring areas on the outlet side (i.e., measuring areas 813 and 823) is obtained as the aforementioned outlet-side Sa. When calculating the total Sa and the outlet side Sa, the values ​​of the Sa of the collection layer 3 in the measuring ranges 811 to 813 can be used instead of the values ​​of the Sa of the collection layer 3 in the measuring ranges 831 to 833.

[0043] Based on the Fig.8, the 3D shape measuring device calculates, with respect to the thickness direction (ie, the direction perpendicular to the paper surface of the drawing), the average position of the surface of the collecting layer 3 in the first cell 231 located at the center of the image in the width direction and the average positions of the surface of the partition wall 22 in the two second cells 232 adjacent to both sides of the first cell 231. Specifically, the average position of the surface of the collecting layer 3 in the stripe region extending in the longitudinal direction at the center of the first cell 231 in the width direction and the average position of the surface of the partition wall 22 in the stripe region extending in the longitudinal direction at the center of each second cell 232 in the width direction are calculated.Then, the average thickness of the collection layer 3 in the first cell 231 is calculated by subtracting the arithmetic mean of the average positions in the two second cells 232 from the average position in the first cell 231. The calculated average thickness is obtained as the average thickness of the collection layer 3 in the measurement area 821. The average thicknesses of the collection layer 3 obtained for corresponding first cells 231 in the area shown in . Fig. 8 are generally the same. The average thicknesses of the collection layer 3, measured in the measurement area 821 by changing the imaging point in various ways using the 3D shape measuring device, are generally the same. The same applies to the other measurement areas 811 to 813, 822 to 823, and 831 to 833.

[0044] After measuring the average thickness of the collection layer 3 in the measurement area 821, the average thickness of the collection layer 3 in each of the measurement areas 822 to 823 is measured using the same method. The average thickness of the collection layer 3 is also measured in each of the measurement areas 811 to 813 using the same method. Then, the arithmetic mean of the average thicknesses of the collection layer 3 in the six measurement areas (i.e., measurement areas 811 to 813 and 821 to 823) is calculated, and this arithmetic mean is obtained as the aforementioned total average thickness. The arithmetic mean of the average thicknesses of the collection layer 3 in the two measurement areas on the outlet side (i.e., measurement areas 813 and 823) is obtained as the aforementioned average thickness of the outlet side.When calculating the total mean thickness and the mean thickness of the outlet side, the mean thicknesses of the collecting layer 3 in the measuring ranges 831 to 833 can be used instead of the mean thicknesses of the collecting layer 3 in the measuring ranges 811 to 813.

[0045] In the Fig. 1 and Fig. 2, the gas flowing into the porous composite 1 flows from the inlets of the first cells 231, whose inlet sides are not closed, into the first cells 231 and flows from the first cells 231 through the collection layer 3 and the partition wall 22 into the second cells 232, whose outlet sides are not closed, as shown in Fig. 2 is indicated by the arrows A1. At this time, particles in the gas are efficiently collected in the collection layer 3.

[0046] Next, an example of the method for producing the porous composite 1 will be described with reference to Fig.9. In the manufacture of the porous composite 1, the outer surface of the tubular outer wall 21 of the base material 2 is first covered with a liquid-impermeable film member. For example, a liquid-impermeable film is wrapped around generally the entire outer surface of the tubular outer wall 21.

[0047] Then, a raw slurry for forming the collection layer 3 is prepared (step S11). The raw slurry is prepared by mixing, for example, particles as the raw material of the collection layer 3 (hereinafter referred to as "collection layer particles"), particles of a pore-forming agent, and a flocculant with water. The collection layer particles include, for example, particles of silicon carbide (SiC) or cerium oxide (CeO2). The raw slurry contains particles (hereinafter referred to as "flocculated particles") formed by flocculation of, for example, collection layer particles and particles of the pore-forming agent. In preparing the raw slurry, the type and amount of the flocculant to be added are determined, for example, so that the particle diameter of the flocculated particles becomes larger than the average pore diameter of the base material 2.This prevents or suppresses the flocculated particles from penetrating into the pores of the base material 2 in step S12 described later. The viscosity of the raw slurry is, for example, in the range of 2 mPa s to 30 mPa s.

[0048] Next, the raw slurry from the cells 23 of the base material 2 is supplied to the first cells 231 in which the collection layer 3 is to be formed, from the inlets of the first cells 231 (i.e., the end portions without the sealing parts 24) (step S12). The water in the raw slurry flows through the partition wall 22 of the base material 2 to the adjacent second cells 232 and flows out of the base material 2 from the end portions of the second cells 232 on the side where no sealing parts 24 are provided. The flocculated particles in the raw slurry do not pass through the partition wall 22 and adhere to the inner surfaces of the first cells 231 to which the raw slurry has been supplied. This forms an intermediate stage in which the flocculated particles generally uniformly adhere to the inner surfaces of the first cells 231 of the base material 2.

[0049] After completion of the supply of a predetermined amount of the raw slurry, the intermediate from which the water has coagulated is dried (step S13). The intermediate is first dried, for example, at room temperature for 12 hours and then further dried by heating at 80°C for 12 hours. Thereafter, the intermediate is fired so that the collected layer particles are bonded together into a large number of flocculated particles adhering to the base material 2 and dispersed on the surface of the base material 2, thereby forming the porous collected layer 3 (step S14). In this firing step, the particles of the pore-forming agent contained in the collected layer 3 are removed by combustion, thereby forming pores in the collected layer 3. In step S14, the firing temperature is, for example, 1200°C, and the firing time is, for example, 2 hours.

[0050] The arithmetic mean height Sa of the surface of the collection layer 3 formed in step S14 can be adjusted, for example, by changing the time required from the start of the supply of the raw slurry in step S12 to the completion of the formation of the intermediate stage (ie, completion of the water outflow from the base material 2). The completion of the formation of the intermediate stage is, for example, the time at which, when the weight of the base material 2 is continuously measured after the supply of the raw slurry, the measured weight is reduced to a predetermined weight. In the method for producing the porous composite 1, the above-mentioned arithmetic mean height Sa becomes smaller by, for example, shortening the time required from the start of the supply of the raw slurry in step S12 to the completion of the formation of the intermediate stage. The shortening of the required time is carried out, for example,by sucking the base material 2 with a suction device or the like in step S12 to promote the outflow of water in the raw slurry out of the base material 2.

[0051] Next, the relationship of the arithmetic mean height Sa (ie, the total Sa and the outlet side Sa) and the mean thickness (ie, the total mean thickness and the outlet side mean thickness) of the collection layer 3 to the pressure loss and the collection efficiency in the porous composite 1 will be described with reference to Tables 1 and 2.

[0052] [Table 1] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Base material material Cordierite Cordierite Cordierite Cordierite Cordierite Cordierite Cordierite Pore ​​diameter (µm) 12 12 12 12 12 12 12 Porosity (%) 48 48 48 48 48 48 48 collective shift material SiC SiC SiC SiC SiC CeO2 CeO2 Total Sa (µm) 5 11 6 4 5 4 6 Sa of the outlet side (µm) 7 14 8 6 7 5 9 Total mean thickness (µm) 32 30 32 36 39 31 27 Average thickness of the outlet side (µm) 46 38 33 45 47 36 39 Average pore diameter (µm) 4.8 5.4 4.7 4.0 6.1 4.1 3.2 Porosity (%) 72 77 71 71 79 72 67 Diameter of the aggregate (µm) 3 3 3 3 3 2 2 Sanunel efficiency ⊚ ⊚ ◯ ⊚ △ ⊚ ⊚ Initial pressure loss ◯ △ ◯ △ ◯ ◯ △

[0052] In Examples 1 to 7, the main material of the base material 2 is cordierite, and the average pore diameter and porosity are 12 µm and 48%, respectively. In Examples 1 to 5, the main material of the collection layer 3 is SiC, and in Examples 6 to 7, the main material of the collection layer 3 is CeO2.

[0053] In Examples 1 to 7, the total Sa of the collection layer 3 is 4 µm to 11 µm, and the Sa of the outlet side is 5 µm to 14 µm. The total average thickness of the collection layer 3 is 27 µm to 39 µm, and the average thickness of the outlet side is 33 µm to 47 µm. The average pore diameter of the collection layer 3 is 3.2 µm to 6.1 µm, and the porosity is 67% to 79%. The average particle diameter of the aggregate constituting the collection layer 3 is 2 µm to 3 µm.

[0054] As in Examples 1 to 7, in Comparative Examples 1 to 6, the main material of the base material 2 is cordierite, and the average pore diameter and porosity are 12 μm and 48%, respectively. In Comparative Examples 1 to 5, the main material of the collection layer 3 is SiC, and in Comparative Example 6, no collection layer 3 is provided. This means that the porous composite 1 of Comparative Example 6 consists only of the base material 2 made of cordierite.

[0055] In Comparative Examples 1 to 5, the total Sa of the collection layer 3 is 5 µm to 41 µm, and the Sa of the outlet side is 6 µm to 84 µm. The total average thickness of the collection layer 3 is 32 µm to 70 µm, and the average thickness of the outlet side is 45 µm to 98 µm. The average pore diameter of the collection layer 3 is 3.7 µm to 5.8 µm, and the porosity is 70% to 78%. The average particle diameter of the aggregate constituting the collection layer 3 is 3 µm.

[0056] In Comparative Examples 1 and 2, the total Sa of the collection layer 3 is greater than 12 µm, and the Sa of the outlet side is also greater than 15 µm. In Comparative Examples 2 to 5, the total average thickness of the collection layer 3 is more than 40 µm, and the average thickness of the outlet side is also more than 50 µm.

[0057] In Examples 1 to 7 and Comparative Examples 1 to 6, it is determined whether the particulate collection efficiency by the porous composite 1 is good or not and whether the suppression of initial pressure loss is good or not (that is, whether the percentage increase in the initial pressure loss is large or small). The collection efficiency is obtained as follows. First, the porous composite 1 of each of the Examples and Comparative Examples is mounted as a GPF in the exhaust system of a passenger car having a direct injection gasoline engine with a displacement of 2 liters, and a vehicle test is conducted using a chassis dynamometer. In the vehicle test, the number of emitted particulates in the exhaust gas while driving in the drive mode according to EU Regulation (RTS95) is measured using a measurement method according to PMP (Particulate Measurement Protocol for EU Regulation).Furthermore, the same vehicle test is conducted without installing the GPF in the above-mentioned exhaust system, and the number of emitted particulates in the exhaust gas is measured using the same measurement method. Using the number of emitted particulates in the case without the GPF as the "reference number of emitted particulates," a value (%) obtained by dividing the difference between the measured number of emitted particulates and the reference number of emitted particulates by the reference number of emitted particulates is determined as the "collection efficiency (%)" for each of the examples and comparative examples.

[0058] The increase in percent of the initial pressure loss is obtained as follows. While the porous composite 1 of each of the examples and comparative examples is heated to room temperature air at a flow rate of 10 Nm 3 / min, first, the pressure difference between the front and back sides of the porous composite 1 (i.e., a differential pressure between the inlet side and the outlet side of air) is measured. Then, the increase in percentage of the pressure difference in each of the examples and comparative examples to the pressure difference in Comparative Example 6 (only the base material 2) is obtained as "increase in percentage of initial pressure loss" in the porous composite 1. Specifically, the increase in percentage (%) of the initial pressure loss is obtained by (AB) / B×100, where A is the pressure difference in each of the examples and comparative examples, and B is the pressure difference in Comparative Example 6.

[0059] In Tables 1 and 2, the collection efficiency results are marked with symbols. Specifically, a result where the collection efficiency is greater than or equal to 92.5% is marked with "⊚ (double circle)", and a result where the collection efficiency is greater than or equal to 90% and less than 92.5% is marked with "◯ (circle)". A result where the collection efficiency is greater than or equal to 87.5% and less than 90% is marked with "Δ (triangle)", and a result where the collection efficiency is less than 87.5% is marked with "× (cross)".

[0060] In Tables 1 and 2, the initial pressure loss suppression results are also marked with symbols. Specifically, a result where the percentage increase in the initial pressure loss is less than 10% is marked with "◯ (circle)", and a result where the percentage increase in the initial pressure loss is greater than or equal to 10% and less than 13% is marked with "Δ (triangle)". A result where the percentage increase in the initial pressure loss is greater than or equal to 13% is marked with "× (cross)".

[0061] In Example 1, the collection efficiency is greater than or equal to 92.5% and the increase in percentage of initial pressure loss is less than 10%, both of which are advantageous. In Example 2, the collection efficiency is greater than or equal to 92.5%, which is advantageous, and the increase in percentage of initial pressure loss is greater than or equal to 10% and less than 13%, which is acceptable. One conceivable reason for the somewhat high increase in percentage of initial pressure loss in Example 2 is that the total Sa and the Sa of the outlet side of the collection layer 3 are greater than 10 µm. In Example 3, the collection efficiency is greater than or equal to 90% and less than 92.5% and the initial pressure loss is less than 10%, both of which are advantageous. One conceivable reason for the somewhat low collection efficiency in Example 3 is that the average thickness of the outlet side of the collection layer 3 is less than 35 µm.

[0062] In Example 4, the collection efficiency is greater than or equal to 92.5%, which is advantageous, and the increase in percentage of the initial pressure loss is greater than or equal to 10% and less than 13%, which is acceptable. One conceivable reason for the somewhat high increase in percentage of the initial pressure loss in Example 4 is that the average pore diameter of the collection layer 3 is less than 4.1 µm. In Example 5, the collection efficiency is greater than or equal to 87.5% and less than 90%, which is acceptable, and the increase in percentage of the initial pressure loss is less than 10%, which is advantageous. Conceivable reasons for the somewhat low collection efficiency in Example 5 are that the average pore diameter of the collection layer 3 is greater than 6 µm and that the porosity is greater than 78%. In Example 6, the collection efficiency is greater than or equal to 92.5% and the increase in percentage of the initial pressure loss is less than 10%, both of which are advantageous.In Example 7, the collection efficiency is greater than or equal to 92.5%, which is advantageous, and the percentage increase in the initial pressure loss is greater than or equal to 10% and less than 13%, which is acceptable. One possible reason for the somewhat high percentage increase in the initial pressure loss in Example 7 is that the average pore diameter of the collection layer 3 is less than 4.1 µm.

[0063] In Comparative Examples 1 to 5, however, the increase in percentage of the initial pressure loss is greater than or equal to 13%. Conceivable reasons for the excessively high increase in percentage of the initial pressure loss in Comparative Example 1 are that the total Sa is greater than 12 µm and that the Sa of the outlet side is greater than 15 µm. Conceivable reasons for the excessively high increase in percentage of the initial pressure loss in Comparative Example 2 are that the total Sa is greater than 12 µm, that the Sa of the outlet side is greater than 15 µm, that the total average thickness is greater than 40 µm, and that the average thickness of the outlet side is greater than 50 µm. Conceivable reasons for the excessively high increase in percentage of the initial pressure loss in each of Comparative Examples 3 to 5 are that the total mean thickness is larger than 40 µm and that the mean thickness of the outlet side is larger than 50 µm.Since no collection layer 3 is provided, the collection efficiency in Comparative Example 6 is only 87.5%.

[0064] As described above, the porous composite 1 includes the porous base material 2 and the porous collection layer 3 formed on the base material 2. The base material 2 has a honeycomb structure whose interior is divided by a partition wall 22 into the plurality of cells 23 extending in the longitudinal direction. The plurality of cells 23 includes the plurality of first cells 231 having one end closed in the longitudinal direction and the plurality of second cells 232 having the other end closed in the longitudinal direction, wherein the plurality of first cells 231 and the plurality of second cells 232 are alternately arranged. The collection layer 3 covers the inner surfaces of the plurality of first cells 231. The total Sa, that is, an arithmetic mean height Sa indicating a surface roughness of the surface of the collection layer 3 in the plurality of first cells 231, is equal to or greater than 0.1 μm and equal to or less than 12 μm.

[0065] This can reduce the frictional resistance between the gas flowing in the first cells 231 and the collection layer 3. This can reduce the pressure loss in the porous composite 1. The unevenness of the surface of the collection layer 3 in the circumferential direction is further reduced at each position of the first cells 231 in the longitudinal direction. This can improve the uniformity of collection of particles in the circumferential direction at each position, so that the collection efficiency of particles in the porous composite 1 can be improved. Since the surface of the collection layer 3 becomes smooth, it is possible to prevent the surface layer portion of the collection layer 3 from chipping or cracking. This can improve the durability of the porous composite 1.

[0066] Furthermore, in the porous composite 1, the total average thickness, that is, an average thickness of the collection layer 3 in the plurality of first cells 231, is greater than or equal to 10 µm and less than or equal to 40 µm. This allows an increase in pressure loss due to the thickening of the collection layer 3 and a decrease in collection efficiency due to the thinning of the collection layer 3 to be suppressed. In other words, the pressure loss in the porous composite 1 can be further reduced, and the collection efficiency can be further improved.

[0067] As described above, the Sa of the outlet side, that is, an arithmetic mean height Sa of the surface of the collection layer 3 at end portions in the plurality of first cells 231, is preferably equal to or greater than 0.1 μm and equal to or less than 15 μm, the end portions being located on one side of one end (that is, outlet side) in the longitudinal direction. Since the surface roughness on the outlet side, where the pressure is high at the initial stage of particulate collection, is reduced as mentioned above, it is possible to further reduce the pressure loss in the porous composite 1 and further improve the collection efficiency.

[0068] As described above, the average thickness of the outlet side, that is, an average thickness of the collection layer 3 at the upper end portions (that is, the end portions on the outlet side) in the plurality of first cells 231, is preferably greater than or equal to 35 µm and less than or equal to 50 µm. This can further reduce the pressure loss in the porous composite 1 and further improve the collection efficiency.

[0069] As described above, the collection layer 3 in the plurality of first cells 231 preferably has an average pore diameter of 0.1 μm or greater and 20 μm or less. This allows an increase in pressure loss due to a decrease in the average pore diameter and a decrease in collection efficiency due to an increase in the average pore diameter to be suppressed. In other words, the pressure loss in the porous composite 1 can be further reduced, and the collection efficiency can be further improved.

[0070] As described above, the collection layer 3 in the plurality of first cells 231 preferably has a porosity of greater than or equal to 50% and less than or equal to 90%. This can effectively suppress the increase in pressure loss in the porous composite 1.

[0071] As described above, the aggregate of the collection layer 3 in the plurality of first cells 231 preferably has an average particle diameter of greater than or equal to 0.1 µm and less than or equal to 5 µm. This can further reduce the pressure loss in the porous composite 1 and further improve the collection efficiency.

[0072] As described above, the collection layer 3 in the plurality of first cells 231 preferably contains at least one selected from silicon carbide, cordierite, mullite, alumina, silicon oxide, titanium oxide, zirconia, iron oxide, and cerium oxide. Since the collection layer 3 is formed using a ceramic material with relatively high thermal resistance as mentioned above, it is possible to appropriately perform the production of the porous composite 1, including the firing step.

[0073] As described above, preferably, no collecting layer 3 exists in the plurality of second cells 232. This can suppress the unnecessary increase in pressure loss in the porous composite 1.

[0074] As described above, the main material of the base material 2 is preferably cordierite. The partition wall 22 preferably has an average pore diameter of 5 µm or greater and 30 µm or less, and the partition wall 22 has a porosity of 30% or greater and 70% or less. This can correspondingly reduce the pressure loss in the porous composite 1 and improve the collection efficiency.

[0075] As described above, the porous composite 1 can reduce pressure loss and improve collection efficiency. Accordingly, the porous composite 1 is particularly suitable for use as a GPF for collecting particulates in an exhaust gas emitted from a gasoline engine.

[0076] The porous composite 1 described above can be modified in various ways.

[0077] The structure of the porous composite 1 can be modified in various ways. For example, the collection layer 3 can be provided on the inner surfaces of all cells 23.

[0078] The applications of the porous composite 1 are not limited to the aforementioned GPF, and the porous composite 1 can be used as any other filter, such as a diesel particulate filter (DPF). Alternatively, the porous composite 1 can be used in applications other than filters.

[0079] The process for producing the porous composite 1 is not limited to the Fig.9 and can be changed in various ways. For example, in step S12, the method for supplying the raw slurry to the base material 2 can be changed in various ways. The supply of the raw material of the collection layer 3 to the base material 2 is not limited to a filter system using the raw slurry and can be performed by various methods, such as immersion, spraying, or drying. The drying method and drying time of the intermediate stage in step S13 and the firing temperature and firing time of the intermediate stage in step S14 can also be changed in various ways.

[0080] The embodiments of the preferred embodiments and variations described above can be combined accordingly as long as they do not contradict each other.

[0081] Although the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and changes may be made without departing from the scope of the invention. Industrial applicability

[0082] The present invention is applicable to a filter for collecting particulates, for example, a gasoline particulate filter for collecting particulates in an exhaust gas discharged from a gasoline engine. List of reference symbols 1 Porous composite 2 Base material 3 Collective shift 21 Exterior wall 22 Partition wall 23 Cell 24 Sealing part 80 samples 91 Straight Line 92 Rectangular area 231 First Cell 232 Second Cell 812, 813, 821 to 823, 831 to 833 measuring range S11 to S14 step

Claims

[1] Porous composite comprising: a porous base material; and a porous collecting layer formed on the base material, wherein the base material has a honeycomb structure whose interior is divided by a partition wall into a plurality of cells extending in a longitudinal direction, wherein the plurality of cells includes a plurality of first cells having one end closed in the longitudinal direction and a plurality of second cells having the other end closed in the longitudinal direction, the plurality of first cells and the plurality of second cells being arranged alternately, wherein the collecting layer is formed in film form on inner surfaces of the plurality of first cells and covers these inner surfaces of the plurality of first cells, wherein a total Sa, ie an arithmetic mean height Sa indicating a surface roughness of a surface of the collecting layer in the plurality of first cells, is greater than or equal to 0.1 µm and less than or equal to 12 µm, and wherein a total average thickness, ie an average thickness of the collection layer in the plurality of first cells, is greater than or equal to 10 µm and less than or equal to 40 µm, wherein a thickness of the collection layer is the distance between the surface of the collection layer and the inner surface of the first cell in the thickness direction. [2] The porous composite according to claim 1, wherein an outlet side Sa, that is, an arithmetic mean height Sa of the surface of the collecting layer at end portions in the plurality of first cells, is equal to or greater than 0.1 µm and equal to or less than 15 µm, the end portions being located on one side of the one ends in the longitudinal direction. [3] The porous composite according to claim 2, wherein an average thickness of the outlet side, that is, an average thickness of the collecting layer at the end portions in the plurality of first cells, is greater than or equal to 35 µm and less than or equal to 50 µm. [4] The porous composite according to any one of claims 1 to 3, wherein the collection layer in the plurality of first cells has an average pore diameter of greater than or equal to 0.1 µm and less than or equal to 20 µm. [5] A porous composite according to any one of claims 1 to 4, wherein the collection layer in the plurality of first cells has a porosity of greater than or equal to 50% and less than or equal to 90%. [6] The porous composite according to any one of claims 1 to 5, wherein an aggregate of the collection layer in the plurality of first cells has an average particle diameter of greater than or equal to 0.1 µm and less than or equal to 5 µm. [7] A porous composite according to any one of claims 1 to 6, wherein the collection layer in the plurality of first cells contains at least one selected from silicon carbide, cordierite, mullite, alumina, silicon oxide, titanium oxide, zirconia, iron oxide and cerium oxide. [8] The porous composite according to any one of claims 1 to 7, wherein the collection layer does not exist in the plurality of second cells. [9] Porous composite according to any one of claims 1 to 8, wherein a main material of the partition wall is cordierite, the partition wall has an average pore diameter of greater than or equal to 5 µm and less than or equal to 30 µm and the partition wall has a porosity of greater than or equal to 30% and less than or equal to 70%. [10] A porous composite according to any one of claims 1 to 9, which is a gasoline particulate filter for collecting particulates in an exhaust gas emitted from a gasoline engine.

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