Honeycomb Filter

Abstract

To provide a honeycomb filter excellent in thermal shock resistance.SOLUTION: A honeycomb filter comprises: a columnar honeycomb base material 4 having a porous partition wall 1 disposed so as to surround a plurality of cells 2 becoming a fluid flow channel extending from an inflow end surface 11 to an outflow end surface 12; an outer peripheral coat layer 3 disposed so as to surround the outer periphery of the honeycomb base material 4; and a porous sealing part 5 disposed at one of an inflow end surface 11 side end and an outflow end surface 12 side end at the cell 2. In the outer peripheral coat layer 3,: the temperature T1 of an inflection point inflecting thermal expansion to shrinkage in the thermal expansion behavior of the outer peripheral coat layer 3 is 1,000-1,500°C; the porosity P1 of the outer peripheral coat layer 3 is 36-48%; and the thermal expansion coefficient C1 of the outer peripheral coat layer 3 at 40-800°C is 2.5-3.5×10-6 / °C.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a honeycomb filter, and more particularly to a honeycomb filter having excellent thermal shock resistance. [Background technology]

[0002] Honeycomb filters using a honeycomb structure have been known as filters for capturing particulate matter in exhaust gases emitted from internal combustion engines such as diesel engines, or as devices for purifying toxic gas components such as CO, HC, and NOx. The honeycomb structure has partition walls made of porous ceramics such as cordierite or silicon carbide, which partition multiple cells. A honeycomb filter is a honeycomb structure in which plugging portions are provided so that openings on the inlet end faces and the outlet end faces of multiple cells are alternately plugged. That is, the honeycomb filter has a structure in which inlet cells that are open on the inlet end face and plugged on the outlet end face, and outlet cells that are plugged on the inlet end face and open on the outlet end face, are alternately arranged across the partition walls. In a honeycomb filter, the porous partition walls of the honeycomb structure function as a filter for capturing particulate matter in exhaust gases. Hereinafter, particulate matter contained in exhaust gases may be referred to as "PM." "PM" stands for "particulate matter."

[0003] On the other hand, when manufacturing honeycomb structures corresponding to various industrial technical fields, a large honeycomb structure having a larger outer diameter (i.e., the diameter of the cross section perpendicular to the axial direction) than usual is sometimes required. When attempting to integrally form such a large honeycomb structure by extrusion molding, for example, the shape of the partition walls at the outer periphery may become unstable, resulting in a deterioration in the product shape and dimensional accuracy of the honeycomb structure.

[0004] Therefore, a technique has been proposed in which the outer peripheral surface of a honeycomb structure is ground with a grinding wheel or the like to adjust the outer diameter to a constant value, and then an outer peripheral coating layer (outer peripheral wall) is provided again on the outer peripheral surface of the ground honeycomb structure (hereinafter also referred to as "honeycomb substrate") (see, for example, Patent Documents 1 and 2). According to such a technique, the outer peripheral coating layer can improve the product shape and dimensional accuracy. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-166296 [Patent Document 2] Japanese Patent Publication No. 2020-45264 Summary of the Invention [Problem to be solved by the invention]

[0006] However, honeycomb filters having an outer coating layer on the outer surface of the honeycomb substrate have a problem in that the difference in thermal expansion between the honeycomb substrate and the outer coating layer is large, and the honeycomb filter may be damaged as the exhaust temperature increases.

[0007] The present invention has been made in consideration of the problems of the prior art. The inventors conducted extensive research to realize a honeycomb filter that is suppressed from breaking due to an increase in exhaust gas temperature and has excellent thermal shock resistance, and as a result, have discovered the following. The thermal expansion behavior of the peripheral coating layer has an inflection point at which the peripheral coating layer changes from expansion to contraction starting from a certain temperature. When the exhaust gas temperature exceeds the inflection point, the peripheral coating layer exhibits contraction behavior. On the other hand, the honeycomb substrate continues to exhibit expansion behavior even when the temperature exceeds the inflection point. Therefore, the difference in expansion and contraction between the honeycomb substrate and the peripheral coating layer generates high stress, resulting in damage to the honeycomb filter. According to the present invention, a honeycomb filter that is suppressed from breaking due to an increase in exhaust gas temperature and has excellent thermal shock resistance is provided. [Means for solving the problem]

[0008] According to the present invention, there is provided the following honeycomb filter.

[0009] [1] A columnar honeycomb substrate having porous partition walls arranged to surround a plurality of cells that serve as fluid flow paths extending from an inflow end face to an outflow end face; an outer periphery coating layer disposed so as to surround the outer periphery of the honeycomb substrate; a porous plugging portion disposed at either an end portion on the inflow end face side or an end portion on the outflow end face side of the cell, The outer peripheral coating layer has an inflection point temperature T1 at which the thermal expansion behavior of the outer peripheral coating layer changes from thermal expansion to contraction of 1000 to 1500°C, and The porosity P1 of the outer coating layer is 36 to 48%, and the thermal expansion coefficient C1 of the outer coating layer between 40 and 800°C is 2.5 to 3.5 × 10 -6 / ℃, honeycomb filter.

[0010] [2] The honeycomb filter according to [1] above, wherein the honeycomb substrate has a porosity P2 of 53 to 60%.

[0011] [3] The honeycomb filter according to the above [1] or [2], wherein the ratio (P1 / P2) of the porosity P1 of the outer peripheral coating layer to the porosity P2 of the honeycomb substrate is 0.6 to 0.9.

[0012] [4] The honeycomb filter according to any one of the above [1] to [3], wherein the outer peripheral coating layer has a surface roughness Ra of 10 to 25 μm.

[0013] [5] The honeycomb filter according to any one of the above [1] to [4], wherein the thickness L1 of the outer peripheral coating layer is 1 to 3 mm.

[0014] [6] The thickness L2 of the partition wall is 0.17 to 0.32 mm, and the cell density of the honeycomb substrate is 30 to 63 cells / cm 2 The honeycomb filter according to any one of the above [1] to [5], wherein:

[0015] [7] The thermal expansion coefficient C2 of the honeycomb substrate between 40 and 800 ° C is 0.2 to 1.5 × 10 -6 The honeycomb filter according to any one of the above [1] to [6], wherein the temperature is 100°C / °C.

[0016] [8] The honeycomb filter according to [7], wherein the ratio (C1 / C2) of the thermal expansion coefficient C1 of the outer peripheral coating layer to the thermal expansion coefficient C2 of the honeycomb substrate is 3 to 12. [Effects of the Invention]

[0017] The honeycomb filter of the present invention exhibits the effect of suppressing breakage due to an increase in exhaust temperature and exhibiting excellent thermal shock resistance. That is, in the honeycomb filter of the present invention, the peripheral coating layer is less likely to shrink even when the exhaust temperature increases, and the difference in expansion and contraction between the honeycomb substrate and the peripheral coating layer is small, thereby effectively suppressing the occurrence of stress at high temperatures. As a result, the honeycomb filter of the present invention has excellent thermal shock resistance.

[0018] Furthermore, since the honeycomb filter of the present invention has excellent thermal shock resistance as described above, it is possible to increase the porosity of the outer coating layer and reduce the heat capacity of the entire honeycomb filter. Therefore, when a catalyst is loaded on the honeycomb filter, the temperature rise rate of the catalyst is improved, and the purification performance is expected to be improved due to the early activation of the catalyst. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a perspective view schematically showing one embodiment of a honeycomb filter of the present invention. [Figure 2] FIG. 2 is a plan view showing the inlet end face side of the honeycomb filter shown in FIG. [Figure 3] FIG. 2 is a plan view showing the outflow end face side of the honeycomb filter shown in FIG. [Figure 4] FIG. 3 is a cross-sectional view schematically showing the AA' cross section of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] While the present invention will be described below with reference to exemplary embodiments, it should be understood that the present invention is not limited to the following exemplary embodiments. Therefore, it should be understood that modifications and improvements to the following exemplary embodiments, based on the ordinary knowledge of those skilled in the art, are also within the scope of the present invention, provided that they do not deviate from the spirit of the present invention.

[0021] (1) Honeycomb filter: One embodiment of the honeycomb filter of the present invention is a honeycomb filter 100 as shown in Figs. 1 to 4. Here, Fig. 1 is a perspective view schematically showing one embodiment of the honeycomb filter of the present invention. Fig. 2 is a plan view showing the inlet end face side of the honeycomb filter shown in Fig. 1. Fig. 3 is a plan view showing the outlet end face side of the honeycomb filter shown in Fig. 1. Fig. 4 is a cross-sectional view schematically showing the A-A' cross section of Fig. 2.

[0022] As shown in FIGS. 1 to 4, the honeycomb filter 100 includes a honeycomb substrate 4, a peripheral coating layer 3 disposed so as to surround the outer periphery of the honeycomb substrate 4, and plugging portions 5. The honeycomb substrate 4 has porous partition walls 1 disposed so as to surround a plurality of cells 2 that serve as fluid flow paths extending from an inlet end face 11 to an outlet end face 12. The honeycomb substrate 4 is a columnar structure having the inlet end face 11 and the outlet end face 12 as both end faces, in which the partition walls 1 are arranged in a lattice pattern. The peripheral coating layer 3 is a peripheral wall disposed so as to surround the outer periphery of the honeycomb substrate 4. The peripheral coating layer 3 is a porous layer obtained by applying a peripheral coating material to the outer peripheral surface of the honeycomb substrate 4, drying the applied peripheral coating material, and firing it.

[0023] The plugging portions 5 are disposed at either the end of the cell 2 on the inflow end face 11 side or the end of the cell 2 on the outflow end face 12 side, and plug the openings of the cell 2. The plugging portions 5 are porous and made of a porous material (i.e., a porous body). In the honeycomb filter 100 shown in FIGS. 1 to 4, predetermined cells 2 having plugging portions 5 disposed at the end of the inflow end face 11 side and the remaining cells 2 having plugging portions 5 disposed at the end of the outflow end face 12 side are alternately arranged with the partition wall 1 in between. Hereinafter, the cells 2 having plugging portions 5 disposed at the end of the inflow end face 11 side may be referred to as "outflow cells 2b." The cells 2 having plugging portions 5 disposed at the end of the outflow end face 12 side may be referred to as "inflow cells 2a."

[0024] The honeycomb filter 100 has a particularly important characteristic in the configuration of the peripheral coating layer 3 disposed so as to surround the outer periphery of the honeycomb substrate 4. The peripheral coating layer 3 will be described in more detail below.

[0025] The peripheral coating layer 3 has an inflection point temperature T1, where the thermal expansion behavior of the peripheral coating layer 3 changes from thermal expansion to contraction, of 1000 to 1500°C. By configuring in this manner, damage to the honeycomb filter 100 due to an increase in exhaust temperature is suppressed, and the honeycomb filter 100 has excellent thermal shock resistance. If the inflection point temperature T1 is less than 1000°C, high stress is generated due to the difference in expansion and contraction between the honeycomb substrate 4 and the peripheral coating layer 3, which may result in damage to the honeycomb filter 100. If the inflection point temperature T1 exceeds 1500°C, the expansion difference between the honeycomb substrate 4 and the peripheral coating layer 3 increases, which may result in high stress and damage to the honeycomb filter 100. Note that, although not particularly limited, the inflection point temperature T1 is preferably 1050 to 1400°C, and more preferably 1100 to 1200°C.

[0026] The thermal expansion behavior of the peripheral coating layer 3 and the inflection point temperature T1 at which thermal expansion changes to contraction can be measured by the following method. First, a differential detection type thermal dilatometer is used to measure the average thermal expansion coefficient of the peripheral coating layer 3 and the thermal expansion behavior associated with dimensional changes of the measurement sample at each temperature range at a heating rate of 10°C / min. Measurement using the thermal dilatometer is started from 40°C and continued up to 1500°C at the same heating rate. If a point (temperature) at which the thermal expansion behavior begins to decrease is identified during measurements from 40°C to 1500°C, that temperature is defined as the "inflection point temperature T1 at which thermal expansion changes to contraction." On the other hand, if a point at which the thermal expansion behavior begins to decrease is not identified during measurements from 40°C to 1500°C, the inflection point temperature T1 is defined as being above 1500°C. The thermal expansion behavior can be measured using a bulk sample prepared by solidifying the peripheral coating material used to prepare the peripheral coating layer 3. If a sample for measurement can be prepared from the outer peripheral coating layer 3, the measurement may be performed using a sample cut out from the outer peripheral coating layer 3.

[0027] In the honeycomb filter 100 of the present embodiment, the porosity P1 of the peripheral coating layer 3 is 36 to 48%, and further, the thermal expansion coefficient C1 of the peripheral coating layer 3 between 40 and 800°C is 2.5 to 3.5 × 10 -6 / °C. For example, by setting the porosity P1 of the peripheral coating layer 3 to 36 to 48%, the porosity of the peripheral coating layer 3 can be increased, and the heat capacity of the entire honeycomb filter 100 can be reduced. Therefore, when a catalyst is supported on the honeycomb filter 100, the temperature rise rate of the catalyst is improved, and improvement in purification performance due to early activation of the catalyst is expected. In addition, the thermal expansion coefficient C1 of the peripheral coating layer 3 between 40 and 800°C is 2.5 to 3.5 × 10 -6 / ° C. is preferable in terms of thermal shock resistance. In this specification, the term "thermal expansion coefficient" refers to the average thermal expansion coefficient measured using a differential detection type thermal dilatometer.

[0028] The porosity P1 of the outer peripheral coating layer 3 may be 36 to 48%, for example, preferably 37 to 48%, and more preferably 38 to 48%. The thermal expansion coefficient C1 of the outer peripheral coating layer 3 between 40 and 800°C is 2.5 to 3.5 × 10 -6 / °C, for example, 2.5 to 3.3 × 10 -6 / °C, and 2.5 to 3.0 × 10 -6 / °C is more preferable.

[0029] The porosity P1 of the outer peripheral coating layer 3 can be measured by the following method: The outer peripheral coating layer 3 is cut out, and the cross-section of the outer peripheral coating layer 3 is photographed with a scanning electron microscope (SEM), and the SEM image is binarized to calculate the porosity of the outer peripheral coating layer 3 from the area ratio.

[0030] The thermal expansion coefficient C1 of the peripheral coating layer 3 between 40 and 800°C can be measured by the following method. The thermal expansion coefficient C1 is calculated by measuring the average thermal expansion coefficient in each temperature range using a differential detection type thermal dilatometer. The heating rate is 10°C / min. When measuring the thermal expansion coefficient C1 of the peripheral coating layer 3 between 40 and 800°C, the average thermal expansion coefficient in each temperature range is measured using a bulk sample prepared by solidifying the peripheral coating material used to prepare the peripheral coating layer 3. If a sample for measurement can be prepared from the peripheral coating layer 3, the measurement may be performed using a sample prepared by cutting out from the peripheral coating layer 3.

[0031] Furthermore, although not particularly limited, the surface roughness Ra of the peripheral coating layer 3 is preferably 10 to 25 μm, and more preferably 13 to 25 μm. For example, when the honeycomb filter 100 is used as a filter for purifying exhaust gas, it may be used in a state where it is housed in a can body such as a metal case. Housed in a can body such as a metal case is sometimes called canning. When canning the honeycomb filter 100, a surface pressure is applied to the outer surface of the honeycomb filter 100 via a holding material such as a mat, and the honeycomb filter 100 is held in the can body. When the surface roughness Ra of the peripheral coating layer 3 is 10 to 25 μm, the holding ability during canning can be improved, and the isostatic strength of the honeycomb filter 100 can be improved.

[0032] The surface roughness Ra of the outer coating layer 3 is a value measured according to arithmetic mean roughness JIS B0601: 2001. The surface roughness Ra of the outer coating layer 3 can be determined by measuring the surface roughness at five arbitrarily selected locations using the above-mentioned measurement method and calculating the average value.

[0033] The thickness L1 of the peripheral coating layer 3 is not particularly limited. However, by setting the thickness L1 of the peripheral coating layer 3 to 1 to 3 mm, the thermal shock resistance and isostatic strength can be further improved. For example, if the thickness L1 of the peripheral coating layer 3 is less than 1 mm, the isostatic strength of the honeycomb filter 100 tends to be lower compared to a honeycomb filter having a thickness L1 within the above-mentioned range. Furthermore, if the thickness L1 of the peripheral coating layer 3 exceeds 3 mm, the heat capacity of the peripheral coating layer 3 increases compared to a honeycomb filter having a thickness L1 within the above-mentioned range, and when a catalyst is loaded on the honeycomb filter 100, the improvement in purification performance may not be fully achieved. The thickness L1 of the peripheral coating layer 3 is preferably, for example, 1.5 to 2.5 mm. The thickness L1 of the peripheral coating layer 3 can be measured using, for example, a scanning electron microscope or a microscope. The thickness L1 of the peripheral coating layer 3 is defined as the average value of measurements taken at the following eight measurement locations. First, the thickness of the peripheral coating layer 3 is measured at eight positions every 45° in the circumferential direction of the end face of the honeycomb substrate 4. Then, the thickness of the peripheral coating layer 3 is measured at each of the eight measurement positions. The average value of the eight measured values ​​is calculated, and the calculated average value is defined as the thickness L1 of the peripheral coating layer 3.

[0034] The peripheral coating layer 3 is composed of a peripheral coating material applied to the peripheral surface of the honeycomb substrate 4. A coating material containing cordierite particles, amorphous silica, and crystalline inorganic fibers can be suitably used as the peripheral coating material. For example, the peripheral coating material can be prepared by adding water, various organic binders, etc. to the above-mentioned raw materials. By controlling the average particle size of the cordierite particles and amorphous silica and the mixing ratio of the above-mentioned raw materials when preparing the peripheral coating material, a peripheral coating layer 3 satisfying the various properties described above can be obtained. The crystalline inorganic fibers are not particularly limited, and well-known fibers can be used. Examples of crystalline inorganic fibers include crystalline alumina silicate fibers and silicon carbide fibers. The crystalline inorganic fibers may be of a single type, or multiple types may be used in combination.

[0035] In the honeycomb filter 100, there are no particular limitations on the configuration of the honeycomb substrate 4 having the porous partition walls 1. However, the preferred embodiments of the honeycomb substrate 4 are as follows.

[0036] The porosity P2 of the honeycomb substrate 4 is preferably 53 to 60%, and more preferably 55 to 60%. The porosity P2 of the honeycomb substrate 4 is a value obtained by measuring the porosity of the partition walls 1 that constitute the honeycomb substrate 4. The porosity P2 of the honeycomb substrate 4 is a value measured by mercury intrusion porosimetry. The porosity P2 of the honeycomb substrate 4 can be measured, for example, using an Autopore 9500 (trade name) manufactured by Micromeritics. The porosity P2 of the honeycomb substrate 4 can be measured using a sample piece obtained by cutting out a portion of the partition wall 1 from the honeycomb substrate 4. The porosity P2 of the honeycomb substrate 4 is preferably a constant value throughout the entire honeycomb substrate 4.

[0037] The ratio (P1 / P2) of the porosity P1 of the outer peripheral coating layer 3 to the porosity P2 of the honeycomb substrate 4 is preferably 0.6 to 0.9, and more preferably 0.6 to 0.85. This configuration provides excellent effects in terms of canning properties and thermal shock resistance.

[0038] In the honeycomb substrate 4, the thickness L2 of the partition walls 1 is preferably 0.17 to 0.32 mm, and more preferably 0.17 to 0.29 mm. The thickness L2 of the partition walls 1 can be measured using, for example, a scanning electron microscope or a microscope. If the thickness L2 of the partition walls 1 is less than 0.17 mm, sufficient strength may not be obtained. On the other hand, if the thickness L2 of the partition walls 1 exceeds 0.32 mm, the pressure loss of the honeycomb filter 100 may increase.

[0039] The thermal expansion coefficient C2 of the honeycomb substrate 4 between 40 and 800°C is 0.2 to 1.5 × 10 -6 / °C, and is preferably 0.2 to 1.0 × 10 -6 / °C. The thermal expansion coefficient C2 of the honeycomb substrate 4 between 40 and 800°C can be measured by the following method. First, a sample piece having the following shape is cut out from the honeycomb substrate 4 as a sample for measuring the thermal expansion coefficient C2 of the honeycomb substrate 4. The sample piece has a rectangular parallelepiped shape with a length of 50 mm in the axial direction of the cells 2 of the honeycomb substrate 4 and lengths of 5 mm × 5 mm in each direction of a surface perpendicular to this axial direction. The thermal expansion coefficient C2 of the honeycomb substrate 4 between 40 and 800°C is the value obtained by measuring the thermal expansion coefficient of the sample piece in the axial direction. The thermal expansion coefficient C2 is calculated by measuring the average thermal expansion coefficient in each temperature range using a differential detection type thermal dilatometer. The measurement conditions are the same as those for measuring the thermal expansion coefficient C1 of the peripheral coating layer 3.

[0040] The ratio (C1 / C2) of the thermal expansion coefficient C1 of the outer peripheral coating layer 3 to the thermal expansion coefficient C2 of the honeycomb substrate 4 is preferably 3 to 12, and more preferably 4 to 10. This configuration provides excellent thermal shock resistance.

[0041] The shape of the cells 2 partitioned by the partition walls 1 is not particularly limited. For example, examples of the shape of the cells 2 in a cross section perpendicular to the extension direction of the cells 2 include polygons, circles, ellipses, etc. Examples of polygons include triangles, rectangles, pentagons, hexagons, and octagons. Note that the shape of the cells 2 is preferably triangles, rectangles, pentagons, hexagons, or octagons. Furthermore, with regard to the shape of the cells 2, all the cells 2 may have the same shape or different shapes. For example, although not shown in the drawings, a mixture of rectangular cells and octagonal cells may be used. Furthermore, with regard to the size of the cells 2, all the cells 2 may have the same size or different sizes. For example, although not shown in the drawings, among a plurality of cells, the size of some cells may be larger and the size of the other cells may be relatively smaller. Note that, in the present invention, a cell means a space surrounded by partition walls.

[0042] The honeycomb substrate 4 has a cell density of the cells 2 partitioned by the partition walls 1 of 30 to 63 cells / cm 2 It is preferable that the density is 31 to 62 particles / cm. 2 With this configuration, the collection performance of the honeycomb filter 100 can be maintained while suppressing an increase in pressure loss.

[0043] The shape of the honeycomb filter 100 is not particularly limited. The honeycomb filter 100 may have a cylindrical shape, such as a circular, elliptical, or polygonal shape, at the inlet end face 11 and the outlet end face 12. The honeycomb substrate 4 may be cylindrical and may further have an outer peripheral wall (not shown) on its outer peripheral side surface that surrounds the partition walls 1 arranged in a lattice pattern, or may not have such an outer peripheral wall. When the honeycomb substrate 4 has an outer peripheral wall, the outer peripheral coating layer 3 is disposed on the outside of this outer peripheral wall. On the other hand, when the honeycomb substrate 4 does not have an outer peripheral wall, the outer peripheral coating layer 3 is disposed on the outer peripheral surface of the honeycomb substrate 4 so as to surround the outermost peripheral portions of the partition walls 1 arranged in a lattice pattern.

[0044] There are no particular limitations on the size of the honeycomb filter 100, for example, the length from the inlet end face 11 to the outlet end face 12 and the size of the cross section perpendicular to the extension direction of the cells 2 of the honeycomb filter 100. When the honeycomb filter 100 is used as a filter for purifying exhaust gases, each size may be selected appropriately so as to obtain optimal purification performance.

[0045] There are no particular limitations on the material of the partition walls 1 that constitute the honeycomb substrate 4. For example, the material of the partition walls 1 preferably contains at least one selected from the group consisting of cordierite, silicon carbide, a silicon-silicon carbide composite material, a cordierite-silicon carbide composite material, silicon nitride, mullite, alumina, and aluminum titanate. In the honeycomb filter 100 of the present embodiment, a suitable example of the material of the partition walls 1 is a material containing at least one of cordierite, silicon carbide, and aluminum titanate.

[0046] There is no particular limitation on the material of the plugging portions 5. For example, the same material as the material of the partition walls 1 described above can be used.

[0047] (2) Honeycomb filter manufacturing method: The method for manufacturing the honeycomb filter of the present invention is not particularly limited, and examples thereof include the following method. First, a plastic clay for manufacturing the honeycomb substrate is prepared. The clay for manufacturing the honeycomb substrate can be prepared by adding, as raw material powder, a material selected from the above-mentioned suitable materials for the partition walls, as appropriate, additives such as a binder, a pore-forming material, and water.

[0048] The thus obtained clay is then extruded to produce a columnar honeycomb formed body having partition walls that define a plurality of cells and an outer peripheral wall that surrounds the partition walls. The obtained honeycomb formed body is then dried, for example, by microwaves and hot air.

[0049] Next, plugging portions are arranged in the openings of the cells of the dried honeycomb formed body. Specifically, for example, first, a plugging material containing raw materials for forming the plugging portions is prepared. Next, a mask is applied to the inlet end face of the honeycomb formed body so that the inlet cells are covered. Next, the previously prepared plugging material is filled into the openings of the outlet cells that are not covered with a mask on the inlet end face side of the honeycomb formed body. Thereafter, the plugging material is filled into the openings of the inlet cells on the outlet end face of the honeycomb formed body using the same method as above.

[0050] Next, the honeycomb formed body in which the plugging portions are disposed in either one of the openings of the cells is fired to produce a plugged honeycomb fired body. The firing temperature and firing atmosphere vary depending on the raw materials, and a person skilled in the art can select the optimum firing temperature and firing atmosphere for the selected materials.

[0051] Next, the peripheral wall of the obtained plugged honeycomb fired body is ground, and then a peripheral coating material is applied to the outer peripheral side of the partition wall to form a peripheral coating layer. In this manner, a honeycomb filter can be manufactured. The peripheral coating material is preferably a coating material containing cordierite particles, amorphous silica, and crystalline inorganic fibers. For example, the peripheral coating material can be prepared by adding water, various organic binders, etc. to the above-mentioned raw materials. Then, when preparing the peripheral coating material, a peripheral coating layer satisfying the characteristics described above can be obtained by controlling the average particle diameters of the cordierite particles and amorphous silica and the mixing ratio of the above-mentioned raw materials. [Example]

[0052] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0053] Example 1 To 100 parts by mass of the cordierite raw material, 2 parts by mass of a pore-forming material, 2 parts by mass of a dispersing medium, and 7 parts by mass of an organic binder were added, mixed, and kneaded to prepare a clay. Alumina, aluminum hydroxide, kaolin, talc, and silica were used as the cordierite raw materials. Water was used as the dispersing medium. Methylcellulose was used as the organic binder. Dextrin was used as the dispersing agent. A water-absorbing polymer with an average particle diameter of 18 μm was used as the pore-forming material. In this example, the average particle diameter of each raw material refers to the particle diameter (D50) at 50% of the integrated value in the particle size distribution determined by laser diffraction and scattering.

[0054] Next, the clay was extruded using a die for producing a honeycomb formed body to obtain a honeycomb formed body having a cylindrical overall shape. The shape of the cells of the honeycomb formed body was rectangular.

[0055] Next, the honeycomb formed body was dried in a microwave dryer and further completely dried in a hot air dryer, after which both end faces of the honeycomb formed body were cut and adjusted to a predetermined size.

[0056] Next, a plugging material for forming plugging portions was prepared. After that, plugging portions were formed using the plugging material at the openings of predetermined cells on the inflow end face side of the dried honeycomb formed body and at the openings of the remaining cells on the outflow end face side.

[0057] Next, the honeycomb formed body on which each plugging portion was formed was degreased and fired to prepare a plugged honeycomb fired body. Next, the outer peripheral wall of the plugged honeycomb fired body was ground to prepare a plugged honeycomb base material.

[0058] Next, a peripheral coating material was prepared by the following method. First, cordierite particles, amorphous silica, crystalline inorganic fibers, an organic binder, and water were prepared as raw materials for the coating material. These were mixed and kneaded to prepare the peripheral coating material. The cordierite particles used had an average particle diameter of 15 μm. The amorphous silica used had an average particle diameter of 300 μm. The crystalline inorganic fibers used had a fiber length of 52 μm. The compounding ratio of the cordierite particles, amorphous silica, and crystalline inorganic fibers was 25 parts by mass of amorphous silica and 20 parts by mass of crystalline inorganic fibers per 100 parts by mass of cordierite particles.

[0059] Next, the above-mentioned peripheral coating material was applied to the peripheral surface of the plugged honeycomb substrate to a predetermined thickness and dried to form a peripheral coating layer. The drying method and drying conditions are not particularly limited and may be adjusted as appropriate. In this manner, the honeycomb filter of Example 1 was manufactured.

[0060] The honeycomb filter of Example 1 was cylindrical, with circular inlet and outlet end faces. The diameters of the inlet and outlet end faces were 267 mm. The length of the honeycomb filter in the cell extension direction was 178 mm. The honeycomb filter of Example 1 had a partition wall thickness L2 of 0.25 mm, a porosity P2 of the partition walls constituting the honeycomb substrate of 53%, and a cell density of 47 cells / cm. 2The results are shown in Table 1. The porosity P2 of the partition walls was measured using Autopore 9500 (trade name) manufactured by Micromeritics.

[0061] The peripheral coating layer disposed so as to surround the peripheral surface of the honeycomb substrate had a porosity P1 of 45%, a thickness L1 of 1.0 mm, and a surface roughness Ra of 15 μm. The porosity P1 of the peripheral coating layer was determined from the area ratio of a cut-out portion of the peripheral coating layer, a cross-sectional SEM image taken with a scanning electron microscope (SEM), and a binarized image. The surface roughness Ra of the peripheral coating layer was measured based on the arithmetic mean roughness JIS B0601:2001.

[0062] The thermal expansion coefficient C1 of the outer peripheral coating layer and the thermal expansion coefficient C2 of the honeycomb substrate were measured by the following method. For the outer peripheral coating layer, the temperature T1 of the inflection point at which the thermal expansion behavior changes from thermal expansion to contraction was also measured.

[0063] [Thermal expansion coefficient C1 of the outer coating layer and the thermal expansion coefficient C2 of the honeycomb substrate] The average thermal expansion coefficient was calculated by measuring the average thermal expansion coefficient in each temperature range using a differential detection type thermal dilatometer. The heating rate was 10°C / min. To measure the thermal expansion coefficient C1 of the peripheral coating layer between 40 and 800°C, a bulk sample was prepared by solidifying the peripheral coating material used to prepare the peripheral coating layer, and the average thermal expansion coefficient was measured in each temperature range. The sample for measuring the thermal expansion coefficient C2 of the honeycomb substrate was prepared by cutting a sample piece of the following shape from the honeycomb substrate. The sample piece for measuring the thermal expansion coefficient C2 of the honeycomb substrate had a rectangular parallelepiped shape with a length of 50 mm in the axial direction of the honeycomb substrate cells and lengths of 5 mm x 5 mm in each direction of the plane perpendicular to this axial direction.

[0064] [Temperature T1 at which the outer coating layer changes from thermal expansion to contraction] Using a differential detection type thermal dilatometer, the average thermal expansion coefficient of the outer coating layer and the thermal expansion behavior associated with the dimensional change of the measurement sample were measured at a heating rate of 10°C / min within each temperature range. Measurements using the thermal dilatometer were performed starting at 40°C and continuing up to 1500°C at the above heating rate. If a point (temperature) at which the thermal expansion behavior began to decrease was identified during measurements from 40°C to 1500°C, that temperature was designated as the "inflection point temperature T1 at which the thermal expansion changes to contraction." On the other hand, if a point at which the thermal expansion behavior began to decrease was not identified during measurements from 40°C to 1500°C, the inflection point temperature T1 was designated as being above 1500°C. The samples used for the measurements were the same as those used to measure the thermal expansion coefficient C1 of the outer coating layer.

[0065] [Table 1]

[0066] [Table 2]

[0067] The honeycomb filter of Example 1 was evaluated for "thermal shock resistance," "purifying performance," and "isostatic strength" by the following methods. Table 2 shows the results.

[0068] [Thermal shock resistance] First, the "ESP failure temperature" of the honeycomb filters manufactured in each of the Examples and Comparative Examples was measured by the following method. The "ESP failure temperature" is an index indicating thermal shock resistance. ESP stands for Electric Furnace Spalling. Specifically, a honeycomb filter was placed in an electric furnace heated to a certain temperature, and after a certain time, it was removed and checked for damage to the peripheral coating layer. This operation was repeated while increasing the temperature in the electric furnace in 25°C increments until damage occurred in the peripheral coating layer, and the temperature at which damage occurred in the peripheral coating layer was measured. The thermal shock resistance was evaluated based on the temperature at which damage occurred in the peripheral coating layer of the honeycomb filters of each of the Examples and Comparative Examples (hereinafter referred to as the "failure temperature"), using the following evaluation criteria. The "Celsius temperature" was used as the failure temperature. Evaluation "Excellent": When the failure temperature of the honeycomb filter of Comparative Example 1 is taken as 100%, if the failure temperature of the honeycomb filter to be evaluated exceeds 110%, the evaluation is "Excellent". Evaluation "Good": When the failure temperature of the honeycomb filter of Comparative Example 1 is taken as 100%, if the failure temperature of the evaluated honeycomb filter is more than 105% and not more than 110%, the evaluation is "Good". Evaluation "passable": When the failure temperature of the honeycomb filter of Comparative Example 1 is taken as 100%, if the failure temperature of the honeycomb filter to be evaluated is more than 100% and 105% or less, the evaluation is "passable". Evaluation "Fail": When the failure temperature of the honeycomb filter of Comparative Example 1 is taken as 100%, if the failure temperature of the honeycomb filter to be evaluated is 100% or less, the evaluation is "Fail".

[0069] [Purification performance] First, a test gas containing NOx was passed through the honeycomb filter. The amount of NOx in the gas discharged from the honeycomb filter was then analyzed using a gas analyzer. The temperature of the test gas flowing into the honeycomb filter was set to 200°C. The temperature of the honeycomb filter and the test gas was adjusted using a heater. An infrared imaging furnace was used as the heater. The test gas used was a mixture of nitrogen with 5% by volume of carbon dioxide, 14% by volume of oxygen, 350 ppm (volume basis) of nitric oxide, 350 ppm (volume basis) of ammonia, and 10% by volume of water. Regarding this test gas, a mixed gas containing water and other gases was prepared separately, and these were mixed in the piping when the test was performed. The gas analyzer used was a "MEXA9100EGR (trade name)" manufactured by HORIBA. The space velocity when the test gas flowed into the honeycomb filter was 100,000 (hr). -1 The NOx purification rate of the honeycomb filter was measured from the amount of NOx in the test gas and the amount of NOx in the gas discharged from the honeycomb filter. The purification performance was evaluated based on the NOx purification rate of the honeycomb filters of each example and comparative example, according to the following evaluation criteria. Evaluation "Excellent": When the NOx purification rate of the honeycomb filter of Comparative Example 1 is taken as 100%, if the NOx purification rate of the honeycomb filter to be evaluated exceeds 120%, the evaluation is "Excellent". Evaluation "Good": When the NOx purification rate of the honeycomb filter of Comparative Example 1 is taken as 100%, if the NOx purification rate of the honeycomb filter to be evaluated is more than 110% and 120% or less, the evaluation is "Good". Evaluation "Fair": When the NOx purification rate of the honeycomb filter of Comparative Example 1 is taken as 100%, if the NOx purification rate of the honeycomb filter to be evaluated is more than 100% and 110% or less, the evaluation is "Fair". Evaluation "Fail": When the NOx purification rate of the honeycomb filter of Comparative Example 1 is taken as 100%, if the NOx purification rate of the honeycomb filter to be evaluated is 100% or less, the evaluation is "Fail".

[0070] Isostatic strength The isostatic strength was measured based on the isostatic fracture strength test specified in M505-87 of the automobile standard (JASO standard) issued by the Society of Automotive Engineers of Japan. The isostatic fracture strength test is a test in which a honeycomb filter is placed in a cylindrical rubber container, covered with an aluminum plate, and isostatically compressed in water. The isostatic strength measured by the isostatic fracture strength test is indicated by the pressurized pressure value (MPa) at which the honeycomb filter breaks. The isostatic strength of the honeycomb filters of each example and comparative example was evaluated according to the following evaluation criteria. Evaluation "Excellent": When the isostatic strength of the honeycomb filter of Comparative Example 1 is taken as 100%, if the isostatic strength of the honeycomb filter to be evaluated exceeds 110%, the evaluation is "Excellent". Evaluation "Good": When the isostatic strength of the honeycomb filter of Comparative Example 1 is taken as 100%, if the isostatic strength of the honeycomb filter to be evaluated is more than 105% and 110% or less, the evaluation is "Good". Evaluation "passable": When the isostatic strength of the honeycomb filter of Comparative Example 1 is taken as 100%, if the isostatic strength of the honeycomb filter to be evaluated is more than 100% and 105% or less, the evaluation is "passable". Evaluation "Fail": When the isostatic strength of the honeycomb filter of Comparative Example 1 is taken as 100%, if the isostatic strength of the honeycomb filter to be evaluated is 100% or less, the evaluation is "Fail".

[0071] Examples 2 to 7 Except for changing the configuration of the honeycomb filter as shown in Table 1, honeycomb filters were produced in the same manner as the honeycomb filter of Example 1. In Examples 2 to 7, the average particle diameter and mixing ratio of the raw materials used in preparing the outer coating material were changed. (Comparative Examples 1 to 5) Honeycomb filters were produced in the same manner as the honeycomb filter of Example 1, except that the configuration of the honeycomb filter was changed as shown in Table 1. In Comparative Examples 1, and 3 to 5, peripheral coating materials were prepared as follows. The cordierite particles used in the peripheral coating material of Example 1 were changed to a mixture containing cordierite particles having an average particle diameter of 15 μm and cordierite particles having an average particle diameter of 35 μm, and peripheral coating materials were prepared. Regarding the amount of cordierite particles used in preparing this peripheral coating material, when the amount of cordierite particles used in the peripheral coating material of Example 1 was taken as 100 mass%, the cordierite particles having an average particle diameter of 15 μm were 50 mass% and the cordierite particles having an average particle diameter of 35 μm were 75 mass%.

[0072] The honeycomb filters of Examples 2 to 7 and Comparative Examples 1 to 5 were also evaluated for "thermal shock resistance," "purifying performance," and "isostatic strength" in the same manner as in Example 1. Table 2 shows the results.

[0073] (result) It was confirmed that the honeycomb filters of Examples 1 to 7 exceeded the performance of the honeycomb filter of Comparative Example 1, which served as the benchmark, in the evaluations of thermal shock resistance, purification performance, and isostatic strength.

[0074] The honeycomb filter of Comparative Example 2 had a porosity P1 of the peripheral coating layer of 32%, and the evaluation result of the thermal shock resistance was "fail." The honeycomb filters of Comparative Examples 3 and 5 had an inflection point temperature T1 of 850°C and a thermal expansion coefficient C1 of the peripheral coating layer of 1.0 × 10 -6 / ° C., and the evaluation result of thermal shock resistance was "unacceptable." The honeycomb filter of Comparative Example 4 had a porosity P1 of the peripheral coating layer of 35%, and the evaluation result of isostatic strength was "unacceptable." [Industrial Applicability]

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

[0076] 1: partition wall, 2: cell, 2a: inlet cell, 2b: outlet cell, 3: outer peripheral coating layer, 4: honeycomb substrate, 5: plugging portion, 11: inlet end face, 12: outlet end face, 100: honeycomb filter.

Claims

1. a columnar honeycomb substrate having porous partition walls arranged to surround a plurality of cells that serve as fluid flow paths extending from an inflow end face to an outflow end face; an outer periphery coating layer disposed so as to surround the outer periphery of the honeycomb substrate; a porous plugging portion disposed at either an end portion on the inflow end face side or an end portion on the outflow end face side of the cell, The peripheral coating layer is formed by applying a peripheral coating material containing cordierite, amorphous silica, and crystalline inorganic fibers to the peripheral side of the honeycomb substrate, and the temperature T1 of the inflection point at which the thermal expansion behavior of the peripheral coating layer changes from expansion to contraction is 1000 to 1500°C, and The porosity P1 of the outer peripheral coating layer is 36 to 48%, and the thermal expansion coefficient C1 of the outer peripheral coating layer between 40 and 800°C is 2.5 to 3.5 × 10 －６ / °C, and the ratio (C1 / C2) of the thermal expansion coefficient C1 of the outer peripheral coating layer to the thermal expansion coefficient C2 of the honeycomb substrate is 3 to 12.

2. 2. The honeycomb filter according to claim 1, wherein the porosity P2 of the honeycomb substrate is 53 to 60%.

3. 3. The honeycomb filter according to claim 1, wherein a ratio (P1 / P2) of a porosity P1 of said outer peripheral coating layer to a porosity P2 of said honeycomb substrate is 0.6 to 0.

9.

4. The honeycomb filter according to any one of claims 1 to 3, wherein the outer peripheral coating layer has a surface roughness Ra of 10 to 25 µm.

5. The honeycomb filter according to any one of claims 1 to 4, wherein the thickness L1 of the outer peripheral coating layer is 1 to 3 mm.

6. The thickness L2 of the partition wall is 0.17 to 0.32 mm, and the cell density of the honeycomb substrate is 30 to 63 cells / cm ２ The honeycomb filter according to any one of claims 1 to 5,

7. The thermal expansion coefficient C2 of the honeycomb substrate between 40 and 800°C is 0.2 to 1.5 × 10 －６ The honeycomb filter according to any one of claims 1 to 6, wherein the temperature is 100°C. / °C.

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