Cellular filter

Abstract

The present application provides a honeycomb filter having excellent thermal shock resistance. The honeycomb filter is provided with: a columnar honeycomb substrate (4) having porous partition walls (1) arranged to surround a plurality of cells (2) forming fluid flow paths extending from an inflow end face (11) to an outflow end face (12); an outer peripheral coating layer (3) provided around the outer periphery of the honeycomb substrate (4); and a porous plugged portion (5) provided at either an end portion on the inflow end face (11) side or an end portion on the outflow end face (12) side of the cells (2), the outer peripheral coating layer (3) being configured such that: the temperature T1 of the inflection point at which thermal expansion is converted to shrinkage in the thermal expansion behavior of the outer peripheral coating layer (3) is 1000 to 1500°C, and the porosity P1 of the outer peripheral coating layer (3) is 36 to 48%, and the thermal expansion coefficient C1 of the outer peripheral coating layer (3) between 40 and 800°C is 2.5 to 3.5 x 10 －6 / °C. －6 / °C.

Description

Technical Field

[0001] This invention relates to honeycomb filters. More specifically, it relates to honeycomb filters with excellent thermal shock resistance. Background Technology

[0002] Previously, honeycomb filters employing a honeycomb structure were known as filters for capturing particulate matter in exhaust gases from internal combustion engines such as diesel engines, and devices for purifying toxic gas components such as CO, HC, and NOx. The honeycomb structure has partitions made of porous ceramics such as cordierite and silicon carbide, which divide the space into multiple compartments. The honeycomb filter is configured such that, for the aforementioned honeycomb structure, sealing portions are arranged such that the openings on the inflow end face and the openings on the outflow end face of the multiple compartments are alternately sealed. That is, the honeycomb filter structure consists of inflow compartments with an open inflow end face and a sealed outflow end face, and outflow compartments with a sealed inflow end face and an open outflow end face, sandwiched between partitions, arranged alternately. Furthermore, in the honeycomb filter, the porous partitions of the honeycomb structure perform a filtering function by capturing particulate matter in the exhaust gas. Hereinafter, particulate matter contained in the exhaust gas is sometimes referred to as "PM". "PM" is short for "particulate matter".

[0003] On the other hand, in manufacturing honeycomb structures for various industrial and technological fields, it is sometimes necessary to have large honeycomb structures with a larger outer diameter than usual (i.e., the diameter of the cross section orthogonal to the axial direction). When it is desired to integrally form such a large honeycomb structure by extrusion molding, for example, the shape of the partitions on the outer periphery is sometimes unstable, resulting in reduced product shape and dimensional accuracy of the honeycomb structure.

[0004] Therefore, the following technology has been proposed: grinding the outer peripheral surface of a honeycomb structure with a grinding stone or the like, adjusting its outer diameter to a certain value, and then applying an outer peripheral coating (outer peripheral wall) to 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 this technology, the shape and dimensional accuracy of the product can be improved by the outer peripheral coating.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2015-166296

[0008] Patent Document 2: Japanese Patent Application Publication No. 2020-45264 Summary of the Invention

[0009] However, honeycomb filters with an outer peripheral coating on the outer periphery of the honeycomb substrate have the following problem: the thermal expansion difference between the honeycomb substrate and the outer peripheral coating is large, and the honeycomb filter sometimes breaks as the exhaust temperature rises.

[0010] This invention was implemented in view of the problems existing in the prior art described above. The inventors of this invention conducted in-depth research to achieve a honeycomb filter that suppresses damage associated with rising exhaust temperatures and exhibits excellent thermal shock resistance, resulting in the following insights. In the thermal expansion behavior of the outer coating, there is an inflection point at a certain temperature where expansion transitions to contraction. When the exhaust temperature exceeds this inflection point, the outer coating exhibits contraction behavior. On the other hand, the honeycomb substrate continues to exhibit expansion behavior even when the temperature exceeds the inflection point. Therefore, due to the difference in expansion and contraction between the honeycomb substrate and the outer coating, high stress is generated, leading to damage to the honeycomb filter. According to this invention, a honeycomb filter that suppresses damage associated with rising exhaust temperatures and exhibits excellent thermal shock resistance, as described above, is provided.

[0011] According to the present invention, a cellular filter is provided as follows.

[0012] [1] A honeycomb filter, characterized in that it comprises:

[0013] A columnar honeycomb substrate having porous partitions configured to surround multiple compartments forming a fluid flow path extending from an inflow end face to an outflow end face;

[0014] A peripheral coating, the peripheral coating being disposed around the periphery of the honeycomb substrate; and

[0015] A porous sealing portion, which is disposed at either the end of the compartment on the inflow end face or the end on the outflow end face.

[0016] The peripheral coating is configured such that the temperature T1 at which the thermal expansion behavior of the peripheral coating transitions from expansion to contraction is 1000–1500°C, and the porosity P1 of the peripheral coating is 36–48%, and the coefficient of thermal expansion C1 of the peripheral coating between 40 and 800°C is 2.5 × 10⁻⁶. －6 / ℃~3.5×10 －6 / ℃.

[0017] [2] The honeycomb filter according to [1] above is characterized in that the porosity P2 of the honeycomb substrate is 53-60%.

[0018] [3] According to the honeycomb filter described in [1] or [2] above, the ratio (P1 / P2) of the porosity P1 of the outer peripheral coating to the porosity P2 of the honeycomb substrate is 0.6 to 0.9.

[0019] [4] The honeycomb filter according to any one of [1] to [3] above is characterized in that the surface roughness Ra of the outer peripheral coating is 10 to 25 μm.

[0020] [5] The honeycomb filter according to any one of [1] to [4] above is characterized in that the thickness L1 of the outer peripheral coating is 1 to 3 mm.

[0021] [6] The honeycomb filter according to any one of [1] to [5] above, characterized in that 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 / cm². 2 .

[0022] [7] The honeycomb filter according to any one of [1] to [6] above, characterized in that the coefficient of thermal expansion C2 of the honeycomb substrate between 40 and 800°C is 0.2 × 10⁻⁶. －6 / ℃~1.5×10 －6 / ℃.

[0023] [8] According to the honeycomb filter described in [7] above, the ratio (C1 / C2) of the thermal expansion coefficient C1 of the outer peripheral coating to the thermal expansion coefficient C2 of the honeycomb substrate is 3 to 12.

[0024] Invention Effects

[0025] The honeycomb filter of the present invention exhibits the following effects: damage associated with rising exhaust temperature is suppressed, and it demonstrates excellent thermal shock resistance. Specifically, even with rising exhaust temperature, the outer coating of the honeycomb filter is unlikely to shrink, and the difference in expansion and contraction between the honeycomb substrate and the outer coating is small, effectively suppressing stress generated at high temperatures. Therefore, the honeycomb filter of the present invention exhibits excellent thermal shock resistance.

[0026] Furthermore, as described above, the honeycomb filter of the present invention exhibits excellent thermal shock resistance, thus enabling an increase in the porosity of the outer coating and consequently reducing the overall heat capacity of the honeycomb filter. Therefore, when a catalyst is supported in the honeycomb filter, the catalyst's heating rate is increased, and it is expected that the catalyst will be activated earlier, thereby improving purification performance. Attached Figure Description

[0027] Figure 1 This is a perspective view schematically illustrating one embodiment of the honeycomb filter of the present invention.

[0028] Figure 2 It means Figure 1 The diagram shows a plan view of the inflow end face of the cellular filter.

[0029] Figure 3 It means Figure 1 The diagram shows a plan view of the outflow end face of the cellular filter.

[0030] Figure 4 It is a schematic representation Figure 2 A cross-sectional view of section A-A'.

[0031] Symbol Explanation

[0032] 1: partition wall, 2: compartment, 2a: inflow compartment, 2b: outflow compartment, 3: outer peripheral coating, 4: honeycomb substrate, 5: sealing part, 11: inflow end face, 12: outflow end face, 100: honeycomb filter. Detailed Implementation

[0033] The embodiments of the present invention will be described below; however, the present invention is not limited to the following embodiments. Therefore, it should be understood that, without departing from the spirit of the present invention, appropriate modifications and improvements to the following embodiments based on the common knowledge of those skilled in the art also fall within the scope of the present invention.

[0034] (1) Honeycomb filter:

[0035] One embodiment of the cellular filter of the present invention is Figures 1-4 The shown is a cellular filter 100. Here, Figure 1 This is a perspective view schematically illustrating one embodiment of the honeycomb filter of the present invention. Figure 2 It means Figure 1 The diagram shows a plan view of the inflow end face of the cellular filter. Figure 3 It means Figure 1 The diagram shows a plan view of the outflow end face of the cellular filter. Figure 4 It is a schematic representation Figure 2 A cross-sectional view of section A-A'.

[0036] like Figures 1-4 As shown, the honeycomb filter 100 includes: a honeycomb substrate 4, a peripheral coating 3 disposed around the outer periphery of the honeycomb substrate 4, and a sealing portion 5. The honeycomb substrate 4 has porous partitions 1, which are configured to surround a plurality of compartments 2, which form a fluid flow path extending from an inflow end face 11 to an outflow end face 12. The honeycomb substrate 4 is a columnar structure in which the aforementioned partitions 1 are arranged in a grid pattern with the inflow end face 11 and the outflow end face 12 as two end faces. The peripheral coating 3 is a peripheral wall disposed around the outer periphery of the honeycomb substrate 4. The peripheral coating 3 is a porous layer obtained by coating the outer peripheral surface of the honeycomb substrate 4 with a peripheral coating material and drying and firing the coated peripheral coating material.

[0037] The sealing part 5 is disposed at either the end of the inflow end face 11 or the end of the outflow end face 12 of the compartment 2, and seals the opening of the compartment 2. The sealing part 5 is a porous component (i.e., a porous body) made of porous material. Figures 1-4 In the shown honeycomb filter 100, a predetermined compartment 2 with a sealing portion 5 at the end on the inflow end face 11 side and a remaining compartment 2 with a sealing portion 5 at the end on the outflow end face 12 side are alternately arranged, sandwiching a partition wall 1. Hereinafter, the compartment 2 with the sealing portion 5 at the end on the inflow end face 11 side is sometimes referred to as "outflow compartment 2b". The compartment 2 with the sealing portion 5 at the end on the outflow end face 12 side is sometimes referred to as "inflow compartment 2a".

[0038] The honeycomb filter 100 has particularly important characteristics in the configuration of the peripheral coating 3 arranged around the outer periphery of the honeycomb substrate 4. The peripheral coating 3 will be described in more detail below.

[0039] The outer peripheral coating 3 is configured such that the temperature T1 at which the thermal expansion behavior of the outer peripheral coating 3 transitions from thermal expansion to contraction is 1000–1500°C. This configuration suppresses damage to the honeycomb filter 100 caused by rising exhaust temperatures, resulting in excellent thermal shock resistance. If the aforementioned inflection point temperature T1 is less than 1000°C, higher stress may occur due to the difference in expansion and contraction between the honeycomb substrate 4 and the outer peripheral coating 3, leading to damage to the honeycomb filter 100. Conversely, if the aforementioned inflection point temperature T1 exceeds 1500°C, higher stress may occur due to the increased difference in expansion between the honeycomb substrate 4 and the outer peripheral coating 3, also leading to damage to the honeycomb filter 100. It should be noted that, although not particularly limited, the aforementioned inflection point temperature T1 is preferably 1050–1400°C, more preferably 1100–1200°C.

[0040] The thermal expansion behavior of the outer peripheral coating 3 and the inflection point T1 from thermal expansion to contraction can be determined by the following method. First, using a differential detection type dilatometer, the heating rate is set to 10°C / min, and the average coefficient of thermal expansion of the outer peripheral coating 3 and the thermal expansion behavior associated with the dimensional changes of the test specimen are measured in each temperature range. The measurement using the dilatometer starts at 40°C and continues until 1500°C is reached at the above heating rate. If the point (temperature) where the thermal expansion behavior begins to decrease is confirmed in the measurement from 40°C to 1500°C, this temperature is set as "the temperature T1 of the inflection point from thermal expansion to contraction". On the other hand, if the point where the thermal expansion behavior begins to decrease cannot be confirmed in the measurement from 40°C to 1500°C, the temperature T1 of the inflection point is set to be higher than 1500°C. Regarding the determination of thermal expansion behavior, the outer peripheral coating material used to make the outer peripheral coating 3 can be solidified to prepare a bulk test specimen, and the thermal expansion behavior can be measured using this bulk test specimen. Alternatively, if a test specimen can be prepared from the outer peripheral coating 3, a specimen cut from the outer peripheral coating 3 can be used for testing.

[0041] Furthermore, in the honeycomb filter 100 of this embodiment, the porosity P1 of the outer peripheral coating 3 is 36-48%, and the coefficient of thermal expansion C1 of the outer peripheral coating 3 between 40 and 800°C is 2.5 × 10⁻⁶. －6 / ℃~3.5×10 －6 / ℃. For example, by having a porosity P1 of 36–48% for the outer peripheral coating 3, the porosity of the outer peripheral coating 3 can be increased, thereby reducing the heat capacity of the entire honeycomb filter 100. Therefore, when the honeycomb filter 100 carries a catalyst, the catalyst's heating rate increases, and it is expected that the catalyst will be activated earlier, thus improving the purification performance. Furthermore, if the coefficient of thermal expansion C1 of the outer peripheral coating 3 between 40 and 800℃ is 2.5 × 10⁻⁶, ... －6 / ℃~3.5×10 －6 / ℃ indicates that the thermal shock resistance is relatively ideal. In this specification, "coefficient of thermal expansion" refers to the average coefficient of thermal expansion measured using a differential thermal expansion meter.

[0042] The porosity P1 of the outer peripheral coating 3 can be 36-48%, preferably 37-48%, and more preferably 38-48%. Furthermore, the coefficient of thermal expansion C1 of the outer peripheral coating 3 between 40 and 800°C is 2.5 × 10⁻⁶. －6 / ℃~3.5×10 －6 / ℃ is sufficient, for example, preferably 2.5×10 －6 / ℃~3.3×10 －6 / ℃, more preferably 2.5×10 －6 / ℃~3.0×10 －6 / ℃.

[0043] The porosity P1 of the outer coating 3 can be determined using the following method: The outer coating 3 can be cut out and photographed using a scanning electron microscope (SEM). The SEM image of the photographed cross-section is binarized, and the porosity of the outer coating 3 is calculated based on the obtained area.

[0044] The coefficient of thermal expansion C1 of the outer peripheral coating 3 between 40 and 800°C can be determined using the following method. A differential thermal expansion meter is used to measure the average coefficient of thermal expansion in each temperature range, and the coefficient of thermal expansion C1 is calculated from this measurement. It should be noted that the heating rate is set to 10°C / minute. In determining the coefficient of thermal expansion C1 of the outer peripheral coating 3 between 40 and 800°C, the outer peripheral coating material used to make the outer peripheral coating 3 is solidified to prepare a bulk sample. Using this bulk sample, the average coefficient of thermal expansion in each temperature range is measured. Alternatively, if a test sample can be prepared from the outer peripheral coating 3, a sample cut from the outer peripheral coating 3 can be used for the measurement.

[0045] Furthermore, although not specifically limited, the surface roughness Ra of the outer peripheral coating 3 is preferably 10 to 25 μm, more preferably 13 to 25 μm. For example, when the honeycomb filter 100 is used as a filter for exhaust gas purification, it is sometimes used in a can housed in a metal casing or similar container. Sometimes, housing the honeycomb filter 100 in a metal casing or similar container is referred to as canning. When canning the honeycomb filter 100, surface pressure is applied to the outer peripheral surface of the honeycomb filter 100 through a holding material such as a gasket, holding it within the container. If the surface roughness Ra of the outer peripheral coating 3 is 10 to 25 μm, the holding ability of the canning can be improved, thereby increasing the isostatic pressure strength of the honeycomb filter 100.

[0046] The surface roughness Ra of the outer peripheral coating 3 is the value obtained by measuring the arithmetic mean roughness JIS B0601:2001. The surface roughness of any 5 randomly selected locations can be measured using the above method, and the average value can be calculated to obtain the surface roughness Ra of the outer peripheral coating 3.

[0047] There is no particular limitation on the thickness L1 of the outer peripheral coating 3. However, by making the thickness L1 of the outer peripheral coating 3 1 to 3 mm, it is possible to further improve the thermal shock resistance and isostatic compressive strength. For example, if the thickness L1 of the outer peripheral coating 3 is less than 1 mm, compared with the case where the thickness L1 is within the above range, there is a tendency for the isostatic compressive strength of the honeycomb filter 100 to decrease. In addition, if the thickness L1 of the outer peripheral coating 3 exceeds 3 mm, compared with the case where the thickness L1 is within the above range, the heat capacity of the outer peripheral coating 3 increases, and when the honeycomb filter 100 carries a catalyst, the improvement effect on purification performance may not be fully realized. The thickness L1 of the outer peripheral coating 3 is preferably, for example, 1.5 to 2.5 mm. For example, the thickness L1 of the outer peripheral coating 3 can be measured using a scanning electron microscope or a microscope. It should be noted that the thickness L1 of the outer peripheral coating 3 is set as the average value of the measured values ​​obtained from the following 8 measurement sites. First, regarding the measurement points for measuring the thickness of the outer peripheral coating 3, eight locations at 45° intervals along the circumference of the end face of the honeycomb substrate 4 will be designated as measurement points. Then, the thickness of the outer peripheral coating 3 will be measured at each of the eight measurement points. The average value of the eight measured values ​​will be calculated, and this average value will be set as the thickness L1 of the outer peripheral coating 3.

[0048] The peripheral coating 3 is composed of a peripheral coating material applied to the outer peripheral surface of the honeycomb substrate 4. The peripheral coating material is preferably a coating material containing cordierite particles, amorphous silica, and crystalline inorganic fibers. For example, water and various organic binders can be added to the above-mentioned raw materials to prepare the peripheral coating material. Furthermore, by controlling the average particle size of the cordierite particles and amorphous silica, and the mixing ratio of the above-mentioned raw materials, the peripheral coating 3 that satisfies the characteristics described above can be obtained during the preparation of the peripheral coating material. It should be noted that there is no particular limitation on the crystalline inorganic fibers used; well-known crystalline inorganic fibers can be used. Examples of crystalline inorganic fibers include crystalline aluminosilicate fibers and silicon carbide fibers. One type of crystalline inorganic fiber can be used, or multiple types can be used in combination.

[0049] In the honeycomb filter 100, there are no particular limitations on the composition of the honeycomb substrate 4 having porous septa 1. However, the preferred embodiment of the honeycomb substrate 4 is as follows.

[0050] The porosity P2 of the honeycomb substrate 4 is preferably 53-60%, more preferably 55-60%. The porosity P2 of the honeycomb substrate 4 is a value obtained by measuring the porosity of the partitions 1 constituting the honeycomb substrate 4. The porosity P2 of the honeycomb substrate 4 is a value obtained by mercury intrusion porosimetry. For example, the Autopore 9500 (trade name) manufactured by Micromeritics can be used to measure the porosity P2 of the honeycomb substrate 4. The measurement of the porosity P2 of the honeycomb substrate 4 can be performed by cutting a portion of the partition 1 from the honeycomb substrate 4 to form a sample piece, and then using this sample piece to measure the porosity P2. It should be noted that the porosity P2 of the honeycomb substrate 4 is preferably a constant value throughout the entire area of ​​the honeycomb substrate 4.

[0051] The ratio (P1 / P2) of the porosity P1 of the outer peripheral coating 3 to the porosity P2 of the honeycomb substrate 4 is preferably 0.6 to 0.9, more preferably 0.6 to 0.85. With this configuration, excellent performance is achieved in terms of canning properties and thermal shock resistance.

[0052] In the honeycomb substrate 4, the thickness L2 of the partition 1 is preferably 0.17 to 0.32 mm, more preferably 0.17 to 0.29 mm. For example, the thickness L2 of the partition 1 can be measured using a scanning electron microscope or a microscope. If the thickness L2 of the partition 1 is less than 0.17 mm, sufficient strength may not be obtained. On the other hand, if the thickness L2 of the partition 1 exceeds 0.32 mm, the pressure loss of the honeycomb filter 100 may increase.

[0053] The coefficient of thermal expansion C2 of the honeycomb substrate 4 between 40 and 800°C is preferably 0.2 × 10⁻⁶. －6 / ℃~1.5×10 －6 / ℃, more preferably 0.2×10 －6 / ℃~1.0×10 －6 / ℃. The coefficient of thermal expansion C2 of the honeycomb substrate 4 between 40 and 800℃ can be determined using the following method. First, as a sample for determining the coefficient of thermal expansion C2 of the honeycomb substrate 4, a sample piece of the following shape is cut from the honeycomb substrate 4. The sample piece is a cuboid with a length of 50 mm in the axial direction extending from the compartment 2 of the honeycomb substrate 4 and a length of 5 mm × 5 mm in each direction of the plane orthogonal to this axial direction. The coefficient of thermal expansion C2 of the honeycomb substrate 4 between 40 and 800℃ is defined as the value obtained by measuring the coefficient of thermal expansion in the aforementioned axial direction of the sample piece thus prepared. The coefficient of thermal expansion C2 is calculated as follows: the average coefficient of thermal expansion in each temperature range is measured using a differential detection type dilatometer, and the coefficient of thermal expansion C2 is calculated therefrom. The measurement conditions are the same as those when measuring the coefficient of thermal expansion C1 of the outer peripheral coating 3.

[0054] The ratio (C1 / C2) of the coefficient of thermal expansion of the outer peripheral coating 3 to the coefficient of thermal expansion of the honeycomb substrate 4 is preferably 3 to 12, more preferably 4 to 10. With this configuration, excellent thermal shock resistance is achieved.

[0055] The shape of the compartment 2 formed by the partition wall 1 is not particularly limited. For example, the shape of the compartment 2 in a cross section orthogonal to the direction in which the compartment 2 extends can be: polygonal, circular, elliptical, etc. As a polygon, examples include: triangle, quadrilateral, pentagonal, hexagonal, octagonal, etc. It should be noted that the shape of the compartment 2 is preferably triangular, quadrilateral, pentagonal, hexagonal, or octagonal. In addition, regarding the shape of the compartment 2, all compartments 2 can have the same shape or different shapes. For example, although the illustration is omitted, quadrilateral compartments and octagonal compartments can coexist. In addition, regarding the size of the compartment 2, all compartments 2 can have the same size or different sizes. For example, although the illustration is omitted, among multiple compartments, some compartments can be larger in size, and the size of other compartments can be relatively smaller. It should be noted that in this invention, a compartment refers to a space surrounded by a partition wall.

[0056] In the honeycomb substrate 4, the cell density of the compartments 2 formed by the partitions 1 is preferably 30 to 63 cells / cm². 2 More preferably, 31–62 cells / cm 2 By constructing it in this way, the trapping ability of the cellular filter 100 can be maintained, and the increase in pressure loss can be suppressed.

[0057] The shape of the honeycomb filter 100 is not particularly limited. Examples of shapes for the honeycomb filter 100 include a cylindrical shape, such as a circle, ellipse, or polygon, where the inflow end face 11 and outflow end face 12 are circular. It should be noted that the honeycomb substrate 4 is cylindrical, and its outer peripheral side may further have an outer peripheral wall (not shown) surrounding the grid-arranged partitions 1, or it may not have such an outer peripheral wall. When the honeycomb substrate 4 has an outer peripheral wall, an outer peripheral coating 3 is provided on the outer side of this outer peripheral wall. On the other hand, when the honeycomb substrate 4 does not have an outer peripheral wall, an outer peripheral coating 3 is provided on the outer peripheral surface of the honeycomb substrate 4 in a manner that surrounds the outermost peripheral portion of the grid-arranged partitions 1.

[0058] There are no particular limitations on the size of the honeycomb filter 100, such as the length from the inflow end face 11 to the outflow end face 12, or the size of the cross section of the honeycomb filter 100 orthogonal to the direction of extension of the compartment 2. When using the honeycomb filter 100 as a filter for exhaust gas purification, the appropriate size can be selected in order to obtain the best purification performance.

[0059] The material of the partition 1 constituting the honeycomb substrate 4 is not particularly limited. For example, the material of the partition 1 preferably includes at least one selected from the group consisting of cordierite, silicon carbide, silicon-silicon carbide composite material, cordierite-silicon carbide composite material, silicon nitride, andalusite, alumina, and aluminum titanate. In the honeycomb filter 100 of this embodiment, a material including at least one of cordierite, silicon carbide, and aluminum titanate can be cited as a preferred example as the material of the partition 1.

[0060] There are no particular restrictions on the material of the sealing part 5. For example, the same material as the material of the partition 1 described above can be used.

[0061] (2) Manufacturing method of honeycomb filter:

[0062] The method for manufacturing the honeycomb filter of the present invention is not particularly limited, and for example, the following method can be described. First, a plastic blank for making a honeycomb substrate is prepared. An additive such as a binder, a pore-forming material, and water can be appropriately added to a material selected from the aforementioned preferred materials of the partition wall as raw material powder to prepare the blank for making a honeycomb substrate.

[0063] Next, the resulting preform is extruded to form a honeycomb structure having partitions that divide the space into multiple compartments and columnar structures arranged around the outer periphery of the partitions. The resulting honeycomb structure is then dried, for example, using microwaves and hot air.

[0064] Next, sealing portions are provided at the openings of the compartments in the dried honeycomb molded body. Specifically, for example, first, a sealing material containing raw materials for forming the sealing portions is prepared. Next, a mask is applied to the inflow end face of the honeycomb molded body in such a way that the inflow compartment is covered. Next, the previously prepared sealing material is filled into the openings of the outflow compartments on the inflow end face side of the honeycomb molded body where no mask has been applied. Then, for the outflow end face of the honeycomb molded body, the sealing material is filled into the openings of the inflow compartments using the same method as described above.

[0065] Next, the honeycomb molded body with sealing sections at any opening in the compartment is fired to produce a sealed honeycomb fired body. The firing temperature and firing atmosphere vary depending on the raw material, and those skilled in the art can select the optimal firing temperature and firing atmosphere for the selected material.

[0066] Next, the outer peripheral wall of the obtained sealed honeycomb sintered body is ground, and then an outer peripheral coating material is applied to the outer peripheral side of the partition wall to form an outer peripheral coating. This allows the manufacture of a honeycomb filter. The outer peripheral coating material is preferably a coating material containing cordierite particles, amorphous silica, and crystalline inorganic fibers. For example, water, various organic binders, etc., can be added to the above raw materials to prepare the outer peripheral coating material. Furthermore, by controlling the average particle size of the cordierite particles and amorphous silica and the mixing ratio of the above raw materials during the preparation of the outer peripheral coating material, an outer peripheral coating that satisfies the characteristics described above can be obtained.

[0067] Example

[0068] The present invention will be further described in detail below through embodiments; however, the present invention is not limited to these embodiments in any way.

[0069] (Example 1)

[0070] Two parts by mass of pore-forming material, two parts by mass of dispersion medium, and seven parts by mass of organic binder were added to 100 parts by mass of cordierite petrochemical raw material, and the mixture was stirred and kneaded to prepare a billet. The cordierite petrochemical raw material used included alumina, aluminum hydroxide, kaolin, talc, and silica. Water was used as the dispersion medium. Methylcellulose was used as the organic binder. Dextrin was used as the dispersant. A water-absorbing polymer with an average particle size of 18 μm was used as the pore-forming material. In this embodiment, the average particle size of each raw material is the particle size at the 50% integral value of the particle size distribution determined by laser diffraction scattering (D50).

[0071] Next, using a die with a honeycomb molding mechanism, the blank is extruded and molded to obtain a honeycomb molded body with an overall cylindrical shape. The cell shape of the honeycomb molded body is quadrilateral.

[0072] Next, the honeycomb molded body is dried using a microwave dryer, and then completely dried using a hot air dryer. Finally, the two end faces of the honeycomb molded body are cut off and adjusted to the specified dimensions.

[0073] Next, a sealing material for forming the sealing portions is prepared. Then, using the sealing material, sealing portions are formed at the openings of designated compartments on the inflow end face side and the openings of remaining compartments on the outflow end face side of the dried honeycomb molded body.

[0074] Next, the honeycomb molded body with each sealing section is degreased and fired to produce a sealed honeycomb fired body. Then, the outer peripheral wall of the sealed honeycomb fired body is ground to produce a sealed honeycomb substrate.

[0075] Next, the peripheral coating material was prepared using 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 raw materials were mixed and kneaded to prepare the peripheral coating material. Cordierite particles with an average particle size of 15 μm were used. Amorphous silica with an average particle size of 300 μm was used. Crystalline inorganic fibers with a fiber length of 52 μm were used. The mixing ratio of cordierite particles, amorphous silica, and crystalline inorganic fibers was: relative to 100 parts by mass of cordierite particles, 25 parts by mass of amorphous silica and 20 parts by mass of crystalline inorganic fibers.

[0076] Next, the aforementioned peripheral coating material is applied to the outer peripheral surface of the sealed honeycomb substrate to a specified thickness and allowed to dry, forming a peripheral coating. There are no particular limitations on the drying method or conditions; they can be adjusted appropriately. Based on this, the honeycomb filter of Example 1 is manufactured.

[0077] The honeycomb filter of Example 1 is a cylindrical honeycomb filter with circular inlet and outlet faces. The diameter of the inlet and outlet faces is 267 mm. Furthermore, the length of the cell in the honeycomb filter is 178 mm. In the honeycomb filter of Example 1, the thickness L2 of the cell wall is 0.25 mm, the porosity P2 of the cell walls constituting the honeycomb substrate is 53%, and the cell density is 47 cells / cm³. 2 The results are shown in Table 1. The porosity P2 of the septa was determined using an Autopore 9500 (trade name) manufactured by Micromeritics.

[0078] Furthermore, the peripheral coating, which is configured to surround the outer periphery of the honeycomb substrate, has 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 is calculated as follows: the peripheral coating is cut out, and images are taken using a scanning electron microscope (SEM). The obtained SEM images of the cross-section are binarized, and the porosity P1 is calculated based on the area ratio. Additionally, the surface roughness Ra of the peripheral coating is measured based on the arithmetic mean roughness JIS B0601:2001.

[0079] Furthermore, the coefficient of thermal expansion C1 of the peripheral coating and the coefficient of thermal expansion C2 of the honeycomb substrate were measured using the following method. Additionally, for the peripheral coating, the temperature T1 at which the thermal expansion behavior transitions from expansion to contraction was also measured.

[0080] [The coefficient of thermal expansion of the outer coating C1 and the coefficient of thermal expansion of the honeycomb substrate C2]

[0081] The average coefficient of thermal expansion in each temperature range was measured using a differential thermal expansion meter, and the coefficient of thermal expansion was calculated accordingly. It should be noted that the heating rate was set to 10°C / minute. In determining the coefficient of thermal expansion C1 of the outer coating between 40 and 800°C, the outer coating material used to prepare the outer coating was solidified to prepare a block specimen. The average coefficient of thermal expansion in each temperature range was measured using this block specimen. A specimen of the following shape was cut from the honeycomb substrate to prepare a specimen for determining the coefficient of thermal expansion C2 of the honeycomb substrate. The specimen used for determining the coefficient of thermal expansion C2 of the honeycomb substrate is a cuboid with a length of 50 mm in the axial direction of the cell extension of the honeycomb substrate and lengths of 5 mm × 5 mm in each direction of the plane orthogonal to this axial direction.

[0082] [T1, the temperature at which the outer coating transitions from expansion to contraction]

[0083] A differential thermal expansion meter was used, with a heating rate of 10°C / min, to measure the average coefficient of thermal expansion of the peripheral coating and the thermal expansion behavior associated with dimensional changes in the test specimens within each temperature range. Measurements using the thermal expansion meter were performed starting at 40°C and continued until 1500°C was reached at the aforementioned heating rate. If the point (temperature) where the thermal expansion behavior begins to decrease was identified during the measurements from 40°C to 1500°C, this temperature was designated as "the temperature T1 at the inflection point from expansion to contraction." Conversely, if the point where the thermal expansion behavior begins to decrease could not be identified during the measurements from 40°C to 1500°C, the inflection point temperature T1 was set to exceed 1500°C. The test specimens used were the same as those used for measuring the coefficient of thermal expansion C1 of the peripheral coating.

[0084] Table 1

[0085]

[0086] Table 2

[0087]

[0088] For the honeycomb filter of Example 1, the following methods were used to evaluate its "thermal shock resistance", "purification performance" and "isostatic pressure strength". The results are shown in Table 2.

[0089] [Thermal shock resistance]

[0090] First, the "ESP breakage temperature" of the honeycomb filters manufactured in each embodiment and comparative example was measured using the following method. It should be noted that "ESP breakage temperature" is an indicator of thermal shock resistance. ESP is an abbreviation for Electric Furnace Spalling. Specifically, the honeycomb filter was placed in an electric furnace heated to a specified temperature, and after a specified time, it was removed to investigate whether the outer peripheral coating had broken. This operation was repeated while increasing the temperature inside the electric furnace by 25°C each time, until the outer peripheral coating broke, and the temperature at which the outer peripheral coating broke was measured. Based on the temperature at which the outer peripheral coating of the honeycomb filters in each embodiment and comparative example broke (hereinafter referred to as "breakage temperature"), the thermal shock resistance was evaluated using the following evaluation criteria. It should be noted that the breakdown temperature is expressed in "Celsius".

[0091] Evaluation "Excellent": When the breakage temperature of the honeycomb filter in Comparative Example 1 is set to 100%, if the breakage temperature of the honeycomb filter to be evaluated exceeds 110%, it is evaluated as "Excellent".

[0092] Evaluation "Good": When the breakage temperature of the honeycomb filter in Comparative Example 1 is set to 100%, the honeycomb filter to be evaluated is rated as "Good" if its breakage temperature exceeds 105% but is below 110%.

[0093] Evaluation of "Pass": When the breakage temperature of the honeycomb filter in Comparative Example 1 is set to 100%, if the breakage temperature of the honeycomb filter to be evaluated exceeds 100% but is below 105%, it is evaluated as "Pass".

[0094] Evaluation of "Unqualified": If the breakage temperature of the honeycomb filter in Comparative Example 1 is set to 100%, and the breakage temperature of the honeycomb filter to be evaluated is below 100%, it is evaluated as "unqualified".

[0095] [Purification Performance]

[0096] First, a test gas containing NOx is flowed into the honeycomb filter. Then, the NOx content in the gas exiting the honeycomb filter is analyzed using a gas analyzer. It should be noted that the temperature of the test gas flowing into the honeycomb filter is set to 200°C. The honeycomb filter and the test gas are conditioned using a heater. An infrared imaging furnace is used as the heater. The test gas is a mixture of nitrogen containing 5% by volume carbon dioxide, 14% by volume oxygen, 350 ppm (volume basis) nitric oxide, 350 ppm (volume basis) ammonia, and 10% by volume water. For this test gas, water and a mixture of the other gases are prepared separately beforehand. During the test, the water and the mixed gas are mixed in the piping. A HORIBA MEXA9100EGR (trade name) gas analyzer is used. Furthermore, the space velocity of the test gas flowing into the honeycomb filter is set to 100,000 (hours). －1 The NOx purification rate of the honeycomb filter was determined based on the NOx content of the test gas and the NOx content of the gas discharged from the honeycomb filter. The purification performance was evaluated using the following evaluation criteria based on the NOx purification rates of the honeycomb filters in each embodiment and comparative example.

[0097] Evaluation "Excellent": If the NOx purification rate of the honeycomb filter in Comparative Example 1 is set to 100%, and the NOx purification rate of the honeycomb filter to be evaluated exceeds 120%, it is evaluated as "Excellent".

[0098] Evaluation "Good": When the NOx purification rate of the honeycomb filter of Comparative Example 1 is set to 100%, the evaluation of the honeycomb filter to be evaluated is set to "Good" if the NOx purification rate exceeds 110% and is below 120%.

[0099] Evaluation "Pass": If the NOx purification rate of the honeycomb filter in Comparative Example 1 is set to 100%, and the NOx purification rate of the honeycomb filter to be evaluated is higher than 100% but lower than 110%, then it is evaluated as "Pass".

[0100] Evaluation of "Unqualified": If the NOx purification rate of the honeycomb filter in Comparative Example 1 is set to 100%, and the NOx purification rate of the honeycomb filter to be evaluated is below 100%, it is evaluated as "unqualified".

[0101] [Isostatic Strength]

[0102] The isostatic pressure strength was determined based on the isostatic destructive strength test specified in the JASO Standard M505-87 issued by the China Automotive Technology and Research Center (CATARC). The isostatic destructive strength test involves placing the honeycomb filter in a rubber cylindrical container, covering it with an aluminum plate, and subjecting it to isotropic compression in water. The isostatic pressure strength determined by the isostatic destructive strength test is expressed as the pressure value (MPa) at which the honeycomb filter fails. Based on the isostatic pressure strength of the honeycomb filters in each embodiment and comparative example, the isostatic pressure strength was evaluated using the following evaluation criteria.

[0103] Evaluation "Excellent": When the isostatic pressure of the honeycomb filter of Comparative Example 1 is set to 100%, if the isostatic pressure of the honeycomb filter to be evaluated exceeds 110%, it is evaluated as "Excellent".

[0104] Evaluation "Good": When the isostatic pressure of the honeycomb filter of Comparative Example 1 is set to 100%, the isostatic pressure of the honeycomb filter to be evaluated is rated as "Good" if it exceeds 105% and is less than 110%.

[0105] Evaluation "Pass": When the isostatic pressure of the honeycomb filter of Comparative Example 1 is set to 100%, if the isostatic pressure of the honeycomb filter to be evaluated exceeds 100% but is less than 105%, it is evaluated as "Pass".

[0106] Evaluation of "Unqualified": If the isostatic pressure strength of the honeycomb filter of Comparative Example 1 is set to 100%, and the isostatic pressure strength of the honeycomb filter to be evaluated is less than 100%, it is evaluated as "unqualified".

[0107] (Examples 2-7)

[0108] The honeycomb filter was modified according to the structure shown in Table 1. Otherwise, the honeycomb filter was fabricated using the same method as the honeycomb filter in Example 1. It should be noted that in Examples 2 to 7, the average particle size and mixing ratio of the raw materials used were changed when preparing the peripheral coating material.

[0109] (Comparative Examples 1-5)

[0110] The honeycomb filter was modified according to Table 1, except that the honeycomb filter was fabricated using the same method as the honeycomb filter in Example 1. It should be noted that in Comparative Examples 1, 3-5, the peripheral coating material was prepared as follows: The cordierite particles used in the peripheral coating material of Example 1 were changed to a mixture comprising cordierite particles with an average particle size of 15 μm and cordierite particles with an average particle size of 35 μm. Regarding the amount of cordierite particles used in the preparation of this peripheral coating material, when the amount of cordierite particles used in the peripheral coating material of Example 1 was set to 100% by mass, the cordierite particles with an average particle size of 15 μm were set to 50% by mass, and the cordierite particles with an average particle size of 35 μm were set to 75% by mass.

[0111] For the honeycomb filters of Examples 2-7 and Comparative Examples 1-5, the "thermal shock resistance", "purification performance" and "isostatic pressure strength" were evaluated using the same method as in Example 1. The results are shown in Table 2.

[0112] (result)

[0113] For the honeycomb filters of Examples 1 to 7, it can be confirmed in the evaluation of thermal shock resistance, purification performance and isostatic strength that they exceed the performance of the honeycomb filter of Comparative Example 1, which is used as a benchmark.

[0114] In the honeycomb filter of Comparative Example 2, the porosity P1 of the outer coating was 32%, and the evaluation result for thermal shock resistance was "unacceptable". In the honeycomb filters of Comparative Examples 3 and 5, the inflection point temperature T1 was 850°C, and the coefficient of thermal expansion C1 of the outer coating was 1.0 × 10⁻⁶. －6 / ℃, the evaluation result for thermal shock resistance is "unacceptable". In the honeycomb filter of Comparative Example 4, the porosity P1 of the outer coating is 35%, and the evaluation result for isostatic pressure strength is "unacceptable".

[0115] Industrial availability

[0116] The honeycomb filter of the present invention can be used as a filter for capturing particulate matter in exhaust gas.

Claims

1. A honeycomb filter, characterized in that, have: A columnar honeycomb substrate having porous partitions configured to surround multiple compartments forming a fluid flow path extending from an inflow end face to an outflow end face; A peripheral coating is disposed around the periphery of the honeycomb substrate; as well as A porous sealing portion, which is disposed at either the end of the compartment on the inflow end face or the end on the outflow end face. The peripheral coating is configured such that the inflection point T1 at which thermal expansion transitions to contraction is 1000℃ to 1500℃, the porosity P1 is 36% to 48%, and the coefficient of thermal expansion C1 between 40℃ and 800℃ is 2.5 × 10⁻⁶. －6 / ℃~3.5×10 －6 / ℃, The surface roughness Ra of the outer peripheral coating is 10 μm to 25 μm.

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

3. The honeycomb filter according to claim 2, characterized in that, The ratio of the porosity P1 of the outer peripheral coating to the porosity P2 of the honeycomb substrate, i.e., P1 / P2, is 0.6 to 0.

9.

4. The honeycomb filter according to any one of claims 1 to 3, characterized in that, The thickness L1 of the outer peripheral coating is 1 mm to 3 mm.

5. The honeycomb filter according to any one of claims 1 to 3, characterized in that, The thickness L2 of the partition wall is 0.17 mm to 0.32 mm, and the cell density of the honeycomb substrate is 30 cells / cm². 2 ~63 pieces / cm 2 .

6. The honeycomb filter according to any one of claims 1 to 3, characterized in that, The coefficient of thermal expansion C2 of the honeycomb substrate between 40℃ and 800℃ is 0.2×10⁻⁶. －6 / ℃~1.5×10 －6 / ℃.

7. The honeycomb filter according to claim 6, characterized in that, The ratio of the coefficient of thermal expansion C1 of the outer peripheral coating to the coefficient of thermal expansion C2 of the honeycomb substrate, i.e., C1 / C2, is 3 to 12.

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