Silicon carbide honeycomb filter

Abstract

The present invention provides a silicon carbide honeycomb filter which comprises: honeycomb segments, each of which has partition walls that define cells which form a plurality of flow channels that extend in the axial direction between end faces, a plugged portion which alternately seals the end faces of the cells in a checker pattern, and an outer peripheral wall; a bonding material layer that is filled into a grid-like gap between the honeycomb segments so as to bond the honeycomb segments with each other; and an outer cover that encloses the bonded honeycomb segments. This silicon carbide honeycomb filter is characterized in that the thickness of the outer peripheral wall is more than 1.5 times but not more than 9 times the thickness of the partition walls.

Description

Silicon carbide honeycomb filter

[0001] The present invention relates to a silicon carbide honeycomb filter that removes particulate matter (PM) and the like from exhaust gas emitted from an internal combustion engine such as a diesel engine, thereby purifying the exhaust gas.

[0002] Because NOx and PM contained in diesel engine exhaust gases can be released into the atmosphere and have adverse effects on humans and the environment, a honeycomb structure supporting a NOx catalyst and a ceramic honeycomb filter for capturing PM have traditionally been installed in the exhaust pipe of diesel engines. An example of a ceramic honeycomb filter for capturing PM in exhaust gas is shown in Figures 10(a) and 10(b). A ceramic honeycomb filter 500 includes a ceramic honeycomb structure 510 having porous partition walls 52 and an outer wall 51 that form numerous flow channels 53a, 53b, and inlet-side plugging portions 56a and outlet-side plugging portions 56b that alternately plug the exhaust gas inlet-side end faces 55a and outlet-side end faces 55b of the flow channels 53a, 53b in a checkerboard pattern. As shown by the dotted arrows in Figure 10(b), exhaust gas flows into the outlet-side sealed flow passage 53b, which opens at the exhaust gas inlet end surface 55a, passes through the communicating holes present on the surface and inside of the partition wall 52, flows into the adjacent inlet-side sealed flow passage 53a, and then flows out from the exhaust gas outlet end surface 55b. As the exhaust gas passes through the communicating holes present on the surface and inside of the partition wall 52, PM in the exhaust gas is captured, thereby purifying the exhaust gas. When the captured PM reaches a predetermined accumulation amount, it is burned, and the ceramic honeycomb structure is regenerated. As the operating environment of such ceramic honeycomb structures becomes increasingly severe, refractory ceramics such as silicon carbide (SiC), which have excellent thermal shock resistance, are increasingly being used as their constituent materials.

[0003] Thermal shock caused by uneven combustion of PM during regeneration and sudden temperature changes in exhaust gases causes thermal stress due to uneven temperature distribution inside the ceramic honeycomb structure, resulting in problems such as cracks, fractures, melting damage, etc. To address this problem, a ceramic honeycomb filter 400 has been proposed, which has the function of dispersing and mitigating thermal stress by integrally bonding multiple honeycomb segments 411 with rectangular outer shapes as shown in Fig. 9 via a bonding material layer 49 as shown in Fig. 8.

[0004] Patent Document 1 discloses a honeycomb filter that suppresses the occurrence of cracks when regenerating by burning collected PM. The honeycomb filter is a columnar honeycomb filter in which a plurality of columnar honeycomb segments are bonded together via a bonding material layer, each honeycomb segment having partition walls that form a plurality of cells extending from one end face to the other end face, at least one honeycomb segment being composed of a central portion and an outer peripheral portion, the thickness of the partition walls in the outer peripheral portion being 101 to 150% of the average thickness of the partition walls in the central portion, and the total area of ​​the partition walls in the outer peripheral portion being 5 to 35% of the total area of ​​the partition walls of the honeycomb segments in a cross section perpendicular to the extension direction of the cells.

[0005] In the honeycomb filter of Patent Document 1, the partition walls are thinned to suppress pressure loss when PM is trapped and to increase the amount of PM trapped before regeneration begins. However, depending on the state of PM accumulation, localized heat generation may occur due to uneven heating or abnormal combustion during regeneration, and the honeycomb filter of Patent Document 1 cannot suppress cracks or melting damage caused by such heat generation.

[0006] Patent Document 2 discloses a honeycomb structure including multiple rectangular prismatic honeycomb segments arranged in a lattice pattern, a bonding material layer bonding the side surfaces of the honeycomb segments together, and an outer wall surrounding the honeycomb segments. Each honeycomb segment has porous partition walls surrounding multiple cells extending axially from the inflow end face to the outflow end face, and an outer wall surrounding the partition walls. The cells are plugged at either the inflow end face or the outflow end face with plugging portions. Axial-extending, bottomed, hollow voids are formed at some or all of the intersections of the lattice-shaped bonding material layer. The ratio of the axial depth of the voids to the axial length of the honeycomb segments is 5% or more, and the ratio of the opening diameter of the voids to the thickness of the bonding material layer is 10 to 140%. Patent Document 2 describes that this structure can suppress the propagation of cracks that occur in the bonding material layer.

[0007] In the examples of Patent Document 2, when the ratio of the void depth to the length of the honeycomb segment is small, at 5 to 20%, voids are provided at all of the intersections, but when the ratio of the void depth to the length is large, at 50 to 80%, voids are provided only at some of the intersections. As such, there are no examples where deep voids are provided at all of the intersections.

[0008] Furthermore, the cross-sectional shape of the voids described in Patent Document 2 is only circular, and in the examples, the voids are formed using cylindrical wooden pieces. When placing cylindrical wooden pieces at the intersections of the lattice gaps between honeycomb segments, the upper limit of the diameter of the cylindrical wooden pieces is √2 times the thickness of the bonding material layer, which is approximately 140%. However, because of tolerances on the side surfaces of honeycomb segments, it is virtually impossible to place cylindrical wooden pieces with a diameter √2 times the thickness of the bonding material layer at the intersections of the lattice gaps. Therefore, the upper limit of the diameter of the cylindrical wooden pieces must be significantly smaller than 140%. Furthermore, even if the diameter of the cylindrical wooden pieces were 140% of the thickness of the bonding material layer, the cross-sectional area of ​​the voids formed by the cylindrical wooden pieces would be too small to adequately suppress cracks.

[0009] From the above structural problems, it has been found that the honeycomb structure of Patent Document 2 does not have sufficient functions for dispersing and mitigating thermal stress, and is unable to sufficiently suppress cracks.

[0010] JP 2021-133283 A JP 2019-171238 A

[0011] Therefore, an object of the present invention is to provide a silicon carbide-based honeycomb filter that can suppress the occurrence of cracks and melting damage in the honeycomb filter due to thermal shock caused by localized heat generation or sudden temperature changes in exhaust gas, without increasing pressure loss.

[0012] As a result of intensive research to achieve the above-mentioned object, the present inventors discovered that (1) by focusing on the relationship between the thickness of the outer wall and the thickness of the partition wall of each honeycomb segment constituting a silicon carbide-based honeycomb filter, it is possible to suppress the occurrence of cracks and melting damage in the honeycomb filter caused by thermal shock due to localized heat generation or sudden temperature changes in the exhaust gas, without increasing pressure loss, and (2) by focusing on the external shape of the cross section perpendicular to the flow path direction of each honeycomb segment and on the shape of the intersection between the bonded honeycomb segments, the above-mentioned effects can be further improved, and have arrived at the present invention.

[0013] That is, the silicon carbide-based honeycomb filter of the present invention comprises honeycomb segments having partition walls that form cells that define a plurality of flow paths extending in the axial direction between both end faces, plugging portions that alternately plug the end faces of the cells in a checkerboard pattern, and an outer wall, a laminating material layer filled in the lattice-like gaps between the honeycomb segments to join them, and an outer skin that surrounds the joined honeycomb segments, and is characterized in that the thickness of the outer wall is more than 1.5 times but not more than 9 times the thickness of the partition walls.

[0014] The thickness of the partition wall is preferably 0.17 to 0.31 mm.

[0015] A preferred silicon carbide honeycomb filter of the present invention comprises honeycomb segments having partition walls forming cells that define a plurality of flow paths extending in the axial direction between both end faces, plugging portions that alternately plug the end faces of the cells in a checkerboard pattern, and an outer wall, a bonding material layer filled in lattice-like gaps between the honeycomb segments to bond them, and an outer skin surrounding the bonded honeycomb segments, wherein the outer shape of a cross section of each honeycomb segment perpendicular to the flow path direction is an octagon formed by providing linear chamfered portions at each corner of a rectangle, and the octagon is formed alternately by first peripheral walls corresponding to sides of the rectangle and second peripheral walls corresponding to the linear chamfered portions, the thickness of the first peripheral walls 17a of each honeycomb segment is more than 1.5 times but not more than 9 times the thickness of the partition walls, and intersection voids where no bonding material is present are formed in the lattice-like gaps between the bonded honeycomb segments at intersections where the second peripheral walls form the outline, The void ratio (t2 / t1), defined as the ratio of the void diameter t2 of the void portion at the intersection to the thickness t1 of the laminating material layer between the first outer peripheral walls, is characterized by being greater than 1.4.

[0016] It is preferable that the cross section of the second outer peripheral wall perpendicular to the flow path direction has a triangular shape formed by the two vertical and horizontal partition walls closest to the second outer peripheral wall and the outer peripheral surface of the second outer peripheral wall, and that the maximum thickness of the second outer peripheral wall, defined by the distance between the central vertex of the triangle and the outer peripheral surface, is thicker than the thickness of the first outer peripheral wall.

[0017] The quadrangle constituting the first outer peripheral wall of the honeycomb segment is preferably a rectangle, more preferably a square.

[0018] The cross-sectional shape of the honeycomb segment is preferably an octagonal shape formed by providing chamfered portions having an inclination angle of 45° at each corner of a square.

[0019] The cross-sectional shape of the intersecting hole preferably has an outline that is substantially in contact with the four opposing second outer peripheral walls.

[0020] The cross-sectional shape of the intersecting hole is preferably square, octagonal or circular.

[0021] In a cross section perpendicular to the flow channel direction of the honeycomb segment, the cross-sectional area of ​​the inlet cells whose outlet end faces are plugged is preferably larger than the cross-sectional area of ​​the outlet cells whose inlet end faces are plugged.

[0022] In the silicon carbide-based honeycomb filter of the present invention, the thickness of the outer wall of the honeycomb segment is more than 1.5 times but not more than 9 times the thickness of the partition wall, and therefore the occurrence of cracks and melting damage can be suppressed without increasing pressure loss. Furthermore, when the outer shape of the cross section perpendicular to the flow path direction of each honeycomb segment is made octagonal by providing chamfered portions at each corner of the quadrangle, and voids are formed at the intersections formed by the second outer wall corresponding to the chamfered portions, it is possible to achieve the maximum effect of dispersing and mitigating thermal stress while maintaining heat conduction between the honeycomb segments.

[0023] 4(b)(a)(b)(c)(c)(d) is a perspective view schematically showing an example of a silicon carbide-based honeycomb filter of the present invention. FIG. 4(b)(a)(b) is a perspective view schematically showing an example of a honeycomb segment used in a silicon carbide-based honeycomb filter. FIG. 4(b)(c)(b) is a front view schematically showing another example of a honeycomb segment. FIG. 4(b)(c)(b) is a front view schematically showing yet another example of a honeycomb segment. FIG. 4(b)(c)(b) is a front view schematically showing yet another example of a honeycomb segment. FIG. 4(b)(c)(b) is a partial front view showing in detail a second outer peripheral wall of the honeycomb segment of FIG. 4(b). FIG. 4(b)(c)(b) is a perspective view schematically showing another example of a silicon carbide-based honeycomb filter of the present invention. FIG. 4(b)(c)(b) is a partial cross-sectional view showing an example of intersection portion voids. FIG. 4(b)(c) is a partial cross-sectional view showing yet another example of intersection portion voids. FIG. 4(b)(c) is a front view schematically showing a die for extrusion-molding a honeycomb segment. FIG. 7(a)(b)(c) is a cross-sectional view taken along line B-B of FIG. 7(a). FIG. 7(b) is a partially enlarged view of FIG. 7(b). 9(a) is a front view schematically showing a die for extrusion-molding a honeycomb formed body in which the maximum thickness of the second peripheral wall is thicker than the thickness of the first peripheral wall. FIG. 9(b) is a perspective view schematically showing a silicon carbide-based honeycomb filter having a conventional divided structure. FIG. 9(c) is a perspective view schematically showing a conventional honeycomb segment. FIG. 9(a) is a cross-sectional view taken along line AA of FIG. 9(a). FIG. 9(c) is a front view schematically showing an example of a conventional silicon carbide-based honeycomb filter. FIG. 9(a) is a cross-sectional view parallel to the axial direction showing the silicon carbide-based honeycomb filter of FIG. 9(a). FIG. 9(c) is a graph showing temperature control in a Drop to Idle test.

[0024] Embodiments of the present invention will be described in detail below with reference to the drawings, but the present invention is not limited to these embodiments, and changes, modifications, or improvements can be made without departing from the scope of the invention.

[0025] [1] Silicon carbide-based honeycomb filter The silicon carbide-based honeycomb filter 100 of the present invention shown in Fig. 1 has honeycomb segments 111 shown in Fig. 2 and a laminating material layer 19 filled in the lattice-like gaps between the honeycomb segments to bond the honeycomb segments 111. The honeycomb segment 111 has an outer peripheral wall 17 and partition walls 12 that form cells 13a, 13b that define a plurality of flow paths extending from one end face 15a to the other end face 15b, and the inlet-side and outlet-side end faces 15a, 15b of the cells 13a, 13b are alternately plugged in a checkerboard pattern with plugging portions 16a, 16b, respectively.

[0026] The silicon carbide-based honeycomb filter 100 of the present invention is characterized in that the thickness of the outer wall 17 of the honeycomb segment 111 is more than 1.5 times and not more than 9 times the thickness of the partition wall 12. Such a thick outer wall 17 ensures the heat capacity of the honeycomb segment 111 even when the partition wall 12 is thin, and therefore, even if a localized temperature rise occurs due to the combustion of unevenly deposited PM during regeneration of the honeycomb filter 100, cracks and melting damage can be suppressed.

[0027] If the thickness of the outer wall 17 of the honeycomb segment 111 is 1.5 times or less the thickness of the partition wall 12, the heat capacity of the honeycomb segment 111 may be insufficient, which may cause cracks or melting damage in the honeycomb filter due to thermal shock or the like. On the other hand, if the thickness of the outer wall 17 of the honeycomb segment 111 exceeds 9 times the thickness of the partition wall 12, the pressure loss of the honeycomb filter becomes too large. The lower limit of the ratio of the thickness of the outer wall 17 to the thickness of the partition wall 12 is preferably 1.6 times, more preferably 1.7 times. The upper limit is preferably 8 times, more preferably 7 times.

[0028] The thickness of the partition walls 12 of the honeycomb segment 111 is preferably 0.17 to 0.31 mm. If the thickness of the partition walls 12 is less than 0.17 mm, not only will the strength of the honeycomb segment 111 be too low, but there is also a risk of cracks or melting damage occurring in the honeycomb filter due to impact, etc. On the other hand, if the thickness of the partition walls 12 exceeds 0.31 mm, the pressure loss of the honeycomb filter will be too large.

[0029] 3 and 4(c), in a cross section perpendicular to the flow direction of the cells of the honeycomb segment 211, the cross-sectional area of ​​the cells (exhaust gas inlet cells) 23b whose outlet end faces are plugged may be larger than the cross-sectional area of ​​the cells (exhaust gas outlet cells) 23a whose inlet end faces are plugged. This increases the amount of PM trapped before regeneration begins, and provides a honeycomb filter in which the pressure loss when PM is trapped is less likely to decrease. The cross-sectional area of ​​the inlet cells 23b is preferably 1.1 to 2.0 times, and more preferably 1.2 to 1.9 times, the cross-sectional area of ​​the outlet cells 23a.

[0030] The outer shape of a honeycomb segment in a cross section perpendicular to the flow path direction is generally quadrangular, but is preferably a rectangle with all corners at 90°, and more preferably a square with all corners at 90° and all sides equal in length. Furthermore, in addition to the quadrangular shape (square shape) without chamfers as shown in Figures 2 and 3, it may also be a quadrangular shape with curved chamfered portions R at the corners as shown in Figure 4(a) or a quadrangular shape with linear chamfered portions C as shown in Figures 4(b) and 4(c).

[0031] In a preferred embodiment of the present invention, the silicon carbide-based honeycomb filter 200 has the following characteristics: (a) the outer shape of a cross section perpendicular to the flow path direction of each honeycomb segment 111 is an octagon formed by providing linear chamfered portions C at each corner of a rectangle, and the octagonal shape is formed by alternating first peripheral walls 17a corresponding to the sides of the rectangle and second peripheral walls 17b corresponding to the linear chamfered portions C; (b) the thickness of the first peripheral walls 17a of the honeycomb segment 111 is more than 1.5 times and not more than 9 times the thickness of the partition walls 12; (c) in the lattice-like gaps between the bonded honeycomb segments 111, intersection voids 20 where no bonding material is present are formed at the intersections formed by the second peripheral walls 17b; and (d) the void ratio (t2 / t1), defined as the ratio of the void diameter t2 of the intersection voids 20 to the thickness t1 of the bonding material layer 19 between the first peripheral walls 17a, is greater than 1.4.

[0032] When forming voids of sufficient size at the intersections of the lattice-like gaps between honeycomb segments, the cross-sectional shape of the honeycomb segment is preferably an octagon formed by providing chamfered portions with an inclination angle of 45° at each corner of a square, as shown in Fig. 4(b). In the example shown in Fig. 4(b), the honeycomb segment 111 has an octagonal outer wall with linear chamfered portions C with an inclination of 45° at each corner of the square, and the octagonal outer wall is made up of a long first peripheral wall 17a corresponding to the sides of the square and a short second peripheral wall 17b corresponding to the linear chamfered portions C.

[0033] Honeycomb segments having chamfered corners preferably have no flow channels in the second peripheral wall at the corners. For example, the honeycomb segment 111 shown in FIG. 4(b) does not have flow channels in the corners where the second peripheral wall 17b is located, and the second peripheral wall 17b preferably has a triangular shape 171 with vertex P at the center of the honeycomb segment 111, as shown in FIG. 4(d). In this case, the maximum thickness L of each second peripheral wall 17b in the center direction (the distance between the peripheral surface 17b' of the second peripheral wall 17b and the vertex P) is thicker than the thickness of the first peripheral wall 17a. In particular, when the honeycomb segment 111 has an octagonal shape with linear chamfered corners at an angle of 45°, the triangle 171 is a right-angled isosceles triangle with the peripheral surface 17b' as the base, and the maximum thickness L is half the length of the peripheral surface 17b' of the second peripheral wall 17b. Such a shape increases the heat capacity of the honeycomb segment 111, and even if a local temperature rise occurs in the honeycomb segment 111 due to the combustion of unevenly deposited PM, the occurrence of cracks can be suppressed.

[0034] When a plurality of honeycomb segments 111 having such octagonal outer walls are bonded together lengthwise and breadthwise, lattice-like gaps are formed between the honeycomb segments 111, and intersections are formed by the four opposing second outer peripheral walls 17b. This is the same when the honeycomb segments 211 shown in Fig. 4(c) are bonded together, so the following description will be given of the case where the honeycomb segments 111 are bonded together, but the description also applies to the case where the honeycomb segments 211 are bonded together.

[0035] Because adjacent second outer peripheral walls 27b are spaced apart by the width of the lattice-like gaps, the cross section of the intersection can have various shapes other than the outline of the second outer peripheral walls 27b. However, as will be described later, the cross-sectional shape of the voids formed at the intersections is determined by the cross-sectional shape of the rod-shaped spacers placed at the intersections. Therefore, it is not necessary to specify the outline of the intersections as spaces that form voids down to the lattice-like gaps, and here we will only specify "the shape that forms the outline of the four opposing second outer peripheral walls 27b."

[0036] When honeycomb segments 111 are joined to form a honeycomb filter 200 as shown in FIG. 5, it is preferable to form intersection voids 20 without any adhesive material at the intersections formed by the four second peripheral walls 17b. As described above, the cross-sectional shape of the intersection voids 20 is determined by the cross-sectional shape of the rod-shaped spacers that can be accommodated in the intersections whose outline is formed by the second peripheral walls 17b. For example, if the cross-sectional shape of the rod-shaped spacers is square or circular and in contact with the second peripheral wall 17b, the cross-sectional shape of the resulting intersection voids 20 will be square or circular. In either case, it is preferable that each intersection void 20 extend in the axial direction from one end face 15a to the other end face 15b. The intersection voids 20 disperse and relieve thermal stress without impairing heat conduction between adjacent honeycomb segments 111, and can suppress cracks and melting damage even if localized heat is generated due to the combustion of unevenly accumulated PM.

[0037] During manufacture, the rod-shaped spacers contact the two second outer peripheral walls 17b located on the lower side, but do not necessarily need to contact the two upper second outer peripheral walls 17b. However, in order to maximize the cross-sectional area of ​​the intersection hole 20 so as to sufficiently suppress cracks, it is preferable that the outline of the intersection hole 20 contacts all of the second outer peripheral walls 17b. However, since a gap of a margin of error is allowed, in this specification it is said that "it is preferable that the outline of the intersection hole 20 is approximately in contact with the second outer peripheral walls 17b."

[0038] 6(a), 6(b), and 6(c) respectively show intersection cavity 20a having a square cross section, intersection cavity 20b having an octagonal cross section, and intersection cavity 20c having a circular cross section.

[0039] In the square cross section void portion 20a shown in FIG. 6(a), all sides in contact with the second outer peripheral wall 17b are connected within the laminating material layer 19, and among the above three types of cross section void portions 20a, 20b, and 20c, t2 2 The ratio of the distance (hole diameter) t2 between the two opposing second peripheral walls 17b to the thickness t1 of the laminating material layer 19 (hole ratio t2 / t1) is preferably greater than 1.4. If the hole ratio t2 / t1 is 1.4 or less, the effect of suppressing the propagation of cracks is insufficient. The hole ratio t2 / t1 is preferably 1.5 or more, more preferably 2 or more. On the other hand, if the hole ratio t2 / t1 is too large, the strength of the honeycomb filter decreases, which is undesirable. The hole ratio t2 / t1 is preferably 7 or less, more preferably 5 or less, and most preferably 4 or less. Therefore, the hole ratio t2 / t1 in the square cross-sectional intersection hole portion 20a is generally in the range of greater than 1.4 to 7, preferably 1.5 to 5, and more preferably 2 to 4. Since the hole ratio t2 / t1 is greater than 1.4, the cross-sectional area of ​​the cross-section hole 20a is 1.4 t1 × 1.4 t1 = 1.96 t1 2 It's super.

[0040] The octagonal cross section of the hole 20b shown in FIG. 6(b) is made up of four sides in contact with the second outer peripheral wall 17b and a side in the width direction of the laminating material layer 19, and has a length of (t2 2 -t1 2) cross-sectional area. From the above cross-sectional area formula, it can be seen that unless t2 is sufficiently larger than t1, the intersection hole 20b cannot ensure a sufficient cross-sectional area. Therefore, the hole ratio t2 / t1 is preferably 1.7 or more, more preferably 2 or more, and most preferably 2.5 or more. As with the square cross section, the upper limit of the hole ratio t2 / t1 is preferably 7, more preferably 5, and most preferably 4. Therefore, the hole ratio t2 / t1 of the intersection hole 20b having an octagonal cross section is preferably in the range of 1.7 to 7, more preferably 2 to 5, and most preferably 2.5 to 4. When the hole ratio t2 / t1 is within the above range, the intersection hole 20b having an octagonal cross section has a sufficiently large cross-sectional area and does not penetrate into the laminating material layer 19, thereby achieving both a cross-sectional area sufficient to sufficiently suppress cracking and bonding strength.

[0041] The circular cross-section hole 20c shown in FIG. 6(c) has a diameter that contacts the second outer peripheral wall 17b, so that (π / 4)t2 2 In order to ensure that the intersection voids 20c have a sufficient cross-sectional area, the void ratio t2 / t1 is preferably 1.5 or more, more preferably 2 or more, and most preferably 2.5 or more. The upper limit of the void ratio t2 / t1 is preferably 7, more preferably 5, and most preferably 4, as in the case of a square cross section. Therefore, the range of the void ratio t2 / t1 in the intersection voids 20c having a circular cross section is preferably 1.5 to 7, more preferably 2 to 5, and most preferably 2.5 to 4. When the void ratio t2 / t1 is within the above range, the intersection voids 20c having a circular cross section have a sufficiently large cross-sectional area and do not penetrate the laminating material layer 19, so that it is possible to achieve both a cross-sectional area sufficient to suppress cracking and bonding strength.

[0042] To summarize the range of the void ratio t2 / t1 of the cross-sectional void portion of all cross-sectional shapes, it is generally greater than 1.4 and up to 7, preferably 1.5-5, and more preferably 2-4.

[0043] In order to prevent cracks from occurring even if a local temperature rise due to the combustion of unevenly deposited PM occurs at any part of each honeycomb segment 111, the ratio of the voids 20 at intersections to all intersections in each honeycomb segment 111 is preferably 30% or more, more preferably 50% or more, and most preferably 70% or more. The upper limit of the ratio of the voids 20 at intersections is preferably 100% of all intersections, but may be 95% or less.

[0044] [2] Manufacturing method of silicon carbide-based honeycomb filter (1) Manufacturing of honeycomb segments 100% by mass of a forming raw material consisting of silicon carbide particles, alumina particles, and magnesium hydroxide particles is mixed with 5 to 15% by mass of an organic binder. The silicon carbide particles preferably have an average particle size of 30 to 50 μm. Furthermore, the total amount of alumina particles and magnesium hydroxide particles is preferably 8 to 15% by mass relative to 100% by mass of silicon carbide particles.

[0045] Examples of the organic binder include methyl cellulose, ethyl cellulose, ethyl methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxyethyl ethyl cellulose, etc. Among these, methyl cellulose or hydroxypropyl methyl cellulose is preferred.

[0046] Water is added to the resulting mixture and kneaded to form a plastic body. To obtain a body with a moldable hardness, the amount of water added is preferably 20 to 50% by mass relative to 100% by mass of the molding raw materials.

[0047] The molded material is extrusion molded using a mold 30 shown in Figures 7(a) and 7(b). The mold 30 has a first surface 31a, a second surface 32a opposite the first surface 31a, a third surface 32b opposite the first surface 31a and located on the outer periphery of the second surface 32a, molded material supply holes 31 opening in the first surface 31a, and square cross-sectional slits 32 communicating with the molded material supply holes 31 and opening in a lattice pattern in the second and third surfaces 32a and 32b. The slits 32 are connected in a lattice pattern within the mold body. The second surface 32a constitutes a region 33a where the lattice-shaped partition walls of the honeycomb molded body are formed, and the third surface 32b, located outside the partition wall forming region 33a, constitutes a region 33b where the outer peripheral wall is formed. The second surface 32a is higher than the third surface 32b by a step H. A guide ring 35 having an opening for regulating the outer peripheral surface shape of the honeycomb molded body is disposed on the third surface 32b so as to surround the partition wall forming region 33a. The opening of the guide ring 35 is sized to cover the outer peripheral portion of the outer peripheral region 33b. A mask 36 for controlling the inflow amount of clay is disposed on the first surface 31a.

[0048] As shown by the arrows in Figure 7(c), the flow direction of the clay discharged from the slits 32 of the third surface 32b in the outer peripheral region 33b is changed by the guide ring 35 toward the partition wall forming region 33a, and then changed to the extrusion direction by the step H. As a result, the force of the clay flowing from the outer peripheral region 33b is less likely to act on the partition walls extruded from the second surface 32a, so the partition walls are not deformed and a honeycomb molded body with a thick outer peripheral wall can be obtained. The thickness of the outer peripheral wall can be adjusted by changing the distance between the inner end of the guide ring 35 and the step H and the position of the inner end of the mask 36.

[0049] A honeycomb formed body in which the maximum thickness L of the second peripheral wall 17b is thicker than the thickness of the first peripheral wall 17a can be formed, for example, using the mold shown in Fig. 7(d). This mold is the same as the mold shown in Fig. 7(a) except that the four corners 32a1, 32a2, 32a3, and 32a4 of the second surface 32a are at the same height as the peripheral region 33b, and the guide ring 35 has triangular closing portions 35a1, 35a2, 35a3, and 35a4 at the four corners of the opening. In Fig. 7(d), the regions (the peripheral region 33b and the four corners 32a1, 32a2, 32a3, and 32a4) that are lower than the partition wall forming region 33a by the step H are hatched.

[0050] The obtained honeycomb formed body is dried, and then processed as necessary to the end faces, periphery, etc. Then, it is fired in an oxidizing atmosphere at a temperature of 1100 to 1350°C to obtain a silicon carbide honeycomb segment. The drying method is not particularly limited, but examples include hot air drying, microwave heating drying, and high-frequency heating drying.

[0051] (2) Manufacturing of Honeycomb Filters The material (laminar material) for laminating honeycomb segments contains a laminating material raw material consisting of silicon carbide aggregate particles and binder particles, an organic binder, and, if necessary, an inorganic binder and a pore-forming material. The binder particles are made of at least one material selected from the group consisting of an aluminum source, a magnesium source, a silica source, and compounds thereof. Examples of the alumina source include alumina or aluminum hydroxide, and examples of the magnesium source include magnesium oxide or magnesium hydroxide. The total amount of the alumina source particles and the magnesium source particles is preferably 5 to 25% by mass relative to 100% by mass of the silicon carbide particles.

[0052] The organic binder may be the same as that used in manufacturing the honeycomb segments. The amount of organic binder added is preferably 5 to 15 mass % relative to 100 mass % of the laminating material raw material.

[0053] Examples of inorganic binders include colloidal silica, colloidal alumina, etc. The amount of inorganic binder added is preferably 40% by mass or less relative to 100% by mass of the laminating material raw material.

[0054] Examples of pore-forming materials include expandable resins, expanded resins, carbon, water-absorbent resins, and fly ash balloons. Among these, expandable resins and expanded resins, which have small particle size variations, are preferred. The amount of pore-forming material added is preferably 2 to 20% by mass relative to 100% by mass of the laminating material raw material.

[0055] Water is added to the resulting mixture and kneaded to produce a laminating material slurry. The amount of water added is preferably 20 to 50% by mass relative to 100% by mass of the laminating material raw materials.

[0056] After the adhesive slurry is applied to the outer peripheral walls 17 of the honeycomb segments 111, the honeycomb segments 111 are pressure-bonded and joined together via the adhesive as shown in Figure 1. The adhesive layer 19 formed between the honeycomb segments 111 at this time has a lattice pattern.

[0057] When manufacturing a honeycomb filter 200 having the intersection holes 20 shown in Fig. 5, rod-shaped spacers having the same dimensions as the intersections and the same length as the honeycomb segments 111 are placed to prevent the bonding material from entering the intersections formed by the four second outer peripheral walls 27b when bonding the honeycomb segments 111. The rod-shaped spacers are preferably made of wood, paper, resin, or other materials that are easily destroyed by fire. The rod-shaped spacers are preferably long enough to extend between both end faces 25a, 25b.

[0058] After drying the adhesive layer 19 between the honeycomb segments 111, it is fired in an oxidizing atmosphere at a temperature of 1100 to 1350°C, whereby the rod-shaped spacers are burned away and a sintered body (precursor of the honeycomb filter) having intersecting voids 20 is formed.

[0059] The outer periphery of the obtained sintered body is machined into a circle using a lathe, and then a skin material containing silicon carbide particles and an inorganic binder is applied to the circular outer periphery to form the skin 11, which is then dried to obtain the silicon carbide-based honeycomb filter 200.

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

[0061] Example 1: A molding raw material consisting of 100% silicon carbide particles, 5.9% alumina particles, and 4.1% magnesium hydroxide particles was mixed with 10% hydroxypropyl methylcellulose as an organic binder. Water was added to the resulting mixture at a ratio of 35% by mass per 100% of the molding raw material, and the mixture was kneaded. The resulting plastic clay was extruded from a mold of a screw molding machine to form a honeycomb segment molded body having a square cross section as shown in FIG. 2, which was then dried at 120°C for 2 hours in a hot air dryer. The end faces 15a and 15b of the cells 13 of the honeycomb segment molded body were then alternately plugged in a checkerboard pattern with a plugging material having the same composition as the clay, and the resulting honeycomb segment molded body was dried to form inlet-side plugging portions 16a and outlet-side plugging portions (not shown).

[0062] A laminating material slurry was produced by mixing and kneading 100% by mass of silicon carbide particles with 5.9% by mass of alumina particles, 4.1% by mass of magnesium hydroxide particles, 4.0% by mass of foamed resin as a pore-forming material, 8.0% by mass of colloidal silica, 10% by mass of hydroxypropyl methylcellulose as an organic binder, and 30% by mass of water. This laminating material slurry was applied to the outer wall 17 of the honeycomb segment molded body, and then 6 × 6 honeycomb segment molded bodies were pressure-bonded and joined as shown in Figure 1.

[0063] After drying the laminating material, it was fired in an oxidizing atmosphere at a temperature of 1300°C, and the outer periphery of the resulting sintered body was machined into a circular shape using a lathe. An outer covering material containing silicon carbide particles and colloidal silica was applied to the circular outer periphery and dried to obtain a silicon carbide-based honeycomb filter 100 with an outer diameter of 190 mm and a total length of 203 mm. The honeycomb segment 111 constituting the honeycomb filter 100 had a square cross section with sides of 35 mm, a peripheral wall 17 thickness of 0.7 mm, a partition wall thickness of 8 mil (0.20 mm), and a cell density of 300 cpsi (46.5 cells / cm). 2 ) The thickness of the laminating material layer 19 between the honeycomb segments 111 was 2 mm.

[0064] Using this silicon carbide-based honeycomb filter, a Drop to Idle test was carried out, which consisted of the following steps: First, an air flow rate of 4.5 Nm was applied to the silicon carbide-based honeycomb filter fixed to a test stand. 3 / min, combustion soot with an average particle size of 0.11 μm was introduced at a rate of 1.57 g / h so that the amount of soot attached per liter of filter was 6 g. In order to reproduce the state where the vehicle suddenly stopped at the top of an uphill road (Drop to Idle), combustion gas was flowed into the honeycomb filter using the temperature control shown in FIG. 11, and combustion was stopped when the honeycomb filter inlet temperature reached 600 °C, allowing the inside of the filter to reach its maximum temperature. Thereafter, the honeycomb filter was removed and checked for any damage to the honeycomb filter. As a result, it was confirmed that no cracks or melting damage occurred in the silicon carbide-based honeycomb filter of Example 1.

[0065] Example 2 A puddle prepared in the same manner as in Example 1 was extruded from a die of a screw molding machine to form a honeycomb segment formed body in which the cross-sectional area of ​​the inlet cells was larger than the cross-sectional area of ​​the outlet cells, as shown in Fig. 3. The honeycomb segment formed body was dried in a hot air dryer at 120°C for 2 hours, and then plugging materials having the same composition as the puddle were alternately filled in a checkerboard pattern at the ends of the cells 23a and 23b, and dried to form inlet-side plugging portions 26a and outlet-side plugging portions (not shown).

[0066] A laminating material slurry prepared in the same manner as in Example 1 was applied to the outer peripheral wall of the honeycomb segment molded body, and 6 × 6 honeycomb segment molded bodies were bonded by pressure bonding. After drying the laminating material, it was fired in an oxidizing atmosphere at a temperature of 1300 °C, and the outer periphery of the obtained sintered body was machined into a circular shape using a lathe. An outer skin material containing silicon carbide particles and colloidal silica was applied to the circular outer periphery and dried to obtain a silicon carbide-based honeycomb filter with an outer diameter of 190 mm and a total length of 203 mm. The honeycomb segment 211 constituting the honeycomb filter had a square cross section with a side of 35 mm, an outer peripheral wall 17 thickness of 1.3 mm, a partition wall thickness of 8 mil (0.20 mm), and a cell density of 300 cpsi (46.5 cells / cm). 2) and the cross-sectional area of ​​the inlet cells 23b was 1.58 times the cross-sectional area of ​​the outlet cells 23a. The thickness of the laminating material layer between the honeycomb segments 211 was 2 mm.

[0067] The same drop to idle test as in Example 1 was carried out, and it was confirmed that the silicon carbide honeycomb filter of Example 2 had a lower maximum temperature than Example 1, and no cracks or melting damage occurred.

[0068] Example 3 The clay prepared in the same manner as in Example 1 was extruded from the mold of a screw molding machine and dried in a hot air dryer at 120°C for 2 hours to form a honeycomb segment molded body having an octagonal cross section with linear chamfers at an inclination angle of 45° on each corner of the square, and with the cross-sectional area of ​​the inlet cells being larger than the cross-sectional area of ​​the outlet cells, as shown in Figure 4(c). The outer periphery of the honeycomb segment molded body consisted of a first peripheral wall 27a corresponding to the sides of the square and a second peripheral wall 27b corresponding to the linear chamfers.

[0069] The end faces of the cells 23a, 23b of the honeycomb segment formed body were alternately plugged in a checkerboard pattern with a plugging material having the same composition as the clay, dried, and then fired at a temperature of 1300°C in an oxidizing atmosphere to obtain a honeycomb segment 211 having an inlet-side plugging portion 26a and an outlet-side plugging portion 26b.

[0070] When arranging the honeycomb segments 211 with the lattice-like gaps interposed therebetween, wooden rod-shaped spacers having a square cross section and the same length as the entire length of the honeycomb segments 211 were placed in advance at the intersections defined by the second outer peripheral walls 27b. The length of one side of the square cross section of the rod-shaped spacer was the length of the second outer peripheral wall 47b plus the thickness t1 of the lattice-like gaps (laminated material layer) × √2.

[0071] A laminating material slurry prepared in the same manner as in Example 1 was applied to the outer peripheral walls of the honeycomb segments 211 except for the rod-shaped spacers, and then 6 × 6 honeycomb segments 211 were pressure-bonded via the laminating material slurry. After drying the laminating material layer formed between the honeycomb segments 211, the laminating material layer was fired in an oxidizing atmosphere at a temperature of 1300°C to burn off the wooden rod-shaped spacers, thereby forming intersection holes 20 having a square cross section and extending axially between both end faces 25a, 25b as shown in Figure 5. The intersection holes 20 had a hole diameter t2 of 7 mm.

[0072] A plugging material was applied to one end face 25a of the intersection hole portion 20 to a depth of 1 mm, and the outer periphery of the honeycomb filter was machined into a circular shape using a lathe. An outer covering material containing silicon carbide particles and colloidal silica was applied to the obtained circular outer periphery and dried to obtain a silicon carbide-based honeycomb filter 200 having an outer diameter of 190 mm and a total length of 203 mm. The honeycomb segment 211 constituting the silicon carbide-based honeycomb filter 200 had an octagonal cross section with linear chamfers at 45° inclination angles on each corner of a 35 mm square, the length of the first peripheral wall 27a was 30 mm, the length of the second peripheral wall 27b was 4 mm, the thickness of the first peripheral wall was 1.3 mm, the maximum thickness L of the second peripheral wall was 2 mm, the thickness of the partition walls 22 was 8 mil (0.20 mm), and the cell density was 300 cpsi (46.5 cells / cm). 2 ) and the cross-sectional area of ​​the inlet cell 33b was 1.58 times that of the outlet cell 33b. The thickness of the laminating material layer was 2 mm.

[0073] The same drop to idle test as in Example 1 was carried out, and it was confirmed that the silicon carbide honeycomb filter of Example 3 had a lower maximum temperature than Example 2, and no cracks or melting damage occurred.

[0074] Comparative Example 1 A clay prepared in the same manner as in Example 1 was extruded from the mold of a screw molding machine to form a honeycomb segment molded body having the shape shown in Figures 9(a) and 9(b), and then dried in a hot air dryer at 120°C for 2 hours.

[0075] The end faces 45a, 45b of the cells 43 of the honeycomb segment 411 were alternately plugged in a checkerboard pattern with a plugging material having the same composition as the clay, dried, and then fired at a temperature of 1300°C in an oxidizing atmosphere to obtain a honeycomb segment 411 having inlet-side plugging portions 46a and outlet-side plugging portions 46b.

[0076] The laminating material slurry prepared in the same manner as in Example 1 was applied to the outer wall 47 of the honeycomb segment 411, and then 6 × 6 honeycomb segments 411 were pressure-bonded together via the laminating material, as shown in Fig. 8. After drying, the obtained honeycomb filter was fired in an oxidizing atmosphere at a temperature of 1300°C, and the outer periphery was machined into a circular shape using a lathe.

[0077] A skin material containing silicon carbide particles and colloidal silica was applied to the circumferential periphery of the honeycomb filter and dried to obtain a silicon carbide-based honeycomb filter 400 having an outer diameter of 190 mm and a total length of 203 mm. The honeycomb segment 411 constituting the honeycomb filter 400 had a square cross section with sides of 35 mm, a peripheral wall thickness of 0.2 mm, a partition wall 42 thickness of 8 mil (0.20 mm), and a cell density of 300 cpsi (46.5 cells / cm). 2 ) The thickness of the laminating material layer 49 was 2 mm.

[0078] The same drop to idle test as in Example 1 was carried out, and as a result, it was confirmed that the silicon carbide honeycomb filter of Comparative Example 1 had a higher maximum temperature than that of Example 1, and cracks and melting damage were generated.

[0079] 100, 200, 400: Silicon carbide-based honeycomb filter 111, 211, 411: Honeycomb segment 11, 21, 41, 51: Outer skin 12, 22, 42, 52: Partition wall 13a, 23a, 43a, 53a: Inlet-side plugged flow passage (outlet cell) 13b, 23b, 43b, 53b: Outlet-side plugged flow passage (inlet cell) 15a, 25a, 45a, 55a: One end face (inlet-side end face) 15b, 25b, 45b, 55b: Other end face (outlet-side end face) 16a, 26a, 46a, 56a: Inlet-side plugging portion 46b, 56b: Outlet-side plugging portion 17, 27, 47: Peripheral wall 17a, 27a: First peripheral wall 17b, 27b: Second peripheral wall 19, 29, 49: Laminating material layers 20, 20a, 20b, 20c: Intersection hole portion 30: Extrusion molding die 31: Supply hole 31a: First surface 32: Slit 32a: Second surface 32b: Third surface 32a1, 32a2, 32a3, 32a4: Corner portion of second surface 33a: Partition wall forming region 33b: Outer periphery region 35: Guide ring 36: Mask H: Step portion L: Maximum thickness of second outer periphery wall t1: Thickness of laminating material layer between first outer periphery walls t2: Hole diameter of intersection hole portion

Claims

1. A silicon carbide-based honeycomb filter comprising honeycomb segments having partition walls that form cells defining a plurality of flow paths extending in the axial direction between both end faces, plugging portions that alternately plug the end faces of the cells in a checkerboard pattern, and an outer peripheral wall, a laminating material layer filled in the lattice-like gaps between the honeycomb segments to join the honeycomb segments, and an outer skin surrounding the joined honeycomb segments, characterized in that the thickness of the outer peripheral wall is more than 1.5 times and not more than 9 times the thickness of the partition walls.

2. 2. The silicon carbide honeycomb filter according to claim 1, wherein the partition walls have a thickness of 0.17 mm to 0.31 mm.

3. 3. A silicon carbide-based honeycomb filter as described in claim 1 or 2, characterized in that, in a cross section perpendicular to the flow direction of the honeycomb segment, the cross-sectional area of ​​an inlet cell whose outlet end face is plugged is larger than the cross-sectional area of ​​an outflow cell whose inlet end face is plugged.

4. A silicon carbide-based honeycomb filter comprising honeycomb segments each having partition walls forming cells defining a plurality of flow paths extending in an axial direction between both end faces, plugging portions for alternately plugging the end faces of the cells in a checkerboard pattern, and an outer peripheral wall, a laminating material layer filled in lattice-like gaps between the honeycomb segments to bond the honeycomb segments, and an outer skin surrounding the bonded honeycomb segments, The outer shape of a cross section perpendicular to the flow path direction of each honeycomb segment is an octagonal shape formed by providing linear chamfered portions at each corner of a rectangle, and the octagonal shape is formed alternately with first peripheral walls corresponding to the sides of the rectangle and second peripheral walls corresponding to the linear chamfered portions, Among the lattice-like gaps between the laminated honeycomb segments, an intersection void portion having no lamination material is formed at an intersection portion where the second outer peripheral wall forms an outline, The thickness t of the laminate layer between the first peripheral walls 1 The hole diameter t of the crossing hole 2 The vacancy ratio (t 2 / t 1 ) is greater than 1.4, The thickness of the first peripheral wall of each honeycomb segment is more than 1.5 times and not more than 9 times the thickness of the partition wall. A silicon carbide honeycomb filter comprising:

5. 5. The silicon carbide based honeycomb filter according to claim 4, wherein the quadrangle constituting the first outer peripheral wall of the honeycomb segment is a square.

6. 6. The silicon carbide honeycomb filter according to claim 5, wherein the cross-sectional shape of the honeycomb segment is an octagon formed by providing chamfered portions having an inclination angle of 45° on each corner of a square.

7. 5. The silicon carbide honeycomb filter according to claim 4, wherein the intersection hole has a cross-sectional shape having an outline substantially in contact with the four opposing second outer peripheral walls.

8. 5. The silicon carbide honeycomb filter according to claim 4, wherein the cross-sectional shape of the intersecting hole is a square, octagon or circle.

9. The silicon carbide-based honeycomb filter according to claim 4, characterized in that a cross section of the second peripheral wall perpendicular to the flow direction has a triangular shape formed by the two vertical and horizontal partition walls closest to the second peripheral wall and the peripheral surface of the second peripheral wall, and the maximum thickness of the second peripheral wall defined by the distance between the central apex of the triangle and the peripheral surface is thicker than the thickness of the first peripheral wall.

10. 5. The silicon carbide honeycomb filter according to claim 4, wherein an inclination angle of each of the linear chamfered portions with respect to a side of the quadrangle is 45°.

11. 5. The silicon carbide honeycomb filter according to claim 4, wherein the partition walls have a thickness of 0.17 mm to 0.31 mm.

12. The silicon carbide-based honeycomb filter according to any one of claims 4 to 11, characterized in that, in a cross section perpendicular to the flow path direction of the honeycomb segment, a cross-sectional area of ​​an inlet cell whose outlet end face is plugged is larger than a cross-sectional area of ​​an outlet cell whose inlet end face is plugged.