Extrusion molding die for manufacturing honeycomb molded body for honeycomb segments constituting silicon carbide honeycomb filter, and method for manufacturing honeycomb molded body using the same

Abstract

To provide a production method for a mold suppressing generation of crack or melting defect generated in a honeycomb filter through heat impact by partial exothermic heat and acute temperature change in exhaust gas without increasing pressure loss and for a honeycomb molding.SOLUTION: A mold to form a honeycomb molding for a honeycomb segment with an outer peripheral wall thicker than a partition wall through extrusion is provided with a mold body and a guide ring attached on an outer peripheral side of the mold body. The mold body comprises: a first surface where a cray supply hole opens; a second surface placed opposite to the first surface, where grate slits in communication with the cray supply hole opens; and a third surface positioned at an opposite side of the first surface and at an outer periphery of the second surface, the second surface constitutes an area forming a grid-like partition wall in a honeycomb body, the third surface constitutes an outer peripheral area forming the outer peripheral wall, the second surface is higher than the third surface by a step part H, and the guide ring has a gap between the third surface and itself and an opening with an enough size to cover the outer peripheral side part of the outer peripheral area.SELECTED DRAWING: Figure 7(b)

Description

[Technical Field]

[0001] The present invention relates to an extrusion molding die for manufacturing honeycomb molded bodies for honeycomb segments that constitute silicon carbide-based honeycomb filters that remove particulate matter (PM) and the like from exhaust gases emitted from internal combustion engines such as diesel engines and purify the exhaust gases, and a method for manufacturing honeycomb molded bodies using the same. [Background technology]

[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 opening at the exhaust gas inlet-side end face 55a, passes through the communication holes present on the surface and inside of the partition wall 52, flows into the adjacent inlet-side sealed flow passage 53a, and flows out from the exhaust gas outlet-side end face 55b. As the exhaust gas passes through the communication holes present on the surface and inside of the partition wall 52, PM in the exhaust gas is captured, and the exhaust gas is purified. 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 harsher, 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 multiple columnar honeycomb segments are bonded together via a bonding material layer, each honeycomb segment having partition walls that form multiple 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 a plurality of rectangular pillar-shaped honeycomb segments arranged in a lattice pattern, a bonding material layer bonding the side surfaces of the honeycomb segments to each other, and an outer wall surrounding the honeycomb segments, where each honeycomb segment has porous partition walls surrounding a plurality of cells extending axially from the inflow end face to the outflow end face, and an outer wall surrounding the partition walls, and the cells are plugged at either the inflow end face or the outflow end face with plugging portions, and bottomed hollow voids extending axially are formed at some or all of the intersections of the lattice-shaped bonding material layer, where 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. Thus, there are no examples where deep voids are provided at all of the intersections.

[0008] Furthermore, Patent Document 2 only describes circular cross-sectional shapes for the voids, 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 there are 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. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent Publication No. 2021-133283 [Patent Document 2] Japanese Patent Application Publication No. 2019-171238 Summary of the Invention [Problem to be solved by the invention]

[0011] Therefore, an object of the present invention is to provide an extrusion molding die for producing honeycomb molded bodies for honeycomb segments that constitute silicon carbide-based honeycomb filters, which can suppress the occurrence of cracks and melting damage in honeycomb filters due to thermal shock caused by localized heat generation or sudden temperature changes in exhaust gases, without increasing pressure loss, and a method for producing honeycomb molded bodies using the same. [Means for solving the problem]

[0012] As a result of intensive research to achieve the above-mentioned object, the 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 due to thermal shock caused by localized heat generation or sudden temperature changes in exhaust gas, without increasing pressure loss, and (2) deformation of the partition wall, which may occur when extruding a clay for a honeycomb molded body to form an outer wall thicker than the partition wall, can be prevented by attaching a guide ring of a desired structure to the outer periphery of the mold body of the extrusion molding mold, and thus conceived the present invention.

[0013] That is, the extrusion molding die of the present invention, which extrudes a honeycomb formed body for a honeycomb segment, has lattice-like partition walls and an outer peripheral wall that form cells that define a plurality of flow paths extending in the axial direction between both end faces, and the outer peripheral wall is thicker than the partition walls, The mold includes a mold body and a guide ring attached to the outer periphery of the mold body, The mold body has a first surface in which moldable material supply holes are opened, a second surface opposite to the first surface in which lattice-shaped slits communicating with the moldable material supply holes are opened, and a third surface opposite to the first surface and located on the outer periphery of the second surface in which lattice-shaped slits communicating with the moldable material supply holes are opened, the second surface constitutes an area for forming lattice-shaped partition walls of the honeycomb formed body, the third surface constitutes an outer peripheral region that forms the outer peripheral wall, the second surface is higher than the third surface by a step; the guide ring has a gap between itself and the third surface and has an opening of a size that covers an outer peripheral portion of the outer peripheral region, The step portion H extends in the extrusion direction of the honeycomb formed body, Opposing the step portion H of the guide ring Side The inner surface is extrusion direction The distance between the step portion H and the inner circumferential surface of the guide ring is smallest as the distance between the step portion H and the inner circumferential surface of the guide ring increases. The end opposite to the extrusion direction The portion is located lower than the second surface.

[0014] The second surface preferably has a square outline.

[0015] It is preferable that a mask is fixed to the outer periphery of the first surface, and that the mask has a gap between itself and the first surface and has a structure that covers the outer periphery of the first surface.

[0016] The second surface is preferably located higher than the opening of the guide ring.

[0017] It is preferable that the four corners of the second surface are flush with the outer peripheral region, and that the opening of the guide ring is square and has triangular closing portions at the four corners.

[0018] The method of the present invention for producing a honeycomb formed body for a honeycomb segment using the above-mentioned extrusion molding die, which has lattice-like partition walls that form cells that define a plurality of flow paths extending in the axial direction between both end faces and an outer peripheral wall, and wherein the outer peripheral wall is thicker than the partition walls, comprises: When the clay that has flowed into the clay supply hole of the extrusion molding die is allowed to flow out through the slit, the flow direction of the clay flowing out from the outer peripheral region is changed by the guide ring toward the partition wall forming region, and then changed to the extrusion direction by the step portion, thereby preventing deformation of the partition wall due to the clay flowing from the outer peripheral region and producing a honeycomb molded body with a thick outer peripheral wall. [Effects of the Invention]

[0019] The extrusion molding die of the present invention has a guide ring attached to the outer peripheral side of the die body, and the guide ring has a gap between it and the third surface that constitutes the outer peripheral region that forms the outer peripheral wall, and has an opening of a size that covers the outer peripheral portion of the outer peripheral region, and the second surface that constitutes the region that forms the lattice-shaped partition walls of the honeycomb molded body is higher than the third surface by the amount of a step.Therefore, the flow direction of the puddle flowing out from the outer peripheral region is changed by the guide ring toward the partition wall forming region, and then changed by the step to the extrusion direction, thereby making it possible to produce a honeycomb molded body with a thick outer peripheral wall while preventing deformation of the partition walls due to the puddle flowing from the outer peripheral region. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a perspective view schematically showing an example of a silicon carbide-based honeycomb filter that can be manufactured using the mold of the present invention. [Figure 2] FIG. 2 is a perspective view schematically showing an example of a honeycomb segment used in a silicon carbide-based honeycomb filter. [Figure 3] FIG. 10 is a front view schematically showing another example of a honeycomb segment. [Figure 4(a)] FIG. 10 is a front view schematically showing still another example of a honeycomb segment. [Figure 4(b)] FIG. 10 is a front view schematically showing still another example of a honeycomb segment. [Figure 4(c)] FIG. 10 is a front view schematically showing still another example of a honeycomb segment. [Figure 4(d)] FIG. 5 is a partial front view showing in detail the second outer peripheral wall of the honeycomb segment of FIG. 4(b). [Figure 5] FIG. 3 is a perspective view schematically showing another example of a silicon carbide-based honeycomb filter that can be manufactured using the mold of the present invention. [Figure 6(a)] FIG. 10 is a partial cross-sectional view showing an example of an intersection hole portion. [Figure 6(b)] FIG. 10 is a partial cross-sectional view showing another example of an intersection hole portion. [Figure 6(c)] FIG. 10 is a partial cross-sectional view showing yet another example of an intersection hole portion. [Figure 7(a)] FIG. 2 is a front view schematically showing a die of the present invention for extrusion-molding a honeycomb segment. [Figure 7(b)] FIG. 7B is a cross-sectional view taken along line BB in FIG. [Figure 7(c)] FIG. 7(b) is a partially enlarged view of FIG. [Figure 7(d)] FIG. 10 is a front view schematically showing a die of the present invention 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. [Figure 8] FIG. 1 is a perspective view schematically showing a conventional silicon carbide honeycomb filter having a divided structure. [Figure 9(a)] FIG. 1 is a perspective view schematically showing a conventional honeycomb segment. [Figure 9(b)] FIG. 9( a ) is a cross-sectional view taken along the line AA in FIG. 9( a ). [Figure 10(a)] FIG. 1 is a front view schematically showing an example of a conventional silicon carbide-based honeycomb filter. [Figure 10(b)]FIG. 10( a ) is a cross-sectional view parallel to the axial direction showing the silicon carbide-based honeycomb filter of FIG. [Figure 11] 10 is a graph showing temperature control in a Drop to Idle test. DETAILED DESCRIPTION OF THE INVENTION

[0021] 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.

[0022] [1] Silicon carbide honeycomb filter 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.

[0023] The silicon carbide-based honeycomb filter 100 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, so that even if unevenly deposited PM is burned during regeneration of the honeycomb filter 100 and a localized temperature rise occurs, cracks and melting damage can be suppressed.

[0024] If the thickness of the outer peripheral 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. On the other hand, if the thickness of the outer peripheral 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 peripheral 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.

[0025] 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.

[0026] 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 makes it possible to provide a honeycomb filter in which pressure loss when PM is trapped is less likely to increase. 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.

[0027] 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 unchamfered quadrangular shape (square shape) 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).

[0028] 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.

[0029] 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.

[0030] 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 at 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.

[0031] 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.

[0032] 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."

[0033] 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.

[0034] 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."

[0035] 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.

[0036] 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 2The 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 that have occurred 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-section 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.

[0037] The octagonal cross section of the cross-section 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 ) from the formula for the cross-sectional area. 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, so that it is possible to achieve both a cross-sectional area sufficient to sufficiently suppress cracks and bonding strength.

[0038] 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 hole 20c has a sufficient cross-sectional area, the hole ratio t2 / t1 is preferably 1.5 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 20c having a circular cross section is preferably in the range of 1.5 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 20c having a circular cross section has a sufficiently large cross-sectional area and hardly penetrates into the laminating material layer 19, so that it is possible to achieve both a cross-sectional area sufficient to sufficiently suppress cracking and bonding strength.

[0039] To summarise the range of the void ratio t2 / t1 of the voids at the intersections 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.

[0040] 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 intersection voids 20 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 intersection voids 20 is preferably 100% of all intersections, but may be 95% or less.

[0041] [2] Manufacturing method for silicon carbide honeycomb filters (1) Manufacturing of honeycomb segments 5 to 15 mass% of an organic binder is mixed with 100 mass% of a forming raw material consisting of silicon carbide particles, alumina particles, and magnesium hydroxide particles. 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 mass% with respect to 100 mass% of the silicon carbide particles.

[0042] 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.

[0043] Water is added to the resulting mixture and kneaded to form a plastic clay. To obtain a moldable clay with a hardness, the amount of water added is preferably 20 to 50% by mass relative to 100% by mass of the molding raw material.

[0044] The molded material is extrusion molded using a mold 30 of the present invention 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.

[0045] 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.

[0046] 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 using, for example, 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.

[0047] The obtained honeycomb formed body is dried, and then processed as necessary to the end faces, outer 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 thereof include hot air drying, microwave heating drying, and high-frequency heating drying.

[0048] (2) Honeycomb filter manufacturing 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 mass% relative to 100 mass% of the silicon carbide particles.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] After drying the laminating material 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 pores 20 is formed.

[0056] 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.

[0057] 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.

[0058] Example 1 A molding raw material consisting of 100% by mass of silicon carbide particles, 5.9% by mass of alumina particles, and 4.1% by mass of magnesium hydroxide particles was mixed with 10% by mass of hydroxypropyl methylcellulose as an organic binder. Water was added to the resulting mixture at a ratio of 35% by mass per 100% by mass of the molding raw material, and the mixture was kneaded. The resulting plastic clay was extruded from a die of a screw molding machine to form a honeycomb segment molded body having a square cross section as shown in FIG. 2, and dried at 120°C for 2 hours in a hot air dryer. Thereafter, the end faces 15a and 15b of the cells 13 of the honeycomb segment molded body were alternately plugged in a checkerboard pattern with a plugging material having the same composition as the clay, and then dried to form inlet-side plugging portions 16a and outlet-side plugging portions (not shown).

[0059] 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 peripheral 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.

[0060] 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.

[0061] 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 a vehicle suddenly stops 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.

[0062] Example 2 The clay 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 clay 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).

[0063] 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.

[0064] 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.

[0065] 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 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.

[0066] 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.

[0067] When arranging the honeycomb segments 211 via the lattice gaps, 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 formed 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 + the thickness t1 of the lattice gaps (laminar layer) × √2.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] Comparative Example 1 The 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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. [Explanation of symbols]

[0076] 100, 200, 400: Silicon carbide honeycomb filter 111, 211, 411: Honeycomb segments 11, 21, 41, 51: Outer skin 12, 22, 42, 52: Bulkhead 13a, 23a, 43a, 53a: inlet-side sealed flow channel (outlet cell) 13b, 23b, 43b, 53b: Outlet-side sealed flow channel (inlet cell) 15a, 25a, 45a, 55a: One end face (inlet end face) 15b, 25b, 45b, 55b: other end face (outlet end face) 16a, 26a, 46a, 56a: Inflow side plugging part 46b, 56b: Outflow side plugging part 17, 27, 47: Outer wall 17a, 27a: First outer wall 17b, 27b: Second outer wall 19, 29, 49: Laminating material layer 20, 20a, 20b, 20c: Intersection hole 30: Extrusion molding die 31: Supply hole 31a: First side 32: Slit 32a: Second Side 32b: The Third Side 32a1, 32a2, 32a3, 32a4: Corners of the second surface 33a: Partition formation area 33b: Outer area 35: Guide ring 35a1, 35a2, 35a3, 35a4: Blocked area 36: Mask H: Multi-layered section L: Maximum thickness of the second outer wall t1: Thickness of the laminate layer between the first outer walls t2: Hole diameter of the crossing hole

Claims

1. A die for extrusion-molding a honeycomb formed body for a honeycomb segment, the die having an outer peripheral wall and lattice-like partition walls that form cells that define a plurality of flow paths extending in an axial direction between both end faces, the outer peripheral wall being thicker than the partition walls, The mold includes a mold body and a guide ring attached to the outer periphery of the mold body, The mold body has a first surface in which moldable material supply holes are opened, a second surface opposite to the first surface in which lattice-shaped slits communicating with the moldable material supply holes are opened, and a third surface opposite to the first surface and located on the outer periphery of the second surface in which lattice-shaped slits communicating with the moldable material supply holes are opened, the second surface constitutes an area for forming lattice-shaped partition walls of the honeycomb formed body, the third surface constitutes an outer peripheral region that forms the outer peripheral wall, the second surface is higher than the third surface by a step H, the guide ring has a gap between itself and the third surface and an opening having a size that covers an outer peripheral portion of the outer peripheral region, The step portion H extends in the extrusion direction of the honeycomb molded body, and the inner surface of the guide ring facing the step portion H is inclined so that the distance between the step portion H and the inner surface increases as the extrusion direction progresses, and the end of the inner surface of the guide ring opposite the extrusion direction, where the distance between the step portion H and the inner surface is the smallest, is located at a lower position than the second surface.

2. 2. The extrusion die according to claim 1, wherein the second surface has a square outline.

3. 2. The extrusion molding die according to claim 1, wherein a mask is fixed to the outer peripheral side of the first surface, and the mask has a gap between itself and the first surface and has a structure that covers the outer peripheral portion of the first surface.

4. 2. The extrusion molding die according to claim 1, wherein the four corners of the second surface are at the same height as the outer peripheral region, and the opening of the guide ring is square and has triangular blocking portions at the four corners.

5. A method for manufacturing a honeycomb formed body for a honeycomb segment, which has lattice-like partition walls that form cells that define a plurality of flow paths extending in an axial direction between both end faces and an outer peripheral wall, and the outer peripheral wall is thicker than the partition walls, using the extrusion molding die according to claim 1, A method characterized by the fact that, when the clay that has flowed into the clay supply hole of the extrusion molding die is made to flow out through the slit, the flow direction of the clay flowing out from the outer peripheral region is changed toward the partition wall formation region by the guide ring, and then changed to the extrusion direction by the step portion H, thereby preventing deformation of the partition walls due to the clay flowing out from the outer peripheral region and producing a honeycomb molded body with a thick outer peripheral wall.

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