Method for manufacturing a honeycomb structure and honeycomb structure

Abstract

Provided are a method for manufacturing a honeycomb structure and a honeycomb structure. The method includes: a step of extruding a green body to produce a honeycomb molded body; a step of drying to obtain a honeycomb dried body; and a step of firing to obtain a honeycomb fired body having a partition wall thickness of 50 μm to 210 μm and a partition wall porosity of 45% to 60%. The pore-forming material in the green body contains cross-linked starch and an acrylic polymer. In the green body, 1.0 parts by mass or more of cross-linked starch is contained in 100 parts by mass of ceramic raw material, with the content of P being less than 0.2 parts by mass. The honeycomb structure has a peripheral side wall and a partition wall, the partition wall is arranged at the inner periphery of the peripheral side wall and divides a plurality of cells, the thickness of the partition wall is 50 μm to 210 μm, the porosity is 45% to 60%, the content of P in the honeycomb structure is 0.01% by mass or more and less than 0.2% by mass, and the isostatic compressive strength is 1.0 MPa or more.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a honeycomb structure and the honeycomb structure. Background Art

[0002] Honeycomb structures are used as filters for collecting particulate matter in exhaust gas discharged from internal combustion engines such as diesel engines, and as catalyst supports for purifying toxic gas components such as CO, HC, and NOx.

[0003] Typically, a honeycomb structure comprises an outer peripheral sidewall and partition walls disposed on the inner circumference of the outer peripheral sidewall and defining a plurality of cells that form a flow path from a first bottom surface to a second bottom surface. A honeycomb structure can be manufactured by kneading a raw material composition obtained by appropriately adding various additives to a ceramic raw material, a pore-forming material, a binder, and a dispersion medium to form a green body. The green body is then extruded through a die defining a predetermined cell structure to produce a honeycomb formed body. The formed body is then cut into predetermined lengths, dried, and then fired.

[0004] In recent years, with the strengthening of exhaust gas restrictions, stricter PM emission standards (PN restrictions: Particle Matter number restrictions) have been introduced, and filters are required to have high PM capture performance (PN high capture efficiency). In addition, the catalyst carrier is also required to be able to quickly heat up to the active temperature of the catalyst by reducing the heat capacity. On the other hand, the honeycomb structure is also required to have a low pressure loss when the exhaust gas flows in, and the difficulty of developing filters that can meet market requirements has increased. In order to obtain a honeycomb structure that meets such required performance, research has been conducted on "thin-walling" to thin the thickness of the partition wall of the honeycomb structure, and "high porosity" to further increase the porosity of the partition wall compared to the past (Patent Document 1).

[0005] However, as the thinning of honeycomb structures progresses, the extrusion molding pressure required to extrude the clay through the extremely narrow die slots has also increased, reaching the limits of the extruder. Therefore, technologies are needed to reduce extrusion molding pressure. In this regard, Patent Document 2 describes that if the amylose ratio of the starch added to the raw material composition is high, the fluidity is improved and the molding pressure is reduced. In particular, it is disclosed that the extrusion molding pressure can be reduced when the amylose:amylopectin ratio is 40:60 to 80:20.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application No. 2007-507667

[0009] Patent Document 2: International Publication No. 2017 / 095916 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] Starch is useful as a component for obtaining a honeycomb structure with high porosity. Therefore, it is believed that when producing a thin-walled and high-porosity honeycomb structure, adding starch at the ratio of amylose to amylopectin described in Patent Document 2 is effective. However, even if the extrusion molding pressure can be reduced by adding starch with an adjusted ratio of amylose to amylopectin to the raw material composition, the strength of the honeycomb structure produced thereby is still insufficient. In particular, the strength of a thin-walled and high-porosity honeycomb structure tends to decrease, so it would be advantageous if this problem could be solved.

[0012] The present invention has been made in light of the above circumstances. One embodiment of the present invention provides a method for producing a thin-walled, high-porosity, and excellent-strength honeycomb structure without placing excessive strain on an extruder. Another embodiment of the present invention provides a thin-walled, high-porosity, and excellent-strength honeycomb structure.

[0013] Methods for solving problems

[0014] The present inventors have conducted intensive research to solve the above-mentioned problems and have found that a combination of an acrylic acid-based polymer and a cross-linked starch is effective as a pore-forming material. The present invention has been completed based on this finding and is exemplified below.

[0015] (1. Method for Manufacturing Honeycomb Structure)

[0016] [Method 1]

[0017] A method for manufacturing a honeycomb structure, wherein the honeycomb structure has an outer peripheral side wall and partition walls, the partition walls are arranged on the inner peripheral side of the outer peripheral side wall and divide a plurality of cells that form a flow path from a first bottom surface to a second bottom surface. The manufacturing method is characterized in that it includes: a step of extruding a molded body containing a ceramic raw material, a pore-forming material, a binder and a dispersion medium through a die having an opening shape defining the plurality of cells, thereby producing a honeycomb formed body; a step of drying the honeycomb formed body to obtain a honeycomb dried body; and a step of firing the honeycomb dried body to obtain a honeycomb fired body having a partition wall thickness of not less than 50 μm and not more than 210 μm and a partition wall porosity of 45% to 60%; the pore-forming material in the molded body contains cross-linked starch and an acrylic polymer, and the molded body contains 1.0 mass part or more of cross-linked starch relative to 100 mass parts of the ceramic raw material under the condition that the P content is less than 0.2 mass part.

[0018] [Method 2]

[0019] The production method according to aspect 1, wherein the kneaded clay contains 1.0 part by mass or more of cross-linked starch with respect to 100 parts by mass of the ceramic raw material under the condition that the P content is 0.1 part by mass or less.

[0020] [Method 3]

[0021] The production method according to aspect 1, wherein the kneaded clay contains 1.0 part by mass or more of cross-linked starch with respect to 100 parts by mass of the ceramic raw material under the condition that the P content is 0.05 parts by mass or less.

[0022] [Method 4]

[0023] The production method according to any one of aspects 1 to 3, wherein the P content in the honeycomb structure is less than 0.2% by mass.

[0024] [Method 5]

[0025] The production method according to any one of aspects 1 to 3, wherein a P content in the honeycomb structure is 0.1% by mass or less.

[0026] [Method 6]

[0027] The production method according to any one of aspects 1 to 3, wherein a P content in the honeycomb structure is 0.05 mass % or less.

[0028] [Method 7]

[0029] The production method according to any one of aspects 1 to 6, wherein the kneaded clay contains 0.5 parts by mass or more of the acrylic polymer per 100 parts by mass of the ceramic raw material.

[0030] [Method 8]

[0031] The production method according to any one of aspects 1 to 7, wherein the ceramic raw material is a cordierite-forming raw material.

[0032] (2. Honeycomb structure)

[0033] [Method 1]

[0034] A honeycomb structure having an outer peripheral side wall and partition walls, wherein the partition walls are arranged on the inner peripheral side of the outer peripheral side wall and divide a plurality of cells forming a flow path from a first bottom surface to a second bottom surface, the thickness of the partition walls is greater than or equal to 50 μm and less than or equal to 210 μm, the porosity of the partition walls is 45% to 60%, the P content in the honeycomb structure is greater than or equal to 0.01 mass% and less than 0.2 mass%, and the isostatic pressure fracture strength is greater than or equal to 1.0 MPa.

[0035] [Method 2]

[0036] The honeycomb structure according to aspect 1, wherein an upper limit of a P content in the honeycomb structure is 0.1 mass % or less.

[0037] [Method 3]

[0038] The honeycomb structure according to aspect 1, wherein an upper limit of a P content in the honeycomb structure is 0.05 mass % or less.

[0039] [Method 4]

[0040] The honeycomb structure according to any one of aspects 1 to 3, wherein the outer peripheral side walls and the partition walls contain cordierite.

[0041] Effects of the Invention

[0042] According to one embodiment of the present invention, a thin-walled, high-porosity, and excellent-strength honeycomb structure can be produced with high productivity without placing excessive burden on the extruder. The honeycomb structure is suitable for use as a filter or catalyst carrier, and is particularly useful as a filter requiring high capture performance (PN high capture efficiency) or a catalyst carrier requiring a high heating rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a perspective view schematically showing a wall-through type honeycomb structure.

[0044] Figure 2 This is a schematic cross-sectional view of a wall-through type honeycomb structure observed in a cross section parallel to the direction in which cells extend.

[0045] Figure 3 It is a perspective view schematically showing a wall-flow type honeycomb structure.

[0046] Figure 4 This is a schematic cross-sectional view of a wall-flow type honeycomb structure observed in a cross section parallel to the direction in which cells extend.

[0047] Figure 5 This is a schematic partial enlarged view of a partition wall of a wall-flow type honeycomb structure observed in a cross section perpendicular to the cell extending direction.

[0048] Description of Reference Numerals

[0049] 100: honeycomb structure, 102: outer peripheral side wall, 103: side surface, 104: first bottom surface, 106: second bottom surface, 108: cell, 112: partition wall, 200: honeycomb structure, 202: outer peripheral side wall, 203: side surface, 204: first bottom surface, 206: second bottom surface, 208a: first cell, 208b: second cell, 209: sealing portion, 212: partition wall. DETAILED DESCRIPTION

[0050] Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood that the present invention is not limited to the following embodiments, and that design changes and improvements may be appropriately made based on the common knowledge of those skilled in the art without departing from the spirit of the present invention.

[0051] <1. Honeycomb structure>

[0052] In one embodiment, the honeycomb structure of the present invention is provided as a wall-through type or wall-flow type honeycomb structure. The use of the honeycomb structure is not particularly limited. For example, it can be used for various industrial uses such as radiators, filters (e.g., GPF, DPF), catalyst carriers, sliding parts, nozzles, heat exchangers, electrical insulation parts, and parts for semiconductor manufacturing equipment. Among them, it can be suitable for use as a filter for capturing particulate matter contained in exhaust gas from internal combustion engines, boilers, etc., and a catalyst carrier for exhaust gas purification catalyst. In particular, the porous honeycomb structure can be suitable for use as an exhaust gas filter and / or catalyst carrier for automobiles.

[0053] exist Figure 1 and Figure 2 , a schematic perspective view and a cross-sectional view of a honeycomb structure 100 that can be used as a wall-through automotive exhaust gas filter and / or catalyst carrier are shown. The honeycomb structure 100 includes an outer peripheral sidewall 102 and partition walls 112. The partition walls 112 are disposed on the inner circumference of the outer peripheral sidewall 102 and define a plurality of parallel cells 108 that form a fluid flow path from a first bottom surface 104 to a second bottom surface 106. The outer surface of the outer peripheral sidewall 102 forms the side surface 103 of the honeycomb structure 100. In the honeycomb structure 100, each cell 108 is open at both ends. Exhaust gas flowing from the first bottom surface 104 into a cell 108 is purified while passing through the cell and then flows out from the second bottom surface 106. It should be noted that, here, the first bottom surface 104 is set as the upstream side of the exhaust gas, and the second bottom surface 106 is set as the downstream side of the exhaust gas, but the distinction between the first bottom surface and the second bottom surface is for convenience, and the second bottom surface 106 can also be set as the upstream side of the exhaust gas, and the first bottom surface 104 can be set as the downstream side of the exhaust gas.

[0054] exist Figure 3 and Figure 42 shows a schematic perspective view and a cross-sectional view of a honeycomb structure 200 that can be used as a wall-flow automotive exhaust gas filter and / or catalyst carrier. The honeycomb structure 200 includes an outer peripheral sidewall 202 and partition walls 212. The partition walls 212 are disposed on the inner circumference of the outer peripheral sidewall 202 and define a plurality of cells 208a and 208b that form a fluid flow path from a first bottom surface 204 to a second bottom surface 206. The outer surface of the outer peripheral sidewall 202 forms a side surface 203 of the honeycomb structure 200.

[0055] In the honeycomb structure 200, the plurality of cells 208a and 208b can be categorized as: a plurality of parallel first cells 208a extending from the first bottom surface 204 to the second bottom surface 206, open on the first bottom surface 204, and having plugging portions 209 on the second bottom surface 206; and a plurality of parallel second cells 208b disposed on the inner side of the outer peripheral sidewall 202, extending from the first bottom surface 204 to the second bottom surface 206, having plugging portions 209 on the first bottom surface 204, and open on the second bottom surface 206. Furthermore, in the honeycomb structure 200, the first cells 208a and the second cells 208b are alternately arranged adjacent to each other with partition walls 212 interposed therebetween.

[0056] When exhaust gas containing particulate matter such as soot is supplied to the first bottom surface 204 on the upstream side of the honeycomb structure 200, the exhaust gas is introduced into the first cells 208a and flows downstream within the first cells 208a. Because the first cells 208a have a sealing portion 209 on the downstream second bottom surface 206, the exhaust gas flows through the partition wall 212 that separates the first cells 208a from the second cells 208b and into the second cells 208b. Since the particulate matter cannot pass through the partition wall 212, it is trapped and accumulates within the first cells 208a. After the particulate matter is removed, the clean exhaust gas that has flowed into the second cells 208b flows downstream within the second cells 208b and flows out through the downstream second bottom surface 206. It should be noted that, here, the first bottom surface 204 is set as the upstream side of the exhaust gas, and the second bottom surface 206 is set as the downstream side of the exhaust gas, but the distinction between the first bottom surface and the second bottom surface is for convenience, and the second bottom surface 206 can also be set as the upstream side of the exhaust gas, and the first bottom surface 204 can be set as the downstream side of the exhaust gas.

[0057] The honeycomb structure can be, for example, cylindrical. The bottom shape of the honeycomb structure is not limited and can be, for example, circular, elliptical, racetrack-shaped, arc-shaped, such as an oblong, polygonal, such as a triangle or a quadrilateral, or other special shapes. The bottom shape of the illustrated honeycomb structure is circular, and the overall shape is cylindrical.

[0058] The height of the honeycomb structure (the length from the first bottom surface to the second bottom surface) is not particularly limited and can be appropriately set according to the use and required performance. The height of the honeycomb structure can be set to, for example, 40 mm to 450 mm. The relationship between the height of the honeycomb structure and the maximum diameter of each bottom surface (the maximum length among the diameters passing through the centers of gravity of each bottom surface of the honeycomb structure) is also not particularly limited. Thus, the height of the honeycomb structure can be longer than the maximum diameter of each bottom surface, and the height of the honeycomb structure can be shorter than the maximum diameter of each bottom surface.

[0059] The cell density of the honeycomb structure (the number of cells per unit cross-sectional area in the direction perpendicular to the direction in which the cells extend) is not particularly limited and can be set to, for example, 6 to 2000 cells / inch2(0.9 to 311 cells / cm2 2 ), further preferably 50 to 1000 cells / inch2(7.8 to 155 cells / cm2 2 ), and particularly preferably 100 to 600 cells / inch2(15.5 to 92.0 cells / cm2 2 ). Here, the cell density is calculated by dividing the number of cells in the entire bottom surface (in the case where there are cells that are plugged, the number of cells is calculated as if the cells are not plugged) by the area of one bottom surface of the honeycomb structure excluding the outer peripheral side wall.

[0060] The thickness of the partition wall in the honeycomb structure is preferably 210 μm or less, more preferably 150 μm or less, and further preferably 100 μm or less, from the viewpoint of suppressing pressure loss and reducing the heat capacity by thinning the wall. In addition, the thickness of the partition wall in the honeycomb structure is preferably 50 μm or more, more preferably 60 μm or more, and further preferably 70 μm or more, from the viewpoint of ensuring strength.

[0061] Figure 5 A schematic partial enlarged view of the partition wall 212 of the honeycomb structure 200 when the wall flow type is observed in the cross section orthogonal to the direction in which the cells extend is shown in FIG. 2. The thickness of the partition wall refers to the length of the line segment N that passes through the partition wall when the centers of gravity C of adjacent cells are connected to each other by the line segment N in the cross section orthogonal to the direction in which the cells extend (the height direction of the honeycomb structure).

[0062] From the viewpoint of suppressing pressure loss and reducing heat capacity by increasing porosity, the porosity of the partition walls is preferably 45% or more, more preferably 50% or more. In addition, from the viewpoint of ensuring the strength of the thin-walled honeycomb structure, the upper limit of the porosity of the partition walls is preferably 60% or less, more preferably 55% or less. Therefore, the porosity of the partition walls is preferably, for example, 45% to 60%, more preferably 50% to 55%. The porosity is measured by mercury intrusion using a mercury porosimeter. The mercury intrusion method is specified in JIS R1655:2003. In this specification, partition wall samples of the honeycomb structure (cubes with a length × width × height = about 13 mm × about 13 mm × about 13 mm) are taken from two locations, near the radial center and near the periphery of the center in the height direction, and the porosity is measured by mercury intrusion, and the average value is used as the measured value.

[0063] The material for the partition wall and the peripheral side wall of the honeycomb structure is not limited, and porous ceramics can be cited. As the type of ceramics, cordierite, mullite, zirconium phosphate, aluminum titanate, silicon carbide (SiC), silicon-silicon carbide composite materials (example: Si combined with SiC), cordierite-silicon carbide composite materials, zirconium oxide, spinel, India stone, sapphire, corundum, titanium dioxide, silicon nitride, etc. can be cited. Moreover, these ceramics can contain one alone or two or more.

[0064] To enhance thermal shock resistance, the partition walls and outer sidewalls of the honeycomb structure preferably contain cordierite. The mass fraction of cordierite in the honeycomb structure is preferably 50% by mass or greater, preferably 70% by mass or greater, and preferably 90% by mass or greater. In a porous honeycomb structure containing cordierite, the mass fraction of cordierite may be substantially 100% by mass, excluding unavoidable impurities.

[0065] In the honeycomb structure, some of the raw materials blended into the raw material composition may remain. As described later, a crosslinking agent containing phosphorus (P) is sometimes used in crosslinked starch. However, if the crosslinking agent contains a large amount of P, aggregates will form in the clay, which can easily lead to increased extrusion molding pressure. Therefore, when the P content in the crosslinked starch used as the pore-forming material is low, the extrusion molding pressure can be reduced, and the residual P concentration in the honeycomb structure is also low.

[0066] Therefore, in one embodiment, the P content in the honeycomb structure is less than 0.2% by mass, preferably less than 0.1% by mass, and more preferably less than 0.05% by mass. From the perspective of improving the effect of reducing extrusion molding pressure, the P content in the honeycomb structure can be less than 0.01% by mass, and can even be 0. However, starch cross-linked with a P-containing cross-linking agent is highly effective in suppressing cell deformation during extrusion molding, resulting in a high effect of improving the strength of the honeycomb structure. Therefore, from the perspective of balancing the effect of reducing extrusion molding pressure, the P content in the honeycomb structure is preferably greater than 0.01% by mass and less than 0.2% by mass, and more preferably greater than 0.01% by mass and less than 0.05% by mass.

[0067] The P content in the honeycomb structure is determined by the following method. First, partition wall samples (0.5 to 5.0 g) are collected from two locations, near the radial center and near the periphery, in the height direction of the honeycomb structure. Sulfuric acid is added to each partition wall sample and heated. After ashing, the sample solution is dissolved in hydrochloric acid. The sample solution is sprayed into a high-temperature argon plasma generated by high-frequency energy, and the emission intensity of the characteristic wavelength of the excited P atoms is measured using a sequential inductively coupled plasma optical emission spectrometer (ICP-OES / AES), and converted into the P content in the honeycomb structure. The average value of the P content in the honeycomb structure obtained from each partition wall sample is used as the measured value.

[0068] One standard for the mechanical strength of a honeycomb structure is the isostatic breaking strength. In the determination of the isostatic breaking strength of a honeycomb structure, the following test is performed: the honeycomb structure is submerged in water in a pressure vessel, and the water pressure is gradually increased, thereby applying isotropic pressure to the honeycomb structure. As the water pressure in the pressure vessel gradually increases, damage eventually occurs in the partition wall and the peripheral side wall of the honeycomb structure. The value of the pressure at which damage occurs (breaking strength) is the isostatic breaking strength. The isostatic breaking strength is measured based on the automotive standard (JASO M505-87) issued by the Japan Association of Automotive Engineers.

[0069] In one embodiment, even if the honeycomb structure is thin-walled and has a high porosity, it can still have an isostatic fracture strength of 1.0 MPa or greater. The isostatic fracture strength of the honeycomb structure is preferably 1.5 MPa or greater, more preferably 2.0 MPa or greater. The upper limit of the isostatic fracture strength is not particularly set, but is generally 3.0 MPa or less, typically 2.5 MPa or less.

[0070] When the honeycomb structure is used as a catalyst carrier, a catalyst corresponding to the purpose can be coated on the surface of the partition wall. The catalyst can be used alone or in combination of two or more. As the catalyst, there is no limitation, and examples include oxidation catalysts (DOCs) for oxidizing and burning hydrocarbons (HC) and carbon monoxide (CO) to increase the exhaust gas temperature, PM combustion catalysts for assisting the combustion of PM such as soot, SCR catalysts and NSR catalysts for removing nitrogen oxides (NOx), and three-way catalysts that can simultaneously remove hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). For example, the catalyst can appropriately contain precious metals (Pt, Pd, Rh, etc.), alkali metals (Li, Na, K, Cs, etc.), alkaline earth metals (Mg, Ca, Ba, Sr, etc.), rare earths (Ce, Sm, Gd, Nd, Y, La, Pr, etc.), transition metals (Mn, Fe, Co, Ni, Cu, Zn, Sc, Ti, Zr, V, Cr, etc.), etc.

[0071] <2. Method for Manufacturing Honeycomb Structure>

[0072] Hereinafter, a method for producing a honeycomb structure according to one embodiment of the present invention will be described by way of example.

[0073] (2-1. Preparation of Honeycomb Molded Body)

[0074] First, after kneading a raw material composition containing a ceramic raw material, a pore-forming material, a binder, and a dispersion medium to form a green clay, the green clay is extruded through a die having a plurality of opening shapes defining the cells, thereby producing a honeycomb formed body having an outer peripheral sidewall, and an inner peripheral side arranged on the outer peripheral sidewall, extending from the first bottom surface to the second bottom surface, and having a plurality of cells with openings on both the first bottom surface and the second bottom surface. Additives such as a dispersant can be added to the raw material composition as needed. During extrusion molding, a die having a desired overall shape, cell shape, wall thickness, cell density, etc. can be used.

[0075] The ceramic raw material remains after firing and is the raw material for forming part of the skeleton of the honeycomb structure as ceramic. As the ceramic raw material, a raw material that can form the above-mentioned ceramic after firing can be used. The ceramic raw material can be provided, for example, in the form of a powder. As the ceramic raw material, cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon nitride, zirconium oxide, spinel, India stone, sapphire, corundum, titanium dioxide and the like can be cited as raw materials for obtaining ceramics. Specifically, without limitation, silicon dioxide, talc, aluminum oxide, kaolin, serpentine, pyrophyllite, brucite, boehmite, mullite, magnesite, aluminum hydroxide and the like can be cited. One type of ceramic raw material can be used alone, or two or more types can be used in combination.

[0076] As a ceramic, cordierite can be suitably used. In this case, a cordierite-forming raw material can be used as a ceramic raw material. The cordierite-forming raw material refers to a raw material that becomes cordierite by firing. As the cordierite-forming raw material, talc, kaolin, alumina, aluminum hydroxide, silicon dioxide, etc. can be used. The cordierite-forming raw material is preferably composed of a chemical composition of 30 to 45% by mass of aluminum oxide (Al2O3) (including aluminum hydroxide converted into alumina), 11 to 17% by mass of magnesium oxide (MgO), and 42 to 57% by mass of silicon dioxide (SiO2).

[0077] Including cordierite raw materials, ceramic raw materials affect the strength of the honeycomb structure, so it is preferred to use raw materials that have been adjusted in particle size by crushing, screening, etc. Specifically, in the volume-based cumulative particle size distribution measured by the laser diffraction scattering method, the lower limit of the cumulative 50% particle size (D50) of each ceramic raw material from the small particle side is preferably 0.1 μm or more, more preferably 0.5 μm or more, and further preferably 1.0 μm or more. In addition, the upper limit of the cumulative 50% particle size (D50) of each ceramic raw material from the small particle side is preferably 30 μm or less, more preferably 20 μm or less, and further preferably 15 μm or less. Therefore, for example, the cumulative 50% particle size (D50) of each ceramic raw material is preferably 0.1 μm or more and 30 μm or less, more preferably 0.5 μm or more and 20 μm or less, and further preferably 1.0 μm or more and 15 μm or less.

[0078] As pore-forming materials, if cross-linked starch and acrylic acid polymers are used in combination, the fluidity of the green clay is significantly improved. Thus, the formability is optimized, and the pore deformation that is easily generated during molding is suppressed. Therefore, as a result, the strength of the honeycomb structure can be improved. In order to make the honeycomb structure thin-walled, it is necessary to extrude the green clay through an extremely narrow die groove, and the extrusion molding pressure also increases, which easily causes deformation of the pore shape (cell deformation). The reason why the pore deformation can be suppressed by using cross-linked starch and acrylic acid polymers as pore-forming materials is not necessarily clear. The present invention is not intended to be limited by theory, but it can be inferred that the water retention effect of cross-linked starch and acrylic acid polymers is related to the optimization of formability. Compared with the case of using only either cross-linked starch or acrylic acid polymer, a significant effect can be obtained when the two are used together.

[0079] In cross-linked starch, one or more cross-linking agents such as formalin, epichlorohydrin, and phosphates are used to cross-link several hydroxyl groups between starch molecules. Examples of cross-linked starch include acetylated adipic acid cross-linked starch, acetylated phosphate cross-linked starch, hydroxypropylated phosphate cross-linked starch, monophosphate cross-linked starch, and phosphate cross-linked starch. One type of cross-linked starch may be used alone, or two or more types may be used in combination.

[0080] Thus, cross-linked starch may contain phosphorus (P). In addition, from the perspective of achieving a high porosity while improving the strength of the honeycomb structure, cross-linked starch containing P is preferred. However, if the P content in the cross-linked starch increases, the screen used for removing impurities during the extrusion molding of the green clay may become clogged, causing an increase in the extrusion molding pressure. Therefore, it is preferable to control the P content in the green clay within a range that does not cause screen clogging.

[0081] The extrusion molding pressure during extrusion molding of the green clay is preferably 15 MPa or less, more preferably 10 MPa or less. A low extrusion molding pressure is preferred, but from the perspective of ensuring strength, green clay that can be extruded at too low an extrusion molding pressure cannot be used. Therefore, the extrusion molding pressure is preferably 1 MPa or more, more preferably 3 MPa or more. Therefore, the extrusion molding pressure is preferably, for example, 1 to 15 MPa, more preferably 3 to 10 MPa.

[0082] Therefore, the green clay preferably contains an acrylic polymer and, relative to 100 parts by mass of the ceramic raw material, contains cross-linked starch under the condition that the P content is less than 0.2 parts by mass, preferably under the condition of 0.1 parts by mass or less, and more preferably under the condition of 0.05 parts by mass or less. The P content in the green clay can be 0.01 parts by mass or less, and further can be 0 parts by mass, relative to 100 parts by mass of the ceramic raw material. From the viewpoint of achieving a high porosity while obtaining the effect of improving the strength of the honeycomb structure, the lower limit of the content of cross-linked starch in the green clay satisfies the preferred conditions of the above-mentioned P content, preferably 1 part by mass or more, more preferably 5 parts by mass or more, and further preferably 10 parts by mass or more, relative to 100 parts by mass of the ceramic raw material. From the viewpoint of suppressing the generation of cracks caused by heat during firing, the upper limit of the content of cross-linked starch in the green clay is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and further preferably 20 parts by mass or less, relative to 100 parts by mass of the ceramic raw material.

[0083] When using starch cross-linked with a cross-linking agent containing P, even if the content of cross-linked starch in the clay is the same, since a greater degree of cross-linking indicates a greater P content, the P content can be used as an indicator of the degree of cross-linking. For example, a cross-linked starch having a P content of 0.01 parts by mass or more and less than 0.20 parts by mass per 10 parts by mass of the cross-linked starch can be used. The P content per 10 parts by mass of the cross-linked starch is preferably 0.01 parts by mass or more and less than 0.15 parts by mass, and more preferably 0.01 parts by mass or more and less than 0.1 parts by mass.

[0084] The P content in the green body is measured by the following method. First, a sample (0.5 to 5.0 g) is collected from the green body. Sulfuric acid is added to each partition sample and heated, and after ashing, the sample solution is prepared by dissolving in hydrochloric acid. The sample solution is sprayed into a high-temperature argon plasma generated by high-frequency energy, and the luminescence intensity of the characteristic wavelength of the excited P atoms is measured using a sequential inductively coupled plasma emission spectrometer (ICP-OES / AES), and the P content in the green body is converted.

[0085] From the viewpoint of achieving a high porosity while obtaining a strength improvement effect of the honeycomb structure, the green body preferably contains 0.5 parts by mass or more of the acrylic polymer, more preferably 0.7 parts by mass or more, and further preferably 1.0 parts by mass or more, with respect to 100 parts by mass of the ceramic raw material. In addition, from the viewpoint of fluidity, the green body preferably contains 10.0 parts by mass or less of the acrylic polymer, more preferably 7.0 parts by mass or less, and further preferably 5.0 parts by mass or less, with respect to 100 parts by mass of the ceramic raw material. Thus, the green body preferably contains 0.5 parts by mass or more and 10 parts by mass or less of the acrylic polymer, more preferably 0.7 to 7.0 parts by mass, and further preferably 1.0 to 5.0 parts by mass, with respect to 100 parts by mass of the ceramic raw material.

[0086] The kind of the acrylic polymer is not limited, and examples include polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, and the like, and in particular, polymethyl methacrylate (PMMA) is one of suitable acrylic polymers. The acrylic polymer can be crosslinked. The acrylic polymer can be used alone or in combination with two or more kinds.

[0087] One or two or more kinds of other known pore-forming materials can also be appropriately added to the green body. Examples include wheat flour, foamed resin, water-absorbing resin, uncrosslinked starch, porous silica, carbon (for example, graphite), ceramic balls, polyethylene, polystyrene, polypropylene, nylon, polyester, phenol, and the like.

[0088] From the perspective of affecting the strength of the honeycomb structure, pore-forming materials such as cross-linked starch and acrylic polymers are preferably materials whose particle size has been adjusted by crushing, screening, etc. Specifically, in the volume-based cumulative particle size distribution measured by the laser diffraction scattering method, the lower limit of the cumulative 50% particle size (D50) of each pore-forming material from the small particle side is preferably 0.1 μm or more, more preferably 1.0 μm or more, and further preferably 5.0 μm or more. In addition, the upper limit of the cumulative 50% particle size (D50) of each pore-forming material from the small particle side is preferably 30.0 μm or less, more preferably 20.0 μm or less, and further preferably 15.0 μm or less. Therefore, for example, the cumulative 50% particle size (D50) of each pore-forming material from the small particle side is preferably 0.1 to 30.0 μm, more preferably 1.0 to 20.0 μm, and further preferably 5.0 to 15.0 μm.

[0089] As the binder, organic binders such as methylcellulose, hydroxypropyl methylcellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol can be exemplified. It is particularly preferred to use methylcellulose and hydroxypropyl methylcellulose in combination. In addition, from the viewpoint of improving the strength of the honeycomb formed body, the content of the binder in the green clay is preferably more than 4 parts by mass, more preferably more than 5 parts by mass, and further preferably more than 6 parts by mass relative to 100 parts by mass of the ceramic raw material, from the viewpoint of suppressing the cracking caused by the abnormal heating in the firing process, the content of the binder in the green clay is preferably less than 9 parts by mass, more preferably less than 8 parts by mass, and further preferably less than 7 parts by mass relative to 100 parts by mass of the ceramic raw material. One type of binder can be used alone, or two or more types can be used in combination.

[0090] As the dispersion medium, water or a mixed solvent of water and an organic solvent such as alcohol can be cited, and water is particularly preferably used. The content of the dispersion medium in the green clay is preferably 30 to 70 parts by mass, more preferably 35 to 65 parts by mass, and further preferably 40 to 60 parts by mass relative to 100 parts by mass of the ceramic raw material. By making the content of the dispersion medium in the green clay 30 parts by mass or more relative to 100 parts by mass of the ceramic raw material, it is easy to obtain the advantage of easy stability of the quality of the honeycomb formed body. By making the content of the dispersion medium in the green clay 70 parts by mass or less relative to 100 parts by mass of the ceramic raw material, the shrinkage during drying becomes smaller, which can suppress deformation. In this specification, the water content of the green clay refers to the value measured by the loss on drying method.

[0091] Dispersants that can be used include ethylene glycol, dextrin, fatty acid soap, and polyether polyol. One type of dispersant may be used alone, or two or more types may be used in combination. The content of the dispersant in the clay is preferably 0 to 2 parts by mass per 100 parts by mass of the ceramic raw material.

[0092] (2-2. Drying of Honeycomb Formed Body)

[0093] Next, the honeycomb molded body is dried to obtain a honeycomb dried body. In the drying step, a publicly known drying method such as hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, freeze drying, or the like can be used. Among them, from the viewpoint of being able to rapidly and uniformly dry the entire molded body, a drying method in which hot air drying is combined with microwave drying or dielectric drying is preferable. In addition, a batch-type drying machine can be used, or a continuous drying machine can be used.

[0094] In the case of forming the sealing portion, after the sealing portion is formed at predetermined positions of the first bottom surface and the second bottom surface of the honeycomb molded body after drying, the sealing portion is dried. The method of sealing the first bottom surface and the second bottom surface of the honeycomb molded body is not particularly limited, and a publicly known method can be used. Regarding the material of the sealing portion, there is no particular limitation, and from the viewpoints of strength and heat resistance, ceramic is preferable. As the ceramic, a ceramic material containing at least one selected from the group consisting of cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon nitride, zirconia, spinel, indialite, sapphirine, corundum, and titanium dioxide is preferable. In order to be able to make the expansion rate at the time of firing the same and to bring about an improvement in durability, the material composition of the sealing portion is more preferably made the same as that of the main portion of the honeycomb molded body.

[0095] (2-3. Firing of the honeycomb dried body)

[0096] After the honeycomb molded body is dried, debinding and firing are performed, whereby a columnar honeycomb structure body can be manufactured. The conditions of the debinding step and the firing step can be publicly known conditions according to the material composition of the honeycomb molded body, and do not need to be particularly described, but examples of specific conditions are given below.

[0097] The debinding step will be described. The combustion temperature of the binder is about 200°C, and the combustion temperature of the pore-forming material is about 300 to 1000°C. Therefore, the debinding step can be performed by heating the honeycomb molded body to a range of about 200 to 1000°C. The heating time is not particularly limited, and is usually about 10 to 100 hours. The honeycomb molded body after the debinding step is referred to as a pre-fired body.

[0098] The firing step also depends on the material composition of the honeycomb molded body, and can be performed, for example, by heating the pre-fired body to 1350 to 1600°C and maintaining it for 3 to 10 hours.

[0099] When a honeycomb structure is used as a catalyst carrier, the catalyst can be supported on the partition wall. The method for supporting the catalyst on the porous partition wall is not particularly limited and can be implemented by a known method, for example, a method in which a catalyst composition slurry is brought into contact with the porous partition wall and then dried and calcined. The catalyst composition slurry preferably contains one or a combination of two or more appropriate catalysts depending on its application.

[0100] Example

[0101] Hereinafter, examples are described for better understanding of the present invention and its advantages, but the present invention is not limited to the examples.

[0102] <A.实施例以及比较例所涉及的蜂窝结构体的制造>

[0103] (1) Raw materials

[0104] Talc, kaolin, alumina, aluminum hydroxide, and silica were prepared as cordierite-forming raw materials. Table 1 shows their cumulative 50% particle diameters (D50) based on volume measured by a laser diffraction scattering method.

[0105] As pore-forming materials, acrylic acid polymers, low-crosslinked starch, medium-crosslinked starch, and highly crosslinked starch were prepared. Polyacrylic acid was used as the acrylic acid polymer. Low-crosslinked starch, medium-crosslinked starch, and highly crosslinked starch are all starches crosslinked with a phosphate-based crosslinking agent, but differ in the degree of crosslinking. Their cumulative 50% particle diameter (D50) based on volume, measured by laser diffraction scattering, is shown in Table 1.

[0106] As auxiliary agents, a binder, a dispersant, and water were prepared. Methyl cellulose was used as the binder, and ethylene glycol was used as the dispersant.

[0107] (2) Preparation of honeycomb molded body

[0108] The raw material compositions prepared by mixing the cordierite-forming raw materials, pore-forming materials, and additives in the mass ratios shown in Table 1 according to the numbers of the Examples and Comparative Examples were kneaded to form green clays of the Examples and Comparative Examples, respectively. Table 1 shows the P content in the green clays relative to 100 parts by mass of the ceramic raw materials, as measured by the above method.

[0109] Each molded clay was then fed into an extruder and extruded through a die of a predetermined shape to obtain a cylindrical honeycomb molded body. The pressure during extrusion molding (extrusion molding pressure) was measured using a pressure sensor. The results are shown in Table 1. The obtained honeycomb molded body was subjected to dielectric drying and hot air drying, and then the two bottom surfaces were cut to a predetermined size and further hot air dried at 70°C for 2 hours.

[0110] (3) Firing

[0111] Next, the honeycomb structures of Examples and Comparative Examples were obtained by heating and degreasing at about 200° C. in air and then firing at 1400° C. for 10 hours in air. The honeycomb structures were produced in the required number for the following test.

[0112] (4) Specifications of honeycomb structure

[0113] The specifications of the obtained honeycomb structure are as follows.

[0114] Overall shape: cylindrical with a diameter of 100mm and a height of 100mm

[0115] Cell shape in a cross section perpendicular to the cell flow direction: Square

[0116] Thickness of partition wall (nominal value based on die specifications): listed in Table 1

[0117] Cell density (number of cells per unit cross-sectional area): listed in Table 1 (cpsi: cells per square inch)

[0118] <B.特性评价>

[0119] Various characteristics evaluations were performed on the honeycomb structures according to the examples and comparative examples obtained above.

[0120] (1) Porosity

[0121] Cell wall samples (cubes measuring approximately 13 mm in length x 13 mm in width x 13 mm in height) were collected from two locations near the radial center and one near the outer periphery of each honeycomb structure. The porosity was measured by mercury intrusion porosimetry, and the average value was used as the measured value. The results are shown in Table 1.

[0122] (2) Determination of isostatic breaking strength

[0123] The isostatic crushing strength of each honeycomb structure was measured based on the automotive standard (JASO M505-87) issued by the Japan Society of Automotive Engineers.

[0124] (3) Determination of P content

[0125] The P content in each honeycomb structure was measured by the above-mentioned measurement method. The results are shown in Table 1.

[0126] [Table 1]

[0127]

[0128] (4) Investigation

[0129] The honeycomb structures involved in the embodiments and comparative examples are all thin-walled and have high porosity. Comparative Examples 1 to 6 are all examples in which only one of acrylic acid polymer and cross-linked starch is used as a pore-forming material. The strength of the honeycomb structures of Comparative Examples 1 to 4 is insufficient. Comparative Examples 5 and 6 using highly cross-linked starch have excellent strength, but the P content increases and the extrusion molding pressure is too high, thereby significantly reducing the extrusion speed and placing an excessive burden on the molding machine. On the other hand, in Examples 1 to 16, by using acrylic acid polymer and cross-linked starch as pore-forming materials, it is possible to produce honeycomb structures with thin walls, high porosity and excellent strength without placing an excessive burden on the extrusion molding machine (the extrusion molding pressure is 15 MPa or less).

Claims

1. A method for manufacturing a honeycomb structure, the honeycomb structure comprising an outer peripheral side wall and partition walls, the partition walls being arranged on the inner peripheral side of the outer peripheral side wall and defining a plurality of cells forming a flow path from a first bottom surface to a second bottom surface, The method for manufacturing the honeycomb structure comprises: A step of extruding a molded body containing a ceramic raw material, a pore-forming material, a binder, and a dispersion medium through a die defining the opening shape of the plurality of cells, thereby producing a honeycomb molded body. a step of drying the honeycomb formed body to obtain a dried honeycomb body, and The step of firing the dried honeycomb body to obtain a honeycomb fired body having a partition wall thickness of 50 μm to 210 μm and a partition wall porosity of 45% to 60%; The pore-forming material in the clay contains cross-linked starch and acrylic acid polymer. The clay contains 1.0 parts by mass or more of cross-linked starch with respect to 100 parts by mass of the ceramic raw material, under the condition that the P content is less than 0.2 parts by mass, The cross-linked starch comprises starch cross-linked by a cross-linking agent containing P, The P content in the honeycomb structure is 0.01 mass % or more and less than 0.2 mass %.

2. The manufacturing method according to claim 1, wherein The kneaded clay contains 1.0 part by mass or more of cross-linked starch with respect to 100 parts by mass of the ceramic raw material, under the condition that the P content is 0.1 part by mass or less.

3. The manufacturing method according to claim 1, wherein The kneaded clay contains 1.0 part by mass or more of cross-linked starch with respect to 100 parts by mass of the ceramic raw material, under the condition that the P content is 0.05 parts by mass or less.

4. The production method according to any one of claims 1 to 3, wherein The P content in the honeycomb structure is 0.1 mass % or less.

5. The production method according to any one of claims 1 to 3, wherein The P content in the honeycomb structure is 0.05 mass % or less.

6. The production method according to any one of claims 1 to 3, wherein The kneaded clay contains 0.5 parts by mass or more of an acrylic polymer based on 100 parts by mass of the ceramic raw material.

7. The production method according to any one of claims 1 to 3, wherein The ceramic raw material is a cordierite raw material.

8. A honeycomb structure produced by the production method according to any one of claims 1 to 7, comprising an outer peripheral side wall and partition walls. The partition wall is disposed on the inner peripheral side of the outer peripheral side wall and defines a plurality of cells forming a flow path from the first bottom surface to the second bottom surface. The thickness of the partition wall is 50 μm or more and 210 μm or less. The porosity of the partition wall is 45% to 60%. The P content in the honeycomb structure is 0.01 mass % or more and less than 0.2 mass %, and the isostatic fracture strength is 1.0 MPa or more.

9. The honeycomb structure according to claim 8, wherein The upper limit of the P content in the honeycomb structure is 0.1 mass % or less.

10. The honeycomb structure according to claim 8, wherein The upper limit of the P content in the honeycomb structure is 0.05 mass % or less.

11. The honeycomb structure according to any one of claims 8 to 10, wherein The outer peripheral sidewalls and partition walls contain cordierite.

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