Method for manufacturing conductive honeycomb structure and method for manufacturing electrically heated carrier

Abstract

To provide a method of producing a honeycomb structure capable of stably forming a required electric resistivity distribution to the honeycomb structure by an easy method, and a method of producing an electrically heating-type carrier.SOLUTION: A method of producing an electroconductive honeycomb structure includes: a molding process of extruding a molding material containing an electroconductive ceramic raw material to obtain a honeycomb molding having an outer peripheral wall, and partition walls for forming a plurality of cells which form passages; a drying process of drying the molding to obtain a honeycomb dried body; and a calcination process of calcining the dried body to obtain a honeycomb calcined body. where the molding process includes a process of controlling a volume of a part becoming pores of the molding so that an absolute value of a difference of a volume fraction of a part becoming pores in a predetermined region of the honeycomb molding to a preliminarily set predetermined porosity of the honeycomb molding becomes less than 0.5%, and the predetermined porosity is a porosity preliminarily set for every predetermined region in a section perpendicular to a passage direction of the cells of the calcined body.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a conductive honeycomb structure and a method for manufacturing an electric heating carrier.

Background Art

[0002] In recent years, an electric heating catalyst (EHC) has been proposed to improve the deterioration of exhaust gas purification performance immediately after engine startup. The EHC is configured such that, for example, a metal electrode is connected to a columnar honeycomb structure made of a conductive ceramic, and the honeycomb structure itself is heated by energization so that the temperature can be raised to the activation temperature of the catalyst before engine startup.

[0003] Patent Document 1 discloses a honeycomb structure having a structure in which the electrical resistivity of a central region is lower than that of an outer peripheral region in a cross section orthogonal to the direction in which cells extend in order to reduce the energy when applying a voltage to the EHC to purify exhaust gas.

[0004] Patent Document 2 discloses a honeycomb structure in which the honeycomb structure portion is composed of an outer peripheral region including side surfaces, a central region that is a central region, and an intermediate region excluding the outer peripheral region and the central region in order to suppress the unevenness of the heat generation distribution and cause uniform heat generation in the EHC more than in the prior art, and the average electrical resistivity A of the material constituting the outer peripheral region, the average electrical resistivity B of the material constituting the central region, and the average electrical resistivity C of the material constituting the intermediate region satisfy the relationship of A ≤ B < C.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the techniques disclosed in Patent Documents 1 and 2, in the manufacturing method of a honeycomb structure, the distribution of electrical resistivity in the honeycomb structure as described above is controlled by controlling the materials constituting the honeycomb structure or the firing conditions in the firing process. However, variations in the atmosphere or temperature are likely to occur inside the kiln used for firing and between kilns, and there are cases where the desired distribution of electrical resistivity is not stably formed, leaving room for improvement.

[0007] The present invention was created in consideration of the above circumstances, and its objective is to provide a method for manufacturing a conductive honeycomb structure and a method for manufacturing an electrically heated carrier that can stably form a desired electrical resistivity distribution within the honeycomb structure in a simple manner. [Means for solving the problem]

[0008] The above problems are solved by the present invention, which is specified as follows: (1) a molding step of extruding a molding raw material containing a conductive ceramic raw material to obtain a honeycomb molded body having an outer peripheral wall and partition walls disposed inside the outer peripheral wall to define a plurality of cells that form flow paths extending from one end face to the other end face; a drying step of drying the honeycomb formed body to obtain a dried honeycomb body; a firing step of firing the dried honeycomb body to obtain a fired honeycomb body; Equipped with the forming step includes a step of controlling the volume ratio of the portions that can become pores of the honeycomb formed body so that the absolute value of the difference between the volume ratio of the portions that can become pores in a predetermined region of the honeycomb formed body and the predetermined porosity of the honeycomb fired body is within 0.5%, A method for manufacturing a conductive honeycomb structure, wherein the predetermined porosity is a porosity that is set in advance for each predetermined region in a cross section of the honeycomb fired body perpendicular to the flow path direction of the cells. (2) a molding step of extruding a molding raw material containing a conductive ceramic raw material to obtain a honeycomb molded body having an outer peripheral wall and partition walls disposed inside the outer peripheral wall to define a plurality of cells that form flow paths extending from one end face to the other end face; a drying step of drying the honeycomb formed body to obtain a dried honeycomb body; a firing step of firing the dried honeycomb body to obtain a fired honeycomb body; Equipped with the drying step includes a step of controlling a volume ratio of a portion that can become a pore in the honeycomb dried body so that an absolute value of a difference between a predetermined porosity set in advance in the honeycomb fired body and a volume ratio of a portion that can become a pore in a predetermined region of the honeycomb dried body is within 0.5%, A method for manufacturing a conductive honeycomb structure, wherein the predetermined porosity is a porosity that is set in advance for each predetermined region in a cross section of the honeycomb fired body perpendicular to the flow path direction of the cells. (3) a step of applying an electrode portion-forming raw material containing a ceramic raw material to a side surface of the honeycomb fired body, and drying the applied material to form a pair of unfired electrode portions on the outer surface of the outer wall across the central axis of the honeycomb fired body, the pair of unfired electrode portions extending in a band-like shape in a flow path direction of the cells, thereby producing a honeycomb fired body with unfired electrode portions; a step of firing the honeycomb fired body with the unfired electrode portions to produce a conductive honeycomb structure having a pair of electrode portions; The method for manufacturing a conductive honeycomb structure according to (1) or (2), further comprising: (4) A method for manufacturing an electrically heated carrier, comprising a step of electrically connecting metal electrodes to each of the pair of electrode portions of the conductive honeycomb structure manufactured by the method according to (3). [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for manufacturing a conductive honeycomb structure and a method for manufacturing an electrically heated carrier, which are capable of stably forming a desired electrical resistivity distribution within a honeycomb structure using a simple method. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic view showing an external appearance of a honeycomb structure according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view illustrating a "central region" and an "outer peripheral region" of a honeycomb structure (fired body) according to an embodiment of the present invention. [Figure 3] 1 is a schematic cross-sectional view perpendicular to the extension direction of cells of an electrically heated carrier according to an embodiment of the present invention. [Figure 4] 1(a) and 1(b) are schematic diagrams illustrating how the concave-convex pattern is formed at the tip of a honeycomb formed body extruded from a forming machine according to an embodiment of the present invention. [Figure 5] 1(a) to 1(d) are cross-sectional schematic diagrams showing examples of concave-convex patterns at the tip of a honeycomb formed body extruded from a forming machine. DETAILED DESCRIPTION OF THE INVENTION

[0011] Next, embodiments of the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes and improvements may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0012] (1. Honeycomb structure) 1 is a schematic view of the appearance of a honeycomb structure 10 according to an embodiment of the present invention. The honeycomb structure 10 includes a columnar honeycomb structure portion 11 and electrode portions 13a and 13b. The electrode portions 13a and 13b may not be included.

[0013] (1-1. Columnar honeycomb structure) The columnar honeycomb structure portion 11 has an outer peripheral wall 12 and partition walls 19 disposed inside the outer peripheral wall 12 to define a plurality of cells 18 that form flow paths extending from one end face to the other end face.

[0014] The outer shape of the columnar honeycomb structure part 11 is not particularly limited as long as it is columnar, and can be, for example, a columnar shape with circular end faces (cylindrical shape), a columnar shape with oval end faces, a columnar shape with polygonal end faces (quadragonal, pentagonal, hexagonal, heptagonal, octagonal, etc.), etc. The size of the columnar honeycomb structure part 11 is set to 2000 to 20000 mm2 in order to increase heat resistance (suppress cracks in the circumferential direction of the outer peripheral wall). 2 It is preferable that the thickness is 5000 to 15000 mm 2 It is more preferable that:

[0015] The material of the columnar honeycomb structure 11 is not limited, but can be selected from the group consisting of oxide ceramics such as alumina, mullite, zirconia, and cordierite, and non-oxide ceramics such as silicon carbide, silicon nitride, and aluminum nitride. Silicon carbide-metal silicon composites and silicon carbide / graphite composites can also be used. Among these, from the viewpoint of achieving both heat resistance and electrical conductivity, it is preferable that the material of the columnar honeycomb structure 11 contains a silicon-silicon carbide composite or a ceramic containing silicon carbide as the main component. When the material of the columnar honeycomb structure 11 is said to be mainly composed of a silicon-silicon carbide composite, it means that the columnar honeycomb structure 11 contains 90% by mass or more of the silicon-silicon carbide composite (total mass) of the entire material. Here, the silicon-silicon carbide composite material contains silicon carbide particles as aggregate and silicon as a binder that bonds the silicon carbide particles, and it is preferable that a plurality of silicon carbide particles are bonded by the silicon so as to form pores between the silicon carbide particles. When the material of the columnar honeycomb structure part 11 is said to be mainly composed of silicon carbide, it means that the columnar honeycomb structure part 11 contains silicon carbide (total mass) in an amount of 90 mass% or more of the entire material.

[0016] When the columnar honeycomb structure 11 contains a silicon-silicon carbide composite material, the ratio of the "mass of silicon as a binder" contained in the columnar honeycomb structure 11 to the sum of the "mass of silicon carbide particles as aggregate" contained in the columnar honeycomb structure 11 and the "mass of silicon as a binder" contained in the columnar honeycomb structure 11 is preferably 10 to 40 mass%, and more preferably 15 to 35 mass%.

[0017] Although there are no limitations on the shape of the cells 18 in a cross section perpendicular to the stretching direction, a square, a hexagon, an octagon, or a combination thereof is preferred. Among these, a square and a hexagon are preferred from the viewpoint of easily achieving both structural strength and heating uniformity.

[0018] The thickness of the partition walls 19 that define the cells 18 is preferably 0.1 to 0.3 mm, and more preferably 0.15 to 0.25 mm. In the present invention, the thickness of the partition walls 19 is defined as the length of the portion of a line segment that connects the centers of gravity of adjacent cells 18 and passes through the partition walls 19 in a cross section perpendicular to the stretching direction of the cells 18.

[0019] The columnar honeycomb structure 11 has a cell density of 40 to 150 cells / cm in a cross section perpendicular to the flow path direction of the cells 18. 2 It is preferable that the number of cells is 70 to 100. 2 It is more preferable that the cell density is within this range. By setting the cell density within this range, the purification performance of the catalyst can be improved while reducing the pressure loss when exhaust gas flows. The cell density is a value obtained by dividing the number of cells by the area of ​​one end face of the columnar honeycomb structure portion 11 excluding the outer wall 12 portion.

[0020] Providing the outer peripheral wall 12 of the columnar honeycomb structure portion 11 is useful from the viewpoint of ensuring the structural strength of the columnar honeycomb structure portion 11 and suppressing leakage of the fluid flowing through the cells 18 from the outer peripheral wall 12. Specifically, the thickness of the outer peripheral wall 12 is preferably 0.05 mm or more, more preferably 0.10 mm or more, and even more preferably 0.15 mm or more. However, if the outer peripheral wall 12 is made too thick, the strength becomes too high, which disrupts the strength balance with the partition walls 19 and reduces thermal shock resistance. Furthermore, an increase in heat capacity generates a temperature difference between the inner and outer peripheral sides of the outer peripheral wall, thereby reducing thermal shock resistance. From these viewpoints, the thickness of the outer peripheral wall 12 is preferably 1.0 mm or less, more preferably 0.7 mm or less, and even more preferably 0.5 mm or less. Here, the thickness of the outer peripheral wall 12 is defined as the thickness in the direction normal to the tangent of the outer peripheral wall 12 at the measurement point when the portion of the outer peripheral wall 12 to be measured is observed in a cross section perpendicular to the extension direction of the cells.

[0021] The average pore diameter of the partition walls 19 of the columnar honeycomb structure portion 11 is preferably 2 to 15 μm, and more preferably 4 to 8 μm. The average pore diameter is a value measured by a mercury porosimeter.

[0022] The partition walls 19 have pores. The porosity of the partition walls 19 is preferably 35 to 60%, and more preferably 35 to 45%. The porosity is a value measured by a mercury porosimeter.

[0023] As shown in FIG. 2, in a cross section perpendicular to the flow direction of the cells 18, the honeycomb structure 10 may have an absolute value of a difference in the porosity of a central region extending from the center of the cross section to ½r and a peripheral region extending from ½r to r, where r is the radius of the cross section, within 0.5%. Note that FIG. 2 simply illustrates the external shape of the cross section of the honeycomb structure 10, and does not illustrate the cells 18, partition walls 19, peripheral wall 12, etc. According to this configuration, in a cross section perpendicular to the flow direction of the cells 18, the porosity of the outer region (peripheral region) is controlled within a predetermined range relative to the porosity of the region extending from the center to the inner side (central region) in the radial direction. Therefore, the electrical resistivity of the peripheral region can be controlled within a predetermined range relative to the electrical resistivity of the central region when the honeycomb structure 10 is used in an EHC. Therefore, when the honeycomb structure 10 is used in an EHC, desired effects can be appropriately obtained, such as reducing the energy required for purifying exhaust gas by applying a voltage or suppressing uneven heat generation distribution to uniformly heat generation.

[0024] Furthermore, the difference in porosity between the central region from the center of the cross section to 1 / 2r and the peripheral region from 1 / 2r to r may be -0.5% or less, +0.5% or more, or -1% or less, +1% or more. In other words, the absolute value of the difference between the porosity of the central region from the center of the cross section to 1 / 2r and the porosity of the peripheral region from 1 / 2r to r is preferably 0.5% or more, more preferably 1% or more. By providing a difference in porosity between the central region and the peripheral region in this way, it is possible to optimize the strength distribution within the honeycomb structure 10 from the perspective of thermal durability. There is no particular upper limit, but it may be -5% or more and +5% or less.

[0025] The columnar honeycomb structure part 11 is made of ceramics and has electrical conductivity. As long as the electrically conductive columnar honeycomb structure part 11 can generate heat by Joule heat when an electric current is passed through it, there is no particular limitation on the electrical resistivity of the ceramics, but it is preferably 0.1 to 200 Ωcm, and more preferably 1 to 200 Ωcm. In the present invention, the electrical resistivity of the columnar honeycomb structure part 11 is a value measured at 25°C by a four-terminal method.

[0026] The electric resistivity distribution within the honeycomb structure 10 may be appropriately controlled to a desired distribution state. The electric resistivity distribution within the honeycomb structure 10, in a cross-section perpendicular to the flow path direction of the cells 18 of the honeycomb structure 10, when the radius of the cross-section is r, the electric resistivity of the outer peripheral region from 1 / 2r to r may be controlled within a predetermined range with respect to the electric resistivity of the central region from the center of the cross-section to 1 / 2r. According to such a configuration, when the honeycomb structure 10 is used for an EHC, desired effects such as reducing the energy when applying a voltage to purify the exhaust gas, or suppressing the deviation of the heat generation distribution and causing uniform heat generation can be appropriately obtained. Also, the electric resistivity distribution within the honeycomb structure 10, for example, as disclosed in Patent Document 1, in order to reduce the energy when applying a voltage to purify the exhaust gas, in a cross-section orthogonal to the direction in which the cells 18 extend, the electric resistivity of the central region may be controlled to be lower than the electric resistivity of the outer peripheral region. Further, as disclosed in Patent Document 2, in order to suppress the deviation of the heat generation distribution and cause uniform heat generation, the honeycomb structure 10 is composed of an outer peripheral region including the side surface, a central region which is the central region, and an intermediate region excluding the outer peripheral region and the central region, and the average electric resistivity A of the material constituting the outer peripheral region, the average electric resistivity B of the material constituting the central region, and the average electric resistivity C of the material constituting the intermediate region may be controlled to satisfy the relationship A ≦ B < C. Also, not limited to these, the electric resistivity distribution within the honeycomb structure 10 may be uniformly controlled, and further, it may be controlled to various electric resistivity distributions according to various purposes. In the present invention, test pieces are collected from each part within the honeycomb structure 10, and the in-plane electric resistivity distribution can be measured by measuring the electric resistivity of the test pieces by the four-terminal method or the like and mapping it.

[0027] (1-2. Electrode part) In the honeycomb structure 10 according to the embodiment of the present invention, a pair of electrode portions 13a, 13b are provided on the outer surface of the outer wall 12, sandwiching the central axis of the columnar honeycomb structure portion 11, so as to extend in a band shape in the flow path direction of the cells 18. By providing the pair of electrode portions 13a, 13b in this manner, the uniform heat generation property of the honeycomb structure can be improved. From the viewpoint of facilitating the spread of current in the axial direction of the electrode portions 13a, 13b, it is desirable that the electrode portions 13a, 13b extend over 80% or more of the length between both end faces of the honeycomb structure, preferably over 90% or more of the length, and more preferably over the entire length. Note that the electrode portions 13a, 13b may not be provided.

[0028] The thickness of the electrode portions 13a, 13b is preferably 0.01 to 5 mm, and more preferably 0.01 to 3 mm. By setting the thickness within this range, uniform heat generation can be improved. The thickness of the electrode portions 13a, 13b is defined as the thickness in the direction normal to the tangent at the measurement point on the outer surface of the electrode portions 13a, 13b when the measurement point is observed on a cross section perpendicular to the extension direction of the cell 18.

[0029] By making the electrical resistivity of the electrode portions 13a, 13b lower than that of the columnar honeycomb structure portion 11, electricity flows preferentially through the electrode portions 13a, 13b, and when current is applied, electricity spreads more easily in the flow path direction and circumferential direction of the cell 18. The electrical resistivity of the electrode portions 13a, 13b is preferably 1 / 10 or less, more preferably 1 / 20 or less, and even more preferably 1 / 30 or less of the electrical resistivity of the columnar honeycomb structure portion 11. However, if the difference in electrical resistivity between the two becomes too large, current will concentrate between the ends of the opposing electrode portions, causing uneven heat generation in the columnar honeycomb structure portion 11. Therefore, the electrical resistivity of the electrode portions 13a, 13b is preferably 1 / 200 or more, more preferably 1 / 150 or more, and even more preferably 1 / 100 or more of the electrical resistivity of the columnar honeycomb structure portion 11. In the present invention, the electrical resistivity of the electrode portions 13a and 13b is a value measured at 25°C by a four-terminal method.

[0030] The electrode portions 13a and 13b may be made of conductive ceramics, metals, or composites (cermets) of metals and conductive ceramics. Examples of metals include, for example, Cr, Fe, Co, Ni, Si, or Ti, or alloys containing at least one metal selected from the group consisting of these metals. Examples of conductive ceramics include, but are not limited to, silicon carbide (SiC), and metal compounds such as metal silicides, such as tantalum silicide (TaSi2) and chromium silicide (CrSi2). Specific examples of composites (cermets) of metals and conductive ceramics include composites of silicon carbide and metal silicon, composites of metal silicides, such as tantalum silicide or chromium silicide, and silicon carbide and metal silicides. Furthermore, composites of one or more of the above metals with one or more insulating ceramics, such as alumina, mullite, zirconia, cordierite, silicon nitride, and aluminum nitride, to reduce thermal expansion.

[0031] (2. Electrically heated carrier) 3 is a schematic cross-sectional view perpendicular to the extension direction of the cells of an electrically heated carrier 30 according to an embodiment of the present invention. The electrically heated carrier 30 includes a honeycomb structure 10 and metal electrodes 33a and 33b electrically connected to electrode portions 13a and 13b of the honeycomb structure 10.

[0032] (2-1. Metal electrode) The metal electrodes 33a and 33b are provided on the electrode portions 13a and 13b of the honeycomb structure 10. The metal electrodes 33a and 33b may be a pair of metal electrodes arranged such that one metal electrode 33a faces the other metal electrode 33b across the central axis of the columnar honeycomb structure portion 11. When a voltage is applied via the electrode portions 13a and 13b, the metal electrodes 33a and 33b are energized and can generate Joule heat in the columnar honeycomb structure portion 11. Therefore, the electrically heated carrier 30 can also be suitably used as a heater. The applied voltage is preferably 12 to 900 V, more preferably 48 to 600 V, but the applied voltage can be changed as appropriate.

[0033] The material of the metal electrodes 33a, 33b is not particularly limited as long as it is a metal, and simple metals and alloys can be used, but from the viewpoints of corrosion resistance, electrical resistivity, and linear expansion coefficient, an alloy containing at least one selected from the group consisting of Cr, Fe, Co, Ni, and Ti is preferable, and stainless steel and an Fe-Ni alloy are more preferable. The shape and size of the metal electrodes 33a, 33b are not particularly limited, and can be designed appropriately depending on the size, electrical conductivity, etc. of the electrically heated carrier 30.

[0034] By supporting a catalyst on the electrically heated carrier 30, the electrically heated carrier 30 can be used as a catalyst body. A fluid such as automobile exhaust gas can be passed through the flow paths of the plurality of cells 18 of the honeycomb structure 10. Examples of the catalyst include precious metal catalysts and other catalysts. Precious metal catalysts include three-way catalysts and oxidation catalysts in which a precious metal such as platinum (Pt), palladium (Pd), or rhodium (Rh) is supported on the surface of alumina pores and a promoter such as ceria or zirconia is included, or alkaline earth metals and platinum are used to convert nitrogen oxides (NO x ) as a storage component of NO x Examples of catalysts that do not use precious metals include NOx storage reduction catalysts (LNT catalysts) containing copper-substituted or iron-substituted zeolites. x Examples include selective catalytic reduction catalysts (SCR catalysts). Two or more catalysts selected from the group consisting of these catalysts may be used. There are no particular limitations on the method for supporting the catalyst, and the method can be carried out in accordance with the conventional method for supporting a catalyst on a honeycomb structure.

[0035] (3. Manufacturing method of honeycomb structure) Next, a description will be given of a manufacturing method of the honeycomb structure 10 according to the embodiment of the present invention. The honeycomb structure 10 according to the embodiment of the present invention can be manufactured by either the manufacturing method according to embodiment 1 in which the porosity (volume ratio of parts that can become pores) is controlled in the molding step, or the manufacturing method according to embodiment 2 in which the porosity (volume ratio of parts that can become pores) is controlled in the drying step.

[0036] <Production method according to embodiment 1> The method for manufacturing the honeycomb structure 10 according to the first embodiment of the present invention includes a forming step for obtaining a honeycomb formed body, a drying step for obtaining a dried honeycomb body, and a firing step for obtaining a fired honeycomb body.

[0037] (molding process) In the molding process, first, a molding raw material containing a conductive ceramic raw material is prepared. The molding raw material is produced, for example, by adding metal silicon powder (metal silicon), a binder, a surfactant, a pore-forming agent, water, etc. to silicon carbide powder (silicon carbide). The mass of the metal silicon is preferably 10 to 40 mass% relative to the total mass of the silicon carbide powder and the metal silicon. The average particle diameter of the silicon carbide particles in the silicon carbide powder is preferably 3 to 50 μm, more preferably 3 to 40 μm. The average particle diameter of the metal silicon (metal silicon powder) is preferably 2 to 35 μm. The average particle diameters of the silicon carbide particles and metal silicon (metal silicon particles) refer to the arithmetic mean diameter on a volume basis when the particle size frequency distribution is measured by laser diffraction. The silicon carbide particles are fine particles of silicon carbide that constitute the silicon carbide powder, and the metal silicon particles are fine particles of metal silicon that constitute the metal silicon powder. This is the blending of the forming raw materials when the material of the honeycomb structure is a silicon-silicon carbide based composite material, and when the material is silicon carbide, metallic silicon is not added.

[0038] Examples of binders include methyl cellulose, hydroxypropyl methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, etc. Among these, it is preferable to use methyl cellulose and hydroxypropoxyl cellulose in combination. The content of the binder is preferably 2.0 to 10.0 parts by mass when the total mass of the silicon carbide powder and the metallic silicon powder is 100 parts by mass.

[0039] The content of water is preferably 20 to 60 parts by mass when the total mass of the silicon carbide powder and the metallic silicon powder is taken as 100 parts by mass.

[0040] Examples of surfactants that can be used include ethylene glycol, dextrin, fatty acid soap, and polyalcohol. These may be used alone or in combination of two or more. The content of the surfactant is preferably 0.1 to 2.0 parts by mass when the total mass of the silicon carbide powder and the metallic silicon powder is 100 parts by mass.

[0041] The pore-forming material is not particularly limited as long as it forms pores after firing, and examples thereof include graphite, starch, foamed resin, water-absorbent resin, silica gel, etc. The content of the pore-forming material is preferably 0.5 to 10.0 parts by mass when the total mass of the silicon carbide powder and metallic silicon powder is 100 parts by mass. The average particle diameter of the pore-forming material is preferably 10 to 30 μm. The average particle diameter of the pore-forming material refers to the arithmetic mean diameter on a volume basis when the frequency distribution of particle size is measured by laser diffraction. When the pore-forming material is a water-absorbent resin, the average particle diameter of the pore-forming material refers to the average particle diameter after water absorption.

[0042] Next, the obtained molding raw materials are kneaded to form a clay (hereinafter also referred to as hoke), and the clay is extruded to produce a honeycomb molded body. The honeycomb molded body has an outer peripheral wall and partition walls disposed inside the outer peripheral wall to define a plurality of cells that form flow paths extending from one end face to the other end face.

[0043] The molding process includes a process of controlling the volume fraction of the portions that can become pores in the honeycomb molded body so that the absolute value of the difference between the predetermined porosity of the honeycomb fired body and the volume fraction of the portions that can become pores in a predetermined region of the honeycomb molded body is within 0.5%. The predetermined porosity is a porosity that is preset for each predetermined region in a cross section perpendicular to the cell flow direction of the honeycomb fired body. Here, the predetermined porosity is the desired porosity in a predetermined region in the honeycomb structure that is finally obtained after the firing process, and specifically, the porosity is set within a range of 35 to 60%. According to this configuration, by controlling the volume fraction of the portions that can become pores in a predetermined region in the molding process, the porosity in a predetermined region in the honeycomb structure that is finally obtained after the firing process can be controlled. As a result, the electrical resistivity in the predetermined region can be controlled. In this way, rather than adjusting the electrical resistivity during the firing process, which is affected by variations in atmosphere or temperature, the electrical resistivity is adjusted by controlling the volume fraction distribution of potential pores within the honeycomb formed body during the firing process. This allows for a simple and stable formation of a desired electrical resistivity distribution within the honeycomb structure. Furthermore, since there is no need to control the porosity within the honeycomb fired body during the firing process, wear on firing tools used during firing, such as the enclosure, shelves on which the product is placed, sand (grain) placed on the shelves, and a lid (top plate) placed on the enclosure, can be reduced. Furthermore, by presetting a predetermined porosity for each predetermined region and controlling the volume fraction so that the absolute value of the difference between the predetermined porosity and the volume fraction of potential pores in a predetermined region of the honeycomb formed body is within 0.5%, a desired porosity distribution can be formed within the final honeycomb structure. As a result, a desired electrical resistivity distribution can be formed within the honeycomb structure. Furthermore, since the porosity of the honeycomb structure is distributed in a predetermined manner, it is possible to form a desired distribution state of material properties such as strength and Young's modulus.

[0044] The volume fraction of the portions that can become pores in the honeycomb formed body refers to the volume fraction of the portions that become pores in a fired body produced by drying and firing the honeycomb formed body (porosity of the honeycomb fired body). The portions that become pores in the fired body correspond to pores, pore-forming material, moisture, etc. at the stage of the honeycomb formed body. Thus, the volume fraction of the portions that can become pores in the honeycomb formed body indicates the volume fraction of the total of pores, pore-forming material, and moisture contained in the honeycomb formed body in a specified region of the honeycomb formed body.

[0045] To measure the volume fraction of the potential pores in a predetermined region of the honeycomb formed body, a sample is first cut out from the predetermined region of the honeycomb formed body, and then dried and fired to obtain a fired body sample. Next, the porosity of this fired body sample is measured using a mercury porosimeter, or by calculating the pore area ratio from an image taken with an SEM (scanning electron microscope), and this is used as the volume fraction of the potential pores in the predetermined region of the honeycomb formed body. The drying and firing conditions for producing the fired body sample are the same as the drying and firing conditions for producing the honeycomb fired body described below.

[0046] The above-mentioned "predetermined region" is not particularly limited, and can be appropriately designed depending on the purpose, for example, in a cross section perpendicular to the flow path direction of the cell, such as a central region and a peripheral region, one semicircular region and the other semicircular region, or a plurality of island-shaped regions and other regions, etc. By setting the predetermined region more precisely, a more precise electrical resistivity distribution can be formed.

[0047] Furthermore, the predetermined region may include a central region extending from the center of the cross section to ½r and a peripheral region extending from ½r to r in a cross section perpendicular to the flow direction of the cells of the honeycomb fired body, where r is the radius of the cross section. In this manner, the step of setting the predetermined region and controlling the volume fraction of the portions that can become pores of the honeycomb formed body may control the absolute values ​​of the differences in the volume fractions of the portions that can become pores in the central region and peripheral region of the honeycomb formed body relative to the predetermined porosities of the central region and peripheral region set in advance in the honeycomb fired body to be within 0.5%. According to this configuration, in the cross section perpendicular to the flow direction of the cells of the finally obtained honeycomb structure, the volume fraction of the portions that can become pores in the outer region (peripheral region) is controlled within a predetermined numerical range relative to the porosity of the region (central region) from the center in the radial direction to the inner region. Therefore, the electrical resistivity of the peripheral region can be controlled within a predetermined range relative to the electrical resistivity of the central region. Therefore, when the honeycomb structure is used in an EHC, desired effects can be obtained as appropriate, such as reducing the energy required to purify exhaust gas by applying voltage, or suppressing uneven heat generation distribution and generating heat uniformly.

[0048] The volume fraction of the portions that can become pores in a predetermined region of the honeycomb formed body can be controlled by (1) controlling the density distribution in the hollow or (2) controlling the density distribution in the honeycomb formed body, as exemplified below. Note that the controls of (1) and (2) may be used in combination.

[0049] (1) Control of density distribution within the kettle By controlling the density distribution in the hoke, it is possible to control the volume ratio of the portions that can become pores in a predetermined region of the honeycomb formed body. Hoke is composed of soil, internal moisture, and internal air, and is produced using a clay kneader. In order to control the volume ratio of the portions that can become pores in a predetermined region of the honeycomb formed body, the density of the hoke is set to 1.5 to 2.2 g / cm. 3 It is preferable that the density is 1.7 to 2.0 g / cm 3It is more preferable that the density of the hoke be within the above range. Examples of methods for controlling the density of the hoke within the above range include controlling the rotation speed of the screw used in the clay kneader, the degree of vacuum in the clay kneader, and / or the temperature distribution in the clay kneader. By controlling the air content within the hoke in a predetermined region using these methods, the volume fraction of the portions that can become pores in a predetermined region of the honeycomb molded body can be controlled. Furthermore, by controlling the rotation speed of the screw, the degree of vacuum in the clay kneader, and the temperature distribution in the clay kneader, the pore-forming material contained in the clay can be intentionally distributed unevenly within the hoke, thereby controlling the volume fraction of the portions that can become pores in a predetermined region of the honeycomb molded body. By controlling the rotation speed of the screw used in the clay kneader, the proportion of bubbles in a predetermined region of the hoke can be controlled. The rotation speed of the screw used in the clay kneader is not particularly limited and can be appropriately selected depending on the desired density distribution within the hoke, but it can be, for example, 600 to 3,000 rpm.

[0050] By controlling the degree of vacuum in the kneader, the proportion of air in a predetermined region in the hoke can be controlled. The degree of vacuum in the kneader is not particularly limited and can be appropriately selected depending on the desired density distribution in the hoke, but can be, for example, -0.09 to -0.10 Pa.

[0051] By controlling the temperature distribution in the kneader, the proportion of internal air in a predetermined region in the kneader can be controlled. The temperature distribution in the kneader can be controlled by adjusting the temperature of the chiller (cooling water circulator) in the kneader or the flow rate of cooling water. The temperature of the chiller in the kneader is not particularly limited, but can be set to -10 to 20°C. The flow rate of cooling water is not particularly limited, but can be set to 5 to 30 m 3 It can be / s.

[0052] (2) Control of density distribution within honeycomb molded body By controlling the density distribution within the honeycomb formed body, it is possible to control the volume fraction of the portions that can become pores in a predetermined region of the honeycomb formed body. By using a forming machine including a die to extrude the forming raw material, and controlling the uneven pattern at the tip of the honeycomb formed body extruded from the forming machine, it is possible to control the amount and flow rate of the clay extruded from the forming machine, and thereby control the volume fraction of the portions that can become pores in a predetermined region of the honeycomb formed body. Methods for controlling the uneven pattern at the tip of the honeycomb formed body extruded from the forming machine include, for example, controlling the temperature distribution within the forming machine, the length in the clay path direction of the squeezing jig provided upstream of the die in the clay path, the hole diameter and pitch arrangement of the back plate, and / or the length of the honeycomb formed body.

[0053] As shown in Figures 4(a) and (b), by controlling the uneven pattern at the tip of a honeycomb formed body formed by extruding clay 42 from a forming machine 40, a difference in flow velocity in the extrusion direction occurs within the honeycomb formed body extruded from the forming machine 40. If the tip of the honeycomb formed body extruded from the forming machine 40 is convex, as shown in Figure 4(a), the flow velocity and soil volume at the central part of the honeycomb formed body extruded from the die 41 will be large in a cross section perpendicular to the cell flow direction, and the porosity will be small. On the other hand, if the tip of the honeycomb formed body extruded from the forming machine 40 is concave, as shown in Figure 4(b), the flow velocity and soil volume at the central part of the honeycomb formed body extruded from the die 41 will be small in a cross section perpendicular to the cell flow direction.

[0054] The uneven pattern at the tip of the honeycomb formed body extruded from the molding machine is not particularly limited, and can be designed appropriately depending on the desired density distribution within the honeycomb formed body. Examples of uneven patterns at the tip of the honeycomb formed body extruded from the molding machine are shown in Figures 5(a) to 5(d). Figure 5(a) shows a pattern in which the center of the tip of the honeycomb formed body 43 is raised, Figure 5(b) shows a pattern in which the center of the tip of the honeycomb formed body 43 is depressed, Figure 5(c) shows a pattern in which the tip of the honeycomb formed body 43 is inclined, and Figure 5(d) shows a pattern in which the tip of the honeycomb formed body 43 has unevenness.

[0055] The uneven pattern at the tip of the honeycomb molded body extruded from the molding machine can be appropriately formed by adjusting the size and distribution of the hole diameters of the back plate, mesh, and / or pressure plate (back pressure) attached to the nozzle of the molding machine.

[0056] By controlling the temperature distribution inside the molding machine, it is possible to control the proportion of air contained in the honeycomb molded body, and thereby to control the density distribution. The temperature distribution inside the molding machine can be controlled by adjusting the temperature of the chiller (cooling water circulator) inside the molding machine or the flow rate of cooling water. The temperature of the chiller inside the molding machine is not particularly limited, but can be set to -10 to 20°C. The flow rate of cooling water is not particularly limited, but can be set to 5 to 30 m 3 It can be / s.

[0057] The density distribution within the honeycomb molded body can be controlled by controlling the length of the clay (forming raw material) in the path direction of the squeezing jig, which is installed upstream of the die in the path of the clay. Increasing the length of the clay in the path direction after squeezing by the squeezing jig increases the transport time, which increases the moisture evaporation rate, especially in the peripheral region, thereby controlling the density distribution within the honeycomb molded body. The length of the clay in the path direction is not particularly limited, but can be 10 to 20 cm. Furthermore, by controlling the ratio of the diameter of the squeezed clay to its length in the path direction, the outer shape of the molded body can be appropriately designed, which allows for more precise control of the moisture evaporation rate and more precise control of the density distribution within the honeycomb molded body. The ratio (A / B) of the diameter (A) of the squeezed clay to its length in the path direction (B) is not particularly limited, but can be 0.8 to 1.5.

[0058] The density distribution within the honeycomb formed body can be controlled by controlling the length of the honeycomb formed body. Increasing the length of the honeycomb formed body increases the transport time, which increases the moisture evaporation rate, especially in the peripheral region, and thereby allows the density distribution within the honeycomb formed body to be controlled.

[0059] (drying process) Next, the obtained honeycomb molded body is dried to produce a dried honeycomb body. The drying method is not particularly limited, and examples thereof include electromagnetic heating methods such as microwave heating drying and high-frequency dielectric heating drying, and external heating methods such as hot air drying and superheated steam drying. Among these, the method of drying a certain amount of moisture by electromagnetic heating and then drying the remaining moisture by external heating is preferred, as it allows the entire molded body to be dried quickly and uniformly without cracking. The drying conditions are preferably such that 30 to 99% by mass of moisture is removed by electromagnetic heating, based on the moisture content before drying, and then the moisture content is reduced to 3% by mass or less by external heating. Dielectric heating drying is preferred as the electromagnetic heating method, and hot air drying is preferred as the external heating method. The drying temperature is preferably 50 to 120°C.

[0060] (Firing process) Next, the obtained dried honeycomb body is fired to produce a fired honeycomb body. Firing conditions are preferably such that the honeycomb body is heated at 1400 to 1500°C for 1 to 20 hours in an inert atmosphere such as nitrogen or argon. After firing, it is preferable to perform an oxidation treatment at 1200 to 1350°C for 1 to 10 hours to improve durability. The degreasing and firing methods are not particularly limited, and firing can be performed using an electric furnace, a gas furnace, or the like.

[0061] The honeycomb fired body may be used as a honeycomb structure as is, or a honeycomb structure having electrode portions may be produced by providing electrode portions on the side surfaces of the honeycomb fired body. A method for producing a honeycomb structure having electrode portions involves first applying an electrode portion-forming raw material containing a ceramic raw material to the side surfaces of the honeycomb fired body and drying the applied material to form a pair of unfired electrode portions on the outer surface of the peripheral wall, sandwiching the central axis of the honeycomb fired body, so as to extend in a band-like shape in the flow path direction of the cells, thereby producing a honeycomb fired body with unfired electrode portions. Next, the honeycomb fired body with unfired electrode portions is fired to produce a honeycomb structure with a pair of electrode portions. The electrode portions may be formed by applying an electrode portion-forming raw material to a dried honeycomb body, rather than the honeycomb fired body, and drying the raw material to form unfired electrode portions, which are then fired to produce a honeycomb fired body with electrode portions.

[0062] The electrode part-forming raw material can be formed by adding various additives appropriately to raw material powders (metal powder and / or ceramic powder, etc.) formulated according to the required characteristics of the electrode part, and kneading them. When the electrode part has a laminated structure, the bonding strength between the metal terminal and the electrode part tends to be improved by making the average particle diameter of the metal powder in the paste for the second electrode part larger than the average particle diameter of the metal powder in the paste for the first electrode part. The average particle diameter of the metal powder refers to the arithmetic mean diameter on a volume basis when measuring the particle size frequency distribution using a laser diffraction method.

[0063] The method of preparing the electrode portion-forming raw material and the method of applying the electrode portion-forming raw material to the honeycomb fired body can be carried out in accordance with known methods for manufacturing honeycomb structures, but in order to give the electrode portion a lower electrical resistivity than the honeycomb structure portion, the metal content can be made higher than that of the honeycomb structure portion, or the particle size of the metal particles can be made smaller.

[0064] Before firing the honeycomb fired body with green electrode parts, the honeycomb fired body with green electrode parts may be dried. Furthermore, before firing, degreasing may be performed to remove binders and the like. The firing conditions for the honeycomb fired body with green electrode parts are preferably heating at 1400 to 1500°C for 1 to 20 hours in an inert atmosphere such as nitrogen or argon. Furthermore, after firing, oxidation treatment is preferably performed at 1200 to 1350°C for 1 to 10 hours to improve durability. The degreasing and firing methods are not particularly limited, and firing can be performed using an electric furnace, a gas furnace, or the like.

[0065] <Production method according to embodiment 2> The method for manufacturing a honeycomb structure according to the second embodiment of the present invention includes a forming step for obtaining a honeycomb formed body, a drying step for obtaining a dried honeycomb body, and a firing step for obtaining a fired honeycomb body.

[0066] (molding process) In the molding step, the same molding raw material as in the manufacturing method of the honeycomb structure according to the above-mentioned embodiment 1 is used, and the molding raw material is extrusion-molded to produce a honeycomb molded body having an outer peripheral wall and partition walls that are disposed inside the outer peripheral wall and define a plurality of cells that form flow paths extending from one end face to the other end face. In the manufacturing method of the honeycomb structure according to embodiment 2, the volume ratio of the parts that can become pores is not controlled in the molding step, but is controlled in the subsequent drying step.

[0067] (drying process) Next, the obtained honeycomb molded body is dried to produce a dried honeycomb body. The drying process includes a step of controlling the volume fraction of the potential pores in the dried honeycomb body so that the absolute value of the difference between the volume fraction of the potential pores in a predetermined region of the dried honeycomb body and the predetermined porosity of the fired honeycomb body is within 0.5%. The predetermined porosity is a porosity preset for each predetermined region in a cross section of the dried honeycomb body perpendicular to the cell flow direction. According to this configuration, by controlling the volume fraction of the potential pores in a predetermined region in the drying process, the porosity in a predetermined region of the finally obtained honeycomb structure can be controlled, and as a result, the electrical resistivity in the predetermined region can be controlled. In this way, rather than adjusting the electrical resistivity in the firing process, which is affected by variations in atmosphere or temperature, the electrical resistivity is adjusted by controlling the distribution of the volume fraction of the potential pores in the dried honeycomb body in the drying process, so that a desired electrical resistivity distribution can be stably formed in the honeycomb structure by a simple method. Furthermore, since there is no need to control the porosity within the honeycomb fired body during the firing process, wear and tear on firing tools used during firing, such as the enclosure, shelves on which the product is placed, sand (grain) to be spread on the shelves, and a lid (top plate) to be placed on the enclosure, can be reduced. Furthermore, by setting a predetermined porosity for each predetermined region and producing a dried honeycomb body so that the absolute value of the difference in volume fraction of the potential pores in a predetermined region of the dried honeycomb body relative to the predetermined porosity is within 0.5%, a desired porosity distribution can be formed in the final honeycomb structure, and as a result, a desired electrical resistivity distribution can be formed in the honeycomb structure. Furthermore, because the porosity of the honeycomb structure is distributed in a predetermined pattern, desired distributions of material properties such as strength and Young's modulus can also be formed.

[0068] The volume fraction of the portions that can become pores in the above-mentioned honeycomb dried body refers to the volume fraction of the portions that become pores in a fired body produced by firing the honeycomb dried body (porosity of the honeycomb fired body). The portions that become pores in the fired body correspond to pores, pore-forming material, moisture, etc. at the stage of the honeycomb dried body. Thus, the volume fraction of the portions that can become pores in the honeycomb dried body indicates the volume fraction of the total of pores, pore-forming material, and moisture contained in the honeycomb dried body in a specified region of the honeycomb dried body.

[0069] Furthermore, the predetermined region may include a central region extending from the center of the cross section to ½r and a peripheral region extending from ½r to r in a cross section perpendicular to the flow path direction of the cells of the honeycomb fired body, where r is the radius of the cross section. In this manner, the step of setting the predetermined region and controlling the volume fraction of the portions that can become pores of the honeycomb dried body may control the absolute values ​​of the differences in the volume fractions of the portions that can become pores in the central region and peripheral region of the honeycomb dried body relative to the predetermined porosities of the central region and peripheral region set in advance in the honeycomb fired body to be within 0.5%. According to this configuration, in the cross section perpendicular to the flow path direction of the cells, the finally obtained honeycomb structure has a porosity of the outer region (peripheral region) controlled to be within a predetermined range relative to the porosity of the region (central region) from the center in the radial direction. Therefore, the electrical resistivity of the peripheral region can be controlled to be within a predetermined range relative to the electrical resistivity of the central region. Therefore, when the honeycomb structure is used in an EHC, desired effects can be obtained as appropriate, such as reducing the energy required to purify exhaust gas by applying voltage, or suppressing uneven heat generation distribution and generating heat uniformly.

[0070] The volume fraction of the portions that can become pores in a predetermined region of the above-mentioned dried honeycomb body may be controlled by (1) controlling the moisture evaporation rate of the honeycomb formed body, as exemplified below. (1) can also be controlled by (2) controlling the distance between parallel plate electrodes used when drying by dielectric heating, or (3) controlling the drying time of the honeycomb formed body, as exemplified below. Note that the controls of (2) and (3) below may be used in combination of two or more of them.

[0071] (1) Controlling the moisture evaporation rate of honeycomb molded bodies By controlling the moisture evaporation rate of the honeycomb formed body, it is possible to control the volume fraction of the portions that can become pores in a predetermined region of the dried honeycomb body. Specifically, in addition to the controls (2) and (3) above, the moisture evaporation rate of the predetermined region of the honeycomb formed body is controlled by controlling the relative humidity and wet-bulb temperature in the furnace during the drying process, and thereby it is possible to control the volume fraction of the portions that can become pores in a predetermined region of the dried honeycomb body.

[0072] (2) Controlling the distance between parallel plate electrodes used when drying by dielectric heating By controlling the inter-electrode distance of the parallel plate electrodes used when drying by dielectric heating, it is possible to control the volume fraction of the portions that can become pores in a predetermined region of the dried honeycomb body. Specifically, by shortening the inter-electrode distance of the parallel plate electrodes, it is possible to increase the moisture evaporation rate of the honeycomb formed body. Furthermore, by increasing the inter-electrode distance of the parallel plate electrodes, it is possible to decrease the moisture evaporation rate of the honeycomb formed body. By controlling the moisture evaporation rate in the honeycomb formed body in this way, it is possible to control the volume fraction of the portions that can become pores in a predetermined region of the dried honeycomb body. The inter-electrode distance of the parallel plate electrodes is not particularly limited and can be appropriately designed depending on the desired moisture evaporation rate. For example, it may be controlled so that it is 5 to 150 mm higher than the honeycomb cover member provided to cover the dried honeycomb body, or it may be controlled so that it is 20 to 40 mm higher than the honeycomb cover member.

[0073] (3) Controlling the drying time of honeycomb molded bodies By controlling the drying time of the honeycomb formed body during the drying process, it is possible to control the volume ratio of the portions that can become pores in a predetermined region of the dried honeycomb body. Specifically, by extending the drying time of the honeycomb formed body, it is possible to increase the moisture evaporation rate, particularly in the peripheral region. Furthermore, by shortening the drying time of the honeycomb formed body, it is possible to suppress the moisture evaporation rate, particularly in the peripheral region. By controlling the moisture evaporation rate within the honeycomb formed body in this way, it is possible to control the volume ratio of the portions that can become pores in a predetermined region of the dried honeycomb body. The drying time of the honeycomb formed body is not particularly limited and can be appropriately designed depending on the desired moisture evaporation rate, but it may be, for example, 10 to 180 minutes or 15 to 30 minutes. Furthermore, the drying time can be adjusted, for example, by controlling the conveying speed of the honeycomb formed body. Reducing the conveying speed of the honeycomb formed body increases the conveying time and therefore the drying time. Furthermore, increasing the conveying speed of the honeycomb formed body reduces the conveying time and therefore the drying time. The transport speed of the honeycomb formed body is not particularly limited and can be appropriately designed depending on the desired moisture evaporation rate, and may be, for example, 50 to 400 mm / min, or 150 to 200 mm / min.

[0074] In the drying step, the drying method is not particularly limited except for controlling any of the above (1) to (3). Examples include electromagnetic heating methods such as microwave heating drying and high-frequency dielectric heating drying, and external heating methods such as hot air drying and superheated steam drying. Among these, it is preferable to dry a certain amount of moisture using the electromagnetic heating method and then dry the remaining moisture using the external heating method, as this allows the entire molded body to be dried quickly, uniformly, and without cracking. As drying conditions, it is preferable to remove 30 to 99% by mass of moisture based on the moisture content before drying using the electromagnetic heating method, and then reduce the moisture content to 3% by mass or less using the external heating method. As the electromagnetic heating method, dielectric heating drying is preferred, and as the external heating method, hot air drying is preferred. The drying temperature is preferably 50 to 130°C, more preferably 80 to 130°C.

[0075] (Firing process) Next, the obtained dried honeycomb body is fired to produce a honeycomb fired body. In the firing step in embodiment 2, the honeycomb fired body can be fired under the same conditions as in the firing step in embodiment 1. Furthermore, similar to embodiment 1, the honeycomb fired body may be used as a honeycomb structure as is, or a honeycomb structure having electrode parts may be produced by providing electrode parts on the side surfaces of the honeycomb fired body.

[0076] (4. Manufacturing method of electrically heated carrier) In one embodiment of the method for manufacturing the electrically heated carrier 30 according to the present invention, a metal electrode is electrically connected to each of a pair of electrode portions of the honeycomb structure 10. Examples of connection methods include laser welding, thermal spraying, and ultrasonic welding. More specifically, a pair of metal electrodes is provided on the surfaces of the electrode portions, sandwiching the central axis of the columnar honeycomb structure portion 11. In this manner, the electrically heated carrier 30 according to the present invention is obtained. With this configuration, the honeycomb structure of the electrically heated carrier has a desired electrical resistivity distribution controlled, making it possible to manufacture an electrically heated carrier that has desired effects, such as reducing the energy required to purify exhaust gases or suppressing uneven heat generation distribution and achieving uniform heat generation.

[0077] (5. Exhaust gas purification device) The electrically heated carrier according to the embodiment of the present invention described above can be used in an exhaust gas purification device. The exhaust gas purification device includes an electrically heated carrier and a metallic tubular member that holds the electrically heated carrier. In the exhaust gas purification device, the electrically heated carrier is installed midway in an exhaust gas flow path through which exhaust gas from an engine flows. [Example]

[0078] The following examples are provided to provide a better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

[0079] <Examples 1 to 3, Comparative Examples 1 and 2> (1. Preparation of clay) A ceramic raw material was prepared by mixing silicon carbide (SiC) powder and metallic silicon (Si) powder in an 80:20 mass ratio. Hydroxypropyl methylcellulose as a binder, a water-absorbent resin as a pore-forming material, and water were added to the ceramic raw material to form a molding raw material. The molding raw material was then kneaded using a vacuum kneader to produce cylindrical clay. The screw rotation speed, degree of vacuum, internal and external temperature difference, and buffing density of the vacuum kneader are shown in Table 1. The binder content was 7.0 parts by mass per 100 parts by mass of the silicon carbide (SiC) powder and metallic silicon (Si) powder. The pore-forming material content was 3.0 parts by mass per 100 parts by mass of the silicon carbide (SiC) powder and metallic silicon (Si) powder. The water content was 42 parts by mass per 100 parts by mass of the silicon carbide (SiC) powder and metallic silicon (Si) powder. The average particle size of the silicon carbide powder was 20 μm, and the average particle size of the metallic silicon powder was 6 μm. The average particle size of the pore-forming material was 20 μm. The average particle sizes of the silicon carbide powder, metallic silicon powder, and pore-forming material refer to the arithmetic mean diameters on a volume basis when the particle size frequency distribution was measured by laser diffraction.

[0080] (2. Preparation of honeycomb formed body) The obtained cylindrical clay was molded using an extrusion molding machine with a grid-like die structure to obtain a cylindrical honeycomb molded body in which each cell shape in a cross section perpendicular to the cell flow direction was hexagonal. At this time, the convexity of the tip of the honeycomb molded body extruded from the extrusion molding machine and the degree of vacuum of the extrusion molding machine were controlled as shown in Table 1. In Examples 1 to 3, the convexity of the tip of the honeycomb molded body was 0 mm, that is, the honeycomb molded body had a flat tip. In Comparative Example 1, the uneven pattern of the tip of the honeycomb molded body extruded from the molding machine was convex (convexity: h1 = 5 mm) as shown in FIG. 5(a), and in Comparative Example 2, it was concave (convexity: h2 = -5 mm) as shown in FIG. 5(b). To determine the volume ratio of the pore portion of the honeycomb molded body, a sample was cut out from the honeycomb molded body so as to include the central region and the outer peripheral region, and a fired body sample was produced from this under the same drying and firing conditions as when producing a honeycomb fired body described below. Next, the porosity of the central region and the peripheral region of the prepared fired body sample was measured by a mercury porosimeter, and this was taken as the volume fraction of the portion that would become the pores of the honeycomb formed body. For the volume fraction of the portion that would become the pores of the dried honeycomb body, a fired body sample was prepared in the same way, and the porosity of the fired body sample was measured and taken as the volume fraction.

[0081] (3. Preparation of dried honeycomb body) Next, the honeycomb formed body was subjected to high-frequency dielectric heating drying, and then dried using a hot air dryer at 120°C for 2 hours to produce a dried honeycomb body. Table 1 shows the transport speed of the honeycomb formed body during the drying process, the height of the electrode used for high-frequency dielectric heating drying, and the dielectric dispersion rate due to the high-frequency dielectric heating drying. The "electrode height" in Table 1 indicates how high the electrode was positioned above the honeycomb cover member that was installed to cover the dried honeycomb body during dielectric heating. The "dielectric dispersion rate" was also calculated by calculating the amount of dispersed moisture from the difference between the mass of the honeycomb formed body and the mass of the dried honeycomb body, and dividing this by the moisture contained in the honeycomb formed body. In this way, in a cross section perpendicular to the flow direction of the cells of the honeycomb fired body, when the radius of the cross section is r, the central region from the center of the cross section to 1 / 2r and the peripheral region from 1 / 2r to r were controlled in advance to have the porosity shown in Table 2. The porosity of the central region and the peripheral region of the honeycomb dried body was measured by a mercury porosimeter, respectively.

[0082] (4. Preparation of honeycomb fired body) Next, the dried honeycomb body was fired in an Ar atmosphere at 1400°C for 3 hours to obtain a fired honeycomb body (a columnar honeycomb structure). The porosity of the obtained fired honeycomb body was measured for each of the central region and the outer peripheral region using a mercury porosimeter.

[0083] The honeycomb structure had a circular end face with a diameter of 100 mm and a height (length of the cells in the flow path direction) of 100 mm. The cell density was 93 cells / cm. 2 The thickness of the partition walls was 101.6 μm, and the average pore diameter of the partition walls was 8.6 μm.

[0084] (5. Evaluation of resistivity) A rod-shaped sample was cut out from the honeycomb fired body, and silver paste and silver wires were placed at four axial positions on the sample, which was then measured using a four-terminal method. The resistivities of the central region and the peripheral region shown in Table 2, which show the measurement results, are the resistivities (%) when the resistivity of a fired body with a porosity of 38.0% in the central region is taken as 100%, and the resistivity (%) when the resistivity of a fired body with a porosity of 38.0% in the peripheral region is taken as 100%, respectively. The test conditions and evaluation results are shown in Tables 1 and 2.

[0085] [Table 1]

[0086] [Table 2]

[0087] (6. Discussion) In Examples 1 to 3, the dried honeycomb bodies were manufactured so that the absolute values ​​of the difference in volume fraction of the portions that could become pores in the central region and the peripheral region of the dried honeycomb body relative to a predetermined porosity (porosity of the honeycomb fired body) were each within 0.5%. As a result, the variation in resistivity between the central region and the peripheral region of the honeycomb structure (the difference between the resistivity of the central region and the resistivity of the peripheral region in Table 2) was 20% or less, and a honeycomb structure with little variation in resistivity was obtained. In both Comparative Examples 1 and 2, the absolute values ​​of the difference in volume fraction of the potential pores in the central and peripheral regions of the dried honeycomb body relative to the predetermined porosity (porosity of the honeycomb fired body) were outside the range of 0.5%, respectively. As a result, the resistivity variation between the central and peripheral regions of the honeycomb structure was 80%, and the desired electrical resistivity distribution was not obtained. In Table 2, for Examples 1 to 3 and Comparative Examples 1 and 2, the "porosity of the dried body" is significantly lower than the "porosity of the fired body." This is because the dried body contains pores as well as pore-forming materials, and these pore-forming materials become pores in the fired body. [Explanation of symbols]

[0088] 10 Honeycomb structure 11 Columnar honeycomb structure 12 Peripheral wall 13a, 13b electrode part 18 cells 19 Bulkhead 30 Electrically heated carrier 33a, 33b metal electrode 40 Molding machine 41 nozzle 42 Clay 43 Honeycomb molded body

Claims

1. a molding step of extruding a molding raw material containing a conductive ceramic raw material to obtain a honeycomb molded body having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and defining a plurality of cells that form flow paths extending from one end face to the other end face; a drying step of drying the honeycomb formed body to obtain a dried honeycomb body; a firing step of firing the dried honeycomb body to obtain a fired honeycomb body; Equipped with the forming step includes a step of controlling the volume ratio of the portions that can become pores of the honeycomb formed body so that the absolute value of the difference between a predetermined porosity set in advance in the honeycomb fired body and a volume ratio of the portions that can become pores in a predetermined region of the honeycomb formed body is within 0.5%, A method for manufacturing a conductive honeycomb structure, wherein the predetermined porosity is a porosity that is set in advance for each predetermined region in a cross section of the honeycomb fired body perpendicular to the flow path direction of the cells.

2. the predetermined region has a central region from the center of the cross section to 1 / 2r and a peripheral region from 1 / 2r to r, where r is a radius of the cross section in a cross section perpendicular to a flow direction of the cells of the honeycomb fired body, A method for manufacturing a conductive honeycomb structure as described in claim 1, wherein the process of controlling the volume fraction of the parts that can become pores in the honeycomb formed body is a process of controlling the absolute value of the difference in the volume fraction of the parts that can become pores in the central region and the peripheral region of the honeycomb formed body relative to the predetermined porosity of the central region and the peripheral region of the honeycomb fired body so that it is within 0.5%.

3. A method for manufacturing a conductive honeycomb structure as described in claim 1 or 2, wherein the volume ratio of the parts of the honeycomb formed body that can become pores indicates the total volume ratio of the pores, pore-forming material, and moisture contained in the honeycomb formed body.

4. The step of controlling the volume ratio of the portions that can become pores of the honeycomb formed body includes using a kneader to knead the forming raw material containing the ceramic raw material so that the density distribution in the forming raw material is 1.5 to 2.2 g / cm 3 The method for manufacturing a conductive honeycomb structure according to any one of claims 1 to 3, further comprising a step of controlling the temperature to the temperature above 100°C.

5. The method for manufacturing a conductive honeycomb structure according to any one of claims 1 to 3, wherein the process of controlling the volume fraction of the portions that can become pores in the honeycomb formed body includes a process of using a kneader to knead the forming raw material containing the ceramic raw material, and controlling the rotation speed of the screw used in the kneader, the degree of vacuum within the kneader, and / or the temperature distribution within the kneader.

6. The step of controlling the volume ratio of the portions that can become pores in the honeycomb formed body includes: A method for manufacturing a conductive honeycomb structure as described in any one of claims 1 to 5, comprising a step of using a molding machine including a die to extrude the forming raw material, controlling the uneven pattern at the tip of the honeycomb formed body extruded from the molding machine, the temperature distribution within the molding machine, the length of a squeezing jig installed upstream of the die in the path direction of the forming raw material, and / or the length of the honeycomb formed body.

7. a molding step of extruding a molding raw material containing a conductive ceramic raw material to obtain a honeycomb molded body having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and defining a plurality of cells that form flow paths extending from one end face to the other end face; a drying step of drying the honeycomb formed body to obtain a dried honeycomb body; a firing step of firing the dried honeycomb body to obtain a fired honeycomb body; Equipped with the drying step includes a step of controlling a volume ratio of a portion that can become a pore in the honeycomb dried body so that an absolute value of a difference between a predetermined porosity set in advance in the honeycomb fired body and a volume ratio of a portion that can become a pore in a predetermined region of the honeycomb dried body is within 0.5%, A method for manufacturing a conductive honeycomb structure, wherein the predetermined porosity is a porosity that is set in advance for each predetermined region in a cross section of the honeycomb fired body perpendicular to the flow path direction of the cells.

8. the predetermined region has a central region from the center of the cross section to 1 / 2r and a peripheral region from 1 / 2r to r, where r is a radius of the cross section in a cross section perpendicular to a flow direction of the cells of the honeycomb fired body, A method for manufacturing a conductive honeycomb structure as described in claim 7, wherein the process of controlling the volume fraction of the parts that can become pores in the honeycomb dried body is a process of controlling the absolute value of the difference in the volume fraction of the parts that can become pores in the central region and the peripheral region of the honeycomb dried body relative to the predetermined porosity of the central region and the peripheral region of the honeycomb fired body so that it is within 0.5%.

9. A method for manufacturing a conductive honeycomb structure as described in claim 7 or 8, wherein the volume ratio of the parts of the honeycomb dried body that can become pores indicates the total volume ratio of the pores, pore-forming material, and moisture contained in the honeycomb dried body.

10. The step of controlling the volume ratio of the portions that can become pores of the honeycomb dried body includes: A method for manufacturing a conductive honeycomb structure described in any one of claims 7 to 9, including a step of controlling the moisture evaporation rate of the honeycomb formed body, the electrode distance between parallel plate electrodes used when drying by dielectric heating, and / or the drying time of the honeycomb formed body.

11. A method for manufacturing a conductive honeycomb structure as described in any one of claims 1 to 10, wherein, in a cross section of the conductive honeycomb structure perpendicular to the flow direction of the cells, when the radius of the cross section is r, the absolute value of the difference in porosity of the central region from the center of the cross section to 1 / 2r to the peripheral region from 1 / 2r to r is within 0.5%.

12. A method for manufacturing a conductive honeycomb structure as described in any one of claims 1 to 10, wherein, in a cross section of the conductive honeycomb structure perpendicular to the flow direction of the cells, when the radius of the cross section is r, the difference in porosity of the central region from the center of the cross section to 1 / 2r and the porosity of the peripheral region from 1 / 2r to r is -0.5% or less and +0.5% or more.

13. a step of applying an electrode portion-forming raw material containing a ceramic raw material to a side surface of the honeycomb fired body, and drying the applied material to form a pair of unfired electrode portions on the outer surface of the outer wall across the central axis of the honeycomb fired body, the pair of unfired electrode portions extending in a band-like shape in a flow path direction of the cells; and a step of firing the honeycomb fired body with the unfired electrode portions to produce a conductive honeycomb structure having a pair of electrode portions; The method for manufacturing a conductive honeycomb structure according to any one of claims 1 to 12, further comprising:

14. A method for manufacturing an electrically heated carrier, comprising a step of electrically connecting metal electrodes to each of the pair of electrode portions of the conductive honeycomb structure manufactured by the method according to claim 13.

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