Honeycomb structure

Abstract

To provide a honeycomb structure which is obtained by combining a plurality of honeycomb segments through an adhesive material layer and can suppress the occurrence of wire breakage of an electric heating wire and deterioration in purification performance.SOLUTION: There is provided a honeycomb structure obtained by combining a plurality of honeycomb segments having partition walls defining and forming a plurality of cells via an adhesive material layer, wherein a catalyst is carried on the honeycomb segments, an electric heating wire is disposed between the adjacent honeycomb segments, the electric heating wire is disposed inside the adhesive material layer, the density of the adhesive material layer is 1.7 g / cm3 or more and 2.2 g / cm3 or less and among the pores in the adhesive material layer, the maximum diameter of the pore in contact with the electric heating wire is 1 mm or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a honeycomb structure. [Background technology]

[0002] In order to purify harmful substances contained in exhaust gas emitted from an engine, an exhaust gas purification device equipped with a honeycomb substrate carrying a catalyst capable of purifying exhaust gas is installed in the exhaust pipe route. In order to improve the efficiency of purifying harmful substances by an exhaust gas purification device, it is necessary to maintain the temperature inside the exhaust gas purification device at a temperature suitable for catalyst activation (hereinafter also referred to as catalyst activation temperature).

[0003] Patent Document 1 discloses a filter (DPF) that collects soot contained in the exhaust gas of a diesel engine to purify the exhaust gas. In this filter, an electric heating wire is disposed between adjacent filters as a heating element to burn the soot accumulated inside the filter. Patent Document 1 also discloses a heat-resistant filler material (adhesive layer) interposed between adjacent filters, which is made of ceramic fiber, silicon carbide powder, and an inorganic binder.

[0004] Also, Patent Document 2 discloses a DPF that uses ceramic balloons as an adhesive layer, and Patent Document 3 discloses a method for manufacturing a DPF that uses a jig that controls the evaporation rate of the adhesive layer, also for DPF applications. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-54643 [Patent Document 2] International Publication No. 2013 / 145243 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-201490 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when an adhesive layer is formed using the material configuration described in Patent Document 1, large pores are usually formed in the adhesive layer. If such large pores are formed in the adhesive layer, the heating wire will be in a dry heating state, and there is a risk of overheating and wire breakage.

[0007] The techniques described in Patent Documents 2 and 3 are intended to prevent the formation of large pores in the adhesive layer, and applying these techniques to the adhesive layer described in Patent Document 1 is thought to prevent the formation of pores. However, the techniques described in Patent Documents 2 and 3, based on the idea of ​​dispersing pores, have the problem of reducing the density of the adhesive layer, resulting in reduced heat transfer performance when heated with an electric heating wire, making it difficult to heat the honeycomb segments. Therefore, when a catalyst is loaded on a filter and used as a catalytic converter, there is a risk of reduced purification performance. Furthermore, if an electric heating wire is interposed in the adhesive layer, it is difficult to cover the honeycomb structure with a jig, as in the technique described in Patent Document 3.

[0008] The present invention has been made to solve the above problems, and aims to provide a honeycomb structure formed by combining multiple honeycomb segments via adhesive layers, which can suppress the occurrence of breakage of the heating wire and the deterioration of purification performance. [Means for solving the problem]

[0009] The honeycomb structure of the present invention is a honeycomb structure formed by combining a plurality of honeycomb segments, each having partition walls that define a large number of cells, via an adhesive layer, wherein a catalyst is supported on the honeycomb segments, and an electric heating wire is disposed between adjacent honeycomb segments, the electric heating wire is disposed inside the adhesive layer, and the density of the adhesive layer is 1.7 g / cm 3 More than 2.2g / cm 3The adhesive layer is characterized in that the maximum diameter of the pores in contact with the heating wire is 1 mm or less.

[0010] According to the honeycomb structure of the present invention, the maximum diameter of the pores in the adhesive layer that are in contact with the heating wire is 1 mm or less, and therefore all pores in contact with the heating wire are small, with a maximum diameter of 1 mm or less, thereby reducing the risk of the heating wire overheating and breaking. In addition, the density of the adhesive layer is 1.7 g / cm 3 As a result, the heat generated by the heating wire can be transmitted to the honeycomb segments that purify gases using a catalyst without reducing the heat transfer effect, and therefore the purification performance can be maintained at a high level. In other words, the reduction in purification performance can be suppressed.

[0011] In the honeycomb structure of the present invention, if the maximum diameter of the pores in contact with the heating wire exceeds 1 mm, the heating wire may be overheated and broken. In addition, the density of the adhesive layer is 1.7 g / cm 3 If the thickness is less than this, the density of the adhesive layer will be low, which may result in poor heat transfer performance when heated with an electric heating wire, and may result in poor purification performance. On the other hand, the density of the adhesive layer is 2.2 g / cm 3 If the temperature exceeds this range, the thermal shock resistance of the honeycomb structure decreases, and the honeycomb structure may be damaged when heated.

[0012] In the honeycomb structure of the present invention, the maximum diameter of the pores in the adhesive layer is preferably less than 2 mm, more preferably 1 mm or less, and further preferably less than 300 μm. In the honeycomb structure of the present invention, when the maximum diameter of the pores in the adhesive layer is less than 2 mm, the maximum diameter of the pores in contact with the heating wire can be easily set to 1 mm or less.

[0013] In the honeycomb structure of the present invention, the density of the adhesive layer is 1.8 g / cm 3 It is preferable that this is equal to or greater than this. In the honeycomb structure of the present invention, the density of the adhesive layer is 1.8 g / cm 3 If the above value is met, the heat transfer performance is increased, and therefore the purification performance can be improved. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view schematically showing an example of a honeycomb structure of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a honeycomb segment in a direction perpendicular to the longitudinal direction. [Figure 3] FIG. 3 is a partial cross-sectional view of the honeycomb structure shown in FIG. [Figure 4] FIG. 4 is an end view of the honeycomb structure shown in FIG. 1 as seen from the first end face side. [Figure 5] FIG. 5A is a schematic front view showing the simulation model, and FIG. 5B is a schematic cross-sectional view taken along line XX shown in FIG. 5A. [Figure 6] FIG. 6 is a graph showing the results of a simulation of the change over time in the maximum temperature at the center of the heating wire provided in the simulation model shown in FIGS. 5A and 5B. [Figure 7] FIG. 7 is an explanatory view schematically showing a cross section of a honeycomb aggregate. [Figure 8] FIG. 8 is an explanatory diagram showing a schematic arrangement of the heating wires.

[0015] (Detailed Description of the Invention) [Honeycomb structure] The honeycomb structure of the present invention will be described below. The honeycomb structure of the present invention is a honeycomb structure formed by combining a plurality of honeycomb segments, each having partition walls that define a large number of cells, via an adhesive layer, wherein a catalyst is supported on the honeycomb segments, and an electric heating wire is disposed between adjacent honeycomb segments, the electric heating wire is disposed inside the adhesive layer, and the density of the adhesive layer is 1.7 g / cm 3 More than 2.2g / cm 3The adhesive layer is characterized in that the maximum diameter of the pores in contact with the heating wire is 1 mm or less.

[0016] FIG. 1 is a perspective view schematically showing an example of a honeycomb structure of the present invention. The honeycomb structure 1 shown in Figure 1 is made up of a combination of multiple honeycomb segments 20 each having partition walls 22 that define a large number of cells 21, and has a first end face 11 through which gas flows in and a second end face 12 through which gas flows out. The direction in which the cells 21 of the honeycomb segment 20 extend (the direction indicated by the double-headed arrow L in FIG. 1) is defined as the longitudinal direction. The honeycomb segments are joined together via an adhesive layer 30 . In addition, an electrode terminal 40 protrudes from the first end face 11 .

[0017] The material forming the honeycomb segments (partition walls) is preferably one with high thermal conductivity, such as SiC.

[0018] The thickness of the partition walls is preferably uniform. Specifically, the thickness of the partition walls is preferably less than 0.30 mm. Also, the thickness is preferably 0.05 mm or more.

[0019] The shape of the cells is not limited to a quadrangular prism, but may be a triangular prism, a hexagonal prism, or the like. The cells may have different shapes, but are preferably all the same, i.e., in a cross section perpendicular to the longitudinal direction of the honeycomb segment, the size of the cells surrounded by the partition walls is preferably the same.

[0020] The porosity of the partition walls is preferably 50% or less. When the porosity of the partition walls is 50% or less, it is possible to achieve both high mechanical strength and exhaust gas purification performance.

[0021] If the porosity of the partition walls exceeds 50%, the porosity becomes too high, which reduces the mechanical strength of the honeycomb segments, making the honeycomb structure more susceptible to cracks, breakage, and the like during use.

[0022] The shape of the honeycomb structure is not particularly limited, and is not limited to a cylindrical shape, but may be a rectangular pillar, an elliptical pillar, an oblong pillar, a rectangular pillar with rounded edges (for example, a triangular pillar with rounded edges), etc.

[0023] When the honeycomb structure has a cylindrical shape, the ratio of the length in the longitudinal direction of the honeycomb structure to the diameter of the end face of the honeycomb structure (length / diameter) is preferably 0.8 or less.

[0024] The length of the honeycomb structure in the longitudinal direction is preferably 200 mm or less, and more preferably 50 mm or more.

[0025] FIG. 2 is a cross-sectional view of a honeycomb segment in a direction perpendicular to the longitudinal direction. When exhaust gas (the flow of exhaust gas is indicated by arrow G in FIG. 2) emitted from an internal combustion engine reaches the honeycomb segment 20, the exhaust gas flows into the cells 21 from the first end face 11 of the honeycomb segment 20. Furthermore, the exhaust gas passes through the cells 21 while coming into contact with the catalyst 23 supported on the partition walls 22. At this time, CO, HC, NO in the exhaust gas are X Harmful gas components such as these are purified by the catalyst 23 carried on the partition walls 22. Then, the exhaust gas flows out of the cells 21 at the second end face 12 of the honeycomb segment 20.

[0026] The catalyst 23 is not particularly limited as long as it can treat exhaust gas, but examples thereof include catalysts made of precious metals such as platinum, palladium, and rhodium, zeolites, etc. The zeolite may be CHA zeolite, and the zeolite may be ion-exchanged with Cu or the like. These catalysts may be used alone or in combination of two or more. When these catalysts are supported, CO, HC, NO X The above harmful exhaust gases can be suitably purified. In particular, it is preferable to use the honeycomb structure as an SCR catalyst that reduces NOx using zeolite as a catalyst.

[0027] Fig. 3 is a partial cross-sectional view of the honeycomb structure shown in Fig. 1. Fig. 3 schematically shows an area in which an electric heating wire is arranged in the honeycomb structure. A heating wire 50 is disposed between adjacent honeycomb segments 20. Electrode terminals 40 are provided on both ends of the heating wire 50, and the electrode terminals 40 protrude from the first end face 11.

[0028] The heating wires may be provided over the entire space between the adjacent honeycomb segments, or may be provided only in a portion thereof.

[0029] In the honeycomb structure 1 shown in Fig. 3, the heating wires 50 are arranged in a predetermined range from the first end face 11 of the honeycomb structure 1 in the longitudinal direction of the honeycomb segment 20. The region where the heating wires are arranged is referred to as the heating wire arrangement region. In Fig. 3, this is the region indicated by the double-headed arrow B. The heating wires 50 are not arranged in a predetermined range from the second end face 12 of the honeycomb structure 1 in the longitudinal direction of the honeycomb segment 20. The region where the heating wires are not arranged is referred to as the heating wire non-arrangement region. In Fig. 3, this is the region indicated by the double-headed arrow C. For example, the heating wire-free region extends from the second end face of the honeycomb structure to at least 20% of the length of the honeycomb structure in the longitudinal direction.

[0030] That is, a heating wire area is provided within a predetermined range from the first end face through which the gas flows in, and a heating wire non-area is provided within a predetermined range from the second end face through which the gas flows out. The heat generated in the region where the heating wire is located near the first end face moves along with the gas flow toward the second end face of the honeycomb structure, so that the entire honeycomb structure can be heated even if no heating wire is located in the region near the second end face.

[0031] The material of the heating wire may be a nickel-chromium alloy, a nickel-chromium-iron alloy, a chromium-iron-aluminum alloy, etc. The heating wire may be in the form of either a wire or a plate. When the heating wire is linear, its diameter is not particularly limited, but is preferably 0.1 to 1 mm. When the heating wire is plate-shaped, its thickness is not particularly limited, but is preferably 0.1 to 0.5 mm, and its width is preferably 1 to 10 mm.

[0032] The heating wire 50 is disposed inside the adhesive layer 30 . The adhesive layer is formed by applying and drying an adhesive paste containing an inorganic binder and inorganic particles. That is, the adhesive layer contains an inorganic binder and inorganic particles. Examples of the inorganic binder include silica sol, alumina sol, etc. These may be used alone or in combination of two or more kinds. The inorganic particles are preferably solid particles with a dense interior, such as alumina particles, silicon carbide particles, and silica particles. It is preferable to use two or more types of particles with different particle sizes. The two types with different particle sizes may be made of the same material or different materials. This increases the density of the adhesive layer.

[0033] The adhesive layer (adhesive paste) preferably further contains inorganic fibers. Examples of the inorganic fibers include ceramic fibers such as silica-alumina fibers, mullite fibers, alumina fibers, and silica fibers. These may be used alone or in combination of two or more. The adhesive paste preferably contains 40 to 70% by weight of inorganic particles, 10 to 30% by weight of inorganic binder, and 0 to 30% by weight of inorganic fibers. Furthermore, it is preferable that the adhesive paste does not contain a pore-forming material or inorganic balloons. The thickness of the adhesive layer is preferably 0.5 to 3 mm.

[0034] The density of the adhesive layer is 1.7 g / cm 3 More than 2.2g / cm 3 The following is the result. The density of the adhesive layer is 1.7 g / cm3 As a result, the heat generated by the heating wire can be transmitted to the honeycomb segments that purify gases using a catalyst without reducing the heat transfer effect, and therefore the purification performance can be maintained at a high level. In other words, the reduction in purification performance can be suppressed. On the other hand, the density of the adhesive layer is 1.7 g / cm 3 If the thickness is less than this, the density of the adhesive layer will be low, which may result in poor heat transfer performance when heated with an electric heating wire, and may result in poor purification performance. In addition, the density of the adhesive layer is 2.2 g / cm 3 If the temperature exceeds this range, the thermal shock resistance of the honeycomb structure decreases, and the honeycomb structure may be damaged when heated.

[0035] The density of the adhesive layer is 1.8 g / cm 3 It is preferable that this is equal to or greater than this. The density of the adhesive layer is 1.8 g / cm 3 If the above value is met, the heat transfer performance is increased, and therefore the purification performance can be improved.

[0036] The density of the adhesive layer is measured by the following method. That is, the same material as the adhesive layer is cured under the same curing conditions as the adhesive layer to prepare a bulk adhesive, and the density of this sample is measured by a known density measurement method.

[0037] Of the pores in the adhesive layer, the maximum diameter of the pores in contact with the heating wire is 1 mm or less. The adhesive layer contains multiple pores, but of the pores in the adhesive layer, all of the pores that come into contact with the heating wire are small, with a maximum diameter of 1 mm or less, thereby reducing the risk of the heating wire overheating and breaking. On the other hand, if the maximum diameter of the pores in contact with the heating wire exceeds 1 mm, the heating wire may overheat and break.

[0038] The shape of the pores in contact with the heating wire may be any shape, such as spherical, oval, or irregular. The pores in contact with the heating wire may be in any manner, for example, the pores may be in contact with only a portion of the heating wire in the circumferential direction, or the pores may be in contact with the entire heating wire in the circumferential direction.

[0039] The maximum diameter of the pores in contact with the heating wire is measured by the following method. That is, the area in the honeycomb structure where the heating wire is present is identified, and that area (however, the area leaving 30 mm from the end face closer to that area (first end face 11 in the honeycomb structure 1 shown in Figure 1)) is cut in 5 mm increments, and the entire cut surface is observed with a measuring microscope to measure the maximum diameter of each pore in contact with the heating wire.

[0040] The maximum diameter of the pores in the adhesive layer is preferably less than 2 mm, more preferably 1 mm or less, and even more preferably less than 300 μm. When the maximum diameter of the pores in the adhesive layer is less than 2 mm, the maximum diameter of the pores in contact with the heating wire can be easily reduced to 1 mm or less.

[0041] The maximum diameter of the pores in the adhesive layer is measured by the following method. That is, the entire honeycomb structure (except for a 30 mm area from the end face closest to the heating wire (first end face 11 in the honeycomb structure 1 shown in Figure 1)) is cut in 5 mm increments, and the entire cut surface is observed with a measuring microscope to measure the maximum diameter of each pore.

[0042] Electrode terminals 40 are connected to both ends of the heating wire 50, and the electrode terminals 40 protrude from the first end face 11. Electricity can be supplied from the electrode terminals 40 to the heating wire 50 to cause the heating wire to generate heat. The electrode terminals 40 are plate-shaped and welded to the heating wire 50. The electrode terminals 40 are connected to each other by wiring 60 that connects the electrode terminals together.

[0043] 3 is a set of heating wires in which a plurality of heating wires (51, 52, 53) are connected in parallel. Electrode terminals 40 are connected to both ends of each heating wire. If the heating wire is a set of heating wires, even if one of the heating wires breaks, the set of heating wires will not break as a whole, so the deterioration of heating performance can be minimized.

[0044] FIG. 4 is an end view of the honeycomb structure shown in FIG. 1 as seen from the first end face side. In the end view of the honeycomb structure 1 shown in Fig. 4, the honeycomb segments 20 are combined lengthwise and widthwise in a lattice pattern. One direction of this lattice pattern is defined as a first direction, and the direction perpendicular to the first direction is defined as a second direction. In FIG. 4, the horizontal direction is the first direction and the vertical direction is the second direction.

[0045] All the heating wires 50 are arranged in the same direction along the first direction. In FIG. 4, the adhesive layer 30a along the first direction, in which the heating wire is arranged, is shown with dark hatching, and the adhesive layer 30b along the second direction, in which the heating wire is not arranged, is shown with light hatching. This configuration can suppress localized heat generation. In addition, since no heating wires are arranged in the second direction perpendicular to the first direction, the adhesive layer can increase the adhesive strength between the honeycomb segments.

[0046] 4, the heating wires arranged on the adhesive layer 30a along the first direction are grouped together as heating wire sets, and the grouped heating wire sets are connected in parallel. This will be explained in detail. The heating wire set arranged in the adhesive layer 30a1 along the first direction between the honeycomb segments is referred to as a first heating wire set 50a1. Another adhesive layer 30a2 is disposed along the first direction between adjacent honeycomb segments at a position different from the position where the first pair of heating wires 50a1 is disposed. The pair of heating wires disposed on the adhesive layer 30a2 is referred to as the second pair of heating wires 50a2. The first heating wire assembly 50a1 and the second heating wire assembly 50a2 are connected in parallel by wiring 60 that connects the electrode terminals. 4, there are six adhesive layers 30a arranged along the first direction, and a heating wire set is disposed on each adhesive layer 30a. The six heating wire sets are connected in parallel by wiring 60.

[0047] When the heating wires are connected in parallel, even if some of the heating wires are broken, the entire circuit made up of the heating wires provided in the honeycomb structure will not be broken, so the deterioration of heating performance can be minimized.

[0048] An example of a method for manufacturing a honeycomb structure of the present invention will be described. The honeycomb structure can be manufactured, for example, by preparing honeycomb segments made of ceramic by a known manufacturing method, and then bonding the honeycomb segments together via an adhesive layer. When forming the adhesive layer on the side surface of the honeycomb segments, a heating wire is arranged between the honeycomb segments, and an electrode terminal is connected to the end of the heating wire so that the electrode terminal protrudes from the first end face of the honeycomb structure.

[0049] When bonding the honeycomb segments, multiple honeycomb segments are arranged so that the surfaces parallel to the first direction in the honeycomb structure are exposed, the above-mentioned adhesive paste that will serve as the adhesive layer is applied, and the heating wire is placed on top of the adhesive paste. Furthermore, a plurality of heating wires are connected in parallel to form a heating wire set, and electrode terminals are exposed from the direction that becomes the first end face of the honeycomb structure.

[0050] The above adhesive paste is further applied on the heating wire, and then the honeycomb segments are arranged on the adhesive paste. This process is repeated to combine the honeycomb segments to form a honeycomb assembly. The honeycomb aggregate is heated to heat and solidify the adhesive paste into an adhesive layer, thereby producing a honeycomb structure. The heat and solidification conditions are preferably 130 to 200°C for 5 to 15 minutes, and the temperature rise rate is preferably 20 to 50°C / min. In the honeycomb structure manufactured in this manner, the maximum diameter of the pores in contact with the heating wire can be made 1 mm or less, and the maximum diameter of the pores in the adhesive layer can be made preferably less than 2 mm (more preferably less than 1 mm, and even more preferably less than 300 μm). The outer periphery of the honeycomb aggregate may be processed to form a desired shape, and after processing, the outer periphery may be coated with a paste similar to the adhesive paste. The electrode terminals are connected together so that the heating wire pairs are connected in parallel. Through the above steps, the honeycomb structure can be manufactured.

[0051] It is also preferable to immerse the manufactured honeycomb structure in a slurry containing the catalyst and then dry it to support the catalyst on the partition walls of the honeycomb structure.

[0052] The following describes the results of a simulation of the temperature rise of the heating wire when the size of the pores in contact with the heating wire is changed.

[0053] FIG. 5A is a schematic front view showing the simulation model, and FIG. 5B is a schematic cross-sectional view taken along line XX shown in FIG. 5A. 5A and 5B has a pair of segments 120 corresponding to adjacent honeycomb segments 20, an adhesive layer 130 arranged between the pair of segments 120, and a heating wire 150 arranged inside the adhesive layer 130. A void 130v (air) is provided in the adhesive layer 130 around the center of the heating wire 150, and the heating wire 150 is exposed in the void 130v. The segments 120 were solid portions without cells (partition walls), and various parameters were set assuming a SiC honeycomb. The density of the adhesive layer 130 was set to 1.74.

[0054] 5A and 5B, the width W of the gap 130v was changed to 0 mm, 1 mm, 2 mm, 3 mm, 5 mm, or 10 mm, and the maximum temperature of the central portion (exposed portion) of the heating wire 150 after electricity was passed through the heating wire 150 was simulated, but heat dissipation was not taken into consideration. When the width W was 0 mm, the simulation was performed with no gap 130v provided in the adhesive layer 130 and the entire heating wire 150 buried in the adhesive layer 130. The simulation results are shown in Figure 6.

[0055] FIG. 6 is a graph showing the results of a simulation of the change over time in the maximum temperature at the center of the heating wire provided in the simulation model shown in FIGS. 5A and 5B.

[0056] As shown in Figure 6, as the width W of the gap 130v increases, the temperature of the heating wire 150 increases more rapidly after electricity is applied, and after a certain amount of time, the temperature exceeds the upper limit temperature (1300°C) during continuous operation in air. However, if the width W of the gap 130v is 1 mm, the upper limit temperature is not exceeded even after 300 seconds, and results comparable to those obtained when there is no gap 130v are obtained. Furthermore, in this model, the entire periphery of the heating wire 150 is an air gap 130v, so the temperature rise is more likely than when the air gap 130v is present only in a portion of the periphery of the heating wire 150, i.e., the simulation is conducted under more severe conditions.

[0057] Therefore, these results show that if the maximum diameter of the pores in contact with the heating wire is 1 mm or less, the risk of the heating wire breaking due to excessive heating can be reduced, regardless of how the pores are in contact with the heating wire. [Example]

[0058] Example 1 52.8% by weight of coarse silicon carbide powder having an average particle size of 22 μm and 22.6% by weight of fine silicon carbide powder having an average particle size of 0.5 μm were mixed, and the resulting mixture was kneaded with 4.6% by weight of an organic binder (methyl cellulose), 0.8% by weight of a lubricant (UNILUBE manufactured by NOF Corporation), 1.3% by weight of glycerin, 2.8% by weight of oleic acid, and 15.1% by weight of water to obtain a raw material composition, which was then extruded using a mold to obtain a honeycomb molded body.

[0059] Next, the honeycomb formed body was dried using a microwave dryer to prepare a dried honeycomb formed body. Next, the dried honeycomb formed body was subjected to a degreasing treatment at 400°C, and then a firing treatment was carried out under the conditions of 2200°C for 3 hours in an argon atmosphere at normal pressure. In this way, a square pillar-shaped honeycomb segment was produced. The dimensions of the honeycomb segment were 36 mm square x 150 mm long, with a partition wall thickness of 7 mil (0.18 mm), a cell shape of a square pillar, a cell density of 300 cpsi, a partition wall porosity of 38%, and an average pore diameter of 11 μm.

[0060] A heat-resistant adhesive paste was prepared according to the formulation shown in Table 1. The average fiber length of the ceramic fibers was 43 μm and the average fiber diameter was 6 μm. Polyvinyl alcohol was used as the water-retaining material.

[0061] [Table 1]

[0062] An electric heating wire (wire-shaped, diameter 0.6 mm) made of Fe-Cr-Al (chromium iron aluminum alloy) was prepared. A honeycomb segment was arranged, an adhesive paste was applied, a heating wire was arranged in a predetermined position, more adhesive paste was applied on the heating wire, and another honeycomb segment was arranged to obtain a honeycomb assembly.

[0063] FIG. 7 is an explanatory view schematically showing a cross section of a honeycomb aggregate. Two honeycomb segments 220 were combined with an adhesive paste 230 interposed therebetween, and three heating wires 250 were disposed inside the adhesive paste 230 . The pitch of the heating wires was 11 mm, the length of the heating wires was 14 mm, and the distance between the heating wires was 54 mm. Three heating wires were connected in parallel to form a set of heating wires.

[0064] FIG. 8 is an explanatory diagram showing a schematic arrangement of the heating wires. The pitch of the heating wire is the distance between adjacent peaks of the meandering heating wire, and is the length indicated by the double-headed arrow P. The length of the heating wire is the height of the peaks (depth of the valleys) of the meandering heating wire, and is the length indicated by the double-headed arrow N. The distance between the heating wires is the distance between adjacent heating wires, and is the length indicated by the double arrow K.

[0065] Furthermore, the honeycomb aggregate was heated under the drying conditions shown in Table 2 to dry and solidify the adhesive paste, forming an adhesive layer and forming a prismatic honeycomb structure.

[0066] [Table 2]

[0067] Table 3 shows the density and thickness of the adhesive layer after drying, and the maximum diameter of the pores in contact with the heating wire.

[0068] [Table 3]

[0069] (Examples 2 and 3, Comparative Examples 1 and 2) A honeycomb structure was obtained in the same manner as in Example 1, except that the formulation of the adhesive paste was changed as shown in Table 1 and the drying conditions of the adhesive paste were changed as shown in Table 2. Table 3 shows the density and thickness of the adhesive layer after drying and the maximum diameter of the pores in contact with the heating wire in each example.

[0070] (heating test) The honeycomb structure was heated by supplying electricity to the heating wire at an output of 10 kW and an applied voltage of 48 V, and the temperature was measured at the center of the honeycomb segment (see point H in FIG. 7) 60 seconds after the start of voltage application. The measurement results are shown in Table 4.

[0071] [Table 4]

[0072] From the results shown in Table 4, the density of the adhesive layer is 1.7 g / cm 3 From the above, it was found that when the maximum diameter of the pores in contact with the heating wire is 1 mm or less, the heat generated by the heating wire can be transmitted to the honeycomb segment without reducing the heat transfer effect. On the other hand, in Comparative Examples 1 and 2, the density of the adhesive layer was 1.7 g / cm 3 Since the diameter of the pores in contact with the heating wires is less than 1 mm or the maximum diameter of the pores in contact with the heating wires exceeds 1 mm, the heat transfer performance is low and the heat generated by the heating wires cannot be efficiently transferred to the honeycomb segments. [Explanation of symbols]

[0073] 1 Honeycomb structure 11 first end face 12 Second end face 20, 220 Honeycomb segment 21 cells 22 Bulkhead 23 Catalyst 30, 130 Adhesive layer 30a, 30a1, 30a2 adhesive layers along the first direction 30b Adhesive layer along the second direction 40 electrode terminal 50, 150, 250 heating wire (assembled heating wire) 50a1 First set of heating wire 50a2 Second set of heating wire 51, 52, 53 heating wire 60 Wiring connecting electrode terminals 120 segments 130v Adhesive layer voids 230 Adhesive paste

Claims

1. A honeycomb structure comprising a plurality of honeycomb segments, each having a partition wall that defines a large number of cells, combined together via an adhesive layer, A catalyst is supported on the honeycomb segments, A heating wire is disposed between adjacent honeycomb segments, the heating wire is disposed inside the adhesive layer, The density of the adhesive layer is 1.7 g / cm ３ Above, 2.2g / cm ３ is as follows: A honeycomb structure characterized in that the maximum diameter of the pores in the adhesive layer that are in contact with the heating wire is 1 mm or less.

2. 2. The honeycomb structure according to claim 1, wherein the maximum diameter of pores in the adhesive layer is less than 2 mm.

3. 3. The honeycomb structure according to claim 2, wherein the maximum diameter of pores in the adhesive layer is 1 mm or less.

4. The density of the adhesive layer is 1.8 g / cm ３ The honeycomb structure according to any one of claims 1 to 3, wherein the honeycomb structure is formed of a material selected from the group consisting of fluororesin, fluororesin, fluoropolymers ...

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