JP2019155336A - Method of manufacturing honeycomb structure - Google Patents

Abstract

To provide a method of manufacturing a honeycomb structure without generating break, and cracks.SOLUTION: The method of manufacturing a honeycomb structure provided with a honeycomb calcined body arranged with a plurality of open holes partitioned by partition walls in a longitudinal direction in parallel includes: an extruding process of extruding a raw material paste containing a ceria zirconia compound oxide particle, and an alumina particle to obtain a honeycomb molded body; a drying process; a defatting process; and a calcination process, where in the drying process, the honeycomb molded body (10) and a micro wave-absorbing member are irradiated with a micro wave while surrounding a side face (11) of the honeycomb molded body with a micro wave-absorbing member (20), the area formed of a shape surrounded by the micro wave-absorbing member in a cross-sectional face orthogonal to a vertical direction is 1.3 or less times an area of the honeycomb molded body in a cross-sectional face orthogonal to a vertical direction, and the average length in a vertical direction of the micro wave-absorbing member is 0.8 or more times a length in a vertical direction of the honeycomb molded body.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a honeycomb structure.

Exhaust gas discharged from internal combustion engines such as automobiles contains harmful gases such as carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons (HC). An exhaust gas purification catalyst that decomposes such harmful gases is also called a three-way catalyst, and a catalyst layer is provided by washing a slurry containing noble metal particles having catalytic activity on a honeycomb monolith substrate made of cordierite or the like. Things are common.

As a method for producing such a monolith substrate, Patent Document 1 forms a ceramic molded body by molding a ceramic raw material composition containing water, and irradiates the ceramic molded body with microwaves under a reduced pressure atmosphere. A method for subsequent firing is disclosed. Patent Document 2 discloses a method of drying a honeycomb formed body under a high humidity condition of 70% or higher humidity.

JP 2012-106484 A Japanese Patent No. 4131103

However, although the method described in Patent Document 1 can promote the evaporation of moisture, cracks may occur on the surface of the dried honeycomb body when the drying time is reduced.
Further, in the method described in Patent Document 2, since the humidity is high, it may take a long time to dry. In particular, when used for drying a honeycomb formed body having a moisture content exceeding 25% by weight, There has been a problem that the external drying rate becomes significantly slower than the internal drying rate.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for manufacturing a honeycomb structure without generating cracks or cracks.

A method for manufacturing a honeycomb structure of the present invention is a method for manufacturing a honeycomb structure including a honeycomb fired body in which a plurality of through holes are arranged in parallel in the longitudinal direction with partition walls therebetween, and the ceria-zirconia composite oxide particles And extruding a raw material paste containing alumina particles to obtain a honeycomb formed body in which a plurality of through holes are arranged in parallel in the longitudinal direction with a partition wall therebetween, and drying the honeycomb formed body to form a honeycomb A drying step for obtaining a dried body, a degreasing step for degreasing the honeycomb dried body to obtain a honeycomb degreased body, and a firing step for firing the honeycomb degreased body. In the drying step, the honeycomb formed body is penetrated. The end surface where the hole is exposed is directed in the vertical direction, and the honeycomb molded body and the microwave absorbing member are surrounded by the microwave absorbing member while surrounding the side surface of the honeycomb molded body. The area of the shape surrounded by the microwave absorbing member in the cross section perpendicular to the vertical direction is 1.3 times or less the area of the honeycomb formed body in the cross section perpendicular to the vertical direction, The average length of the microwave absorbing member in the vertical direction is 0.8 times or more the vertical length of the honeycomb formed body.

In the method for manufacturing a honeycomb structured body of the present invention, in the drying step, the honeycomb molded body and the microwave absorbing member are irradiated with microwaves while the side surfaces of the honeycomb molded body are surrounded by the microwave absorbing member.
Since the microwave absorbing member is close to the side surface of the honeycomb formed body, a part of moisture contained in the honeycomb formed body can be absorbed to promote the drying of the honeycomb formed body. Furthermore, since the honeycomb formed body is heated by the microwave irradiation and the microwave absorbing member is also heated, it plays a role of a heater for heating the honeycomb formed body from the outside. Therefore, the honeycomb molded body is heated from the inside by the microwave and also heated from the side by the microwave absorber, and moisture is uniformly removed from the honeycomb molded body, so that cracks and cracks occur. Can be suppressed.
In the cross section perpendicular to the vertical direction, the area surrounded by the microwave absorbing member is 1.3 times or less the area of the honeycomb molded body, so that the microwave absorbing member is sufficiently on the surface of the honeycomb molded body. They are close to each other and there are few gaps between the honeycomb formed body and the microwave absorbing member. Therefore, drying of the honeycomb formed body by the above-described microwave absorbing member proceeds efficiently.

In the method for manufacturing a honeycomb structure of the present invention, the area of the shape surrounded by the microwave absorbing member in the cross section perpendicular to the vertical direction is 1.2 times the area of the honeycomb formed body in the cross section perpendicular to the vertical direction. The following is preferable.
In the cross section perpendicular to the vertical direction, when the area of the shape surrounded by the microwave absorbing member is 1.2 times or less the area of the honeycomb molded body, there is a gap between the honeycomb molded body and the microwave absorbing member. Further, the drying of the honeycomb formed body by the microwave absorbing member proceeds more efficiently.

In the method for manufacturing a honeycomb structured body of the present invention, the atmospheric pressure in the drying step is preferably 9000 Pa or less.
When the atmospheric pressure in the drying process is 9000 Pa or less, the evaporation of moisture is promoted, and the time required for the drying process can be shortened.

In the method for manufacturing a honeycomb structured body of the present invention, it is preferable that the moisture content of the honeycomb formed body before the drying step is 25% by weight or more.
In the method for manufacturing a honeycomb structure of the present invention, even a honeycomb molded body having a moisture content of 25% by weight or more can be dried in a short time without generating cracks or cracks. Particularly suitable for drying the body.

In the method for manufacturing a honeycomb structure of the present invention, the weight ratio of the ceria-zirconia composite oxide particles in the raw material paste is preferably 15 to 35% by weight.
In the method for manufacturing a honeycomb structure of the present invention, cracks are generated even in a honeycomb molded body in which the weight ratio of ceria-zirconia composite oxide particles (hereinafter also referred to as CZ particles) in the raw material paste is 15 to 35% by weight. Since it can be dried in a short time without being generated, it is particularly suitable for drying a honeycomb formed body formed by forming a raw material paste in which the weight ratio of CZ particles is in the above range.

In the method for manufacturing a honeycomb structure of the present invention, the frequency of the microwave irradiated in the drying step is preferably 902 to 928 MHz or 2400 to 2500 MHz.

In the method for manufacturing a honeycomb structure of the present invention, the microwave absorbing member is selected from the group consisting of cerium oxide, aluminum oxide, aluminum nitride, titanium oxide, zirconium oxide, zinc oxide, lead zirconate titanate, and barium titanate. It is preferable to contain at least one selected from the above.
When the microwave absorbing member is made of the above material, the honeycomb formed body can be easily heated from the outside by microwave irradiation.
In addition, as a material which comprises a microwave absorption member, the thing whose microwave half-depth at 2500 MHz is about 15 cm is preferable, for example, aluminum oxide etc. are mentioned.

In the method for manufacturing a honeycomb structured body of the present invention, the microwave absorbing member is preferably a porous body obtained by drying the raw material paste.
When the microwave absorbing member is a porous body obtained by drying the raw material paste, the amount of heat generated by the honeycomb formed body and the microwave absorbing member becomes approximately the same when irradiated with microwaves. Difficult to generate temperature difference with outside. Further, when the microwave absorbing member is a porous body, it becomes easy to absorb moisture contained in the honeycomb formed body, and therefore, variation in the moisture content of the honeycomb formed body can be suppressed.

In the method for manufacturing a honeycomb structured body of the present invention, the microwave absorbing member is composed of a plurality of plate-like microwave absorbers arranged at substantially equal intervals along the side surface of the honeycomb formed body. In the cross section perpendicular to the vertical direction, the microwave absorbing member is preferably arranged so that the center of gravity of the honeycomb formed body and the center of gravity of the shape surrounded by the microwave absorbing member substantially overlap each other.
The microwave absorbing member is composed of a plurality of plate-like microwave absorbers arranged at equal intervals along the side surface of the honeycomb molded body, and the shape surrounded by the center of gravity of the honeycomb molded body and the microwave absorbing member If the center of gravity is arranged so as to be substantially overlapped in a cross section perpendicular to the vertical direction, the honeycomb formed body is heated substantially uniformly from the outside, so that the moisture content in the honeycomb formed body is less likely to vary.

In the method for manufacturing a honeycomb structured body of the present invention, it is preferable that a microwave absorber is further brought into contact with the upper surface and / or the lower surface of the honeycomb formed body in the drying step.
By bringing the microwave absorber into contact with the upper surface and / or the lower surface of the honeycomb molded body, the honeycomb molded body can also be heated from the upper surface and / or the lower surface of the honeycomb molded body.

In the method for manufacturing a honeycomb structured body of the present invention, in the drying step, the honeycomb formed body and the microwave absorbing member are preferably covered with a humidity control member.
In the drying process, the moisture around the honeycomb molded body can be kept constant by covering the honeycomb molded body and the microwave absorbing member with the humidity control member, thereby further suppressing variation in the amount of moisture in the honeycomb molded body. can do.

FIG. 1 is a perspective view schematically showing an example of a drying step in the method for manufacturing a honeycomb structure of the present invention. 2 is a cross-sectional view taken along line AA in FIG. 3 (a) and 3 (b) are diagrams in which the honeycomb formed body and the microwave absorbing member in FIG. 2 are schematically separated. FIG. 4 is a side view of FIG. FIG. 5 is a perspective view schematically showing another example of the drying process. FIG. 6 is a perspective view schematically showing still another example of the drying process.

(Detailed description of the invention)
A method for manufacturing a honeycomb structure of the present invention is a method for manufacturing a honeycomb structure including a honeycomb fired body in which a plurality of through holes are arranged in parallel in the longitudinal direction with partition walls therebetween, and the ceria-zirconia composite oxide particles And extruding a raw material paste containing alumina particles to obtain a honeycomb formed body in which a plurality of through holes are arranged in parallel in the longitudinal direction with a partition wall therebetween, and drying the honeycomb formed body to form a honeycomb A drying step for obtaining a dried body, a degreasing step for degreasing the honeycomb dried body to obtain a honeycomb degreased body, and a firing step for firing the honeycomb degreased body. In the drying step, the honeycomb formed body is penetrated. The end surface where the hole is exposed is directed in the vertical direction, and the honeycomb molded body and the microwave absorbing member are surrounded by the microwave absorbing member while surrounding the side surface of the honeycomb molded body. The area of the shape surrounded by the microwave absorbing member in the cross section perpendicular to the vertical direction is 1.3 times or less the area of the honeycomb formed body in the cross section perpendicular to the vertical direction, The average length of the microwave absorbing member in the vertical direction is 0.8 times or more the vertical length of the honeycomb formed body.

Hereinafter, the molding process, the drying process, the degreasing process, and the firing process will be described.

(Molding process)
In the forming step, a raw material paste containing CZ particles and alumina particles is extruded to obtain a honeycomb formed body in which a plurality of through holes are arranged in parallel in the longitudinal direction with a partition wall therebetween.
The raw material paste may further contain inorganic fibers, organic binders, pore formers, molding aids, dispersion media, and the like.

Ceria-zirconia composite oxide constituting CZ particles is a material used as a cocatalyst (oxygen storage material) of an exhaust gas purification catalyst. As the ceria-zirconia composite oxide, those in which ceria and zirconia form a solid solution are preferable.

The ceria-zirconia composite oxide may further contain a rare earth element other than cerium. As rare earth elements, scandium (Sc), yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), Examples thereof include ytterbium (Yb) and ruthenium (Lu).

The ceria-zirconia composite oxide preferably contains 20% by weight or more of ceria, more preferably contains 25% by weight or more, and preferably contains 70% by weight or less, more preferably 60% by weight or less. preferable. The ceria-zirconia composite oxide preferably contains 80% by weight or less of zirconia, and more preferably contains 70% by weight or less. Since such a ceria-zirconia composite oxide has a small heat capacity, the temperature of the honeycomb structure easily rises, and the warm-up performance can be improved.

The average particle size of the CZ particles is preferably 1 to 50 μm from the viewpoint of improving the thermal shock resistance. The average particle size of the CZ particles is more preferably 1 to 30 μm. When the average particle size of the CZ particles is 1 to 50 μm, the surface area is increased when the honeycomb structure is formed, and thus the oxygen storage capacity can be increased.

The type of alumina particles is not particularly limited, but is preferably θ-phase alumina particles (hereinafter also referred to as θ-alumina particles).
By using the θ-phase alumina particles as a partition material for the ceria-zirconia composite oxide, it is possible to suppress the alumina particles from being sintered together by heat during use, so that the catalytic function can be maintained. Furthermore, heat resistance can be improved by making alumina particles into the θ phase.

The average particle diameter of the alumina particles is not particularly limited, but is preferably 1 to 10 μm and more preferably 1 to 5 μm from the viewpoint of improving gas purification performance and warm-up performance.

In the manufactured honeycomb structure, the average particle diameter of the CZ particles and the alumina particles is obtained by taking an SEM photograph of the honeycomb structure using a scanning electron microscope (SEM, S-4800 manufactured by Hitachi High-Tech). be able to.
Moreover, the average particle diameter of the CZ particles and the alumina particles which are the raw materials of the honeycomb structure can be obtained by a laser diffraction particle size distribution measuring apparatus (MASTERSIZER 2000 manufactured by MALVERN).

As the alumina binder, boehmite is preferable.
Boehmite is an alumina monohydrate represented by the composition of AlOOH, and is favorably dispersed in a medium such as water. Therefore, it is preferable to use boehmite as an alumina binder.
Moreover, the moisture content in a raw material paste can be made low by using boehmite, and a moldability can be improved.

Although it does not specifically limit as a material which comprises inorganic fiber, For example, an alumina, a silica, silicon carbide, a silica alumina, glass, potassium titanate, an aluminum borate etc. are mentioned, You may use 2 or more types together. Of these, alumina fibers are preferred.

The aspect ratio of the inorganic fiber is preferably 5 to 300, more preferably 10 to 200, and still more preferably 10 to 100.
The inorganic fiber means one having an aspect ratio of 5 or more.

Although it does not specifically limit as an organic binder, Methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, polyethyleneglycol, a phenol resin, an epoxy resin etc. are mentioned, You may use 2 or more types together.

Although it does not specifically limit as a pore making agent, For example, acrylic resin, coke, starch, etc. are mentioned. In this invention, it is preferable to use 2 or more types among acrylic resin, coke, and starch.
The pore-forming agent means a material used for forming pores in the fired body when the fired body is produced.

Although it does not specifically limit as a shaping | molding adjuvant, Ethylene glycol, dextrin, a fatty acid, fatty acid soap, a polyalcohol etc. are mentioned, You may use together 2 or more types.

Although it does not specifically limit as a dispersion medium, Alcohol, such as water, organic solvents, such as benzene, methanol, etc. are mentioned, You may use 2 or more types together.

When CZ particles, alumina particles, alumina fibers, and an alumina binder are used as the raw materials described above, these blending ratios are CZ particles: 25 to 75% by weight, alumina based on the total solid content remaining after the firing step in the raw materials. Particles: 15 to 35% by weight, alumina fibers: 5 to 15% by weight, alumina binder: 5 to 20% by weight are preferable.

When preparing the raw material paste, it is preferable to mix and knead, and it may be mixed using a mixer, an attritor or the like, or may be kneaded using a kneader or the like.

In the molding step, the above raw material paste containing ceria-zirconia composite oxide particles, alumina particles, and alumina binder is extruded to obtain a honeycomb molded body in which a plurality of through holes are arranged in parallel in the longitudinal direction with partition walls. .

The shape of the honeycomb formed body is not particularly limited, but a cylindrical shape is preferable. Moreover, it is preferable that the diameter in the case of a cylindrical shape is 150 mm or less.
Further, the shape of the honeycomb formed body may be a prismatic shape, and when it is a prismatic shape, it is preferably a quadrangular prism shape.

(Drying process)
In the drying step, the honeycomb molded body and the microwave absorbing member are irradiated with microwaves while the end surface where the through holes of the honeycomb molded body are exposed is directed in the vertical direction and the side surfaces of the honeycomb molded body are surrounded by the microwave absorbing member.

The drying process in the manufacturing method of the honeycomb structure of the present invention will be described with reference to FIG.
FIG. 1 is a perspective view schematically showing an example of a drying step in the method for manufacturing a honeycomb structure of the present invention.
As shown in FIG. 1, in the drying step in the method for manufacturing a honeycomb structured body of the present invention, the end faces 10a and 10b where the through holes of the honeycomb formed body 10 are exposed are vertically oriented (the direction indicated by the arrow z in FIG. 1). Turn to. A side surface 11 of the honeycomb formed body 10 is surrounded by a microwave absorbing member 20. In this state, the drying process is performed by irradiating the honeycomb formed body 10 and the microwave absorbing member 20 with microwaves.
The microwave absorbing member 20 is composed of twelve plate-like microwave absorbers 21, and the twelve microwave absorbers 21 are arranged at substantially equal intervals along the side surface 11 of the honeycomb formed body 10. A gap 22 is formed between the microwave absorbers 21. Further, the microwave absorber 21 is not in contact with the honeycomb formed body 10 at the contact portion between the microwave absorbers 21, and a gap 13 (see FIG. 2) is formed. The twelve microwave absorbers 21 are fixed to the side surface 11 of the honeycomb formed body 10 by holding members 30.

2 is a cross-sectional view taken along line AA in FIG. FIG. 2 is also a cross-sectional view in a direction perpendicular to the vertical direction (directions indicated by arrows x and y in FIG. 1).
Also in the cross section perpendicular to the vertical direction, the centroid g ₁ of the honeycomb molded body 10, the center of gravity g ₂ of the microwave absorbing member 20 is substantially overlapped.

The area of the shape surrounded by the microwave absorbing member in FIG. 2 and the area of the honeycomb formed body will be described with reference to FIGS. 3 (a) and 3 (b).
3 (a) and 3 (b) are diagrams in which the honeycomb formed body and the microwave absorbing member in FIG. 2 are schematically separated. 3A corresponds to the cross-sectional view shown in FIG. 2 with the honeycomb formed body 10 removed, and FIG. 3B shows the cross-sectional view shown in FIG. 2 with the microwave absorbing member 20 removed. Equivalent to.
As shown in FIG. 3A, the shape surrounded by the microwave absorbing member 20 is formed by the side 21 a closest to the honeycomb formed body 10 of the microwave absorbing member 21 constituting the microwave absorbing member 20. a rectangular Pa, the area is _{S 1.} On the other hand, the area of the honeycomb molded body 10, the volume of the through holes in the honeycomb molded body 10 also includes, its area is S _2. Then, the area _{S 1} is 1.3 times or less of the area _{S 2 (S 1 / S 2} ≦ 1.3).
When the honeycomb molded body is not surrounded only by the side closest to the honeycomb molded body of the microwave absorber constituting the microwave absorbing member, the shape formed by extending the above sides of the microwave absorber is mutually The shape is surrounded by the microwave absorbing member.

In the cross section perpendicular to the vertical direction, the area of the shape surrounded by the microwave absorbing member may be 1.3 times or less of the area of the honeycomb formed body in the cross section perpendicular to the vertical direction, and 1.2 times or less. It is preferable that it is 1.1 times or less.
Note that, in the cross section perpendicular to the vertical direction, the area surrounded by the microwave absorbing member does not become smaller than the area of the honeycomb formed body, and therefore the magnification is 1.0 times the minimum value. In this case, there is no gap between the microwave absorbing member and the honeycomb formed body.
When the said magnification exceeds 1.3 times, the balance of the heating from the outside of a honeycomb molded object is bad, and it becomes easy to generate | occur | produce a crack.

FIG. 4 is a side view of FIG.
As shown in FIG. 4, the average length L ₂ in the vertical direction of the microwave absorbing member 20 is 0.8 times or more the vertical length L ₁ of the honeycomb formed body 10.
In addition, let the average length of the perpendicular direction of a microwave absorption member be an average value of the length of the perpendicular direction of the microwave absorption member measured in two places. When a microwave absorption member consists of two or more microwave absorbers, let the average value of the length of the perpendicular direction of all the microwave absorbers be the average value of the length of the vertical direction of a microwave absorption member. At this time, the length of each microwave absorber in the vertical direction is an average value of the lengths of the microwave absorbers measured in two places in the vertical direction.

The average length in the vertical direction of the microwave absorbing member may be 0.8 times or more the vertical length of the honeycomb formed body.
The average length of the microwave absorbing member is preferably 0.9 times or more of the length of the honeycomb formed body.
The average length of the microwave absorbing member is preferably 1.1 times or less, more preferably 1.0 times or less of the length of the honeycomb formed body.

The microwave absorbers are preferably arranged at substantially equal intervals along the side surface of the honeycomb formed body. When the microwave absorbers are arranged at substantially equal intervals along the side surface of the honeycomb formed body, the honeycomb formed body can be easily heated uniformly.

The microwave absorbing member preferably contains at least one selected from the group consisting of cerium oxide, aluminum oxide, aluminum nitride, titanium oxide, zirconium oxide, zinc oxide, lead zirconate titanate, and barium titanate. More preferably, aluminum is included.
When the microwave absorbing member contains the above material, the honeycomb formed body can be easily heated from the outside by microwave irradiation.

As a material constituting the microwave absorbing member, a material having a microwave half depth of about 15 cm at 2500 MHz is preferable, and examples thereof include aluminum oxide.

The shape of the microwave absorbing member may be any shape that can surround the side surface of the honeycomb molded body. For example, plate-shaped microwave absorbers are arranged at substantially equal intervals along the side surface of the honeycomb molded body. And an annular shape or a cylindrical shape having a hollow portion that is substantially the same as or slightly larger than the outer diameter of the honeycomb formed body.
At this time, it is preferable that the center of gravity of the microwave absorbing member substantially overlaps the center of gravity of the honeycomb formed body in the vertical direction.

When the microwave absorbing member is composed of a plurality of microwave absorbers, a holding member may be used to fix the plurality of microwave absorbers to the side surface of the honeycomb formed body.
Examples of the holding member include an elastic string, a band, and the like.
When plate-like microwave absorbers are arranged on the side surfaces of the honeycomb molded body at approximately equal intervals, the microwave is fixed by fixing the outside of the microwave absorber with a band having elasticity (for example, a band like a rubber band). The position of the absorber can be fixed.

The microwave absorbing member may be a porous body or a dense body, but is preferably a porous body.
When the microwave absorbing member is a porous body, it becomes easy to absorb moisture contained in the honeycomb formed body, so that variation in the moisture content of the honeycomb formed body can be suppressed.

The microwave absorbing member is more preferably a porous body obtained by drying a raw material paste used to obtain a honeycomb formed body.
When the microwave absorbing member is a porous body obtained by drying the raw material paste, the amount of heat generated by the honeycomb formed body and the microwave absorbing member becomes approximately the same when irradiated with microwaves. Difficult to generate temperature difference with outside.

Although the atmospheric pressure in a drying process is not specifically limited, It is preferable that it is 9000 Pa or less, and it is more preferable that it is 6700 Pa or less.

Although the wavelength of the microwave irradiated to the honeycomb formed body and the microwave absorbing member in the drying step is not particularly limited, it is preferably 902 to 928 MHz or 2400 to 2500 MHz, and more preferably 2400 to 2500 MHz.

Although the output of a microwave is not specifically limited, It is preferable that it is 500-10000W.
The microwave irradiation time is not particularly limited, but is preferably 5 to 100 minutes.

(Degreasing process)
In the degreasing step, the honeycomb dried body is heated to obtain a honeycomb degreased body.
The maximum temperature when heating the honeycomb dried body in the degreasing step is preferably less than 800 ° C, and more preferably 350 to 700 ° C. The heating time at the maximum temperature is preferably 60 minutes or less.

Although the oxygen concentration in a degreasing process is not specifically limited, It is preferable that it is 1-21 volume%.
Although the temperature increase rate in a degreasing process is not specifically limited, It is preferable that it is 0.5-10 degreeC / min.

(Baking process)
Subsequently, a firing step of firing the honeycomb degreased body to obtain a honeycomb fired body is performed.
It is preferable that the temperature of a baking process is 800-1300 degreeC, and it is more preferable that it is 900-1200 degreeC. Moreover, it is preferable that it is 1 to 24 hours, and, as for the time of a baking process, it is more preferable that it is 3 to 18 hours. Although the atmosphere of a baking process is not specifically limited, It is preferable that oxygen concentration is 1-21 volume%.

The firing step may be performed continuously from the degreasing step, or may be performed separately after completion of the degreasing step.
When performing a baking process continuously from a degreasing process, you may use the furnace used as a degreasing furnace as a baking furnace.
In addition, whether the degreasing of the honeycomb dried body is completed in the degreasing step is confirmed by the weight change rate. Specifically, it is assumed that the degreasing is completed by confirming that the weight of the honeycomb degreased body is changed with respect to the weight of the honeycomb dried body by the weight of the organic matter contained in the raw material.

Through the above steps, a honeycomb structure made of a honeycomb fired body can be manufactured.

(Supporting process)
Next, a supporting process for supporting a noble metal on the partition walls of the honeycomb structure will be described. A honeycomb catalyst can be obtained by supporting a noble metal on the partition walls of the honeycomb structure.

Examples of the method for supporting the noble metal on the partition include a method in which the honeycomb fired body or the honeycomb structure is immersed in a solution containing the noble metal or the complex, and then pulled up and heated.
In the loading step, the loading amount of the noble metal is preferably 0.1 to 15 g / L, and more preferably 0.5 to 10 g / L.

(Other processes)
In the method for manufacturing a honeycomb structured body of the present invention, an outer peripheral coat layer may be formed on the outer peripheral surface of the honeycomb fired body obtained by the firing step.
Examples of the method for forming the outer peripheral coat layer on the outer peripheral surface of the honeycomb fired body include a method in which the outer peripheral coat layer paste is applied to the outer peripheral surface excluding both end faces of the honeycomb fired body and then dried and solidified.
Examples of the outer coat layer paste include the same composition as the raw material paste.

A plurality of honeycomb fired bodies obtained by the firing process may be bonded via an adhesive layer.
As a method of bonding a plurality of honeycomb fired bodies through an adhesive layer, a method of applying an adhesive layer paste to the outer peripheral surface excluding both end faces of the plurality of honeycomb fired bodies, bonding them, and drying and solidifying them Is mentioned. Examples of the adhesive layer paste include those having the same composition as the raw material paste.

Another example of the drying step constituting the method for manufacturing a honeycomb structure of the present invention will be described.

FIG. 5 is a perspective view schematically showing another example of the drying process.
In FIG. 5, microwave absorbers 40 a and 40 b are further in contact with the upper surface 10 a and the lower surface 10 b of the honeycomb formed body 10.
When the microwave absorbers 40a and 40b are further in contact with the upper surface 10a and the lower surface 10b of the honeycomb formed body 10, not only the microwave absorbing member 20 is heated from the side surface of the honeycomb formed body 10, but also the microwave absorber. Since the honeycomb molded body 10 is also heated from the upper surface 10a and the lower surface 10b by 40a and 40b, the drying of the honeycomb molded body 10 easily proceeds uniformly.

The size of the microwave absorber that is in contact with the upper surface and / or the lower surface of the honeycomb molded body is not particularly limited, but in the cross section perpendicular to the vertical direction, the cross sectional area of the microwave absorber is the cross sectional area of the honeycomb molded body. It is preferable that it is 0.2-1.0 times.
When the microwave absorber that is in contact with the upper surface and / or the lower surface of the honeycomb molded body has a shape having a through hole, the direction of the through hole of the microwave absorber is the same as the direction of the through hole of the honeycomb molded body. It is preferable to arrange the microwave absorber as described above. By disposing the microwave absorber in the above direction, moisture easily escapes from the honeycomb formed body.

FIG. 6 is a perspective view schematically showing still another example of the drying process.
In FIG. 6, the humidity control is performed by the honeycomb molded body 10, the microwave absorbing member 20 surrounding the side surface 11 of the honeycomb molded body 10, and the microwave absorbers 40 a and 40 b in contact with the upper surface 10 a and the lower surface 10 b of the honeycomb molded body 10. Covered by the member 50.
When the honeycomb molded body 10, the microwave absorbing member 20, and the microwave absorbers 40 a and 40 b are covered with the humidity control member 50 during the microwave irradiation, the honeycomb molded body 10, the microwave absorbing member 20, and the microwave are covered. Since the water vapor released from the absorbers 40a and 40b stays in the humidity control member 50 for a long time, the rapid change in the vapor pressure around the honeycomb molded body 10, the microwave absorption member 20, and the microwave absorbers 40a and 40b. It is possible to suppress the evaporation (drying) of water from proceeding rapidly only with a part of the honeycomb formed body 10.
Therefore, generation | occurrence | production of the crack in a drying process can further be suppressed.

As the humidity control member, a material having low microwave absorbability and low water vapor permeability is preferable.
Examples of materials having low microwave absorption and low water vapor permeability include polyethylene, polyethylene terephthalate, polypropylene, polyvinylidene chloride, polyvinyl chloride, and polymethylpentene.
The shape of the humidity control member is not particularly limited as long as it can cover the honeycomb molded body and the microwave absorbing member together, but may be a bag-like or box-like three-dimensional shape, and may be a belt-like or sheet-like shape. There may be.
In the case of a bag shape or a box shape, a method such as accommodating the honeycomb formed body and the microwave absorbing member in the internal space, closing the opening of the bag, and covering the bag can be mentioned.
In the case of a strip shape, a method of wrapping a strip-shaped humidity adjusting member around a honeycomb molded body and a microwave absorbing member to cover most of the surface thereof can be mentioned.
The humidity control member may completely cover the honeycomb formed body and the microwave absorbing member, but the structure does not allow any water vapor generated from the honeycomb formed body to leak outside, and gradually releases the internal water vapor. It is preferable.

(Example)
Examples in which the present invention is disclosed more specifically are shown below. In addition, this invention is not limited only to a following example.

[Preparation of raw material paste]
26.4% by weight of CZ particles (average particle diameter: 2 μm), 13.2% by weight of θ-alumina particles (average particle diameter: 2 μm), and alumina fibers (average fiber diameter: 3 μm, average fiber length: 60 μm). 5.3% by weight, boehmite as an alumina binder, 11.3% by weight, methyl cellulose as an organic binder, 5.3% by weight, acrylic resin as a pore-forming agent, 2.1% by weight, and coke as a pore-forming agent, 2. A raw material paste was prepared by mixing and kneading 6% by weight, 4.2% by weight of polyoxyethylene oleyl ether which is a surfactant as a molding aid, and 29.6% by weight of ion-exchanged water.

[Molding process]
The raw material paste was extruded using an extruder, and a cylindrical honeycomb formed body was produced.
The honeycomb formed body has a columnar shape with a diameter of 149.3 mm and a length of 150 mm, a density of through holes of 65.1 pieces / cm ² (420 cpsi), and a partition wall thickness of 0.165 mm (6.5 mil). Met.

[Drying process]
Example 1
A raw material paste formed into a sheet having a thickness of about 10 mm is cut into a predetermined shape and dried at 120 ° C. for 10 minutes, whereby a microwave absorber having a thickness of 10 mm × width 40 mm × length 120 mm (porous) )
Twelve of these microwave absorbers are arranged at equal intervals on the side surface of the honeycomb molded body, and the microwave absorber is fixed to the side surface of the honeycomb molded body with a rubber band, and then placed in a drying furnace decompressed to 6700 Pa. Then, the honeycomb formed body was dried by irradiating with a microwave having a frequency of 2500 MHz.
At this time, in the cross section perpendicular to the vertical direction, the shape surrounded by the microwave absorbing member was a regular dodecagon with a side of 40 mm, and the area was 17914 mm ² . On the other hand, in the cross section perpendicular to the vertical direction, the shape of the honeycomb formed body was a circle having a diameter of 149.3 mm and the area was 17502 mm ² . The magnification of the area of the shape surrounded by the microwave absorbing member determined from the above area with respect to the area of the honeycomb formed body was 1.02.
The microwave output was 1470 W, and the irradiation time was 12 minutes.
No dents or cracks were found on the surface of the obtained honeycomb dried body.

[Degreasing process and firing process]
A honeycomb fired body according to Example 1 was manufactured by degreasing and firing the dried honeycomb body at 1100 ° C. for 10 hours.

(Example 2)
Two honeycomb molded bodies having the same cell pattern, cell density, cell partition wall thickness, diameter of 77 mm, and length of 86 mm were prepared from the honeycomb molded body and dried at 120 ° C. for 10 minutes to obtain a microwave absorber. It was.
A honeycomb fired body according to Example 2 was obtained in the same procedure as in Example 1 except that the microwave absorber was further arranged so as to be in contact with the upper surface and the lower surface of the honeycomb formed body.
After completion of the drying process, no dents or cracks were observed on the surface of the dried honeycomb body.

(Example 3)
All of the honeycomb molded body, the microwave absorber disposed on the side surface of the honeycomb molded body, and the microwave absorber disposed on the upper surface and the lower surface of the honeycomb molded body are accommodated in a polypropylene tube having a diameter of 200 mm, and the upper surface And the lower surface was loosely covered with an industrial stretch film (made of polyvinylidene chloride, thickness 15 μm) to cover all of the honeycomb formed body and the microwave absorbing member with a humidity control member, and the same procedure as in Example 2 Thus, a honeycomb fired body according to Example 3 was obtained. The drying furnace was depressurized more time than in Examples 1 and 2 so that the inside of the polypropylene tube was gradually depressurized.
After completion of the drying process, no dents or cracks were observed on the surface of the dried honeycomb body.

Example 4
A honeycomb fired body according to Example 4 was manufactured in the same procedure as Example 1 except that the dimensions of the microwave absorber were changed to thickness 10 mm × width 86 mm × length 150 mm and the number was changed to 6. did.
In the cross section perpendicular to the vertical direction, the shape surrounded by the microwave absorbing member was a regular hexagon having a side of about 86.2 mm, and its area was 19300 mm ² . The area of the shape surrounded by the microwave absorbing member determined from the above area was 1.10 times the area of the honeycomb formed body.
After completion of the drying process, no dents or cracks were observed on the surface of the dried honeycomb body.
Note that a slight gap is generated between the microwave absorbers, and the shape surrounded by the microwave absorbing member is a shape obtained by extending the surface closest to the honeycomb formed body of the microwave absorber.

(Comparative Example 1)
A honeycomb fired body according to Comparative Example 1 was obtained in the same procedure as in Example 1 except that the microwave absorber was not disposed. When the surface of the dried honeycomb body was observed after the drying process, many cracks were generated on the end face.

(Comparative Example 2)
A honeycomb fired body according to Comparative Example 2 was obtained in the same procedure as in Example 4 except that the number of microwave absorbers arranged on the side surface of the honeycomb formed body was changed to three. When the surface of the dried honeycomb body was observed after the drying process, cracks were found on the end faces.
In the cross section perpendicular to the vertical direction, the shape surrounded by the microwave absorbing member is a regular triangle having a side of 259 mm, and the area surrounded by the microwave absorbing member in the cross section perpendicular to the vertical direction is the area of the honeycomb formed body. It was 1.65 times.
In addition, since the end surfaces of the microwave absorbers are not in contact with each other, a regular triangle having a side of 259 mm is a shape obtained by extending the surface closest to the honeycomb molded body of the microwave absorber.

From the above results, it was found that when the method for manufacturing a honeycomb structured body of the present invention was used, dents and cracks were hardly generated in the dried honeycomb body.

DESCRIPTION OF SYMBOLS 10 Honeycomb molded object 11 Side surface 13 of honeycomb molded object Crevice 20 Microwave absorption member 21 Microwave absorber 22 Crevice 30 Holding member 40a, 40b Microwave absorber 50 Humidity control member S ₁ Area surrounded by microwave absorption member Area of S ₂ honeycomb molded body

Claims (11)

A method for manufacturing a honeycomb structure including a honeycomb fired body in which a plurality of through holes are arranged in parallel in a longitudinal direction with a partition wall therebetween,
An extrusion process for obtaining a honeycomb formed body in which a plurality of through holes are arranged in parallel in the longitudinal direction with a partition wall therebetween, by extruding a raw material paste containing ceria-zirconia composite oxide particles and alumina particles;
A drying step of drying the honeycomb formed body to obtain a honeycomb dried body;
A degreasing step of degreasing the honeycomb dried body to obtain a honeycomb degreased body;
A firing step of firing the honeycomb degreased body,
In the drying step, a microwave is applied to the honeycomb molded body and the microwave absorbing member while an end surface where the through-holes of the honeycomb molded body are exposed is directed vertically and a side surface of the honeycomb molded body is surrounded by the microwave absorbing member. Irradiate
The area of the shape surrounded by the microwave absorbing member in the cross section perpendicular to the vertical direction is not more than 1.3 times the area of the honeycomb formed body in the cross section perpendicular to the vertical direction, and the vertical direction of the microwave absorbing member is The method for manufacturing a honeycomb structure according to claim 1, wherein an average length in a direction is 0.8 times or more a vertical length of the honeycomb formed body. The honeycomb structure according to claim 1, wherein an area of the shape surrounded by the microwave absorbing member in a cross section perpendicular to the vertical direction is 1.2 times or less of an area of the honeycomb formed body in the cross section perpendicular to the vertical direction. Body manufacturing method. The method for manufacturing a honeycomb structured body according to claim 1 or 2, wherein an atmospheric pressure in the drying step is 9000 Pa or less. The method for manufacturing a honeycomb structure according to any one of claims 1 to 3, wherein the moisture content of the honeycomb formed body before the drying step is 25 wt% or more. The method for manufacturing a honeycomb structure according to any one of claims 1 to 4, wherein a weight ratio of the ceria-zirconia composite oxide particles in the raw material paste is 15 to 35 wt%. The method for manufacturing a honeycomb structure according to any one of claims 1 to 5, wherein a frequency of the microwave irradiated in the drying step is 902 to 928 MHz or 2400 to 2500 MHz. The microwave absorbing member includes at least one selected from the group consisting of cerium oxide, aluminum oxide, aluminum nitride, titanium oxide, zirconium oxide, zinc oxide, lead zirconate titanate, and barium titanate. A method for manufacturing a honeycomb structured body according to any one of claims 6 to 10. The method for manufacturing a honeycomb structured body according to any one of claims 1 to 7, wherein the microwave absorbing member is a porous body obtained by drying the raw material paste. The microwave absorbing member is composed of a plurality of plate-like microwave absorbers arranged at substantially equal intervals along the side surface of the honeycomb formed body,
9. The microwave absorbing member is disposed so that a center of gravity of the honeycomb molded body and a center of gravity of the shape surrounded by the microwave absorbing member substantially overlap each other in a cross section perpendicular to the vertical direction. The manufacturing method of the honeycomb structure as described. The method for manufacturing a honeycomb structure according to any one of claims 1 to 9, wherein in the drying step, a microwave absorber is further brought into contact with an upper surface and / or a lower surface of the honeycomb formed body. The method for manufacturing a honeycomb structure according to any one of claims 1 to 10, wherein in the drying step, the honeycomb formed body and the microwave absorbing member are covered with a humidity control member.

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