JP3274027B2 - Method for manufacturing aluminum titanate honeycomb body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a honeycomb body used for a catalyst carrier or a diesel particulate filter (hereinafter referred to as DPF), and more particularly to a method for manufacturing an aluminum titanate honeycomb body.

[0002]

2. Description of the Related Art A DPF is formed by alternately closing both side openings of cells of a heat-resistant honeycomb body, and collects particulates in exhaust gas flowing into the cells. Then, the DPF is regenerated by removing the collected particulates by combustion, and the particulates are collected again.

Here, when the collected particulates are burned, excessive thermal stress acts on the DPF.
Heat resistance of 1000 ° C. or higher and high thermal shock resistance are essential for PF, and the use of cordierite having low thermal expansion has been studied conventionally. However, even in cordierite, there is a concern that cracks may be generated due to excessive thermal stress acting on the DPF, and development of a material having excellent thermal shock resistance has been an issue.

[0004] For example, Japanese Patent Application Laid-Open No. 1-167282 discloses a DPF using aluminum titanate as a material. Aluminum titanate is excellent in heat resistance and has a very small coefficient of thermal expansion, so that it exhibits high thermal shock resistance and is considered promising as a material for DPF. Aluminum titanate crystals have a large thermal anisotropy, and the a-axis and the b-axis have positive thermal expansion coefficients, while the c-axis has a negative thermal expansion coefficient. Therefore, at the time of cooling from high temperature to room temperature after sintering, microcracks are introduced into grains or grain boundaries due to thermal anisotropy of crystal axes.

[0005] When the aluminum titanate sintered body having such microcracks is heated, even if the crystal grains thermally expand, the expansion is absorbed by opening and closing of the microcracks, so that the apparent thermal expansion coefficient decreases. is there. Generally, the thermal shock resistance (R) is expressed by the following equation. The thermal shock resistance (R) increases as the coefficient of thermal expansion (α) decreases.

R = σ (1−ν) / Eα (σ: strength, ν: Poisson's ratio, E: Young's modulus) That is, by optimally controlling the amount of microcracks generated, titanic acid having a very small thermal expansion coefficient A highly durable DP that can be made of an aluminum sintered body and is free from cracks even when the temperature rises rapidly during regeneration
F can be manufactured.

[0007]

In order to generate microcracks in the aluminum titanate sintered body, it is necessary to increase the difference between the thermal expansion of the a-axis and the b-axis and the thermal expansion of the c-axis of the crystal. Therefore, it is necessary to make the particle size of the aluminum titanate powder appropriate. However, aluminum titanate crystals are columnar particles, and it has been clarified that the larger the particle size, the more the orientation along the extrusion direction occurs during extrusion molding, and sintering is performed in that state.

When extruding a honeycomb body, a die as shown in FIGS. 5 and 6 is used. This die has feed hole 1
00, and an intersecting slit 101 communicating with the supply hole 100, and the extruded material passes through the intersecting slit 101 from the supply hole 100.
And is extruded from the intersection slit 101 to form a honeycomb body. Here, in the conventional die, the center of the supply hole 100 coincides with the center of the intersection 102 of the intersection slit 101, and in the portion extruded from the intersection 102, the aluminum titanate particles remain supplied from the supply hole 100. Yes, not oriented. However, in the cross slit 101 facing the partition wall of the supply hole 100, the flows from the adjacent supply holes 100 collide with each other and flow together, so that the columnar aluminum titanate particles try to orient in the extrusion direction at that portion. I do.

Therefore, when the DPF is formed using the aluminum titanate powder containing the large columnar particles as described above, the large columnar particles are easily oriented particularly along the longitudinal direction (extrusion direction) of the honeycomb cell. Although the thermal expansion coefficient in the longitudinal direction is small, the thermal expansion coefficient in the radial direction (perpendicular to the longitudinal direction) increases, and the thermal expansion coefficient becomes anisotropic, which causes cracks due to thermal stress.

The present invention has been made in view of such circumstances, and it is an object of the present invention to prevent the orientation of aluminum titanate particles during extrusion in the production of a honeycomb body.

[0011]

In order to achieve the object of the present onset to solve the above problems
The manufacturing method of the honeycomb body made of bright aluminum titanate,
Aluminum titanate powder was granulated and the granulation process and, communicates with the supply hole and the supply holes fused aluminum titanate powder each other in granule form a granulated powder by heating exchange
With a difference slit, the opening pitch and opening diameter of the supply hole
At least one is greater than the pitch of the intersection of the intersection slits
Using a die, feed the extruded material consisting of granulated powder
The extruded body is extruded into a honeycomb shape by being supplied from the intersection slit and extruded from the cross slit to form an extruded body, and a firing step of sintering the extruded body is sequentially performed.

[0012]

[0013]

According to the production method of the present invention, the aluminum titanate powder is granulated, and is further made into a granulated powder in which the powders are fused by heating. By the granulation, a powder in which the aluminum titanate powder is randomly aggregated is formed, and further, since the powders are fused and held, there is no orientation of the aluminum titanate powder in the granulated powder,
Since the granulated powder is not deformed even when extruded from the die, the orientation of the aluminum titanate powder does not occur. Therefore, since the orientation of the aluminum titanate powder does not occur in the compact, a honeycomb body having no orientation and no anisotropy in coefficient of thermal expansion can be produced even in a sintered body.

Further, in the manufacturing method of the present invention , a die is used in which at least one of the opening pitch and the opening diameter of the supply holes is larger than the pitch of the intersection of the intersection slits.
Therefore, the number of openings of the supply holes is smaller than the number of intersections of the intersection slits, and the number of portions where a plurality of flows collide and merge and flow at the intersection slits facing the partition walls of the supply holes is reduced. The portion where the powder is oriented is also reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention , as the aluminum titanate powder, it is desirable to use a mixture of a fine powder having a small particle size and a coarse powder having a large particle size. The mixing weight ratio of the powder is preferably in the range of 9: 1 to 6: 4. If there is too much coarse powder, sintering becomes difficult and strength becomes insufficient,
If the amount of the fine powder is too large, the shrinkage at the time of sintering is increased, and the dimensional accuracy is reduced. In addition, a fine powder has an average particle size of 0.5
Powder having a mean particle size of 5 to 5 μm.
0 μm powder.

In order to granulate the aluminum titanate powder in the present invention , known methods such as a spray drying method and a tumbling granulation method can be used. The particle size of the granulated product may be any value as long as it can pass through the intersection slit of the die during extrusion molding.
μm or less. In order to fuse the aluminum titanate powders in the granules into a granulated powder, calcining or flame melting can be performed. This fusion only needs to be performed with a force that does not cause breakage due to stress in the molding process. In addition, in order to prevent fusion of the granules during fusion, it is preferable to perform calcination while flowing with a rotary kiln or the like.

If the granules are fused together, it is necessary to perform a step of crushing and classifying the obtained granulated powder. In this case, in order to prevent the granulated powder from being crushed into primary particles, it is desirable to adjust the time and crushing conditions. The granulated powder is kneaded with a combustible powder and a binder, extruded from a die to form a honeycomb-shaped formed body, and 1450 to 15
By firing at 50 ° C., a honeycomb body is obtained.

In order to obtain a DPF, the honeycomb cells of the molded body are alternately closed in a checkered pattern at both ends using a plugging material such as aluminum titanate powder and sintered to produce a DPF. it can. Further, in the present invention, the upper limit of the opening pitch or the opening diameter of the supply holes is not particularly limited as long as the cell wall of the honeycomb body can be formed without causing a problem such as underfilling. [ Reference Example 1 ] (Granulation step) A coarse aluminum titanate powder having an average particle diameter of 20 µm and a fine aluminum titanate powder having an average particle diameter of 3 µm were prepared, and the weight ratio of coarse powder: fine powder was 7: 3. The mixture was mixed to prepare a mixed powder.

This mixed powder was granulated to a particle size of 100 μm or less by a spray drying method, and the granulated product 1 was put into a hopper 10 shown in FIG. Hydrogen gas is supplied to the combustion furnace 11 from around the jet port, and is ignited at the jet port to form a chemical flame 12. The granulated body 1 is melted by the flame 12 and becomes a granulated powder 14 in which the primary particles 13 of the aluminum titanate powder are fused and integrated as schematically shown in FIG.

Although a chemical flame is used in this embodiment , a plasma flame or the like may be used. Alternatively, a granulated body may be put in a square sheath or the like and calcined at 1400 to 1500 ° C. for several hours to be fused. Can also. (Crushing step) In the above-mentioned granulated powder, the granules are fused together and the particle size is 10
Some of them exceeded 0 μm.
It was crushed and classified to have a particle size of less than 0 μm. Note that 100
After classifying and removing the particles pulverized to less than μm, particles having a particle size of 100 μm or more were pulverized again to less than 100 μm so that the granulated powder was not excessively pulverized to primary particles. (Molding process) The average particle size is 50 with respect to 100 parts by weight of the crushed granulated powder.
20 parts by weight of carbon black of 12 μm and 12 parts by weight of methyl cellulose as a binder were mixed and kneaded with a pressure kneader.

The kneaded material was extruded using a conventional die shown in FIGS. 5 and 6, to obtain a honeycomb-shaped formed body. (Firing step) The obtained compact is placed on a plate of a material whose shrinkage is equal to or greater than that of the compact placed on the table, and between the plate and the compact, and between the plate and the plate, respectively. It was fired at 1450-1550 ° C. for 4 hours in the air with zirconia coarse particles (average particle diameter 100 μm) interposed. Zirconia coarse particles reduce friction, and the plate shrinks at the same shrinkage as the molded body, so the difference in shrinkage between the upper end and the lower end of the molded body is a specified value (2 mm)
It was as follows.

The coefficient of thermal expansion of the obtained honeycomb body was measured in the extrusion direction and two directions perpendicular to the extrusion direction, and the results are shown in Table 1. Reference Example 2 FIGS. 3 and 4 are schematic diagrams of a die used in this reference example .
This die 2 has a supply hole 20 and a cross slit 21,
The cross slit 21 is similar to the conventional die shown in FIG. However, the supply hole 20 is located at the intersection 2 of the intersection slit 21.
The pitch of the supply holes 20 is twice as large as the pitch of the intersection of the intersection slits.

Then, carbon black 20 having an average particle size of 50 μm was added to 100 parts by weight of the same mixed powder as in Reference Example 1.
12 parts by weight of methyl cellulose as a binder and 12 parts by weight of a binder were mixed and kneaded with a pressure kneader. This kneaded product was extruded using the above die. The kneaded material flows into the intersection slit 21 from the supply hole 20 as shown in FIG.
The main stream (a) flowing through the cross slit 21 located in the front in the extrusion direction of 0 and the merge (b) generated by the collision of the flows from the adjacent supply holes 20 are extruded from the cross slit 21.

In this confluence (b), the aluminum titanate powder in the extruded material is oriented, but when compared in the same area range, the number of confluences (b) is smaller than that of the conventional die shown in FIGS. 5 and 6. Also, the orientation of the aluminum titanate powder becomes smaller than before. The obtained molded body was fired in the same manner as in Reference Example 1, and the coefficient of thermal expansion was measured in the same manner. Table 1 shows the results.

The supply hole 2 of the die 2 used in the present embodiment is
0 corresponds to the conventional die shown in FIG. 5 in which every other supply hole 100 is closed, but every three holes as shown in FIG. 7 or every three holes as shown in FIG. A die corresponding to the plugged one can also be used. 7 and 8, the supply holes 100 corresponding to closing are shown in black. Reference Example 3 FIG. 9 shows a schematic view of a die used in this reference example . The die 3 has an elliptical supply hole 30, and is the same as the reference example 2 except that the major diameter of the supply hole 30 is more than two including the intersections 32 of the intersection slits 31.

Using this die 3, extrusion molding was performed in the same manner as in Reference Example 2 . Molding using this die 3 reduces the confluence (b) and the orientation of the aluminum titanate powder as compared with the conventional die. The obtained molded body is a reference example
It was fired in the same manner as in Example 1, and the coefficient of thermal expansion was measured in the same manner.
Table 1 shows the results.

A die in which the density of the supply holes 30 is further reduced as shown in FIG. 10, and a die in which the supply holes 30 of the die 3 in FIG. 9 are closed every other or every two as shown in FIGS. 11 and 12. Can be used. ( Example ) The same as Reference Example 1 except that the die used in Reference Example 2 shown in FIGS. 3 and 4 was used. That is, the granulated powder was extruded using the die of FIG. 3 and fired similarly to form a honeycomb body. The thermal expansion coefficient is shown in Table 1. (Conventional Example) Extrusion molding was performed in the same manner as in Reference Example 2 using the conventional die shown in FIGS. 5 and 6. The obtained molded body was fired in the same manner as in Reference Example 1, and the coefficient of thermal expansion was measured in the same manner. Table 1 shows the results.

[0028]

[Table 1] (Evaluation) From Table 1, the honeycomb body obtained by the manufacturing method of Reference Example was
It is clear that the difference in the coefficient of thermal expansion between the extrusion direction and the orthogonal direction is smaller than in the conventional example. And granulation as in the example
If both the formation of the powder and the extrusion molding using the die of FIG. 3 are performed at the same time, the difference becomes zero, indicating that the anisotropy of the coefficient of thermal expansion has been eliminated.

[0029]

According to the method for manufacturing a honeycomb body made of aluminum titanate of the present invention, since the aluminum titanate powder is prevented from being oriented in the extrusion direction during extrusion molding, the anisotropy of the coefficient of thermal expansion is reduced. It is possible to manufacture a honeycomb body which is prevented and has excellent thermal shock resistance.

[Brief description of the drawings]

FIG. 1 is a schematic structural explanatory view of an apparatus for producing granulated powder used in one embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining that primary particles of a granulated body are fused to change into a granulated powder in one embodiment of the present invention.

FIG. 3 is a plan view of a main part of a die used in one embodiment of the present invention.

FIG. 4 is a sectional view taken along line AA of FIG. 3;

FIG. 5 is a plan view of a main part of a die used in a conventional example.

FIG. 6 is a sectional view taken along line BB of FIG. 5;

FIG. 7 is a plan view of a main part of the die, showing another mode of the die used in the example of the present invention.

FIG. 8 is a plan view of a relevant part of another embodiment of the die used in the embodiment of the present invention.

FIG. 9 shows a die used in a reference example of the present invention, and is a plan view of a main part of the die.

FIG. 10 is a plan view of a main part of the die, showing another mode of the die used in the reference example of the present invention.

FIG. 11 is a plan view of a relevant part of another embodiment of the die used in the reference example of the present invention.

FIG. 12 shows another embodiment of the die used in the reference example of the present invention, and is a plan view of a main part of the die.

[Explanation of symbols]

1: Granulated body 13: Primary particle 1
4: Granulated powder 2.3: Die 20/30: Supply hole 21
31: Intersection slit 22 ・ 32: Intersection

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tomohiko Nakanishi 14 Iwatani, Shimowasumi-cho, Nishio-shi, Aichi, Japan Inside the Automobile Parts Research Institute, Inc. (56) References JP-A-3-271151 (JP, A) JP-A Heisei 1-167282 (JP, A) JP-A-49-113789 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B28B 3/00-5/12 B01J 35/04 301 B01J 32 / 00

Claims (1)

(57) [Claims] 1. A granulating step of granulating aluminum titanate powder and fusing the aluminum titanate powder in the granulated body by heating to form a granulated powder; and supplying holes and communicating with the supply holes. With an intersecting slit
At least one of the opening pitch and the opening diameter of the supply holes is determined by the
Using a die larger than the pitch of the intersection of the difference slit,
Extruded material consisting of granulated powder is supplied from the supply hole and
A method for manufacturing a honeycomb body made of aluminum titanate, comprising sequentially performing a forming step of extruding a honeycomb shape by extruding through a slit to form an extruded body, and a firing step of sintering the extruded body.