JP6542549B2 - Method of manufacturing honeycomb structure - Google Patents

Description

  The present invention relates to, for example, a method of manufacturing a honeycomb structure used for a DPF that traps particulate matter in exhaust gas and a catalyst that purifies exhaust gas.

  For example, as in Patent Document 1, a DPF (Diesel Particulate Filter) for capturing particulate matter in exhaust gas is mounted in an exhaust passage of a diesel engine. For the DPF, a ceramic honeycomb structure excellent in heat resistance is used. The honeycomb structure is made of a porous material having three-dimensionally connected pores, and has a cylindrical outer peripheral wall, and a lattice-like cell wall integrally formed on the inner side of the outer peripheral wall to define a plurality of cells. Equipped with The honeycomb structure functions as a wall flow type DPF by selectively sealing the open part of the cell. In the wall flow DPF, exhaust gas moves between cells by flowing in pores formed in the cell walls.

JP, 2011-174383, A

  By the way, when the pressure loss of the exhaust gas in the exhaust passage increases, the output of the engine may decrease or the fuel efficiency may deteriorate. Therefore, for the honeycomb structure, it is desired to reduce the flow path resistance in the cell wall.

  An object of the present invention is to provide a method for manufacturing a honeycomb structure capable of reducing the flow path resistance in a cell wall.

  A method for manufacturing a honeycomb structure that solves the above-mentioned problems is a method for manufacturing a honeycomb structure having cell walls that partition a plurality of cells, and is made of an aggregate composed of inorganic compound particles, and fibers. The method includes a kneading step of kneading a mixture containing a pore forming material to prepare a clay, a molding step of molding a green body having a honeycomb structure using the clay, and a firing step of firing the green body.

  According to the above configuration, linear pores are likely to be formed by the fibers constituting the pore forming material in the cell walls of the honeycomb structure. As a result, compared to the case where the pore forming material is formed of a particulate material, the number of communication holes penetrating the cell wall is increased, and the flow path resistance in the cell wall can be reduced.

In the method for manufacturing a honeycomb structure, it is preferable that the diameter of the fibers constituting the pore forming material is 3 μm or more and 20 μm or less.
According to the above configuration, when the diameter of the fiber forming the pore forming material is 3 μm or more and 20 μm or less, the decrease in mechanical strength can be suppressed while reducing the flow path resistance in the cell wall.

In the method for manufacturing a honeycomb structure, it is preferable that a length of fibers constituting the pore forming material is 0.2 times or more as large as a design thickness of the cell wall.
According to the above configuration, the communication hole penetrating the cell wall is formed by the plurality of fibers by the length of the fiber constituting the pore forming material being 0.2 times or more the design thickness of the cell wall Can also reduce the complexity of the pore structure.

In the method for manufacturing a honeycomb structure, it is preferable that a length of fibers constituting the pore forming material is 1.2 times or less of a design thickness of the cell wall.
According to the above configuration, when the length of the fibers forming the pore forming material is 1.2 times or less of the design thickness of the cell wall, the fibers are less likely to be entangled in the kneading step or the forming step. As a result, the complication of the pore structure can be suppressed. Moreover, it is also possible to form the pore which penetrates a cell wall by one fiber by containing the fiber longer than the design thickness of a cell wall. As a result, the flow path resistance in the cell wall can be effectively reduced.

In the method for manufacturing a honeycomb structure, the ratio of the bulk volume of the pore forming material to the bulk volume of the aggregate is preferably 0.2 or more and 3.0 or less.
By setting the volume ratio as in the above configuration, it is possible to suppress the decrease in strength of the honeycomb structure based on the porosity while reducing the flow path resistance of the cell wall per unit volume of the honeycomb structure. .

It is a perspective view which shows the perspective view structure of an example of a honeycomb structure. It is the elements on larger scale which show the planar structure of the end surface of a honeycomb structure. It is a flowchart which shows an example of the manufacturing process in the manufacturing method of the honeycomb structure of one Embodiment. It is sectional drawing which shows typically the cross-section of a cell wall. It is sectional drawing which shows typically the cross-section of wall flow type DPF. It is sectional drawing which shows typically the cross-section of the cell wall which carry | supported the catalyst metal.

One embodiment of a method for manufacturing a honeycomb structure will be described with reference to FIGS. 1 to 6. First, an example of a honeycomb structure will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1 and FIG. 2, the ceramic honeycomb structure 10 is formed of a porous material having three-dimensionally connected pores, and has an outer peripheral wall 11 having a cylindrical shape and an inner side of the outer peripheral wall 11. And an integrally formed cell wall 12. The cell walls 12 are formed in a lattice shape, and define a plurality of cells 13 which are open at both ends of the honeycomb structure 10 and extend along the axial direction of the outer peripheral wall 11. The honeycomb structure 10 functions as a wall flow type DPF by selectively sealing the openings of the cells 13 at both ends. In addition, the honeycomb structure 10 functions as a catalyst by supporting a catalyst metal. In the honeycomb structure 10 functioning as the DPF or the catalyst, the design thickness t of the cell wall 12 is set to 100 μm or more and 500 μm or less. The cell wall 12 may be formed in a lattice shape, and is not limited to the configuration in which the cell 13 having a rectangular opening is partitioned as shown in FIG. 2, for example, a configuration in which a cell having a hexagonal opening is partitioned. It may be

  An example of a method of manufacturing the above-described honeycomb structure 10 will be described with reference to FIG. In the honeycomb structure 10, a kneading step (step S11) of kneading a raw material to prepare a clay, a molding step of molding a compact using a clay (step S12), and a drying step of drying the compact (step S13). ), And manufactured through a firing step (step S14) of firing the dried molded body.

  In the kneading step, the clay of the honeycomb structure 10 is prepared by adding water to a mixture containing an aggregate, a binder, a lubricant, a pore former and the like and sufficiently kneading the mixture. As the aggregate, inorganic compound particles having an average particle diameter of 1 μm or more and 10 μm or less are used. When, for example, alumina, talc or kaolin is used as this inorganic compound particle, a cordierite crystal having excellent heat resistance can be obtained by firing. As the inorganic compound particles, those which are excellent in heat resistance after firing, for example, aluminum titanate or silicon carbide can be used.

  The pore-forming material is composed of fibers 14 that are gasified by oxidation in a later firing step. The fibers 14 constituting the pore forming material have a thin thread-like shape with a diameter D and a length L, and for example, the ratio of the length L to the diameter D (= L / D) is 5 or more. Further, the diameter D is an average value of the length of the largest width portion in the cross section of the fiber 14, and is, for example, the diameter of the circle when the cross section of the fiber 14 is a circle. For the fibers 14, synthetic fibers such as nylon (polyamide) and polyethylene terephthalate (PET) can be used, and vegetable fibers such as wood pulp can be used. When the pore forming material is composed of the fibers 14, linear pores are easily formed in the cell wall 12 of the honeycomb structure 10. As a result, compared to the case where the pore forming material is formed of a particulate material, the number of communication holes penetrating the cell wall 12 is increased, and the flow path resistance in the cell wall 12 can be reduced.

  The diameter D of the fibers 14 constituting the pore forming material is set to 3 μm or more and 20 μm or less. Thereby, pores having a pore diameter of several μm to several tens of μm are formed in the honeycomb structure 10. By setting the diameter D of the fibers 14 to 3 μm or more, it is possible to suppress the pore diameter from being excessively reduced. On the other hand, by setting the diameter D of the fibers 14 to 20 μm or less, the pore diameter can be prevented from becoming excessively large, and the decrease in the mechanical strength of the honeycomb structure 10 can be suppressed.

  Further, by setting the diameter D of the fibers 14 in the above-described range, the honeycomb structure 10 having an average pore diameter of less than 35 μm can be obtained. Thereby, when the application of the honeycomb structure 10 is DPF, sufficient capture performance of particulate matter can be obtained. In addition, an average pore diameter is a value prescribed | regulated based on the measurement result of pore distribution using the mercury intrusion method, Comprising: For example, it is a pore diameter corresponding to the peak of log differential pore volume.

  The length L of the fibers 14 is set to 0.2 times or more and 1.2 times or less of the design thickness t of the cell wall 12. By setting the length L of the fibers 14 to be 0.2 times or more the design thickness t, the pore structure is complicated even if the pores penetrating the cell wall 12 are formed by a plurality of fibers. Thus, the flow path resistance in the cell wall 12 can be reduced. It is also possible to form pores penetrating the cell wall 12 with one fiber 14 by the fibers 14 longer than the design thickness t of the cell wall 12. Therefore, the flow path resistance in the cell wall 12 can be effectively reduced. Further, by setting the length L of the fiber 14 to 1.2 times or less of the design thickness t, the fibers 14 are less likely to be entangled during kneading and molding, whereby the pore diameter becomes excessively large. And the complexity of the pore structure can be suppressed. When the design thickness t of the cell wall 12 is 100 μm to 500 μm, the length L of the specific fiber 14 is 50 μm to 500 μm in the range of 0.2 times to 1.2 times the design thickness t. It is set to the following.

  The ratio R (= V2 / V1) of the bulk volume V2 of the pore forming material to the bulk volume V1 of the aggregate is set to 0.2 to 3.0. Thereby, the honeycomb structure 10 having a porosity of 40% or more and 75% or less measured by mercury porosimetry is obtained. When the porosity is 40% or more, the flow path resistance of the cell wall 12 per unit volume of the honeycomb structure 10 can be reduced, and sufficient when the application of the honeycomb structure 10 is a catalyst A specific surface area is obtained. On the other hand, when the porosity is 75% or less, the decrease in mechanical strength in the honeycomb structure 10 can be suppressed. In addition, a bulk volume is a volume at the time of implementing tapping equivalent to a tap density measurement method.

In the forming step, the above-mentioned clay is extruded using an extrusion forming machine and cut at a predetermined length to form a formed body which is the honeycomb structure 10 before firing.
In the drying step, the moisture contained in the molded body is evaporated by holding the molded body at a drying temperature (for example, about 120 ° C.) for a certain period of time. The drying step is performed under the atmosphere.

  In the firing step, the shaped body that has undergone the drying step is heated to the firing temperature over, for example, about 20 hours, and then the shaped body is maintained at the firing temperature for about 1 to 5 hours. In the firing step, in the process of raising the temperature of the formed body, for example, at 150 ° C. to 600 ° C., the fiber 14 constituting the pore forming material is dissolved and the component such as carbon of the fiber 14 is oxidized and the fiber 14 disappears from the formed body Do. Then, the molded body after firing is cooled to manufacture a honeycomb structure 10 having pores.

  The atmosphere and the firing temperature in the firing step are set according to the material of the aggregate. When the honeycomb structure 10 is cordierite, the firing step is performed in the atmosphere, and the firing temperature is about 1350 ° C. to 1450 ° C. When the honeycomb structure 10 is aluminum titanate, the firing step is performed in the atmosphere, and the firing temperature is about 1500 ° C. to 1600 ° C. When the honeycomb structure 10 is silicon carbide, a firing step is performed under an inert gas atmosphere, and the firing temperature is about 2000 ° C. to 2200 ° C.

  The firing step may include a dissolving step of holding the shaped body at a melting temperature near the melting point of the fiber 14 for a certain period of time in the process until the shaped body is heated up to the firing temperature. The firing step may include a pre-firing step of holding the formed body at a pre-firing temperature near 600 ° C. at which the carbon component of the pore forming material is oxidized, for a certain period of time. According to such a configuration, it is possible to fire the formed body after the fibers 14 contained in the formed body are completely eliminated.

  As shown in FIG. 4, in the cell walls 12 of the honeycomb structure 10 manufactured by the above-described manufacturing method, a thin three-dimensionally connected thin line is formed by the gaps between aggregates which are inorganic compound particles and the space where the fibers 14 disappear. Holes 15 are formed. The pores 15 communicate the cells 13 partitioned by the cell walls 12. Moreover, the ratio of a linear part is high because the pore forming material is comprised with the fiber 14, and the pore 15 penetrates the cell wall 12 compared with the case where a pore forming material is comprised with a particulate-form material The communication holes increase. Therefore, in the honeycomb structure 10, the flow passage resistance in the cell wall 12 can be reduced.

  And as shown in FIG. 5, when the application of the honeycomb structure 10 mentioned above is DPF 16, as the honeycomb structure 10, the resin mask which selectively obstruct | occludes the opening part of the cell 13, for example is an edge part. The opening portion of the unmasked cell 13 is filled with the plugging slurry by mounting and immersing the end portion thereof in the plugging slurry containing ceramic particles and the like. Then, the filled plugging slurry is dried and fired to form a plugged portion 17 that closes the cell opening. By forming the plugged portions 17 at both ends, the honeycomb structure 10 is provided with a function as a wall flow DPF. In the DPF 16 having such a configuration, the pressure loss of the exhaust gas can be reduced because the flow path resistance in the cell wall 12 is small.

  Further, as shown in FIG. 6, when the application of the above-described honeycomb structure 10 is a DPF supporting a catalyst, the honeycomb structure 10 is immersed in a catalyst slurry containing a catalyst metal 18. At this time, since the flow resistance in the cell wall 12 is small, the catalyst slurry can be filled to the details of the pores 15. Then, the catalyst slurry is dried and fired to impart the catalyst function to the honeycomb structure 10.

  In the catalyst using the honeycomb structure, as the amount of the catalyst carried is increased, the catalyst performance is improved, while the open area of the cell is decreased, whereby the pressure loss of the exhaust gas is increased. In this respect, in the catalyst using the honeycomb structure 10 described above, the catalyst slurry is filled up to the details of the pores 15 so that the reduction of the open area of the cells 13 is suppressed, and more catalyst metal 18 is supported. It can be done. Therefore, the catalyst performance can be enhanced while suppressing the pressure loss of the exhaust gas.

According to the method for manufacturing a honeycomb structure described above, the following effects can be obtained.
(1) By forming the pore forming material with the fibers 14, pores having a high proportion of linear portions in the honeycomb structure 10 are easily formed. As a result, communication holes passing through the cell wall 12 increase, and the flow path resistance in the cell wall 12 can be reduced.

  (2) By setting the diameter D of the fibers 14 to 3 μm or more, it is possible to suppress the pore diameter from becoming excessively small. Therefore, when the application of the honeycomb structure 10 is a catalyst, the honeycomb structure 10 can support a catalyst metal in the pores 15.

  (3) By setting the diameter D of the fibers 14 to 20 μm or less, the pore diameter can be prevented from becoming excessively large. As a result, the reduction in mechanical strength of the honeycomb structure 10 can be suppressed. In addition, when the application of the honeycomb structure 10 is DPF, sufficient capture performance of particulate matter can be obtained.

  (4) By setting the length L of the fiber 14 to be 0.2 times or more the design thickness t of the cell wall 12, the pores 15 penetrating the cell wall 12 are formed by the plurality of fibers 14 It will be easier.

  (5) By including the fiber 14 longer than the design thickness t of the cell wall 12, it is also possible to form the pore 15 penetrating the cell wall 12 with one fiber 14. Thereby, the flow path resistance in the cell wall 12 can be effectively reduced.

  (6) By setting the length L of the fiber 14 to 1.2 times or less of the design thickness t of the cell wall 12, the fibers 14 are less likely to be entangled during kneading and molding, and the pore diameter is excessive And the complication of the pore structure can be suppressed.

  (7) The flow resistance of the cell wall 12 per unit volume of the honeycomb structure is reduced by setting the ratio R of the bulk volume V2 of the pore forming material to the bulk volume V1 of the aggregate to 0.2 or more. be able to. Further, by setting the ratio R to 3.0 or less, it is possible to suppress a decrease in the mechanical strength of the honeycomb structure based on the porosity.

  (8) In the DPF using the honeycomb structure 10, the pressure loss of exhaust gas can be reduced while maintaining the capture performance equivalent to that of the DPF using the honeycomb structure using the particulate material as the pore forming material .

  (9) In the catalyst using the honeycomb structure 10, the pressure loss of exhaust gas can be reduced while the catalyst performance is improved, as compared with the catalyst using the honeycomb structure having the particulate material as the pore forming material. it can.

In addition, the said embodiment can also be changed suitably as follows and can also be implemented.
The ratio R of the volume V2 of the pore forming material to the volume V1 of the aggregate may be less than 0.2 or more than 3.0. According to such a configuration, it is possible to manufacture a honeycomb structure in which pressure loss is suppressed under various porosities.

  The pore-forming material may contain fibers 14 having a length L less than 0.2 times the design thickness t of the cell wall 12, or a length L greater than 1.2 times The fibers 14 may be included. According to such a configuration, it is possible to improve the freedom of the pore structure while suppressing the flow path resistance in the cell wall 12.

  The pore former may contain fibers 14 having a diameter D of less than 3 μm, or may contain fibers 14 having a diameter D of more than 20 μm. According to such a configuration, it is possible to manufacture a honeycomb structure in which pressure loss is suppressed under various pore sizes.

The drying step may be part of the firing step. That is, the drying step and the firing step may be performed continuously in the same furnace.
-When the application of the honeycomb structure 10 is DPF, plugged portions may be formed between the forming step and the drying step. In such a case, a mask is attached to the end of the compact, and the end is immersed in the plugging slurry. Then, the filled plugging slurry is dried in the next drying step and fired in the next firing step.

  t Design thickness, 10: honeycomb structure, 11: outer peripheral wall, 12: cell wall, 13: cell, 14: fiber, 15: pore, 16: DPF, 17: plugging portion.

Claims (1)

A method for manufacturing a honeycomb structure capable of functioning as a wall flow type catalyst by arranging cell walls that partition a plurality of cells in a lattice and carrying a wall flow type DPF or a catalyst metal ,
Kneading a mixture comprising an aggregate composed of inorganic compound particles and a pore-forming material composed of fibers to prepare a clay;
A forming step of forming a formed body having a honeycomb structure using the clay;
And a firing step of firing the compact .
The design thickness of the cell wall is 100 μm to 500 μm,
The aggregate is inorganic compound particles having an average particle diameter of 1 μm to 10 μm,
The diameter of fibers constituting the pore forming material is 3 μm or more and 20 μm or less,
The length of the fibers constituting the pore forming material is set to 50 μm to 500 μm within the range of 0.2 times to 1.2 times the design thickness of the cell wall,
A method for manufacturing a honeycomb structure, wherein a ratio of a bulk volume of the pore forming material to a bulk volume of the aggregate is 0.2 or more and 3.0 or less .