WO2013024744A1

WO2013024744A1 - Honeycomb filter

Info

Publication number: WO2013024744A1
Application number: PCT/JP2012/070079
Authority: WO
Inventors: 健太郎岩崎
Original assignee: 住友化学株式会社
Priority date: 2011-08-12
Filing date: 2012-08-07
Publication date: 2013-02-21
Also published as: JP2013039513A

Abstract

　A honeycomb filter (100) comprising a plurality of parallel flow channels (110) divided by porous partition walls (120), the plurality of flow channels (110) comprising flow channels (110a) and other flow channels (110b) adjacent thereto, wherein the end sections of the flow channels (110a) are sealed at one side of the honeycomb filter (100), and the end sections of the other flow channels (110b) are sealed at the other side of the honeycomb filter (100), and the maximum height (Rz) of at least one among a region (A) in the partition walls (115a) of the flow channels (110a) and a region (B) in the partition walls (115b) of the other flow channels (110b) is not more than 55.00μm.

Description

Honeycomb filter

The present invention relates to a honeycomb filter.

The honeycomb filter is used as a ceramic filter for removing the collected matter from the fluid containing the collected matter, for example, for purifying exhaust gas exhausted from an internal combustion engine such as a diesel engine or a gasoline engine. Used as an exhaust gas filter. Such a honeycomb filter has a plurality of parallel flow paths partitioned by partition walls (see, for example, Patent Document 1 below).

JP 2005-270755 A

However, in the conventional honeycomb filter, when the fluid containing the collected matter flows in from the one end side and flows out from the other end side in the honeycomb filter, the pressure is increased as the collected matter is collected in the honeycomb filter. It is difficult to sufficiently suppress the increase in loss. Therefore, it is required for the honeycomb filter to reduce the pressure loss as compared with the related art.

The present invention has been made in view of such circumstances, and an object thereof is to provide a honeycomb filter capable of reducing pressure loss.

That is, the honeycomb filter according to the present invention is a honeycomb filter having a plurality of parallel flow paths partitioned by a porous partition wall, wherein the plurality of flow paths includes the first flow path and the first flow path. A second flow path adjacent to the flow path, the end of one end of the honeycomb filter in the first flow path is sealed, and the other end side of the honeycomb filter in the second flow path The end is sealed, and the maximum height Rz of at least a part of the inner wall of at least one of the first flow path or the second flow path is 55.00 μm or less.

By the way, in the flow path through which the fluid containing the trapped material flows, if the inner wall of the flow path has a region having a large maximum height Rz, the movement of the fluid is prevented in the region, and the honeycomb filter As the collection object is collected, the flow path is easily blocked by the collection object. On the other hand, in the honeycomb filter according to the present invention, the maximum height Rz of at least a part of the inner wall of at least one of the first flow path or the second flow path is 55.00 μm or less. It becomes easy to suppress that an inner wall prevents the movement of a fluid. Moreover, it becomes easy to suppress that the flow path is blocked by the collected matter as the collected matter is collected by the honeycomb filter. Therefore, in the honeycomb filter according to the present invention, pressure loss can be reduced.

The average value of the maximum height Rz on the inner wall is preferably 56.00 μm or less. In this case, the pressure loss can be further reduced.

The arithmetic average roughness Ra of the region of the inner wall is preferably 9.000 μm or less. In this case, the inner wall of the flow path is further easily prevented from interfering with fluid movement. Moreover, it becomes easier to further suppress the flow path from being blocked by the collected matter as the collected matter is collected by the honeycomb filter. Therefore, the pressure loss can be further reduced.

The average value of the arithmetic average roughness Ra on the inner wall is preferably 8.000 μm or less. In this case, the pressure loss can be further reduced.

Moreover, the partition may contain aluminum titanate. In this case, durability against thermal stress of the honeycomb filter can be improved.

The honeycomb filter according to the present invention can reduce the pressure loss as compared with the conventional one. Such a honeycomb filter is suitably used as a ceramic filter for removing the collected matter from the fluid containing the collected matter.

FIG. 1 is a perspective view showing a honeycomb filter according to an embodiment of the present invention. FIG. 2 is a view taken along the line II-II in FIG. FIG. 3 is an example of the surface shape of a predetermined measurement region on the inner wall of the flow path. FIG. 4 is a diagram schematically showing a pressure loss measuring device. FIG. 5 is a diagram showing measurement results of pressure loss.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings as necessary. However, the present invention is not limited to the following embodiments. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

<Honeycomb filter>
FIG. 1 is a perspective view showing a honeycomb filter according to the present embodiment, and FIG. 2 is a view taken along the line II-II in FIG. As shown in FIGS. 1 and 2, the honeycomb filter 100 is a cylindrical body having a plurality of flow paths 110 arranged in parallel to each other. Each of the plurality of flow paths 110 is partitioned by a partition wall 120 that extends parallel to the central axis of the honeycomb filter 100. The flow path 110 includes a flow path (first flow path) 110a constituting a part of the flow path 110 and a flow path (second flow path) 110b constituting the remaining part of the flow path 110. Have.

One end of the honeycomb filter 100 in the flow channel 110a is opened as a gas inlet on one end surface 100a of the honeycomb filter 100, and the other end of the honeycomb filter 100 in the flow channel 110a is opened in the honeycomb filter 100. The other end surface 100b of 100 is sealed by the sealing portion 130. On the other hand, the end portion on one end side of the honeycomb filter 100 in the channel 110b is sealed by the sealing portion 130 on the one end surface 100a, and the end portion on the other end side of the honeycomb filter 100 in the channel 110b is on the other end surface 100b. It opens as a gas outlet.

The flow path 110b is adjacent to the flow path 110a. In the honeycomb filter 100, the flow paths 110a and the flow paths 110b are alternately arranged to form a lattice structure. The

flow paths

110a and 110b are perpendicular to both end faces of the honeycomb filter 100, and are arranged in a square arrangement when viewed from the end face, that is, the central axes of the

flow paths

110a and 110b are respectively located at the apexes of the square. . The cross section perpendicular | vertical to the axial direction (longitudinal direction) of the said flow path in

flow path

110a, 110b is square shape, for example.

The maximum height Rz of at least a part of the inner wall of at least one of the flow channel 110a or the flow channel 110b is 55.00 μm or less. For example, the maximum height Rz of at least a part of the region A (see FIG. 2) in the inner wall 115a of the flow channel 110a that is a flow channel on the gas inflow side is 55.00 μm or less. Furthermore, the maximum height Rz of at least a part of the region B (see FIG. 2) in the inner wall 115b of the flow channel 110b that is the flow channel on the gas outflow side may be 55.00 μm or less. The maximum height Rz refers to the maximum height based on JIS B 0601: 2001. From the viewpoint of further reducing the pressure loss, the maximum height Rz is preferably 50.00 μm or less, and more preferably 48.00 μm or less.

The positions of the area A and the area B are not particularly limited, and may be the center position of the honeycomb filter 100 in the axial direction of the flow path 110, and may be located on the one end face 100a side or the other end face 100b side from the center position. It may be. The size of the areas A and B is, for example, 298 μm × 224 μm. Each of the flow paths 110 may include a plurality of regions having a maximum height Rz of 55.00 μm or less on one inner wall, and an inner wall having a region having a maximum height Rz of 55.00 μm or less. You may have two or more.

The average value of the maximum height Rz measured on at least one inner wall of the flow channel 110a or the flow channel 110b is preferably 56.00 μm or less, more preferably 55.00 μm or less, from the viewpoint of further reducing the pressure loss. More preferably, it is 0.000 μm or less. The average value of the maximum height Rz is the maximum of the three regions when three regions located along the axial direction of the flow channel are arbitrarily selected from one inner wall of the flow channel to be measured. The average value of height Rz is said.

From the viewpoint of further reducing the pressure loss, the arithmetic average roughness Ra of the above region that gives the maximum height Rz of 55.00 μm or less is preferably 9.000 μm or less, more preferably 8.000 μm or less, and 7.500 μm or less. Further preferred. The arithmetic average roughness Ra refers to the arithmetic average roughness based on JIS B 0601: 2001.

From the viewpoint of further reducing the pressure loss, the average value of the arithmetic average roughness Ra measured on at least one inner wall of the channel 110a or the channel 110b is preferably 8.000 μm or less, and more preferably 7.500 μm or less. The average value of the arithmetic average roughness Ra means that the three regions located along the axial direction of the flow channel are arbitrarily selected from the inner wall of one of the flow channels to be measured. The average value of arithmetic average roughness Ra is said. In the present embodiment, from the viewpoint of further reducing the pressure loss, the average value of the maximum height Rz is 56.00 μm or less and the arithmetic average roughness Ra on at least one inner wall of the flow channel 110a or the flow channel 110b. Is preferably 8.000 μm or less.

The length of the honeycomb filter 100 in the longitudinal direction of the

flow paths

110a and 110b is, for example, 30 to 300 mm. When the honeycomb filter 100 is a cylindrical body, the outer diameter of the honeycomb filter 100 is, for example, 10 to 300 mm. The inner diameter (the length of one side of the square) of the cross section perpendicular to the axial direction of the

flow paths

110a, 110b is, for example, 0.5 to 1.2 mm. The average thickness (cell wall thickness) of the partition wall 120 is, for example, 0.1 to 0.5 mm.

In the honeycomb filter 100, the partition wall 120 is porous, and includes, for example, porous ceramics (porous ceramic sintered body). The partition wall 120 has a structure that allows fluid (for example, exhaust gas containing fine particles such as soot) to pass therethrough. Specifically, a large number of communication holes (flow channels) through which fluid can pass are formed in the partition wall 120. The porosity (open porosity) of the partition wall 120 is, for example, 30 to 70% by volume. The pore diameter (pore diameter) of the partition wall 120 is, for example, 5 to 30 μm. The porosity and the pore diameter of the partition wall 120 can be adjusted by the particle diameter of the raw material, the added amount of the pore forming agent, the kind of the pore forming agent, and the firing conditions, and can be measured by a mercury intrusion method.

The partition wall 120 may contain aluminum titanate, and may further contain magnesium or silicon. The partition 120 is made of, for example, porous ceramics mainly made of an aluminum titanate crystal. “Mainly composed of an aluminum titanate-based crystal” means that the main crystal phase constituting the aluminum titanate-based ceramic fired body is an aluminum titanate-based crystal phase. An aluminum titanate crystal phase, an aluminum magnesium titanate crystal phase, or the like may be used.

When the partition wall 120 contains aluminum titanate and magnesium, the composition formula of the partition wall 120 is, for example, Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ , and the value of x is preferably 0.03 or more. 0.03-0.20 is more preferable, and 0.03-0.18 is still more preferable. The partition 120 may contain a trace component derived from a raw material or a trace component inevitably included in the manufacturing process.

When the partition 120 contains silicon, the partition 120 may contain the glass phase derived from a silicon source powder. The glass phase refers to an amorphous phase in which SiO ₂ is the main component. In this case, the glass phase content is preferably 4% by mass or less. When the glass phase content is 4% by mass or less, an aluminum titanate-based ceramic fired body that satisfies the pore characteristics required for a ceramic filter such as a particulate filter is easily obtained. The glass phase content is preferably 2% by mass or more.

The partition wall 120 may include a phase (crystal phase) other than the aluminum titanate crystal phase or the glass phase. Examples of the phase other than the aluminum titanate-based crystal phase include a phase derived from a raw material used for producing an aluminum titanate-based ceramic fired body. More specifically, the phase derived from the raw material is a phase derived from an aluminum source powder, a titanium source powder and / or a magnesium source powder that remains without forming an aluminum titanate-based crystal phase during the manufacture of the honeycomb filter. Examples of the phase derived from the raw material include phases such as alumina and titania. The crystal phase forming the partition wall 120 can be confirmed by an X-ray diffraction spectrum.

The honeycomb filter 100 is suitable as a particulate filter that collects a collection object such as soot contained in exhaust gas from an internal combustion engine such as a diesel engine or a gasoline engine. For example, in the honeycomb filter 100, as shown in FIG. 2, the gas G supplied from the one end face 100a to the flow path 110a passes through the communication hole in the partition wall 120 and reaches the adjacent flow path 110b, and the other end face 100b. Discharged from. At this time, the collected matter in the gas G is collected on the surface of the partition wall 120 or in the communication hole and removed from the gas G, whereby the honeycomb filter 100 functions as a filter.

In addition, this invention is not necessarily limited to embodiment mentioned above, A various change is possible in the range which does not deviate from the summary. For example, the partition 120 is not limited to including aluminum titanate, and may include ceramics such as cordierite, silicon carbide, mullite, or a metal substance. In addition, the cross section of the flow path perpendicular to the axial direction of the flow path in the honeycomb filter 100 is not limited to a rectangular shape such as a square shape, but a hexagonal shape, an octagonal shape, a triangular shape, a circular shape, an elliptical shape, or the like. It may be. Furthermore, the honey-comb filter 100 is not restricted to a cylindrical body, A cube, a rectangular parallelepiped, etc. may be sufficient.

<Honeycomb filter manufacturing method>
Next, a method for manufacturing the honeycomb filter 100 will be described. The manufacturing method of the honeycomb filter 100 includes, for example, (a) a raw material preparation step of preparing a raw material mixture containing the ceramic powder and additives, and (b) forming a raw material mixture to obtain a formed body having a flow path. A molding step, and (c) a firing step for firing the molded body, and (d) a sealing step for sealing one end of each flow path between the molding step and the firing step or after the firing step. .

[Step (a): Raw material preparation step]
In the step (a), the ceramic powder and the additive are mixed and then kneaded to prepare a raw material mixture. Examples of the additive include a hole forming agent (pore forming agent), a binder, a plasticizer, a dispersant, and a solvent.

Hereinafter, a method for manufacturing a honeycomb filter having partition walls containing aluminum titanate will be described as an example. The ceramic powder includes at least an aluminum source powder and a titanium source powder, and may further include a magnesium source powder and a silicon source powder.

(Aluminum source powder)
The aluminum source powder is a powder of a compound that becomes an aluminum component constituting the partition wall. Examples of the aluminum source powder include alumina (aluminum oxide) powder. Examples of the crystal type of alumina include γ-type, δ-type, θ-type, and α-type, and may be indefinite (amorphous). The crystal type of alumina is preferably α type.

The aluminum source powder may be a powder of a compound that is led to alumina by firing alone in air. Examples of such a compound include an aluminum salt, aluminum alkoxide, aluminum hydroxide, metal aluminum and the like.

The aluminum salt may be an aluminum inorganic salt with an inorganic acid or an aluminum organic salt with an organic acid. Specific examples of the aluminum inorganic salt include aluminum nitrates such as aluminum nitrate and ammonium aluminum nitrate; aluminum carbonates such as ammonium carbonate aluminum and the like. Examples of the aluminum organic salt include aluminum oxalate, aluminum acetate, aluminum stearate, aluminum lactate, and aluminum laurate.

Specific examples of the aluminum alkoxide include, for example, aluminum isopropoxide, aluminum ethoxide, aluminum sec-butoxide, aluminum tert-butoxide and the like.

Examples of the aluminum hydroxide crystal type include a gibbsite type, a bayerite type, a norosotrandite type, a boehmite type, and a pseudo-boehmite type, and may be amorphous (amorphous). Examples of amorphous aluminum hydroxide include an aluminum hydrolyzate obtained by hydrolyzing an aqueous solution of a water-soluble aluminum compound such as an aluminum salt or an aluminum alkoxide.

The aluminum source powder may be one type or two or more types. The aluminum source powder may contain trace components that are derived from the raw materials or inevitably contained in the production process.

In the aluminum source powder, the particle size (center particle size, D50) equivalent to a volume-based cumulative percentage of 50% measured by a laser diffraction method is preferably 20 to 60 μm. By adjusting D50 of the aluminum source powder within this range, an aluminum titanate ceramic fired body exhibiting excellent porosity can be obtained, and the firing shrinkage rate can be more effectively reduced. The D50 of the aluminum source powder is more preferably 25 to 60 μm.

(Titanium source powder)
The titanium source powder is a powder of a compound that becomes a titanium component constituting the partition walls, and is, for example, a titanium oxide powder. Titanium oxide is, for example, titanium (IV) oxide, titanium (III) oxide, or titanium (II) oxide, and preferably titanium (IV) oxide. The crystal forms of titanium (IV) oxide are anatase, rutile, and brookite. The titanium oxide may be amorphous (amorphous). The titanium oxide is more preferably anatase type or rutile type titanium (IV) oxide.

The titanium source powder may be a powder of a compound that is led to titania (titanium oxide) by firing alone in the air. For example, titanium salt, titanium alkoxide, titanium hydroxide, titanium nitride, titanium sulfide, titanium It is a metal.

Examples of the titanium salt include titanium trichloride, titanium tetrachloride, titanium (IV) sulfide, titanium sulfide (VI), and titanium sulfate (IV). Titanium alkoxides include, for example, titanium (IV) ethoxide, titanium (IV) methoxide, titanium (IV) t-butoxide, titanium (IV) isobutoxide, titanium (IV) n-propoxide, titanium (IV) tetraisopropoxide, And these chelating products.

The titanium source powder may be one type or two or more types. The titanium source powder may contain a trace component derived from the raw material or unavoidably contained in the production process.

In the titanium source powder, the volume-based cumulative particle diameter (D50) measured by laser diffraction method is preferably 0.1 to 25 μm. The D50 of the titanium source powder is more preferably 1 to 20 μm in order to achieve a sufficiently low firing shrinkage rate.

The titanium source powder may show a bimodal particle size distribution. When the titanium source powder having such a bimodal particle size distribution is used, the particle size of the particles forming the peak having the larger particle size measured by the laser diffraction method is preferably 20 to 50 μm.

The mode diameter of the titanium source powder measured by the laser diffraction method is usually 0.1 to 60 μm.

The molar ratio of the aluminum source powder in terms of Al ₂ O ₃ (alumina) and the titanium source powder in terms of TiO ₂ (titania) in the raw material mixture (aluminum source powder: titanium source powder) is preferably 35:65 to 45 : 55, more preferably 40:60 to 45:55. Within such a range, by using the titanium source powder excessively with respect to the aluminum source powder, it becomes possible to more effectively reduce the firing shrinkage rate of the molded body of the raw material mixture.

(Magnesium source powder)
The raw material mixture may further contain a magnesium source powder. When the raw material mixture contains a magnesium source powder, the obtained aluminum titanate ceramic fired body is a fired body containing aluminum magnesium titanate crystals. The magnesium source powder is not only magnesia (magnesium oxide) powder but also a powder of a compound introduced into magnesia by firing alone in air. Such compounds are, for example, magnesium salts, magnesium alkoxides, magnesium hydroxide, magnesium nitride, and metallic magnesium.

Magnesium salts include, for example, magnesium chloride, magnesium perchlorate, magnesium phosphate, magnesium pyrophosphate, magnesium oxalate, magnesium nitrate, magnesium carbonate, magnesium acetate, magnesium sulfate, magnesium citrate, magnesium lactate, magnesium stearate, magnesium salicylate , Magnesium myristate, magnesium gluconate, magnesium dimethacrylate, and magnesium benzoate.

Examples of the magnesium alkoxide include magnesium methoxide and magnesium ethoxide.

As the magnesium source powder, a powder of a compound serving both as a magnesium source and an aluminum source can be used. Such a compound is, for example, magnesia spinel (MgAl ₂ O ₄ ).

When using a powder of a compound that serves as both a magnesium source and an aluminum source as the magnesium source powder, it is included in the amount of Al ₂ O ₃ (alumina) equivalent of the aluminum source powder and a compound powder that serves as both the magnesium source and the aluminum source. The molar ratio between the total amount of Al ₂ O ₃ (alumina) equivalent of the Al component and the amount of TiO ₂ (titania) equivalent of the titanium source powder is adjusted to be within the above range in the raw material mixture.

The magnesium source powder may be one type or two or more types. The magnesium source powder may contain trace components that are derived from the raw materials or inevitably contained in the production process.

In the magnesium source powder, the particle size (D50) equivalent to a volume-based cumulative percentage of 50% as measured by a laser diffraction method is preferably 0.5 to 30 μm. The D50 of the magnesium source powder is more preferably 3 to 20 μm from the viewpoint of reducing the firing shrinkage of the molded body.

The content of magnesium source powder in terms of MgO (magnesia) in the raw material mixture is based on the total amount of aluminum source powder in terms of Al ₂ O ₃ (alumina) and titanium source powder in terms of TiO ₂ (titania). The molar ratio is preferably 0.03 to 0.15, more preferably 0.03 to 0.12. By adjusting the content of the magnesium source powder within this range, an aluminum titanate-based ceramic fired body having a large pore diameter and porosity with improved heat resistance can be obtained relatively easily.

(Silicon source powder)
The raw material mixture may further contain a silicon source powder. The silicon source powder is a powder of a compound that becomes a silicon component and is contained in the aluminum titanate ceramic fired body. By using the silicon source powder in combination, a heat-resistant aluminum titanate ceramic fired body is obtained. Is possible. The silicon source powder is, for example, a powder of silicon oxide (silica) such as silicon dioxide or silicon monoxide.

The silicon source powder may be a powder of a compound led to silica by firing alone in air. Such compounds are, for example, silicic acid, silicon carbide, silicon nitride, silicon sulfide, silicon tetrachloride, silicon acetate, sodium silicate, sodium orthosilicate, feldspar, glass frit, preferably feldspar, glass frit, industrially Glass frit is more preferable because it is easily available and has a stable composition. Glass frit refers to flakes or powdery glass obtained by pulverizing glass. It is also preferable to use a powder made of a mixture of feldspar and glass frit as the silicon source powder.

When using a glass frit, it is preferable that the yield point of the glass frit is 600 ° C. or higher from the viewpoint of further improving the thermal decomposition resistance of the obtained aluminum titanate ceramic fired body. In this specification, the yield point of the glass frit is determined by measuring the expansion of the glass frit from a low temperature using a thermomechanical analyzer (TMA: Thermo Mechanical Analysis). Is defined.

As the glass constituting the glass frit, a general silicate glass containing silicate [SiO ₂ ] as a main component (50 mass% or more in all components) can be used. The glass constituting the glass frit includes, as other components, alumina [Al ₂ O ₃ ], sodium oxide [Na ₂ O], potassium oxide [K ₂ O], calcium oxide [ CaO], magnesia [MgO] and the like may be included. The glass constituting the glass frit may contain ZrO ₂ in order to improve the hot water resistance of the glass itself.

The silicon source powder may be one type or two or more types. The silicon source powder may contain a trace component derived from the raw material or inevitably contained in the production process.

In the silicon source powder, the particle size (D50) equivalent to a 50% cumulative percentage on a volume basis measured by a laser diffraction method is preferably 0.5 to 30 μm. The D50 of the silicon source powder is more preferably 1 to 20 μm in order to obtain a fired body having higher mechanical strength by further improving the filling factor of the molded body.

When the raw material mixture includes a silicon source powder, the content of the silicon source powder in the raw material mixture is the sum of the aluminum source powder in terms of Al ₂ O ₃ (alumina) and the titanium source powder in terms of TiO ₂ (titania). The amount is usually 0.1 to 10 parts by mass, preferably 0.1 to 5 parts by mass in terms of SiO ₂ (silica) with respect to 100 parts by mass.

In the manufacture of a honeycomb filter, a compound containing two or more metal elements among titanium, aluminum, silicon and magnesium as a raw material powder, such as a composite oxide such as magnesia spinel (MgAl ₂ O ₄ ), is used. be able to. In this case, the compound can be considered to be the same as the raw material in which the respective metal source compounds are mixed. Based on such an idea, the content of the aluminum source, the titanium source, the magnesium source and the silicon source in the raw material mixture is adjusted within the above range.

The raw material mixture may contain aluminum titanate or aluminum magnesium titanate. For example, when aluminum magnesium titanate is used as a constituent of the raw material mixture, the aluminum magnesium titanate contains a titanium source, an aluminum source and magnesium. Corresponds to a raw material mixture that also has a source.

Aluminum titanate or aluminum magnesium titanate may be prepared from a honeycomb filter obtained by this production method. For example, when the honeycomb filter obtained by the present manufacturing method is damaged, the damaged honeycomb filter or its fragments can be pulverized and used. The powder obtained by pulverization can be aluminum magnesium titanate powder.

(Additive)
As the pore forming agent, those formed by a material that disappears at a temperature lower than the temperature at which the molded body is degreased and fired in the firing step can be used. In degreasing and firing, when a molded body containing a hole forming agent is heated, the hole forming agent disappears due to combustion or the like. As a result, a space is created at the location where the pore-forming agent was present, and the ceramic powder located between the spaces shrinks during firing, so that a communication hole through which fluid can flow is formed in the partition wall. Can be formed.

The pore-forming agent is, for example, corn starch, barley starch, wheat starch, tapioca starch, bean starch, rice starch, pea starch, coral starch, canna starch, potato starch (potato starch). The average particle diameter of the pore forming agent is, for example, 5 to 25 μm. When the raw material mixture contains a hole forming agent, the content of the hole forming agent is, for example, 1 to 25 parts by mass with respect to 100 parts by mass of the ceramic powder.

The binder is, for example, celluloses such as methyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose; alcohols such as polyvinyl alcohol; salts such as lignin sulfonate; waxes such as paraffin wax and microcrystalline wax. Content of the binder in a raw material mixture is 20 mass parts or less with respect to 100 mass parts of ceramic powder, for example.

Examples of the plasticizer include alcohols such as glycerin; higher fatty acids such as caprylic acid, lauric acid, palmitic acid, alginic acid, oleic acid, and stearic acid; stearic acid metal salts such as Al stearate, and polyoxyalkylene alkyl ethers. . The content of the plasticizer in the raw material mixture is, for example, 0 to 10 parts by mass with respect to 100 parts by mass of the ceramic powder.

Examples of the dispersant include inorganic acids such as nitric acid, hydrochloric acid, and sulfuric acid; organic acids such as oxalic acid, citric acid, acetic acid, malic acid, and lactic acid; alcohols such as methanol, ethanol, and propanol; interfaces such as ammonium polycarboxylate It is an activator. The content of the dispersant in the raw material mixture is, for example, 0 to 20 parts by mass with respect to 100 parts by mass of the ceramic powder.

The solvent is, for example, water, and ion-exchanged water is preferable in terms of few impurities. When the raw material mixture contains a solvent, the content of the solvent is, for example, 10 to 100 parts by mass with respect to 100 parts by mass of the ceramic powder.

[Step (b): Molding step]
In the step (b), a ceramic molded body having a predetermined shape having a honeycomb structure is obtained. In the step (b), for example, a so-called extrusion molding method in which the raw material mixture is extruded from a die while being kneaded by a single screw extruder can be employed.

[Step (c): Firing step]
In the step (c), degreasing (calcination) for removing a hole forming agent or the like contained in the molded body (in the raw material mixture) may be performed before firing the molded body. Degreasing is performed in an atmosphere having an oxygen concentration of 0.1% or less.

In this specification, “%” used as a unit of oxygen concentration means “volume%”. By controlling the oxygen concentration in the degreasing step (at the time of temperature rise) to a concentration of 0.1% or less, heat generation of the organic matter can be suppressed and cracking after degreasing can be suppressed. In degreasing, degreasing is performed in an atmosphere having an oxygen concentration of 0.1% or less, whereby a part of organic components such as a pore-forming agent is removed, and the remainder is carbonized and remains in the ceramic molded body. preferable. Thus, the trace amount of carbon remains in the ceramic molded body, so that the strength of the molded body is improved and the ceramic molded body can be easily charged into the firing step. Examples of such an atmosphere include an inert gas atmosphere such as nitrogen gas and argon gas, a reducing gas atmosphere such as carbon monoxide gas and hydrogen gas, and a vacuum. In addition, firing may be performed in an atmosphere with a low water vapor partial pressure, or steaming with charcoal may reduce the oxygen concentration.

The maximum temperature for degreasing is preferably 700 to 1100 ° C, more preferably 800 to 1000 ° C. By increasing the maximum degreasing temperature from about 600 to 700 ° C to 700 to 1100 ° C, the strength of the ceramic body after degreasing is improved by grain growth. It becomes easy. In addition, degreasing preferably suppresses the rate of temperature rise until reaching the maximum temperature as much as possible in order to prevent cracking of the ceramic molded body.

Degreasing is used for normal firing of tubular electric furnace, box-type electric furnace, tunnel furnace, far-infrared furnace, microwave heating furnace, shaft furnace, reflection furnace, rotary furnace, roller hearth furnace, gas combustion furnace, etc. A similar furnace is used. Degreasing may be performed batchwise or continuously. Moreover, degreasing may be performed by a stationary method or a fluid method.

The time required for degreasing may be a time sufficient for a part of the organic component contained in the ceramic molded body to disappear, and preferably 90 to 99% by mass of the organic component contained in the ceramic molded body. It is time to disappear. Specifically, although it varies depending on the amount of the raw material mixture, the type of furnace used for degreasing, temperature conditions, atmosphere, etc., the time for keeping at the maximum temperature is usually 1 minute to 10 hours, preferably 1 to 7 hours. is there.

The ceramic molded body is fired after the above degreasing. The firing temperature is usually 1300 ° C. or higher, preferably 1400 ° C. or higher. Moreover, a calcination temperature is 1650 degrees C or less normally, Preferably it is 1550 degrees C or less. The rate of temperature increase up to the firing temperature is not particularly limited, but is usually 1 to 500 ° C./hour. When the silicon source powder is used, it is preferable to provide a step of holding at a temperature range of 1100 to 1300 ° C. for 3 hours or more before the firing step. Thereby, melting and diffusion of the silicon source powder can be promoted.

Calcination is preferably performed in an atmosphere having an oxygen concentration of 1 to 6%. By setting the oxygen concentration to 6% or less, combustion of residual carbides generated by degreasing can be suppressed, so that the ceramic molded body is hardly cracked during firing. Moreover, since moderate oxygen exists, the organic component of the finally obtained aluminum titanate ceramic molded body can be completely removed. The oxygen concentration is preferably 1% or more because carbide (soot) derived from organic components does not remain in the obtained aluminum titanate-based ceramic fired body. Depending on the type and usage ratio of the raw material mixture, that is, the aluminum source powder, titanium source powder, magnesium source powder and silicon source powder, it may be fired in an inert gas such as nitrogen gas or argon gas, or carbon monoxide You may bake in reducing gas, such as gas and hydrogen gas. Further, the firing may be performed in an atmosphere in which the water vapor partial pressure is lowered.

Firing is usually performed using conventional equipment such as a tubular electric furnace, box-type electric furnace, tunnel furnace, far-infrared furnace, microwave heating furnace, shaft furnace, reflection furnace, rotary furnace, roller hearth furnace, gas combustion furnace, etc. Done. Firing may be performed batchwise or continuously. Moreover, baking may be performed by a stationary type or may be performed by a fluid type.

The firing time may be a time sufficient for the ceramic molded body to transition to the aluminum titanate-based crystal, and varies depending on the amount of raw material, type of firing furnace, firing temperature, firing atmosphere, etc., but usually 10 minutes to 24 hours.

[Step (d): Sealing step]
Step (d) is performed between step (b) and step (c) or after step (c). When performing step (d) between step (b) and step (c), after sealing one end of each flow path of the unfired ceramic molded body obtained in step (b) with a sealing material In the step (c), the sealing material is fired together with the ceramic molded body to obtain a sealing portion that seals one end of the flow path. When the step (d) is performed after the step (c), one end of each flow path of the ceramic molded body obtained in the step (c) is sealed with a sealing body, and then the sealing body is baked together with the ceramic molded body. By doing so, the sealing part which seals one edge part of a flow path is obtained. As the sealing material, the same mixture as the raw material mixture can be used.

A honeycomb filter can be obtained through the above steps. The honeycomb filter has a shape that substantially maintains the shape of the molded body immediately after the molding in the step (b), but after the step (b), the step (c) or the step (d), a grinding process or the like is performed, It can also be processed into a desired shape.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<Production of honeycomb filter>
(Example 1)
Raw material powder of aluminum magnesium titanate (Al ₂ O ₃ powder, TiO ₂ powder, MgO powder), SiO ₂ powder, ceramic powder having a composite phase of aluminum magnesium titanate, alumina and aluminosilicate glass (composition formula at the time of preparation) : 41.4Al ₂ O ₃ -49.9TiO ₂ -5.4MgO-3.3SiO ₂ , where the numerical values represent molar ratios), pore formers, organic binders, lubricants, plasticizers, dispersants and water A raw material mixture containing (solvent) was prepared. The content of main components in the raw material mixture was adjusted to the following values.

[Components of raw material mixture]
Al ₂ O ₃ powder: 37.3 parts by mass TiO ₂ powder: 37.0 parts by mass MgO powder: 1.9 parts by mass SiO ₂ powder: 3.0 parts by mass Ceramic powder: 8.8 parts by mass Porous forming agent: potato 12.0 parts by weight of organic binder 1: methylcellulose (manufactured by Samsung Precision Chemical Co., Ltd .: MC-40H), 5.5 parts by weight of organic binder 2: hydroxypropylmethylcellulose (manufactured by Samsung Precision Chemical Co., Ltd.) : PMB-40H), 2.4 parts by mass

A columnar honeycomb filter (DPF) having the structure shown in FIGS. 1 and 2 was produced by extruding after kneading the above raw material mixture. The aluminum titanate conversion rate (AT conversion rate) of the honeycomb filter of Example 1 was measured and found to be 100%. The AT conversion rate is a peak appearing at a position of 2θ = 27.4 ° in the powder X-ray diffraction spectrum of the powder obtained by pulverizing the honeycomb filter of Example 1 in a mortar (titania-rutile phase (110)). since the integrated intensity of the _{surface) (I T), 2θ =} 33.7 ° of the peak appearing at the position [aluminum magnesium titanate phase (230) face] and the integrated intensity _{(I AT)} of, calculated by the following equation (1) did.
AT conversion rate (%) = I _AT / (I _T + I _AT ) × 100 (1)

The length of the honeycomb filter in the axial direction of the flow path was 152 mm. The outer diameter of the honeycomb filter was 144 mm. The density of the flow path (cell density) was 300 cpsi. The cross-sectional inner diameter (the length of one side of the square) of the flow path was 1.2 mm. The thickness of the partition between the flow paths was 0.30 mm. The porosity of the partition walls was 45% by volume, and the pore diameter of the partition walls was 15 μm.

(Comparative Example 1)
A honeycomb filter (DPF) having a plurality of parallel flow paths partitioned by partition walls made of SiC was prepared. The length of the honeycomb filter in the axial direction of the flow path was 140 mm. The outer diameter of the honeycomb filter was 144 mm. The partition wall thickness between the channels was 0.33 mm.

(Comparative Example 2)
A honeycomb filter (DPF) having a plurality of parallel flow paths partitioned by partition walls made of SiC was prepared. The length of the honeycomb filter in the axial direction of the flow path was 152 mm. The outer diameter of the honeycomb filter was 144 mm. The thickness of the partition between the flow paths was 0.28 mm.

<Surface roughness measurement>
One flow path from each honeycomb filter was selected as a measurement target. Three measurement regions were arbitrarily selected from one inner wall of the flow channel to be measured, and the maximum height Rz and the arithmetic average roughness Ra of each measurement region were measured in accordance with JIS B 0601: 2001. The surface shape of each measurement region was measured with a Keyence laser microscope VK-8500. An example of the surface shape of the measurement region is shown in FIG. The size of the measurement area was 298 μm × 224 μm in all cases. Table 1 shows the measurement results of the maximum height Rz and the arithmetic average roughness Ra.

<Pressure loss measurement>
The pressure loss measurement during soot deposition was performed as follows. FIG. 4 shows a schematic diagram of a pressure loss measuring apparatus. For pressure loss measurement, a soot generator (trade name: REXS, manufactured by Matter Engineering) 200 and a large compressor device 210 were used. One end face of the honeycomb filter was connected to the soot generating device 200, and the compressor device 210 was connected to a pipe connecting the honeycomb filter and the soot generating device 200.

To the soot generator 200, propane gas was supplied at a flow rate of 2 L / min, nitrogen gas was supplied at a flow rate of 2 L / min, and air was supplied at a flow rate of 1000 L / min. The soot generated from the soot generator 200 is artificial soot generated by incomplete combustion of propane gas. In the soot generator 200, the average particle diameter of soot is controlled by the air flow rate, oxygen concentration, and the like. can do. In the measurement, the average particle diameter of the soot was adjusted to about 90 nm. The flow rate of air containing soot was adjusted to 200 Nm ³ h ⁻¹ by the compressor device 210.

In order to grasp the pressure loss behavior during soot deposition, the pressure difference before and after the honeycomb filter (the pressure difference ΔP between the pressure P1 and the pressure P2 in FIG. 4) was recorded while supplying soot inside the honeycomb filter. FIG. 5 shows the results of measuring the pressure loss with the increase in the soot deposition amount using the honeycomb filters of Example 1 and Comparative Examples 1 and 2. As shown in FIG. 5, in Example 1, it is confirmed that the pressure loss value is smaller than in Comparative Examples 1 and 2. Moreover, in Example 1, it is confirmed that the increase amount of the pressure loss accompanying the increase in the amount of soot deposition is small compared with Comparative Examples 1 and 2.

DESCRIPTION OF SYMBOLS 100 ... Honeycomb filter, 110 ... Channel, 110a ... Channel (first channel), 110b ... Channel (second channel), 115a, 115b ... Inner wall, 120 ... Partition, A, B ... Area.

Claims

A honeycomb filter having a plurality of parallel flow paths partitioned by a porous partition wall,
The plurality of flow paths have a first flow path and a second flow path adjacent to the first flow path,
An end of one end of the honeycomb filter in the first flow path is sealed;
The end of the other end side of the honeycomb filter in the second flow path is sealed,
A honeycomb filter, wherein a maximum height Rz of at least a part of an inner wall of at least one of the first flow path or the second flow path is 55.00 μm or less.
The honeycomb filter according to claim 1, wherein an average value of maximum heights Rz on the inner wall is 56.00 µm or less.
The honeycomb filter according to claim 1 or 2, wherein the arithmetic average roughness Ra of the region of the inner wall is 9.000 µm or less.
The honeycomb filter according to any one of claims 1 to 3, wherein an average value of arithmetic average roughness Ra on the inner wall is 8.000 µm or less.
The honeycomb filter according to any one of claims 1 to 4, wherein the partition wall contains aluminum titanate.