JP2010095399A - Coating material for forming porous film and porous film, ceramic filter, exhaust gas purifying filter and method for manufacturing ceramic filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating material for forming a porous film capable of forming a porous film of a ceramics on the surface of a supporting body consisting of the porous ceramics such as DPF, to provide the porous film, to provide a ceramic filter obtained by forming the ceramic film on the surface of the supporting body of the porous ceramics, to provide its manufacturing method, and to provide an exhaust gas purifying filter. <P>SOLUTION: The coating material for forming the porous film is the coating material containing oxide particulates and a dispersion medium, and the oxide particulates have an average primary particle diameter of ≥10 nm and ≤1,000 nm, a tap bulk density of ≥0.1 g/cm<SP>3</SP>and ≤1.5 g/cm<SP>3</SP>and an average secondary particle diameter in the coating material of ≥0.1 μm and ≤10 μm and a viscosity of the coating material is ≥2 mPa s and ≤1,000 mPa s. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a coating material for forming a porous film, a porous film, a ceramic filter, an exhaust gas purification filter, and a method for producing a ceramic filter. More specifically, the present invention removes particulate matter from exhaust gas discharged from automobile diesel engines and the like. For forming a porous film on the partition wall surface of an exhaust gas purification filter, a porous film obtained by applying and heat-treating this porous film-forming paint, The present invention relates to a ceramic filter having a porous membrane formed on the surface of a porous ceramic support, an exhaust gas purification filter provided with the ceramic filter, and a method for producing the ceramic filter.

Conventionally, as a filter with low pressure loss during use and high particulate collection efficiency, the pore diameter is smaller than the pore diameter of the porous support and has a thickness on the surface of the porous support having a large pore diameter. A filter provided with a thin porous membrane is known.
As such a filter, a ceramic filter in which a porous film made of ceramics is formed on the surface of a support made of porous ceramics is known.
In this ceramic filter, the porous membrane is formed by forming a laminated body made of ceramic particles having a small particle diameter on the surface of a support made of porous ceramics and heat-treating the laminated body. As a method for controlling the pore size of the porous film according to the size of the particles to be collected, a method of adjusting the particle size of the ceramic particles constituting the laminate is used.

By the way, when a porous film having a pore size smaller and thinner than that of the porous ceramic is formed on the surface of the support made of the porous ceramic, the particle diameter of the ceramic particles constituting the porous film is made porous. It was necessary to make it smaller than the pore diameter of the ceramic. For this reason, when forming a porous film, there existed a possibility that the ceramic particle which comprises this porous film might penetrate | invade in the pore of porous ceramics.
Therefore, various methods for solving such problems have been proposed.

For example, there is a method for hydrophobizing a porous substrate made of ceramic and using an aqueous slurry containing ceramic particles having a small particle diameter so that the aqueous slurry does not enter the pores of the porous substrate. It has been proposed (for example, Patent Document 1). In this method, in order to adhere the aqueous slurry to the surface of the porous substrate, a substance that removes the hydrophobizing agent or lowers its function is added to the aqueous slurry.
A method of forming a porous film by using ceramic particles having a small particle size as secondary particles having a size equal to or larger than the pore size of the porous support in advance and using a slurry containing the secondary particles. As a method for producing secondary particles, a method of pre-calcining ceramic particles (for example, Patent Document 2) or a method of adding a flocculant to a slurry to aggregate ceramic particles (for example, Patent Document 3). ) Has been proposed.

  Furthermore, a method has been proposed in which the pores of the porous support are filled with a removable substance, the pores are closed, and then a slurry containing ceramic particles having a small particle diameter is applied to the surface of the porous support. As a method for closing the pores, a flammable substance is used as a removable substance, and the flammable substance is burned and removed by a subsequent firing step (for example, Patent Document 4), or water or alcohol is used as a removable substance. A method of removing these water and alcohol by using and drying after application (for example, Patent Documents 5 and 6) has been proposed.

On the other hand, various substances contained in exhaust gas discharged from automobile diesel engines cause air pollution and have caused various environmental problems. In particular, particulate matter (PM) contained in exhaust gas is also said to cause allergic diseases such as asthma and hay fever.
In general, in an automobile diesel engine, an exhaust gas purification filter called DPF (Diesel Particulate Filter) is used to collect particulate matter. In this DPF, both ends of a gas flow path made of a ceramic honeycomb structure are sealed in a checkered pattern, one gas flow path is an exhaust gas inflow cell (inflow gas flow path), and the other gas flow path is exhaust gas. This is an outflow cell (outflow gas flow path), and particulate matter in the exhaust gas is collected when the exhaust gas passes through the pores in the partition wall between the inflow cell and the outflow cell. (For example, Patent Document 7).

In this DPF, it is particularly required to improve the collection characteristics of particulate matter having a submicron diameter. However, in the conventional DPF, the average pore diameter of the partition wall is about 5 to 50 μm. The collection efficiency (based on PM weight) in the DPF in a state where no P is deposited does not reach 90%. As PM is deposited on the partition wall, a PM layer is formed on the partition wall, and a new layer is formed on the PM layer. By collecting PM, the collection efficiency in the DPF is improved and approaches 100%. As described above, it is known that the conventional DPF has a high collection efficiency after the PM layer is formed, but the collection efficiency in a state where the PM deposition amount is small is not always satisfactory (non-patent) Reference 1).
JP 2000-218114 A JP-A-11-33322 JP-A-11-188217 JP-A-1-274815 Japanese Patent Publication No. 63-66566 JP 2000-288324 A JP-A-9-77573 SAE Technical Paper 980545 American Society of Automotive Engineers Published in 1998 (SAE Technical Paper 980545, Society of Automotive Engineers (1998))

As described above, in the conventional DPF, since the average pore diameter of the partition wall is on the order of 5 to 50 μm and a micron diameter, the particulate matter having a sub-micron diameter smaller than the average pore diameter is collected. There was a problem that was not easy.
In order to improve the collection characteristics of particulate matter with submicron diameter, it is one method to reduce the average pore diameter of the partition wall, but when the average pore diameter of the partition wall is reduced, the particle size of the submicron diameter is reduced. Although the substance collection characteristic is improved, the air permeability as the DPF is reduced and the pressure loss is increased, so that there is a problem that a sufficient exhaust gas flow rate cannot be obtained. That is, the conventional DPF cannot achieve both high collection efficiency and low pressure loss (sufficient exhaust gas flow rate) particularly in a state where the amount of accumulated PM is small, and a material that satisfies both of these performances has been demanded.
Therefore, it is considered that the average pore diameter of the partition walls in the DPF remains 5 to 50 μm, and a porous film having an average pore diameter of several tens nm to 5 μm is formed on the surface of the partition walls. When forming this porous film, it is conceivable to apply the above-described conventional technique.

However, the DPF having such a porous membrane also has the following problems.
For example, in order to form a porous film having an average pore diameter of 100 nm, the primary particle diameter of the particles constituting the porous film needs to be about 40 to 60 nm. This particle diameter is the average pore diameter of the DPF. The size is about a few hundredths. As described above, the primary particle diameter of the particles constituting the porous film is very small compared to the particle diameter of the porous film in the above-described prior art on the order of submicron to micron.
Therefore, when the conventional technique is applied as it is when forming the porous film on the partition walls of the DPF, it is difficult to avoid a part of the particles constituting the porous film from flowing into the pores of the partition walls.

Furthermore, the DPF has, for example, an elongated cylindrical shape with a 1 mm square cross section and a length of 150 mm in which each cell is sealed at one end, and these cells are positioned at the sealing end portions of adjacent cells. In contrast to the special shape in which the sealing end portions are alternately provided so as to be opposite to each other and overlapped to form a honeycomb shape, the above-described porous support in the prior art has a plate shape or a diameter. Is a cylinder in the order of centimeters. Therefore, even if an attempt is made to apply the above-described conventional technique when forming a porous film on the partition walls of the honeycomb structure which is the main part of the DPF, the application is difficult because the shape is greatly different. Moreover, even if the conventional technique is applicable, the process becomes complicated, and it is necessary to devise materials to be used, which may increase the manufacturing cost.
As described above, the technology for forming a porous film on the surface of the partition walls of the honeycomb structure in the DPF has not yet been established.

The present invention has been made to solve the above-described problems, and is a porous film-forming coating material capable of forming a ceramic porous film on the surface of a support made of porous ceramics such as DPF. And a porous membrane, a ceramic filter having the porous membrane formed on the surface of a porous support made of porous ceramics, and a method for producing the same.
It is another object of the present invention to provide an exhaust gas purification filter that can obtain a high collection efficiency even when the amount of particulate matter deposited is small and at the same time has a low pressure loss.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that when forming a ceramic porous film using fine particles mainly composed of oxides such as alumina and zirconia, the average primary particle diameter , Containing fine particles containing an oxide whose tap bulk density and average secondary particle size in the paint are controlled, and a dispersion medium containing water as a component, and having a viscosity of 2 mPa · s or more and 1000 mPa · s or less It was found that a porous film of a ceramic can be formed on the surface of a porous support made of porous ceramics by using a controlled coating for forming a porous film, and the present invention has been completed. It was.

That is, the coating material for forming a porous film of the present invention is a coating material for forming a porous film comprising fine particles containing an oxide as a component and a dispersion medium, and the fine particles have an average primary particle diameter of 10 nm. More than and 1000 nm or less, the tap bulk density is 0.1 g / cm ³ or more and 1.5 g / cm ³ or less, the average secondary particle size in the paint is 0.1 μm or more and 10 μm or less, and the viscosity of the paint is It is 2 mPa · s or more and 1000 mPa · s or less.

  The oxide is preferably one or more selected from the group consisting of alumina, zirconia, titania, zinc oxide, silica, yttria, mullite, cordierite, aluminum titanate, and magnesia.

  The porous film of the present invention is a porous film obtained by heat-treating a coating film obtained by applying the coating material for forming a porous film of the present invention, and the average pore diameter of this porous film is 0.02 μm. It is characterized by being not less than 5 μm and a porosity of not less than 35% and not more than 90%.

  The ceramic filter of the present invention is characterized in that the porous membrane of the present invention is formed on the surface of a porous support made of porous ceramics having an average pore diameter of 5 μm or more and 50 μm or less.

  The exhaust gas purification filter of the present invention comprises the ceramic filter of the present invention.

  In the method for producing a ceramic filter of the present invention, a coating film is formed by applying the porous film-forming coating material of the present invention to the surface of a porous support made of porous ceramics having an average pore diameter of 5 μm or more and 50 μm or less. Then, this coating film is heat-treated.

According to the coating material for forming a porous film of the present invention, the average primary particle diameter of fine particles containing an oxide as a component is 10 nm or more and 1000 nm or less, and the tap bulk density is 0.1 g / cm ³ or more and 1.5 g / cm ^3. Hereinafter, the average secondary particle diameter in the paint is controlled to 0.1 μm or more and 10 μm or less, and the viscosity of the paint is controlled to 2 mPa · s or more and 1000 mPa · s or less. When applied to the surface of the body, the fine particles can be prevented from entering the pores of the porous support. Therefore, it is possible to easily form a ceramic porous film having excellent homogeneity having an average pore diameter of 0.02 μm or more and 5 μm or less on the surface of a porous support made of porous ceramics.
In addition, since the coating film can be formed by simply applying the coating material for forming a porous film on the surface of the porous support, the shape of the porous support can be used regardless of the shape of the porous support. Without being restricted, a porous film having excellent homogeneity can be easily formed on the surface.

  According to the porous film of the present invention, the porous film is obtained by heat-treating the coating film obtained by applying the porous film-forming coating material of the present invention. Since the porosity is 02 μm or more and 5 μm or less and the porosity is 35% or more and 90% or less, a porous film capable of collecting fine particles can be obtained.

  According to the ceramic filter of the present invention, since the porous membrane of the present invention is formed on the surface of the porous support made of porous ceramics having an average pore diameter of 5 μm or more and 50 μm or less, an effective average as a filter The pore diameter can be controlled to 0.02 μm or more and 5 μm or less. Therefore, it is possible to collect particulate matter having a submicron diameter, and it is possible to improve the collection characteristics of the particulate matter and obtain a ceramic filter with low pressure loss.

  According to the exhaust gas purification filter of the present invention, since the ceramic filter of the present invention is provided, it is possible to achieve both high PM collection efficiency and low pressure loss.

According to the method for producing a ceramic filter of the present invention, the coating film is formed by applying the coating material for forming a porous film of the present invention on the surface of a porous support made of a porous ceramic having an average pore diameter of 5 μm or more and 50 μm or less. Then, this coating film is heat-treated, so that a ceramic porous film having excellent porosity with a pore size on the order of submicron is easily formed on the surface of a porous support made of porous ceramics. be able to.
In addition, since the coating film can be formed by simply applying the coating material for forming a porous film on the surface of the porous support, the shape of the porous support can be used regardless of the shape of the porous support. Without being restricted, a porous film having excellent homogeneity can be easily formed on the surface. As described above, it is possible to manufacture a ceramic filter having low cost and excellent mass productivity.

The best mode for carrying out the porous film-forming coating material and porous membrane, ceramic filter, exhaust gas purification filter, and ceramic filter manufacturing method of the present invention will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

"Porous film forming paint"
The coating material for forming a porous film of the present embodiment is a coating material for forming a porous film comprising fine particles containing an oxide as a component and a dispersion medium, and the fine particles have an average primary particle diameter of 10 nm or more and 1000 nm or less, tap bulk density of 0.1 g / cm ³ or more and 1.5 g / cm ³ or less, average secondary particle diameter in the paint is 0.1 μm or more and 10 μm or less, and the viscosity of this paint is 2 mPa · s to 1000 mPa · s.

As the fine particles, oxide fine particles containing an oxide as a main component are preferable. As the oxide, alumina, zirconia, titania, zinc oxide, silica, yttria, mullite (aluminum silicate), cordierite (magnesium aluminum silicate). ), Aluminum titanate, and magnesia are preferably used.
Here, the reason why the main component of the fine particles is an oxide is that the heat resistance of the porous film obtained by the porous film-forming coating material can be sufficiently ensured. For example, in the case of a ceramic filter such as DPF, the temperature of the exhaust gas may rise to about 1000 ° C., and thus the heat resistance up to about 1000 ° C. is required even for the material of the porous membrane.

Here, the relationship between the pore diameter and the porosity of the porous film formed by the fine particles in the porous film-forming coating material of the present embodiment will be described.
In general, it is known that the pore diameter and the porosity are determined by the average particle diameter of fine particles forming a film. Here, if the shape of the fine particles is an isotropic shape close to a sphere, there is no particular problem in the correlation between the two. However, when there is anisotropy in the shape of the fine particles, there is a shift in the correlation between the two. This is because the average particle size is only a dimensional value, and the shape of the particles is not taken into consideration.

Next, “tap bulk density” will be described. The “tap bulk density” is “tap bulk density” defined in Japanese Industrial Standard JIS R 1628-1997 “Bulk Density Measurement Method of Fine Ceramics Powder”. A method for measuring tap bulk density is also specified.
The reason why the tap bulk density of the fine particles is smaller than the true density (true specific gravity) is that voids are formed between the fine particles. That is, the ratio (ρt / ρr) between the tap bulk density (ρt) and the true density (ρr) indicates the porosity, that is, the porosity.

  Here, the main factors that determine the tap bulk density are the primary particle size and particle shape of the fine particles. When there is no difference in the particle shape, the smaller the average primary particle diameter of the fine particles, the smaller the tap bulk density and the higher the porosity of the resulting porous film, but the smaller the pore diameter. Further, when the primary particle diameters of the fine particles are equal, the higher the shape anisotropy of the fine particles, the smaller the tap bulk density, and the higher the porosity of the resulting porous film and the larger the pore diameter.

  Therefore, by defining the primary particle diameter and tap bulk density of the fine particles contained in the porous film-forming paint of this embodiment, the pore diameter and porosity of the porous film formed using the paint of this embodiment Can be controlled.

Considering the above points, the average primary particle diameter of the fine particles is preferably 10 nm or more and 1000 nm or less, more preferably 10 nm or more and 700 nm or less, and further preferably 15 nm or more and 500 nm or less.
Further, the tap bulk density of the fine particles is preferably 0.1 g / cm ³ or more and 1.5 g / cm ³ or less, more preferably 0.1 g / cm ³ or more and 1.3 g / cm ³ or less, and still more preferably. It is 0.2 g / cm ³ or more and 1.2 g / cm ³ or less.

This is because if the average primary particle diameter and tap bulk density of the fine particles are limited to the above ranges, the target average pore diameter of the present invention is 0.02 μm or more and 5 μm or less, and the porosity is 35% or more and 90% or less. It is shown that a porous film can be formed.
In addition, the pore diameter of the porous film can be controlled to a desired value by mixing and using a plurality of types of fine particles having different average primary particle diameters and tap bulk densities within the above range.

Furthermore, the reason why the average primary particle diameter of the fine particles is limited to the above range is that, when the average primary particle diameter is less than 10 nm, the average pore diameter of the porous film formed using the present paint is not dependent on the shape of the fine particles. This is because the pressure loss increases when exhaust gas or the like flows into the filter. Moreover, the production of fine particles having an average primary particle diameter of less than 10 nm is expensive and is not preferable from the viewpoint of productivity.
If the tap bulk density of the fine particles is less than 0.1 g / cm ³ , it becomes difficult to maintain the stability of the coating material for forming a porous film containing the fine particles, and such particles are produced with high productivity. Since it becomes difficult to do, it is not preferable.

In addition, when the average primary particle diameter exceeds 1000 nm or the tap bulk density exceeds 1.5 g / cm ³ , the particle diameter becomes excessive, so that a porous film having an average pore diameter of 5 μm or less can be obtained. This is not preferable because it is difficult to obtain a paint having good stability.

Such fine particles are dispersed in a dispersion medium to form a coating material for forming a porous film.
This dispersing step is preferably performed by a wet method. Moreover, as a disperser used in this wet method, any of an open type and a closed type can be used. For example, a ball mill, a stirring mill, a jet mill, a vibration mill, an attritor, a high speed mill, a hammer mill, etc. are suitable. Used for.
Examples of the ball mill include a rolling mill, a vibration mill, and a planetary mill. Examples of the stirring mill include a tower mill, a stirring tank mill, a flow pipe mill, and a tubular mill.

As the dispersion medium, water or an organic solvent is preferably used. In addition, a single polymer monomer or oligomer or a mixture thereof may be used as necessary.
Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, diacetone alcohol, furfuryl alcohol, ethylene glycol and hexylene glycol, and esters such as methyl acetate and ethyl acetate. , Diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dioxane, tetrahydrofuran, acetone , Ketones such as methyl ethyl ketone, acetylacetone, acetoacetate, N, N-dimethylform Acid amides such as amide, toluene, aromatic hydrocarbons such as xylene are preferably used, it is possible to use a mixture of one only or two or more of these solvents.

Among these dispersion media, water, alcohols, and ketones are preferable for coatings, and among these, water and alcohols are more preferable, and water is most preferable.
In addition, as the polymer monomer, acrylic or methacrylic monomers such as methyl acrylate and methyl methacrylate, and epoxy monomers are preferably used. Moreover, as said oligomer, a urethane acrylate oligomer, an epoxy acrylate oligomer, an acrylate oligomer etc. are used suitably.

  In this coating material, surface modification of the fine particles may be performed in order to increase the affinity between the fine particles and the dispersion medium. When the fine particles are oxide fine particles such as alumina and zirconia, the surface modifiers include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, cysteamine, tetramethylammonium hydroxide, aminoethanediol and the like. Although it is mentioned, it is not limited to these, What is necessary is just a surface modifier which has a functional group which adsorb | sucks to the surface of oxide microparticles | fine-particles, and has an end group which has affinity with a dispersion medium.

The viscosity of the paint is preferably 2 mPa · s or more and 1000 mPa · s or less, more preferably 2 mPa · s or more and 500 mPa · s or less, and further preferably 2 mPa · s or more and 300 mPa · s or less.
Here, the reason for limiting the viscosity of the paint to the above range is that when the viscosity is less than 2 mPa · s, the surface of the porous support made of porous ceramics having an average pore diameter of 5 μm or more and 50 μm or less, In particular, when applied to the surface of the partition wall of the DPF, this paint can easily enter the inside of the porous support, that is, the pores of the partition wall of the DPF, thereby forming a porous film on the surface of the porous support. This is because it becomes difficult to do so. On the other hand, when the viscosity exceeds 1000 mPa · s, the paint cannot be sufficiently penetrated into the inside of the filter substrate constituted by the porous support, particularly the inside of the cell of the DPF, or the inside of the filter substrate, particularly the DPF. This is because it is not preferable because a desired porous film is not formed or a porous film having a uniform thickness is difficult to form because it becomes difficult to remove excess paint in the cell. .

The average secondary particle diameter of the fine particles in the paint is preferably 0.1 μm or more and 10 μm or less, more preferably 0.1 μm or more and 8 μm or less, and further preferably 0.1 μm or more and 7 μm or less.
Here, the reason why the average secondary particle diameter of the fine particles in the paint is limited to the above range is that if the average secondary particle diameter of the fine particles in the paint is less than 0.1 μm, the average pore diameter of the paint is 5 μm or more. In addition, when applied to the surface of a porous support made of porous ceramics of 50 μm or less, this paint can easily enter the inside of the porous support and form a porous film on the surface of the porous support. This is because it becomes difficult. Also, if the average secondary particle diameter of the fine particles exceeds 10 μm, it is not preferable because it becomes difficult to ensure the dispersion stability of the paint or it becomes difficult to obtain a homogeneous porous film.

The content of the fine particles in the paint can be appropriately selected so that the viscosity of the paint and the average secondary particle diameter of the fine particles in the paint are within the range of the present invention, and preferably 2% by mass or more and 60% by mass. Hereinafter, it is more preferably 3% by mass or more and 50% by mass or less, and further preferably 5% by mass or more and 40% by mass or less.
Here, if the content of the fine particles in the paint is less than 2% by mass, the viscosity of the paint tends to be less than 2 mPa · s, or it is necessary to increase the number of coatings in order to obtain a desired film thickness. Since productivity may be inferior, it is not preferable. On the other hand, if the content of fine particles exceeds 60% by mass, it is difficult to ensure the dispersion stability of the paint, and it becomes difficult to obtain a uniform porous film.

This paint may appropriately contain a hydrophilic or hydrophobic polymer or the like in order to provide a binder function between the fine particles and a porous support made of porous ceramics such as DPF. The polymer and the like can be appropriately selected within the range in which the average secondary particle diameter of the fine particles in the coating material and the viscosity of the coating material are in desired values while being dissolved in the dispersion medium.
Here, when water is used as a dispersion medium, examples of hydrophilic polymers include synthetic alcohols such as polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol, polyacrylamide, polystyrene sulfonic acid, polyvinyl pyrrolidone polyacrylate, and polyallylamine. Molecules; polysaccharides such as cellulose, dextrin, dextran, starch, chitosan, pectin, agarose, carrageenan, chitin and mannan; proteins such as gelatin, casein, collagen, laminin, fibronectin and elastin can be used.
Further, substances such as gels and sols derived from these synthetic polymers, polysaccharides, proteins and the like can also be used.

The ratio of the mass of the polymer to the mass of the fine particles in the paint (the mass of the polymer / the mass of the fine particles) is within a range where the average secondary particle diameter of the fine particles in the paint and the viscosity of the paint are within desired values. The range of 0 or more and 1 or less is preferable.
Since the above polymer is a component that is eventually volatilized, decomposed or burned out by heat treatment and does not remain in the porous membrane, if the above ratio exceeds 1, the content of the polymer is too high, This is not preferable because it causes an increase in cost.

In order to ensure the dispersion stability of the paint or to improve the coating property, a surfactant, preservative, stabilizer, antifoaming agent, leveling agent and the like may be appropriately added. These can be appropriately selected so that the average secondary particle diameter of the fine particles in the coating material and the viscosity of the coating material are in a desired range.
There are no particular restrictions on the amount of these surfactants, preservatives, stabilizers, antifoaming agents, leveling agents and the like, and the viscosity of the paint and the average secondary particle size of the fine particles in the paint are within the scope of the present invention. Thus, what is necessary is just to add according to the objective to add.

According to this coating material for forming a porous film, a ceramic porous film having an average pore diameter of 0.02 μm or more and 5 μm or less and excellent in homogeneity can be easily formed on the surface of the support.
This coating for forming a porous film can form a coating film by simply applying it, so it is easy to form a porous film with excellent homogeneity on the surface without being restricted by the shape of the object. can do.

"Porous membrane"
The porous film of the present embodiment can be obtained by applying the above-mentioned porous film-forming coating material to the surface of a porous support made of porous ceramics, and heat-treating the obtained coating film.
This porous membrane preferably has an average pore diameter of 0.02 μm to 5 μm, and a porosity of 35% to 90%.
The coating method may be appropriately selected according to the shape and material of the porous support and is not particularly limited, but a coating method such as wash coating or dip coating can be used.

  At the time of application, the porous support may be in a dry state, but the porous support is immersed in a solvent, and the air in the pores of the porous support is replaced with a solvent in advance. Those are preferred. The reason for this is that air remaining in the pores of the porous support is released as bubbles from the porous support during or after the coating process, and the porous film is not partially formed. This is because there is an effect that a uniform porous film can be obtained.

In addition to the dispersant, the coating film contains the above-described polymer, surfactant, preservative, stabilizer, antifoaming agent, leveling agent, and the like as necessary. In addition, heat treatment is performed to form a microporous structure in the coating film.
The heat treatment temperature is preferably 200 ° C. or higher and 2000 ° C. or lower, more preferably 300 ° C. or higher and 1500 ° C. or lower.
The heat treatment time is preferably 0.25 hours or more and 10 hours or less, more preferably 0.5 hours or more and 5 hours or less.
The atmosphere during this heat treatment is not particularly limited, and may be any of an oxidizing atmosphere such as air, an inert atmosphere such as nitrogen, argon, neon, or xenon, or a reducing atmosphere such as hydrogen or carbon monoxide. Can be done.

"Ceramic filter"
The ceramic filter of this embodiment has a structure in which the above porous film is formed on the surface of a porous support made of porous ceramics having an average pore diameter of 5 μm or more and 50 μm or less.
As the shape of the porous support, in accordance with the purpose of use, that is, the type of collection target object, its shape and size, use environment conditions (use in gas or liquid, use temperature, etc.), etc., A tubular shape, a honeycomb shape, or the like can be selected as appropriate.
The ceramic filter of the present embodiment is particularly suitable as an exhaust gas purification filter, and examples of the exhaust gas purification filter include a DPF that is an exhaust gas purification filter used in an automobile diesel engine described later.

"Exhaust gas purification filter"
1 is a partially broken perspective view showing a DPF that is an exhaust gas purification filter used in an automobile diesel engine according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a partition structure of the DPF. FIG. 3 is an enlarged view of a surface indicated by a symbol β.

The DPF 10 includes a filter base (porous support) 11 made of a cylindrical porous ceramic having a large number of pores (pores), a gas flow path 12 formed in the filter base 11, and the gas flow. The flow path 12 is roughly constituted by a porous film 13 provided on the inner wall surface 12a of the inflow cell 12A in which the upstream end of the exhaust gas is opened.
The filter base 11 is a honeycomb structure made of heat-resistant porous ceramics such as silicon carbide, cordierite, aluminum titanate, and silicon nitride, and has an average pore diameter along the axial direction that is the flow direction of the exhaust gas G. A honeycomb structure is formed by partition walls 14 made of porous ceramics having a size of 5 μm or more and 50 μm or less, and a hollow area in the axial direction surrounded by the partition walls 14 forms a large number of cellular gas flow paths 12.
One end surface α of both end surfaces in the axial direction of the filter base 11 is an inflow surface into which the exhaust gas G containing particulate matter flows, and the other end surface γ has removed the particulate matter from the exhaust gas G. The discharge surface is for discharging the purified gas C.

The gas flow path 12 has a structure in which the upstream end and the downstream end are alternately closed when viewed from the flow direction (longitudinal direction) of the exhaust gas G, that is, the upstream side that is the inflow side of the exhaust gas G. An inflow cell 12A having an open end and an outflow cell 12B having a downstream end that is the side from which the purified gas C is discharged are configured.
On the inner wall surface 12a of the inflow cell 12A (surface on the inflow cell 12A side of the partition wall 14), a porous film 13 made of oxide heat-resistant fine particles is formed. The porous membrane 13 is formed of oxide particles having high heat resistance and high heat resistance. The DPF 10 is heated to a high temperature of about 1000 ° C. when the collected particulate matter 30 is removed by combustion. This is because there is a possibility.

The porous film 13 is an independent film on the inner wall surface 12a of the inflow cell 12A without substantially entering the pores of the porous ceramics constituting the partition wall 14 of the filter base 11. That is, the highly heat-resistant oxide fine particles forming the porous film 13 are prevented from entering the inside of the partition wall 14 of the filter base 11, and the inflow cell without blocking the pores formed in the partition wall 14. It is formed on the inner wall surface 12a of 12A.
Since the porous membrane 13 has a large number of pores, the pores communicate with each other, and as a result, the porous membrane 13 has a filter-like porous shape having through holes.

The porous membrane 13 preferably has an average pore diameter of 0.02 μm to 5 μm and a porosity of 35% to 90%.
The reason is that when the average porosity and the average pore diameter are smaller than these ranges, the pressure loss when the exhaust gas G containing the particulate matter 30 flows into the DPF 10 becomes high, while the average This is because, when the porosity and the average pore diameter are larger than these ranges, the collection rate of the particulate matter 30 and the efficiency during filter regeneration are lowered.
Thus, in order to make the average pore diameter and the average porosity of the porous membrane 13 within the above ranges, the average primary particle diameter is 10 nm or more and 1000 nm or less, and the tap bulk density is 0.1 g / cm ³ or more. In addition, it is preferable to use oxide fine particles having high heat resistance of 1.5 g / cm ³ or less.

  In the DPF 10, as shown in FIG. 2, the exhaust gas G containing the particulate matter 30 that has flowed in from the inlet side, that is, the end surface α side, flows through the inflow cell 12A from the end surface α side to the end surface γ side. And passes through the partition wall 14 of the filter base 11. At this time, the particulate matter 30 contained in the exhaust gas G is collected and removed by the porous film 13 formed on the inner wall surface 12a on the inflow cell 12A side of the partition wall 14, and the particulate matter 30 is removed. The purified gas C flows through the outflow cell 12B from the end surface α side to the end surface γ side, and is finally discharged from the discharge port side, that is, the end surface γ side.

According to the DPF 10 of the present embodiment, the average pore diameter in the partition wall 14 of the filter base 11 is 5 to 50 μm, which is the same as the average pore diameter of the partition wall 14 acting as a filter body in the conventional DPF. A sufficient exhaust gas flow can be obtained without causing an increase in loss.
Further, the average pore diameter of the porous membrane 13 formed on the inner wall surface 12a on the inflow cell 12A side of the partition wall 14 is 0.02 to 5 μm, which is larger than the pore diameter of the porous support (conventional DPF filter body). Therefore, the particulate matter is captured by the porous film 13 from the stage where the deposition amount is small, and high collection efficiency can be obtained regardless of the deposition amount of the particulate matter.

Next, the manufacturing method of DPF10 of this embodiment is demonstrated.
First, a filter substrate 11 having a honeycomb structure made of heat-resistant porous ceramics such as silicon carbide, cordierite, aluminum titanate, silicon nitride or the like is prepared.
The filter base 11 may be in a dry state, but it is preferable to immerse the filter base 11 in a solvent and replace the air in the pores of the partition walls 14 of the filter base 11 with a solvent in advance.

  Here, it is preferable to replace the air in the pores of the partition wall 14 with a solvent. The air remaining in the pores is released as bubbles from the partition wall 14 in the coating step, and the porous film 13 is used. This is because there is an effect that a uniform porous film can be obtained by suppressing a situation where the film is not partially formed.

  Examples of the solvent include water, methanol, ethanol, 1-propanol, 2-propanol, diacetone alcohol, furfuryl alcohol, alcohols such as ethylene glycol and hexylene glycol, esters such as acetic acid methyl ester and ethyl acetate, Diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dioxane, tetrahydrofuran and other ethers, acetone, methyl ethyl ketone , Ketones such as acetylacetone and acetoacetate, N, N-dimethylformamide, etc. Acid amides, toluene, aromatic hydrocarbons such as xylene are preferably used, it is possible to use a mixture of one only or two or more of these solvents.

Among these solvents, water, alcohols, and ketones are preferable, and water, alcohols having 1 to 3 carbon atoms, acetone, and methyl ethyl ketone are more preferable.
When immersing the filter base in the solvent, the solvent and the filter base may be allowed to stand, and ultrasonic waves are applied to the solvent and the filter base, or the liquid is boiled and then cooled. By this method, the air in the pores of the filter base may be easily released to the outside.

Next, the above-mentioned coating material for forming a porous film is applied to the inner wall surface 12a of the inflow cell 12A of the filter base 11 to form a coating film.
The method for applying the porous film-forming coating material is not particularly limited, and a coating method such as a wash coating method or a dip coating method can be used.
Further, after coating, excess paint may be removed by using compressed air or the like in excess of the amount necessary to obtain a desired film thickness.

In addition, when the coating film of desired thickness is not obtained by one coating, you may repeat application | coating and drying until it becomes a desired film thickness.
The drying in this case should just be dried to the extent that a coating film having a uniform thickness is formed in the next coating, and does not need to be a drying process that is a pre-process of heat treatment in the next process. Moreover, the process of drying to such an extent that the solvent which substituted the air previously by immersion remains in the pores of the partition wall 14 and the already applied porous film forming coating material is not mixed with the solvent may be used.

Next, heat treatment is performed on the filter substrate 11 on which the coating film is formed.
The heat treatment temperature is preferably 200 ° C. or higher and 2000 ° C. or lower, more preferably 300 ° C. or higher and 1500 ° C. or lower.
The heat treatment time is preferably 0.25 hours or more and 10 hours or less, more preferably 0.5 hours or more and 5 hours or less.
These heat treatment temperature and heat treatment time are preferably selected in consideration of the components and particle diameters of the fine particles in the coating film and the components and amounts of the dispersant contained in the coating film.

The atmosphere of the heat treatment is not particularly limited, and can be appropriately selected from an oxidizing atmosphere such as air, an inert atmosphere such as nitrogen, argon, neon, and xenon, and a reducing atmosphere such as hydrogen and carbon monoxide. . Upon selection, it is preferable to select an optimum atmosphere in consideration of the material of the support, the fine particle components in the coating film, the heat treatment temperature, the heat treatment time, and the like.
By this heat treatment, the dispersion medium or polymer contained in the coating film is volatilized, decomposed or burned off and removed, and the fine particles in the coating film are fused together to form a porous film 13 having a microporous structure. Is done.

  According to this DPF 10, since the porous film 13 is formed on the inner wall surface 12a of the inflow cell 12A of the filter base 11 made of porous ceramics, the particulate matter 30 contained in the exhaust gas G is removed, and a clean purified gas is obtained. C can be discharged. Therefore, the purification performance of the exhaust gas G can be improved.

According to this method for manufacturing the DPF 10, it is possible to easily obtain the DPF 10 in which the porous film 13 is formed on the inner wall surface 12a of the inflow cell 12A of the filter base 11 made of porous ceramics.
In addition, since the coating film can be formed simply by applying the above-described porous film-forming coating material to the inner wall surface 12a of the inflow cell 12A of the filter base 11, the filter base 11 can have any shape. Without being restricted by the shape or the like of the substrate 11, the porous film 13 having excellent homogeneity can be easily formed on the surface.
As described above, the DPF 10 having low cost and excellent mass productivity can be manufactured.

  In this embodiment, the DPF has been described as an example of the ceramic filter. However, the ceramic filter is not limited to the DPF, and a conventionally known cylindrical filter, a large number in the axial direction of the column, may be used. The present invention can be sufficiently applied not only to a lotus root filter having a through-hole, but also to a structure or composition more complicated than a DPF.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these Examples.

"Example 1"
(Preparation of paint)
45 g of alumina (Al ₂ O ₃ ) fine particles A-1 (average primary particle size: 10 nm, tap bulk density: 0.1 g / cm ³ ), 2.25 g of a polycarboxylic acid-based dispersant, and 253 g of water are mixed for 2 hours by a ball mill. As a result, an alumina dispersion A having a solid content of 15% by mass was obtained.
Next, 167 g of this alumina dispersion A, 30 g of a methylcellulose aqueous solution containing 15% by mass of methylcellulose A (2% aqueous solution viscosity at 25 ° C. is 15 mPa · s), and 53 g of water are stirred and mixed for 1 hour using a magnetic stirrer. A coating material A of Example 1 in which alumina fine particles were dispersed in water was obtained.

(Evaluation of paint)
The viscosity of this paint A at 25 ° C. was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.).
Moreover, the average secondary particle diameter of the alumina fine particles in the paint A was measured by a dynamic light scattering method using a measuring device HPPS (manufactured by Malvern Instruments).

(Formation of porous film)
A SiC honeycomb filter (DPF, average pore diameter: 10 μm, porosity: 42%) was immersed in pure water, and ultrasonic waves were applied for 30 minutes. Thereafter, the sample was kept in pure water for 12 hours with the application of ultrasonic waves stopped. By this operation, water was filled in the pores of the honeycomb filter.
Next, the honeycomb filter was dipped in paint A and then dip-coated, and then dried at 150 ° C. for 1 hour, and further fired at 500 ° C. in air for 2 hours.
This operation was repeated three times to obtain the DPF of Example 1 in which the alumina porous film mainly composed of alumina fine particles was formed on the surface of the honeycomb filter.

(Evaluation of porous membrane)
The DPF of Example 1 was broken to a small size, and the surface and cross section of the partition walls were observed using a field emission scanning electron microscope (FE-SEM) S-4000 (manufactured by Hitachi Instrument Service Co., Ltd.). As a result, the amount of fine particles inside the partition was small, and a porous film having a thickness of about 20 μm was formed on the surface of the partition.
FIG. 3 shows a field emission scanning electron microscope (FE-SEM) image of a cross section of the partition wall of the DPF of Example 1.

The average pore diameter and porosity of the fractured DPF were measured by mercury porosimetry using a mercury porosimeter AutoPore IV 9505 (manufactured by Shimadzu Corporation).
Similarly, an average pore diameter and porosity in a SiC honeycomb filter (DPF, average pore diameter: 10 μm, porosity: 42%) in which a porous film is not formed are shown in a mercury porosimeter AutoPoreIV 9505 (manufactured by Shimadzu Corporation). Was measured by mercury porosimetry.
Next, from the average pore diameter and porosity in the fractured DPF, the average pore diameter and porosity in the honeycomb filter, the mass of the honeycomb filter, and the mass of the alumina fine particles attached to the surface of the honeycomb filter, The average pore diameter and porosity of the porous film formed on the surface were calculated.
These results are shown in Table 1.

"Example 2"
167 g of the alumina dispersion A in Example 1, 30 g of a methylcellulose aqueous solution containing 15% by mass of methylcellulose B (the viscosity of a 2% aqueous solution at 25 ° C. is 100 mPa · s), and 53 g of water are stirred and mixed for 1 hour using a magnetic stirrer. A paint B of Example 2 in which alumina fine particles were dispersed in water was obtained.
Using this coating material B, in the same manner as in Example 1, the coating material was evaluated, and the porous film was formed and evaluated.
These results are shown in Table 1.

"Example 3"
167 g of the alumina dispersion A of Example 1, 30 g of methylcellulose aqueous solution containing 15% by mass of methylcellulose C (2% aqueous solution viscosity at 25 ° C. of 1000 mPa · s), and 53 g of water were stirred and mixed for 1 hour using a magnetic stirrer. A paint C of Example 3 was obtained in which alumina fine particles were dispersed in water.
Using this paint C, the paint was evaluated and the porous film was formed and evaluated in the same manner as Example 1.
These results are shown in Table 1.

Example 4
45 g of alumina fine particles A-2 (average primary particle size: 60 nm, tap bulk density: 0.6 g / cm ³ ), 2.25 g of a polycarboxylic acid-based dispersant and 253 g of water were mixed for 2 hours with a ball mill, and the solid content was 15 A mass% alumina dispersion D was obtained.
Then, 167 g of this alumina dispersion D, 30 g of a methylcellulose aqueous solution containing 15% by mass of methylcellulose A (the viscosity of a 2% aqueous solution at 25 ° C. is 15 mPa · s), and 53 g of water are stirred and mixed for 1 hour using a magnetic stirrer. A coating material D of Example 4 in which alumina fine particles were dispersed in water was obtained.
Using this coating material D, in the same manner as in Example 1, the coating material was evaluated and the porous film was formed and evaluated.
These results are shown in Table 1.

"Example 5"
Stir and mix 1 g of alumina dispersion D in Example 4 and 30 g of methylcellulose aqueous solution containing 15% by mass of methylcellulose B (2% aqueous solution viscosity at 25 ° C. of 100 mPa · s) and 53 g of water using a magnetic stirrer for 1 hour. A paint E of Example 5 in which alumina fine particles were dispersed in water was obtained.
Using this paint E, in the same manner as in Example 1, the paint was evaluated, and the porous film was formed and evaluated.
These results are shown in Table 1.

"Example 6"
Agitated and mixed with 167 g of the alumina dispersion D of Example 4, 30 g of methylcellulose aqueous solution containing 15% by mass of methylcellulose C (the viscosity of 2% aqueous solution at 25 ° C. is 1000 mPa · s) and 53 g of water for 1 hour using a magnetic stirrer. A coating material F of Example 6 was obtained in which alumina fine particles were dispersed in water.
Using this coating material F, in the same manner as in Example 1, the coating material was evaluated and the porous film was formed and evaluated.
These results are shown in Table 1.

"Example 7"
45 g of alumina fine particles A-3 (average primary particle size: 200 nm, tap bulk density: 1.1 g / cm ³ ), 2.25 g of a polycarboxylic acid-based dispersant, and 253 g of water were mixed for 2 hours by a ball mill, and the solid content was 15 A mass% alumina dispersion G was obtained.
Then, 167 g of this alumina dispersion G, 30 g of a methylcellulose aqueous solution containing 15% by mass of methylcellulose A (the viscosity of a 2% aqueous solution at 25 ° C. is 15 mPa · s), and 53 g of water are stirred and mixed for 1 hour using a magnetic stirrer. A coating material G of Example 7 in which alumina fine particles were dispersed in water was obtained.
Using this paint G, the paint was evaluated and the porous film was formed and evaluated in the same manner as in Example 1.
These results are shown in Table 1.

"Example 8"
The alumina dispersion G167 of Example 7 and 30 g of a methylcellulose aqueous solution containing 15% by mass of methylcellulose B (2% aqueous solution viscosity at 25 ° C. of 100 mPa · s) and 53 g of water were stirred and mixed for 1 hour using a magnetic stirrer. A paint H of Example 8 in which alumina fine particles were dispersed in water was obtained.
Using this paint H, the paint was evaluated and the porous film was formed and evaluated in the same manner as in Example 1.
These results are shown in Table 1.

"Example 9"
The alumina dispersion G167 of Example 7, 30 g of a methylcellulose aqueous solution containing 15% by mass of methylcellulose C (the viscosity of a 2% aqueous solution at 25 ° C. is 1000 mPa · s), and 53 g of water were stirred and mixed for 1 hour using a magnetic stirrer. A paint I of Example 9 was obtained in which alumina fine particles were dispersed in water.
Using this coating material I, in the same manner as in Example 1, the coating material was evaluated and the porous film was formed and evaluated.
These results are shown in Table 1.

"Example 10"
45 g of alumina fine particles A-4 (average primary particle size: 1000 nm, tap bulk density: 1.5 g / cm ³ ), 2.25 g of a polycarboxylic acid-based dispersant and 253 g of water are mixed for 2 hours by a ball mill, and the solid content is 15 A mass% alumina dispersion J was obtained.
Next, this alumina dispersion J167g, methylcellulose aqueous solution 10g containing 15% by mass of methylcellulose A (2% aqueous solution viscosity at 25 ° C. of 15 mPa · s), and water 73g were stirred and mixed for 1 hour using a magnetic stirrer. A coating material J of Example 10 in which alumina fine particles were dispersed in water was obtained.
Using this paint J, in the same manner as in Example 1, the paint was evaluated and the porous film was formed and evaluated.
These results are shown in Table 1.

"Example 11"
45 g of titania (TiO ₂ ) fine particles (average primary particle size: 40 nm, tap bulk density: 0.6 g / cm ³ ), 2.25 g of a polycarboxylic acid-based dispersant, and 253 g of water were mixed for 2 hours by a ball mill, and the solid content was A 15% by weight titania dispersion K was obtained.
Then, 167 g of this titania dispersion K, 30 g of methylcellulose aqueous solution containing 15% by mass of methylcellulose A (the viscosity of 2% aqueous solution at 25 ° C. is 15 mPa · s), and 53 g of water are stirred and mixed for 1 hour using a magnetic stirrer. A paint K of Example 11 in which titania fine particles were dispersed in water was obtained.
Using this paint K, in the same manner as in Example 1, the paint was evaluated and the porous film was formed and evaluated.
These results are shown in Table 1.

"Example 12"
90 g of yttria-stabilized zirconia (YSZ) fine particles (average primary particle size: 40 nm, tap bulk density: 0.8 g / cm ³ ), 4.5 g of polycarboxylic acid-based dispersant, and 205.5 g of water were mixed for 2 hours with a ball mill. A yttria-stabilized zirconia dispersion L having a solid content of 30% by mass was obtained.
Then, 167 g of this yttria-stabilized zirconia dispersion L, 30 g of methylcellulose aqueous solution containing 15% by mass of methylcellulose A (2% aqueous solution viscosity at 25 ° C. is 15 mPa · s), and 53 g of water were stirred for 1 hour using a magnetic stirrer The paint L of Example 12 in which yttria-stabilized zirconia fine particles were mixed and dispersed in water was obtained.
Using this coating material L, in the same manner as in Example 1, the coating material was evaluated and the porous film was formed and evaluated.
These results are shown in Table 1.

"Example 13"
90 g of zinc oxide (ZnO) fine particles (average primary particle size: 40 nm, tap bulk density: 0.8 g / cm ³ ), 4.5 g of a polycarboxylic acid-based dispersant, and 205.5 g of water are mixed for 2 hours with a ball mill to form a solid A zinc oxide dispersion M having a content of 30% by mass was obtained.
Then, 167 g of this zinc oxide dispersion M, 30 g of a methylcellulose aqueous solution containing 15% by mass of methylcellulose A (the viscosity of a 2% aqueous solution at 25 ° C. is 15 mPa · s), and 53 g of water are stirred and mixed for 1 hour using a magnetic stirrer. A paint M of Example 13 was obtained in which zinc oxide fine particles were dispersed in water.
Using this coating material M, in the same manner as in Example 1, the coating material was evaluated and the porous film was formed and evaluated.
These results are shown in Table 1.

“Comparative Example 1”
83 g of the alumina dispersion A in Example 1, 16.7 g of a methylcellulose aqueous solution containing 15% by mass of methylcellulose D (the viscosity of a 2% aqueous solution at 25 ° C. is 3 mPa · s), and 150 g of water are stirred for 1 hour using a magnetic stirrer. The paint N of Comparative Example 1 was obtained by mixing and dispersing alumina fine particles in water.
Using this coating material N, in the same manner as in Example 1, the coating material was evaluated and applied to the honeycomb filter (DPF).
Moreover, when the surface and cross section of the partition of DPF were observed using the field emission type scanning electron microscope (FE-SEM) similarly to Example 1, the porous film was not formed in the surface of the partition. It was confirmed.
These results are shown in Table 1.

“Comparative Example 2”
167 g of the alumina dispersion A in Example 1 and 30 g of methylcellulose aqueous solution containing 15% by mass of methylcellulose E (2% aqueous solution viscosity at 25 ° C. of 2000 mPa · s) and 53 g of water were put into the flask, stirred and mixed by hand shaking, A coating material P of Comparative Example 2 in which alumina (Al ₂ O ₃ ) fine particles were dispersed in water was obtained.
Using this paint P, the paint was evaluated in the same manner as in Example 1.
Moreover, application | coating to a honey-comb filter (DPF) was performed using this coating material P. FIG.
Moreover, when the surface and cross section of the partition of DPF were observed using the field emission scanning electron microscope (FE-SEM) in the same manner as in Example 1, the particles were not fixed uniformly, and the porous structure was porous. It was confirmed that no film was formed.
These results are shown in Table 1.

“Comparative Example 3”
45 g of alumina fine particles A-1 (average primary particle diameter: 10 nm, tap bulk density: 0.1 g / cm ³ ), 2.25 g of a polycarboxylic acid dispersant, 253 g of water, and zirconia beads having a diameter of 0.1 mm are used. Was dispersed for 4 hours using an existing sand grinder to obtain an alumina dispersion Q having a solid content of 15% by mass.
Then, 167 g of this alumina dispersion Q, 30 g of methylcellulose aqueous solution containing 15% by mass of methylcellulose A (the viscosity of 2% aqueous solution at 25 ° C. is 15 mPa · s), and 53 g of water are stirred and mixed for 1 hour using a magnetic stirrer. A coating material Q of Comparative Example 3 in which alumina fine particles were dispersed in water was obtained.

Using this coating material Q, in the same manner as in Example 1, the coating material was evaluated and applied to the honeycomb filter (DPF).
Moreover, when the surface and cross section of the partition of DPF were observed using the field emission type scanning electron microscope (FE-SEM) similarly to Example 1, the porous film was not formed in the surface of the partition. It was confirmed.
These results are shown in Table 1.

“Comparative Example 4”
45 g of alumina fine particles A-5 (average primary particle diameter: 2000 nm, tap bulk density: 1.6 g / cm ³ ), 2.25 g of a polycarboxylic acid-based dispersant and 253 g of water were mixed for 2 hours by a ball mill, and the solid content was 15 A mass% alumina dispersion R was obtained.
Next, this alumina dispersion R167 g, 30 g of methylcellulose aqueous solution containing 15% by mass of methylcellulose A (the viscosity of 2% aqueous solution at 25 ° C. is 15 mPa · s), and 53 g of water are stirred and mixed for 1 hour using a magnetic stirrer. A coating material R of Comparative Example 4 in which alumina fine particles were dispersed in water was obtained.
When the stirring and mixing of the coating material R were stopped, the alumina fine particles immediately started to settle, and separated into two layers of the alumina fine particle precipitate and the supernatant liquid in a short time.
Thereby, it turned out that this coating material R is not suitable as a coating material for porous film formation.

It is a partially broken perspective view which shows DPF of one Embodiment of this invention. It is sectional drawing which shows the partition structure of DPF of one Embodiment of this invention. It is a field emission scanning electron microscope (FE-SEM) image which shows the cross section of the partition of DPF of Example 1 of this invention.

Explanation of symbols

10 DPF
DESCRIPTION OF SYMBOLS 11 Filter base | substrate 12 Gas flow path 12A Inflow cell 12B Outflow cell 13 Porous membrane 14 Partition 30 Particulate matter (alpha), (gamma) End face G Exhaust gas C Purified gas

Claims (6)

A coating for forming a porous film comprising fine particles containing an oxide as a component and a dispersion medium,
The fine particles have an average primary particle diameter of 10 nm or more and 1000 nm or less, a tap bulk density of 0.1 g / cm ³ or more and 1.5 g / cm ³ or less, an average secondary particle diameter in the paint of 0.1 μm or more and 10 μm or less,
The coating material for forming a porous film, wherein the viscosity of the coating material is 2 mPa · s or more and 1000 mPa · s or less.   The oxide is one or more selected from the group consisting of alumina, zirconia, titania, zinc oxide, silica, yttria, mullite, cordierite, aluminum titanate, and magnesia. The coating material for forming a porous film according to the description. A porous film formed by heat-treating a coating film obtained by applying the porous film-forming paint according to claim 1 or 2,
The porous membrane has an average pore diameter of 0.02 μm or more and 5 μm or less, and a porosity of 35% or more and 90% or less.   A ceramic filter comprising the porous membrane according to claim 3 formed on the surface of a porous support made of porous ceramics having an average pore diameter of 5 µm or more and 50 µm or less.   An exhaust gas purification filter comprising the ceramic filter according to claim 4.   A coating film is formed by applying the coating material for forming a porous film according to claim 1 or 2 on the surface of a porous support made of a porous ceramic having an average pore diameter of 5 μm or more and 50 μm or less. A method for producing a ceramic filter, characterized by heat-treating.

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