JP2003327483A - Ceramic composition and method of manufacturing ceramic filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic composition less liable to break particles in the mixing or molding the ceramic composition and capable of easily holding the plasticity in the molding and molding with good dimensional precision and a method of manufacturing a ceramic filter. <P>SOLUTION: The ceramic composition is one kind of a particle selected from the group consisting of a solid resin particle, a hollow resin particle, a thermally expanding micro-capsule and a thermally expanded micro-capsule which have a polar group (preferably a group having hydrophilicity) on the surface (and preferably contains a fluidity imparting agent or water holding agent) and a method of manufacturing the ceramic filter using the composition. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a ceramic composition and a ceramic filter, and more specifically,
The present invention relates to a ceramic composition suitably used for manufacturing a porous ceramic filter and the like and a method for manufacturing a ceramic filter.

[0002]

2. Description of the Related Art In recent years, as a porous ceramic filter, a partition wall of a honeycomb structure made of cordierite has a porous structure, and such partition wall is passed to allow a fluid such as gas to flow. Various porous honeycomb filters having a filter function have been proposed.
It is used as a filter for collecting particulates of exhaust gas discharged from a diesel car (a diesel particulate filter).

In such a porous ceramic filter, the average pore diameter (hereinafter referred to as pore diameter) of the porous material and the porosity are very important factors that determine the performance of the filter, and especially the diesel particulate matter. In the case of a porous ceramic filter such as a filter, a filter having a large pore size and a large porosity is desired in view of the collection efficiency of fine particles, pressure loss, and collection time.

Conventionally, in order to achieve the above-mentioned demand, a method using a pore-forming material has been studied. For example, a porous ceramic filter can be obtained by firing a ceramic molded body containing various pore-forming materials at a high temperature. However, in order to obtain a ceramic filter, it is also desired to mold a ceramic molded body with dimensional accuracy.

Therefore, for example, Japanese Patent Laid-Open No. 5-330943
The publication describes that by using graphite as a pore-forming material, a porous ceramic product with good dimensional accuracy can be obtained. However, an unfired ceramic composition is difficult to maintain its plasticity having an appropriate molding processability, its fluidity decreases with the passage of time and becomes brittle, and a ceramic molded body with good dimensional accuracy can be stably manufactured. It was difficult to do. Further, when the ceramic composition is mixed, the pore-forming material may be destroyed, and it may not function sufficiently as the pore-forming material. In particular, resin particles and hollow particles with little burning calories are easily broken.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, the object of the present invention is to prevent the pore-forming material from breaking during mixing or molding of the ceramic composition, and to easily maintain the plasticity during molding and to reduce the size. It is an object of the present invention to provide a ceramic composition that can be molded with high precision and a method for manufacturing a ceramic filter using the same.

[0007]

The ceramic composition according to claim 1 comprises solid resin particles having polar groups on the surface, hollow resin particles, thermally expandable microcapsules, and thermally expanded microcapsules. It is characterized by containing at least one kind of pore former selected from the group.

In the heat-expandable microcapsule according to claim 2, the pore-forming material is a heat-expanded microcapsule, and the heat-expanded microcapsule is expanded by heating the heat-expandable microcapsule in water. It is characterized by being obtained.

The ceramic composition according to claim 3 is the ceramic composition according to claim 1 or 2, wherein the polar group of the pore-forming material has hydrophilicity.

A ceramic composition according to a fourth aspect is the ceramic composition according to any one of the first to third aspects, wherein the ceramic composition contains a fluidity imparting agent and water. .

A ceramic composition according to a fifth aspect is the ceramic composition according to any one of the first to fourth aspects, wherein the ceramic composition contains a water retention agent.

According to a sixth aspect of the present invention, there is provided a method for producing a ceramic filter, wherein at least the pore-forming material according to any one of the first to fifth aspects, the ceramic composition and an organic binder are dry mixed. After that, the ceramic composition obtained in the kneading step and the kneading step, in which a molding aid is added and mixed and kneaded, is extruded and shaped into a predetermined shape, and the shaped article obtained in the shaping step is degreased. The method is characterized in that after degreasing in (1), firing is performed in the firing step.

The present invention will be described in detail below. The ceramic composition of the present invention has, as a pore-forming material, at least one selected from the group consisting of solid resin particles having a polar group on the surface, hollow resin particles, thermally expandable microcapsules, and thermally expanded microcapsules. It contains one kind of particles. The presence of the polar group on the surface makes it difficult for the particles to be broken at the time of mixing or molding the ceramic composition, and can easily maintain the plasticity at the time of molding.

As a method for obtaining the particles having a polar group on the surface, for example, a monomer having a polar group, a multifunctional monomer and a mixed monomer composed of other monomers, and a non-polymerizable organic solvent are used. Are mixed to prepare a monomer solution, and the monomer solution is suspended in a polar solvent, and then the monomer component is polymerized to obtain resin particles encapsulating the non-polymerizable organic solvent. It can be obtained by removing the organic solvent. The obtained particles are hollow resin particles.

In the above-mentioned polymerization method, when the non-polymerizable organic solvent is a highly volatile solvent, heat-expandable microcapsules can be obtained. When the heat-expandable microcapsules are heated above the softening point of the shell polymer, the contained organic solvent is volatilized and expanded to obtain hollow heat-expanded microcapsules.

If a non-polymerizable organic solvent is not used in the above polymerization method, solid resin particles can be obtained.
Further, by heat-treating the heat-expandable microcapsules in a polar medium typified by water, it is possible to obtain heat-expanded microcapsules containing many polar groups on the particle surface.

Therefore, the particles are not easily broken during the mixing and molding of the ceramic composition. Further, the ceramic composition can be imparted with plasticity and can be easily molded. In addition, it also exhibits excellent dispersibility in the ceramic composition. That is, the thermally expanded microcapsules superior to the thermally expanded microcapsules obtained by the dry heat treatment can be obtained. Probably, it is considered that the polar group is trapped inside the shell when it is thermally expanded by the dry heat treatment, while the polar group is likely to appear on the surface of the shell layer when the heat treatment is performed under the wet condition. Therefore, it is presumed that the microcapsules can be made to contain water by being heated in water and expanded in water, so that the ceramic composition does not have an excess or deficiency of water lost in the ceramic composition during molding, and it becomes difficult to dry. To be done. Moreover, it is presumed that the large number of polar groups present on the surface of the shell layer facilitates the dispersion of the microcapsules in the ceramic.

That is, the thermally expanded microcapsules absorb excess water contained in the ceramic composition, while providing the water contained in the microcapsules to the ceramic composition as the ceramic composition dries. Therefore, the ceramic composition is kept in an appropriate amount of water, and the binder resin such as methyl cellulose can maintain a strong shape-retaining force for a long time. Therefore, the ceramic composition is tough and yet retains sufficient plasticity, and a tough and light fired ceramic product is easily obtained.

It was also found that the dispersibility of the microcapsules is further enhanced by adding a coagulation inhibitor such as a silane compound to the thermally expanded microcapsules before the wet heat treatment.

The thermally expanded microcapsules are
It is preferable to make the particle sizes uniform by a method such as classification. The particles having a small particle size may include unexpanded microcapsules that could not be expanded by the heat treatment. By removing these particles, the water retention capacity of the ceramic composition can be efficiently increased. The presence of unexpanded microcapsules can be confirmed from the phenomenon that the true specific gravity of the thermally expanded microcapsules is reduced by removing the particles having a small particle size.

Examples of the polar group of the monomer having the polar group include a carboxyl group, a glycidyl group, an amino group, an amide group, an ester group, a pyridyl group, a hydroxyl group, an alkoxyl group, a sulfonyl group, a phosphoric acid group and a phosphorus group. Examples thereof include acid ester group, nitro group, cyano group and the like. As a preferable monomer, a mixed monomer including a hydrophilic monomer can be mentioned.

The polar group on the surface of the pore-forming material preferably has hydrophilicity, and the monomer having the polar group is preferably a hydrophilic monomer. Since the hydrophilic monomer has a higher affinity for a polar solvent than an organic solvent, it is considered that the hydrophilic monomer is localized at the oil droplet interface in the oil droplets suspended in the monomer solution. Easy to form the surface part of the wall surface.

The hydrophilic monomer preferably has a solubility in water of 1% by weight or more, for example, methyl (meth) acrylate, (meth) acrylonitrile, (meth) acrylamide, (meth) acrylic acid, Glycidyl (meth) acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate
, Dimethylaminomethyl methacrylate, vinyl pyridine, 2-acryloyloxyethyl phthalic acid, itaconic acid, fumaric acid, maleic anhydride, succinic acid and the like. Of these, methyl (meth) acrylate and glycidyl (meth) acrylate are preferable because the hardness and softness of the resin particles can be easily adjusted. Further, those having an acidic functional group on the surface are preferable, and examples thereof include maleic anhydride, methacrylic acid, and succinic acid. These may be used alone or in combination of two or more.

In order to sufficiently increase the polarity of the outer wall surface of the resin particles, the proportion of the hydrophilic monomer is 10 to 10 of the monomer component.
It is preferably 99.9% by weight, and more preferably 30 to 99.9% by weight.

As the polyfunctional monomer constituting the above monomer component, for example, di (meth) acrylate, tri (meth) acrylate, etc. are preferably used. Examples of the di (meth) acrylate include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, 1,6- Hexanediol di (meth) acrylate, trimethylolpropane di (meth) acrylate and the like can be mentioned. Examples of the tri (meth) acrylate include trimethylolpropane tri (meth) acrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, and the like. To be

Examples of polyfunctional monomers other than those mentioned above include pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, diallyl phthalate, diallyl maleate. Examples thereof include di- or triallyl compounds such as diallyl fumarate, diallyl succinate and triallyl isocyanurate, and divinyl compounds such as divinylbenzene and butadiene.

These polyfunctional monomers can be used alone or in combination of two or more kinds.

In order to increase the compression resistance strength of the resin particles and prevent the particles from agglomerating during the polymerization, the proportion of the polyfunctional monomer is 0.1 to 30% by weight of the monomer component. It is preferably 0.3 to 5% by weight.

The other monomer constituting the above-mentioned monomer component is added for the purpose of improving mechanical strength, chemical resistance and moldability, and the kind thereof is not particularly limited. For example, ethyl (meth) acrylate is used. , Propyl (meth) acrylate, butyl (meth) acrylate, cumyl methacrylate, cyclohexyl (meth) acrylate, mistyryl (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate -Aryl (meth) acrylates such as styrene; aromatic vinyl monomers such as styrene, α-methylstyrene, p-methylstyrene, p-chlorostyrene; vinyl esters such as vinyl acetate and vinyl propionate; vinyl chloride, chloride Halogen-containing monomers such as vinylidene; ethylene, propylene, butadiene and the like. These may be used alone or in combination of two or more.

If the amount of the above-mentioned other monomer used is too large, the hydrophilicity of the monomer component is lowered and the formation of the outer wall of the resin particles is hindered. Therefore, the amount of the monomer component is 89.9% by weight or less. Is preferred, more preferably 69.
It is 9% by weight or less.

It is desirable that the non-polymerizable organic solvent added to the monomer component is localized at the center of the oil droplet in the oil droplet suspended in the monomer solution, and has a solubility in water of 0.
It preferably has a hydrophobicity of 2% by weight or less, and the kind thereof is not particularly limited, but for example, butane, pentane, hexane, cyclohexane, toluene, xylene and the like are preferably used. Among them, butane, pentane, hexane and cyclohexane, which have high volatility, are more preferable.

If the amount of the non-polymerizable organic solvent added is too small, the porosity of the particles will be low, and if it is too large, the porosity will be too high and the strength of the particles will be reduced, so 100 parts by weight of the monomer component is added. On the other hand, it is preferably 1 to 400 parts by weight, more preferably 10 to 200 parts by weight.

Fluidity is imparted to the ceramic composition by containing water. It is more preferable that a fluidity-imparting agent is contained in addition to water in order to improve the fluidity of the ceramic composition. Thereby, the particles are less likely to be broken and the plasticity at the time of molding becomes good. Examples of the fluidity-imparting agent defined in the present invention include electrolytes, acids, salts of acidic substances, salts of basic substances and neutralized salts. Of these, substances that can be hydrolyzed by water in the ceramic composition are preferable.

The above-mentioned acid is not particularly limited, and examples thereof include inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as phosphoric acid and carboxylic acid. Specific examples thereof include melamine sulfonic acid and hydroxy poly. Examples thereof include carboxylic acid, polyethylene carboxylic acid, polyalkyl sulfonic acid, alkylnaphthalene sulfonic acid, melamine sulfonic acid, polycarboxylic acid and polystyrene sulfonic acid. The above-mentioned salt is not particularly limited as long as it is a compound in which a cation and an anion are generated in the form of neutralizing the charge, and examples thereof include an acid salt and a basic salt, and an addition compound of an organic base and an acid.

Of these, an addition compound of an organic base and an acid is preferable, and examples thereof include naphthalene sulfonate, alkylallyl sulfonate, and soda salt of amylene / maleic anhydride copolymer (“Quinflo-540 manufactured by Nippon Zeon Co., Ltd.”). ",
"Quinflo-542"), a partial amide ammonium salt of an amylene / maleic anhydride copolymer ("Quinflo-543" manufactured by Nippon Zeon Co., Ltd.) and the like are preferably used. These may be used alone or in combination of two or more.

It is preferable that the above-mentioned ceramic composition contains a water retention agent, since the plasticity at the time of molding can be easily maintained. Examples of the water retention agent include glycerin, ethylene glycol, diethylene glycol, ethylene glycol monoalkyl ether, diethylene glycol monoalkyl ether, triethylene glycol monoalkyl ether, and dimethyl sulfoxide. Polyglycol ether, methyl polysiloxane, methyl polycyclosiloxane, methylphenyl polysiloxane,
Copolymers of dimethyl siloxane and methyl (polyoxyethylene) siloxane, copolymers of dimethyl siloxane and methyl (polyoxyethylene) siloxane and methyl (polyoxypropylene) siloxane, methyl polysiloxane and methyl polycyclosiloxane In addition to liquid silicone compounds such as mixed liquids, mixed liquids of trimethylsiloxysilicic acid and methylpolysiloxane, lepurinic acid,
3-methoxybutyl acetate, 3-methoxy-1-butanol, 3-methyl-3-methoxybutanol, 3-
Methyl-1,5-pentanediol, methyl ethyl ketone oxime, methyl isobutyl carbitol, formamide, formalin, 1,5-pentanediol, pentaerythritol, 1,6-hexanediol, propylene glycol monomethyl ether -Tel, Propylene Glyco-
, Dipropylene glycol, γ-butyl lactone,
1,4-butanediol, 1,3-butanediol, 4
-Hydroxy-2-butanone, neopentyl glycol,
Butyl lactate, ethyl lactate, trimethylolpropane, trimethylolethane, triacetin, thioglycol, thioglycerol, diacetone alcohol
, Sebacic acid, 3,3-dimethoxypropionitrile, N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, dimethyl sulfoxide, 1,3-dihydroxyacetone, ethyleneglyco- Ludiacetate, cyclohexanone dimethyl acetal, cyclohexanone, cyclohexano-
, Tetrahydrofurfuryl alcohol, glyoxylic acid, octandiol, ethylene cyanohydrin, ethylene glycol monomethyl ether, ethylene glyco-
Rumonoethyl ether, ethylene glycol monobutyl ether, ethylene glycol, diethylene glycol
, Diethylene glycol dimethyl ether, triethylene glycol, ethylene carbonate, isoprene glycol, 2,5-dimethyl-3-hexyne-2,5-
Diol, 2,5-dimethyl-2,5-hexanedio-
And glycerin, N-methyl-2-pyrrolidone, sulfolane, 1,2,6-hexanetriol and the like. These may be used alone or in combination of two or more.

The ceramic raw material used in the ceramic composition of the present invention is not particularly limited.
Jellite, talc, silica, kaolin, baked kaolin,
Aluminum hydroxide, alumina, mullite, zircon,
Examples thereof include spinel, silicon carbide, silicon nitride, zirconia, forsterite, spodumene, aluminum titanate, and ucryptite. These may be used alone or in combination of two or more. . In addition, a cordierite raw material prepared by blending talc, silica, kaolin, calcined kaolin, alumina, aluminum hydroxide, etc. so as to become cordierite after calcining can also be mentioned. In addition, since the mechanical strength of the sintered body tends to be insufficient only with cordierite, it is preferable that the cordierite raw material is added to the cordierite. Further, it may be a composition which is a precursor of the ceramic raw material.

The above-mentioned ceramic composition may be an organic binder for facilitating the retention of the shape of the ceramic raw material composition formed in the unfired stage, or the ceramic raw material composition may be plasticized or have a lubricity on the surface. If necessary, a molding aid for facilitating the molding may be added.

Examples of the organic binder include cellulose ether such as methyl cellulose, cone starch, polyvinyl alcohol, ammonium alginate and the like. Further, as the molding aid, for example,
Examples thereof include sodium stearate, glycerin, sodium ammonia, and diglycol stearate.
These may be used alone or in combination of two or more.

The method for producing the ceramic filter of the present invention is selected from the group consisting of solid resin particles having polar groups on the surface, hollow resin particles, thermally expandable microcapsules, and thermally expanded microcapsules. At least one pore-forming material, a ceramic composition, and an organic binder are dry-mixed, and then a kneading step in which a molding aid is added and mixed and kneaded, and the ceramic composition obtained in the kneading step is extruded and molded. The present invention is characterized by including a shaping step of shaping into a filter shape and a firing step of firing the shaped article obtained in the shaping step after a degreasing step. The pore former may be hydrated before being mixed. Also,
Water may be added after the raw materials are dry mixed.

[0041]

EXAMPLES Examples of the present invention will be described below.
It is not limited to the following example. (Examples 1 to 5 and Comparative Examples 1 and 2) The monomer components, the non-polymerizable organic solvent and the polymerization initiator in the compounding amounts shown in Table 1 were mixed and stirred to prepare a monomer solution. It was mixed with the polar medium shown in No. 1, ion-exchanged water was further added, and the mixture was stirred with a homogenizer to prepare a suspension monomer solution.
On the other hand, ion-exchanged water was put into a 20-liter polymerization vessel equipped with a stirrer, a jacket, a reflux condenser and a thermometer. Then, stirring was started to depressurize the inside of the polymerization vessel to deoxygenate the inside of the vessel, then nitrogen was injected to return the pressure to atmospheric pressure, the inside was made into a nitrogen atmosphere, and then the above suspension monomer solution was added. The ingredients were added all at once in the polymerization vessel, and the temperature of the polymerization vessel was raised to 80 ° C. to initiate polymerization. Polymerization was completed in 5 hours, and after aging for 1 hour, the polymerization vessel was cooled to room temperature. After dehydrating the slurry with a dehydrator (centre),
It was dried sufficiently to obtain heat-expandable microcapsules. Next, the obtained heat-expandable microcapsules were heated and thermally expanded to obtain heat-expanded microcapsules. Then, in Examples 1 to 4 among the obtained heat-expandable microcapsules, the heat-expandable microcapsules were expanded in heated dry air. In addition, in Example 4, sieving was performed to substantially remove microcapsules of 20 μm or less. In Example 5, high-pressure steam was blown into the thermally expandable microcapsules dispersed in water to thermally expand the microcapsules to obtain thermally expanded microcapsules. The true specific gravities of the thermally expanded microcapsules of Example 4 and Example 5 were almost the same.

Cordierite 28 as a ceramic raw material
An extrudable ceramic composition was obtained by kneading 4 g of heat-expandable microcapsules (85% by weight of water, 15% by weight of heat-expandable microcapsules) containing 3 g, 14.2 g of methylcellulose and water. It was Next, the obtained ceramic composition was shaped by an extrusion molding method to obtain an unfired ceramic molded body (kneaded clay).

The following evaluation was carried out using the obtained ceramic molded body, and the results are shown in Table 1.

(Puddle hardness) Penetration was measured using the obtained ceramic molded body (kneaded clay) (manufactured by Nippon Oil Testing Machine Industry Co., Ltd .:
AN201 needle penetration tester) was performed. The load was set to 200 g, and how much the needle penetrated into the sample puddle for 5 seconds (0.1 mm) was measured. (Puddle density): The lower the numerical value, the better the property against particle destruction. The obtained ceramic molded body (kneaded clay) was cut into a constant volume, and each sample piece was weighed. Then, the density was calculated by dividing by the volume and evaluated according to the following criteria. ◎: Less than 1.4 ○: 1.4 or more and less than 1.6 △: 1.6 or more and less than 1.7 ×: 1.7 or more

(Shape after firing) After the obtained ceramic composition is shaped by an extrusion molding method and dried, the temperature rising rate is 40.
The temperature is increased to 500 ° C. at a rate of ℃ / hour, degreasing is performed for 1 hour, and further firing is performed at 2100 ° C. for 2 hours in an inert gas atmosphere to produce a porous ceramic filter. Shrinkage, chipping, roundness, etc.) was visually evaluated according to the following criteria. ○: Good shape ×: Bad shape

(Comprehensive evaluation): ◎, ○,
The evaluation was made in four grades of Δ and ×. ⊚: Kneaded clay density is less than 1.4 and kneaded clay hardness is less than 150. ○: When the kneaded clay density is 1.4 or more and less than 1.6 and the kneaded clay hardness is less than 200, or when the kneaded clay density is less than 1.4 and the kneaded clay hardness is 150
If more than 200. Δ: When the kneaded clay density is 1.6 or more and less than 1.7 and the kneaded clay hardness is less than 200, or when the kneaded clay hardness is 200 or more at all kneaded clay densities. X: Other than the above.

[0047]

[Table 1]

The components used in Table 1 are as follows. AN: acrylonitrile MMA: methyl methacrylate MAA: methacrylic acid MAH: maleic anhydride HOMS: 2-methacryloyloxyethyl succinic acid ST: styrene monomer IBOA: isobornyl acrylate

[0049]

EFFECTS OF THE INVENTION The ceramic composition and the method for producing a ceramic filter of the present invention have the above-mentioned constitution, and the particles are not easily broken during mixing and molding of the ceramic composition, and the plasticity during molding is easily maintained. It is possible to obtain a ceramic filter having a good shape with good dimensional accuracy.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshiyuki Kosaka             1259 Izumi, Mizuguchi-cho, Koga-gun, Shiga Sekisui Chemical Co., Ltd.             Within the corporation (72) Inventor Masahiro Yamanaka             1259 Izumi, Mizuguchi-cho, Koga-gun, Shiga Sekisui Chemical Co., Ltd.             Within the corporation F-term (reference) 4D019 AA01 BA05 BB06 BB07 BC12                       CA01 CB04 CB07

Claims (6)

[Claims] 1. A solid resin particle having a polar group on its surface,
A ceramic composition comprising at least one pore-forming material selected from the group consisting of hollow resin particles, thermally expandable microcapsules, and thermally expanded microcapsules. 2. The ceramic composition according to claim 1, wherein the thermally expanded microcapsules are microcapsules obtained by expanding the thermally expandable microcapsules by subjecting them to heat treatment in water. 3. The ceramic composition according to claim 1, wherein the polar group of the pore-forming material has hydrophilicity. 4. The ceramic composition according to claim 1, wherein the ceramic composition contains a fluidity-imparting agent and water. 5. The ceramic composition according to any one of claims 1 to 4, wherein the ceramic composition contains a water retention agent. 6. Solid resin particles having a polar group on the surface,
At least one pore-forming material selected from the group consisting of hollow resin particles, thermally expandable microcapsules, and thermally expanded microcapsules, a ceramic composition, and an organic binder are dry-mixed and then molded. Extruding and molding the ceramic composition obtained in the kneading step and the kneading step of adding and kneading an auxiliary agent, and shaping in a predetermined shape and degreasing the shaped article obtained in the shaping step in the degreasing step After that, the method for producing a porous ceramic filter is characterized by firing in a firing step.