WO2003004132A1 - Method for manufacturing porous ceramic filter - Google Patents

Abstract

A method for manufacturing a porous ceramic filter, characterized in that a ceramic composition comprising a silicon carbide as a primary component and hollow polymer particles as an agent for pore formation is formed into an article having a predetermined shape, and then the resultant formed article is fired.

Description

 Specification

 Method for manufacturing porous ceramic filter

Technical field

 The present invention relates to a method for producing a porous ceramic filter having high porosity and high heat resistance.

Conventional technology

 In recent years, as a porous ceramic filter, the partition walls of a honeycomb structure formed by sintering silicon carbide (SiC) powder have been made to have a porous structure. Various porous honeycomb filters having a filter function for a fluid have been proposed, and have been put to practical use, for example, as a filter (diesel particulate filter) for collecting particulates of exhaust gas discharged from diesel vehicles.

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

Conventionally, the pore size of a ceramic filter has been controlled by appropriately selecting the aggregate particle size of a ceramic composition as a raw material. As a method of controlling the pore size in order to improve the filter performance, for example, a method of adding an organic polymer to a ceramic composition has been proposed (Japanese Patent Application Laid-Open No. 2000-288832). No. 5). On the other hand, as a method for improving the porosity, for example, Japanese Patent Application Laid-Open No. 3-215374 discloses an average particle diameter of 100 to 150 μπι and an average particle diameter of 20 μm. the S i C powder having a particle size distribution 9 0 weight _^0/0 or within% is present, interconnected by crushing a surface portion thereof, so as to remain in the molded body during not collapse inside the force its There has been proposed a method of firing after molding and compression.

However, in these methods, since the bonding of the SiC particles constituting the porous body is based only on the particle growth of the SiC fine particles, the mechanical strength decreases as the porosity increases, There is a problem that it is difficult to achieve both porosity and strength characteristics. Also, a method of adding a pore-forming agent such as graphite is generally used, but the porosity is further improved. If a large amount of a pore-forming agent is used, the firing time will be prolonged and the manufacturing process will take a long time. There was a problem that a large strain was applied to the body and cracks occurred in the formed body. Accordingly, there is a need for a method of manufacturing a porous filter that can impart low thermal expansion and thermal shock resistance and improve porosity.

 In view of the above problems, an object of the present invention is to provide a method for manufacturing a porous ceramic filter which has low thermal expansion and thermal shock resistance and has improved porosity.

Disclosure of the invention

 With the aim of solving the above problems, the present inventors have conducted intensive studies on a method of manufacturing a porous ceramic filter that can fully satisfactorily address these various problems. It has been found that a porous ceramic filter with improved porosity without thermal deformation can be obtained by shaping a predetermined molded body from a ceramic composition using hollow polymer particles as a pore-forming agent and then firing it. Thus, the present invention has been completed.

 That is, the present invention is characterized in that a predetermined molded body is molded from a ceramic composition containing silicon carbide powder as a main component and containing hollow polymer particles as a pore-forming agent, and then the molded body is fired.

 Hereinafter, the present invention will be described in more detail.

 In the present invention, in order to obtain a porous ceramic filter, a ceramic composition containing silicon carbide (SiC) powder as a main component and hollow polymer particles as a pore-forming agent is used. In the above ceramic composition, the amount of the hollow polymer particles added is not particularly limited, but if the amount is too small, sufficient porosity cannot be obtained, and if the amount is too large, the strength of the fired ceramic molded body decreases. Preferably, the content is 10 to 50% by weight in the composition. As the above hollow polymer particles, those having an average particle size of 5 to 100 μπι and a compressive strength of 10% or more of 1.5 MPa are preferable.

If the average particle size is smaller than 5 im, the pore size of the obtained porous ceramic filter becomes smaller, the pressure loss of the filter increases, and the collection time becomes shorter. On the other hand, when the average particle size is larger than 10 Οπι, the pore size of the ceramic filter increases, The pressure loss of the filter decreases, but the collection efficiency decreases.

 Further, in order to prevent the hollow polymer particles from being broken by mechanical shearing force at the stage of shaping the ceramic composition into a predetermined molded body, it is preferable that the 10% compressive strength is 1.5 MPa or more. .

 Furthermore, even among hollow particles having the same porosity, it has been found that hollow particles having a honeycomb-like morphology comprising a plurality of pores have superior compressive strength. That is, by using hollow polymer particles having a plurality of pores as the pore-forming agent, the number of particles broken in the process of forming the filter is reduced, and the porosity can be improved.

 The method for producing the hollow polymer particles is not particularly limited, but a production method comprising the following two steps of suspension polymerization and solvent removal is preferred.

 That is, a monomer solution is prepared by mixing a non-polymerizable organic solvent with a mixed monomer composed of a hydrophilic monomer, a polyfunctional monomer and other monomers, and the monomer solution is suspended in a polar solvent. It comprises a first step of polymerizing the components to obtain polymer particles containing the non-polymerizable organic solvent, and a second step of removing the organic solvent in the polymer particles to obtain hollow polymer particles.

 In the above production method, the polymerization method is not particularly limited, but it is preferable to use a suspension polymerization method because it is easy to control the particle diameter and easily form particles containing effective voids.

 Since the hydrophilic monomer constituting the above monomer component 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 suspended oil droplets of the monomer solution, resulting in polymerization. Thereby, the outer wall surface of the hollow polymer particles is formed.

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-hydroxyl methacrylate, 2-hydroxypropyl methacrylate, butyl pyridine, 2-acryloyloxetyl phthalic acid, itaconic acid, fumaric acid, dimethylaminomethyl methacrylate And the like, and preferably, methyl methacrylate, (meth) acrylic acid, 2-hydroxyethyl methacrylate and the like. These can be used alone or in combination of two or more. If the amount of the hydrophilic monomer used is too small, the outer wall surface of the hollow polymer particles will not be sufficiently formed, and the porosity of the hollow polymer particles will decrease, so that 10 to 99.9% by weight of the monomer component will be used. Preferably, the weight is more preferably 30 to 99.9. / ₀ .

 The polyfunctional monomer constituting the above monomer component is added for the purpose of improving the compression resistance of the particles, and di (meth) acrylate and tri (meth) acrylate are suitably used. Examples of the di (meth) acrylate include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, and 1,6-hexanediol di (meth). Acrylate, trimethylolpropanedi (meth) acrylate, and the like. Examples of the tri (meth) acrylate include trimethylolpropane tri (meth) acrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, and pentaerythritol tri (meth) acrylate. Examples of the polyfunctional monomer other than the above include, for example, pentaerythritol tetra (meth) acrylate, dipentaerythritolhexa (meth) acrylate, diarylphthalate, diarylmalate, diarylfumarate, diarylsuccinate, triallylisolate. Examples thereof include di- or triallyl compounds such as cyanurate and the like, and dibutyl compounds such as dibutylbenzene and butadiene.

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

 If the amount of the polyfunctional monomer used is too small, the compression resistance of the hollow polymer particles is not sufficient, and if the amount is too large, the aggregation of the particles occurs during polymerization. %, Preferably 0.3 to 5% by weight.

Other monomers constituting the above-mentioned monomer component are added for the purpose of improving mechanical strength, chemical resistance and formability, and the type thereof is not particularly limited. For example, ethyl (meth) acrylate, propyl (meth) ) Acrylate, butyl (meth) acrylate, Tamyl methacrylate, cyclohexyl (meth) acrylate, mystyrinole (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate Alkyl (meth) acrylates such as styrene; α-methylstyrene, ρ-methylstyrene, ρ-chlorostyrene and other aromatic vinyl monomers; butyl esters such as butyl acetate and butyl propionate; vinyl chloride, vinylidene chloride Halogen-containing monomers such as ethylene; propylene; butadiene; These can be used alone or in combination of two or more.

 If the amount of the other monomer is too large, the hydrophilicity of the monomer component is reduced, and the outer wall of the hollow polymer particles is prevented from being formed. Therefore, the content of the other monomer is preferably 89.9% by weight or less, More preferably, it is 69.9% by weight or less.

 The non-polymerizable organic solvent added to the monomer component is desirably localized at the center of the oil droplets in the oil droplets suspended in the monomer solution, and has a water solubility of 0.2% by weight or less. The type is not particularly limited, but for example, butane, pentane, hexane, cyclohexane, toluene, xylene and the like are preferably used. Above all, highly volatile butane, pentane, hexane and cyclohexane are more preferred.

 If the amount of the non-polymerizable organic solvent is too small, the porosity of the particles will be low, and if too large, the porosity will be too high and the strength of the particles will be reduced. It is preferably 1 to 400 parts by weight, more preferably 10 to 200 parts by weight.

 In the method for producing a porous ceramic filter of the present invention, first, a talc powder component such as talc and calcined talc as an inorganic binder, a silica powder represented by amorphous silica, a pore-forming agent, Kaolin, calcined kaolin, boron oxide, alumina, aluminum hydroxide and the like are appropriately blended to prepare a ceramic composition mainly composed of SiC powder. The amount of the inorganic binder to be added to the SiC powder is not particularly limited, and is appropriately determined depending on the quality of the hollow polymer particles and the like.

 A plasticizer, a binder and the like are added to the ceramic composition thus prepared in the same manner as in the conventional method, and the plastic composition is plasticized to obtain a shapeable extrusion molding raw material.

The raw material is extruded into a honeycomb formed body having a predetermined shape, dried, and then fired at a temperature of 160 to 220 ° C. Manufacture a porous ceramic filter. In the production method of the present invention, low thermal expansion is imparted to the porous ceramic filter, and porosity and thermal shock resistance are improved by incorporating hollow polymer particles as a pore-forming agent into the ceramic composition. (1) It is possible to provide a filter capable of suppressing the rise in pressure loss while maintaining the collection efficiency and effectively extending the collection time.

 That is, by replacing the organic particles, which are conventional pore-forming agents, with hollow polymer particles of the same weight, the volume occupied by the pore-forming agent increases, and the porosity can be improved. In addition, when replaced by hollow polymer particles of the same volume, the heat of combustion of the particles during firing decreases, and the strain applied to the ceramic molded product is reduced, so that low thermal expansion properties are imparted and thermal shock resistance is improved. .

BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, the power for explaining the embodiment of the present invention is not limited to the following example.

• Preparation of hollow polymer particles

 Mix the monomer components, the non-polymerizable organic solvent and the polymerization initiator in the amounts shown in Table 1, stir to prepare a monomer solution, and then ion-exchange water (50% by weight of the total amount) and disperse The suspension was added and stirred with a homogenizer to prepare a suspended monomer solution. On the other hand, the remaining ion-exchanged water, sodium chloride sodium, sodium nitrite, sodium chloride and hydrochloric acid in the amounts shown in Table 1 were placed in a 20-liter polymerization vessel equipped with a stirrer, jacket, reflux condenser and thermometer. Sodium hydroxide was added and stirring was started.

 Next, the pressure in the polymerization vessel was reduced to deoxygenate the inside of the vessel, and then nitrogen was injected to return the pressure to atmospheric pressure. After the inside was set to a nitrogen atmosphere, the above suspended monomer solution was added all at once. Then, the temperature of the polymerization vessel was raised to 80 ° C. to start polymerization. After 5 hours, the polymerization was completed. After an aging period of 1 hour, the polymerization reactor was cooled to room temperature.

 The slurry was dehydrated with a centrifuge and the organic solvent was removed by vacuum drying to obtain hollow polymer particles (a) to (e).

 · Solid polymer particles (f)

 Expandable particles (“F-85D” manufactured by Matsumoto Yushi Co., Ltd.) were heated at 170 ° C. for 1 minute, and solid polymer particles were used.

The following performance evaluation was performed on the hollow polymer particles (a) to (e) and the solid particles (f), and the results are shown in Table 1. (1) Average particle size

 Particles are sampled from three arbitrary locations, and the volume average particle size of the hollow polymer particles is measured for each sample using a laser diffraction single particle size distribution analyzer “LA-910” manufactured by Horiba, Ltd. The average was determined.

 (2) Internal morphology

 The equatorial section of the hollow polymer particles was applied to a thin film, and the internal morphology was observed with a transmission electron microscope.

 (3) Ratio (= hollow pore diameter Z particle outer diameter)

 Measure the hollow pore diameter of the 10 randomly selected particles (measure the average of the longest and shortest diameters of all the hollow pores in the particles and use the average) to determine the particle outer diameter.

The ratio (= hollow pore diameter / particle outer diameter) to (using the above average particle diameter) was calculated.

(4) Porosity

The porosity of the hollow polymer particles was measured using an Amcone earth porosimeter “2000”. Mercury filling pressure ^2, OOO k gZcm 2 and then, using a hollow polymer particle sample 0. 5 g sample from any location in the evaluation.

 (5) Compressive strength

 The 10% compressive strength of the hollow polymer particles was measured using a micro compression tester “MCTM-500” manufactured by Shimadzu Corporation.

 The components used in Table 1 are as follows.

 MMA: methyl methacrylate, MAC: methacrylic acid

 I BM: Isobutyl methacrylate

 TMP: Trimethylolpropane triatarylate

 DPE: dipentaerythritol hexaacrylate

 A I BN: azobisisobutyronitrile

 PVP: Polybutylpyrrolidone

 Colloidal silica, calcium phosphate: 20% by weight aqueous solution

 Hydrochloric acid: 35% by weight aqueous solution

 (Examples 1-4, Comparative Example 1)

90% by weight of SiC, 5% by weight of boron oxide, 2% by weight of kaolin and 3% by weight of alumina 70 parts by weight of the inorganic mixture consisting of 30 parts by weight of the hollow polymer particles shown in Table 2 and 100 parts by weight of the mixed ceramic composition were mixed with 15 parts by weight of methylcellulose and water added. In addition, it was kneaded to obtain an extrudable clay.

Then, each clay obtained by shaping by a known extrusion molding method, rib thickness: 4 3 0 m, the number of cells: 1 6 diameter having a Z cm ^2: 1 1 8 mm,髙of: 1 A 52-mm cylindrical honeycomb structure was fabricated. Next, after drying this honeycomb structure, the temperature was raised to 500 at a heating rate of 40 ° C./hour, a degreasing step was performed for 1 hour, and further performed under an inert gas atmosphere at 2100 ° C. And fired for 2 hours to obtain a porous ceramic filter.

 (Comparative Example 2)

 A porous ceramic finoleta was obtained in the same manner as in Example 2, except that solid polymer particles (f) were used as the pore former.

 The following performance evaluations were performed on the porous ceramic filters obtained in the above Examples and Comparative Examples, and the results are shown in Table 2.

 (5) Thermal expansion coefficient

 The thermal expansion coefficient in the height direction (A-axis) and in the cylinder diameter direction (B-axis) was measured using “TMA100” manufactured by Seiko Istrungmen. The measurement temperature was 40 to 800 ° C, and the heating rate was 40.

 (6) Porosity

 The porosity was measured by the same method. The sample used was the filter obtained.

Industrial applications

 The method for producing a porous ceramic filter of the present invention has the above-described configuration, and by using hollow polymer particles as a pore-forming agent, a porous ceramic filter having a high porosity and a high thermal shock resistance can be obtained. it can.

Therefore, the obtained porous ceramic filter is suitably used especially as a diesel particulate filter. 【table 1】

 Types of hollow polymer particles (a) (b) (C) (d) (e) (f)

 MMA 39 45 45 45 70

 Hydrophilic

Monomer ¹ ~

 MAC — 4.2 ―

 Other monomers-IBM 10.3 24.2 24.2 20 2.9 F-85D

 TMP — 0.8 0.8 0.8 one

 Multifunctional

 Monomer

 DPE 0.7 1 1 1 1 170 ° C Medium

Sky

 Pentane 30 30 30 30 ― 1 minute Po Organic solvent

Hexane 20 ― ― ―

 1 Polymerization initiator AIBN 0.25 0.25 0.25 0.25 0.25 particles

Child colloidal silica 40 30 one 40

 Dispersant Calcium phosphate

Dull

 E. Rivier pyrrolone 0.3 0.3 0.3 0.3 0.3 parts

 Sodium chloride 20 20 20 20 20

 Sodium nitrite 0.05 0.05 0.05 0.05 0.05

 Hydrochloric acid 0.2 0.15 ― 0.2 Sodium hydroxide 0.1 0.1 0.1 ―

 Water 209 209 209 209 209 Average particle size (μm) 12.5 10.9 55.4 9.3 14.3 34.5

 Internal morphology of particles Porous Porous Porous Monoporous Nonporous Monoporous performance

 Ratio (hollow pore diameter / particle outer diameter) 0.04 0.04 0.03 0.74 0.98

 Porosity (%) 53.2 32.4 34.4 34.2 2.8 Unmeasurable value

10% compressive strength (MPa) 4.92 6.71 6.58 3.11 34.7 0.24 [Table 2] Example Comparative example

1 2 3 4 1 2 Structure (a) (b) (c) (d) (e) (f) Hole

Agent Ratio in ceramic composition 30 30 30 30 30 30 F A-axis 0.46 0.60 0.61 0.60 0.82 0.79 Thermal expansion coefficient

(X 10E-6 / ° C) B-axis 0.82 1.15 1.12 1.14 1.32 1.28

Porosity (%) 56 54 54 53 48 49

Claims

The scope of the claims  1. A porous ceramic characterized by shaping a predetermined molded body from a ceramic composition containing silicon carbide powder as a main component and containing hollow polymer particles as a pore-forming agent, and then firing the molded body. Manufacturing method of filter.  2. The porous ceramic filter according to claim 1, wherein the pore former comprises hollow polymer particles having an average particle size of 5 to: L 00 μπι, 10% compressive strength of 1.5 MPa or more. Method.  3. The method according to claim 1, wherein the pore former comprises hollow polymer particles having a plurality of hollow pores, and the pore diameter of the hollow pores is 0.5 times or less the outer diameter of the hollow polymer particles. 3. The method for producing a porous ceramic filter according to claim 2.