JP6701540B1 - Porous material for manufacturing porous ceramic filters - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a crack due to combustion heat of a pore forming agent in the production of a porous ceramic filter. In order to suppress the amount of heat generation, use of hollow particles and firing in a low oxygen atmosphere have been proposed. However, hollow particles are fragile, and equipment modification is required to create a low oxygen atmosphere. An object of the present invention is to provide a pore-forming material which is solid particles but can suppress heat generation even in the conventional firing process. SOLUTION: A self-ignition temperature is 350° C. or higher and 80% by mass or more of a monomer having one (meth)acryloyl group and 10% by mass or less of a monomer having two or more (meth)acryloyl groups are copolymerized. Solid particles containing a polymer contained as a component and further containing 0.5 to 5% by mass of polyvinyl alcohol on the surface, and exhibiting no heat generation in the range of 150 to 350° C. in differential thermal analysis. A pore-forming material for producing a porous ceramic filter. [Selection diagram] Figure 1

Description

TECHNICAL FIELD The present invention relates to a pore-forming material for producing a porous ceramic filter, which can suppress heat generation during firing.

In recent years, as a porous ceramic filter, a partition wall of a honeycomb structure made of cordierite or silicon carbide has a porous structure, and such a partition wall is allowed to pass through, thereby providing a filter function for a fluid such as gas. Various types of porous honeycomb filters provided have been proposed and put into practical use, for example, as a filter for collecting fine particles of exhaust gas discharged from diesel vehicles (diesel particulate filter). Further, with the tightening of exhaust gas regulations, the mounting of a similar filter (gasoline particulate filter) on a gasoline vehicle is under study.

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

As a method for improving the porosity, a method is generally used in which graphite particles or the like are added as a pore-forming material to the ceramic composition, and this is decomposed during the firing step to form the pores. However, if a large amount of pore-forming material is used in order to further improve the porosity, the filter is distorted due to an increase in combustion heat of the pore-forming material, which causes a problem that the filter is cracked.

To solve this problem, Patent Document 1 discloses that by using hollow polymer particles as a pore-forming material, the absolute amount of the polymer is reduced and the amount of heat generation is suppressed. Further, Patent Document 2 discloses that the calorific value is suppressed by preventing the gas generated by the decomposition of the pore-forming material from burning by performing the firing step in a low oxygen atmosphere.

JP, 2006-336021, A JP, 2010-001184, A

However, Patent Document 1 has a problem that when the hollow polymer particles are mixed or molded with the ceramic composition, the particles are easily broken by mechanical shearing force. In addition, since it is hollow, the number of manufacturing steps is larger than that of ordinary polymer particles, resulting in high cost. In Patent Document 2, a large-scale facility refurbishment is inevitable to make the firing process a low oxygen atmosphere. An object of the present invention is a porous ceramic which, while being solid particles obtained by a simple method, can suppress heat generation in the firing step, is easily uniformly dispersed in kneading, and can be used in the conventional firing step. It is to provide a pore forming material for manufacturing a filter.

The present inventors can suppress the amount of heat generated in the firing step by using a monomer having a high autoignition temperature as a monomer component of a polymer constituting the pore forming material, and further by allowing polyvinyl alcohol to be present on the surface of the pore forming material. The inventors have found that the dispersibility can be improved and have reached the present invention.

That is, the present invention is achieved by the following means.
(1) 90 % by mass or more of a monomer having a spontaneous ignition temperature of 350° C. or more and having one (meth)acryloyl group, and 10% by mass or less of a monomer having two or more (meth)acryloyl groups are copolymerized components. Solid particles containing 0.5 to 5% by mass of polyvinyl alcohol on the surface thereof, and not exhibiting heat generation in the range of 150 to 350° C. in differential thermal analysis. Porous material for the production of porous ceramic filters.
(2) The pore-forming material for producing a porous ceramic filter according to (1), wherein the spontaneous ignition temperature is 350° C. or higher and the monomer having one (meth)acryloyl group is methyl methacrylate.
(3) The pore-forming material for producing a porous ceramic filter according to (1) or (2), wherein the monomer having two or more (meth)acryloyl groups is ethylene glycol dimethacrylate.
(4) The pore-forming material for producing a porous ceramic filter according to any one of (1) to (3), which has an average particle diameter of 10 to 100 μm.
(5) The pore-forming material for producing a porous ceramic filter according to any one of (1) to (4), which contains 3 to 20 mass% of water with respect to the total mass.
(6) Manufacture of a porous ceramic filter characterized by firing a shaped article made of a ceramic composition containing the pore-forming material for manufacturing a porous ceramic filter according to any one of (1) to (5). Method.

The pore-forming material for producing a porous ceramic filter of the present invention can suppress the occurrence of cracks in the firing step, can be obtained by a simple method, and can be used in the conventional firing step. The pore former of the present invention having such performance is useful as a porous material for a ceramic structure made of cordierite, silicon carbide or the like, and for example, a diesel particulate filter or a gasoline particulate filter is produced. It can be used as a pore forming material.

FIG. 3 is a diagram showing a differential thermal analysis chart of Example 1. 6 is a diagram showing a differential thermal analysis chart of Comparative Example 1. FIG.

The present invention will be described in detail below. The pore-forming material for producing a porous ceramic filter of the present invention is a polymer having a spontaneous ignition temperature of 350° C. or higher and a monomer having one (meth)acryloyl group (hereinafter, also referred to as monomer A) as a copolymerization component. Is included. The removal of the pore-forming material is performed in the temperature rising process (also referred to as a degreasing process) up to the firing temperature. When the monomer gas is generated as a result, it is possible to suppress ignition and burning immediately. That is, heat is generated during decomposition, but heat is not generated by combustion, so strain due to overheating is suppressed, and the occurrence of cracks can be suppressed. The spontaneous ignition temperature of the monomer A is preferably 400° C. or higher.

The copolymerization ratio of the monomer A in the polymer is 80% by mass or more, preferably 85% by mass or more, and more preferably 90% by mass or more. Furthermore, when high mechanical strength is not required, it is also possible to employ 100% by mass of the monomer A. On the other hand, when mechanical strength is required, it is desirable to copolymerize a monomer for introducing a cross-linking structure as described below. Therefore, the copolymerization ratio of the monomer A is adjusted according to the copolymerization ratio. .. However, when the copolymerization ratio of the monomer A is less than 80% by mass, the amount of heat generation is insufficiently suppressed.

Examples of the monomer A include methyl methacrylate, ethyl methacrylate, methyl acrylate, and ethyl acrylate.

Further, in the above polymer, a monomer having two or more (meth)acryloyl groups (hereinafter, also referred to as monomer B) can be used as another copolymerization component. By using the monomer B, a crosslinked structure is generated in the polymer, so that the mechanical strength of the pore former can be increased. From this viewpoint, the copolymerization ratio of the monomer B is preferably 0.5% by mass or more, more preferably 1% by mass or more, further preferably 3% by mass or more, but in the case where high mechanical strength is not required. It is also possible to employ that the monomer B is not used. On the other hand, when a large amount of the monomer B is used, the amount of heat generated increases, so the copolymerization ratio is 10% by mass or less, preferably 8% by mass or less.

Examples of the monomer B include ethylene glycol dimethacrylate, ethylene glycol diacrylate, trimethylolpropane trimethacrylate, and the like.

The above-mentioned polymer may contain a monomer other than the above-mentioned two kinds of monomers as a copolymerization component as long as the effect of the present invention can be obtained. Examples of such a monomer include styrene, acrylonitrile, vinyl acetate and the like.

The pore-forming material for producing a porous ceramic filter of the present invention contains polyvinyl alcohol on its surface. Since the pore-forming material of the present invention contains the above-described monomer A and monomer B as main components, it has high hydrophobicity. However, since a water solvent is used when mixing and kneading the pore-forming material with the ceramic composition, the pore-forming material with high hydrophobicity tends to agglomerate into agglomerated particles, and the final pore size is It becomes uneven. Therefore, in the present invention, by making the surface of the pore-forming material contain highly hydrophilic polyvinyl alcohol, the pore-forming material is easily made compatible with water. This makes it easier to uniformly disperse the pore-forming material as primary particles in the ceramic composition without forming agglomerated particles.

The content of the polyvinyl alcohol is preferably 0.5 to 5% by mass, more preferably 1 to 3% by mass with respect to the mass of the above-mentioned polymer. When the content of polyvinyl alcohol is less than 0.5% by mass, a sufficient dispersion effect may not be obtained. Further, polyvinyl alcohol is contained in the pore-forming material by being added to the system during the polymerization reaction as described later, but when the amount of polyvinyl alcohol added is large, fine particles that are not effective in forming pores are generated. Many may be generated. From such a viewpoint, it is desirable that the content of polyvinyl alcohol be 5% by mass or less.

The polyvinyl alcohol is not particularly limited, and may be a completely saponified type or a partially saponified type, and both may be mixed. Specific examples include Kuraray Poval PVA-217, PVA-224, PVA-103, PVA-117, PVA-124, and PVA-424H manufactured by Kuraray Co., Ltd.

The pore-forming material for producing a porous ceramic filter of the present invention is solid particles. By being solid, it is possible to prevent the particles from being deformed or broken by mechanical shearing force when mixed or molded with the ceramic composition. Here, the solid particles in the present invention refer to particles that do not have a hollow structure or a porous structure, and specifically, voids are not confirmed when the cross section is observed by SEM at a magnification of 2000 times. Say

Furthermore, the pore-forming material for producing a porous ceramic filter of the present invention does not generate heat in the range of 150 to 350° C. in the differential thermal analysis under the conditions described later. Thereby, the generation of cracks in the firing process can be suppressed. Here, "does not show heat generation" means that the differential thermal analysis value does not become positive.

In the pore-forming material for producing a porous ceramic filter of the present invention, the average particle size determined by the method described below is preferably 10 to 100 µm, more preferably 12 to 85 µm, and further preferably 15 to 70 µm. This average particle size is more useful as a pore-forming material for a particulate filter.

Furthermore, when using for a particulate filter, it is desirable that the size of the holes to be formed be as uniform as possible. From this, it is desirable that the pore diameter of the porous ceramic filter manufacturing material of the present invention is as uniform as possible.

The pore-forming material for producing a porous ceramic filter of the present invention preferably contains water, and the content thereof is preferably 3 to 20% by mass, more preferably 4 to 15% by a measuring method described later. It is mass %, more preferably 5 to 8 mass %. Since it contains a certain amount of water, it becomes easy to uniformly disperse it when kneading it with the ceramic composition, and therefore it becomes easy to mix quickly.

The method for producing the pore-forming material for producing the porous ceramic filter of the present invention is not particularly limited, but for example, in a water medium containing polyvinyl alcohol, a polymerization initiator, the above-mentioned monomer A, monomer B and If necessary, other monomers may be added and dispersed, suspension polymerization may be performed, and the particle size distribution may be adjusted by classification. In suspension polymerization, solid particles are obtained unless a special formulation is used.

Further, the method for producing a porous ceramic filter using the pore-forming material for producing a porous ceramic filter of the present invention is not particularly limited, and for example, the pore-forming material of the present invention may be treated with a mixture of ceramic compositions. After shaping, it can be obtained by firing so that the pore former disappears. In addition, as a ceramic composition, a cordierite composition and a silicon carbide composition can be mentioned.

The cordierite composition is a MgO.Al ₂ O ₃ .SiO ₂ -based ceramics, and when preparing the cordierite composition, the ceramic raw material is not particularly limited. It can be prepared by blending silica powder typified by amorphous silica, kaolin, calcined kaolin, alumina, aluminum hydroxide and the like.

Similarly, a silicon carbide composition also includes a talc powder component such as talc or baked talc as an inorganic binder in silicon carbide powder, silica powder represented by amorphous silica, kaolin, calcined kaolin, boron oxide, and alumina. , Aluminum hydroxide and the like are appropriately mixed to prepare a ceramic composition containing silicon carbide powder as a main component.

In the method for producing a porous ceramic filter of the present invention, in the mixture of the ceramic composition and the pore-forming material of the present invention, the addition amount of the pore-forming material of the present invention is not particularly limited, but if it is too small, the pore-forming effect Is not observed, and if the content is too large, the strength of the ceramic molded body after firing is reduced, so a ratio of 10% by mass to 90% by mass in the mixture is preferable.

Further, the shaping method of the mixture is not particularly limited, for example, a columnar continuous shaped object having a cross-sectional shape of the shaped object to be obtained is shaped by an extrusion molding method, and this continuous shaped object is Examples thereof include a method of cutting into a size of a shaped article and a method of shaping by a press molding method. The ceramic composition is plasticized by adding a plasticizer, a binder and the like as in the conventional case.

The shaped product shaped as described above is usually dried and then calcined. The firing temperature varies depending on the composition of the ceramic composition, and when the cordierite composition is used, it is preferably 1380°C or higher and 1440°C or lower, and when the silicon carbide composition is used, it is preferably 1600°C or higher and 2200°C or lower.

Examples will be shown below for facilitating the understanding of the present invention, but these are merely examples, and the gist of the present invention is not limited thereto.

<Polyvinyl alcohol content>
300 g of water is added to 100 g of particles, stirred at 60° C. for 6 hours, and filtered. 1 to 2 g of the filtrate is accurately weighed (W1 [g]). It is dried with a hot air dryer at 120° C. for 2 hours, and the residue after drying is precisely weighed (W2 [g]). From the above results, the polyvinyl alcohol content [%] was calculated by the following formula.
Polyvinyl alcohol content [%]=[{(300/W1)×W2}/100]×100

<Differential thermal analysis>
DTA was evaluated using DTG-60 manufactured by Shimadzu Corporation. Whether 4 to 6 mg of particles are weighed in an aluminum cell, and the temperature inside the device is raised from 35°C to 500°C at a heating rate of 10°C/min under an air flow to show heat generation in the range of 150°C to 350°C. Was evaluated.

<Dispersibility in water (hydrophilicity)>
0.5 g of dried particles was gently added to 50 g of water, and the time from the introduction until all the particles on the water surface were dispersed in water was measured and judged according to the following criteria. When the judgment is ⊚ or ◯, it is easy to uniformly disperse the particles in the ceramic composition as primary particles without aggregating.
⊚: Disperses within 5 minutes ◯: Disperses within 10 minutes ×: Particles remain on the water surface even at 20 minutes

<Average particle diameter (D50)>
From the volume-based particle size distribution obtained by measurement using a Shimadzu SALD2300, a volume-based cumulative percentage equivalent 50% particle size was determined, and this was taken as the average particle size.

<Water content>
About 1 to 2 g of sample particles are precisely weighed (W3 [g]). The particles are dried for 2 hours at 120° C. in a hot air dryer, and the dried particles are precisely weighed (W4 [g]). From the above results, the water content [%] is calculated by the following formula.
Water content [%]=(W3−W4)/W4×100

[Example 1]
263.2 parts by mass of methyl methacrylate and 16.8 parts by mass of ethylene glycol dimethacrylate as monomers and 1.1 parts by mass of dilauroyl peroxide as an initiator were dissolved in a monomer dispersion tank. Next, 712.2 parts by mass of water and 6.7 parts by mass of Kuraray Poval PVA-217 (manufactured by Kuraray Co., Ltd.) were added and dispersed for 1 minute with a homomixer, and then polymerized at 70° C. for 70 minutes while stirring. Then, it was subjected to centrifugal dehydration to obtain solid particles of Example 1. The spontaneous ignition temperature of methyl methacrylate is 421°C.

[Example 2]
Solid particles of Example 2 were obtained in the same manner as in Example 1 except that the amounts of the monomers used were changed to 252 parts by mass of methyl methacrylate and 28 parts by mass of ethylene glycol dimethacrylate. ..

[Example 3]
A solid of Example 3 was prepared in the same manner as in Example 1, except that the amounts of the monomers used in Example 1 were changed to 277.2 parts by mass of methyl methacrylate and 2.8 parts by mass of ethylene glycol dimethacrylate. The particles were obtained.

[Example 4]
Solid particles of Example 4 were obtained in the same manner as in Example 1 except that the amount of the monomer blended was changed to 280 parts by mass of methyl methacrylate.

[Example 5]
Solid particles of Example 5 were obtained in the same manner as in Example 1, except that the amount of PVA-217 added was changed to 3.0 parts by mass.

[Example 6]
Solid particles of Example 6 were obtained in the same manner as in Example 1 except that PVA-217 was changed to Kuraray Poval PVA-224 (manufactured by Kuraray Co., Ltd.).

[Comparative Example 1]
The solid particles of Comparative Example 1 were obtained in the same manner as in Example 1, except that the amount of the monomer blended was changed to 196 parts by mass of methyl methacrylate and 84 parts by mass of ethylene glycol dimethacrylate. .

[Comparative example 2]
Solid particles of Comparative Example 2 were obtained in the same manner as in Example 1, except that the monomer methyl methacrylate was changed to butyl acrylate. The spontaneous ignition temperature of butyl acrylate is 292°C.

[Comparative Example 3]
The particles obtained in Example 1 were mixed with water in an amount 3 times the particle mass, stirred at 60° C. for 6 hours, and centrifuged to obtain solid particles of Comparative Example 3.

Table 1 shows the evaluation results of the particles obtained in the above-mentioned Examples and Comparative Examples. Further, differential thermal analysis charts of the particles obtained in Example 1 and Comparative Example 1 are shown in FIGS.

Each of the particles of Examples 1 to 6 does not generate heat in the range of 150 to 350° C. in the differential thermal analysis, has good dispersibility in water, and is suitable as a pore-forming material for producing a porous ceramic filter. It was something. On the other hand, in Comparative Example 1, the amount of the monomer having two or more (meth)acryloyl groups was too large, and in Comparative Example 2, the monomer having a low self-ignition temperature was used, so that the calorific value was too large. .. Furthermore, in Comparative Example 3, the amount of polyvinyl alcohol on the surface was too small, so that the dispersibility in water was poor.

Moreover, 30 parts by mass of the particles of Example 1, 90% by mass of SiC, 5% by mass of boron oxide, 2% by mass of kaolin, 70 parts by mass of a ceramic composition consisting of 3% by mass of alumina, 15 parts by mass of methylcellulose and mixed water were mixed and kneaded. Then, the kneaded material was extrudable. At this time, the solid particles of Example 1 were not formed into agglomerated particles and could be well dispersed. Then, the obtained kneaded material was formed into a cylindrical honeycomb structure having a rib thickness of 430 μm, a cell number of 16 pieces/cm ² , a diameter of 118 mm and a height of 152 mm by a known extrusion molding method. After the obtained honeycomb structure is dried, a degreasing process is performed at a temperature rising rate of 40° C./h and 500° C. for 1 hour, and further, it is fired in an inert gas atmosphere at 2100° C. for a holding time of 2 hours to obtain a porous structure. A quality ceramic filter was obtained. When the obtained filter was visually observed, it did not have cracks.

On the other hand, in the above-described method for producing a porous ceramic filter, the filter produced by using the particles of Comparative Example 1 and the particles of Comparative Example 2 instead of the particles of Example 1 had cracks.

Claims (6)

90 % by mass or more of a monomer having a self-ignition temperature of 350° C. or more and having one (meth)acryloyl group, and 10% by mass or less of a monomer having two or more (meth)acryloyl groups as copolymerization components. It is a solid particle containing a polymer and further containing 0.5 to 5% by mass of polyvinyl alcohol on the surface, and showing no heat generation in the range of 150 to 350° C. in the differential thermal analysis. Porous material for the production of porous ceramic filters.
The pore-forming material for producing a porous ceramic filter according to claim 1, wherein the monomer having a spontaneous ignition temperature of 350°C or higher and having one (meth)acryloyl group is methyl methacrylate. The pore-forming material for producing a porous ceramic filter according to claim 1 or 2, wherein the monomer having two or more (meth)acryloyl groups is ethylene glycol dimethacrylate. The pore-forming material for producing a porous ceramic filter according to any one of claims 1 to 3, which has an average particle diameter of 10 to 100 µm. The porous material for producing a porous ceramic filter according to any one of claims 1 to 4, which contains 3 to 20% by mass of water. A method for producing a porous ceramic filter, comprising: firing a shaped article made of a ceramic composition containing the pore-forming material for producing a porous ceramic filter according to any one of claims 1 to 5.

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