JP2005067943A - Pore forming material for ceramic composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pore forming material for a ceramic composition which hardly destructs particles in the mixing or the forming of the ceramic composition and can easily obtain a ceramic formed body having large porosity. <P>SOLUTION: This pore forming material comprises at least one kind of particles selected from the group consisting of hollow resin particles, thermally expanded microcapsules and a mixture of the thermally expanded microcapsules with thermally expandable microcapsules in which the particles having ≥20 μm diameter occupy ≥20% frequency in a particle distribution shown by number frequency and the absolute specific gravity is <0.04. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pore former for a ceramic composition used for forming, for example, a porous ceramic filter.

  In recent years, as a porous ceramic filter, the honeycomb structure made of cordierite has a porous structure, and a porous structure is allowed to pass through such a partition to provide a filter function for a fluid such as a gas. Porous honeycomb filters have been developed, and are used, for example, as filters for collecting particulates of exhaust gas discharged from diesel vehicles (diesel particulate filters).

  In such a porous ceramic filter, the average pore diameter and porosity of the porous material are very important factors that determine the performance of the filter, and are particularly suitable for porous ceramic filters such as a diesel particulate filter. Therefore, a filter having a large average pore diameter and high porosity has been demanded from the relationship between the collection efficiency of exhaust gas particulates, pressure loss, and collection time.

  Conventionally, in order to achieve such a demand, a method using a pore former has been studied. For example, a porous ceramic filter can be obtained by firing a ceramic molded body (ceramic composition) containing various pore formers at a high temperature. At this time, in order to obtain a ceramic filter having excellent quality, it is also required to mold the ceramic molded body with high dimensional accuracy.

Various attempts have been made to satisfy such demands. For example, a method for producing a porous ceramic with high dimensional accuracy by using graphite as a pore former is disclosed.
JP-A-5-330943

  However, even in the above porous ceramic manufacturing method, the unfired ceramic composition is difficult to maintain an appropriate plasticity suitable for forming, so that the fluidity decreases with time and becomes fragile. There is a problem that it is difficult to stably form a high-quality ceramic molded body. In addition, when mixing (kneading) or forming the ceramic composition, the pore former may be destroyed and the pore former may not function sufficiently. In particular, resin particles and hollow particles having low combustion energy are easily destroyed.

  In view of the above problems, an object of the present invention is to provide a pore former for a ceramic composition, in which particles are not easily broken during mixing or molding of the ceramic composition, and a ceramic molded body having a high porosity can be easily obtained. There is to do.

  The pore former for ceramic composition according to the invention of the present invention (the present invention) is selected from the group consisting of hollow resin particles, thermally expanded microcapsules and a mixture of thermally expanded microcapsules and thermally expandable microcapsules. In the particle size distribution of at least one kind of particles, and the particle size distribution as seen by number frequency%, particles having a size of 20 μm or more occupy a frequency of 20% or more.

  According to a second aspect of the present invention, there is provided the pore former for a ceramic composition according to the first aspect, wherein the true specific gravity is less than 0.04 in the pore former for the ceramic composition according to the first aspect.

  According to a third aspect of the present invention, there is provided a pore former for a ceramic composition according to the first or second aspect of the present invention, wherein the microcapsule after thermal expansion is 50% by weight of a nitrile monomer. The non-nitrile monomer is formed by a polymer obtained from a monomer composition containing 49.9% by weight or less of a non-nitrile monomer and 0.05 to 2% by weight of a bifunctional or higher functional crosslinker and / or a long side chain crosslinker. A heat-expandable microcapsule composed of a volatile expansion agent encapsulated in the outer shell that is gaseous at a temperature below the softening point of the polymer, and has a particle size Is 1 to 150 μm, and the expansion ratio is 20 to 100 times.

  In the pore forming material for ceramic composition of the present invention (hereinafter sometimes simply referred to as “pore forming material”), particles having a particle size of 20 μm or more occupy a frequency of 20% or more in the particle size distribution in terms of number frequency%. is required.

  Usually, in the particle size distribution of the pore former (particles), an average particle size or the like is often expressed by volume frequency%. In this case, if the pore former is made of, for example, a thermally expanded microcapsule, and the unexpanded thermally expandable microcapsule is mixed, the volume of the thermally expanded microcapsule is not expanded. Since it is very large compared to the volume of the capsule, the volume frequency% of the thermally expanded microcapsules is large, and the number of unexpanded thermally expandable microcapsules is at most a small volume frequency%. There is a case.

  In the pore former according to the present invention, particles having a size of 20 μm or more occupy a frequency of 20% or more in the particle size distribution of the number frequency%, so that the presence of particles having a small volume is small. Therefore, when the pore former of the present invention is used for a ceramic composition, since the number of particles having an effective particle size is large, a ceramic molded body having a large porosity can be easily obtained.

  The pore former of the present invention was used for a ceramic composition when the particle size distribution as seen by number frequency% was such that particles of 20 μm or more accounted for less than 20% of the frequency. In this case, the number of particles having an effective particle size is insufficient, and a ceramic molded body having a large porosity cannot be obtained.

  The method for measuring the particle size distribution in terms of the number frequency% may be any particle size distribution measuring method and is not particularly limited. For example, the pore former to be measured is dispersed in an aqueous medium. It is preferable to prepare a water-based medium dispersion and measure the particle size distribution of the particles in the water-based medium dispersion using a particle size distribution measuring apparatus using a laser diffraction scattering method. At this time, in the particle size distribution display software attached to the measuring instrument, by switching the particle size distribution normally displayed in terms of volume to the particle size distribution displayed in terms of number, it is possible to obtain the particle size distribution in terms of number frequency%. . Based on the data thus output, it may be determined whether or not particles having a size of 20 μm or more occupy a frequency of 20% or more in the particle size distribution in terms of the number frequency%.

  In addition, the pore former of the present invention may be used as it is when particles having a particle size distribution of 20 μm or more in the particle size distribution as viewed by number frequency% occupy a frequency of 20% or more. In the case where particles having a particle size of 20 μm or more occupy only a frequency of less than 20%, for example, sieving, classification by specific gravity, etc. are performed so that particles of 20 μm or more in the particle size distribution occupy a frequency of 20% or more. Just do it.

  The classification based on the specific gravity is performed, for example, by dispersing the pore-forming material to be classified in water, removing particles that have settled in water, and collecting the particles that have floated on the water surface, with an opening of about 15 to 60 μm, preferably an opening. Washing with running water on a mesh surface of metal, plastic, cloth or the like of about 32 μm may be performed by continuing the cleaning while updating the mesh surface until the washing water does not become cloudy.

  The pore former of the present invention preferably has a true specific gravity of less than 0.04. By setting the true specific gravity of the pore former to less than 0.04, when the pore former of the present invention is used for a ceramic composition, a ceramic molded body having a higher porosity can be obtained. When the true specific gravity of the pore former of the present invention is 0.04 or more, it may not be possible to obtain a ceramic molded body having a higher porosity when used for a ceramic composition.

  The pore former of the present invention is hollow as long as particles having a particle size of 20 μm or more occupy a frequency of 20% or more and preferably a true specific gravity of less than 0.04 in the particle size distribution in terms of number frequency%. It may consist of any of resin particles, thermally expanded microcapsules, and a mixture of thermally expanded microcapsules and thermally expandable microcapsules. The hollow resin particles, the thermally expanded microcapsules and the mixture of the thermally expanded microcapsules and the thermally expandable microcapsules may be used alone or in combination of two or more.

  Among the hollow resin particles, thermally expanded microcapsules, and mixtures of thermally expanded microcapsules and thermally expandable microcapsules, the pore former of the present invention includes 50% by weight or more of a nitrile monomer and a non-nitrile monomer 49. An outer shell formed by a polymer obtained from a monomer component containing 9% by weight or less and a bifunctional or higher functional crosslinker and / or a long side chain crosslinker of 0.05 to 2% by weight; It is formed by heating and foaming a thermally expandable microcapsule composed of a volatile expansion agent enclosed in the outer shell that becomes gaseous at a temperature below the softening point, and has a particle size of 1 to 150 μm and foamed. It is preferably made of thermally expanded microcapsules with a magnification of 20 to 100 times.

  By making the pore-forming material of the present invention composed of such heat-expanded microcapsules, the pore-forming material of the present invention has a frequency of 20% or more of particles having a particle size of 20 μm or more in the particle size distribution in terms of number frequency%. When it is used as a ceramic composition, the true specific gravity is easily less than 0.04 and the number of unexpanded thermally expandable microcapsules is reduced. A ceramic molded body having a higher porosity can be obtained more easily.

  The monomer component used to obtain the polymer that forms the outer shell of the thermally expandable microcapsule is a nitrile monomer of 50% by weight or more, a non-nitrile monomer of 49.9% by weight or less, and a bifunctional or more functional crosslinking agent. And / or a monomer component containing 0.05 to 2% by weight of a crosslinking agent having a long side chain, more preferably 89.5 to 99.95% by weight of a nitrile monomer, and 0 to 10% by weight of a non-nitrile monomer. % And a monomer component containing 0.05 to 2% by weight of a bifunctional or higher functional crosslinker and / or a long side chain crosslinker.

  The nitrile monomer is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, and among them, acrylonitrile and methacrylonitrile are preferably used. These nitrile monomers may be used alone or in combination of two or more. These nitrile monomers are preferably nitrile monomers that do not contain halogen.

  When the content of the nitrile monomer in the monomer component is less than 50% by weight, the mechanical properties such as the mechanical strength of the outer shell formed by the polymer obtained from the monomer component and the thermally expandable microcapsule are increased. It may be insufficient.

  The non-nitrile monomer is not particularly limited. For example, acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and dicyclopentenyl acrylate, methyl methacrylate, ethyl methacrylate, Examples thereof include methacrylic acid esters such as butyl methacrylate and isobornyl methacrylate, styrenes such as styrene and α-methylstyrene, vinyl acetate and the like. Among these, vinyl acetate is preferably used. These non-nitrile monomers may be used alone or in combination of two or more. These non-nitrile monomers are preferably non-nitrile monomers that do not contain halogen.

  When the content of the non-nitrile monomer in the monomer component exceeds 49.9% by weight, the mechanical strength of the outer shell formed by the polymer obtained from the monomer component and the mechanical strength of the thermally expandable microcapsule, etc. The physical properties may be insufficient.

  The bifunctional or higher functional crosslinking agent is not particularly limited. For example, divinyl ether, divinylbenzene, diallylamine, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, trimethylolpropane. Trimethacrylate, glycerin dimethacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, triethylene glycol diacrylate, dimethylol tricyclodecane diacrylate, trimethylol Propanetriacrylate, pentaerythritol triacrylate, trimethylolpropane acrylate benzoate, 2-hydro Shi-3-acryloyloxy propyl methacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hexaacrylate, dipentaerythritol hexa methacrylate. These bifunctional or higher functional crosslinking agents may be used alone or in combination of two or more.

  The crosslinking agent having a long side chain is not particularly limited. For example, PEG # 200 (polyethylene glycol having a number average molecular weight of 200) diacrylate, PEG # 400 (polyethylene glycol having a number average molecular weight of 400) Diacrylate, PEG # 600 (polyethylene glycol having a number average molecular weight of 600) diacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, dimethylol tricyclodecane diacrylate EO (ethylene oxide) modified trimethylolpropane triacrylate, PEG # 200 dimethacrylate, PEG # 400 dimethacrylate, PEG # 600 dimethacrylate, and the like. These crosslinking agents having a long side chain may be used alone or in combination of two or more.

  The bifunctional or higher functional crosslinking agent and the crosslinking agent having a long side chain may be used alone or in combination.

  When the content of the bifunctional or higher functional crosslinking agent and / or the long side chain crosslinking agent in the monomer component is less than 0.05% by weight, crosslinking of the polymer obtained from the monomer component is sufficiently advanced. However, the outer shell formed by this polymer and thus the mechanical properties such as the mechanical strength of the thermally expandable microcapsule may be insufficient, and conversely, the bifunctional or higher functional crosslinking agent in the monomer component and / or Or, if the content of the crosslinking agent having a long side chain exceeds 2% by weight, the crosslinking density of the polymer obtained from this monomer component becomes too high, and the outer shell formed by this polymer and thus the thermally expandable microcapsule It may become too hard and the thermally expandable microcapsules may not sufficiently expand.

  In the heat-expandable microcapsule, a volatile expansion agent that becomes gaseous at a temperature equal to or lower than the softening point of the polymer is enclosed in an outer shell formed of a polymer obtained from the monomer component.

  The volatile swelling agent may be any volatile swelling agent as long as it is gaseous at a temperature below the softening point of the polymer, and is not particularly limited. Low molecular weight hydrocarbons such as ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, petroleum ether, tetramethylsilane, trimethylethylsilane, trimethyl Examples include alkyl silanes such as isopropyl silane and trimethyl-n-propyl silane, compounds that are thermally decomposed by heating and become gaseous. Among them, n-butane, isobutane, n-pentane, isopentane, n-hexane, Petroleum ether or the like is preferably used. These volatile swelling agents may be used alone or in combination of two or more.

The method for producing the thermally expandable microcapsules is not particularly limited. For example, the monomer component is mixed with the volatile swelling agent and the polymerization initiator to prepare a monomer solution, and the monomer solution is appropriately mixed. A known production method may be used in which suspension polymerization is carried out in an aqueous dispersion medium containing a dispersion stabilizer and, if necessary, an auxiliary stabilizer.
Japanese Examined Patent Publication No. 42-26524

  The polymerization initiator may be a polymerization initiator generally used for suspension polymerization, and is not particularly limited, but is preferably an oil-soluble polymerization initiator that is soluble in the monomer component used. Examples thereof include dialkyl oxide, diacyl peroxide, peroxyester, peroxydicarbonate, and azo compound.

  Specific examples of the polymerization initiator are not particularly limited. For example, dialkyl peroxides such as methyl ethyl peroxide, di-t-butyl peroxide, and dicumyl peroxide, isobutyl peroxide, and benzoyl peroxide. Diacyl peroxide such as oxide, 2,4-dichlorobenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, t-butyl peroxypivalate, t-hexyl peroxypivalate, t-butyl peroxyneo Decanoate, t-hexylperoxyneodecanoate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, 1,1,3,3,3-tetramethylbutylperoxyneodecanoate, kumi Ruperoxyneodecanoate, (α, α-bisneodecane Peroxyesters such as (noylperoxy) diisopropylbenzene, bis (4-t-butylcyclohexyl) peroxydicarbonate, di-n-propyloxydicarbonate, di-isopropylperoxydicarbonate, di (2-ethylethylperoxy) Oxy) dicarbonate, dimethoxybutylperoxydicarbonate, peroxydicarbonate such as di (3-methyl-3-methoxybutylperoxy) dicarbonate, 2,2′-azobisisobutyronitrile, 2,2 ′ -Azo compounds such as azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), 1,1'-azobis (1-cyclohexanecarbonitrile), etc. Is mentioned. These polymerization initiators may be used alone or in combination of two or more.

  The dispersion stabilizer may be a dispersion stabilizer generally used for suspension polymerization, and is not particularly limited. For example, silica such as colloidal silica, magnesium hydroxide, aluminum hydroxide, hydroxide hydroxide Examples thereof include diiron, calcium phosphate, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, barium carbonate, and magnesium carbonate. These dispersion stabilizers may be used alone or in combination of two or more.

  Although the usage-amount of the said dispersion stabilizer is not specifically limited, It is preferable that it is 0.1-20 weight part of dispersion stabilizers with respect to 100 weight part of monomer components.

  The auxiliary stabilizer may be an auxiliary stabilizer generally used for suspension polymerization, and is not particularly limited. For example, a condensation product of diethanolamine and aliphatic dicarboxylic acid, urea and formaldehyde Condensation products, water-soluble nitrogen-containing compounds such as polyvinylpyrrolidone and polyethyleneimine, polyethylene oxide, gelatin, methylcellulose, polyvinyl alcohol, dioctylsulfosuccinate, sorbitan ester, various emulsifiers and the like can be mentioned. These auxiliary stabilizers may be used alone or in combination of two or more.

  An aqueous dispersion medium containing a dispersion stabilizer, an auxiliary stabilizer and the like is prepared by blending a dispersion stabilizer, an auxiliary stabilizer and the like with water such as deionized water. The pH of the aqueous phase (aqueous dispersion medium) at the time of suspension polymerization is not particularly limited, and can be appropriately determined depending on the type of dispersion stabilizer and auxiliary stabilizer used. For example, when silica such as colloidal silica is used as the dispersion stabilizer, suspension polymerization is performed in an acidic environment. In order to make the aqueous phase acidic, an acid such as hydrochloric acid may be added as necessary to adjust the pH of the aqueous phase to 3-4. For example, when using magnesium hydroxide, calcium phosphate or the like as a dispersion stabilizer, suspension polymerization is performed in an alkaline environment. In order to make the aqueous phase alkaline, the pH of the aqueous phase may be adjusted to 10 to 11 by adding an alkali such as aqueous ammonia or potassium hydroxide as necessary.

  An example of a preferred combination of a dispersion stabilizer and an auxiliary stabilizer is, for example, a combination of colloidal silica and a condensation product. The colloidal silica may be used alone, or two or more types having different particle diameters may be used in combination. The condensation product is not particularly limited. For example, a condensation product of diethanolamine and an aliphatic dicarboxylic acid is preferably used. Among them, a condensation product of diethanolamine and adipic acid or diethanolamine and A condensation product with itaconic acid is more preferably used. These condensation products may be used alone or in combination of two or more.

  By using such a combination of dispersion stabilizer and auxiliary stabilizer, a thermally expandable microcapsule having a uniform particle shape can be obtained. At this time, for example, by using an inorganic salt such as sodium chloride or sodium sulfate in combination, a thermally expandable microcapsule having a more uniform particle shape can be obtained.

  The amount of colloidal silica used in the above combination may be appropriately adjusted depending on the particle diameter, and is not particularly limited, but is preferably 1 to 20 parts by weight of colloidal silica with respect to 100 parts by weight of the monomer component. More preferably, it is 2 to 10 parts by weight. Further, the amount of the condensation product used in the above-mentioned combination may be appropriately adjusted depending on the kind thereof, and is not particularly limited, but is 0.05 to 2 parts by weight of the condensation product with respect to 100 parts by weight of the monomer component. It is preferable that Furthermore, the usage-amount of inorganic salt should just be adjusted suitably with the kind, Although it does not specifically limit, It is preferable that it is 0-100 weight part of inorganic salt with respect to 100 weight part of monomer components.

  Other examples of the preferred combination of the dispersion stabilizer and the auxiliary stabilizer include, for example, a combination of colloidal silica and a water-soluble nitrogen-containing compound. The colloidal silica may be used alone, or two or more types having different particle diameters may be used in combination. The water-soluble nitrogen-containing compound is not particularly limited. For example, polyvinyl pyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, tetramethylammonium hydroxide, polydimethylaminoethyl methacrylate, polydimethylaminoethyl acrylate, etc. Polydialkylaminoalkyl (meth) acrylate represented by polydimethylaminopropyl acrylamide, polydimethylaminopropyl acrylamide represented by polydimethylaminopropyl methacrylamide, polyacrylamide, polycationic acrylamide, polyamine sal Phon and polyallylamine are mentioned, and among them, polyvinylpyrrolidone is preferably used. These water-soluble nitrogen-containing compounds may be used alone or in combination of two or more.

  When using a combination of the above colloidal silica and a water-soluble nitrogen-containing compound, preferably polyvinylpyrrolidone, the particle size of the thermally expandable microcapsule is adjusted using colloidal silica and / or a water-soluble nitrogen-containing compound, preferably polyvinylpyrrolidone. However, it is preferable to adjust the amount of the water-soluble nitrogen-containing compound, preferably polyvinylpyrrolidone, because it is easy to handle.

  Furthermore, as another example of a preferable combination of the dispersion stabilizer and the auxiliary stabilizer, for example, a combination of magnesium hydroxide or calcium phosphate and various emulsifiers may be mentioned.

  The order of adding each of the above components to the aqueous dispersion medium may be arbitrary, and is not particularly limited. Usually, water such as deionized water, a dispersion stabilizer, and auxiliary stabilizing if necessary are used in the polymerization reactor. An aqueous dispersion medium containing a dispersion stabilizer and an auxiliary stabilizer is prepared by charging the agent. If necessary, a compound such as alkali metal nitrite, stannous chloride, stannic chloride, potassium dichromate, etc. is added.

  The monomer component and the volatile swelling agent may be added separately to the aqueous dispersion medium to form an oily mixture in the aqueous dispersion medium, but usually the monomer component and the volatile swelling agent are mixed in advance. After forming the oily mixture, the oily mixture is added to the aqueous dispersion medium.

  The polymerization initiator may be added in advance to the oily mixture, but the polymerization initiator may be added after stirring the aqueous dispersion medium and the oily mixture in the polymerization reactor. Alternatively, the aqueous dispersion medium and the oily mixture may be stirred and mixed in a separate container, and then the mixture may be charged into the polymerization reactor.

  A ceramic composition obtained by mixing the pore former of the present invention with a ceramic raw material such as an inorganic mixture can be usually formed into a ceramic molded body having an appropriate shape by extrusion molding or the like. Next, the formed ceramic molded body is dried and then fired to produce a porous ceramic molded body such as a porous ceramic filter.

  The pore former for ceramic composition of the present invention comprises at least one kind of particles selected from the group consisting of hollow resin particles, thermally expanded microcapsules and a mixture of thermally expanded microcapsules and thermally expandable microcapsules. In addition, in the particle size distribution in terms of the number frequency%, particles of 20 μm or more occupy a frequency of 20% or more, so that the particles are not easily broken when mixing or forming the ceramic composition, and the porosity is high. A ceramic molded body can be easily obtained.

  The pore former for a ceramic composition of the present invention has a true specific gravity of less than 0.04 and / or a nitrile monomer of 50 wt% or more, a non-nitrile monomer of 49.9 wt% or less, and An outer shell formed by a polymer obtained from a monomer component containing 0.05 to 2% by weight of a bifunctional or higher functional crosslinker and / or a long side chain crosslinker, and gaseous at a temperature below the softening point of the polymer. It is formed by thermally foaming a thermally expandable microcapsule composed of a volatile expansion agent enclosed in the outer shell, and has a particle size of 1 to 150 μm and an expansion ratio of 20 to 100 times. By making the microcapsule after thermal expansion, the above-described effect is more sure.

  In order to describe the present invention in more detail, examples are given below, but the present invention is not limited to these examples.

(Example 1)
A monomer component was prepared by stirring and mixing 49 parts by weight of acrylonitrile, 49 parts by weight of methyl methacrylate, 1.8 parts by weight of vinyl acetate, and 0.2 parts by weight of divinylbenzene. Next, 11 parts by weight of isobutane, 8 parts by weight of n-pentane and 1.5 parts by weight of azobisisobutyronitrile were added to 100 parts by weight of the monomer component, and the mixture was stirred and mixed to prepare a monomer solution. Also, 300 parts by weight of deionized water, 60 parts by weight of an aqueous dispersion of silica (solid content 20% by weight), 0.1 parts by weight of sodium nitrite, 0.5 parts by weight of polyvinylpyrrolidone, 100 parts by weight of sodium chloride and 0 parts of hydrochloric acid An aqueous dispersion medium was prepared by stirring and mixing 4 parts by weight. Next, the monomer solution and the aqueous dispersion medium were mixed, ion exchange water was further added, and the mixture was stirred and mixed with a homogenizer to prepare a suspended monomer solution.

  On the other hand, ion-exchanged water was charged into a 20 liter polymerization reactor equipped with a stirrer, a jacket, a reflux condenser and a thermometer. Next, stirring was started, the inside of the polymerization reactor was depressurized and deoxygenated, then nitrogen gas was injected to return the pressure to atmospheric pressure, and the inside of the polymerization reactor was filled with a nitrogen gas atmosphere. The turbid monomer solution was charged all at once into the polymerization reactor, and the polymerization reactor was heated to 80 ° C. to initiate the polymerization reaction. The polymerization reaction was completed in 5 hours, and after a aging period of 1 hour, the polymerization reactor was cooled to room temperature. The obtained slurry was dehydrated with a dehydrator (centre) and then sufficiently dried to produce thermally expandable microcapsules. Next, the thermally expandable microcapsules obtained were thermally expanded in heated dry air to produce thermally expanded microcapsules. Then, the thermally expanded microcapsules were dispersed in water, and then on a 390 mesh wire mesh. Particles having a small particle diameter were removed to such an extent that the filtrate did not become cloudy with running water, and dried to produce a pore former.

(Example 2)
A monomer component was prepared by stirring and mixing 66 parts by weight of acrylonitrile, 30 parts by weight of methacrylonitrile, 3.7 parts by weight of vinyl acetate, and 0.3 parts by weight of divinylbenzene. Next, 20 parts by weight of n-pentane and 1.5 parts by weight of azobisisobutyronitrile were added to 100 parts by weight of the monomer component, and the mixture was stirred and mixed to prepare a monomer solution. A suspended monomer solution was prepared in the same manner as in Example 1 except that this monomer solution was used.

  A thermally expandable microcapsule, a thermally expanded microcapsule, and a pore former were prepared in the same manner as in Example 1 except that the suspension monomer solution was used.

(Comparative Example 1)
A monomer component was prepared by stirring and mixing 8 parts by weight of acrylonitrile and 92 parts by weight of methyl methacrylate. Next, 11 parts by weight of isobutane, 8 parts by weight of n-pentane and 1.5 parts by weight of azobisisobutyronitrile were added to 100 parts by weight of the monomer component, and the mixture was stirred and mixed to prepare a monomer solution. A suspended monomer solution was prepared in the same manner as in Example 1 except that this monomer solution was used.

  A thermally expandable microcapsule and a thermally expanded microcapsule were produced in the same manner as in Example 1 except that the suspension monomer solution was used. Next, the obtained heat-expanded microcapsules were dried as they were without removing small-diameter particles with running water to produce a pore former.

(Comparative Example 2)
A monomer component was prepared by stirring and mixing 20 parts by weight of acrylonitrile, 20 parts by weight of methacrylonitrile and 60 parts by weight of methyl methacrylate. Next, 11 parts by weight of isobutane, 8 parts by weight of n-pentane and 1.5 parts by weight of azobisisobutyronitrile were added to 100 parts by weight of the monomer component, and the mixture was stirred and mixed to prepare a monomer solution. A suspended monomer solution was prepared in the same manner as in Example 1 except that this monomer solution was used.

  A thermally expandable microcapsule and a thermally expanded microcapsule were produced in the same manner as in Example 1 except that the suspension monomer solution was used. Next, the obtained heat-expanded microcapsules were dried as they were without removing small-diameter particles with running water to produce a pore former.

  Using a laser diffraction / scattering particle size distribution meter (trade name “HORIBA LA910”, manufactured by HORIBA, Ltd.), the particle size of each pore former obtained in Example 1 and Example 2 and Comparative Example 1 and Comparative Example 2 was used. Was measured, and the frequency of particles of 20 μm or more in the particle size distribution in terms of the number frequency% was obtained. The results are shown in Table 1.

  Next, each pore-forming material obtained in Examples 1 and 2 and Comparative Example 1 and Comparative Example 2 in which 283 g of cordierite, 14.2 g of methyl cellulose and water were contained as ceramic raw materials After mixing 42.5 g of the material (15% by weight of material and 85% by weight of water) to prepare an extrudable ceramic composition, the resulting ceramic composition was shaped by an extrusion method to obtain an unfired ceramic. A formed body (kneaded material) was formed.

  Subsequently, the clay density of the obtained ceramic molded body (kneaded clay) was measured by the following method, and the resistance to breakage of the pore former was evaluated. The results are shown in Table 1.

[Measurement method of dredged soil density]
After cutting the ceramic molded body (kneaded material) to a constant volume and measuring its weight, the measured weight is divided by the volume to calculate the kneaded clay density. The resistance to destruction was evaluated. The lower the dredged soil density, the better the resistance to breakage of the pore former.
[Criteria]
◎ ...... The soil density is less than 1.4 g / cm ³ .
○ The soil density is 1.4 g / cm ³ or more and less than 1.6 g / cm ³ .
Δ: The clay density is 1.6 g / cm ³ or more and less than 1.7 g / cm ³ .
X ... The soil density is 1.7 g / cm ³ or more.

  As is clear from Table 1, the pore formers of Example 1 and Example 2 according to the present invention each had a low clay density and an excellent resistance to fracture. In contrast, the pore formers of Comparative Example 1 and Comparative Example 2 in which the frequency of particles having a particle size of 20 μm or more in the particle size distribution in terms of number frequency% was less than 20% both had high clay density and resistance to fracture. Was bad.

  As described above, the pore former for ceramic composition of the present invention is less likely to break particles during mixing or molding of the ceramic composition, and a ceramic molded body having a large porosity can be easily obtained. It is suitably used as a pore former to be contained in a ceramic composition for producing various porous ceramic molded bodies such as porous ceramic filters.

Claims (3)

  In the particle size distribution consisting of at least one kind of particles selected from the group consisting of hollow resin particles, thermally expanded microcapsules and a mixture of thermally expanded microcapsules and thermally expandable microcapsules, A pore former for a ceramic composition, characterized in that particles of 20 μm or more occupy a frequency of 20% or more.   2. The pore former for ceramic composition according to claim 1, wherein the true specific gravity is less than 0.04.   Thermally expanded microcapsules contain 50% by weight or more of nitrile monomer, 49.9% by weight or less of non-nitrile monomer, and 0.05 to 2% by weight of a bifunctional or higher functional crosslinker and / or a long side chain crosslinker Thermally expandable microcapsule comprising an outer shell formed of a polymer obtained from a monomer component containing benzene, and a volatile expansion agent encapsulated in the outer shell that becomes gaseous at a temperature below the softening point of the polymer The pore former for ceramic composition according to claim 1 or 2, wherein the pore size is 1 to 150 µm and the expansion ratio is 20 to 100 times. .