JP2728273B2 - Manufacturing method of porous ceramics - Google Patents

Description

The present invention relates to a novel method for producing a porous ceramic body useful as a filter, an adsorbent, a catalyst carrier, a fireproof heat insulating material, a sound absorbing material, a building material, and the like.

[Conventional technology]

Porous ceramics have excellent functions and characteristics due to the properties possessed by ceramics such as heat resistance, chemical stability, abrasion resistance, electric insulation, and the properties caused by pores. A method has been proposed.

As a typical method of making porous, there are a method of sintering green of ceramic powder having a uniform particle diameter and an organic binder under normal pressure, and a method of bonding ceramic powder with a binder such as clay or vitreous flux. In these methods, voids existing mainly between the powders become pores, so that the shape of the pores is wedge-shaped, and the porosity is generally 30 to 50% or less,
There is a disadvantage that the porosity cannot be increased. Also,
Since the porosity and the size of the pores greatly depend on the size of the powder and the particle size distribution of the powder, there is a problem that the size and shape of the powder must be strictly adjusted to obtain a desired porous body.

As another method, there is a method of firing a green obtained from a mixture of a powder of a combustible substance such as a ceramic powder, an organic binder, a starch, a wood powder, a rice flour, a wax, a synthetic resin, carbon, and a pyrolytic substance. is there. In this method, the pores are formed mainly by removing powders of a combustible substance, a thermally decomposable substance, and the like, and thus the pore diameter depends on the size of these powders. In general, these materials have problems in that it is difficult to adjust the particle size, that it is difficult to obtain a fine powder, that a great deal of work is required to make the powder size uniform, and that ash may enter as impurities. As a method for improving this point, there is a method of extracting a green consisting of ceramic powder, an organic binder, and a water-soluble particulate substance in water, followed by baking (Japanese Patent Laid-Open No. 59-83972). Reducing the particle size of the active substance,
There are problems that it is difficult to adjust the particle size and that the extraction operation is troublesome.

The method of impregnating a combustible foam with a ceramic powder slurry and adhering it, followed by firing (JP-A-55-24585), has the advantage that the resulting porous body has a so-called skeletal structure and therefore has a high porosity. On the other hand, it has problems such as low strength and a large pore size. In addition, there is a method of forming pores with a foaming agent (JP-A-60-195073), but there is a problem that it is difficult to adjust the pore diameter.

The present inventors have previously proposed a novel production method having no problems as described above, by mixing a ceramic powder, a polymerizable unsaturated compound, an emulsifier, and water to form a water-in-oil emulsion, and then forming the inverse emulsion. After curing, drying and baking were proposed (Japanese Patent Application No. 62-104829).

[Problems to be solved by the invention]

The present invention further relates to a method for producing a novel porous body having no problems as described above, the purpose of which is to have a small pore diameter, the pores are continuous pores, and are evenly distributed throughout the ceramics. Another object of the present invention is to provide a method for producing a porous ceramic body in which the porosity can be easily adjusted in a wide range.

[Means for solving the problem]

In view of the present situation, the present inventors have made intensive studies and as a result, calcined a cured product of the inverse emulsion obtained by mixing and dispersing ceramic powder in a water-in-oil emulsion having a polymerizable unsaturated compound as an oil layer. It has been found that the object of the present invention can be achieved also by this method, and the present invention has been completed.

That is, the present invention provides a water-in-oil emulsion containing a ceramic powder by mixing ceramic powder with a water-in-oil emulsion comprising a polymerizable unsaturated compound, an emulsifier, and water, and then polymerizing the unsaturated polymer in the inverse emulsion. The present invention relates to a method for producing a porous ceramic body, characterized in that a cured product obtained by subjecting a compound to radical polymerization or redox polymerization is dried and then fired.

In the present invention, the polymerizable unsaturated compound is characterized in that it acts as an oil layer of the inverse emulsion and, after polymerization, also acts as a binder for the ceramic powder dispersed in the oil layer. Water is evenly dispersed in the oil layer as droplets. When this water is evaporated after the polymerization, the portion becomes pores, and thus the cured product becomes porous. When the porous cured product is fired by a usual method, pores formed by evaporating water remain in the ceramic and become porous ceramic.

Examples of the ceramic powder in the present invention include alumina, zirconia, magnesia, zinc oxide, tin oxide, iron oxide, titanium oxide, spinel, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium carbonate, silicon carbide, silicon nitride, and nitride. Aluminum and the like are preferred, but are not limited thereto as long as they have sinterability and do not cause significant phase separation of the inverse emulsion. Further, these may be used by being appropriately mixed, and yttrium oxide, cerium oxide,
Sintering aids such as lithium oxide, borate and silicate, binders such as vitreous flux, and other coloring agents may be added.

As the polymerizable unsaturated compound, any compound capable of undergoing radical polymerization or redox polymerization and capable of forming an inverse emulsion may be used. Typical examples thereof include styrenes such as styrene, α-methylstyrene, and divinylbenzene. Methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, ethylene glycol diacrylate, trimethylol Acrylic esters and acrylic acid such as propane triacrylate,
Examples include vinyl acetate, vinyl pyridines, diallyl phthalate, acrylonitrile, maleic anhydride, unsaturated polyesters and the like. These are used alone or in appropriate combination.

As emulsifiers, sorbitan tristearate, sorbitan monostearate, sorbitan sesquiolate, sorbitan monooleate, sorbitan monopalmitate,
Higher fatty acid esters of sorbitan such as sorbitan monolaurate, higher fatty acid esters of glycerol or polyglycerol such as glycerol stearate and polyglycerol, higher fatty acid esters of polyethylene glycol such as diethylene glycol stearate, diethylene glycol oleate and polyoxyethylene oleate, polyoxy Nonionic surfactants such as ethylene oleyl ether, polyoxyethylene dodecyl phenyl ether, and polyoxyethylene nonyl phenyl ether; polyalkylene glycols such as polypropylene glycol and polybutylene glycol having an average molecular weight of 1,000 to 10,000 and succinic anhydride; An adduct with a dibasic acid anhydride such as maleic acid or hexahydrophthalic anhydride. Neutralized calcium or magnesium of a polyalkylene glycol derivative having a hydroxyl group, calcium or magnesium of a polyester oligomer having a carboxyl group at the end comprising an alkylene glycol and a dibasic acid, neutralized with an amine, and the like. It is not limited to these emulsifiers as long as they have an action of producing the emulsifier. Of these,
Sorbitan tristearate, sorbitan monostearate, sorbitan sesquiolate, sorbitan monooleate, sorbitan monopalmitate and the like are particularly preferred. Further, these emulsifiers may be used alone or in combination of two or more in order to obtain a desired effect.

 Next, a manufacturing method will be described.

In the present invention, first, a polymerizable unsaturated compound, an emulsifier,
Water is mixed to form an inverse emulsion, and then the resulting inverse emulsion is mixed with ceramic powder. A mixer such as a paddle-type, propeller-type, or turbine-type stirrer with a blade or a colloid mill is used to generate an inverse emulsion, and a ceramic powder is mixed with a ball mill, pebble mill, colloid mill, etc. A kneader such as a kneader, a kneader, a pony mixer, and a screw extruder can be used, but is not limited thereto. If necessary, a dispersing agent or an antifoaming agent may be appropriately used in order to uniformly disperse the ceramic powder or to prevent generation of bubbles.

The method of the present invention has the advantage that the viscosity is low because no ceramic powder is present in the process of forming the inverse emulsion, and it is easy to emulsify, so that a large amount of energy is not required for stirring when the inverse emulsion is formed. In addition, ceramic powder is added after the formation of the inverse emulsion,
In the process of dispersing the powder, there is an effect that emulsion particles, that is, water droplets become small.

Regarding the composition of the inverse emulsion containing the ceramic powder, the weight ratio of the ceramic powder, the polymerizable unsaturated compound and water is desirably 100: 10 to 50:10 to 300. The ratio of water is very closely related to the bulk specific gravity of a cured product or a ceramic obtained by firing. That is, as the ratio of water increases, the bulk specific gravity decreases and the porosity increases. Conversely, when the ratio of water is small, the bulk specific gravity and strength increase, and the porosity decreases. The smaller the ratio of the polymerizable unsaturated compound is, the easier the baking is and the more economically preferable. However, the strength of the cured product is reduced, and the viscosity of the inverse emulsion tends to increase.

An appropriate amount of the emulsifier is 5 to 100 parts by weight based on 100 parts by weight of the polymerizable unsaturated compound. When a neutralized product of an unsaturated polyester oligomer is used, the neutralizing agent acts as an emulsifier and at the same time acts as a binder by being incorporated into the polymer, so that there is no particular problem even if the added amount is large. However, if the total amount of the emulsifier and the polymerizable unsaturated compound is too large, baking becomes difficult.

Next, the polymerizable unsaturated compound in the inverse emulsion is subjected to radical polymerization or redox polymerization to obtain a cured product. The polymerization is carried out using a usual polymerization initiator and a redox polymerization initiator. Typical examples thereof include peroxide polymerization initiators such as hydrogen peroxide, potassium persulfate, ammonium persulfate, benzoyl peroxide, lauroyl peroxide, methyl ethyl ketone peroxide, t-butyl hydroperoxide, and the like. Redox polymerization initiators comprising a combination of a polymerization initiator and a reducing substance such as sodium bisulfite, ferrous salt, dimethylaniline, cobalt naphthenate, sulfinic acid and the like can be mentioned. The amount of the polymerization initiator used is 0.0 with respect to 100 parts by weight of the polymerizable unsaturated compound.
2-5 parts by weight are desirable.

The polymerization temperature and the polymerization time are preferably from 100 ° C. or lower to 1 to 48 hours. The polymerization conditions are not limited to these, but significant evaporation of water during polymerization should be avoided.

A cured product obtained by polymerizing a ceramic powder-containing inverse emulsion has water uniformly dispersed in the system, and is dried to obtain a porous cured product in which water is evaporated. Drying methods include hot air drying, internal heating drying, vacuum drying, freeze drying and the like.

When the porous cured product is fired by a usual method, organic substances are first removed by oxidative decomposition or thermal decomposition, and then ceramic powder is sintered or bonded to obtain a ceramic porous body. The firing conditions are preferably set to 1000 ° C. or higher at a temperature increase rate of 1 to 200 ° C./hr. Factors that determine the sintering conditions include the type of ceramic powder, particle size, the type of material constituting the cured product and their composition ratio, the size and shape of the cured product, the furnace atmosphere, and the like.
An appropriate selection may be made in consideration of these factors.
In a temperature range in which organic substances are removed, in order to prevent cracks and deformation, it is preferable that the heating rate is reduced and firing is performed over time. At this time, if the cured product has a crosslinked structure, the rate of temperature rise in this temperature range can be increased,
This is advantageous because less energy is required for firing. Crosslinking can be performed by copolymerizing a polyfunctional unsaturated compound. Examples of the polyfunctional unsaturated compound include divinylbenzene, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, ethylene glycol diacrylate, trimethylolpropane triacrylate, diallyl phthalate,
And unsaturated polyesters.

In the ceramic porous body obtained according to the present invention, pores are uniformly distributed. The size of the pores is relatively constant, most of which is 7 to 8 μm or less, however, depending on the manufacturing conditions, pores having a larger size may be mixed. The shape of the pores is generally spherical or a shape in which a plurality of spherical pores are partially fused, but if the pores in the cured product before firing are not too large compared to the size of the ceramic powder, The shape becomes less clear. The ceramic powder becomes a continuous layer by firing, while the pores are mostly continuous pores.

〔Example〕

Example 1 100 parts by weight of a 0.15% by weight ammonium persulfate aqueous solution was gradually added to 30 parts by weight of a mixture of 21.6 parts by weight of styrene, 2.4 parts by weight of trimethylolpropane trimethacrylate, and 6.0 parts by weight of sorbitan monooleate with a cruciform stirring blade. Upon stirring, an inverse emulsion was obtained. Next, 130 parts by weight of the obtained inverse emulsion and alumina (AES-22
S, manufactured by Sumitomo Chemical Co., Ltd.) was mixed with a pole mill for 24 hours. Then, after defoaming, pour it into the mold,
After polymerization for 24 hours, the resin was taken out of the mold and dried at 60 ° C. to obtain a porous cured product. The cured product was further cut to a size of 12.7 mm × 6.3 mm × 76.2 mm.

Next, this was put into an electric furnace for firing, heated to 1450 ° C. in air at a rate of 50 ° C./hr, kept for 5 hours, and then cooled to obtain a porous ceramic body. No crack or deformation was observed in this porous body.

Observation of the cut surface of the cured product and the ceramics with a scanning electron microscope revealed that the cured product had spherical pores of 4 to 5 μm or less distributed uniformly. The ceramics also had a substantially spherical shape or a shape in which a plurality of spherical pores were partially fused, and were uniformly distributed. Table 1 shows the properties of the cured product and the ceramics.

Example 2 A reverse emulsion was obtained by vigorously stirring with a cross-shaped stirring blade while gradually adding 60 parts by weight of a 0.21% by weight aqueous solution of ammonium persulfate to 25 parts by weight of a mixture of 20 parts by weight of styrene and 5 parts by weight of sorbitan sesquiolate. . Next, 85 parts by weight of the obtained inverse emulsion and alumina (AES-22S) 100
Parts by weight were mixed in a ball mill for 48 hours. Subsequently, after defoaming, the mixture was poured into a mold, polymerized at 60 ° C. for 24 hours, taken out of the mold, and dried at 60 ° C. to obtain a porous cured product.

Next, the cured product cut in the same manner as in Example 1 was placed in an electric furnace to be baked, heated to 600 ° C. at a heating rate of 5 ° C./hr in air, allowed to cool once, and then heated. Speed 50 ° C / hr
The temperature was raised to 1450 ° C., kept for 5 hours, and then cooled to obtain a porous ceramic body. No crack or deformation was observed in this porous body.

When the fracture surface was observed in the same manner as in Example 1, spherical pores of 2 to 3 μm or less were uniformly distributed in the cured product.
Pores were evenly distributed in the ceramics. Table 1 shows the properties of the cured product and the ceramics.

Example 3 Polypropylene glycol having a molecular weight of 2053 in advance
205.3 parts by weight and 9.8 parts by weight of maleic anhydride in an inert gas
A neutralized product (hereinafter abbreviated as PPGMA (P-Mg)) obtained by neutralizing 100 parts by weight of the adduct obtained by reacting at 120 ° C. for 5 hours with 0.92 parts by weight of magnesium oxide was synthesized.

Next, 50 parts by weight of a mixture of 36.0 parts by weight of styrene, 4.0 parts by weight of trimethylolpropane trimethacrylate, and 10.0 parts by weight of PPGMA (P-Mg) were gradually added with 50 parts by weight of a 0.5% by weight aqueous solution of ammonium persulfate to form a cruciform stirring blade. After vigorous stirring, an inverse emulsion was obtained. Next, 100 parts by weight of the obtained inverse emulsion and 100 parts by weight of alumina (AES-11, manufactured by Sumitomo Chemical Co., Ltd.) were mixed in a ball mill for 40 hours. Thereafter, a hardened material cut and processed in the same manner as in Example 2 was obtained.

Next, the cut hardened material is put into an electric furnace to be fired, heated in air to 600 ° C at a heating rate of 20 ° C / hr, and then heated to 1350 ° C at a heating rate of 50 ° C / hr. After holding for 5 hours, the mixture was cooled to obtain a ceramic porous body. No crack or deformation was observed in this porous body.

When the fractured surface was observed in the same manner as in Example 1, pores of 1 μm or less were uniformly distributed in the cured product. Pores were evenly distributed in the ceramics. Table 1 shows the properties of the cured product and the ceramics.

[Effects] The production method of the present invention is a method of firing a cured product of an inverse emulsion containing ceramic powder. In this method, pores are mainly formed by evaporation of water. Therefore, the pores are distributed evenly throughout the pores, the pore diameter is small, the shape of the pores is generally spherical or a shape in which a plurality of spherical pores are partially fused, the composition in the cured product It has the features that it can be freely adjusted in a wide range from a large porosity to a small porosity simply by changing the ratio, that the production method is easy, and that a cured product can be cut. The present invention, in addition to these,
Since an inverse emulsion is formed in advance with a polymerizable unsaturated compound, an emulsifier, and water, it is extremely easy to form an inverse emulsion.Because ceramic powder is added after the formation of an inverse emulsion, it is present in the emulsion during dispersion of the powder. It has the characteristics that the diameter of small water droplets is smaller and the pores in the cured product and ceramics are smaller,
It is an industrially advantageous production method and can be widely used.

The ceramic porous body obtained according to the present invention is useful for filters, adsorbents, catalyst carriers, heat-insulating materials, sound-absorbing materials, building materials, etc. by utilizing its features.

Claims (3)

(57) [Claims] 1. A water-in-oil emulsion comprising a polymerizable unsaturated compound, an emulsifier and water, mixed with a ceramic powder to form a water-in-oil emulsion containing the ceramic powder, and then the polymerizable unsaturated compound in the inverse emulsion. A method for producing a porous ceramic body, comprising drying a cured product obtained by subjecting a compound to radical polymerization or redox polymerization, followed by firing. 2. The method according to claim 1, wherein the emulsifier is sorbitan tristearate, sorbitan monostearate, sorbitan sesquiolate, sorbitan monooleate, or sorbitan monopalmitate. Law. 3. The method according to claim 1, wherein the cured product is cross-linked by a polyfunctional unsaturated compound.