JPH0641394B2 - Method for producing porous titania sintered body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a porous titania sintered body and a method for producing the same. More specifically, a porous titania sintered body as a ceramic porous body, which is expected to have many application fields such as a sensor, a catalyst, a separating material, a medical material, a heat insulating material, a refractory material and the like, and a method for producing the same. Regarding

(B) Conventional technology and problems As a conventional method for producing a porous ceramic body, which is expected to have many application fields as high-temperature functional materials such as sensors, catalysts, separation materials, medical materials, heat insulating materials, and refractory materials, Generally, a method of kneading a material that disappears by firing at a low temperature (for example, a resin) and a ceramic powder, molding the mixture, and then firing at a high temperature to leave only the ceramics and sinter the ceramic powder is generally used. . At this time,) mixing water-soluble resin such as polyvinyl alcohol, water and ceramics powder,
) Thermoplastic resins such as polystyrene, polyethylene, polypropylene and ceramic powder are heated and kneaded,
) Resin, its solvent, and ceramic powder are mixed.

However, in any of the above methods, the green body is mixed by kneading, so that the inside of the green body is inevitably in a non-uniform state with a portion having a large amount of resin and a portion having a small amount of resin. Therefore, the sintered body obtained by firing this has only non-uniform pores. In addition, when the porosity is increased, the resin content is further increased, and the above problem becomes more serious.

The inventor of the present invention has earnestly studied about a method for obtaining a ceramics porous body, and as a result, fine titania powder was once made into a fine resin-coated porous titania sphere, and if the spheres were assembled and sintered, the uniformity was excellent. The fact that a porous titania sintered body having a pore distribution can be obtained was found, and the present invention was completed.

(C) Means for Solving the Problems Thus, according to the present invention, a porous titania sintered body obtained by assembling and sintering porous titania spheres, and a titania powder surface-treated with a lipophilic agent And a polymerizable vinyl-based monomer, and a mixture of an organic solvent that is compatible with the above-mentioned monomer and that is not substantially compatible with water, if necessary, are dispersed in an aqueous system to suspend the monomer. By polymerizing by turbid polymerization, a porous titania sphere consisting of an aggregate of titania powder coated with a resin is obtained, and then the resin-coated porous sphere is assembled and pressure-molded, and then the sphere is sintered. There is provided a method for producing a porous titania sintered body, characterized in that the coating resin is removed to obtain a porous sintered body by heat treatment at a temperature at which it can be separated.

The present invention relates to a porous titania sintered body which is formed by assembling resin-coated porous titania spheres once produced from titania powder as constituent elements, and further pressing and sintering them. The sintered body of the present invention can be manufactured by the following method. That is, a mixture of titania powder surface-treated with a lipophilic agent and a polymerizable vinyl-based monomer is prepared, and in some cases, an organic solvent that is compatible with the monomer and is substantially incompatible with water. Is added to the mixture to suppress an increase in viscosity with an increase in the amount of titania powder in the mixture, and to expand the amount range of the titania powder added, and in the oily dispersion of the mixture in an aqueous system, individual oils are added. It is possible to hold the droplets spherically dispersed, by which the titania powder (primary particles) dispersed in each oil droplet is aggregated into a spherical shape, and once, a resin-coated porous titania sphere is produced, This is a method in which the particles are further assembled into a predetermined shape, pressure-molded, and then heated to remove the coating resin and sinter to form a porous body.

In the above method, the surface-treated titania powder is
It means that the titania powder only has to be surface-treated before the polymerization of the polymerizable vinyl-based monomer used. Therefore, the titania powder may be surface-treated in advance before being added to the polymerizable vinyl-based monomer or the mixture of the monomer and the predetermined organic solvent, and the polymerizable vinyl-based monomer may be added. Alternatively, titania powder may be added to a mixture of a predetermined organic solvent and a lipophilic agent used for surface treatment for surface treatment. The surface treatment is a treatment in which titania powder is brought into contact with the lipophilic agent to adsorb or bond the lipophilic agent on the surface of the powder.
The treatment is achieved by a usual mechanical method or the like. That is, a mixture composed of a lipophilic agent and titania powder, or a mixture composed of a lipophilic agent, titania powder and a polymerizable vinyl-based monomer, at room temperature or under cooling, for example, a propeller blade or a homogenizer at high speed. It is achieved by stirring.

The titania powder used in this invention has a finally obtained sintered body as a sensor, a catalyst, a separating material, a medical material, a heat insulating material,
Any material that can be suitably used as a high temperature functional material such as a refractory material may be used, and the particle size is such that, when particles having a large particle size are used, the titania powder is obtained from dispersed oil droplets during aqueous suspension polymerization. It is easily desorbed to the aqueous phase, and it becomes difficult for the resin-coated porous titania particles to maintain a spherical shape. On the other hand, in the case of using particles having an ultrafine particle diameter, even if a large amount of an organic solvent is added as a viscosity reducing agent, the viscosity is lowered until it can be dispersed in water as spherical oil droplets during aqueous suspension. Therefore, the titania powder has a particle diameter of 0.01 to 2.
It is preferably between 0 μm and 0.1 to 1.5 μm
Is preferred.

The lipophilic agent used in the present invention has a functional group capable of strongly adsorbing or binding to the titania powder, and a hydrocarbon having a high affinity for the polymerizable vinyl monomer, or a functional group capable of binding to the monomer. A substance having a group can be used. Examples thereof include higher fatty acids such as oleic acid, stearic acid and palmitic acid, unsaturated carboxylic acids such as acrylic acid and methacrylic acid, and polar groups such as aminoethyl acrylate, hydroxyethyl acrylate and cyanoethyl acrylate. Acrylic ester, a titanate coupling agent, a coupling agent such as a silane coupling agent and the like can be mentioned. Among these, those having a functional group that strongly binds to the titania powder, such as a titanate coupling agent and a silane coupling agent, are preferable. Examples include pyrophosphate-type titanate coupling agents such as isopropyl tris (dioctylpyrophosphate), bis (dioctylpyrophosphate) titanate, and phosphate-type titanate coupling agents tetraoctylbis (ditridecylphosphate) titanate. Examples of the silane coupling agent include vinyltrichlorosilane, vinyltrimethoxysilane, and -methacryloxypropyltrimethoxysilane having a radically polymerizable functional group.

As the polymerizable vinyl-based monomer used in this invention,
Any known monomer can be used as it is, as long as it can exist as spherical oil droplets in a state of being dispersed in an aqueous system and can form a polymer under the polymerization conditions. The monomers may be used alone or in combination of two or more, and may be used in combination with a known crosslinking agent. Preferred examples of the monomer include acrylic acid esters such as methyl acrylate and ethyl acrylate, ethyl methacrylate such as methyl methacrylate and ethyl methacrylate, and aromatic vinyl compounds such as styrene. Suitable examples of the cross-linking agent include methacrylic acid esters of polyhydric alcohols such as ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate and trimethylolpropane trimethacrylate, and divinylbenzene. Further, the polymerization initiator may be any that is soluble in the polymerizable vinyl-based monomer used, for example, benzoyl peroxide, lauroyl peroxide, diacetyl peroxide and other commonly used peroxides and azobis. Examples thereof include azo compounds such as isobutyronitrile and azobisdimethylvaleronitrile.

The organic solvent used in the present invention, in order to make the resin-coated porous titania spheres once obtained excellent in spherical shape,
Used as needed. As the organic solvent, a solvent that is compatible with the polymerizable vinyl-based monomer and substantially not compatible with water is used. By "not practically compatible with water" is meant insoluble or slightly soluble in water. This organic solvent is used for adjusting the viscosity of the mixture of the titania powder and the polymerizable vinyl-based monomer described below, and is therefore 3.0 centipoise (c) at room temperature.
P) Those having a viscosity of the following or less are preferable, and those having an affinity with the polymerizable vinyl-based monomer used are more preferable. Examples of such organic solvents include acetic acid esters such as methyl acetate and ethyl acetate, hydrocarbons such as hexane and heptane, ketones such as methyl ethyl ketone and methyl isobutyl ketone, and aromatic hydrocarbons such as benzene and toluene.

In the present invention, a slurry-like mixture is prepared from the titania powder surface-treated with the above lipophilic agent, the polymerizable vinyl-based monomer, the organic solvent added as necessary, and the like. In the preparation of this slurry, the titania powder is formed in the resin-coated porous titania spheres described below to form an aggregate by aggregation of the titania powders, and as a result, a resin-coated porous titania spheres can be obtained in an amount sufficient. Used. This amount is set according to the specific gravity and properties of the titania powder used. For example, from the viewpoint of porosity and sphericity of the titania particles obtained, used in an amount of 150 parts by weight or more based on 100 parts by weight of the polymerizable vinyl-based monomer, 230
It is preferably used in the range of ˜1000 parts by weight.
Further, the lipophilic agent is determined by the minimum coating area of the lipophilic agent and the specific surface area of the titania powder used, but is usually used in the range of 0.2 to 3.0 parts by weight with respect to the titania powder. . Further, the organic solvent is used in an amount necessary to adjust the slurry mixture to a viscosity capable of maintaining spherical oil droplets when dispersed in an aqueous system described below. The amount is 1 to 100 parts by weight of the polymerizable vinyl monomer.
Suitably used in the range of 200 parts by weight, 1
It is preferably used in the range of 150 to 150 parts by weight. When the amount is 200 parts by weight or more, it is difficult to obtain the substantial strength of the polymer that binds the titania powders together, which is not preferable. Further, the polymerization initiator is usually used in the range of 0.1 to 2.0% by weight of the polymerizable vinyl monomer used. The slurry-like mixture prepared above is prepared into a uniform slurry by the same mechanical method as the above-mentioned surface treatment.

In the present invention, the slurry-like mixture prepared as described above is dispersed in an aqueous system, and the polymerizable vinyl-based monomer in the mixture is subjected to the polymerization conditions. The above dispersion is achieved by the same mechanical method as described above. At this time, the dispersion conditions are set so that the resin-coated titania spheres having a particle size range described later are dispersed by the size of the oil droplets. The above-mentioned polymerization can be achieved by adjusting it according to the kind of the polymerizable vinyl-based monomer used, but the usual suspension polymerization conditions can be applied as it is.

An aggregate of titania powder coated with a resin composed of a polymer of a polymerizable vinyl monomer in an aqueous system by the above dispersion / polymerization, which is a spherical and porous resin having a particle size of 1 μm to 1 mm. A coated titania sphere is obtained. The titania spheres are filtered and dried by a conventional method. The particle size is appropriately selected depending on the porosity or density of the sintered product which is the final product described below.

In the present invention, the resin-coated porous titania sphere obtained as described above is pressure-molded into a predetermined shape. The pressurizing condition at this time varies depending on the size of the resin-coated porous titania spheres used, but is applied with a pressure sufficient to maintain the desired shape of the molded body. In the case of the above-mentioned molding, it is possible to use an adhesive such as a binder for maintaining a desired shape, but it is not so preferable because it may remain in the sintered body due to carbonization during firing described later. The aggregate of resin-coated titania spheres held in a desired shape by pressure molding is then subjected to heat treatment. This heat treatment is carried out at a temperature at which the resin-coated titania spheres in the aggregate can be sintered but cannot be fused. Here, the above-mentioned fusion means a state in which spheres are melted and become substantially non-porous. Therefore, the heat treatment is performed under the condition that the coating resin is incinerated and removed and the titania spheres can be sintered together. In this case, it is preferable that the porosity of each individual titania sphere is maintained. In the above heat treatment, on the one hand, the coating resin is not carbonized in the process of being incinerated, and on the other hand, the titania powder to be sintered is not excessively fused due to the crystal growth accompanying sintering so that the porosity is not impaired. In addition, the heating temperature, the heating time, and the temperature rising state to the heating temperature are selected. The heating temperature is set to about 950 to 1200 ° C. 950 ° C
In the following, the titania spheres obtained with low strength after sintering are destroyed, and in the case of 1200 ° C. or more, crystals grow too much during sintering and the porous state of the titania spheres obtained can be maintained.
In this case, the temperature is preferably 1000 to 1100 ° C. Further, as the temperature rising state to the heating temperature, it is necessary to take a long time (for example, 5 hours) until the temperature rises to 1000 ° C. in order to avoid carbonization of the resin.

By the heat treatment, the porous titania spheres are aggregated and sintered to obtain a porous titania sintered body. In the present invention, the strength of the obtained porous titania sintered body depends on its application. Is appropriately selected. This strength can be achieved by adjusting the conditions of the heat treatment.

By the treatment as described above, a porous titania sintered body obtained by assembling and sintering porous titania spheres having a particle diameter of 1 to 50 μm as a constitutional unit can be obtained.

In the method of the present invention, the pore diameter of the porous structure of the resin-coated porous titania sphere can be controlled by adjusting the content of the titania powder used. The particle size of the porous titania spheres can be controlled by adjusting the particle size of the resin-coated porous titania spheres. Therefore, the porosity or density of the finally obtained porous titania sintered body can be adjusted by adjusting the particle diameter of the spheres.

(D) Action According to the present invention, a titania powder surface-treated with a lipophilic agent, a polymerizable vinyl-based monomer, and an organic solvent which is added as the case requires, A thin layer of polymerizable vinyl-based monomer is formed on the treated surface. When the mixture in this state is dispersed as an oil droplet in a water system, the oil droplet is held in a spherical shape, and the polymerizable vinyl-based monomer in each oil droplet is subjected to polymerization in that state, thereby giving a titania powder. Are coated with a polymer, and the titania powders are bound by the polymer at the contact points of the powders, so that a porous and spherical resin-coated titania sphere is obtained once. Next, the resin-coated porous titania spheres are pressed and assembled into a predetermined shape,
When it is further subjected to heat treatment, the coating resin is incinerated and removed, and as a result, the titania powder particles that have been aggregated into a spherical shape in one spherical body are fused to form a porous sintered spherical body, and at the same time, these porous bodies are formed. The sintered spheres are fused at the spherical contact portion to obtain a porous titania sintered body.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

(E) Examples Example 1 Preparation of resin-coated titania spheres In a beaker of 1, 279 g of methyl methacrylate, a silane coupling agent [-methacryloxypropyltrimethoxysilane, Toray Silicone Co., Ltd. SZ603.
0]] 21.0 g, azobisisobutyronitrile 0.6
After adding 0 g and completely dissolving, titanium oxide (rutile type, particle size 0.2 μm, JR-600 manufactured by Teikoku Kako Co., Ltd.)
A) Add 700 g, and use a stirrer equipped with a propeller blade to
000 rpm. Surface treatment for 30 minutes.

5 Metathesis magnesium pyrophosphate 6 in autoclave 6
0 g and 2.6 g of water containing 2.6 kg of sodium dodecylbenzene sulfonate were added, and then the above slurry was added to suspend the mixture, and after nitrogen substitution, the stirring speed was 500 rpm. And was polymerized at 60 ° C. After the polymerization was completed, the mixture was cooled to room temperature, the dispersant was decomposed with hydrochloric acid, and then separated by filtration. When the obtained particles were observed with a scanning electron microscope (SEM), they were spherical particles having a central diameter of about 10 μm and contained a plurality of titanium oxide oxides (titania) coated with polymethylmethacrylate (PMMA) resin. It formed a porous structure by assembling.

Production of Porous Titania Sintered Body PMMA-coated titania sphere 1 obtained as described above
g was filled in a molding die (diameter 11.8φ × depth 20 mm) and pressurized at a pressure of 1 t / cm ² . The density of the molded body after pressing was 0.5 g / cm ³ .

Next, the pressure-molded product composed of the above-mentioned PMMA-coated titania sphere aggregate was put into an electric furnace and fired at 1000 ° C. for 2 hours to obtain 0.81 g of a porous titania sintered body.
This sintered body has a diameter of 11.0 mm, a thickness of 5 mm, and a density of 1.7.
It was 0 g / cm ³ . In addition, this sintered body was
As a result of observation in (M), it was observed that the porous titania spheres were intimately sintered to form a porous sintered body having a uniform pore size and a uniform pore distribution.

Examples 2 and 3 and Comparative Example The same method as in Example 1 was performed except that the firing temperature in the electric furnace was changed. The results are shown in [Table 1].

From the density values in [Table 1] above, it can be seen that when the pressure-molded body of PMMA-coated titania spheres is fired at a temperature of 1000 to 1200 ° C., it is molded into a porous sintered body. Of these, the firing temperature in Example 3 was 12
When the sintered body obtained at 00 ° C. was observed by SEM, the porosity of the individual titania spheres, which is a structural unit, was impaired by crystal growth as compared with the case at 1000 ° C. The porosity obtained by sintering was maintained, and the pore distribution was uniform.

(F) Effect of the Invention According to the present invention, a porous titania sintered body having a uniform pore distribution can be easily produced with good reproducibility directly from a resin-coated porous titania sphere obtained by a polymerization method. Therefore, it is possible to easily supply a ceramic porous body that can be used in many application fields as a highly functional material such as industrial medical materials and cosmetics, and also as a highly functional material such as a sensor, a catalyst, and a refractory material.

Claims (1)

[Claims] 1. A titania powder surface-treated with a lipophilic agent, a polymerizable vinyl-based monomer, and the above-mentioned monomer, which is optionally added, are compatible with each other and are substantially incompatible with water. A mixture comprising an organic solvent is dispersed in an aqueous system, and the above monomer is polymerized by suspension polymerization to obtain a porous titania sphere consisting of an aggregate of titania powder coated with a resin, and then the resin-coated porous A characteristic is that a porous sintered body is obtained by collecting the spherical spheres, press-molding the spheres, and then heat-treating the spheres at a temperature at which they can be sintered but cannot be fused to remove the coating resin. And a method for producing a porous titania sintered body.