Processes for producing anatase titanium oxide and titanium oxide coating material

Abstract

Production processes are provided which can produce, at a relatively low temperature and in a reduced number of steps, anatase titanium oxide powder having high photocatalytic activity and large specific surface area and anatase titanium oxide slurry having high storage stability and dispersibility. The slurry thus obtained can also be coated, as a coating material having photocatalytic activity, on materials having low heat resistance. In the production process of anatase titanium oxide powder according to the present invention, a titania sol solution, a titania gel, or a titania sol-gel mixture is heat treated in a closed vessel under pressure, and the treated product is then dried to produce anatase titanium oxide powder. In the production process of anatase titanium oxide slurry according to the present invention, a titania sol solution, a titania gel, or a titania sol-gel mixture is heat treated in a closed vessel under pressure, and the treated product is then dispersed / stirred to produce anatase titanium oxide slurry.

Description

TECHNICAL FIELD The present invention relates to a process for producing anatase titanium oxide particularly having high photocatalytic activity as one of photocatalysts used, for example, as environment cleaning materials, for example, for the removal of harmful materials, the deodorisation / decomposition of offensive odor substances, antifouling, and sterilization, and more particularly to a process for producing anatase titanium oxide powder having high photocatalytic activity and large specific surface area, and a process for producing anatase titanium oxide slurry, containing the anatase titanium oxide powder, with excellent stability and dispersibility. The present invention also relates to a process for producing a coating material of titanium oxide as one of photocatalysts used, for example, as environment cleaning materials, for example, for the removal of harmful materials, the deodorisation / decomposition of offensive odor substances, antifouling, and sterilization. More ...

AI Technical Summary

Benefits of technology

An object of the first invention is to provide a process for producing anatase titanium oxide powder wherein a titania sol, a titania gel, or a titania sol-gel mixture is heat treated in a closed vessel to hybridize the effect of pressure, whereby anatase titanium oxide powder having high photocatalytic activity and large specific surface area can be produced at a low heat treatment temperature of 250° C. or below via a small number of steps in a simple manner.

Another object of the first invention is to provide a process for producing anatase titanium oxide slurry wherein anatase titanium oxide produced by heat treatment within a closed vessel under pressure is subjected to, for example, ultrasonic dispersion or stirring in the solvent used in the preparation of a titania sol, a titania gel, or a titania sol-gel mixture, whereby anatase titanium oxide slurry, which is very stable, is free from settling of titanium oxide particles, and can also be coated on the surface of materials having low heat resistance, can be produced at room temperature.

Further, the introduction of pressurized inert gas into the closed vessel can also regulate the pressure within the closed vessel.

Accordingly, an object of the second invention is to provide production processes of anatase titanium oxide powder and aqueous anatase titanium oxide slurry, wherein a substantially organic solvent-free, aqueous titania sol, titania gel, or titania sol-gel mixture is heat treated in a closed vessel under pressure, whereby anatase titanium oxide powder having high photocatalytic activity and large specific surface area and aqueous anatase titanium oxide slurry can be produced at a low heat treatment temperature of 270° C. or below, preferably 240° C. or below, without the generation of any organic solvent at the time of drying via a small number of steps in a simple manner.

Further, the introduction of pressurized inert gas into the closed vessel can also regulate the pressure within the closed vessel.

An object of the third invention is to provide a process for producing a titanium oxide coating material wherein, for example, a liquid prepared by treating a titania sol solution, a titania gel, or a titania sol-gel mixture with ozone gas is used to produce a titanium oxide coating material which can realize coating of titanium oxide having excellent photocatalytic activity at a low temperature, can be coated onto members with high adhesion strength, which can be maintained for a long period of time, and has excellent transparency which does not deteriorate the appearance of members. Another object of the third invention is to provide a process for producing a titanium oxide coating material wherein a liquid prepared by treating a titania sol solution, a titanic gel, or a titania sol-gel mixture with ozone gas is mixed with titania powder or titania slurry to produce a binder that can maintain adhesion to materials having low adhesion strength for a long period of time although the photocatalytic activity is high.

Problems solved by technology

In the production of anatase titanium oxide powder by the gas phase process, all the above production processes have drawbacks such as the necessity of using a special apparatus in the production of anatase titanium oxide due to the adoption of high-temperature reaction atmosphere (generally 800° C. or above in the case of the gas phase process) and the use of highly reactive titanium chloride as a starting material.

In this process, however, a special apparatus should be disadvantageously used for the preparation of anatase titanium oxide.

The production of anatase titanium oxide powder by the sulfuric acid process is disadvantageous in that the number of steps is large and, for example, the operation is very complicate.

Due to this high temperature, the coating material cannot be coated on base materials having low heat resistance.

Therefore, usable base materials are limited.

In the preparation of the coating material, dispersing powdery anatase titanium oxide in a solvent causes the coagulation of titanium oxide particles which makes it impossible to maintain the activity of the particulate photocatalyst.

Further, in the form of the coating material, for example, the dispersion of anatase titanium oxide in the solution is heterogeneous, and, with the elapse of the time, titanium oxide particles disadvantageously settle at the bottom of the solution.

That is, the coating material has a problem of storage stability.

As with the above technique, the problem of particle coagulation or the like occurs also in the method where metatitanic acid is prepared from ilmenite as a starting material by the sulfuric acid process, and nitric acid is added to the metatitanic acid, followed by the dispersion of titanium oxide in the mixture.

However, when the adhesion of anatase titanium oxide onto the surface of the member with high adhesion strength is contemplated, as described in Japanese Patent Laid-Open Nos. 99041-1996 and 277147 / 1996, there is a problem such that treatment at a high temperature of 300° C. or above is necessary and, thus, titanium oxide cannot be coated onto members having low heat resistance.

As described in Japanese Patent Laid-Open No. 131834 / 1996, when organic matter is mixed, the photocatalyst decomposes the organic matter and thus cannot maintain the adhesion strength.

Therefore, there is a limitation on the long-term persistence of the photocatalytic activity.

Likewise, in the case of polymers, such as polymethyl methacrylate (PMMA), the decomposition of PMMA takes place by the photocatalytic activity, leading to a limitation on the persistence of adhesion strength.

This deteriorates the photocatalytic activity.

Further, in the prior art technique, as described in the above publication, there are two coating steps which render the process complicate.

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