Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2000-06-02
2002-01-08
Jones, Deborah (Department: 1775)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S349000, C106S286400, C106S287190
Reexamination Certificate
active
06337301
ABSTRACT:
TECHNICAL FIELD
This invention relates to a composition comprising a photo-catalytic metal oxide.
The photo-catalytic metal oxide-containing composition of the invention is characterized in that the photo-catalytic activity is maintained at a sufficiently high level, the viscosity increase with time is extremely reduced and the workability is excellent, and thus, the photo-catalytic composition is suitably coated as a film-forming material on a base material.
BACKGROUND ART
In recent years, extensive researches have been made for utilizing the photo-catalytic action of metal oxides such as titanium oxide. The photo-catalytic metal oxide has excellent functions, for example, of preventing pollution by removing harmful substances, of decomposing ammonia and sulfur compounds in air for purification, and of sterilization. Thus, the use of photo-catalytic metal oxides is being expected in various fields. Particles of the photo-catalytic metal oxide are utilized in various forms depending upon the particular intended use thereof, such as bulk particles, a sol and a film. In view of the practical use, the photo-catalytic metal oxide particles are made into a film in many cases because of ease in handling.
As the method of forming photo-catalytic metal oxide particles into a film, a sol-gel method is known wherein a photo-catalytic metal oxide film is formed on a surface of glass sheet as a base material, from a metal alkoxide raw material. The sol-gel method is, however, disadvantageous in that the starting material is expensive and the working environment is polluted and a problem arises in safety because a large quantity of an organic solvent is used. Further, the process of firmly bonding a film of the photo-catalytic metal oxide to the base material must be performed at a high temperature. Thus, a base material used for a sol-gel method must be heat-resistant and this is an obstacle to enlargement of the use.
Attempts have been proposed for bonding photo-catalytic metal oxide particles onto a base material through a binder such as a film-forming composition comprising a hydrolysate of a hydrolyzable silicon compound as a binder in Japanese Unexamined Patent Publication No. H8-164334 (Japanese unexamined patent publication is hereinafter abbreviated to “JP-A”), and a coating composition comprising a film-forming material comprising a siloxane polymer or silicate, and a hydrolyzable silane derivative monomer as a binder in JP-A H9-188850. These proposed compositions contain a hydrolyzable silicon compound, which is gradually hydrolyzed to allow a polycondensation reaction to proceed. As a result, the composition undergo decrease in adhesion strength or increase of viscosity during storage, and thus, the pot life is undesirably shortened.
A coating composition comprising titanium oxide having photo-catalytic activity, a hydrolyzable organic metal compound, and an aqueous solvent has been proposed in JP-A H9-40872. The organic metal compound is subject to hydrolysis, and thus, the increase in viscosity of the composition and the reduction of adhesion strength thereof occur during storage of the composition. Therefore, the proposed composition must be used as a two-pack type composition, and the addition of water and a catalyst must be carried out immediately before the coating, and thus, the handling property is poor.
Various attempts have heretofore been made to use a film of a photo-catalytic metal oxide by fixing the film to be supported on a base material such as glass or plastic material. However, the level of properties required for the fixed photo-catalytic metal oxide film is high, and photo-catalytic metal oxide films capable of satisfying the requirements have not yet been found.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a composition comprising a photo-catalytic metal oxide capable of maintaining the photo-catalytic activity at a sufficiently high level, exhibiting an increase of viscosity with time only to a negligible extent, having good workability, and exhibiting good adhesion when the composition is coated as a film-forming material on a base material.
Another object of the invention is to provide a film made from the above-mentioned photo-catalytic metal oxide-containing composition.
Still another object of the invention is to provide a composite of a photo-catalytic metal oxide film with a base material, which is formed by coating a surface of the base material with the photo-catalytic metal oxide-containing composition, and is characterized as being transparent and possessing high adhesion between the film and the base material whereby the film is not easily separated from the base material.
As a result of extensive investigations for photo-catalytic metal oxide-containing compositions using various film-forming materials, the present inventors have found that a photocatalytic metal oxide-containing composition having incorporated therein a specific zirconium compound is suitable as a film-forming material capable of maintaining the photocatalytic activity at a sufficiently high level, exhibiting an increase of viscosity with time only to a negligible extent, having good workability, and exhibiting good adhesion when the composition is coated as a film-forming material on a base material.
Thus, in one aspect of the present invention, there is provided a composition comprising metal oxide particles having photo-catalytic activity, a solvent-soluble and non-hydrolyxable zirconium compound, and a solvent.
In another aspect of the present invention, there is provided a film made from the above-mentioned composition comprising the photo-catalytic metal oxide particles.
In a further aspect of the present invention, there is provided a composite of a film with a base material, said film being formed from the above-mentioned composition comprising the photo-catalytic metal oxide particles.
BEST MODE FOR CARRYING OUT THE INVENTION
The photo-catalytic metal oxide particles for use in the present invention comprise particles of a metal oxide exhibiting a catalytic activity for oxidation-reduction reaction of an organic compound when the metal oxide particles are irradiated with light having an energy larger than the band gap between the conduction band and the valence band of the crystal.
As specific examples of the photo-catalytic metal oxide particles, there can be mentioned particles of rutile titanium oxide, anatase titanium oxide, brookite titanium oxide, strontium titanate, tin oxide, zinc oxide and iron oxide.
The photo-catalytic reaction occurs in the vicinity of the surface of the metal oxide particle, and accordingly, the metal oxide particle preferably has a small particle size. However, those having an average particle diameter of smaller than about 0.005 &mgr;m are difficult to produce, therefore, the average particle diameter is usually in the range of about 0.005 to about 0.3 &mgr;m, preferably from about 0.01 to about 0.1 &mgr;m. The specific surface area is preferably in the range of about 50 to about 300 m
2
/g.
Of the photo-catalytic metal oxides, titanium oxide is most preferably because it is commercially available as finely divided particles, and harmless and chemically stable. Any conventional titanium oxide prepared by known methods can be used in the invention. In the case where titanium oxide is prepared by hydrolysis, the titanium oxide-containing sol prepared by hydrolysis can be used. Alternatively, the titanium oxide-containing sol is formed into a finely divided titanium oxide powder, which is then dispersed in a liquid medium to prepare a photo-catalytic oxide composition. Finely divided titanium oxide particles may also be prepared by a vapor phase method. Especially preferably finely divided titanium oxide particles are prepared by a method of hydrolyzing titanium chloride or titanium sulfate because the operation is easy and the cost is low.
The hydrolysis method is not particularly limited, but it is preferable that hydrolysis is performed in a hydrolysis vessel equipped with a reflux condenser while the
Murase Noriko
Nakamura Hidenori
Ohkubo Takashi
Ohmori Masahiro
Uotani Nobuo
de la Peña James
Jones Deborah
Showa Denko Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
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