Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2002-09-03
2004-08-17
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S432000, C428S688000, C428S689000, C428S701000, C428S702000, C502S242000, C502S309000, C502S349000, C502S350000, C106S286100, C106S286400, C106S286800, C427S377000, C427S376200
Reexamination Certificate
active
06777091
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a substrate on which a photocatalytic film having titanium oxide as a primary component is coated and a method for producing the same.
BACKGROUND ART
Substrates (articles) on whose surface a photocatalytic film is coated are widely used in, for example, windowpanes of buildings requiring fouling resistance, antibacterial property, and the like, indicator panels of electronic displaying instruments, casings of portable equipment, sanitary installations, frames of medical facilities, apparatus in the field of biotechnology such as DNA analysis and the like. The substrates on which a photocatalytic film containing titanium oxide as a primary component is coated are widely used in order to provide fouling resistance, antibacterial property, deodorizing function and the like to the such substrate surfaces.
Such photocatalytic films are coated by sputtering processes, and it is known that crystalline titanium dioxide films are preferable as such films in order to increase the photocatalytic activity of the photocatalytic films and make the fouling resistance performance better. However, in order to coat on a substrate a titanium dioxide film having good crystallinity, there is a problem of requiring heating the substrate to be coated at a temperature of 300° C. or more (Japanese Patent Laid-Open No. 10-1 52396).
In addition, there are known photocatalytic films prepared by irradiating a metallic titanium target with electron beams in an oxidizing atmosphere to coat an amorphous titania (non-crystalline titanium oxide) film on a glass plate, followed by calcination it at a temperature of 400 to 500° C. or more to form rutile-typed titania crystal (Japanese Patent Laid-Open No. 10-146251) and processes for photocatalytic films of crystalline titanium dioxide prepared by coating a metallic titanium or titanium oxide film on a glass plate by sputtering, followed by calcination it (Japanese Patent Laid-Open Nos. 10-278165 and 10-146251).
However, coating a photocatalytic film on a substrate heated at high temperatures by a sputtering process that are carried out in an atmosphere at reduced pressure causes releasing impurity gases such as moisture from the inner wall of the heated decompressing container (film-forming chamber container), and therefore has technical problems of being difficult in making reduced-pressure atmosphere good purity. In other words, in order to make reduced-pressure atmosphere good purity necessary to obtain a good photocatalytic activity, a vacuum exhausting system in a big way is required to sputtered-film-forming equipment, causing problems of increasing the cost of coating a photocatalytic film.
In addition, methods of crystallizing the above-mentioned amorphous titanium oxide and metallic titanium films in the air by heating and calcination have problems of poor productivity because of requiring calcination for a sufficient period of time at high temperatures (heat treatment) and expensive calcination equipment and elongating the heating cycle. Furthermore, there are problems of not obtaining readily photocatalytic films with good reproductivity.
DISCLOSURE OF THE INVENTION
A subject of the present invention is to solve the above-mentioned problems. A first purpose of the present invention is to provide a substrate on which a photocatalytic film having high photocatalytic activity is coated. A second purpose of the present invention is to provide a method capable of producing a substrate with such photocatalytic film without the need of heating at a high temperature in the film-coating step.
The present invention have been achieved by finding that when a titanium oxide film coated on the surface of a substrate by a sputtering process which is amorphous or at a state where the crystallinity has not sufficiently developed is heated and crystallized with controlling the oxygen-defect state of the film, it can be formed to a photocatalytic film containing titanium oxide as a primary component and having good photocatalytic activity.
One embodiment of the invention is a substrate with photocatalytic film comprising a substrate and a photocatalytic film coated on the substrate, wherein said photocatalytic film is coated on said substrate by sputtering a target containing titanium in an atmosphere at reduced pressure, contains titanium oxide as a primary component, and has a sheet resistance of 10
9
to 10
13
&OHgr;/□.
The photocatalytic film having a titanium oxide film as a primary component according to the present invention is a crystalline titanium dioxide film containing anatase-typed crystal and characterized by a controlled oxygen-defect state of the film. In the case that a titanium dioxide film contains an almost stoichiometric amount of titanium and oxygen, its sheet resistance is at a level of 10
15
&OHgr;/□ or more. By contrast, the photocatalytic film according to the present invention is formed to an oxygen-defect state, whereby the sheet resistance of the film can be controlled in the range of 10
9
to 10
13
&OHgr;/□.
Although the reason is not clear why the degree of the photocatalytic activity of a titanium oxide film depends on the oxygen-defect state of the titanium dioxide film, it is likely that the oxygen deficiency can be contributed to the energy level of the crystalline titanium oxide film.
The relationship between the photocatalytic activity and the sheet resistance of the titanium dioxide film indicates that when the sheet resistance is more than 10
13
&OHgr;/□ and the amount of oxygen deficiency is reduced, the photocatalytic activity is decreased. By contrast, when the sheet resistance is less than 10
9
&OHgr;/□, that is, when the oxygen deficiency is present at a more amount than that indicated by 10
9
&OHgr;/□ sheet resistance (the oxygen in the titanium oxide film is reduced to a smaller amount than that corresponding to the stoichiometric amount of titanium dioxide), the photocatalytic activity is reduced, if anything. The titanium oxide photocatalytic film according to the present invention has a sheet resistance controlled within the range of 10
9
to 10
13
&OHgr;/□, and therefore has high photocatalytic activity.
The photocatalytic film according to the present invention is coated on a substrate by a sputtering process. The film is coated by employing metallic titanium or a metal having metallic titanium as a primary component as a target, and sputtering it in reduced pressure atmosphere comprising a mixed gas of an inert gas such as argon and oxygen or oxygen gas alone. The controlling of the oxygen deficiency of the titanium oxide film can be achieved by controlling the total pressure of the atmosphere gas and the partial pressure of oxygen during sputtering the target.
Also, the photocatalytic film according to the present invention can be coated by employing, as a target, titanium dioxide that has the stoichiometric composition or is at a state where the oxygen is somewhat more defect than the stoichiometric amount (sometimes referred to as titanium suboxide), and sputtering it in reduced pressure atmosphere comprising a mixed gas of an inert gas such as argon and oxygen or oxygen gas alone. The controlling of the oxygen deficiency in the titanium oxide film can be achieved by controlling the total pressure of the atmosphere gas and the partial pressure of oxygen during sputtering the target.
The sheet resistance of the photocatalytic film may be controlled so as to be within 10
9
to 10
13
&OHgr;/□ by heat treatment after coating on the substrate.
In the present invention, the sheet resistance can be controlled such that the titanium dioxide film immediately after coating has the resistance range described above, and preferably is controlled in combination with the resistance controlling during coating and the resistance controlling by heat treatment after coating. This can result in the formation of a photocatalytic film having a higher surface hardness.
The heat treatment is carried out such that the contract
Anzaki Toshiaki
Kijima Yoshifumi
Blackwell-Rudasill G.
Jones Deborah
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