Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-10-02
2002-11-12
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S327000, C428S328000, C428S329000, C428S330000, C428S331000, C428S332000, C428S333000, C428S336000, C502S208000, C502S242000, C502S150000, C502S352000, C502S351000, C502S349000, C502S343000, C106S436000, C106S438000
Reexamination Certificate
active
06479141
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a photocatalytic coating composition providing a thin film exhibiting excellent photocatalytic activity without giving interference color; and to a product having, on its surface, a thin film formed from the photocatalytic coating composition.
(2) Description of the Related Art
Recently, products having a titanium dioxide coating formed thereon exhibiting a photocatalytic activity have been used in a variety of fields in order to prevent staining by means of removing a harmful substance; to decompose pollutants such as ammonia and sulfur compounds in the air for removal, and to sterilize bacteria. When irradiated with light, photocatalytic titanium dioxide exhibits activity for a redox reaction in the irradiated area. Therefore, photocatalytic titanium dioxide is used in such a state that it is held on an exposed surface of a substrate. In order to maximize the effect of titanium dioxide held on a substrate, a coating of titanium dioxide is applied onto a surface of the substrate, so that the titanium dioxide forms a thin film. Examples of products on which titanium dioxide is held in such a manner include an illumination lamp, a mirror, and window glass used in deodorization and stain-proofing.
One method for forming titanium dioxide thin film is application of a coating composition containing titanium dioxide and a binder onto a surface of a substrate through a method such as spray-coating, dip-coating, flow-coating, spin-coating, roll-coating, or brush-coating, followed by drying and/or firing.
The thus-formed thin film formed through coating generally has an uneven thickness. In addition, difference in refractive index between the film and the substrate gives interference colors, resulting in undesirable appearance. Particularly in these days, environmental cleanliness of living space is a growing concern, and interior products having a titanium dioxide thin film thereon have been more widely used. Thus, there is still demand for mitigating the drawback in appearance.
Meanwhile, when a high-refractive-index hard coat is formed on a surface of a transparent substrate such as transparent plastic or glass, there has been proposed formation of a hard coat film by use of particles of composite oxide comprising titanium dioxide, silicon oxide, and zirconium oxide and/or aluminum oxide so as to prevent generation of interference bands given by difference in refractive index between a substrate and the hard coat film (Japanese Unexamined Patent Publication (Kokai) No. 48940/1996).
However, when titanium dioxide is used in the form of such composite oxide particles so as to provide a photocatalytic coating film, the photocatalytic activity of titanium dioxide is manifested insufficiently, which is disadvantageous.
In order to impart hydrophilicity and durability to a photocatalytic titanium dioxide film, there has been proposed a photocatalytic coating film which is made of a composite material containing titania and an amorphous metal oxide and incorporates finely divided particles of silica and/or alumina therein (Japanese Unexamined Patent Publication (Kokai) No. 68092/1998). This photocatalytic coating film is formed by applying onto a substrate a composite sol liquid containing titania sol capable of being dehydration-polycondensed, metal oxide sol capable of forming an amorphous metal oxide by dehydration-polycondensation, and a colloidal solution of silica and/or alumina, followed by firing. The coating film formed of a composite material of titania and an amorphous metal oxide and finely divided particles of silica and/or alumina effectively enhances hydrophilicity and durability, but, interference colors cannot be prevented.
SUMMARY OF THE INVENTION
In view of the aforementioned problems involved in the prior art, an object of the present invention is to provide a photocatalytic titanium dioxide coating composition which provides a thin film exhibiting excellent photocatalytic activity without giving interference color.
The present inventors have found that when a small amount of particles of an inorganic compound other than titanium dioxide (or particles of an organic compound convertible to particles of an inorganic compound during firing of a coating film), the particles having a relatively large particle diameter, is incorporated in a coating composition containing photocatalytic titanium dioxide, a thin film exhibiting excellent photocatalytic activity and no interference color is formed. The present invention have been completed on the basis of this finding.
Accordingly, in one aspect of the present invention, there is provided a photocatalytic titanium dioxide coating composition comprising (a) finely-divided titanium dioxide particles exhibiting photocatalytic activity, (b) particles of an inorganic compound other than titanium dioxide, or particles of an organic compound convertible to particles of an inorganic compound on firing, (c) a binder, and (d) a solvent, characterized in that the particles of an inorganic compound have an average particle diameter which is larger than that of the finely divided titanium dioxide particles and falls within the range of about 0.1 &mgr;m to about 1.0 &mgr;m; the inorganic compound particles are substantially insoluble in the solvent; and the amount of the inorganic compound particles is in the range of about 0.5% to about 7% by weight based on the weight of the finely divided titanium dioxide particles.
In another aspect of the present invention, there is provided a product having a photocatalytic titanium dioxide thin film formed on a surface of a substrate, which thin film is formed from a photocatalytic titanium dioxide coating composition comprising (a) finely-divided titanium dioxide particles exhibiting photocatalytic activity, (b) particles of an inorganic compound other than titanium dioxide, or particles of an organic compound convertible to particles of an inorganic compound on firing, (c) a binder, and (d) a solvent; said particles of an inorganic compound having an average particle diameter which is larger than that of the finely divided titanium dioxide particles and falls within the range of about 0.1 &mgr;m to about 1.0 &mgr;m; said inorganic compound particles being substantially insoluble in the solvent; and the amount of the inorganic compound particles being in the range of about 0.5% to about 7% by weight based on the weight of the finely divided titanium dioxide particles.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The photocatalytic titanium dioxide coating composition of the invention, and the product having a photocatalytic titanium dioxide thin film of the invention will be described in detail.
The finely divided titanium dioxide particles exhibiting photocatalytic activity, used in the invention, exhibit photocatalytic activity predominantly for a redox reaction of an organic compound, when irradiated with light having energy greater than a band gap between a conduction band and a valence band of a titanium dioxide crystal. No particular limitation is imposed on the finely divided titanium dioxide particles used in the invention, and crystalline particles are preferred. Although the crystal structure may be of anatase type, rutile type, or brookite type, brookite type is particularly preferred.
However, since finely divided titanium dioxide particles exhibiting excellent photocatalytic activity are preferred, the finely divided titanium dioxide particles preferably have a small particle diameter. Fine titanium dioxide particles having an average particle diameter less than about 0.004 &mgr;m are difficult to produce, and typically, the finely divided particles used have an average particle diameter of about 0.004 &mgr;m to about 0.1 &mgr;m, preferably about 0.005 &mgr;m to about 0.1 &mgr;m and more preferably about 0.006 &mgr;m to about 0.09 &mgr;m. The finely divided titanium dioxide particles have a specific surface area of preferably at least about 20 m
2
/g, more preferably about 20 m
2
/g to about 300 m
2
/g.
Ohmori Masahiro
Sanbayashi Masayuki
Showa Denko K.K.
Thibodeau Paul
Uhlir Nikolas J.
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