Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-08-31
2003-06-24
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S323000, C428S332000, C428S334000, C428S335000, C428S336000, C428S426000, C428S428000, C428S432000, C428S446000, C428S448000, C428S688000, C428S689000, C428S697000, C428S913000
Reexamination Certificate
active
06582839
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an article with a photocatalytic film, such as an automotive or architectural window pane. The article is provided with anti-fogging function, stain resistance, hydrophilicity and good visibility in rainy weather.
Japanese Patent Laid-open Publication JP-A-9-328336 discloses a composition for forming a photocatalytic film. This composition comprises (1) TiO
2
grains having an average grain diameter of less than 100 nm, (2) Zr-containing compound, and (3) Si-containing compound. The composition is such that the weight ratio of the Zr-containing compound to the TiO
2
grains is from 0.02 to 0.5 in terms of oxide and that the weight ratio of the Si-containing compound to the TiO
2
grains is from 0.2 to 2.5 in terms of oxide.
JP-A-10-216528 discloses a photocatalytic article comprising a substrate and a catalytic film formed thereon. This catalytic film is a combination of photocatalytic grains and a binder containing 60-90 wt % of silica and 10-40 wt % of zirconia.
JP-A-9-227159 discloses a vehicular front or rear window glass having a substantially transparent layer bonded to a substrate. This layer contains a photocatalytic semiconductor material.
JP-A-10-156999 discloses a photocatalytic layer made of a mixture of silica and titania. JP-A-9-271731 discloses a photocatalytic member having a top surface comprising titanium oxide and silicon oxide as major components. JP-A-9-56788 discloses an article for bathroom, having a photocatalytic layer made of a mixture of silica and titania.
JP-A-11-35342 discloses a multi-functional glass having a soda-lime glass substrate, a first layer formed on the substrate, and a second layer formed on the first layer. The first layer is a SiO
2
film containing at least one member selected from Ti and metal elements having electronegativities close to that of Ti. The second layer is a TiO
2
film or a SiO
2
film in which TiO
2
fine particles are dispersed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an article with a photocatalytic film, which is improved in photocatalytic activity, abrasion resistance and chemical resistance.
It is another object of the present invention to provide a process for producing such article.
According to the present invention, there is provided an article comprising a substrate; and a photocatalytic film covering said substrate. This film comprises (1) a film-forming component comprising ZrO
2
and SiO
2
and (2) TiO
2
crystals dispersed in said film-forming component, said ZrO
2
, said SiO
2
and said TiO
2
crystals respectively being in amounts of 25-60 wt %, 15-50 wt % and 25-45 wt %, based on a weight of said film.
According to the present invention, there is provided a first process for producing the article. The first process comprises (a) providing a coating liquid comprising a first raw material of said ZrO
2
, a second raw material of said SiO
2
, and a third raw material of said TiO
2
crystals; (b) applying said coating liquid to a surface of said substrate, thereby forming thereon a precursory film; and (c) subjecting said precursory film to a heat treatment at a temperature of 300-700° C., thereby turning said precursory film into said photocatalytic film.
According to the present invention, there is provided a second process for producing the article. The second process comprises (a) providing a coating liquid comprising a first raw material of said ZrO
2
, a second raw material of said SiO
2
, and a third raw material of said TiO
2
crystals; (b) applying said coating liquid to a surface of said substrate, thereby forming thereon a precursory film; and (c) subjecting said precursory film to a first baking at a temperature of 560-700° C., thereby turning said precursory film into said photocatalytic film.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
We unexpectedly found that an article according to the invention is improved in photocatalytic activity (e.g., stain resistance and hydrophilicity), abrasion resistance and chemical resistance (e.g., acid resistance and alkali resistance) by specifying respective amounts of ZrO
2
, SiO
2
and TiO
2
crystals as above, particularly by increasing the amount of ZrO
2
relative to that of TiO
2
crystals as above. For example, the obtained article becomes satisfactory in an alkali resistance test for Category A of Japanese Industrial Standard (JIS) R 3221 and thus can practically be used as an exterior window pane such as automotive or architectural window pane.
As stated above, the respective amounts of ZrO
2
, SiO
2
and TiO
2
crystals are specified. Particularly, TiO
2
crystal fine grains, for example, having an average grain size of not greater than 30 nm, are preferably used as at least part of a raw material of TiO
2
crystals of the photocatalytic film. Due to these features, the photocatalytic film does not have cracks even if the baking of the precursory film is conducted at a high temperature at which a glass plate (substrate) can be bent into a curved glass plate. Generally speaking, such high temperature tends to make a photocatalytic film inferior in photocatalytic activity. According to the invention, however, the photocatalytic film does not become inferior in photocatalytic activity by such high temperature, due to the above features. Therefore, it is not necessary to provide an alkali barrier layer between the glass plate and the photocatalytic film for preventing the movement of alkali components of the glass plate into the photocatalytic film.
The total amount of ZrO
2
, SiO
2
and the TiO
2
crystals of the photocatalytic film is preferably at least 90 wt %, based on the weight of the film, in order to have photocatalytic activity and durability such as abrasion resistance, acid resistance and alkali resistance. Besides these essential components, the film may optionally comprise not greater than 10 wt % of at least one component such as amorphous TiO
2
, colloidal silica, other oxides (e.g., Al
2
O
3
, B
2
O
3
and SnO
2
), ions (Cr ion and V ion) and carbon. The TiO
2
crystals of the film may have an average grain size of not greater than 30 nm or not greater than 20 nm.
In case that the article is used as an automotive window pane, it is preferable to dispose the photocatalytic or hydrophilic film on an outer side of automobile.
In case that a glass plate is used as the substrate in the second process, the glass plate may be bent into a curved glass plate after the first baking or when the precursory film and the glass substrate are subjected to the first baking.
In order to improve the film in transparency and durability, the third raw material of the first process is preferably TiO
2
grains having an average grain size of not greater than 20 nm, and that of the second process is preferably those grains having an average grain size of not greater than 30 nm.
The first raw material of the first and second processes is preferably zirconium chloride or zirconium nitrate in order to improve the photocatalytic film in durability, particularly abrasion resistance, acid resistance and alkali resistance. Examples of the zirconium chloride include zirconium chloride, zirconium oxychloride octahydrate, and a chlorine-containing zirconium alkoxide represented by the general formula Zr(OC
m
H
2m+1
)
x
Cl
y
where m, x and y are integers and x+y=4. Examples of the zirconium nitrate include zirconium oxynitrate dihydrate. The ZrO
2
content of the film is not lower than 25 wt % in order to have the film provided with alkali resistance and photocatalytic activity. If it is higher than 60 wt %, the film becomes inferior in abrasion resistance and/or photocatalytic activity. The ZrO
2
content of the film is preferably from 25 to 45 wt %. As ZrO
2
is added to the film, the film is improved in alkali resistance. Furthermore, the film is remarkably improved in photocatalytic activity if the ZrO
2
content of the film is not lower than 25 wt %.
The second raw material of the first and second processes is not particularly limited, so long as i
Honjo Hiroshi
Nishida Yoshihiro
Yamamoto Hideki
Yamazaki Seiji
Central Glass Company Limited
Crowell & Moring LLP
Jones Deborah
Piziali Andrew T
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