U.S. patent application number 10/682616 was filed with the patent office on 2004-04-15 for article coated with photocatalyst film, method for preparing the article and sputtering target for use in coating the film.
This patent application is currently assigned to Nippon Sheet Glass Co., Ltd.. Invention is credited to Anzaki, Toshiaki, Arai, Daisuke, Kijima, Yoshifumi.
Application Number | 20040069615 10/682616 |
Document ID | / |
Family ID | 26581444 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040069615 |
Kind Code |
A1 |
Anzaki, Toshiaki ; et
al. |
April 15, 2004 |
Article coated with photocatalyst film, method for preparing the
article and sputtering target for use in coating the film
Abstract
This invention relates to an article having a substrate with a
photocatalyst coating film formed thereon by ae sputtering method,
characterized in that the photocatalyst coating film comprises
titanium oxide as a main component and at least one kind of metal
having a sputtering rate for Ar being 0.9 to 2.7 times that of Ti,
preferably at least one kind of metal selected from the group
consisting of Fe, V, Mo, Nb, Al and Cr, in an amount of 0.01 to 10
wt % in terms of the sum of such metals. The coating film is formed
by a method using a Ti metal sputtering target or a Ti sub-oxide
sputtering target containing the metal in an amount of 0.01 to 10
wt % in terms of the sum of such metals, or a method using two
kinds of targets for two sputtering cathodes and applying reversing
potential so as to have a cathode and an anode alternately.
Inventors: |
Anzaki, Toshiaki;
(Osaka-shi, JP) ; Arai, Daisuke; (Osaka-shi,
JP) ; Kijima, Yoshifumi; (Osaka-shi, JP) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
Nippon Sheet Glass Co.,
Ltd.
Osaka-shi
JP
|
Family ID: |
26581444 |
Appl. No.: |
10/682616 |
Filed: |
October 9, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10682616 |
Oct 9, 2003 |
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10168253 |
Sep 23, 2002 |
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10168253 |
Sep 23, 2002 |
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PCT/JP00/09092 |
Dec 21, 2000 |
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Current U.S.
Class: |
204/192.15 ;
204/192.12 |
Current CPC
Class: |
C23C 14/3464 20130101;
C23C 14/08 20130101; B01J 35/002 20130101; C23C 14/3414 20130101;
C23C 14/06 20130101; C23C 14/083 20130101; B01J 37/34 20130101;
B01J 35/004 20130101 |
Class at
Publication: |
204/192.15 ;
204/192.12 |
International
Class: |
C23C 014/34 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 1999 |
JP |
11-363022 |
Dec 12, 2000 |
JP |
2000-378033 |
Claims
What is claimed is:
1. An article having a substrate and a photocatalyst coating film
formed thereon by a sputtering method, characterized in that the
photocatalyst coating film comprises: 1) titanium oxide as a main
component and 2) at least one kind of metal having a sputtering
rate for Ar, which has at least one kind of energy in a 100 eV to
2000 eV ion energy area, being 0.9 to 2.7 times that of Ti.
2. An article with the photocatalyst film coated thereon according
to claim 1, wherein said sputtering rate of said metal is 9 to 2.3
times that of Ti.
3. An article with the photocatalyst film coated thereon according
to claim 1, wherein the metal is at least one metal selected from
the group consisting of Fe, V, Mo, Nb, Al and Cr.
4. An article with the photocatalyst film coated thereon according
to claim 1, wherein the metal is at least one metal selected from
the group consisting of Fe, V, Mo and Nb.
5. An article with the photocatalyst film coated thereon according
to claim 1, wherein the metal is at least one metal selected from
the group consisting of Fe, V and Mo.
6. An article with the photocatalyst film coated thereon according
to one of claims 1.about.5, wherein the content of the metal is
0.01.about.10 wt % in terms of such metals.
7. A Ti metal sputtering target containing at least one metal
selected from the group of metals described in one of claims
1.about.6 in an amount of 0.01.about.10 wt % in terms of the sum of
such metals
8. A Ti sub-oxide sputtering article containing at least one metal
selected from the group of metals described in one of claims
1.about.6 in an amount of 0.01 to 10 wt % in terms of the sum of
such metals.
9. A method for preparing a photocatalyst film coated article,
characterized in that the article is prepared by a reactive
sputtering method using oxygen gas and at least a sputtering target
described in claim 7 in a method for coating a substrate with a
photocatalyst film comprising titanium oxide as a main component
and at least one kind of metal having a sputtering rate for Ar,
which has at least one kind of energy in a 100 to 2000 eV ion
energy area, being 0.9 to 2.7 times that of Ti.
10. A method for preparing a photocatalyst film coated article,
characterized in that the article is prepared by a sputtering
method using at least a sputtering target described in claim 8 in a
method for coating a substrate with a photocatalyst film comprising
titanium oxide as a main component and at least one kind of metal
having a sputtering rate for Ar, which has at least one kind of
energy in a 100 eV to 2000 eV ion energy area, being 0.9 to 2.7
times that of Ti.
11. A method for preparing a photocatalyst film coated article,
characterized in that two cathodes respectively having a sputtering
target of a metal or a metal oxide comprising the photocatalyst
film attached adjoining each other, voltage is applied to reverse
the polarity of two cathodes alternately so that when one cathode
is the negative pole, the other cathode is the positive pole while
when said the other cathode is the negative pole, said one cathode
is the positive pole, and the two targets are sputtered
simultaneously by a glow discharging plasma caused therefrom in a
method for coating a substrate by a photocatalyst film comprising
titanium oxide as a main component and at least one kind of metal
having a sputtering rate for Ar, which has at least one kind of
energy in a 100 eV to 2000 eV ion energy area, being 0.9 to 2.7
times that of Ti.
12. An article coated with a photocatalyst film characterized in
that it is prepared by the method described in one of claims 9
through 11.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] When a substrate coated with a photocatalyst film is a glass
plate, the glass plate is used in a wide range of fields, for
example, window glass for architectural windows, windows for LCDs
(liquid crystal display) and PDPs (plasma display panel), a glass
substrate for DNA analysis that is used in the field of
biotechnology, solar cell panel, etc. Further, when a substrate
coated with a photocatalyst film is a resin frame, contamination
preventive properties are given to such equipment and facilities as
portable information terminal devices, sanitary facilities, medical
facilities, electronic devices, etc. Thus, when coated on various
kinds of substrates, a photocatalyst film provides properties to
the substrate surfaces by which they exhibit very little
contamination or any contamination is easily removed. Further, a
photocatalyst film has anti-bacteria action and is applicable to
biomedical inspection chips such as a bio chip or a chemical chip.
This invention relates to an article having a substrate coated with
a photocatalyst film, a method for preparing the article and
sputtering targets for use in coating the film.
[0003] 2. Description of the Related Art
[0004] In Japanese Laid-Open Patent Publication No HEI 10-66879,
glass plates coated with a titanium oxide film, a zinc oxide film
or a tungsten oxide film are disclosed as articles with a
photocatalyst film formed on substrates and it is stated that these
are best suited for containing such metals as platinum, palladium,
nickel, copper, tin in this photocatalyst film in order to improve
the photocatalyst activity. It is also stated that this
photocatalyst film is coated by reactive sputtering in inactive gas
containing oxygen using a metal corresponding to metal oxide
forming the photocatalyst film as a target.
[0005] In Japanese Laid-Open Patent Publication No. HEI 11-92176,
articles coated with a photocatalyst film comprising titanium
oxide, etc. obtained by a sputtering method and containing such
metallic ions as platinum, nickel, chrome, cobalt, tin, niobium,
tantalum doped into its surface by the ion implanting method are
disclosed.
[0006] Further, in Japanese Laid-Open Patent Publication No. HEI
11-60281, a photocatalyst glass with a first layer of SiO.sub.2
film containing Al.sub.2O formed on the surface of a soda lime
silica glass and a second layer comprising TiO.sub.2 as a main
component formed thereon is disclosed. It is also stated that it is
better to mix a metal oxide of Al.sub.2O.sub.3, P.sub.2O.sub.5,
B.sub.2O, ZrO.sub.2, SnO.sub.2 or Ta.sub.2O into the TiO.sub.2 film
thoroughly for the purpose of improving film minuteness, film
strength, and alkali resistance, giving conductivity and cutting
ultraviolet rays. It is further stated that these metallic oxide
films are coated by thermally decomposing such organic metallic
compounds as metallic alkoxide, metallic acetyl-acetonert, etc.
[0007] Further, in FIG. 1 of Japanese Laid-Open Patent Publication
No. HEI 10-330131, a photocatalyst coated glass article having a
good hydrophilic multi-layer structure comprising an Si.sub.2 base
layer, a TiO.sub.2 photocatalyst layer and an SiO.sub.2 top layer
formed on a plate glass is disclosed. It is stated that this
photocatalyst layer comprises mainly titanium oxide with Al.sub.2O,
Y.sub.2O, Ta.sub.2 O.sub.5 and La.sub.2O.sub.5 intermixed. It is
also stated that these photocatalyst metallic oxide layers are
laminated and formed by an electron beam vaporization method.
[0008] Out of the existing technology described above, the
photocatalyst film disclosed in Japanese Laid-Open Patent
Publication No. HEI 10-66879 has such metals as platinum,
palladium, etc. mixed in a titanium oxide film in order to increase
photocatalyst activity. However, in the oxygen reactive sputtering
method using a metal target of titanium, there was such a problem
that it was difficult to contain a fixed amount of platinum or
palladium as a catalyst activity improving agent in the metallic
state without oxidizing the platinum or palladium while oxidizing
titanium when coating a titanium oxide film containing such metals
as platinum. Further, in the sputtering method using a target of
titanium oxide, there was such a problem that it was difficult to a
manufacture oxide sintered matter having metallic powder of
platinum dispersed uniformly therein.
[0009] In the doping of metallic ion by the ion implanting method
disclosed in Japanese Laid-Open Patent Publication No. HEI
11-92176, there were such problems that 1) excessive or
insufficient doping giving uneven density resulted as metallic ions
were dispersed in the depth direction of a film so that uniform
doping of the film was impossible, 2) the grid disorder around the
substituting side of the implanted metal becomes large and as a
result, a dopant does not only function as a donor or an acceptor
but also a drop of the photocatalyst activity is caused by increase
of recombination center, 3) an amount of ions implanted cannot be
greatly increased, 4) several kinds of dopants cannot be implanted
at a time while controlling their densities, and 5) as metallic
ions are used for doping by ion implantation, it is difficult to
apply the metallic ion doping to large sized substrates such as
structural window glasses, solar cell panels that are installed on
the roof of a house, or glass plates used in relatively large
displays.
[0010] In the existing technology stated in Japanese Laid-Open
Patent Publication No. HEI 11-60281, there was such a problem that
after coating organic metallic compounds such as metal alkoxide,
metallic acetyl-acetonert, etc. on a substrate, it was necessary to
heat the substrate at a high temperature of 500.about.600.degree.
C., so this technology could not be applied to thermally restricted
substrates such as resin made substrates.
[0011] Further, the photocatalyst layer of the existing technology
shown in FIG. 1 of Japanese Laid-Open Patent Publication No. HEI
10-330131 is laminated and coated by an electron beam vaporization
method and it is therefore difficult to apply this technology to
large substrates such as, for example, a structural window glass, a
solar cell panel installed on a roof of a house, and a relatively
large display unit.
[0012] This invention is made for solving the problems involved in
the existing technologies described above and it is a first object
to provide articles having more improved photocatalyst activity. A
second object of this invention is to provide an article having
improved photocatalyst activity even when the surface is large. A
third object of this invention is to provide a photocatalyst
function to the surface of a substrate even when its thermal
resistance is relatively weak. A fourth object of this invention is
to provide a method to efficiently coat a substrate with an
improved photocatalyst film.
SUMMARY OF THE INVENTION
[0013] This invention relates to an article having a substrate with
a photocatalyst coating film formed thereon by a sputtering method,
characterized in that the photocatalyst coating film comprises: 1)
titanium oxide as a main component and 2) at least one kind of
metal having a sputtering rate for Ar, which has at least one kind
of energy in the ion energy area of 100 to 2000 eV, being 0.9 to
2.7 times that of Ti, preferably at least one kind of metal
selected from the group consisting of Fe, V, Mo, Nb, Al and Cr.
[0014] The photocatalyst film of this invention contains titanium
oxide as a main component and at least one metal selected from the
group consisting of Fe, V Mo, Nb, Al and Cr as a component in a
small amount. In order to improve the photocatalyst activity of
titanium oxide, one or more than two kinds of metals can be
contained.
[0015] Generally, the improvement of the photocatalyst activity of
titanium oxide by metal ion doping has been studied for a long
time, and many metals have been examined as additive metals having
the effect of improving the photocatalyst activity (for example,
"Chemical Introduction 39, Inorganic Photochemical", 1st Edition,
Page 128, Gakkai Shuppan Center, 1983, "Titanium Oxide", 1st
Edition, Page 178, Gihodo, 1991). The reason for the improvement of
the photocatalyst activity of titanium oxide by these metals is not
clear but is considered that these metal atoms are replaced by some
of the titanium atoms bonding to oxygen in the titanium oxide, the
coordinating state of the atoms changes, resulting in an increase
in active catalyst sites (for example, a defective site in a
so-called dangling bonded state wherein the coordination of the
atoms is cut and part of electrons belonging to oxygen or titanium
are placed in the free state having no bonding mate). It is also
considered that the catalytic action is improved when the density
of easily exciting electrons and electron holes is increased even
at room temperature as a result of metallic doping.
[0016] This invention relates to an article having a substrate and
a photocatalyst coating film formed thereon by the sputtering
method. The present inventors confirmed that effective improvement
of photocatalyst activity could not be recognized simply by doping
a titanium oxide film with well known metals by an ordinary method
only and as a result of detailed study, found that the problem can
be solved by preparing a photocatalyst film by two methods
described below.
[0017] The inventors found two methods for forming a photocatalyst
coating film: 1) a method for forming a film by the sputtering
method using a Ti metal sputtering target or a Ti sub-oxide
sputtering target containing at least one kind of metal having a
sputtering rate (also called a sputter rate) for Ar, which has at
least one kind of energy in the ion energy area of 100 to 2000 eV,
being 0.9 to 2.7 times that of Ti, preferably at least one kind of
metal selected from the group consisting of Fe, V, Mo, Nb, Al and
Cr, in an amount of 0.01 to 10 wt % in terms of the sum of such
metals and 2) a method for forming a film by the sputtering method
by providing two kinds of targets for two sputtering cathodes and
applying reversing potential so as to have a cathode and an anode
alternately.
[0018] In the method 1, a metal for doping a titanium oxide
sputtering film is at least one kind of metal having a sputtering
rate for Ar, which has at least one kind of energy in a 100 to 2000
eV ion energy area, being 0.9 to 2.7 times of that of Ti,
preferably at least one kind of metal selected from the group of
Fe, V, Mo, Nb, Al and Cr.
[0019] A metal doped titanium oxide film is formed on a substrate
using a Ti metal sputtering target or a Ti sub-oxide sputtering
target containing this metal in an amount of 0.01 to 10 wt % in
terms of the sum of such metals by a reactive sputtering method
using oxygen gas or an ordinary sputtering method. At this time, if
the sputtering rate of the metal differs from that of Ti, the
composition of the sputtering target may become largely different
from that of the formed film. An uneven metal doping, that is, a
metal segregation is caused and the improvement of the
photocatalyst activity is impeded. Therefore, the sputtering rate
of the doping metal should be 0.9 to 2.7 times that of Ti,
preferably 0.9 to 2.3 times. If the sputtering rate of the metal is
less than 0.9 times that of Ti, the film composition becomes Ti
rich, which is not preferable, and the metal doping effect is
scarcely displayed. If larger than 2.7 times, the film composition
becomes metal rich and metal segregation is recognized. This is
also not preferable as the improvement of the photocatalyst
activity is impeded. Such change in composition and metal
segregation can be further suppressed when the sputtering rate of
the metal is made smaller than 2.3 times that of Ti.
[0020] A sputtering method in a pressure reduced argon containing
gas or a reactive sputtering method in oxygen plasma using pressure
reduce mixed gas containing argon and oxygen using a metal
corresponding to such oxide as a target can be adopted as a
sputtering method. As a means for generating discharge plasma in
the above sputtering method, DC glow discharge, intermediate
frequency glow discharge, or high frequency glow discharge can be
used. In the sputtering method using a metal as a target, it is
desirable to use oxygen in an amount of 10 to 1000% in terms of the
sum of argon and oxygen. The sputtering is better performed under a
reduced pressure of 0.07 to 7 Pa.
[0021] For a sub-oxide target that is used for implanting more than
two kinds of metals in a photocatalyst coating film, a mixed powder
of metal oxide or compound metal oxide powder can be used.
According to the degree of conductivity of the target that is
obtained, either DC or AC or a high frequency power source is used.
As a metal target, an alloy target or a mixed metal target of
powdered sintered matter is used.
[0022] The method 2 described above is a method for sputtering two
targets at the same time. In this method, two cathodes having metal
or metal oxide sputtering targets forming a photocatalyst coating
film are arranged adjacent to each other and glow discharge plasma
is generated by applying voltage by reversing the polarities of
these cathodes alternately so that one cathode becomes the positive
pole when the other is the negative pole or vice versa, thereby
sputtering two targets simultaneously.
[0023] At this time, if the sputtering rate of the metal differs
largely from that of Ti, the target composition and the formed film
composition become largely different or uneven metal doping, that
is, metal segregation is caused and the improvement of the
photocatalyst activity is impeded. So, for the same reason as in
the method 1, the sputtering rate of the doping metal should be 0.9
to 2.7 times that of Ti, preferably 0.9 to 2.3 times.
[0024] In the above two sputtering methods, a more crystalline
catalyst film can be coated on a substrate even at a low
temperature by forming the film while applying the plasma to the
film by applying a bias voltage to the substrate or closing the
distance between the substrate and targets.
[0025] Further, when coating the photocatalyst film on a substrate
having a relatively large surface, for example, a window glass
plate for a structure, it is preferable to coat the substrate by
passing in front of a sputtering target for coating a uniformly
thick film on the entire substrate.
[0026] In this invention, when metals are distributed uniformly in
a sputtering target in advance, or when two kinds of targets in
different compositions are sputtered simultaneously, a uniform film
composition can be achieved. As the film can be coated using the
method 1 or 2, there are no such problems as non-uniformity of
metals that becomes a problem in the ion implanting method, drop in
photocatalyst activity caused by the grating disorder of titanium
oxide, control of metal doping amount, difficulty of doping of
plural metals, etc. Further, as this is a sputtering method, it is
easy to apply to a substrate having a large surface area such as a
window glass of a structure, a solar cell panel installed on a
house roof, or a glass plate that is used for a relatively large
display unit and, also, is suited to bio chips and chemical chips
for which highly uniform quality is demanded.
[0027] A specific example of a doping metal in this invention is at
least one metal selected from the group consisting of Fe, V, Mo,
Nb, Al and Cr. Of these metals, Fe, V, Mo, Nb and Cr act as donors
in a titanium oxide film, supply electrons and contribute to
improvement of photocatalyst activity by increasing carrier
density. Aluminum acts as an accelerator in the titanium oxide,
supplies electron holes and also contributes to the improvement of
photocatalyst activity by the increase in carrier density. Of these
metals, Fe, V and Mo have a large effect in improving catalytic
activity, are stable, and are especially preferable.
[0028] When using a donor and an acceptor simultaneously, if they
are simply mixed, carriers supplied by them offset each other when
generated and are not preferable. It is therefore preferred to
separate the existing areas of a donor and an acceptor in the film
in the direction of depth so that different kinds of generated
carriers do not bind again. According to a crystallographic study
by the X-ray diffraction analytical method of the photocatalyst
film of this invention, the photocatalyst film can exhibit various
kinds of crystal structure. For example, a titanium oxide anatase
structure, a mixed structure of microcrystalline and amorphous
anatase titanium oxide, a mixed structure of anatase crystal and
rutile crystal, and a structure containing a considerable amorphous
layer can be taken. In any film structure, the photocatalyst
activity is larger than that of a structure composed of a single
component of titanium oxide.
[0029] The photocatalyst film of this invention does not
necessarily require complete crystallinity. It is sufficient if
there is a certain order of intermediate distance in the grating
group of titanium oxide. In the photocatalyst film of this
invention, in connection to an energy band structure followed by
electrons and electron holes, if the quantum density at the edge
portion of the energy band is in a slightly dim state for the
amorphous structure, the photocatalyst activity is rather large.
From this, in the photocatalyst film of this invention, absorption
of light containing visible light in a long wavelength and
generation of a carrier take place when compared with titanium
oxide alone.
[0030] The content of the metal oxide in a small amount in the
photocatalyst film in terms of the sum of such metal oxide is
preferred at 0.01 to 10 wt % on the metal base in the film. At a
content of 0.01 to 10 wt %, the catalyst activity improving effect
is scarcely recognized and when exceeding 10 wt %, the intermediate
distance order of the grating structure of titanium oxide is
disturbed remarkably, the moving distance of the photocatalyst
carrier becomes short, and the photocatalyst activity becomes
small. Therefore, a content above 10 wt % is not preferable.
[0031] Kinds of substrates that are used in this invention are not
limited particularly but, for example, such inorganic materials as
glass ceramics, quartz, metallic materials such as aluminum and
stainless steel, and resin materials such as polycarbonate,
polymethyl methacrylate, silicone, polystyrene, polyimide etc. can
be used.
[0032] When light is applied to an article of this invention, the
photocatalyst film is excited and such actions as antibacterial,
deodorization, decomposition of organic articles, and hydrophilic
operation are displayed. Thus, the articles of this invention are
given properties whereby the surface is scarcely contaminated or
contamination is easily removed and bacteria or viruses are rarely
bred.
[0033] The metal contained in the photocatalyst film of this
invention as a main component coated on a substrate for improving
the photocatalystic activity can be distributed uniformly in the
direction of the thickness of the titanium oxide photocatalyst film
or distributed in different amounts in the thickness direction.
When distributing a different amount in the thickness direction, a
greater amount shall be distributed to the side of the
photocatalyst film close to the substrate or a greater amount may
be distributed to the side of the photocatalyst film receiving the
light opposite to the substrate side.
[0034] To make the content of the above metal different in the
direction of thickness of the photocatalyst film, a metal film or a
metal oxide film or a titanium oxide film containing metal is
formed on a substrate and a titanium oxide film is laminated
thereon or a titanium oxide film is formed on a substrate and a
laminated article is formed by laminating a titanium oxide film
containing the above-mentioned metal or a metal oxide thereon, and
implanting a metal into the titanium oxide film through the surface
of this laminated article by the thermal diffusion method. The
photocatalyst film thus obtained is able to accelerate the
diffusion of impurities and film crystallization simultaneously.
With a metal as an additive in the direction of thickness of the
film, it is possible to diffuse the carrier polarity by making the
energy band structure asymmetrical while providing an inclined
concentration. As a result, the film can be made to have a high
catalyst activity preventing the recombination quenching in a film.
This is particularly preferable when using the photocatalyst film
for solar cell elements.
[0035] A metal can be contained in a photocatalyst by thermal
diffusion. One method is to heat a substrate when forming a
laminated material on the substrate and another method is to post
heat a laminated material formed on a substrate. Both of these
methods can be used. In order to contain metal oxide in a
photocatalyst film by thermal diffusion, the temperature of a
substrate when coating on a laminated material is normally above
150.degree. C. and it is better to heat the substrate to
250.degree. C. or above. Further, to diffuse and contain a metal in
a laminated material formed on a substrate by post-heating, it is
normally more preferable to heat the substrate to 150.degree. C. or
above. The upper limit of the heating temperature in both methods
can be decided in a range so as not to damage the substrate.
[0036] The thickness of a photocatalyst film comprising titanium
oxide as a main component should be set at more than 20 nm in order
to provide photocatalyst activity at a level considered practical.
Also, a thickness of below 2000 nm is preferred from the economical
viewpoint inasmuch as the photocatalyst activity does not increase
even at a thickness greater than 2000 nm.
[0037] This invention is to provide a Ti metal sputtering target or
a Ti sub-oxide sputtering target containing at least one metal
selected from the group of metals at 0.01 to 10 wt % of the sum of
such metals. These targets are useful for forming the metallic ion
doped photocatalyst film and are capable of efficiently and stably
supplying photocatalyst films having high photocatalyst
activity.
[0038] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description when taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 is a sectional view of preferred embodiments of an
article coated with a photocatalyst film of this invention;
[0040] FIG. 2 is an essential part sectional view of a sputtering
device using the photocatalyst film coating method of this
invention;
[0041] FIG. 3 is a schematic diagram showing a sputtering device
using the photocatalyst film coating method of this invention (the
DC planar method);
[0042] FIG. 4 is a schematic diagram showing another sputtering
device using the photocatalyst film coating method of this
invention (the dissimilar metals simultaneous discharge
method);
[0043] FIG. 5 is a schematic diagram showing yet another sputtering
device using the photocatalyst film coating method of this
invention (the DM method); and
[0044] FIG. 6 is a schematic diagram showing yet another sputtering
device using the photocatalyst film coating method of this
invention (the DC cylindrical method).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] FIG. 1 is a sectional view of a photocatalyst film coated
article as an embodiment of this invention. FIG. 1(a) shows an
article 10 of this invention having a photocatalyst film 12 formed
on a glass plate 11 as a substrate. FIG. 1(b) shows the article 10
of this invention having the glass plate 11 with a metal oxide film
13 and the photocatalyst film 12 laminated and coated thereon with
a metal contained in the substrate side by thermal diffusion,
wherein a diffusion layer 14 exists in the photocatalyst film 12.
In FIG. 1(c), the photocatalyst film 12 and the metal oxide 13 are
laminated in that order on the glass plate 11 as a substrate, the
metal oxide is contained in the photocatalyst film surface by
thermal diffusion, and the diffusion layer 14 is formed.
[0046] FIG. 2 is a sectional view of essential parts of a
sputtering device for explaining a method for coating the
photocatalyst film of this invention on a substrate. Argon gas or
oxygen gas is introduced from a gas induction tube 5 into a film
forming device that forms the photocatalyst film on a substrate. At
the same time, the inside of the film forming device is exhausted
by a vacuum exhaust pump and regulated to an atmospheric space
reduced to a fixed pressure. The pressure and gas composition of
the atmosphere of this pressure reduced space is regulated by a
vacuum exhaust pump, an induced gas amount and a pressure
regulating valve (not shown) so as to enable the sputtering.
[0047] When negative voltage is applied to cathodes 1A, 1B from a
power source 7, targets 2A and 2B are sputtered by such positive
ions as argon in glow discharge plasma generated on the surfaces of
the targets. Sine waves, pulse waves, and time asymmetrical waves
can be used for applying voltage to the cathodes. Any wave capable
of Fourier development is also suitable. If targets are not
conductive, high frequency is applied. The reference zero potential
of the applied voltage waveform is normally the same as the earth
potential of a film forming device. Further, a DC bias having a
polarity common to the two cathodes may be applied at the same
time. In this case, the earth potential of a film forming device
and the reference zero potential of the above-mentioned waveform
are normally floating and have no relation to each other.
[0048] A negative voltage is applied to the cathodes 1A and 1B from
the power source 7. At this time, electric charges accumulated on
the surfaces of the targets are destaticized by reversing
polarities of the respective cathodes alternately by an oscillator
(a polarity converter) 8 so that the cathode 1B becomes the
positive pole when the cathode of the cathode 1A is the negative
pole while the cathode 1A becomes the positive pole when the
cathode 1B is the negative pole. From a instantaneous point of
view, the targets 2A, 2B provided on the surfaces of the two
cathodes are sputtered by the alternately reversing glow discharge
3 generated by applying a negative voltage to one cathode and a
positive voltage to the other cathode.
[0049] A reversing frequency for reversing polarity is preferred at
10 kHz or above. If less than 1 kHz, the charge eliminating action
on the target surfaces drops, plus ion action to voltage
oscillation is delayed and the charge eliminating action on the
target surfaces is scarcely obtained and therefore, it is preferred
to set the reversing frequency at 1 MHz or below.
[0050] Waveforms of applied voltage are not especially limited if
they are well-balanced applied voltage waveforms such as sine
waves, square pulse waves, and time asymmetrical waves in which
charges of surfaces of the two target materials are neutralized
relative to the time base.
[0051] When the cathode polarity is reversed by the above-mentioned
preferable reversing frequency, the so called cathode sputtering is
carried out intermittently for each target microscopically. When
the reversing period of polarity is selected in the preferable
range described above, the targets 1A and 1B are sputtered at the
same time when viewed in broad perspective and the photocatalyst
film is coated on the substrate.
[0052] Electric charges accumulated on the two target surfaces-are
neutralized by reversed potential and reversed current, and two
targets are sputtered while destaticized. Therefore, no thermal
shock is caused during the dielectric breakdown in the
photocatalyst film by the electric charges accumulated on the film
surface. As a result, abnormal discharge (arcing, corona, etc.)
resulting from the thermal shock is suppressed or no longer
caused.
[0053] By the cleaning action to sputter the two target surfaces by
glow discharge plasma, the photocatalyst film is coated on the
targets while removing the film accumulated on the eroded surfaces
of the targets. Therefore, the accumulation of electrical
insulating film on the eroded surfaces of the two targets is
suppressed, the so-called anode electrode vanishing phenomenon
observed when coating a metal oxide film using a ordinary single
target is not incurred and the glow discharge plasma does not stop
during the photocatalyst film coating. Thus, even when a metal is
used as a target, a reactive gas such as oxygen for the sputtering
gas or the substrate is heated, and it is possible to coat a fine
photocatalyst film of metal oxide stably on the substrate.
[0054] When a target is of a planar (a rectangular parallepiped)
type, a backing plate that is normally composed of copper as a main
component, a cooling mechanism for cooling the packing plate and a
reinforced magnet for constructing a magnetron are provided on the
back of each target in one integral body with the target or
separately. Further, in order to increase close adhesion on the
surfaces of a target material and a packing plate, it is better to
plate a normally copper made backing plate surface with nickel or
indium.
[0055] Further, when a cylindrical shape target is used, it is
possible to use such a well known method whereby a cylindrical
target material is prepared on the surface of a cylindrical packing
cylinder, magnetron magnets are arranged linearly on the inner
tangent line in the longitudinal direction, and this cylinder is
rotated together with a target without moving the magnet. As a
result, the whole surface of the target can be provided as an
erosion area and the target use efficiency can be improved. In
addition, the cooling effect of the target surface resulting from
the shift caused by the erosion can be improved.
[0056] The results when the photocatalyst film of this invention is
coated on a glass plate will be shown below in detail by comparing
the embodiments with comparison examples.
[0057] (Film Costing Conditions)
[0058] Distance Ls between a substrate and a target: 100 mm
[0059] Distance Lc between two targets: 30 mm
[0060] The distance between two targets is preferred as close as
possible to a distance between a substrate and a target or less for
uniform doping.
[0061] Sputtering method: Largely divided into the following two
methods:
[0062] 1) A DC sputtering using a DC power source (expressed as DC
in Tables 1.about.3: see FIGS. 3, 4 and 6; one DC power source is
connected to each of the two targets in FIG. 4)
[0063] 2) An applied voltage alternate reverse sputtering using an
internal frequency power source (expressed as the DM method in
Table 1.about.3: A power source capable of applying a sine wave
with a reversing frequency set at 40 kHz by the oscillator in FIG.
2 is used.).
[0064] Sputtering power: Regulated in the range of voltage 400
.about.600V, charging electric power 2.about.20 kW.
[0065] Sputtering gas: When coating a metal oxide film on a metal
oxide used as a target, gas containing 1.about.15 vol. % oxygen in
argon is used; and when coating a metal oxide film on a metal used
as a target, argon gas containing 10.about.50 vol. % oxygen is
used.
[0066] Sputtering pressure: 0.5 Pa
[0067] Substrate temperature at film coating: As shown in Tables
1.about.3. "Room Temp." shown in Tables 1.about.3 indicates that
the substrate was not heated.
[0068] Heat treatment after film forming: As shown in Tables
1.about.3. The heat treatment was carried out under atmospheric
conditions.
[0069] Target composition: Shown in metal base wt %: (photocatalyst
activity improving metal/(photocatalyst activity improving
metal+titanium metal).times.100. In Tables 1.about.3, shown in the
form "Ti-aM". This denotes a Ti main component target containing a
wt % M metal. However, in the case of a sub-oxide target, a value
converted to a metal base.
[0070] Sputtering rate (M/Ti): Ratios of sputtering rates of added
metal to those of Ti when sputtered in Ar at 500V are shown in
Tables 1.about.2. Values of sputtering rates are shown in, for
example, "Metal Data Book", Revised 3 Edition. Page 389, Maruzen
(1993) and "Basis of Thin Film Preparation", First Edition, Pages
126.about.130, Nikkan Kogyo Shimbunsha (1983).
[0071] (Photocatalyst Film)
[0072] Adding metal ratio: The amount of metal contained in the
film is expressed in the metal base. Values of added metals/(added
metal+Ti) are shown in Tables 1.about.3.
[0073] Film thickness: Using a transmission electron microscope,
film thickness was measured by observing the fractured
surfaces.
[0074] (Evaluation of Photocatalyst Film Activity)
[0075] Triolein (glycerol triolate,
C.sub.17H.sub.33COOCH(CH.sub.2OCOC.sub- .17H.sub.33).sub.2) was
coated on a 100 mm square sample surface to 0.1 mg/cm.sup.2,
ultraviolet rays were applied successively at a strength 3
mW/cm.sup.2 using an UV lamp, and rates of triolein that is
decomposed with lapse of time were measured. Using glass plates
without the photocatalyst film formed as reference samples, changes
in triolein weight on the photocatalyst film caused by ultraviolet
rays applied were measured 3 times; after 48 hours, 60 hours and 90
hours, and the photocatalyst activity was classified into the
following four ranks by times required for the complete
decomposition of triolein.
[0076] Almost 100% of triolein is decomposed within 48 hours:
.circleincircle.
[0077] Almost 100% of triolein is decomposed within 60 hours:
.largecircle.
[0078] Almost 100% of triolein is decomposed within 90 hours:
.DELTA.
[0079] After 90 hours, triolein still remains: X
[0080] Embodiment 1
[0081] A metal target comprising Ti as a main component containing
0.2 wt % Fe metal in a sputtering device shown in FIG. 3 (the
sputtering rate of Fe and Ti was 2.16). After the film forming
device was once exhausted to the vacuum state at
1.3.times.10.sup.-3 Pa, mixed gas of argon and oxygen (70% vol. %
argon, 30 vol. % oxygen) was introduced and the pressure in the
film forming device was maintained at 0.4 Pa. Thereafter, the
target was sputtered by providing a cathode with the power from a
DC power source and a 100 mm square size glass plate composed of
soda lime silica was passed in front of the target, so that a 250
nm thick photocatalyst film was formed on the glass plate. The film
coating conditions and the photocatalyst activity evaluation
results are shown in Table 1. When this glass plate was taken out
of the film forming device and the photocatalyst activity of the
photocatalyst film of the obtained article was evaluated, almost
100% of triolein was decomposed after 48 hours. As this article has
a larger photocatalyst activity than the article obtained in the
comparison example shown on Table 3, the improvement of the
photocatalyst activity of the titanium oxide film formed by a
method to mix metallic element Fe in a sputtering target was
recognized.
[0082] Embodiment 2
[0083] Under the same conditions as those in Embodiment 1 excepting
that a titanium metal target containing Fe in the added amount of 1
wt % on the metal base was used, a 250 nm thick photocatalyst film
was coated on a glass plate. The coating conditions and the
evaluation of the photocatalyst activity are shown on Table 1. The
photocatalyst film of the obtained article has a larger
photocatalyst activity than that of the article obtained in the
comparison example shown in Table 3 described later and the effect
of this invention was recognized.
[0084] Embodiment 3
[0085] Under the same conditions as those in Embodiment 1 excepting
that a titanium target with 0.5 wt % V added (a ratio of the
sputtering rates of V and Ti was 1.27) was used, a 250 nm thick
photocatalyst film was formed on a glass plate. The coating
conditions and the evaluation of photocatalyst activity are shown
in Table 1. The photocatalyst film of the obtained article has a
larger photocatalyst activity than that of the article obtained in
the comparison example shown in Table 3 described later and the
effect of this invention was recognized.
[0086] Embodiment 4
[0087] Using a sputtering device having two rotational cylindrical
targets as shown in FIG. 4, a Mo doped titanium oxide film (50 nm
thick) was formed on a glass substrate by simultaneously
discharging dissimilar targets of Ti and Mo (the ratio of Mo and Ti
sputtering rates was 1.57). The doping amount of Mo added to the
titanium oxide film was regulated by applying electric power from a
DC sputter power source to each target, separately. The coating
conditions and the evaluation of the photocatalyst activity are
shown in Table 1. The obtained article has a photocatalyst activity
greater than that of the article obtained in the comparison example
shown in Table 3 described later and the effect of this invention
was recognized.
1TABLE 1 Embodi- Embodi- Embodi- Embodi- ment ment ment ment Item 1
2 3 4 [Coating Conditions] Target composition Ti-0.2Fe Ti-1Fe
Ti-0.5V Ti, Mo Sputtering ratio (M/Ti) 2.16 2.16 1.27 1.57 Kind of
target Metal Metal Metal Metal Sputtering method DC DC DC
Dissimilar metals same time discharging Cathode shape Planar Planar
Planer Cylindrical Sputtering Gas Ar:O.sub.2 Ar:O.sub.2 Ar:O.sub.2
Ar:O.sub.2 [Volume rate] [=70:30] [=70:30] [=70:30] [=70:30]
Substrate temperature Room Room Room Room (.degree. C.) temp. temp.
temp. temp. Heat treatment after None None None None film forming
[Photocatalyst film] Film composition TiO.sub.2:Fe TiO.sub.2:Fe
TiO.sub.2:V TiO.sub.2:Mo Added metal weight 0.2 1.0 0.5 3.0 ratio
Film thickness (nm) 250 250 250 250 Photocatalyst activity
.circleincircle. .largecircle. .circleincircle. .largecircle.
evaluation
[0088] Embodiment 5
[0089] Under the same conditions as those in Embodiment 1 except
that a titanium metal target with 2 wt % of Nb added (the
sputtering ratio of Nb and Ti was 1.18) was used, the photocatalyst
film was formed on a glass plate and thereafter, heat treated for
one hour at 300.degree. C. in the atmosphere, and a 300 nm thick
photocatalyst film was obtained. The coating conditions and the
evaluation of the photocatalyst activity are shown in Table 2. The
photocatalyst film has a photocatalyst activity greater than that
of the article obtained in the comparison example shown in Table 3
described later and the effect of this invention was
recognized.
[0090] Embodiment 6
[0091] A titanium oxide film doped with two kinds of metals: Fe and
V doped was formed on a glass substrate by the DM method (the dual
magnetron method) using a sputtering device shown in FIG. 5 (the
ratio of the sputtering rates of Fe and Ti was 1.27). The coating
conditions and the evaluation of the photocatalyst activity are
shown in Table 2. The photocatalyst film of the obtained article
has a photocatalyst activity greater than the article obtained in
the comparison example shown in Table 3 and the effect of this
invention was recognized.
[0092] Embodiment 7
[0093] Using a Ti target with 3 kinds of metals added: Fe, V and Mo
shown in Table 2 as a Ti target, a titanium oxide film doped with
the above-mentioned 3 kinds of metals was formed on a glass
substrate (the ratio of the sputtering rates of Fe and Ti was 2.16,
that of V and Ti was 1.27 and that of Mo and Ti was 1.57) in the
same manner as in Embodiment 6 excepting that a gas containing
equal volumes of Ar and O.sub.2 was used as the sputtering gas. The
coating conditions and the evaluation of the photocatalyst activity
are shown in Table 2. The photocatalyst film of the obtained
article has a photocatalyst activity greater than that of the
article obtained in the comparison example shown in Table 3
described later and the effect of this invention was
recognized.
[0094] Embodiment 8
[0095] Using a titanium sub-oxide target with 3 kinds of metals
added: Fe, V and Mo shown in Table 2, the titanium oxide film doped
with these 3 kinds of metals was formed on a glass substrate heated
to 250.degree. C. in the Ar gas (Ar:O.sub.2=90:10) containing a
small amount of O.sub.2, using the sputtering device shown in FIG.
6 (the ratio of the sputtering rates of Fe and Ti was 2.16 and that
of Mo and Ti was 1.57). The coating conditions and the evaluation
of the photocatalyst activity are shown in Table 2. The
photocatalyst film of the obtained article has a photocatalyst
activity greater than those of the article obtained in the
comparison example shown in Table 3 described later and the effect
of this invention was recognized.
2TABLE 2 Embodiment Embodiment Embodiment Embodiment Item 5 6 7 8
[Coating Conditions] Target Composition Ti-2Nb Ti-0.5Fe-0.5V
Ti-0.5Fe-1V- Ti-0.5Fe-1V- 0.5Mo 0.5Mo Sputtering ratio 1.18 2, 16,
1.27 2.16, 1.27, 1.57 2.16, 1.27, 1.57 (M/Ti) Kind of Target Metal
Metal Metal TiOx Sub-Oxide Sputtering Method DC DM Method DM Method
DC Cathode Shape Planar Cylindrical Cylindrical Cylindrical
Sputtering Gas Ar:O.sub.2 Ar:O.sub.2 Ar:O.sub.2 Ar:O.sub.2 [Volume
Rate] [=70:30] [=60:40] [=50:50] [=90:10] Substrate Room temp. Room
temp. Room temp. 250 Temperature (.degree. C.) None Heat Treatment
after 300.degree. C., 1 h 250.degree. C., 1 h None None Film
Forming [Photocatalyst Film] Film Composition TiO.sub.2:Nb
TiO.sub.2:Fe, V TiO.sub.2:Fe, V, Mo TiO.sub.2:Fe, V, Mo Added Metal
Wt. 2.0 Fe0.5, V0.5 Fe0.5, V1, Mo Fe0.5, V1, Mo Ratio 0.5 0.5 Film
Thickness (nm) 300 250 250 250 Photocatalyst .largecircle.
.circleincircle. .circleincircle. .largecircle. Activity
Evaluation
COMPARISON EXAMPLES 1 and 2
[0096] Articles having a photocatalyst film comprising titanium
oxide containing no metal were coated on glass substrates. The
coating conditions and the evaluation results of the obtained
photocatalyst film are shown in Table 3. The photocatalyst activity
of the obtained articles was lower than that of the articles in the
embodiments.
COMPARISON EXAMPLES 3 and 4
[0097] Photocatalyst films doped with metals of which the
sputtering rates of added metals and Ti were outside the scope of
claims of this invention were produced. A titanium oxide film doped
with Pt of which the ratio of the sputtering rate to Ti is 2.75 was
produced in Comparison Example 3 and a titanium oxide film doped
with Pd of which the ratio of the sputtering rate was 4.08 was
produced in Comparison Example 4 using the same method as in
Embodiment 1. The coasting conditions of the film and the
evaluation results of the obtained photocatalyst films are shown in
Table 3. The photocatalyst activity of the obtained articles was
lower than that of the articles in the embodiments and the effect
of this invention is clear.
[0098] From the embodiments and the comparison examples shown
above, it is clear that the photocatalyst film described in the
embodiments of this invention has a more improved photocatalyst
activity than a photocatalyst film that is composed of titanium
oxide only or a photocatalyst film having a ratio of the sputtering
rates of metal and Ti outside the range of the claims of this
invention. Further, it can be seen that when coating a
photocatalyst film on a substrate by the sputtering method using a
set of two cathodes, voltage is applied to these two cathodes so as
to reverse the polarity of the cathodes alternately. It is also
clear that when a Ti metal target or a Ti sub-oxide target with a
specified metal of this invention added is used, it is possible to
supply a film doped with a specified metal ion, having a high
photocatalyst activity, efficiently and stably.
3TABLE 3 Compari- Compari- Compari- Compari- son son son son
Example Example Example Example Item 1 2 3 4 [Coating Conditions]
Target Compositions Ti Ti Ti-2.8Pt Ti-4Pd Ratio of Sputtering . . .
. . . 2.75 4.08 Rates (M/Ti) Kind of Target Metal TiOx Metal Metal
sub-oxide Sputtering Method DC DC DC DC Cathode Shape Planar Cylin-
Planar Cylindrical drical Sputtering Gas Ar:O.sub.2 Ar:O.sub.2
Ar:O.sub.2 Ar:O.sub.2 [Volume Rate] [=70:30] [=90:10] [=70:30]
[=70:30] Substrate Room 250 Room Room Temperature (.degree. C.)
temp. temp. temp. Heat Treatment after None None None None Film
Forming [Photocatalyst Film] Film Composition TiO.sub.2 TiO.sub.2
TiO.sub.2:Pt TiO.sub.2:Pd Added Metal Wt 0 0.0 2.8 4.0 Rate Film
Thickness (nm) 250 250 250 250 Photocatalyst .DELTA. X .DELTA. X
Activity Evaluation
[0099] A photocatalyst film comprising titanium oxide as a main
component of an article of this invention contains specified metals
in a specified amount, which increase the photocatalyst
activity.
[0100] A photocatalyst coating film of this invention is formed on
a substrate by a sputtering method using a Ti metal target or a Ti
sub-oxide target containing at least one metal having a sputtering
rate for Ar of 0.9 to 2.7 times that of Ti. Ar has at least a kind
of energy in a 30 to 50 eV ion energy area. Therefore,
non-uniformity and segregation of doping metals can be prevented
and thereby, a drop in the photocatalyst activity can be
suppressed. Also, this photocatalyst film is applicable to a
substrate comprising materials having a relatively small heat
resistance.
[0101] When a Ti metal target or a Ti sub-oxide target with a
specified metal of this invention added is used, it is possible to
supply a photocatalyst film doped with a specified metal ion,
having a high photocatalyst activity efficiently and stably.
[0102] In addition, by a method for coating a photocatalyst film on
articles of this invention, a photocatalyst film having a large
photocatalyst activity can be coated at a high coating speed.
* * * * *