U.S. patent application number 10/352200 was filed with the patent office on 2003-07-31 for titanium oxide photocatalyst thin film and production method of titanium oxide photocatalyst thin film.
This patent application is currently assigned to FUJI XEROX CO., LTD.. Invention is credited to Akutsu, Eiichi, Hashimoto, Kazuhito, Maruyama, Tatsuya, Ohtsu, Shigemi.
Application Number | 20030143437 10/352200 |
Document ID | / |
Family ID | 27606380 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030143437 |
Kind Code |
A1 |
Ohtsu, Shigemi ; et
al. |
July 31, 2003 |
Titanium oxide photocatalyst thin film and production method of
titanium oxide photocatalyst thin film
Abstract
The present invention provides a titanium oxide photocatalytic
thin film having a surface layer containing silicon oxide and
titanium oxide and a production method for producing a titanium
oxide photocatalytic thin film having a surface layer containing
silicon oxide and titanium oxide and comprising a step of radiating
excimer beam to the titanium oxide thin film while heating
substrate on which the titanium oxide thin film is disposed in
vacuum or gas atmosphere in the presence of a silicon-including
compound.
Inventors: |
Ohtsu, Shigemi;
(Ashigarakami-gun, JP) ; Maruyama, Tatsuya;
(Ashigarakami-gun, JP) ; Akutsu, Eiichi;
(Ashigarakami-gun, JP) ; Hashimoto, Kazuhito;
(Yokohama-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
FUJI XEROX CO., LTD.
Tokyo
JP
|
Family ID: |
27606380 |
Appl. No.: |
10/352200 |
Filed: |
January 28, 2003 |
Current U.S.
Class: |
428/701 ;
427/551; 428/702 |
Current CPC
Class: |
C23C 14/083 20130101;
C23C 14/58 20130101; A01N 59/00 20130101; A01N 2300/00 20130101;
A01N 25/34 20130101; C03C 17/23 20130101; C03C 2217/212 20130101;
A01N 59/16 20130101; C03C 2217/71 20130101; A01N 59/16 20130101;
C03C 17/3417 20130101; A01N 59/16 20130101 |
Class at
Publication: |
428/701 ;
428/702; 427/551 |
International
Class: |
B05D 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2002 |
JP |
2002-23175 |
Claims
What is claimed is:
1. A titanium oxide photocatalytic thin film comprising a surface
layer including silicon oxide and titanium oxide.
2. A titanium oxide photocatalytic thin film according to claim 1,
wherein the titanium oxide photocatalytic thin film is disposed on
a substrate.
3. A titanium oxide photocatalytic thin film according to claim 1,
wherein the titanium oxide photocatalytic thin film is disposed on
a substrate and at least one of a reflection prevention film and a
protection film is disposed between the titanium oxide
photocatalytic thin film and the substrate.
4. A titanium oxide photocatalytic thin film according to claim 1,
wherein the film thickness of the titanium oxide photocatalytic
thin film is in a range from 10 to 120 nm or 180 to 230 nm.
5. A production method of a titanium oxide photocatalytic thin film
comprising a surface layer including silicon oxide and titanium
oxide, the production method comprising the steps of: forming a
titanium oxide thin film on a substrate; and radiating excimer beam
to the titanium oxide thin film while heating the substrate in a
vacuum or a gas atmosphere in the presence of a compound, which
includes silicon.
6. A production method of a titanium oxide photocatalytic thin film
according to claim 5, wherein the compound, which includes silicon,
is a compound containing --Si--O-- bond.
7. A production method of a titanium oxide photocatalytic thin film
according to claim 5, wherein the gas atmosphere is one of a
reductive gas atmosphere and a nitrogen gas atmosphere.
8. A production method of a titanium oxide photocatalytic thin film
according to claim 5, wherein the heating temperature of the
substrate is in a range from room temperature to 300.degree. C.
9. A production method of a titanium oxide photocatalytic thin film
according to claim 5, wherein the heating temperature of the
substrate is in a range from 50.degree. C. to 230.degree. C.
10. A production method of a titanium oxide photocatalytic thin
film according to claim 5, wherein the substrate comprises a
plastic substrate and the substrate heating temperature is in a
range from room temperature to the heat resistant temperature of
the plastic substrate.
11. A production method of a titanium oxide photocatalytic thin
film according to claim 5, further comprising the step of disposing
a reflection prevention film between the titanium oxide thin film
and the substrate.
12. A production method of a titanium oxide photocatalytic thin
film according to claim 11, wherein the reflection prevention film
comprises an inorganic oxide thin film.
13. A production method of a titanium oxide photocatalytic thin
film according to claim 11, wherein the refractive index of the
reflection prevention film is within a range from 1.5 to 2.3.
14. A production method of a titanium oxide photocatalytic thin
film according to claim 11, wherein the refractive index of the
reflection prevention film is between the refractive index of the
substrate and the refractive index of the titanium oxide
photocatalytic thin film; and the optical film thickness, as
expressed by a product of the film thickness and the refractive
index of the reflection prevention film, is one of 1/4 of a
wavelength and a whole number multiple of 1/4 of the wavelength,
wherein the wavelength is in the vicinity of the center of the
visible light range.
15. A production method of a titanium oxide photocatalytic thin
film according to claim 11, wherein the optical film thickness of
the reflection prevention film, as expressed by a product of the
film thickness and the refractive index of the reflection
prevention film, is in a range from 110 nm to 160 nm or 330 nm to
480 nm.
16. A production method of a titanium oxide photocatalytic thin
film according to claim 5, further comprising a step of disposing a
protection film between the titanium oxide thin film and the
substrate wherein the substrate comprises a plastic substrate.
17. A production method of a titanium oxide photocatalytic thin
film according to claim 16, wherein the protection film comprises
an inorganic oxide thin film.
18. A production method of a titanium oxide photocatalytic thin
film according to claim 17, wherein the inorganic oxide thin film
is selected from a group consisting of an amorphous titanium oxide
thin film, SnO.sub.2 thin film, a SiO.sub.2 thin film, and an ITO
thin film.
19. A production method of a titanium oxide photocatalytic thin
film according to claim 16, wherein the refractive index of the
protection film is in a range from 1.4 to 2.3.
20. A production method of a titanium oxide photocatalytic thin
film according to claim 16, wherein the refractive index of the
protection film is between the refractive index of the substrate
and the refractive index of the titanium oxide photocatalytic thin
film; and the optical film thickness, as expressed by a product of
the film thickness and the refractive index of the protection film,
is one of 1/4 of a wavelength and a whole number multiple of 1/4 of
the wavelength, wherein the wavelength is in the vicinity of the
center of the visible light range.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a titanium oxide
photocatalyst thin film having photocatalytic activities such as
antibacterial action, anti-pollution, air purification, ultra high
hydrophilicity and the like on a substrate and its production
method.
[0003] 2. Description of the Related Art
[0004] In recent years, a photocatalyst or a photosemiconductor
having the photocatalytic function or the photovoltaic function has
been drawing attention. There are many application methods have
been proposed, for example, titanium oxide, which is a
photocatalyst (photosemiconductor), is said to oxidize and
decompose organic stains adhering to surface, nitrogen oxide (NOx),
sulfur oxide (SOx), air pollutants such as malodorous substances,
bacteria, and the like owing to the oxidation reaction based on the
photocatalytic reaction and as an practical application example, a
method for removing air pollutants under sunray (Japanese Patent
Application Laid-Open (JP-A) No. 6-315614) by attaching a titanium
oxide photocatalyst to walls of buildings, a method for
disinfecting bacteria (JP-A No. 7-102678) by attaching a titanium
oxide catalyst to walls, handrails and the like in a hospital, a
method for decomposing pollutants in water (JP-A No. 5-92192) by
dispersing a titanium oxide catalyst powder in wastewater and
radiating light of a ultraviolet lamp, a method for lessening the
cleaning and maintenance work of a fluorescent lamp or luminaire
(JP-A No. 9-129012) owing to self-cleaning reaction, and the
like.
[0005] Further, based on its photoreaction, a photocatalytic thin
film is known to have surface made highly hydrophilic and a variety
of applications for anticlouding of mirrors (of bathrooms,
automobiles), lens, glass windows and the like are supposed to be
possible.
[0006] Further, when the photocatalytic thin film is disposed on
the surfaces of building outer walls, automotive glass, and window
glass, based on the hydrophilicity of the film surfaces, besides
that hydrophobic stains are hard to adhere to, even if stains
adhere, they are decomposed and owing to the hydrophilicity of the
forgoing photocatalytic thin film, the stains or their decomposed
substances are known to have self-cleaning function that they are
easily washed out by rain or washing with water.
[0007] With respect to the foregoing photocatalytic thin film, the
following methods are generally well known: a titanium compound
such as a titanium alkoxide, a titanium acetate and the like are
hydrolyzed and then applied to the surface of a substrate and dried
and after that, sintered at 500.degree. C. or higher to obtain an
anatase type titanium oxide film; after an amorphous titanium oxide
layer is formed by a deposition method, the obtained amorphous
titanium oxide layer is annealed at 400.degree. C. or higher to
form an anatase type titanium oxide-containing layer; the surface
of metal titanium is oxidized at 500.degree. C. or higher to
crystallized the surface; while a substrate being heated at
250.degree. C. or higher, an anatase type titanium oxide film is
obtained by RF sputtering method.
[0008] The foregoing photocatalytic thin film is provided with its
hydrophilicity upon receiving ultraviolet rays. However, the
hydrophilicity has a characteristic in that the hydrophilicity is
weakened if it is kept in a dark place for about a weak. In order
to improve the defects, JP-A No. 2001-98187 discloses a
photocatalytic hydrophilic member bearing on the substrate surface,
a surface layer including a photocatalytic titanium oxide coated
with an alkali silicate and an inorganic acid particle (silica or
the like) with an isoelectric point of pH 5 or lower and when an
alkali silicate other than the photocatalyst is contained in the
surface layer, the surface is provided with hydrophilicity as high
degree as 20.degree. or lower water wettability angle and the
hydrophilicity retention property in the case of storage in a dark
place is improved. Further, JP-A No. 9-57912 discloses a composite
material having good water hydrophilicity retention property for a
long duration even in the case of storage in the dark by forming a
hydrophilicity layer such as silica or silicone resin (containing
hydroxy group) on a photocatalytic semiconductor thin film.
[0009] All these methods are either a titanium oxide particle or a
titanium oxide thin film coated with silica or the like on the
surface and owing to the surface coating film existence, they have
a problem that the photocatalytic capability such as an organic
decomposition activity by the titanium oxide particle or the
titanium oxide thin film is deteriorated. Further, in order to
increase the photocatalytic activity, a method for solving the
problem is that the photocatalytic film is thickened, however the
method has a disadvantage that interference coloration occurs since
titanium oxide has a high refractive index and therefore, the
thickness cannot be thickened so much.
SUMMARY OF THE INVENTION
[0010] Taking the above-mentioned problems into consideration, the
present invention aims to provide a photocatalytic thin film having
retainable photocatalytic activity even in the case of storage in
the dark and its production method.
[0011] Providing the following titanium oxide photocatalytic thin
film and the production method of the same can solve the
above-mentioned problems.
[0012] A first aspect of the invention provides a titanium oxide
photocatalytic thin film comprising a surface layer including
silicon oxide and titanium oxide.
[0013] A second aspect of the invention provides the titanium oxide
photocatalytic thin film, according to the first aspect, wherein
the titanium oxide photocatalytic thin film is disposed on a
substrate.
[0014] A third aspect of the invention provides the titanium oxide
photocatalytic thin film, according to the first aspect, wherein
the titanium oxide photocatalytic thin film is disposed on a
substrate and at least one of a reflection prevention film and a
protection film is disposed between the titanium oxide
photocatalytic thin film and the substrate.
[0015] A fourth aspect of the invention provides the titanium oxide
photocatalytic thin film, according to the first aspect, wherein
the film thickness of the titanium oxide photocatalytic thin film
is in a range from 10 to 120 nm or 180 to 230 nm.
[0016] A first aspect of the invention provides a production method
of a titanium oxide photocatalytic thin film comprising a surface
layer including silicon oxide and titanium oxide, the production
method comprising the steps of: forming a titanium oxide thin film
on a substrate; and radiating excimer beam to the titanium oxide
thin film while heating the substrate in a vacuum or a gas
atmosphere in the presence of a compound, which includes
silicon.
[0017] A second aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the first aspect, wherein the titanium oxide photocatalytic thin
film is disposed on a substrate.
[0018] A third aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the first aspect, wherein the titanium oxide photocatalytic thin
film is disposed on a substrate and at least one of a reflection
prevention film and a protection film is disposed between the
titanium oxide photocatalytic thin film and the substrate.
[0019] A fourth aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the first aspect, wherein the film thickness of the titanium oxide
photocatalytic thin film is in a range from 10 to 120 nm or 180 to
230 nm.
[0020] A fifth aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the first aspect, wherein the heating temperature of the substrate
is in a range from 50.degree. C. to 230.degree. C.
[0021] A sixth aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the first aspect, wherein the substrate comprises a plastic
substrate and the substrate heating temperature is in a range from
room temperature to the heat resistant temperature of the plastic
substrate.
[0022] A seventh aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the first aspect, further comprising the step of disposing a
reflection prevention film between the titanium oxide thin film and
the substrate.
[0023] An eighth aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the seventh aspect, wherein the reflection prevention film
comprises an inorganic oxide thin film.
[0024] A ninth aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the seventh aspect, wherein the refractive index of the reflection
prevention film is within a range from 1.5 to 2.3.
[0025] A tenth aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the seventh aspect, wherein the refractive index of the reflection
prevention film is between the refractive index of the substrate
and the refractive index of the titanium oxide photocatalytic thin
film; and the optical film thickness, as expressed by a product of
the film thickness and the refractive index of the reflection
prevention film, is one of 1/4 of a wavelength and a whole number
multiple of 1/4 of the wavelength, wherein the wavelength is in the
vicinity of the center of the visible light range.
[0026] An eleventh aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the seventh aspect, wherein the optical film thickness of the
reflection prevention film, as expressed by a product of the film
thickness and the refractive index of the reflection prevention
film, is in a range from 110 nm to 160 nm or 330 nm to 480 nm.
[0027] An twelfth aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the first aspect, further comprising a step of disposing a
protection film between the titanium oxide thin film and the
substrate wherein the substrate comprises a plastic substrate.
[0028] A thirteenth aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the twelfth aspect, wherein the protection film comprises an
inorganic oxide thin film.
[0029] A fourteenth aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the thirteenth aspect, wherein the inorganic oxide thin film is
selected from a group consisting of an amorphous titanium oxide
thin film, SnO.sub.2 thin film, a SiO.sub.2 thin film, and an ITO
thin film.
[0030] A fifteenth aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the twelfth aspect, wherein the refractive index of the protection
film is in a range from 1.4 to 2.3.
[0031] A sixteenth aspect of the invention provides the production
method of a titanium oxide photocatalytic thin film, according to
the twelfth aspect, wherein the refractive index of the protection
film is between the refractive index of the substrate and the
refractive index of the titanium oxide photocatalytic thin film;
and the optical film thickness, as expressed by a product of the
film thickness and the refractive index of the protection film, is
one of 1/4 of a wavelength and a whole number multiple of 1/4 of
the wavelength, wherein the wavelength is in the vicinity of the
center of the visible light range.
[0032] A seventeenth aspect of the invention provides the
production method of a titanium oxide photocatalytic thin film,
according to the twelfth aspect, wherein the optical film thickness
of the protection film is in a range from 10 nm to 160 nm or 330 nm
to 480 nm.
[0033] An eighteenth aspect of the invention provides the
production method of a titanium oxide photocatalytic thin film,
according to the first aspect, wherein the titanium oxide thin film
is disposed by a method selected from a group consisting of a
sputtering method, an electron beam deposition method, and an ion
plating method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1A is a graph showing an XPS measurement result of a
titanium oxide thin film before the treatment of Example 1.
[0035] FIG. 1B is a graph showing an XPS measurement result of a
titanium oxide thin film after the treatment.
[0036] FIG. 2 is a graph of FIG. 1B in which the compounded peak of
Ti--O and Si--O is separated into Ti--O and Si--O.
[0037] FIG. 3 is a magnified graph of Ti.sub.2p3/2 of the XPS
measurement result before and after the treatment of Example 1.
[0038] FIG. 4 is a graph showing a contact angle of the
photocatalytic thin film to water with the lapse of time before and
after the treatment in Example 1 and Example 2.
[0039] FIGS. 5A, 5B, 5C, and 5D are diagrams showing composite
materials having a photocatalytic thin film of the invention.
[0040] FIG. 6 is a conceptual diagram showing an apparatus for
carrying out a production method of the invention. In FIG. 6, the
reference numeral 10 represents a substrate, 20 represents an
annealing apparatus, 21 represents a chamber, 22 represents excimer
beam radiation means, 24 represents heating means, and 40
represents vacuum discharge means.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] A production method of a titanium oxide photocatalytic thin
film of the invention comprises a step of radiating excimer beam to
a titanium oxide thin film while heating the substrate bearing a
titanium oxide thin film in vacuum or a gas atmosphere in the
presence of a silicon compound. Unlike those produced by the
above-mentioned conventional methods for coating titanium oxide
surface with silica, a photocatalytic thin film obtained by this
method does not cause photocatalytic activity deterioration and
maintains a low contact angle to water. Further, since the titanium
oxide photocatalytic thin film obtained by the method has its
activity, even if the film thickness is made thin, sufficiently
high photocatalytic activity can be obtained. Accordingly,
interference color can be eliminated from the light attributed to a
high refractive index of titanium oxide and high transparency in
the visible ray region. Further, this method has an advantage that
the treatment time can be short and any large scale apparatus is
required, as compared with a conventional method.
[0042] The titanium oxide photocatalytic thin film obtained by this
method is characterized in that the surface layer contains silicon
oxide and titanium oxide. The layer containing silicon oxide and
titanium oxide includes a surface layer of a mixture containing
silicon oxide and titanium oxide, a surface layer of a mixture
containing a compounded oxide of silicon oxide and titanium oxide.
Owing to such a surface layer of the invention, the titanium oxide
photocatalytic thin film is provided with excellent ultra high
hydrophilicity and photocatalytically active characteristic as
described above.
[0043] As the substrate to be employed for a production method of
the invention, a glass substrate, a plastic substrate such as a
plastic film, sheet, plate or the like, a ceramic substrate such as
a ceramic sheet, ceramic plate or the like, and the like can be
exemplified without any limit. As the plastic substrate, for
example, films, sheets, or plates of plastics of polyethylene
terephthalate, polyethylene naphthalate, polyether ether ketone,
polyether sulfone, polysulfone, polyether imide, polyether ketone,
polyphenylene sulfide, polyallylate, polyimide, polycarbonate,
Arton and the like can be exemplified and they are preferably
flexible based on the applications.
[0044] To form the titanium oxide thin film with a high
photocatalytic effect, since the heating temperature of the
titanium oxide thin film is preferable to be a relatively high, in
the case a plastic substrate is used as a substrate, it is
preferable to use a plastic substrate with higher heat resistance.
As the heat resistant plastic substrate, polyimide (heat resistant
temperature 331.degree. C.), polycarbonate (PC) (heat resistant
temperature 205.degree. C.), polyether sulfone (PES) (heat
resistant temperature 223.degree. C.), polysulfone (PS) (heat
resistant temperature 190.degree. C.), Norbornene resin (trade
name; Arton) (heat resistant temperature 171.degree. C.).
Specially, heat resistant PC and PES have high transparency and
heat resistance to a temperature as high as about 220 degree and
less optical anisotropy.
[0045] In the invention, the phrase, heat resistant temperature of
a plastic substrate, means the glass transition temperature of
about 100 to 230.degree. C.
[0046] In the case a plastic substrate is used as a substrate, the
thickness is preferably 30 to 300 .mu.m, further preferably 80 to
230 .mu.m.
[0047] In the case that a photocatalytic thin film to be produced
by the method of the invention is used for anticlouding or
stain-proofing articles which reflect light or transmit light, the
substrate is also required to a light transmission property
(hereinafter, simply referred to as transparency in some
cases).
[0048] The titanium oxide thin film in the invention may include
any of an amorphous titanium oxide thin film, a titanium oxide thin
film in which an amorphous portion and a crystalline portion are
mixed, or a crystalline titanium oxide thin film. By heating a
titanium oxide thin film containing an amorphous portion while
excimer beam being radiated, crystallization and formation of the
foregoing surface layer are carried out. Further, by carrying out
the treatment of the invention to the crystalline titanium oxide
thin film, the foregoing surface layer formation is carried
out.
[0049] Further, it is general that as the film thickness of the
titanium oxide thin film can be increased more, the photocatalytic
activity is increased more, however interference coloration is
caused owing to the high refractive index of titanium oxide.
However, according to the production method of the invention, even
if the film thickness of the titanium oxide thin film is thin,
sufficiently high photocatalytic activity can be obtained.
[0050] In the case the photocatalytic thin film is used for an
application for which transparency is required, the titanium oxide
thin film is also required to be transparent and generally, taking
the center wavelength .lambda. of the visible light and the
refractive index n of anatase type titanium oxide into
consideration, the film thickness of the titanium oxide thin film
is preferably .lambda./(2.times.n) or shorter or whole number
multiple of .lambda./(2.times.n). Supposing that the foregoing the
center wavelength is 550 nm and the refractive index of the anatase
type titanium oxide is 2.53, .lambda./(2.times.n)=109 nm and
therefore, the film thickness of titanium oxide is preferable to be
110 nm or thinner or about 220 nm. However, since the transparency
to a certain degree can be obtained even if the film thickness is
slightly different from those in the entire visible light
wavelength region, practically in a range from 10 to 120 nm and 180
nm to 230 nm, transparency can be obtained without appearance of
the interference color.
[0051] In the production method of the invention, as a method for
forming a titanium oxide thin film, a sputtering method, an RF
sputtering method, an EB deposition method, an ion plating method
and the like can be employed.
[0052] In the case of producing a titanium oxide thin film on a
plastic substrate, film formation is preferably carried out by the
sputtering method or the RF sputtering method by which the film
formation is made possible even at a relatively low temperature,
for example, a heat resistant temperature (230.degree. C. or lower)
of those with good transparency among a variety of presently well
known plastics and scarcely accompanied with damages on the
substrate.
[0053] As the compound which includes silicon (the
silicon-including compound) made coexisting in the treatment of the
invention, either inorganic or organic compound is possible and
more practically, a --Si--O-- including compound can be exemplified
and glass, quartz, silicon and the like are examples of the
inorganic compound and silicone resin, silicone rubber, silicone
oil, polysilane, silane gas and the like are examples of the
organic compound.
[0054] The foregoing silicon-including compound is preferably put
in a system where the treatment is carried out and arranged so as
to radiate excimer beam to the silicon-including compound
itself.
[0055] For example, while the treatment system in the production
method of the invention being covered with quartz glass (for
example, in the case of carrying out a production method of the
invention in a quartz bell jar), the treatment (heating and excimer
beam radiation) of the invention may be carried out or as a member
of a production apparatus to be employed for the production method
of the invention, a member made of silicone resin is employed, so
that the surface layer of the titanium oxide photocatalytic thin
film can be made a layer including silicon oxide and titanium oxide
as described above.
[0056] Although it depends on the heating time, the heating
temperature of the substrate is high enough to be a room
temperature (25.degree. C.) or higher, preferably 50.degree. C. or
higher, in order to convert the amorphous state to crystalline or
polycrystalline state and obtain a titanium oxide thin film having
a high photocatalytic effect and at the same time form the surface
layer as described above. In order to increase the crystallinity
and efficiently form the surface layer, the heating temperature is
better to be high. Accordingly, the upper limit temperature of
heating is not particularly limited, however in terms of the
heating method selection, heating temperature control, energy loss
and the like, it is preferably about 300.degree. C., more
preferably about 250.degree. C. In order to efficiently increase
the crystallinity degree, and to make the heating condition
adequate, it is preferable to heat a substrate to 100 to
200.degree. C.
[0057] In the case the substrate is a plastic substrate, the
heating upper limit temperature is the heat resistant temperature
of the plastic substrate. What the heating resistant temperature of
the plastic substrate is, in the case of the foregoing plastic
substrates, at highest about 230.degree. C. Further, from the above
described viewpoint, even in the case of the plastic substrate,
heating is preferably at about 100 to 200.degree. C. (nevertheless,
in the case the heat resistant temperature of the plastic substrate
is at 200.degree. C. or lower, it is in a range up to its heat
resistant temperature).
[0058] For the excimer beam radiation, a commonly sold excimer lamp
is preferable to be employed. Further, as the wavelength of excimer
beam is shorter, the beam energy is more intense and UV rays with
wavelength of 365 nm or shorter, preferably 308 nm or shorter, are
preferable to be employed (for example, UV rays of 308 nm, 202 nm,
172 nm).
[0059] Even the excimer beam radiation dose of about 1 to 50
mW/cm.sup.2 can sufficiently convert a titanium oxide thin film to
a photocatalytic thin film. Further, it is general that as the
excimer beam radiation time is longer, a titanium oxide thin film
can be converted into a photocatalyst thin film better. Although
depending on the excimer beam wavelength, beam intensity, heating
temperature, in the case of using an excimer lamp with a wavelength
of 172 nm, beam intensity of 10 mW/cm.sup.2, and a heating
temperature of 125.degree. C., the radiation time is proper to be
30 seconds to at longest 20 minutes. Further, although depending on
whether emphasis of the treatment of the invention is put on both
crystallization of an amorphous titanium oxide and formation of the
foregoing surface layer or on only formation of the surface layer,
the beam radiation time of the excimer lamp is sufficient to be
about 15 minutes in the former case and about 1 minute in the
latter case.
[0060] The ambient atmosphere at the time of heating and excimer
beam radiation is vacuum or a gas atmosphere. The term, vacuum,
generally means the vacuum degree of about 10.sup.-2 Pa, however
taking other conditions into consideration, it can be properly
selected. As the gas atmosphere, for example, one or more kinds of
gases such as hydrogen gas, nitrogen gas, ammonia gas, rare gas
such as He, Ne, Ar, and carbon monoxide can be employed. The gas
atmosphere preferably reductive atmosphere containing hydrogen gas
and more preferably atmosphere having a low oxygen partial
pressure. In order to lower the oxygen partial pressure, the
heating temperature of a titanium oxide thin film can be
decreased.
[0061] For example, in the case the treatment of the invention is
carried out in a highly pure nitrogen gas reductive atmosphere
containing 2 to 5% (explosion limit or lower) of hydrogen (in the
case of using an apparatus having a capacity of, for example, 1 L,
the flow rate is controlled to be 0.5 to 2 L/min), amorphous state
is converted to be polycrystalline and lattice defects of oxygen is
caused and thus carrier concentration of the titanium oxide thin
film is increased to improve the photoelectric properties and the
photocatalytic properties. The pressure of the reductive atmosphere
may be normal pressure (atmospheric pressure) and may be decreased
pressure.
[0062] In the case a layer containing silicon oxide and titanium
oxide is formed, the photocatalytic properties such as ultra high
hydrophilicity and the like can be well retained even in a dark
place and kept for 3 months or longer.
[0063] Further, in the case the photocatalytic thin film produced
by the method of the invention is required to have a light
transmissive property, a reflection prevention film is disposed on
a light transmissive substrate and a titanium oxide thin film is
disposed on the reflection prevention film or the optical film
thickness of the titanium oxide thin film is controlled to be a
specified thickness, so that light reflection between the light
transmissive substrate and the titanium oxide thin film can be
prevented from occurring and the thin film with remarkably high
light transmittance can be obtained.
[0064] The refractive index of the reflection prevention film can
be controlled to be in a range from 1.5 to 2.3.
[0065] The foregoing reflection prevention film can be composed of,
for example, an inorganic oxide dielectric.
[0066] As the inorganic oxide dielectric to be employed for the
reflection prevention film, there are SnO.sub.2, ITO, CeF.sub.3,
ZnS, MgO, Gd.sub.2O.sub.3, Sc.sub.2O.sub.3, ZrO.sub.2, SiO,
HfO.sub.2, CeO.sub.2, and the like. Specially, ZrO.sub.2 is
generally used as a material of a dielectric thin film with a high
refractive index. The reflection prevention film of an inorganic
oxide dielectric can be easily formed to be thin by a sputtering
method, a RF sputtering method, an electron beam deposition method
and the like.
[0067] In the case the reflection prevention film is a monolayer,
the refractive index n is preferably to be between the refractive
index of the foregoing light transmissive substrate and the
refractive index of the titanium oxide photocatalytic thin film and
the optical film thickness represented by a product of the film
thickness and the reflective index of the protection film is
preferably 1/4 of wavelength in the vicinity of the visible ray
range or a whole number multiple of 1/4 of the wavelength in terms
of the elimination of light reflection between the light
transmissive substrate and the titanium oxide thin film.
[0068] For example, in the case a substrate is of glass with 1.5
refractive index 1.5 and a titanium oxide photocatalytic thin film
of titanium oxide with 2.5 refractive index, assuming the center
wavelength of visible light rays is 550 nm, a film having a
refractive index in the middle of them, about 1.8 to 2.0, for
example a ZrO.sub.2 with a refractive index of 2.06, and having a
film thickness of 69 nm [550/(4.times.2.06)=69] or its whole number
multiple is effective to be employed as the reflection prevention
film. Practically, such a film with a film thickness 63 nm to 75 nm
may be usable. Further in the case of ITO with a refractive index
of 1.9, an ITO film with a film thickness of about 72 nm
[550/(4.times.1.9)=72] or its whole number multiple is effective to
be employed. Practically, such a film with a film thickness of 66
nm to 78 nm may be usable. However, since a practical refractive
index of a reflection prevention film differs depending on the film
formation conditions, it is required to determine the film
thickness depending on the alteration.
[0069] Generally, if the optical film thickness, the product of the
film thickness of the reflection prevention film and the refractive
index, is within a range 110 nm to 160 nm or within a range from
330 nm to 480 nm, reflection can be effectively prevented.
[0070] Further, in place of formation of the reflection prevention
film on a substrate, occurrence of light reflection between a
titanium oxide photocatalytic thin film and a substrate can be
prevented by controlling the optical film thickness represented by
the product of the film thickness and the refractive index of the
titanium oxide thin film to be 1/2 of wavelength in the vicinity of
the center of the visible light range or shorter or to be whole
number multiple of 1/2 of wavelength in the vicinity of the center
of the visible light range.
[0071] As one example, assuming the center wavelength of visible
light rays is 550 nm, in the case titanium oxide with a refractive
index of 2.5 is used as a titanium oxide photocatalytic thin film,
for example, the thickness of the titanium oxide thin film may be
controlled to be not more than about 550/(2.times.2.5)=110 (nm) or
its whole number multiple. (It is not necessary to strictly adjust
to be the numeral value).
[0072] Further, in the case a plastic substrate is used as a
substrate, the plastic substrate is sometimes deteriorated owing to
the photocatalytic reaction of the titanium oxide. Accordingly, to
suppress the deterioration of the photocatalytic film, it is
preferable to form a protection film of an oxide compound between
the plastic substrate and the titanium oxide photocatalytic film.
The refractive index of the protection film is proper to be in a
range from 1.4 to 2.3 from a viewpoint of the transparency.
[0073] Practically, a ZrO.sub.2 thin film, an ITO thin film and the
like can be used. In this case, the protection film may be used as
the foregoing reflection prevention film. Accordingly, as the
protection film, those similar to a ZrO.sub.2 thin film, a
SnO.sub.2 thin film, a SiO.sub.2 thin film, an ITO thin film as the
foregoing reflection prevention film may be use.
[0074] Besides, an amorphous titanium oxide thin film may be used
as the protection film. Since the film thickness of the amorphous
titanium oxide thin film (about 2.5 refractive index) can be
controlled to be several 10 nm, no practical effect is caused on
the transparency.
[0075] Further, the refractive index of the foregoing protection
film is preferably between the refractive index of the foregoing
substrate and the refractive index of the titanium oxide
photocatalytic thin film and the optical film thickness represented
by a product of the film thickness and the reflective index of the
protection film is preferably 1/4 of wavelength in the vicinity of
the visible ray range or its whole number multiple in terms of the
prevention of light transmission property even if the protection
film is formed.
[0076] Generally, if the optical film thickness of the protection
film is in a range from 10 nm to 160 nm or in 330 nm to 480 nm, the
protection film performs the function as a protection film without
deteriorating the transparency.
[0077] A photocatalytic thin film of the invention may be in form
of a composite material, as described above, of a substrate and a
reflection prevention film, a protection film layered thereon.
[0078] In the case the substrate of the foregoing composite
material is a flexible plastic substrate, it may be rolled like a
roll and may be advantageously used for the purpose of stain
prevention of outer walls of buildings and the like. Further, the
substrate of the foregoing composite material is a light
transmissive plastic substrate or a light transmissive flexible
plastic substrate, the material may be advantageously used for
anticlouding and stainproofing for glass windows, mirrors and the
like.
[0079] Further, in the foregoing composite material, if a
reflection prevention film as described above is disposed between
the substrate and the titanium oxide photocatalytic thin film, the
light transmission property is improved and therefore, the material
is especially preferable for articles which reflect light or
transmit light.
[0080] Further, in the case the substrate is a plastic substrate,
formation of a protection layer between the substrate and the
titanium oxide photocatalytic thin film prevents undesirable
effects of the activity of the photocatalytic thin film on the
substrate, so that even if the composite material is in
environments under which the material is exposed to light for a
long term, the plastic substrate can be prevented from
deterioration.
[0081] An example of the foregoing composite material is shown.
FIG. 5A shows a composite material provided with a glass substrate
(the thickness of 0.7 mm) and a titanium oxide photocatalytic thin
film of a film thickness of 200 nm thereon and the titanium oxide
film is made to have a thickness for suppressing reflection. FIG.
5B shows a composite material provided with a PES film (the
thickness of 150 .mu.m) and a titanium oxide photocatalytic thin
film of a film thickness of 200 nm thereon. FIG. 5C shows a
composite material provided with an Arton film (the thickness of
188 .mu.m) and an ITO film with a film thickness of 75 nm as a
protection film and also as a reflection prevention film and a
titanium oxide photocatalytic thin film of a film thickness of 200
nm thereon. FIG. 5D shows a composite material provided with a PES
film (the thickness of 0.15 mm) and an amorphous titanium oxide of
a film thickness of 10 nm and a titanium oxide photocatalytic thin
film of a film thickness of 200 nm thereon. These titanium oxide
photocatalytic thin films have a refractive index of 2.5.
[0082] Next, one example of an experimental apparatus (hereinafter,
in some cases referred to as an annealing apparatus) to be employed
for the titanium oxide photocatalytic thin film production method
of the invention will be described below.
[0083] FIG. 6 is a schematic conceptual diagram showing one example
of an annealing apparatus for carrying out the treatment of the
invention under the reductive gas atmosphere (heating and excimer
beam radiation) and the annealing apparatus 29 has a chamber 21 for
storing a base material bearing a titanium oxide thin film
(hereinafter, in some cases referred to as a substrate), excimer
beam radiation means 22, heating means 24, a heat transmission
plate 26 for transmitting heat from the heating means, means for an
ambient gas introduction and discharge which is not illustrated, an
ambient gas introduction route 27, an ambient gas discharge route
28, and vacuum gas discharge means 40. The reference numeral 10
denotes a substrate provided with a base material and a titanium
oxide thin film disposed thereon. Further, although it is not
illustrated, temperature detection means is installed between the
substrate 10 and the heat transmission plate 26 and by the
unillustrated temperature detection means, the temperature of the
substrate can be controlled. Further, at the time of using the
apparatus, the oxygen partial pressure in the chamber is to be
decreased and to decrease the oxygen partial pressure, it is
possible to decrease the oxygen partial pressure by introducing a
reductive gas for a prescribed time without using the vacuum
discharge means and therefore, in such a case, no vacuum discharge
means may be installed. As the excimer beam radiation means, an
excimer lamp is preferable and as the heating means, a heater for
heating electrically is preferable and also, as the heat
transmission plate, for example, a heat transmissive ceramic plate
is employed and as temperature detection means, for example, a
thermocouple may be employed. As the vacuum gas discharge means,
for example, a turbo molecular pump is employed.
[0084] Further, the foregoing chamber may be a bell jar made of
synthetic quartz and a jig to be put in the bell jar is preferably
one made of synthetic quartz. Further, as a heater, a silicone
rubber heater may be used. The foregoing synthetic quartz and
silicone rubber heater can be used as a silicon-including compound
in the production method of the invention.
[0085] In the case of using vacuum gas discharge means, the
substrate 10 is put on the heat transmission plate 26 and after
that, the chamber is evacuated to be vacuum once by the vacuum gas
discharge means 40 to decrease the oxygen partial pressure in the
inside. The heat transmission plate 26 is heated by the heating
means 24 to increase the temperature of the substrate. When the
substrate temperature reaches the treatment temperature of the
invention, the reductive gas of such as hydrogen-nitrogen mixed gas
and the like is introduced into an annealing apparatus and after
the reductive gas is sufficiently passed, the excimer beam
radiation is started.
[0086] Further, in the annealing apparatus in the case the
photocatalytic thin film production of the invention is carried out
under vacuum, in place of the ambient gas introduction and
discharge means of the annealing apparatus in FIG. 6, vacuum gas
discharge means for discharging the gas in the inside of the
apparatus, for example, a turbo molecular pump may be
installed.
[0087] Since it is possible to carry out low temperature annealing
in the photocatalytic thin film production method of the invention,
there is an advantage that no special heating means, temperature
control means and the like are required to be employed and
economical means may be used.
EXAMPLES
[0088] Hereinafter, the present invention will be described
practically with reference to examples, however the invention is
not at all limited to these examples.
Example 1
[0089] An anatase type titanium oxide with a film thickness of 200
nm was formed on a 0.7 mm-thick alkali-free glass substrate
(Corning 1737 glass) at 250.degree. C. substrate temperature by RF
sputtering method. Next, using an experimental apparatus as
illustrated in FIG. 1 (a bell jar of a capacity of about 1 L and
made of synthetic quartz as a chamber and a jig in the bell jar is
made of synthetic quartz and as a heater, a silicone rubber heater
is used), after vacuum treatment (10.sup.-2 Pa) was previously
carried out to remove oxygen, under highly pure nitrogen gas
atmosphere containing 3% of hydrogen gas (flow rate: 1 L/min,
atmospheric pressure), the foregoing glass substrate on which the
titanium oxide was formed was heated at 150.degree. C. and while
the temperature being kept, excimer beam (wavelength: 172 nm, beam
intensity: 10 mW/cm.sup.2) was radiated for 10 minutes by an
excimer lamp (Ushio Inc.).
[0090] XPS analysis of the obtained thin film treated by excimer
beam was carried out. FIGS. 1A and 1B show the XPS measurement
results of a titanium oxide thin film before and after the
treatment. FIG. 1A is the measurement result before treatment and
the peak of O--Ti is observed. Further, FIG. 1B shows the
measurement result after treatment and the peaks of O--Ti and O--Si
are observed. Further, FIG. 2 shows the result of simulation
treatment of FIG. 1B by separating the peaks of O--Ti and O--Si and
the dotted line is the raw data and the curve (1) and the curve (2)
show simulation lines of O--Si and O--Ti, respectively. Further,
FIG. 3 shows the peak of Ti.sub.2p3/2 of titanium dioxide before
and after the treatment and the curve (3) shows that before
treatment and the curve (4) shows that after treatment. As being
understood from FIG. 3, it can be confirmed that crystallization is
promoted by the treatment of the invention.
[0091] On the other hand, as a result of the peak separation
analysis of the XPS analysis, the average of the mole ratio of
Ti--O and Si--O from the surface to 5 nm of the obtained titanium
oxide photocatalytic thin film was found 34:30. Further, in the
portion deeper than the portion from the surface to 5 nm of the
titanium oxide photocatalytic thin film, no Si--O was practically
detected.
[0092] According to these facts, the surface layer of the
photocatalytic thin film obtained in this example was found to be a
hybrid layer containing titanium oxide and silicon oxide.
[0093] Further, the contact angle of the foregoing photocatalytic
thin film to water in a dark place was investigated. It was
maintained to be 5.degree. or lower for at least 3 months. FIG. 4
shows the result together with the contact angle of the titanium
oxide thin film before heating and excimer beam radiation treatment
(in the figure, the result up to 40 days is shown). As FIG. 4
shows, the result of the contact angle without treatment of the
invention is found increased to 33.degree. after 40 days, whereas
it is kept 5.degree. or lower by carrying out the treatment of the
invention.
[0094] Further, in order to investigate the photocatalytic
activity, the coloring material decomposition characteristic was
investigated to find sufficient photocatalytic activity.
Example 2
[0095] An anatase type titanium oxide with a film thickness of 200
nm was formed at 150.degree. C. substrate temperature by RF
sputtering method after a 75 nm-thick ITO film was formed on a 0.15
mm-thick plastic sheet substrate (PES film produced by Sumitomo
Bakelite Co., Ltd.). Next, using the same experimental apparatus as
that of the Example 1, heating and excimer beam radiation was
carried out in the same conditions as the Example 1, except that
the heating temperature of the plastic sheet substrate was changed
to be 130.degree. C.
[0096] In the same manner as the Example 1, XPS analysis of the
obtained excimer beam-treated thin film was carried out to find
that a hybrid film of silicon oxide and titanium oxide is formed on
the surface.
[0097] Further, as a result of investigation on the contact angle
retention property of the foregoing photocatalytic thin film to
water in a dark place, the contact angle was found kept at
5.degree. or lower for at least 3 months. FIG. 4 shows the result
together with the contact angle of the titanium oxide thin film
before heating and excimer beam radiation treatment (in the figure,
the result up to 40 days is shown). As FIG. 4 shows, the result of
the contact angle without treatment of the invention is found
increased to 33.degree. after 40 days, whereas it is kept 5.degree.
or lower by carrying out the treatment of the invention.
[0098] Further, in order to investigate the photocatalytic
activity, the coloring material decomposition characteristic was
investigated to find sufficient photocatalytic activity.
Example 3
[0099] After a 75 nm-thick ITO film was disposed on a 188 .mu.m
thick Arton film substrate, an anatase type titanium oxide with a
film thickness of 110 nm was formed at 150.degree. C. substrate
temperature by RF sputtering method. Next, using the same
experimental apparatus as that of the Example 1, heating and
excimer beam radiation was carried out in the same conditions as
the Example 2.
[0100] In the same manner as the Example 1, XPS analysis of the
obtained excimer beam-treated thin film, evaluation on the contact
angle retention property in a dark place, and evaluation on the
photocatalytic activity are carried out to find similar results as
those of the Example 1.
Example 4
[0101] A 10 nm-thick amorphous titanium dioxide was formed without
heating on a 0.15 mm-thick plastic sheet substrate (PES film
produced by Sumitomo Bakelite Co., Ltd.) and then substrate
temperature was risen to 150.degree. C., an anatase type titanium
oxide with a film thickness of 200 nm was formed by RF sputtering
method.
[0102] Next, using the same experimental apparatus as that of the
Example 1, heating and excimer beam radiation was carried out in
the same conditions as the Example 1, except that the heating
temperature of the plastic sheet substrate was changed to be
130.degree. C.
[0103] In the same manner as the Example 1, XPS analysis of the
obtained excimer beam-treated thin film, evaluation on the contact
angle retention property in a dark place, and evaluation on the
photocatalytic activity are carried out to find similar results as
those of the Example 1.
[0104] Unlike a conventional titanium oxide film bearing a silica
coating on the surface, the titanium oxide photocatalytic thin film
of the invention does not cause photocatalytic activity
deterioration even in the case it is kept in a dark place for a
long term and a small contact angle to water can be maintained.
Further, since the photocatalytic thin film of the invention has a
high activity, sufficiently high photocatalytic activity can be
obtained even if the film thickness is made thin. Accordingly,
interference color of the light based on the high refractive index
of titanium oxide can be eliminated and high transparency in a
visible light range can be provided.
[0105] Further, the photocatalytic thin film production method of
the invention has advantages that the treatment time is short and
no large-scale apparatus is required, as compared with a
conventional method.
* * * * *