U.S. patent application number 15/083999 was filed with the patent office on 2016-10-06 for photocatalytic coating composition.
The applicant listed for this patent is TOTO LTD.. Invention is credited to Susumu ADACHI, Tetsuya FUKUSHIMA, Takeshi IKEDA, Hiroaki SHIMOMURA.
Application Number | 20160288091 15/083999 |
Document ID | / |
Family ID | 57015865 |
Filed Date | 2016-10-06 |
United States Patent
Application |
20160288091 |
Kind Code |
A1 |
FUKUSHIMA; Tetsuya ; et
al. |
October 6, 2016 |
PHOTOCATALYTIC COATING COMPOSITION
Abstract
Provided by the present invention is a photocatalytic coating
composition having small viscosity change rate and excellent
storage stability. The photocatalytic coating composition comprises
photocatalyst particles, a dispersion medium, a thickener, and at
least one selected from the group consisting of primary to tertiary
alkanol amines, wherein the thickener is at least one selected from
the group consisting of a polysaccharide thickener containing
glucuronic acid and/or rhamnose in its main chain and a layered
silicate, the ratio of the mass of the at least one selected from
the group consisting of primary to tertiary alkanol amines relative
to the mass of total solid content in the photocatalytic coating
composition is in the range of 2.5% or more by mass to 25% or less
by mass, and liquid property of the photocatalytic coating
composition is basic.
Inventors: |
FUKUSHIMA; Tetsuya;
(Fukuoka, JP) ; SHIMOMURA; Hiroaki; (Fukuoka,
JP) ; ADACHI; Susumu; (Fukuoka, JP) ; IKEDA;
Takeshi; (Fukuoka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOTO LTD. |
Kitakyushu-shi |
|
JP |
|
|
Family ID: |
57015865 |
Appl. No.: |
15/083999 |
Filed: |
March 29, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08K 2003/2244 20130101;
C09D 5/1693 20130101; C08K 2003/2241 20130101; C09D 5/1687
20130101; B01J 21/063 20130101; B01J 35/004 20130101; C09D 7/41
20180101; C08K 3/36 20130101; B01J 37/0219 20130101; C09D 5/1618
20130101 |
International
Class: |
B01J 21/06 20060101
B01J021/06; B01J 35/00 20060101 B01J035/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2015 |
JP |
2015-074527 |
Mar 31, 2015 |
JP |
2015-074528 |
Sep 30, 2015 |
JP |
2015-193891 |
Sep 30, 2015 |
JP |
2015-193892 |
Claims
1. A photocatalytic coating composition comprising photocatalyst
particles, a dispersion medium, a thickener, and at least one
selected from the group consisting of primary to tertiary alkanol
amines, wherein the thickener is at least one selected from the
group consisting of a polysaccharide thickener containing
glucuronic acid and/or rhamnose in its main chain and a layered
silicate, the ratio of the mass of the at least one selected from
the group consisting of primary to tertiary alkanol amines relative
to the mass of total solid content in the photocatalytic coating
composition is in the range of 2.5% or more by mass to 25% or less
by mass , and liquid property of the photocatalytic coating
composition is basic.
2. The photocatalytic coating composition according to claim 1,
wherein the polysaccharide thickener comprises Diutan gum and/or
Welan gum.
3. The photocatalytic coating composition according to claim 1,
wherein an inorganic compound other than the photocatalyst
particles is further contained therein.
4. The photocatalytic coating composition according to claim 3,
wherein the inorganic compound is fine particles of an oxide and/or
a hydroxide.
5. The photocatalytic coating composition according to claim 1,
wherein the ratio of the mass of total solid content in the
photocatalytic coating composition relative to the mass of the
entire photocatalytic coating composition is in the range of 0.1%
or more by mass to 10% or less by mass.
6. The photocatalytic coating composition according to claim 1,
wherein pH of the photocatalytic coating composition is in the
range of 8.0 or more to 12.0 or less.
Description
FIELD OF INVENTION
[0001] The present invention relates to a photocatalytic coating
composition having, owing to its excellent physical properties, a
good application workability so that a homogeneous photocatalyst
coated film having uniform thickness can be stably formed for a
long period of time on a surface of a base.
BACKGROUND ART
[0002] In recent years, a photocatalyst such as titanium oxide has
been used in many use applications including an exterior material
of an architectural structure. A photocatalyst excited by a light
can decompose various harmful substances, and utilizing this
property allows a surface of a base coated with a photocatalyst to
be cleaned. In addition, a photocatalyst which is excited by a
light makes a surface of a base coated with the photocatalyst
hydrophilic, and the hydrophilic properties thus imparted allow a
dirt which is attached to the surface to be easily washed out by
water. It is widely known that the photocatalyst coated film like
this is formed by applying a coating solution which contains a
photocatalyst. Besides, a photocatalyst coated film mainly used is
transparent so as not to damage the design of a base such as an
exterior material.
[0003] A technology in which hydrophilicity is given to a surface
of a glass, a mirror, or the like by using, as a coating solution
which contains a photocatalyst, an aqueous dispersion which
contains photocatalyst particles and an inorganic binder has been
known (see, for example, PTL 1: JP 2001-89706 A). In the technology
described in PTL 1, a transparent coated film is obtained by highly
dispersing fine photocatalyst particles and an inorganic binder
such as an alkaline silicate salt. PTL 1 also discloses that in
order to suppress uneven coating of the coating solution so that
the coated film may have a uniform film thickness, the coating
solution is impregnated into an unwoven cloth and is applied to a
base by sliding it to one direction at a constant speed. Namely, in
this technology, a worker involved in application has been required
to have a high skill.
[0004] In order to form a satisfactory photocatalyst coated film
without requiring a high skill to a worker, various ingenuities
have been exercised. For example, as to an apparatus or a tool for
assisting the application work, in JP 2003-026447 A (PTL 2), a
method in which application is conducted while a roller is in the
fixed state is proposed; and in JP 2010-247054 A (PTL 3), it is
proposed that a laser irradiation means and a metronome are
combined with a spraying apparatus.
[0005] Also, with regard to improvement of a composition of a
coating solution focusing on rheology, for example, it is proposed
in PTL 1 that a surfactant or a thickener is added to a dispersion
in order to control viscosity of the dispersion. It is proposed in
JP 2004-143443 A (PTL 4) that a thickener is used and that a
surfactant and a solvent having a high boiling point are added.
[0006] However, even with these technologies, the status quo is
that a high skill is required to a worker involved in application
especially when a coating solution is applied on the spot to a
large area such as a wall surface. In order to form a satisfactory
photocatalyst coated film without requiring the special skill as
mentioned above, further improvement of the coating solution is
necessary.
CITATION LIST
Patent Literature
[0007] PTL 1: JP 2001-089706 A [0008] PTL 2: JP 2003-026447 A
[0009] PTL 3: JP 2010-247054 A [0010] PTL 4: JP 2004-143443 A
SUMMARY OF THE INVENTION
[0011] The present inventors have now found that when a certain
thickener and a certain amine compound are added, a photocatalytic
coating composition having a small viscosity change rate and
excellent storage stability can be realized. In addition, it has
been found that when a photocatalytic coating composition like this
is used, without any need for a special application skill, a
homogeneous photocatalyst coated film having uniform thickness can
be formed on a surface of a base, and also the characteristics
thereof can be stably expressed and kept for a long period of time.
The present invention has been made on the basis of such
findings.
[0012] Therefore, the present invention has an object to provide a
photocatalytic coating composition having small viscosity change
rate and excellent storage stability. In addition, the present
invention has an object to provide a photocatalytic coating
composition which has a good application workability and can form a
homogeneous photocatalyst coated film having uniform thickness on a
surface of a base.
[0013] That is, the photocatalytic coating composition according to
the present invention is a photocatalytic coating composition
comprising photocatalyst particles, a dispersion medium, a
thickener, and at least one selected from the group consisting of
primary to tertiary alkanol amines, wherein the thickener is at
least one selected from the group consisting of a polysaccharide
thickener containing glucuronic acid and/or rhamnose in its main
chain and a layered silicate, the ratio of the mass of the at least
one selected from the group consisting of primary to tertiary
alkanol amines relative to the mass of total solid content in the
photocatalytic coating composition is in the range of 2.5% or more
by mass to 25% or less by mass, and liquid property of the
photocatalytic coating composition is basic.
[0014] The photocatalytic coating composition according to the
present invention has small temperature dependency in its viscosity
and excellent storage stability for a long period of time with a
small viscosity change rate. In addition, regardless of kind of the
base, a homogeneous photocatalyst coated film having uniform
thickness can be formed on a surface of a base without applying in
a skilled working method in which a conventional application tool
is used or without using a special application apparatus. In
particular, even when on-site application is made to an area larger
than a window or the like, such as a wall surface, without any need
for a special application skill or technique, a satisfactory
photocatalyst coated film can be easily formed without causing
liquid dripping due to excess application or poor appearance such
as uneven coating and coating streaks. In addition, excellent
application workability or easiness as mentioned above can be kept
stably for a long period of time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a secondary electron image of the surface of the
photocatalyst coated film obtained by using the photocatalytic
coating composition according to the present invention.
[0016] FIG. 2 is a magnified image of the B part in the secondary
electron image of FIG. 1.
[0017] FIG. 3 is a magnified image of the D part in the secondary
electron image of FIG. 1.
[0018] FIG. 4 is a backscattered electron image of a cross section
of the photocatalyst coated film obtained by using the
photocatalytic coating composition according to the present
invention.
[0019] FIG. 5 is a magnified image of the i part in the
backscattered electron image of FIG. 4.
[0020] FIG. 6 is a magnified image of the ii part in the
backscattered electron image of FIG. 4.
DESCRIPTION OF THE INVENTION
Thickener
[0021] In the present invention, a thickener means a substance
which is added to control rheology and increases the viscosity of
the photocatalytic coating composition. The photocatalytic coating
composition according to the present invention is a basic aqueous
dispersion with low solid content, and therefore, it is required
that the thickener preferably has the following characteristics:
the thickener has a high water solubility; the thickener can
thicken the composition with a small quantity; the thickener has a
thickening property which is not damaged in basic and high
temperature conditions; the thickener has color which is not left
during drying.
[0022] In the present invention, as the thickener which shows the
above-mentioned characteristics, at least one selected from the
group consisting of a polysaccharide thickener containing
glucuronic acid and/or rhamnose in its main chain and a layered
silicate may be preferably used. Examples of the polysaccharide
thickener containing glucuronic acid and/or rhamnose in its main
chain include Diutan gum and/or Welan gum. The layered silicate is
preferably in a bared state without the treatment of
hydrophobization. Examples of the layered silicate preferably
include synthetic hectorite (commercial names: Laponite RD and
Laponite B, manufactured by BYK Japan KK) and synthetic saponite
(commercial name: Lucentite, manufactured by Co-op Chemical Co.,
Ltd.; and Sumecton SA, manufactured by Kunimine Industries Co.,
Ltd.). Any of natural and synthetic layered silicates may be used,
among them, synthetic layered silicates are more preferable because
they are colorless.
[0023] In the present invention, the thickener changes rheology of
the photocatalytic coating composition thereby contributing to make
the application work of the composition remarkably easy. In
addition, the thickener can express a significant thickening effect
even in a small addition amount and can form a transparent
photocatalyst coated film, therefore, they are preferable.
Furthermore, the thickener has a small temperature dependency in
viscosity change, and therefore, for example, when the application
work of the photocatalytic coating composition is done outdoor, a
constant rheology property can be obtained regardless of the
outdoor temperature, so that variability in application work due to
environmental factors can be suppressed.
[0024] Addition amount of the thickener to the photocatalytic
coating composition is preferably in the range of 0.05% or more by
mass to 1% or less by mass, while more preferably in the range of
0.1% or more by mass to 0.8% or less by mass. By virtue of this,
there is no liquid dripping or the like during the application work
to a large area such as an exterior wall, so that the
photocatalytic coating composition can be applied with a simple
application tool to form a homogeneous coated film.
Primary to Tertiary Alkanol Amines
[0025] In the present invention, primary to tertiary alkanol amines
have an effect to stabilize the particle components such as the
photocatalyst particles; as well as thickeners such as the layered
silicates and the polysaccharide thickeners containing glucuronic
acid and/or rhamnose in its main chain, in the photocatalytic
coating composition. That is, the alkanol amines are added to
suppress a reaction or an agglomeration of particle components such
as the photocatalyst particles and later-mentioned inorganic
oxides, and further not to inhibit the composition thickening due
to formation of a network by way of the thickener. By virtue of
this, the photocatalytic coating composition having excellent
storage stability for a long period of time can be obtained.
[0026] When the liquid property of the photocatalytic coating
composition is basic, in the photocatalytic coating composition,
all the particle components are dispersed or dissolved with
carrying negative charge. If the thickener is added in order to
improve application workability, charge balance of the
photocatalytic coating composition is lost, so that there is a
possibility that viscosity of the photocatalytic coating
composition becomes unstable. So as to stabilize the particle
components and the thickener in the photocatalytic coating
composition, it is considered necessary to stabilize the charge of
the composition and to stabilize solubility of the thickener into
the composition. Addition of primary to tertiary alkanol amines has
an effect to stabilize both of them. That is, it is considered that
primary to tertiary alkanol amines can stabilize an electric charge
and also can maintain the solubility of the thickener since they
have a nitrogen in the form of an amine which readily coordinate
with the thickener, and at the same time have an alkanol group.
[0027] In substitution for primary to tertiary alkanol amines,
sodium hydroxide or ammonia may be added. In this case, the
photocatalytic coating composition can be stabilized at a certain
viscosity by stabilizing an electric charge of the composition. On
the other hand, primary to tertiary alkanol amines further have an
effect to enhance hydrophilicity of the thickener, the alkanol
amines can give a stability for a long period of time to the
photocatalytic coating composition, so that sodium hydroxide and/or
ammonia may be further added to primary to tertiary alkanol
amines.
[0028] In addition, in substitution for primary to tertiary alkanol
amines, an alkyl amine may be added. In this case, it has an effect
to stabilize an electric charge of the photocatalytic coating
composition and readily coordinate with the thickener as well as
primary to tertiary alkanol amines. On the other hand, primary to
tertiary alkanol amines further have an effect to facilitate
hydration of the thickener, the alkanol amines can enhance
stability of the viscosity of the photocatalytic coating
composition, so that an alkyl amine may be further added to primary
to tertiary alkanol amines.
[0029] Preferable examples of primary to tertiary alkanol amines
include dimethyl ethanol amine, methyl diethanol amine, ethanol
amine, diethanol amine, triethanol amine, diethyl ethanol amine,
dibutyl ethanol amine, .beta.-aminoethyl ethanol amine, methyl
ethanol amine, ethyl ethanol amine, ethyl diethanol amine, n-butyl
ethanol amine, n-butyl diethanol amine, t-butyl ethanol amine,
t-butyl diethnaol amine, .beta.-aminoethyl isopropanol amine and
diethyl isopropanol amine and the like. Among them, dimethyl
ethanol amine and methyl diethanol amine are more preferable.
[0030] Primary to tertiary alkanol amines are added such that the
ratio of the mass of the primary to tertiary alkanol amines
relative to the mass of total solid content in the photocatalytic
coating composition may be in the range of 2.5% or more by mass to
25% or less by mass. When the addition amount of the primary to
tertiary alkanol amines is adjusted to 2.5% or more by mass, the
photocatalytic coating composition having a small viscosity change
rate and an excellent storage stability can be obtained. In
addition, liquid dripping during application work can be
effectively prevented. When the addition amount of the primary to
tertiary alkanol amines is adjusted to 25% or less by mass, the
amount of non-particle components in the photocatalytic coating
composition can be lowered, so that the photocatalyst coated film
can have sufficient strength. In addition, the photocatalyst coated
film can have good weather fastness. When the primary to tertiary
alkanol amines are contained such that the liquid property of the
photocatalytic coating composition may be adjusted to basic,
preferably to pH of 8.0 or more to 12.0 or less, dispersion
stability and viscosity stability of the photocatalytic coating
composition can be more enhanced. In the present invention, if
primary to tertiary alkanol amines are contained in various raw
materials of the photocatalytic coating composition (for example,
primary to tertiary alkanol amines contained in a zirconia sol),
the addition amount of the primary to tertiary alkanol amines means
the total amount including the amount of the primary to tertiary
alkanol amines contained in the raw materials.
Photocatalyst Particles
[0031] In the present invention, photocatalyst particles mean
particles having a photocatalytic activity. Specifically,
photocatalyst particles may be particles which generate active
oxygen species (.O.sub.2.sup.-, .O.sup.-, .OH, H.sub.2O.sub.2,
.HO.sub.2, and the like) to decompose an organic substance by a
photocatalytic reaction which takes place by irradiation of a
light, especially a UV light or a visible light, or which generates
a positive hole, i.e., hole in the valence band by photoexcitation
which takes place by irradiation of a UV light or a visible
light.
[0032] Examples of the photocatalyst particles like this include
metal oxide semiconductors showing a photoresponsive property such
as titanium oxide, zinc oxide, tin oxide, niobium oxide, strontium
titanate, bismuth vanadate and tungsten oxide. When at least one
photocatalyst particle selected from the group consisting of the
metal oxide semiconductors is used, a photocatalyst coated film
having an excellent photocatalytic activity such as an
antibacterial activity and an antivirus activity and also having a
high hydrophilifiability can be obtained. Preferable photocatalyst
particles are titanium oxides.
[0033] Titanium oxide may be any of an amorphous titanium oxide and
a crystalline-type titanium oxide. A preferable titanium oxide is a
crystalline-type titanium oxide. Examples of the crystalline-type
titanium oxide preferably include at least one titanium oxide
selected from the group consisting of an anatase-type titanium
oxide, a rutile-type titanium oxide and a brookite-type titanium
oxide. Among them, an anatase-type titanium oxide has a high
photocatalytic activity and a high hydrophilifiability , so that it
is more preferable. In addition, titanium oxides may also be used
as photocatalyst particles having an enhanced photoresponsibility
to a visible light by doping with an element such as nitrogen or by
supporting a copper compound or an iron compound on a surface
thereof.
[0034] In the present invention, titanium oxide may be used in any
form of a sol and a particle.
[0035] Titanium oxide in the form of a sol may be obtained, for
example, by liquid phase method, that is, a method in which a
solution dissolved titanium oxide raw material therein is
hydrolyzed or neutralized to obtain titanium oxide, by using
titanium chloride or titanyl sulfate as a raw material. The
titanium oxide obtained by liquid phase method tends to have low
crystallinity of rutile and large specific surface area. In this
case, the titanium oxide may be fired or the like to obtain a
titanium oxide having optimum crystallinity and specific surface
area. A solvent usable may be but is not particularly limited to
water, alcohols, ketones, and a mixture thereof. Examples of the
alcohols include methanol, ethanol, 1-propanol, 2-propanol,
1-butanol, and a mixture thereof. Examples of the ketones include
acetone, acetylacetone, methyl ethyl ketone, and a mixture
thereof.
[0036] Titanium oxide in the form of particle may be obtained, for
example, by gas phase method, that is, a method in which titanium
oxide is obtained by gas phase reaction of titanium tetrachloride
with oxygen, by using titanium tetrachloride as a raw material. The
titanium oxide obtained by gas phase method has uniform average
particle diameter. The titanium oxide also has high crystallinity
because it is produced via a high temperature process. As a result,
the titanium oxide obtained provides the photocatalytic coating
composition with good antibacterial activity and antivirus activity
in both a bright place and a dark place as well as with good
decomposition property of an organic compound.
[0037] Particle diameter of the photocatalyst particle is
preferably in the range of 1 nm or more to 50 nm or less, while
more preferably in the range of 5 nm or more to 20 nm or less. When
the particle diameter is preferably 1 nm or more while more
preferably 5 nm or more, photocatalytic activity and
hydrophilization performance thereof can be satisfactorily
expressed. When the particle diameter is preferably 50 nm or less
while more preferably 20 nm or less, scattering of a visible light
does not readily take place, so that the photocatalyst coated film
having excellent transparency can be obtained. Here, the particle
diameter is calculated as a number average value of the measured
lengths of 100 particles in a fracture cross section of the
photocatalyst coated film which is obtained by the method as
mentioned later, each of the particles being observed by a scanning
electron microscope at a magnification of 200,000 times. If the
shape of the observed particle is almost circle, the length of the
particle means a diameter of the particle. If the shape of the
observed particle is non-circular, the length of the particle is
calculated as an approximate value of (major axis+minor
axis)/2.
[0038] Addition amount of the photocatalyst particles in the
photocatalytic coating composition is preferably in the range of
0.05% or more by mass to 5% or less by mass, while more preferably
in the range of 0.1% or more by mass to 1% or less by mass. When
the photocatalyst particles are contained within this range, the
photocatalytic activity and the hydrophilization performance can be
satisfactorily expressed, and further, the photocatalyst coated
film can be prevented from becoming too thick.
Dispersion Medium
[0039] The photocatalytic coating composition according to the
present invention comprises a dispersion medium. According to a
preferred embodiment of the present invention, the dispersion
medium mainly contains water. "A dispersion medium mainly
containing water" is what contains water in the range of 60 parts
or more by mass to 100 parts or less by mass, while preferably in
the range of 80 parts or more by mass to 100 parts or less by mass,
in 100 parts by mass of the dispersion medium. When a mixed solvent
containing a mixture of water and an organic solvent other than
water is used, the organic solvent is preferably what is soluble in
water.
[0040] Examples of the water-soluble organic solvent preferably
include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol,
2-butanol, t-butanol, pentanol, hexanol, cyclobutanol,
cyclopentanol, cyclohexanol, ethylene glycol, propylene glycol,
glycerin, methyl cellosolve and ethyl cellosolve. In the present
invention, at least one organic solvent selected from the group
consisting of the above compounds may be used.
[0041] Preferably, the photocatalytic coating composition according
to the present invention contains the dispersion medium such that
total solid content contained in the composition is adjusted to
0.1% or more by mass to 10% or less by mass. When the dispersion
medium is contained within this range, the photocatalyst coated
film which is transparent and has excellent appearance can be
obtained.
Inorganic Compound
[0042] According to a preferred embodiment of the present
invention, the photocatalytic coating composition according to the
present invention comprises an inorganic compound. In the present
invention, an inorganic compound means inorganic compounds other
than the photocatalyst particle as mentioned above. Examples of the
inorganic compound preferably include fine particles of an
inorganic oxide and/or an inorganic hydroxide. Containing these
fine particles, the photocatalytic coating composition can have
excellent stability and enhance harmful substances removing
capacity of the photocatalyst coated film. Examples of the
inorganic oxide and/or inorganic hydroxide preferably include at
least one compound selected from the group consisting of silica,
zirconia, zirconium hydroxide, a water-soluble zirconium compound,
alumina, hafnia and ceria. At least one compound selected from the
group consisting of silica, zirconia, zirconium hydroxide and a
water-soluble zirconium compound is more preferable. When these
compounds are contained, the photocatalyst coated film can obtain
excellent film performance, namely, strength, transparency, and
harmful substances removing capacity. Because silica is excellent
as a binder, adhesion of the photocatalyst coated film to a base is
strong, so that silica is especially preferable. Because at least
one compound selected from the group consisting of zirconia,
zirconium hydroxide and a water-soluble zirconium compound has high
removing capacity of harmful substances such as NOx, so that the
above compounds are preferable. By virtue of this, the
photocatalyst coated film having excellent transparency can be
obtained. In the present invention, inorganic compounds can be used
in both a sol form and a particle form. In order to obtain the
photocatalyst coated film having high transparency, inorganic
compounds in the form of a sol are preferably used.
[0043] Particle diameter of the inorganic compound is preferably 50
nm or less. When the particle diameter is within this range,
scattering of a visible light does not readily take place, so that
the photocatalyst coated film having excellent transparency can be
obtained. In addition, when the particle diameter is 20 nm or less,
an effect as a binder becomes higher so that the photocatalyst
coated film can have excellent adhesion. Here, the particle
diameter is calculated as a number average value of the measured
lengths of 100 particles in a fracture cross section of the
photocatalyst coated film which is obtained by the method as
mentioned later, each of the particles being observed by a scanning
electron microscope at a magnification of 200,000 times. If the
shape of the observed particle is almost circle, the length of the
particle means a diameter of the particle. If the shape of the
observed particle is non-circular, the length of the particle is
calculated as an approximate value of (major axis+minor
axis)/2.
[0044] Addition amount of the inorganic compound in the
photocatalytic coating composition is preferably in the range of
0.05% or more by mass to 9.9% or less by mass, while more
preferably in the range of 0.1% or more by mass to 8% or less by
mass. When the inorganic compound is contained within this range,
an effect as a binder can be satisfactorily expressed, and further,
the photocatalyst coated film can be prevented from becoming too
thick, so that excellent transparency can be obtained.
Binder
[0045] According to a preferred embodiment of the present
invention, the photocatalytic coating composition according to the
present invention comprises a binder. A binder allows solid
components such as the photocatalyst particles and the inorganic
compound to fix to a surface of a base. As the binder, any of an
organic binder and an inorganic binder can be used. Examples of the
inorganic binder include hydrolysable silane compounds such as
ethyl silicate and methyl ethyl silicate; alkaline silicate such as
lithium silicate and potassium silicate; metal oxide precursors
such as zirconium hydroxide; and amorphous metal oxides. Examples
of the organic binder include a polymer binder. The polymer binder
is polymerized to form a thin film, or alternatively, polymer
dispersoids are fused by evaporation of the dispersion medium to
form a thin film.
[0046] As the polymer binder, any of a natural resin and a
synthetic resin can be used. Examples of the synthetic resin
include an acryl resin, a hydrolysable silicone, an acryl silicone
resin, a silicone resin, an epoxy resin, a urethane resin, a phenol
resin, a polyurethane resin, an acrylonitrile/styrene copolymer
resin, an acrylonitrile/butadiene/styrene copolymer (ABS) resin, a
polyester resin and a fluorine resin. These resins which are
silicone-modified or halogen-modified may be used as well. Among
them, at least one resin selected from a silicone resin, a
silicone-modified resin and a fluorine resin can be preferably used
as the binder. According to a more preferred embodiment of the
present invention, the binder is blended in a form of a dispersion
such as emulsion and dispersion of these resins and is present in
an aqueous coating composition.
[0047] Addition amount of the binder may be properly determined,
the amount is usually in the range of about 10% or more by mass to
about 65% or less by mass, preferably 20% or more by mass, more
preferably 30% or more by mass, and preferably 55% or less by mass,
more preferably 45% or less by mass, relative to total mass of
solid components in the aqueous coating composition. When the
amount of the binder is within the range like this, the
photocatalyst particles can be desirably exposed while keeping
mechanical strength of the photocatalyst coated film, so that
excellent photocatalytic activity can be expressed. When the binder
is contained, the photocatalyst coated film having excellent
adhesion can be obtained.
Other Additives
Colorant
[0048] In the present invention, the photocatalytic coating
composition may contain a colorant. When a colorant is added,
visibility of the part where the photocatalytic coating composition
is applied can be enhanced so that the applied part can be easily
distinguished from the unapplied part by the difference in
appearance, and as a result, the application workability improves.
As the colorant, a material which is visible during application
work while the color of which disappears in the end is preferable.
Specifically, a pH indicator which becomes colorless along with
change of pH, an organic colorant the color of which disappears by
photolysis with a solar light or decomposition with a
photocatalyst, and the like are preferable.
[0049] Examples of the colorant include pH indicators such as
phenolphthalein, thymolphthalein, bromocarboxy thymolphthalein,
o-cresolphthalein, cyanine, a-naphtholphthalein, p-nitrophenol, and
a mixture thereof; organic pigments such as an azo pigment, a
phthalocyanine pigment, and a condensed polycyclic pigment; and
various dyes such as a direct dye, an acidic dye, a basic dye, a
mordant dye, and a reactive dye. Among them, a basic dye is
preferably used. The basic dye is soluble in water and has a high
coloring property even in a small amount, whereas has low light
fastness. Thus, the basic dye has properties that while the
visibility is high the color readily disappear by a light. Examples
of the basic dye preferably include auramine, malachite green and
methylene blue.
[0050] Addition amount of the colorant may be properly determined
within the purpose that the color of the colorant is visible during
application work and disappears in the end. Addition amount of the
colorant is preferably, for example, in the range of 0.001% or more
by mass to 0.05% or less by mass, more preferably in the range of
0.005% or more by mass to 0.01% or less by mass.
[0051] The basic dye such as methylene blue can be dispersed in the
basic photocatalytic coating composition but has a tendency to
change its color by chemical change during storage. As a result,
there is a risk that the visible period may be restricted during
application work. In the present invention, the layered silicate
which is contained as one of the thickeners in the photocatalytic
coating composition suppresses color change of the basic dye over
time, so that an initial color tone can be kept stably. The reason
for this is considered that the basic dye molecule showing a
cationic character is intercalated between layers of the layered
silicate by its cation exchange capacity so that it is stabilized
or protected in the basic photocatalytic coating composition. As a
result, the photocatalytic coating composition according to the
present invention can ensure a proper visible period while
expressing excellent visibility during application work. According
to a preferred embodiment of the present invention, when the
layered silicate is used in combination with other thickener, i.e.,
a polysaccharide thickener which contains glucuronic acid and/or
rhamnose in its main chain, for example, Diutan gum and/or Welan
gum, color stability and dispersibility of the basic dye as well as
viscosity stability (storage stability) of the photocatalytic
coating composition can be more enhanced.
Surfactant
[0052] In the present invention, the photocatalytic coating
composition may contain a surfactant. When a surfactant is
contained, the surface tension of the photocatalytic coating
composition is lowered so that the composition having excellent
leveling property during a coated film is formed can be obtained.
In addition, due to the action of the surfactant, evaporation of
the dispersion medium becomes uniform, so that thickness of the
photocatalyst coated film can be made uniform. The surfactant is
preferably a substance which has high solubility into water
contained in the dispersion medium as a main component and has a
high effect to lower the surface tension. Examples of the
surfactant like this include a nonionic surfactant, an ether-type
nonionic surfactant, an ester-type nonionic surfactant, a
polyalkylene glycol-type nonionic surfactant, a fluorine-type
nonionic surfactant, a silicon-type nonionic surfactant, an
olefin-type surfactant, an acetylenediol-type surfactant, and a
polyether-modified silicone-type surfactant. When these surfactants
are added in an amount of preferably 0.01% or more by mass to 0.5%
or less by mass, the surface tension of the composition can be
satisfactorily lowered so that the uniform photocatalyst coated
film having high transparency can be obtained.
Defoamer
[0053] In the present invention, the photocatalytic coating
composition may contain a defoamer. When a defoamer is contained,
foaming or generation of air bubbles during application of the
composition can be suppressed. Examples of the defoamer preferably
include a silicone-type defoamer having a high safety.
Pigment
[0054] In the present invention, the photocatalytic coating
composition may contain a pigment in such an addition amount that
the effects of the present invention are not damaged. As the
pigment, at least one selected from the group consisting of a
coloring pigment, an extender pigment, and a functional pigment may
be used. When the pigment is contained, the photocatalyst coated
film can be provided with a concealing property, and the coated
film which can keep coloration for a long period of time can be
formed, or alternatively, when the functional pigment is used, for
example, a functional coated film having a reflective property of
an infrared beam may be formed.
Total Solid Content Concentration
[0055] According to a preferred embodiment of the present
invention, the ratio of the mass of total solid content in the
photocatalytic coating composition relative to the mass of the
entire photocatalytic coating composition is in the range of 0.1%
or more by mass to 10% or less by mass. When the mass ratio of
total solid content is within this range, a transparent
photocatalyst coated film can be obtained. When the mass ratio of
total solid content is 0.1% or more by mass, desirable appealing
performances such as photocatalytic activity, for example,
self-cleaning (anti-fouling) property, harmful gases decomposing
property and antibacterial and antivirus properties, can be
obtained. When the mass ratio of total solid content is 10% or less
by mass, the photocatalyst coated film having excellent appearance
can be obtained. In the present invention, total solid content
concentration in the photocatalytic coating composition means the
ratio of the mass of total solid content (namely, components for
forming the coated film) contained in the photocatalyst coated
film, which is formed by applying the photocatalytic coating
composition to a base to form a coated film, followed by drying the
coated film at the temperature of 105.degree. C. or higher to
110.degree. C. or lower, relative to the mass of the entire
photocatalytic coating composition.
Liquid Property
[0056] Liquid property of the photocatalytic coating composition
according to the present invention is basic. By virtue of this, the
photocatalytic coating composition having excellent dispersion
stability and viscosity stability can be obtained. According to a
preferred embodiment of the present invention, the photocatalytic
coating composition has pH of 8.0 or more to 12.0 or less. When pH
is 12.0 or less, the safety of the composition can be ensured. The
component for adjusting the liquid property of the photocatalytic
coating composition to basic is preferably but not particularly
limited to primary to tertiary alkanol amines.
Method for Producing the Photocatalytic Coating Composition
[0057] The photocatalytic coating composition of the present
invention is prepared by mixing the above-mentioned components in
such an addition amount that predetermined addition amounts of the
components may be attained. Raw material of each particle component
is preferably in the form of a sol. By virtue of this, the particle
diameter of each particle component can be made small. The sol is
preferably basic or neutral.
Photocatalytic Body
[0058] The photocatalytic coating composition of the present
invention is applied to a surface of a base to form the
photocatalyst coated film. In this way, a photocatalytic body
comprising at least the base and the photocatalyst coated film
formed on the surface of the base is obtained.
Base
[0059] A base to which the photocatalytic coating composition
according to the present invention is applied may be a material, on
a surface of which the photocatalyst coated film can be formed. The
base may be various materials regardless of an inorganic material
and an organic material. Examples of the base include a single base
composed of general members, for example, ceramic-based inorganic
materials such as fiber-reinforced cement board, plaster board,
concrete member, wall paper, fiber, metal, ceramic, glass and tile;
and resin materials such as PMMA and polycarbonate; as well as a
composite base composed of two or more of the above members.
Alternatively, a base having an organic coating or the like treated
on the surface thereof may be used.
Pretreatment of Base
[0060] In the present invention, it is preferable to ensure a
wetting property of the surface of the base by pretreating the
base. By virtue of this, a uniform photocatalyst coated film can be
formed. Means to ensure the wetting property preferably include a
cleaning agent containing a surfactant and cleaning with abrasives
or the like such as cerium oxide powders. An organic coating may be
conducted on the surface of the pretreated base.
Application to Base
[0061] Application of the photocatalytic coating composition to the
base may be done by an application method widely and generally used
in on-site application such as brush coating, roller coating, spray
coating, and coating using a sponge, an unwoven cloth, a paint pad
and the like.
[0062] Preferably, the application amount of the photocatalytic
coating composition of the present invention is controlled such
that thickness of the photocatalyst coated film after drying is
about 1 .mu.m, although the application amount depends on
concentrations of the solid components and the binder contained in
the photocatalytic coating composition. When the film thickness in
this range is ensured, sufficient photocatalytic activity and
hydrophilifiability can be obtained.
Formation of Photocatalyst Coated Film
[0063] After the photocatalytic coating composition of the present
invention is applied to the base, a wet film formed of the
photocatalytic coating composition which spreads in a wet state on
the surface of the base is dried to form the photocatalyst coated
film. The wet film may be dried at normal temperature. The wet film
may be, if necessary, dried by heating. The drying temperature is
preferably in the range of 5.degree. C. or higher to 500.degree. C.
or lower. When a polymer binder is used as the binder or when a
resin component is contained in at least part of the base, the wet
film may be dried, for example, at temperature in the range of
10.degree. C. or higher to 200.degree. C. or lower, taking the
heat-resistant temperature of the binder or the resin component
into consideration.
Photocatalyst Coated Film
[0064] The thickness of the photocatalyst coated film is preferably
in the range of 0.5 .mu.m or more to 5 .mu.m or less. When the film
thickness is 0.5 .mu.m or more, an excellent performance can be
obtained. When the film thickness is 5 .mu.m or less, generation of
cracks can be prevented, so that excellent appearance can be
obtained.
EXAMPLES
Kind of the Polysaccharide Thickeners and Viscosity Change
Reference Examples 1 to 6
[0065] Firstly, test was carried out to study the relationship
between kind of thickeners and viscosity change. As the thickeners,
Diutan gum and Welan gum which contain glucuronic acid and rhamnose
in their main chains; xanthan gum which does not contain neither
glucuronic acid nor rhamnose in its main chain but contains
glucuronic acid in its side chain; guar gum which does not contain
neither glucuronic acid nor rhamnose in its main chain and in its
side chain; sodium carboxymethyl cellulose; and hydroxyethyl
cellulose were used. These thickeners each were added to
ion-exchanged water with the ratio shown in Table 1, and the
resulting mixture was stirred well to prepare aqueous solutions 1
to 6 of Reference Examples 1 to 6. The viscosity changes of these
aqueous solutions 1 to 6 were measured.
<Viscosity Change>
[0066] The aqueous solutions 1 to 6 were stored in a constant
temperature bath at 60.degree. C., and 1 week later, viscosities of
the aqueous solutions 1 to 6 (6 rpm at 25.degree. C.) were measured
with a Brookfield viscometer (manufactured by Toki Sangyo Co.,
Ltd., TV-10, spindle M2) to obtain the change rates relative to the
initial viscosities. The measurement conditions of the Brookfield
viscometer were that the rotation speed of a rotor was 6 rpm and
the measurement temperature was 25.degree. C. As to the rotor, a M2
rotor was used. As shown in Table 1, in Reference Examples 1 and 2
in which Diutan gum or Welan gum containing glucuronic acid and
rhamnose in their main chains was used, there were substantially no
viscosity changes after 1 week. On the other hand, in Reference
Example 3 in which xanthan gum containing glucuronic acid in its
side chain was used, the viscosity of the aqueous solution
decreased after 1 week. Also in Reference Examples 4 to 6 in which
thickeners were used which do not contain neither gluconic acid nor
rhamnose in their main chains and side chains, the viscosity of the
aqueous solutions decreased after 1 week. The viscosity change rate
was calculated by dividing the value obtained by subtracting the
initial viscosity from the viscosity after 1 week by the value of
the initial viscosity (unit: %). The evaluation criteria were as
follows: when the viscosity change rate was in the range of +15% to
-10%, the result was judged to be OK, while the rate was outside
the above range, the result was judged to be NG.
[0067] Therefore, in the tests regarding the photocatalytic coating
composition described later, polysaccharide thickeners containing
gluconic acid and/or rhamnose in their main chains were used as the
thickener.
TABLE-US-00001 TABLE 1 Total solid Thickener content Viscosity (6
rpm, 25.degree. C.) mPa s % by concentration 60.degree. C.,
Viscosity OK or Kind mass (% by mass) Initial after 1 week change
rate NG Reference Diutan gum 0.1 0.1 543 541 -0.40% OK Example 1
Reference Welan gum 0.15 0.15 283 265 -6.40% OK Example 2 Reference
Xanthan gum 0.3 0.3 237 50 -78.90% NG Example 3 (10 days) Reference
Guar gum 0.4 0.4 176 105 -40.3% NG Example 4 Reference Sodium 0.2
0.2 214 56 -73.8% NG Example 5 carboxymethyl cellulose Reference
Hydroxyethyl 1 1 223 121 -45.7% NG Example 6 cellulose
Preparation of Photocatalytic Coating Compositions
Examples 1 to 10 and Comparative Examples 1 to 11
[0068] The thickener was added to ion-exchanged water, and then the
resulting mixture was stirred well. An aqueous dispersion of
anatase-type titanium oxide was provided as the photocatalyst
particle. Water dispersion-type colloidal silica and zirconia sol
were provided as the inorganic compounds. Next, the photocatalyst
particle and the inorganic compounds were added so that the weight
ratio of the aqueous dispersion of anatase-type titanium
oxide/water dispersion-type colloidal silica/zirconia
sol=3.5/86.5/10. Next, an alkanol amine, a defoamer, a surfactant
and a colorant were added in this order. In this way, the
photocatalytic coating composition was obtained. Addition amounts
of each component were properly adjusted such that the total solid
content concentration is predetermined value. Here, the total solid
content concentration means total concentration of the
photocatalyst particles, the inorganic compounds, solid component
of the thickener, solid component of the defoamer, solid component
of the surfactant and solid component of the colorant, relative to
the entire photocatalytic coating composition. Kinds of each
component and the addition amounts thereof are shown in Table
2.
[0069] Meanwhile, the alkanol amine ratio means the ratio of the
mass of the primary to tertiary alkanol amines in the
photocatalytic coating composition relative to the mass of total
solid content in the photocatalytic coating composition.
TABLE-US-00002 TABLE 2 Alkanol amine Defoamer alkanol Photocatalyst
Inorganic Silicon Surfactant amine particle particle type Nonionic
Thickener ratio TiO2 SiO2 ZrO2 defoamer surfactant % by % by (% by
(% by (% by (% by (% by (% by Kind mass Kind mass mass) mass) mass)
mass) mass) mass) Example 1 Diutan gum 0.10 Dimethyl ethanol 0.50
9.3% 0.19 4.8 0.55 0.30 0.30 amine Triethanol amine 0.08 Example 2
Welan gum 0.15 Dimethyl ethanol 0.50 9.3% 0.19 4.8 0.55 0.30 0.30
amine Triethanol amine 0.08 Example 3 Diutan gum 0.10 Methyl
diethanol 1.20 20.6% 0.19 4.8 0.55 0.30 0.30 amine Triethanol amine
0.08 Example 4 Diutan gum 0.10 Dimethyl ethanol 0.50 9.3% 0.19 4.8
0.55 0.30 0.30 amine Triethanol amine 0.08 Example 5 Diutan gum
0.10 Dimethyl ethanol 0.10 2.9% 0.19 4.8 0.55 0.30 0.30 amine
Triethanol amine 0.08 Example 6 Diutan gum 0.10 Dimethyl ethanol
0.05 2.5% 0.11 2.6 0.30 0.30 0.30 amine Triethanol amine 0.04
Example 7 Layered 0.80 Dimethyl ethanol 1.00 17.1% 0.19 4.8 0.55
0.30 0.30 silicate amine (synthetic Triethanol amine 0.08
hectorite) Example 8 Diutan gum 0.10 Dimethyl ethanol 0.10 3.8%
0.11 2.6 0.30 0.30 0.30 amine Synthetic 0.040 Triethanol amine 0.04
layered silicate Example 9 Diutan gum 0.10 Dimethyl ethanol 0.10
3.8% 0.11 2.6 0.30 0.30 0.30 amine Synthetic 0.020 Triethanol amine
0.04 layered silicate Example 10 Diutan gum 0.10 Dimethyl ethanol
0.10 3.7% 0.11 2.6 0.30 0.30 0.30 amine Synthetic 0.20 Triethanol
amine 0.04 layered silicate Comparative Diutan gum 0.10 Sodium
hydroxide 1.00 1.3% 0.19 4.8 0.55 0.30 0.30 Example 1 Triethanol
amine 0.08 Comparative Diutan gum 0.10 Ammonia 0.30 1.3% 0.19 4.8
0.55 0.30 0.30 Example 2 Triethanol amine 0.08 Comparative Diutan
gum 0.10 Tetraethyl 0.70 1.3% 0.19 4.8 0.55 0.30 0.30 Example 3
ammonium hydroxide Triethanol amine 0.08 Comparative Diutan gum
0.10 Triethanol amine 0.08 1.3% 0.19 4.8 0.55 0.30 0.30 Example 4
Comparative Welan gum 0.15 Triethanol amine 0.08 1.3% 0.19 4.8 0.55
0.30 0.30 Example 5 Comparative Diutan gum 0.10 Dimethyl ethanol
0.05 2.1% 0.19 4.8 0.55 0.30 0.30 Example 6 amine Triethanol amine
0.08 Comparative Diutan gum 0.10 Dimethyl ethanol 0.01 1.4% 0.11
2.6 0.30 0.30 0.30 Example 7 amine Triethanol amine 0.04
Comparative Layered 0.80 Triethanol amine 0.08 1.3% 0.19 4.8 0.55
0.30 0.30 Example 8 silicate (synthetic hectorite) Comparative
Alkaline 0.60 Triethanol amine 0.08 1.3% 0.19 4.8 0.55 0.30 0.30
Example 9 swelling thickener Comparative Urethane 0.40 Triethanol
amine 0.08 1.3% 0.19 4.8 0.55 0.30 0.30 Example 10 associative
thickener Comparative Diutan gum 0.10 Dimethyl ethanol 0.00 1.3%
0.19 4.8 0.55 0.30 0.30 Example 11 amine Synthetic 0.040 Triethanol
amine 0.08 layered silicate Colorant Methylene Total solid
Viscosity (6 rpm, 25.degree. C.) mPa s blue content 60.degree. C.,
60.degree. C., trihydrate concentration after after 4 Viscosity OK
or (% by mass) (% by mass) pH Initial 1 week weeks change rate NG
Example 1 0.0 6.2 9.7 604 586 549 -9.1% OK Example 2 0.0 6.3 -- 292
323 -- 10.6% OK Example 3 0.0 6.2 9.6 595 598 568 -4.5% OK Example
4 0.010 6.2 -- 596 587 569 -4.5% OK Example 5 0.010 6.2 9.4 595 583
564 -5.2% OK Example 6 0.0050 3.7 -- 586 562 -- -4.1% OK Example 7
0.0 6.3 -- 390 422 403 8.2% OK Example 8 0.010 3.8 9.3 635 639 573
0.6% OK Example 9 0.0050 3.7 9.4 672 650 594 -3.3% OK Example 10
0.0050 3.9 9.4 781 878 840 12.4% OK Comparative 0.0 6.2 -- 590 571
511 -13.4% NG Example 1 Comparative 0.0 6.2 -- 592 544 433 -26.9%
NG Example 2 Comparative 0.0 6.2 -- 598 492 377 -37.0% NG Example 3
Comparative 0.0 6.2 -- 602 316 -- -47.5% NG Example 4 Comparative
0.0 6.3 -- 299 219 -- -26.8% NG Example 5 Comparative 0.0050 6.2 --
592 261 -- -55.9% NG Example 6 Comparative 0.0050 3.7 -- 573 701 --
22.3% NG Example 7 Comparative 0.0 6.3 -- 339 199 207 -41.3% NG
Example 8 Comparative 0.0 6.1 -- 186 gel -- -- NG Example 9
Comparative 0.0 5.9 -- 315 gel -- -- NG Example 10 Comparative
0.0050 6.2 9.1 705 -- 355 -49.6% NG Example 11
Evaluation
<Viscosity Change>
[0070] The photocatalytic coating composition was stored in a
constant temperature bath at 60.degree. C., and 1 week later and 4
weeks later, the photocatalytic coating composition was taken out.
The viscosity of the photocatalytic coating composition before
storage, the viscosity of the photocatalytic coating composition
after storage for 1 week, and the viscosity of the photocatalytic
coating composition after storage for 4 weeks were measured with a
Brookfield viscometer (manufactured by Toki Sangyo Co., Ltd.,
TV-10, spindle M2) to obtain the change rate relative to the
initial viscosity. The measurement conditions of the Brookfield
viscometer were that the rotation speed of a rotor was 6 rpm and
the measurement temperature was 25.degree. C. As to the rotor, a M2
rotor was used. The viscosity change rate was calculated by
dividing the value obtained by subtracting the initial viscosity
from the viscosity after 1 week or the viscosity after 4 weeks
which has a larger difference from the initial viscosity by the
value of the initial viscosity (unit: %). That is, the viscosity
change rate is calculated as a value of plus (+) when the viscosity
after storage is increased relative to the initial viscosity, while
the viscosity change rate is calculated as a value of minus (-)
when the viscosity after storage is deceased relative to the
initial viscosity. The evaluation criteria were as follows: when
the viscosity change rate was in the range of +15% to -10%, the
result was judged to be OK, while the rate was outside the above
range, the result was judged to be NG. The results were as shown in
Table 2.
<Uniformity and Homogeneity of Photocatalyst Coated Film
1>
[0071] An acryl styrene resin emulsion paint (undercoating paint)
was applied on a surface of a fiber-reinforced cement board (JIS
A5430/50 mm.times.50 mm.times.3 mm T) so that the application
amount is 370 g/m.sup.2 with a roller, and then the resulting
product was cured at normal temperature for 1 day. Next, the
photocatalytic coating composition of Example 1 was applied once
with the application amount of 20 g/m.sup.2 at one time with a
roller, and then the resulting product was cured at normal
temperature for 1 day to prepare a photocatalytic body. Part of the
photocatalytic body was cut off and observed with a scanning
electron microscope (manufactured by Hitachi, Ltd., S-800) at an
acceleration voltage of 7 kV and at a magnification of 50 to 5000
times to obtain SEM images of a surface and a cross section of the
photocatalyst coated film. The results were as shown in FIGS. 1 to
6. FIGS. 1 to 3 show secondary electron images of the surface.
FIGS. 4 to 6 show backscattered electron images of the cross
section. FIGS. 2 and 3 are magnified images of part B and part D,
respectively, of FIG. 1. FIGS. 5 and 6 are magnified images of part
i and part ii, respectively, of FIG. 4. It was confirmed that the
homogeneous photocatalyst coated film having uniform surface and
thickness could be obtained due to the photocatalytic coating
composition according to the present invention.
<Uniformity and Homogeneity of Photocatalyst Coated Film
2>
[0072] The photocatalytic coating composition of Example 4 was
applied on an exterior wall of an architectural structure, and
uniformity of the coated film was evaluated. Application surface
was a part of the surface of the exterior wall, the part having
width of 4 m and height of 10 m. An aqueous paint containing an
acryl styrene resin emulsion and a white pigment was applied on the
application surface; and then the resulting product was left
overnight to form an undercoat. The photocatalytic coating
composition of Example 4 was locally sprayed on an about 30% area
of the entire surface of the undercoat with a garden sprayer in an
application amount of 40 g/m.sup.2; and immediately after the
spraying, the photocatalytic coating composition was spread on the
entire application surface with a trowel brush (brushed application
tool). The application was finished when the photocatalytic coating
composition was confirmed to be uniformly spread in a wet state by
sliding the trowel brush up and down, and side to side. Throughout
the application work, the photocatalytic coating solution never
dripped down outside the application surface.
[0073] As a control, 0.01% by mass of methylene blue relative to
the photocatalytic coating composition of Comparative Example 4 was
added to the composition to prepare the photocatalytic coating
composition of Comparative Example 5. The photocatalytic coating
composition of Comparative Example 5 was applied on an exterior
wall of an architectural structure in the same manner as in Example
4. The photocatalytic coating composition of Comparative Example 5
dripped down outside the application surface, and also, when the
trowel brush was slid up and down, and side to side, a uniform
coated film could not be formed.
* * * * *