JPH10195333A - Water-based coating composition capable of forming nitrogen oxide decomposing coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating material which can form a coating film which is not deteriorated by the oxidation action of the constituent powder and is excellent in oxidation resistance, weathering resistance, chemical resistance, long-term use resistance, staining resistance and the property of decomposing nitrogen oxides by dispersing at least one photocatalytically active powder selected among titanium dioxide and zinc oxide powders in a water-soluble silicate coating binder. SOLUTION: The water-soluble silicate coating binder mainly consists of a water-soluble silicate (a) and a curing agent (b). Components (a) is exemplified by a modified water-soluble silicate obtained by reacting an alkali metal silicate (1) and an oxide and/or a hydroxide (2) of a metal selected among aluminum, a group IIA metal and a transition metal with a water-soluble silicate material (A) represented by the formula: M2 O.xSiO2 .yH2 O (wherein M is a group IA alkali metal, N(CH2 OH)4 or the like; and x and y are each a positive number). The curing agent (b) is exemplified by a product among phosphoric acid, a condensed phosphate, a water-soluble silicate material (B) of the formula: M2 O.xSiO2 .y'H2 O (wherein y' is a positive number or 0) with a condensed phosphate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a silicate-based aqueous coating composition containing a powder having photocatalytic activity and capable of forming a nitrogen oxide decomposable coating film.

[0002]

2. Description of the Related Art In recent years,
As a part of the living environment purification, it has been proposed to apply a photocatalytically active paint to guardrails, tunnel inner walls, and the like in order to reduce nitrogen oxides due to exhaust gas around automobile roads.

[0003] Titanium dioxide and zinc oxide having photocatalytic activity are optical semiconductors and have a band gap of about 3 eV, so that they are easily excited by irradiation of sunlight or artificial illumination light to generate holes and OH radicals. It has strong oxidizing properties and has the effect of oxidizing nitrogen oxides and eventually converting them to nitric acid, and of decomposing them into nitrogen and water.

Conventionally, nitrogen oxide decomposable paints such as fluororesins have been proposed because titanium dioxide and zinc oxide having photocatalytic activity show strong oxidizing properties upon irradiation with light.
The binder is easily oxidized, and the resulting coating film has poor weather resistance and is easily decomposed and deteriorated, so that it cannot withstand long-term use and is not practical.

It is an object of the present invention to provide a powder having photocatalytic activity which is not deteriorated by the oxidizing action, has good oxidation resistance, weather resistance and chemical resistance, can withstand long-term use, has stain resistance and nitrogen oxide An object of the present invention is to provide a paint capable of forming a coating film having excellent decomposability.

The present inventors have made intensive studies to achieve the above object, and as a result, have found that the above object can be achieved by using a water-soluble silicate-based binder as a paint binder, and thus complete the present invention. Reached.

[0007]

That is, the present invention is characterized in that at least one kind of powder having photocatalytic activity selected from titanium dioxide and zinc oxide powder is dispersed in a water-soluble silicate paint binder. The present invention provides an aqueous coating composition capable of forming a nitrogen oxide decomposable coating film.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a water-soluble silicate-based paint binder generally comprises a water-soluble silicate (a) and a curing agent (b) as main components.

[0009] Representative examples of water-soluble silicate (a) a water-soluble silicate (a), selected from (1) an alkali metal silicate, (2) aluminum, and transition metals belonging to Group IIA of the periodic table Metal oxides and / or hydroxides of the general formula M ₂ O.xSiO ₂ .yH
₂ O (where M represents an alkali metal belonging to Group IA of the periodic table, N (CH ₂ OH) ₄ , N (C ₂ H ₄ OH) ₄ or C (NH ₂ ) ₂ NH, and x and y represent And a modified water-soluble silicate obtained by heating and reacting with the water-soluble silicate raw material (A) represented by a positive number.

The alkali metal silicate (1) comprises an alkali metal belonging to Group IA of the periodic table and silicic acid, and has the general formula (Alk) ₂ O.xSiO ₂ .yH ₂ O [where (Alk) is It represents an alkali metal belonging to Group IA of the periodic table (Li, K, Na, Cs, etc., and x and y are positive numbers). As alkali metal silicates, sodium silicate, lithium silicate,
Examples thereof include potassium silicate and cesium silicate, which are usually used in the form of an aqueous solution.

The oxides and / or hydroxides of aluminum, metals selected from metals belonging to Group IIA of the Periodic Table and transition metals to be reacted to obtain the modified water-soluble silicate (2) include: Aluminum oxide, aluminum hydroxide; magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxide, strontium oxide,
Oxides and hydroxides of metals belonging to Group IIA of the periodic table such as strontium hydroxide and barium oxide; oxides and hydroxides of transition metals such as zinc oxide, zirconium oxide, zirconium hydroxide and vanadium hydroxide Can be mentioned.

In order to obtain the modified water-soluble silicate (2), a water-soluble compound is reacted with an oxide and / or hydroxide of the above-mentioned aluminum, a metal belonging to Group IIA of the periodic table and a transition metal. The silicate raw material (A) has the general formula M
_{2 O · xSiO 2 · yH 2} O ( where the alkali metal M belongs to Group IA of the periodic _{table, N (CH 2 OH) 4} , N
(C ₂ H ₄ OH) ₄ or C (NH ₂ ) ₂ NH,
x and y are positive numbers). In this general formula, the numerical value of x is preferably about 1 to 5, and the numerical value of y is particularly limited as long as the composition finally obtained has an appropriate viscosity and the coating workability cannot be reduced. There is no.

Examples of the water-soluble silicate raw material (A) include the alkali metal silicate, a quaternary ammonium silicate composed of quaternary ammonium and silicic acid, and a guanidine silicate composed of guanidine and silicic acid. Can be.
The alkali metal silicate, quaternary ammonium silicate and guanidine silicate are usually used in the form of an aqueous solution. Examples of the quaternary ammonium silicate include tetramethanol ammonium silicate and tetraethanol ammonium silicate.

The water-soluble silicate raw material (A) can be made into a water-soluble silicate aqueous solution by dissolving or dispersing in water. The concentration of the water-soluble silicate aqueous solution is about 10-60% by weight
It is possible to adjust the viscosity so that the final composition obtained by adding water so as to have a viscosity within the range is suitable for coating.

The modified water-soluble silicate (2) comprises one or more of a mixture of at least one of the above-mentioned metal oxides and / or hydroxides and one or more of the above-mentioned water-soluble silicate raw materials (A). It is obtained by reacting the above mixture with heating and stirring. The reaction conditions vary depending on the pressure, but at normal pressure, the temperature is about 50 to 100 ° C. for about 3 to 72 hours.

The weight ratio of the solid content of the water-soluble silicate raw material (A) to the oxide and / or hydroxide of the metal is as follows:
In the latter ratio, the range of 100: 0.5 to 100: 50 is
It is desirable from the viewpoints of water resistance, chemical resistance, and film strength of the obtained film.

In the composition of the present invention, the above-mentioned modified water-soluble silicate (2) is preferable as the water-soluble silicate in the binder of the water-soluble silicate paint.

Curing agent (b) As the curing agent in the binder of the water-soluble silicate paint, (1) phosphoric acid, (2) condensed phosphate, and (3) general formula M ₂ O.xSiO ₂ .y'H ₂ O (where M is an alkali metal belonging to Group IA of the periodic table, N (CH ₂ OH)
₄ , N (C ₂ H ₄ OH) ₄ or C (NH ₂ ) ₂ NH, wherein x is a positive number, y ′ is a positive number or 0) and condensed with a water-soluble silicate raw material (B) Reaction products with phosphates and the like can be mentioned.

The above-mentioned condensed phosphate (2) has a general formula
M ′ _i O _j .mP ₂ O ₅ .nH ₂ O (where M ′ represents a metal, i, j, and m are positive numbers and i / j = 2 / metal (M ′) valence, m Is a number of 0.25 or more, and n is 0
Or represents a positive number. ) Is used as a composite oxide containing zinc and / or magnesium and / or calcium, for example, ZnO-Ti
_{O 2, MgO-TiO 2,} CaO-TiO 2, MgO-
Examples thereof include those obtained by neutralizing with a composite oxide represented by Fe ₂ O ₃ or ZnO—Al ₂ O ₃ , and further, if necessary, drying or heating and crushing. During the production of the condensed phosphate (2), in addition to the phosphate and the composite oxide,
If necessary, a siliceous powder such as silica powder or diatomaceous earth may be added and mixed. By adding and mixing the siliceous powder, drying and heat-curing can be performed uniformly and quickly, and the product obtained by drying or heating and firing can be very easily crushed.
The amount of the siliceous powder is preferably 50% by weight or less, more preferably 5 to 40% by weight, based on the condensed phosphate.

Examples of the phosphate neutralized by the above-mentioned composite oxide include, for example, calcium monobasic phosphate, magnesium monobasic phosphate, aluminum monobasic phosphate, copper monobasic phosphate, iron monobasic phosphate, and the like.
Primary phosphates such as primary manganese phosphate and primary zinc phosphate; these primary phosphates are further added with 2Al ₂ O ₃ .3P ₂ O
_{5 · 3H 2 O, 2CaO ·} P 2 O 5 · H 2 O, 2MgO
· Second phosphate salt, such as _{P 2 O 5 · H 2 O} , Al 2 O 3 ·
2P ₂ O ₅ · 3H ₂ sesquicarbonate phosphate or CaH such as O
_A mixture of ₂ P ₂ O _{7 and the} like so that m is 0.25 or more can be given.

When the curing agent (b) is a reaction product (3) of a water-soluble silicate raw material (B) and a condensed phosphate,
The water-soluble silicate raw material (B) has the general formula: M ₂ O · xSiO ₂
· Y'H represented by ₂ O is intended to encompass the water-soluble silicate material (A), as the condensation phosphate can be used those described as the condensation phosphate (2).

The reaction between the water-soluble silicate raw material (B) and the condensed phosphate to obtain the reaction product (3) proceeds simply by mixing the two. Due to the strong reactivity of the two, if they are simply mixed and reacted, a large lump is formed. Therefore, it is desirable to carry out the reaction of this system while pulverizing and mixing using a mixing and dispersing device such as a sand mill or an attritor. This reaction is preferably carried out in the presence of water, such as using an aqueous solution as the water-soluble silicate raw material (B),
By doing so, the reaction product (3) can be obtained in the form of a slurry.

The mixing ratio of the water-soluble silicate raw material (B) and the condensed phosphate in this reaction system is such that the condensed phosphate is 30 parts by weight based on 100 parts by weight of the solid content of the water-soluble silicate raw material (B).
It is preferably in the range of 0 to 2000 parts by weight.

In the composition of the present invention, the curing agent (b) in the binder of the water-soluble silicate paint may be a reaction product (3) of a water-soluble silicate raw material (B) and a condensed phosphate. It is suitable.

In the composition of the present invention, the water-soluble silicate paint binder can be used without any particular limitation as long as it is a water-soluble silicate binder that can be used for paints. It is preferable that the modified water-soluble silicate (2) is used, and the reaction product (3) of the water-soluble silicate raw material (B) and the condensed phosphate is used as the curing agent (b).

In the composition of the present invention, the binder of the water-soluble silicate paint comprises a water-soluble silicate (a) and a curing agent (b).
In the case where the main component is a solid content of the water-soluble silicate (a), the solid content of the curing agent (b) is preferably in the range of 10 to 150 parts by weight based on 100 parts by weight of the solid content. It is.

In the water-soluble silicate paint binder,
When the water-soluble silicate (a) is the modified water-soluble silicate (2) and the curing agent (b) is a reaction product (3) of the water-soluble silicate raw material B and the condensed phosphate, The ratio of the two components is more preferably in the range where the solid content of the reaction product (3) is 60 to 150 parts by weight based on 100 weight parts of the solid content of the modified water-soluble silicate (2).

Powder Having Photocatalytic Activity In the present invention, titanium dioxide used as a powder having photocatalytic activity can be used without any particular limitation as long as it has photocatalytic activity. Type titanium dioxide. Suitable commercial products of anatase type titanium dioxide include, for example, ST-01 and ST manufactured by Ishihara Techno Co., Ltd.
-21 and ST-31.

As the zinc oxide used as the powder having photocatalytic activity, any zinc oxide having photocatalytic activity can be used without any particular limitation. Suitable commercial products are, for example, those manufactured by Sakai Chemical Co., Ltd. Zinc Hua No. 1 special product.

The powder having photocatalytic activity is excited by absorbing ultraviolet light such as sunlight or artificial illumination light, for example, ultraviolet light having a wavelength of 400 nm or less, preferably light having a wavelength of 285 nm to 380 nm. And OH
Generates radicals, which exhibit strong oxidizing performance, oxidize nitrogen oxides by contact with nitrogen oxides in the air to convert them to nitric acid, and decompose nitrogen oxides to produce nitrogen and water Sometimes.

In the composition of the present invention, the amount of the powder having photocatalytic activity is preferably 5 to 65 parts by weight, more preferably 10 to 50 parts by weight, based on 100 parts by weight of the total solid content of the aqueous coating composition of the present invention. More preferably, it is within the range of parts.

The composition of the present invention comprises a water-soluble silicate-based paint binder and a powder having photocatalytic activity as essential components, and if necessary, pigments, fillers, and fluidity modifiers usually used in the paint industry. And the like.

The coating composition of the present invention can be applied to a substrate by spray coating, brush coating, roller coating or the like. The thickness of the coating is not particularly limited, but is preferably in the range of usually 10 to 300 microns, more preferably 20 to 150 microns.
The coating can be cured by baking at 120 to 200 ° C. for about 15 to 60 minutes.

Examples of the object to be coated with the coating composition of the present invention include asbestos cement, concrete, mortar, calcium silicate plate, gypsum board, other inorganic building materials, and metals. The object coated with the coating composition of the present invention contains a high concentration in exhaust gas of automobiles and the like by an oxidizing action of at least one kind of powder having photocatalytic activity selected from titanium dioxide and zinc oxide powder in the coating film. The oxidized nitrogen oxide can be oxidized and decomposed, and the nitrogen oxide concentration can be reduced. Further, the coating composition of the present invention uses an inorganic water-soluble silicate-based coating binder as a binder, and does not deteriorate due to the oxidizing action of the powder having photocatalytic activity, and has water resistance, weather resistance, chemical resistance, and stain resistance. Excellent coating film can be formed.

[0035]

The present invention will be described more specifically with reference to the following examples.

Hereinafter, "parts" and "%" are based on weight, respectively.

Preparation of Modified Water-Soluble Silicate Aqueous Solution Production Example 1 A 30% aqueous solution of potassium silicate (x = 3) was placed in a reaction vessel.
0 parts, 40 parts of a 25% aqueous solution of lithium silicate (x = 4), 2.5 parts of magnesium oxide and 2 parts of aluminum oxide were mixed and reacted at 90 ° C. for 10 hours with stirring.
A modified silicate aqueous solution-1 was obtained.

Production Example 2 In a reaction vessel, 100 parts of a 50% aqueous solution of sodium silicate (x = 2), 1 part of zinc oxide and 10 parts of water were mixed and reacted at 80 ° C. for 72 hours with stirring. A modified silicate aqueous solution-2 was obtained.

Production Example 3 of Condensed Phosphate Preparation Example 3 Phosphate (m is about 1.2) comprising 70 parts of first magnesium phosphate and 30 parts of aluminum sesquiphosphate was added with zinc hydroxide 2
8 parts and 22 parts of aluminum hydroxide were mixed and calcined to obtain a composite oxide. 150 parts of the obtained composite oxide was mixed with 30 parts of silica powder, fired at 160 ° C. for 5 hours, and then pulverized to obtain a condensed phosphate.

Production Example 4 of Hardener Component Production Example 4 50 parts of the condensed phosphate obtained in Production Example 3 and potassium silicate (x =
50 parts of a 30% aqueous solution of 3), 40 parts of “ST-01” (manufactured by Ishihara Techno Co., Ltd., anatase type titanium dioxide having photocatalytic activity, trade name) and 40 parts of water were charged in a pebble mill, and it took 24 hours. The mixture was mixed, reacted, and dispersed to obtain a white slurry-like curing agent component-1 having a fineness of 10 μm or less on a fineness gauge.

Production Example 5 50 parts of the condensed phosphate obtained in Production Example 3 and potassium silicate (x =
3) 50 parts of a 30% aqueous solution, 20 parts of "ST-01" (manufactured by Ishihara Techno Co., Ltd., anatase type titanium dioxide having photocatalytic activity, trade name), "Zinchua No. 1 special product" (Sakai Chemical Co., Ltd.) 20 parts of zinc oxide powder having photocatalytic activity) and 40 parts of water were charged in a pebble mill, and mixed, reacted and dispersed in 24 hours, and the fineness of the fines gauge was 10%.
A white slurry-like curing agent component-2 having a size of not more than μm was obtained.

Production Example 1 of Coating Composition The modified silicate aqueous solution-1 obtained in Production Example 1 and the curing agent component-1 obtained in Production Example 4 were mixed so that the solid content ratio became 1/1. Thus, a white aqueous coating composition was obtained.

Example 2 A white aqueous paint was prepared by mixing the aqueous modified silicate solution-2 obtained in Production Example 2 and the curing agent component-2 obtained in Production Example 5 so that the solid content ratio became 1/1. A composition was obtained.

Comparative Example 1 "Lumiflon LF-942" (manufactured by Asahi Glass Co., Ltd., fluororesin solution, trade name) and "Coronate EH" (manufactured by Nippon Polyurethane Industry Co., Ltd., isocyanurate solution of hexamethylene diisocyanate, trade name) ) And the solid content ratio is the former /
Mixing was performed so that the latter ratio was 70/30 to obtain a resin solution. In this resin solution, the resin solid content of this resin solution is 1
An amount of 50 parts by weight of "ST-01" (manufactured by Ishihara Techno Co., Ltd., trade name of anatase type titanium dioxide having a photocatalytic activity) and 100 parts by weight of cyclohexanone were added to 00 parts by weight, and the pigment was mixed. Is dispersed to a fineness gauge of 10 μm or less, and “Formate TK-1” (organic tin-based curing catalyst manufactured by Takeda Pharmaceutical Co., Ltd.) is added in an amount of 0.1% based on 100 parts by weight of the resin solid content. A white fluororesin-based paint was obtained in addition to 1 part by weight.

Comparative Example 2 In Comparative Example 1, 25 parts by weight of “ST-01” and “Zinchua No. 1 special product” were used instead of 50 parts by weight of “ST-01”.
Comparative Example 1 except that a mixture with 25 parts by weight (Zinc flower having photocatalytic activity, trade name, manufactured by Sakai Chemical Co., Ltd.) was used.
Was carried out in the same manner as described above to obtain a white fluororesin-based coating material having a bump of 10 μm or less.

Comparative Example 3 "Ethylsilicate 40" (manufactured by Nippon Colcoat Co., Ltd.)
A low-condensation product of orthoethyl silicate, an average of about hexamer, trade name) was condensed in the presence of water and a hydrochloric acid catalyst to obtain an ethyl silicate condensate solution. In this ethyl silicate condensate solution, 50 parts of “ST-01” (manufactured by Ishihara Techno Co., Ltd., anatase type titanium dioxide having photocatalytic activity, trade name) was added to 100 parts by weight of the resin solid content of the solution.
The resulting mixture was mixed with 100 parts by weight of isopropanol, and the pigment was dispersed to obtain a white ethyl silicate condensed paint having a fineness of 10 μm or less on a fineness gauge.

Comparative Example 4 "ST-0" was added to 100 parts by weight of resin solid content of "Magiclon No. 1000 Clear" (manufactured by Kansai Paint Co., Ltd., acrylic-melamine resin clear paint, trade name).
1 "(manufactured by Ishihara Techno Co., Ltd., photocatalytically active anatase titanium dioxide, trade name) in an amount of 50 parts by weight,
25 parts by weight of xylene and 25 parts by weight of ethylene glycol monoethyl ether are mixed, and the pigment is dispersed.
A melamine resin-based paint was obtained.

Preparation of Coated Plate Each of the paints obtained in Examples 1 and 2 and Comparative Examples 1 to 4 was coated on an aluminum plate having a surface subjected to chromate conversion treatment and having a thickness of 2 mm, and baked to obtain a coated plate. Obtained. The dry film thickness was 1 for the paints of Examples 1 and 2 and Comparative Examples 1 to 3.
00 μm, and 50 μm for the paint of Comparative Example 4.
The drying conditions were as follows: the paints of Examples 1 and 2 were 200 ° C. for 60 minutes, the paints of Comparative Examples 1 and 2 were 140 ° C. for 30 minutes, the paint of Comparative Example 3 was 180 ° C. for 30 minutes, and the paint of Comparative Example 4 was 1
30 minutes at 50 ° C.

Test of Coated Plate Various tests were performed on the coated plate obtained as described above according to the following test methods. The test results are shown in Table 1 below.

Test Method Accelerated Weathering Resistance: Q using an accelerated weathering tester manufactured by Q Panel Co.
According to UV accelerated weathering test. The test conditions were UV irradiation 1
The test was conducted up to 90 cycles, with 6 hours (60 ° C.) to 8 hours of water condensation (50 ° C.) as one cycle, and the number of cycles in which cracks occurred on the coated surface was investigated and described. If the coating surface does not crack in 90 cycles, it is described as 90 <.

Alkali resistance: The coated plate was immersed in a 5% aqueous sodium hydroxide solution kept at 80 ° C. for 30 minutes, pulled up, and the coated surface was evaluated according to the following criteria.

：: No abnormality was observed on the coated surface. ：: Slight decrease in gloss was observed, but cracking, swelling, peeling, and dissolution of the coating film were not observed. Δ: Swelling was observed on the coated surface. No dissolution of the coating film observed X: Dissolution of the coating film observed.

Acid resistance: 1N-sulfuric acid aqueous solution 0.5c on the coated surface
c was dropped in a spot form, heated at 80 ° C. for 30 minutes, washed with water, and the state of the coated surface was evaluated. No abnormalities are observed on the coated surface (◎), abnormalities such as remarkable gloss and swelling are observed (×).
段 階, △, Δ, × were judged in four stages.

Nitrogen oxide decomposability: The coated plate is 30 mm long,
The coated plate is cut into a size of 50 mm in width and the height of the coated plate is 400 mm.
mm, 400 mm in width and 500 mm in depth. The inside of the reaction vessel is composed of 0.1 ppm of nitrogen oxide (NO) and air as atmospheric gas. After irradiating with a high-pressure mercury lamp from the upper part of the reaction vessel at an irradiation intensity of ² mW / cm ^{2 for} 1 hour, the concentration of nitrogen oxides in the reaction vessel was measured by “Portable NOX Analyzer NOA305” (manufactured by Shimadzu Corporation, nitrogen oxide analyzer, trade name) It measured using. The nitrogen oxide concentration (ppm) is indicated.

Exposure contamination: A painted plate was installed at an angle of 30 ° south on the Tokyo Plant of Kansai Paint Co., Ltd., and an outdoor exposure test was conducted for 6 months. The degree of contamination of the coated plate after the test was evaluated by a difference from an unexposed initial coated plate (lightness difference ΔL ^* in the CIE color system). The coated plate after the test was measured as it was without washing with water, and the coated plate after washing with a sponge was used to wash the surface lightly to remove dirt.

[0056]

[Table 1]

[0057]

The coating composition of the present invention contains a powder having photocatalytic activity capable of oxidizing and decomposing nitrogen oxides. (In tunnels, around places with heavy traffic), it can oxidize and decompose nitrogen oxides contained in high concentrations in vehicle exhaust gas, etc., lowering nitrogen oxide concentrations be able to. Further, the coating composition of the present invention uses an inorganic water-soluble silicate-based coating binder as a binder, does not deteriorate due to the oxidizing action of the powder having photocatalytic activity, and has excellent oxidation resistance, weather resistance, and chemical resistance. It can withstand long-term use and can form a coating film having excellent stain resistance and nitrogen oxide decomposability.

Claims (5)

[Claims] 1. A water-soluble silicate paint binder containing at least one selected from titanium dioxide and zinc oxide powder.
An aqueous coating composition capable of forming a nitrogen oxide decomposable coating film, characterized by dispersing powders having various photocatalytic activities. 2. It comprises (a) a water-soluble silicate, (b) a curing agent, and (c) at least one powder having photocatalytic activity selected from titanium dioxide and zinc oxide powder as main components. The coating composition according to claim 1, wherein 3. The water-soluble silicate (a) comprises aluminum,
An oxide and / or hydroxide of a metal selected from metals and transition metals belonging to Group IIA of the Periodic Table and a general formula M ₂ O
· XSiO ₂ · yH ₂ O (however, M is among groups IA
Alkali metals belonging to the group, N (CH ₂ OH) ₄ , N (C
₂ H ₄ OH) ₄ or C (NH ₂₎ represents ₂ NH, claim x and y are modified water-soluble silicate obtained allowed heating reacting a soluble silicate represented by a positive number) 2
The coating composition according to any one of the preceding claims. 4. The curing agent (b) has a general formula: M ₂ O.xS
iO ₂ · y′H ₂ O (where M is an alkali metal belonging to Group IA of the periodic table, N (CH ₂ OH) ₄ , N (C ₂ H
₄ OH) ₄ or C (NH ₂ ) ₂ NH, wherein x is a positive number, y ′ is a positive number or 0), and is a reaction product of a water-soluble silicate and a condensed phosphate. 4. The coating composition according to 2 or 3. 5. The coating composition according to claim 1, wherein the total solid content is 100 parts by weight.
The coating composition according to any one of claims 1 to 4, comprising 5 to 65 parts by weight of a powder having photocatalytic activity.