JP2003138163A - Photocatalyst coating composition and method for producing the same and photocatalyst using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photocatalyst coating composition comprising silica sol and titania sol, produced by a specified means, causing no corrosion of production equipment, having hydrophilicity just after film formation, having high adhesive strength to a substrate. SOLUTION: This coating composition is obtained by mixing the silica sol adjusted to pH 8-12 with an amine and the titania sol adjusted to pH 8-12 with an amine and then diluting the mixture with solvent such as isopropyl alcohol.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a photocatalyst coating composition and the like for fixing a substance having a photocatalytic activity directly on an arbitrary substrate or indirectly through a primer in a film form.

[0002]

2. Description of the Related Art Titanium oxide is a typical photocatalyst. However, it is difficult to use a powder alone as a photocatalyst, and it is necessary to support and fix it on some kind of substrate. As a binder for fixing this, silica, a sol such as alumina, an inorganic substance such as amorphous titanium oxide,
Highly weather-resistant resins such as fluorine and silicone are used, but recently, the use of the photocatalyst film's high hydrophilicity to prevent the adhesion of dirt has attracted attention, and silica is used to maintain its hydrophilicity. Since the presence of silica sol is essential, the use of silica sol as a binder is the mainstream.

For example, many coating compositions have been proposed in which a silica sol obtained by adding an acid to an alkoxysilane and hydrolyzing it is used as a binder and mixed with a titania sol to further improve the adhesion of the coating film. It has been proposed to add a silane coupling agent or the like to. However, the above acidic coating composition may corrode the equipment used, and the acid remaining in the film after forming a film on the substrate may deteriorate the substrate and the primer.

Although there are examples of silica binders using alkali metal silicates such as sodium silicate and lithium silicate, in the case of photocatalysts, it is said that the alkali metal adheres to the particle surface to reduce the activity. As with the case where the alkali content is an acid, it may corrode the equipment used, which is not preferable.

Another example of using an alkaline silica sol is a photocatalyst composition in which a silica sol obtained by hydrolyzing an alkoxysilane in the presence of a basic catalyst is dispersed in a photocatalyst (JP-A-10-85599). There is. However, in order to store the silica sol in an alkaline state, it is necessary to allow a large amount of water to coexist, and when water is insufficient, gelation proceeds extremely rapidly. Therefore, in alkaline hydrolysis, since the concentration of alkali ions is reduced by being diluted with water, it is uneconomical to add an excess of alkali ions, and the hydrolysis rate is low, and the characteristics of the obtained sol are also low. It is likely to have an adverse effect.

[0006]

SUMMARY OF THE INVENTION In order to improve the photocatalyst coating composition, which has been problematic in the prior art,
It is an object to provide a photocatalyst coating composition containing a specific silica sol and titania sol.

[0007]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors to achieve the above object, a composition for photocatalyst coating containing a silica sol and a titania sol produced by the following specific method was used as an apparatus. The present invention has been completed by discovering that it does not corrode, has hydrophilicity immediately after film formation, has high adhesion strength to a substrate, and does not cause deterioration of the substrate.

That is, the present invention provides a photocatalyst coating composition containing silica sol and titania sol,
The present invention relates to a photocatalyst coating composition, which contains an amine and has a pH of 8 to 12. Such a pH 8-12 alkaline photocatalytic coating composition typically uses an amine to provide a pH of 8-12.
And a titania sol adjusted to pH 8 to 12 with amine or ammonia.

The present invention also relates to a photocatalyst coating composition, wherein the silica sol is obtained by hydrolyzing an alkoxysilane in an acidic region.

The present invention also relates to a photocatalyst coating composition, wherein the titania sol is obtained from peptized metatitanic acid as a raw material.

The method for producing the photocatalyst coating composition of the present invention comprises a silica sol and an amine obtained by hydrolyzing an alkoxysilane in an acidic region in water having a mass ratio of silica sol to SiO ₂ of 50 to 500 times. To produce an alkaline silica sol having a pH of 8 to 12, and adding amine or ammonia to the titania sol to give a pH of 8 to 12
Twelve alkaline titania sols are produced, and the alkaline silica sol and the alkaline titania sol are mixed.

The photocatalyst body of the present invention is characterized in that the photocatalyst coating composition having any one of the above-mentioned constitutions and the photocatalyst coating composition obtained by the above-mentioned production method are coated on the substrate.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Silica sol is typically made of alkoxysilane as a raw material. As the alkoxysilane, those having a methyl group, an ethyl group or a propyl group can be used, but considering the harmfulness of the alcohol produced by hydrolysis and the alkoxysilane itself and the availability, tetraethoxysilane is used. Is particularly preferable.

Hydrolysis of the alkoxysilane is carried out by diluting the alkoxysilane with a solvent such as ethanol or isopropyl alcohol, mixing it with an acid solution, and conducting it in an acidic region of pH 3 or less to obtain a silica sol.

As the acid used for the hydrolysis, any acid can be used as long as the pH is set to 3 or less to allow the hydrolysis to proceed rapidly and the stability of the produced silica sol can be maintained. In the case of forming a film, nitric acid and hydrochloric acid are preferable because organic acids and sulfuric acid remain in the film and there is a risk of degrading the initial hydrophilicity and the primer.

The pH of the silica sol is adjusted to 8 to 12, preferably 9 to 11 by adding silica sol and an amine in water whose mass ratio is 50 to 500 times that of SiO _{2 in} the silica sol to obtain an alkaline silica sol.

When the mass ratio of water to the silica sol is less than 50 times, the silica sol tends to gel, which is not preferable, and when it exceeds 500 times, the amount of amine to be added is unfavorably large.

The amine contributes to the stabilization of the individual silica sols while at the same time neutralizing the acid used for hydrolysis. Addition of ammonia and alkaline substances such as sodium hydroxide and potassium hydroxide is conceivable if the acid used for hydrolysis is neutralized and the pH is adjusted to a region where the alkaline silica sol is stable. .

However, the aqueous ammonia solution is at room temperature,
Under normal pressure, the upper limit is around pH 10, which is easily vaporized. Therefore, it can be used as an additive for neutralizing the acid used for hydrolysis and assisting the dispersion of the titania sol. For silica sol as a substance, there is a possibility that it will be out of the stable pH range. On the other hand, amine has a function of stabilizing the silica sol by adhering to the surface of colloidal particles of silica sol, but this effect cannot be expected with ammonia, and amine cannot be substituted with ammonia.

Further, in the coating composition to which sodium hydroxide or potassium hydroxide is added, sodium ions or potassium ions remain in the photocatalyst film after coating, which coats the photocatalyst surface and lowers the activity. Base material,
Other areas around the coating film may be contaminated or corroded. Especially with sodium or the like, there is a high possibility that the bond of silica constituting the coating film is broken and the coating film strength is lowered. On the other hand, the amine diffuses in the drying step after coating and does not remain in the coating film, so that the harm seen in alkali metal ions does not occur.

The amine that can be used may be any of aliphatic amines having a methyl, ethyl, propyl, butyl or amyl group, as long as it exhibits solubility in water and properties as an alkali. , Butylamine and amylamine are particularly preferred. Further, these may be mixed and used, and may be used in combination with an aromatic amine such as aniline.

The pH adjustment with amine is 8-12, preferably 9-11. If the pH is less than 8, gelation of the silica sol is rapid, and if the pH exceeds 12, it is necessary to add a large amount of excess amine, which is not preferable.

The titania sol typically has an average particle size of 10
A dispersion of titanium oxide having a thickness of -100 nm is used, but in order to obtain high transparency in the coating film, it is preferable to use a metatitanic acid slurry that has been completely peptized with hydrochloric acid or nitric acid. The deflocculated metatitanic acid is neutralized and washed to remove the acid, and is made alkaline by adding amine or ammonia, and is dispersed in a homogenizer before use.

The titania sol has a TiO ₂ concentration of 1 to 50% by mass, preferably 10 to 20% by mass, p
H is 8 to 12, preferably 9 to 11. When the TiO ₂ concentration is less than 1% by mass, sufficient photocatalytic activity is not exhibited when the coating film is formed, and when it exceeds 50% by mass, the viscosity becomes high and it becomes difficult to handle, which is not preferable. Also, the pH
When the value is less than 8, the titania sol aggregates and the viscosity increases,
If it exceeds 12, it is not preferable because a large amount of excess amine needs to be added.

The silica sol and the titania sol are
The mixture is mixed at a mass ratio of TiO ₂ / SiO ₂ of 1/9 to 9/1 and diluted with a solvent such as ethanol or isopropyl alcohol to a solid content of 0.5 to 5 mass%, and then the pH of the composition is 8 to
A photocatalytic coating composition of the present invention which is No. 12 is obtained.

The photocatalyst coating composition of the present invention comprises:
Since it is alkaline, it does not corrode the device, and the photocatalyst coated with this on the substrate has excellent hydrophilicity immediately after film formation, and
Has strong adhesion.

As a method for applying the photocatalyst coating composition of the present invention onto a substrate, known methods can be used. Depending on the type of the substrate, a roll coating method, a flow coating method, a spraying method, a dipping method, A suitable coating method such as a spin coating method can be selected.

The base is aluminum, iron, titanium,
It can be formed from at least one or more of metals such as nickel, chrome and copper and alloys containing one or more of the above metals, glass, ceramics, cement, wood, synthetic resin, resin film, cloth, fiber, paper and the like. .

When the primer treatment is applied to the substrate, resins such as acrylic, urethane and silicone can be used.

[0030]

EXAMPLES Examples and comparative examples of the present invention will be described, but the present invention is not limited to these examples. In the evaluation of the photocatalysts produced in Examples and Comparative Examples, the corrosiveness to the substrate is gloss, the transparency of the coating film is a haze value, the adhesive strength of the coating film is a tape peeling test, and the hydrophilicity of the coating film is water vapor. The presence or absence of dew condensation and the photocatalytic activity were determined by the resolution of acetaldehyde or NOx.

[0031]

Example 1 0.1N while stirring a mixed solution of 30 g of tetraethoxysilane and 60 g of isopropyl alcohol.
10 g of nitric acid aqueous solution was added. The total amount of tetraethoxysilane was hydrolyzed in about 30 minutes to obtain an acidic silica sol having a pH of 2. While stirring 100 g of pure water, 80 g of this acidic silica sol was dropped, and at the same time, amylamine 1.
A 0 mol / L aqueous solution was added dropwise to adjust the pH to 9.9 to 10.1.
Was maintained in the range to obtain an alkaline silica sol. Next, a titania sol obtained by peptizing nitric acid with a primary particle diameter of 15 nm of metatitanic acid (TiO ₂ concentration 10.0 mass%,
pH 2) adjusted to pH 10 with butylamine,
The alkaline silica sol was mixed in a TiO ₂ / SiO ₂ mass ratio of 50/50. This was diluted with isopropyl alcohol to obtain a photocatalyst coating composition having a solid content concentration of 2.5% by mass. A degreased stainless steel plate is immersed in this coating composition and allowed to stand at room temperature for 24 hours.
After leaving it for a while, it was taken out and washed with water, and then 20 # was measured with a gloss meter GM-26 manufactured by Murakami Color Research Lab, and the gloss was measured using a filter. The gloss of the stainless plate is
It was 71% before immersion and the same as 71% after immersion at room temperature for 24 hours, and was not corroded.

[0032]

Example 2 A PET film prepared by adding 10% by mass of a silane coupling agent to an acrylic silicone resin was coated with a bar coater (03) and baked at 120 ° C. for 10 minutes to prepare a primer. The coating agent of Example 1 was diluted with isopropyl alcohol to a solid content concentration of 1% by mass and applied on the primer with a bar coater (03), and baked at 120 ° C. for 1 minute. This film had a haze value of 2% or less and exhibited a strength of 100/100 in a tape peeling test. When the film immediately after baking was covered with an aluminum foil to prevent irradiation of ultraviolet rays and placed on the surface of the boiling water at a position of 5 cm with the coating surface facing downward, no dew condensation was observed. Also, put the coating film 5 cm ² in a glass vial with an internal volume of 120 mL, inject an amount of acetaldehyde gas to a concentration of 10 ppm in the bottle, and irradiate with black light of ultraviolet rays of 0.1 mW / cm ² for 12 hours. I just did
The acetaldehyde concentration in the bottle was 1 ppm or less.

[0033]

[Comparative Example 1] A mixture of 30 g of tetraethoxysilane and 60 g of isopropyl alcohol was added to 40 g of an amylamine 1.0 mol / L aqueous solution while stirring,
H increased up to 12, heat generation was observed and viscosity increased at the same time, and the liquid completely gelled in about 10 minutes.

[0034]

Comparative Example 2 While stirring a mixed solution of 30 g of tetraethoxysilane and 60 g of isopropyl alcohol, 40 g of an amylamine 0.1 mol / L aqueous solution was added. The pH was 9.1. After 24 hours, the mixed liquid was collected with a microsyringe, and a gas chromatograph (G-380 manufactured by Yanaco) was used.
0 detector FID), about 50% of tetraethoxysilane remained unreacted.

[0035]

Comparative Example 3 While stirring a mixed solution of 30 g of tetraethoxysilane and 60 g of isopropyl alcohol, 0.1 N
10 g of nitric acid aqueous solution was added. The total amount of tetraethoxysilane was hydrolyzed in about 30 minutes to obtain an acidic silica sol having a pH of 2. Next, a titania sol obtained by peptizing nitric acid with a primary particle diameter of 15 nm of metatitanic acid (TiO ₂ concentration: 10.
0% by mass, pH 2) and the acidic silica sol are mixed with Ti
_They were mixed so that the mass ratio of O ₂ / SiO ₂ was 50/50. This was diluted with isopropyl alcohol to obtain a coating composition having a solid content concentration of 2.5% by mass. A degreased stainless steel plate was immersed in this coating composition, allowed to stand at room temperature for 24 hours, then taken out and washed with water, and then washed with a Murakami Color Research Lab gloss meter GM-26.
#, Measured gloss with filter. The gloss of the stainless steel plate was significantly reduced to 67% before immersion and 30% after immersion at room temperature for 24 hours, and the stellenless plate also lost its original metallic luster and turned white.

[0036]

Comparative Example 4 A bar coater (03) was prepared by preparing a primer on a PET film in the same manner as in Example 2 and diluting the coating composition of Comparative Example 3 with isopropyl alcohol to a solid content concentration of 1% by mass. Apply at 120 ℃
Baked for 1 minute. The haze value of this film is 2% or less,
The tape peeling test showed a strength of 100/100. When this film was placed 5 cm above the boiling water surface in the same manner as in Example 2, water droplets with a diameter of 2 to 3 mm were attached to the entire surface. In the same manner as in Example 2, the decomposition performance of 10 ppm of acetaldehyde was measured for the test piece of 5 cm ² . UV 0.1mW /
Irradiation at cm ² for 12 hours lowered the acetaldehyde concentration to 3 ppm.

[0037]

Example 3 Commercial cement was mixed with water, put in a mold and dried to prepare a cement plate of 50 mm × 100 mm × 10 mm. Directly to this, 0.2 g of the coating agent of Example 1 was applied by brush and dried at room temperature to prepare a test piece. The NOx purification capacity of the test piece was measured as follows. Two test pieces are placed side by side in a glass Petri dish type reaction vessel having an inner diameter of 156 mm and a depth of 32 mm.
Air connected in series and containing 1 ppm of NO gas at 1.
Flowed 5 L. The NOx concentration at the outlet is measured by the chemiluminescence detection type NOx measuring device ML9841A of Measuring Service Co., Ltd.
It was 1.0 ppm when measured by. From above the reaction vessel, use a black light to generate an ultraviolet ray of 0.6 mW
When the irradiation was performed at a dose of 1 / cm ² , the NOx concentration at the outlet changed to 0.1 ppm after 1 hour. The test piece after 12 hours was
No change in appearance was observed.

[0038]

Comparative Example 5 A test piece was prepared by applying 0.2 g of the acidic coating agent of Comparative Example 3 to the same cement plate as in Example 3. In the same manner as in Example 3, the NOx purification ability by UV irradiation was measured. The NOx concentration at the outlet was 1.0 ppm before ultraviolet irradiation and 0.5 ppm after 1 hour. The test piece after 12 hours had partial white blur.

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Claims (5)

[Claims] 1. A photocatalyst coating composition comprising silica sol and titania sol, wherein the composition contains an amine and has a pH of 8 to 12. 2. The photocatalyst coating composition according to claim 1, wherein the silica sol is obtained by hydrolyzing an alkoxysilane in an acidic region. 3. The photocatalyst coating composition according to claim 1, wherein the titania sol is obtained by using peptized metatitanic acid as a raw material. 4. An alkaline silica sol having a pH of 8 to 12 is produced by adding silica sol obtained by hydrolyzing an alkoxysilane in an acidic region to water having a mass ratio of silica sol to SiO ₂ of 50 to 500 times, and an amine. Then
PH 8 by adding amine or ammonia to titania sol
A method for producing a composition for photocatalyst coating, which comprises producing an alkaline titania sol of Nos. 1 to 12 and mixing the alkaline silica sol and the alkaline titania sol. 5. A photocatalyst in which the photocatalyst coating composition according to any one of claims 1 to 3 or the photocatalyst coating composition obtained by the production method according to claim 4 is applied on a substrate thereof. body.