JPH1135887A - Coating liquid for forming fouling removing film and photocatalyst-supporting substrate produced by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To industrially and advantageously obtain the subject substrate useful for soundproofing walls of roads, telephone booths, etc., by coating the surface of a substrate with a solution containing fine semiconductor particles having photocatalyst actions and polysilazanes and then curing the formed coating film. SOLUTION: This substrate is obtained by mixing an organic solvent such as preferably m-xylene with a dispersing agent in an amount of 5-50 wt.% based on the weight of photocatalytic fine particles (preferably titanium oxide), mixing the resultant mixture with the photocatalytic fine particles, preparing a fine particle dispersion, then mixing the resultant dispersion with a solution of polysilazanes (a polysilazane adduct to a silicon alkoxide, etc.), suitably diluted with m-xylene, etc., and having 100-50,000, preferably 300-5,000 number- average molecular weight, preparing a solution, dipping a prewashed substrate (a metal, ceramics, a plastic, etc.), in the resultant solution or coating the substrate with the solution by brushing, etc., and drying the formed coating film at a temp. of 80-120 deg.C for 10-60 min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating solution for forming a stain removing film and a substrate carrying a photocatalyst, and more particularly, to a stain removing film forming film for forming a film containing a photocatalyst for automatically removing stains. The present invention relates to a coating liquid, a photocatalyst-carrying substrate formed by applying the coating liquid on a substrate, and then curing the coating liquid, and a method for producing the same.

[0002]

2. Description of the Related Art Semiconductor fine particles having a photocatalytic action (hereinafter referred to as "photocatalytic particles"), for example, titanium oxide, iron oxide, tungsten oxide, zinc oxide, zinc sulfide, cadmium sulfide, strontium titanate, molybdenum sulfide and the like are used. sterilization, malodor deodorizing, antifouling, reduction of CO _2, direct decomposition of the NO _X and SO _X, performing the cleaning of contaminated rivers and lakes are already known.

[0003] Examples of such removal of contaminants using a photocatalyst include soundproof walls of roads, guardrails, signs, and the like.
A photocatalyst is adhered to the surface of a traffic light, an outer wall of a building, a telephone box or the like (hereinafter, these structures and the like are referred to as “substrate” in the present specification), and SO in the exhaust gas of diesel engine is
A method of self-cleaning by oxidatively decomposing dirt such as F (organic substance soluble in an organic solvent) or the like.

As a method for attaching these photocatalysts to the surface of a substrate to be stain-proofed, there have been conventionally (1) a method of applying a precursor of the photocatalyst to the surface of the substrate and baking it at about 600 ° C.
(2) a method of supporting the photocatalyst on the substrate surface using an organic binder; (3) when the substrate is plastics, apply the photocatalyst to the heated substrate surface and press with a mold to apply the photocatalyst to the substrate surface or Buried near the surface (Japanese Unexamined Patent Publication No. 9-16)
No. 4091).

However, the method (1) has a drawback that since the treatment is performed at a high temperature, equipment and processing are expensive, and if the substrate is large, the treatment is difficult. Also,
The method (2) has a problem in that the organic binder around the photocatalyst is decomposed due to the photocatalysis, the function as a binder is lost, and the photocatalyst falls off the substrate, so that the life of the photocatalyst is short. Further, the method (3) has a problem that equipment cost is high because a mold is required, and processing is difficult when the substrate is large.

[0006]

Accordingly, there is a need for a method for economically producing a photocatalyst-carrying substrate having a longer life at a lower temperature than conventional methods.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, polysilazane is used as a binder for supporting photocatalyst particles. The present invention has been found to solve all the problems when an organic binder is used, since the ceramics replace ceramics, and completed the present invention.

[0008] That is, an object of the present invention is to provide a coating liquid for forming a stain removal film containing photocatalyst particles and polysilazanes. It is another object of the present invention to provide a photocatalyst-carrying substrate having a cured polysilazane film having photocatalyst particles dispersed on the surface.
Still another object of the present invention is to provide a method for producing a photocatalyst-carrying substrate in which the above-mentioned coating solution is applied to the surface of a substrate and then cured.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The coating liquid for forming a stain-removing film of the present invention (hereinafter referred to as "coating liquid") is produced by mixing photocatalyst particles and polysilazanes according to a known method.

The semiconductor fine particles (photocatalyst particles) having a photocatalytic action used in the present invention include titanium oxide (Ti).
O ₂ ), iron oxide (Fe ₂ O ₃ ), tungsten oxide (W
O ₂ ), zinc oxide (ZnO), zinc sulfide (ZnS), cadmium sulfide (CdS), strontium titanate (S
Known fine particles of a photocatalyst such as rTiO ₂ ) and molybdenum sulfide (MoS ₂ ) can be used. Among these, titanium oxide is preferably used.

On the other hand, polysilazanes are represented by the following general formula:

Embedded image (In the formula, R ¹ , R ² and R ³ are each independently a hydrogen atom; a group in which a group bonding to silicon or nitrogen such as an alkyl group, an alkenyl group, a cycloalkyl group and an aryl group is carbon; an alkylsilyl group An alkylamino group or an alkoxy group, provided that at least one of R ¹ , R ² and R ³ is a hydrogen atom) and has a number average molecular weight of 100 to 50,000. It is a compound derived from polysilazane.

The polysilazane used in the present invention is, for example, a polysilazane-added polysilazane obtained by heating and reacting the above-mentioned polysilazane and silicon alkoxide (JP-A-5-238827), and a heating reaction of the above-mentioned polysilazane and glycidol. The resulting glycidol-added polysilazane (JP-A-6-122852) and the alcohol-added polysilazane obtained by heating and reacting the above-mentioned polysilazane with an alcohol (JP-A-6-240208)
Metal carboxylate / polysilazane obtained by reacting the above polysilazane with a metal carboxylate containing nickel, titanium, platinum, rhodium or the like (Japanese Patent Laid-Open No. 6-2991)
No. 18), the above-mentioned polysilazane and acetylacetonato complex (including Ni, Pt, Pd, Al, Rh and the like as metals)
Acetylacetonate complex-added polysilazane (JP-A-6-306329) and the like obtained by reacting
It means a polysilazane derivative that can be fired at a temperature of not more than ° C. Further, the invention is not limited thereto, and includes other polysilazane derivatives that can be fired at the above-mentioned temperature.

[0013] Among these polysilazanes, those having a number average molecular weight of 300 to 5000 are preferably used.
Further, those having a number average molecular weight of 1,000 to 1,400 are preferably used.

The coating liquid for forming a stain-removing film of the present invention is produced by appropriately mixing the above photocatalyst fine particles and polysilazane. The polysilazane derivative (polysilazane) has a different viscosity depending on the molecular weight and molecular structure. Is a liquid or solid having the general formula
It is preferably handled as a polysilazane solution appropriately diluted with various organic solvents such as -xylene and o-xylene. Needless to say, when the polysilazane is a liquid having a low viscosity, it can be handled as a polysilazane solution as it is.

Further, photocatalyst fine particles can be directly mixed with the above-mentioned polysilazane solution, but in order to disperse the photocatalyst fine particles more evenly in the coating solution, m-xylene, o -It is preferable to prepare a fine particle dispersion by mixing a dispersant with various organic solvents such as xylene, and photocatalytic fine particles, and then mix the polysilazane solution and the fine particle dispersion to form a coating liquid.

The fine particle dispersion is prepared by adding a dispersant and photocatalyst fine particles to an organic solvent and mixing for 0.5 to 10 hours, preferably 1 to 5 hours, to obtain a fine particle dispersion. Furthermore, there is no particular limitation on the dispersant used for preparing the fine particle dispersion, and an organic polymer that is soluble in the organic solvent used, generates and dissipates carbon dioxide and water by the calcination treatment, and does not adversely affect the resulting calcination product. Any compound can be used. Commercially available trade names include, for example, Solsperse # 3000, #
9000 and # 17000, preferably # 90
00 and # 17000 are used. The amount of the dispersant is preferably from 5 to 50% by weight, particularly preferably from 10 to 30% by weight, based on the weight of the fine particles.

The fine particle dispersion thus obtained is mixed with a polysilazane solution appropriately diluted with an organic solvent such as m-xylene or o-xylene to prepare a coating solution.
The amount of the organic solvent for diluting the polysilazane, the mixing ratio of the diluted polysilazane solution and the fine particle dispersion may be appropriately determined depending on the desired film thickness, the amount of the fine particles dispersed in the film, and the dispersion state of the fine particles. . The amount of the fine particles in the fine particle dispersion and the amount of the fine particles in the coating liquid are not particularly limited, and may be determined according to the photocatalytic ability required depending on the application.

Next, a method for manufacturing a photocatalyst-carrying substrate using the above-mentioned coating solution will be described. First, it is preferable to clean the surface of the substrate before applying the coating liquid to the substrate. This cleaning treatment is performed by degreased with a commercially available neutral detergent, and then washed with pure water or the like.
What is necessary is just to dry at 0 degreeC for 20 to 60 minutes. Alternatively, it may be washed with an organic solvent such as alcohol and xylene.

There are no particular restrictions on the material of the substrate, which is the raw material for the production of the photocatalyst-carrying substrate, and metals, glass, ceramics,
What is necessary is just to select a plastics suitably according to a use.
This substrate is a board, a molded body, a structure, and the like, which are mainly used outdoors and in an environment that is easily contaminated. Examples of the board include a soundproof wall of a road, a guardrail, a road sign, a traffic light,
An outer wall of a building, a telephone booth and the like can be mentioned.

Next, a coating solution is applied to the substrate. There is no particular limitation on the method used for the application, and a conventionally used method such as dipping, brush coating, flow coating, or spray coating is applied to the shape and size of the substrate. It can be appropriately selected according to the situation.

The substrate thus applied is further dried and cured. Dry at 80-120 ° C for 10
All you have to do is 60 minutes. Curing treatment conditions can be appropriately selected according to the substrate material used. For example, leave in air at room temperature for 1 to 3 days or in air at 100 to 250 ° C.
Baking for 1 to 3 hours, or 9 in humid air.
You may heat at 0-120 degreeC for 3-5 hours.

In this manner, the polysilazane in the coating solution is cured by oxidation in air, hydrolysis by heating in humid air, and oxidation and hydrolysis in room temperature, and a photocatalyst is deposited on the surface and inside. It becomes a dense coating of dispersed Si-O-based or Si-NO-based ceramics. This coating has excellent corrosion resistance, heat resistance, and abrasion resistance, and has high adhesion to a substrate. Further, since the coating is made of ceramics, it is not decomposed by the photocatalyst and deteriorated. Therefore, it can be used permanently as a photocatalyst.

The photocatalyst-carrying substrate of the present invention thus obtained has excellent corrosion resistance and the like of the coating film itself, and furthermore, the photocatalyst particles dispersed in the coating film can maintain the action as a catalyst for a long period of time. The present invention is advantageously applied to articles to which dirt easily adheres, for example, soundproof walls of roads, guardrails, road signs, traffic lights, outer walls of buildings, telephone boxes, and the like.

[0024]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

EXAMPLE 1 (1) Preparation of Titanium Oxide Dispersion Titanium oxide (Aerosil P-25 manufactured by Nippon Aerosil Co., Ltd.)
5 g, dispersant (Zeneca Mori Solsperse # 17000)
1 g and 50 g of m-xylene were mixed in a ball mill for 3 hours to prepare a titanium oxide dispersion.

(2) Production of Photocatalyst-Supporting Substrate A 20% by weight polysilazane (N-L114 manufactured by Tonen; low-temperature firing type; number average molecular weight: 900) m-xylene solution was prepared, and this solution and the titanium oxide of (1) were prepared. The dispersion liquid was mixed at a weight ratio of 1: 2 to obtain a coating liquid. Then, 1
A 05 × 85 × 3 mm soda lime glass plate was degreased with a commercially available neutral detergent, washed with pure water, and then dried at 80 ° C. for 1 hour. The above coating solution was applied to the glass plate by flowing coating, and then heated at 97 ° C. for 3 hours in humid air to form a film in which titanium oxide was dispersed on the glass plate. The TiO ₂ / SiO ₂ (molar ratio) of the coating was 0.6.

Example 2 Titanium oxide was dispersed on a glass plate in the same manner as in Example 1 (2) except that the weight ratio of the polysilazane solution and the titanium oxide dispersion was 1: 4. A coating was formed. The TiO ₂ / SiO ₂ (molar ratio) of the coating was 1.2.

TEST EXAMPLE 1 Photocatalytic Test: The photocatalytic ability of the coatings obtained in Examples 1 and 2 was evaluated by testing the reduction performance of silver nitrate (AgNO ₃ ). The photocatalyst-carrying substrate of each example was immersed in 30 ml of a 0.4% by weight silver nitrate aqueous solution placed in a petri dish, and the temporal change of the silver nitrate aqueous solution was observed under irradiation with sunlight. As a comparative example, an untreated soda lime glass plate was used. Table 1 shows the results.

[0029]

[Table 1]

The results show that the substrates of Examples 1 and 2 decompose silver nitrate reductively and have photocatalytic activity.

[0031]

The photocatalyst-supporting substrate of the present invention uses ceramics for the binder, so that the binder is not deteriorated by the photocatalyst, the photocatalyst particles can be held for a long period of time, and the photocatalyst-supporting substrate can function as a long-life catalyst. it can. Therefore, the present invention is advantageously applied to a substrate of an article to which dirt easily adheres, for example, a soundproof wall of a road, a guardrail, a road sign, a traffic light, an outer wall of a building, a telephone box, and the like.

Further, according to the method of the present invention, 300 to 25
Since the treatment can be performed at a low temperature of 0 ° C. or less, there is no restriction on the material of the target substrate, a material having low heat resistance such as plastics can be used, and self-cleaning ability can be given to many substrates. that's all

Claims (6)

[Claims] 1. A coating liquid for forming a stain removal film, comprising semiconductor fine particles having a photocatalytic action and polysilazanes. 2. The coating liquid for forming a stain removing film according to claim 1, wherein the semiconductor fine particles having a photocatalytic action are titanium oxide. 3. A photocatalyst-carrying substrate having a cured polysilazane film having a photocatalyst dispersed on its surface. 4. The photocatalyst-carrying substrate according to claim 1, wherein the photocatalyst is titanium oxide. 5. A method for producing a photocatalyst-carrying substrate, comprising applying a solution containing semiconductor fine particles having photocatalytic activity and polysilazanes to the surface of the substrate, and then curing the solution. 6. The method for producing a photocatalyst-carrying substrate according to claim 5, wherein the semiconductor fine particles having a photocatalytic action are titanium oxide.