Photocatalyst coating film and its formation

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a photocatalytic coating formed on a substrate such as a wall surface of a toilet or a kitchen for the purpose of deodorizing, antibacterial action, etc., and a method for forming the photocatalytic coating.

【0002】

[Conventional technology]

Anatase-type TiO2 has been proposed in Japanese Patent Publication No. 2-62499 as a photocatalyst that advances a photocatalytic reaction by being irradiated with ultraviolet rays. In this photocatalyst, the adsorbed water reacts with the holes of the photocatalyst by irradiation with ultraviolet rays, and hydroxyl radicals (OH)^*) Is generated, and this hydroxyl radical reacts with ammonia as follows to deodorize. NH₃+ 2OH^*= 1 / 2N₂+ 2H₂O [0003]

Also, TiO₂As a method for forming a photocatalyst film composed of TiO, a spray method, a dipping method, a spin coating method, or the like is used.₂Known methods include a wet method in which a sol film is formed and then heat-treated (calcined), a dry method by sputtering, CVD, or the like, or a method in which metallic titanium is anodized. As a wet method, there is one disclosed in Japanese Patent Application Laid-Open No. 1-288321, and this method is TiO.₂After spraying the sol on ceramic paper, which is a fibrous material, and heat-treating at 400 to 700 ° C, SnO₂By spraying the sol and heat-treating at 400 to 700 ° C, a photocatalytic film that can enhance the oxidative decomposition of aldehydes is formed.

【0004】

[Problems to be Solved by the Invention]

Among the methods for forming the photocatalyst film described above, the dry method and the anodic oxidation method are difficult to apply to the wall surface of a toilet or kitchen because the member of the other party for forming the photocatalyst film is limited. Further, in the case of the wet method, a photocatalyst film is easily formed on tiles, plate materials, etc., but there is a problem in terms of film strength, such as the film being damaged and falling off when the surface is repeatedly rubbed. In addition, when the sintering temperature is raised to increase the film strength, TiO₂The structure of the above changes to the rutile type, and the photocatalytic activity decreases as it is. Furthermore, in those disclosed in Japanese Patent Application Laid-Open No. 1-288321, TiO₂Less active SnO₂Will cover the entire surface of the coating.

【0005】

Further, when trying to increase the film strength, cracks are likely to occur. That is, as shown in FIG. 5 (a), TiO on the surface of the tile 100.₂When a sol containing the particles 101 is applied and heat-treated (sintered), cracks 102 are generated as shown in FIG. 5 (b). The cause of this is that the phase transition to the rutile type causes volume shrinkage (increased density), and TiO before sintering.₂The spacing between particles 101 is L₀However, it is a rutile type, and after sintering, the distance between particles is L due to volume diffusion to the other party.₁(L₁<L₀), Which is considered to result in cracks.

【0006】

[Means for solving problems]

In order to solve the above problems, the photocatalyst coating according to the present invention uses anatase-type titanium oxide particles as its main constituent material, the intervals between these titanium oxide particles are substantially equal before and after sintering, and the neck portion between the titanium oxide particles is formed. Condensed a substance with a higher vapor pressure than titanium oxide.

【0007】

Further, in the method for forming a photocatalyst film according to the present invention, a titanium oxide sol and a sol of a substance having a higher vapor pressure than titanium oxide are mixed, and this mixed sol is applied onto a substrate such as a tile, and then the rutile type is formed. It was made to be sintered at a temperature equal to or lower than the phase transition temperature.

【0008】

[Action]

The surface with a positive curvature of the titanium oxide particles has a high vapor pressure, and the surface with a negative curvature, that is, the surface of the neck formed by the two titanium oxide particles has a low vapor pressure. As a result, SnO has a higher vapor pressure than titanium oxide on the neck.₂Etc. are condensed, and sintering is performed by this vaporization-condensation mechanism.

【0009】

[Example]

Examples of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a diagram schematically showing a photocatalyst coating film according to the present invention, in which the photocatalyst coating film 1 is formed on a substrate 2 having a smooth surface such as a tile by a wet method.

【0010】

Photocatalyst coating 1 is TiO of 0.1 μm or less₂Particles 3 ... are sintered and composed, and SnO is on the neck.₂4 condenses, thickens the neck and TiO₂The bond between the particles 3 is strengthened, and as a result, the film strength is increased.

【0011】

To form the above photocatalyst film 1, TiO₂SnO in the sol₂The sol is mixed and stirred, applied onto the substrate 2, and heat-treated (sintered) in a predetermined temperature range. In addition, TiO₂The sol concentration should be about 4 to 6 wt%, and NH₃Adjusted to pH 11 with solution, TiO₂The average primary particle size of the particles is 0.01 μm (10 nm), and SnO₂The sol concentration should be about 10 wt% and NH₃Adjusted to pH 11 with solution, SnO₂The average primary particle size of the particles shall be 0.0035 μm. The average primary particle size shown here is the crystallite size (primary particle) obtained from the half width of the XRD (X-ray diffraction) diffraction line.

【0012】

Where SnO₂Is TiO₂Because the vapor pressure is higher than that of TiO before sintering₂The spacing between particles 3 is L as shown in Fig. 2 (a).₀However, the vapor pressure is high on the surface of the titanium oxide particles 3 having a positive curvature, and the vapor pressure is low on the surface having a negative curvature, that is, the surface of the neck portion where the two titanium oxide particles 3 abut. As a result, as shown in Fig. 2 (b), SnO has a higher vapor pressure than titanium oxide at the neck.₂Enters, condenses as shown in Fig. 2 (c), and is sintered by the vaporization-condensation mechanism. Then, when sintering is performed by the vaporization-condensation mechanism, TiO after sintering is performed.₂Particle spacing L₂Is the interval L before sintering₀Since it is almost equal to, cracks and the like do not occur.

【0013】

As mentioned above, TiO before and after sintering₂Photoactivity (R) as a photocatalytic coating without substantially changing the particle spacing₃₀) To be 50% or more, SnO as shown in Fig. 3.₂TiO₂It is necessary to set the ratio (internal ratio) to 20 to 70%. The blending ratio indicates the weight ratio of the solid content contained in each sol. In addition, the photoactivity was evaluated by decomposing methyl mercaptan, and the removal rate (R) 30 minutes after light irradiation.₃₀) Was used as an index. Specifically, a 150-square tile with a photocatalytic coating formed in an 11 L glass container is placed at a distance of 8 cm from the light source (BLB fluorescent lamp 4W), and methyl mercaptan gas is injected into the container so as to be 3 to 5 ppm. After confirming that there was no adsorption in the dark, the fluorescent lamp was turned on and the concentration change was measured over time by gas chromatography. Where R₃₀= (x₀-x₃₀) / x₀× 100% However, x₀= Initial concentration [ppm] x₃₀= Concentration after 30 minutes [ppm] In addition, the film strength was evaluated by performing sliding wear using a plastic eraser, comparing changes in appearance, and evaluating as follows in four stages. : No change for 40 round trips : 10 to 40 times of sliding caused scratches, the film peeled off, and the glaze was visible. : Scratched after sliding 5 to 9 times, the film peeled off, and the glaze was visible. ×: Sliding 4 times or less caused scratches, the film peeled off, and the glaze was visible. [0014]

Further, FIG. 4 is a graph showing the relationship between the heat treatment temperature and the photoactivity, which is TiO.₂When an organic stabilizer is added to the sol, the photoactivity decreases, but in each case, the heat treatment temperature is set to 300 to 850 ° C. This is because activity is unlikely to occur when the heat treatment temperature is less than 300 ° C, and TiO when the heat treatment temperature exceeds 850 ° C.₂This is because the structure of anatase changes from anatase to rutile.

【0015】

[Effect of the invention]

As described above, the photocatalyst film according to the present invention is vaporized by applying a sol containing titanium oxide particles and a substance having a higher vapor pressure than titanium oxide to a tile or the like and sintering it at a predetermined temperature. Since the film is formed by sintering by the condensation mechanism, the intervals between the titanium oxide particles are substantially equal before and after the sintering, and cracks are unlikely to occur. In addition, SnO is on the neck between titanium oxide particles.₂Etc. are condensed, so that the peeling strength of the coating film is increased. Especially SnO₂Etc. (TiO)₂By setting the internal ratio to 20 to 70%, both film strength and photoactivity can be satisfied, and by heat treatment in the range of 300 ° C or more and 850 ° C or less, sufficient photoactivity can be obtained. Can be obtained.

[Simple explanation of drawings]

[Figure 1]

The figure which showed typically the photocatalyst film which concerns on this invention. [Figure 2]

(a) is the TiO of the present application₂A diagram showing the state of particles before sintering, (b) a diagram showing a state during sintering, and (c) a diagram showing a state after sintering. [Fig. 3]

TiO₂And SnO₂Graph showing the relationship between the composition of [Fig. 4]

Graph showing the relationship between heat treatment temperature and photoactivity [Fig. 5]

(a) is the conventional TiO₂The figure which shows the state before sintering of the sol, (b) is the figure which shows the state after rutile type sintering. [Fig. 6]

(a) is the conventional TiO₂The figure which shows the state before sintering of the particle, (b) is the figure which shows the state after sintering. [Explanation of symbols]

1 ... photocatalytic coating, 2 ... substrate, 3 ... TiO₂Particles, 4 ... SnO₂。