Method for producing titanium oxide photocatalyst thin film

The present invention relates to a method for producing a titanium oxide-based photocatalytic thin film. More specifically, the present invention relates to a method for producing a titanium oxide-based photocatalytic thin film having high catalytic activity.

Titanium oxide thin films are coated on the surfaces of various base materials, and by utilizing the strong decomposing power and hydrophilicity of titanium oxide by light, it has been utilized for applications such as cleaning, deodorizing, and antibacterializing the surface of base materials.

However, at present, the coating of titanium oxide thin films is mainly applied to inorganic base materials (ceramics, metals, etc.) such as exterior tiles, glass, exterior wall coatings, and filters inside air purifiers. Applications are also being studied for coating organic materials such as plastic materials on substrates (Patent Documents 1 and 2). A method of forming a titanium oxide thin film on an organic material such as a plastic film has been proposed. Although a titanium oxide-based photocatalytic thin film can be obtained by this method, a sufficiently high catalytic activity cannot be obtained, and improvement in the catalytic activity has been desired.

<patcit num="1"><text>JP 2006-116461</text></patcit><patcit num="2"><text>JP 2006-272757</text></patcit>

<p> The present invention solves the above problems and provides a method for producing a titanium oxide-based photocatalytic thin film having high catalytic activity.</p>

<p> That is, the present invention is a method for producing a titanium oxide-based photocatalytic thin film, which comprises forming a thin film of a titanium oxide-based material containing peroxotitanium on a base material and then plasma-treating the titanium oxide-based thin film surface. I will provide a.</p>

<p> According to the present invention, a titanium oxide-based photocatalytic thin film having improved catalytic activity can be produced.</p>

[Base material] The base material on which the titanium oxide-based thin film is formed is not particularly limited. In particular, examples of the base material that can be expected to be effective in the present invention include organic materials such as plastic films, molded products, and textile products. In addition, metals such as aluminum, stainless steel and iron, and ceramic products such as glass and tile can also be used. Specifically, vinyl chloride resin, polyethylene, polypropylene, polycarbonate, acrylic resin, polyacetal, fluororesin, silicone resin, EVA (ethylene-vinyl acetate copolymer), NBR (acrylonitrile-butadiene rubber), PET (polyethylene terephthalate) , EVOH (ethylene-vinyl alcohol copolymer), polyimide resin, PPS (polyphenylene sulfide), ABS (acrylonitrile-butadiene-styrene) resin, melamine resin and other films, laminates or molded products.

[Formation of titanium oxide thin film] The titanium oxide-based material that can be used for forming a thin film in the present invention is a titanium oxide-based material containing peroxotitanium among the titanium oxide-based materials conventionally known as photocatalysts. In particular, a titanium oxide-based material containing peroxotitanium having an anatase-type crystal structure is preferable. Peroxotitanium is titanium peroxide in which a part of the Ti-O-Ti bond is converted into a Ti-OO-Ti bond as shown in the following structural formula.

<chemistry num="1"><img file="JP2009106905A_D0001.tif" /></chemistry>

Examples of the coating liquid of the titanium oxide-based material containing peroxotitanium include a peroxotitanium aqueous solution, a peroxo-modified anatase sol, a mixture thereof, and a peroxotitanium-based coating agent which is a composite liquid of other materials . Commercially available coating liquids for peroxotitanium-containing titanium oxide-based materials include Sagan Coat (trade name: TPX sol, anatase-type peroxotitanium-containing titanium dioxide aqueous dispersion, peroxotitanium solid content concentration 0.85% by mass, manufactured by Tiosky Corporation). Coat (trade name TAK-A, aqueous dispersion of titanium dioxide containing peroxotitanium, peroxotitanium solid content concentration 0.85% by mass, manufactured by Tiotechno) and the like can be mentioned. These coating liquids may be used alone or in combination of two or more. Peroxotitanium is preferably contained in the titanium oxide-based material in an amount of 0.1% by mass or more, particularly 0.2 to 5% by mass.

Coating of the coating liquid can be carried out by a method already technically established. Specifically, a titanium oxide thin film is used by using a dip coating method, a spin coating method, a spray coating method, a brush coating method, an impregnation method, a roll method, a wire bar method, a die coating method, a gravure printing method, an inkjet method, or the like. To form. Further, a thin film may be formed by using a method such as vacuum vapor deposition, sputtering, or ion plating as a dry coating method.

The thickness of the titanium oxide-based thin film is usually 0.01 to 10 μm, preferably 0.05 to 2 μm. If the titanium oxide thin film layer is too thin, the photocatalytic activity is inferior, and if it is too thick, peeling, cracking, warpage, etc. occur, and a suitable thin film cannot be formed.

[Plasma treatment of titanium oxide thin film] The surface on which the titanium oxide-based thin film is formed on the base material is subjected to plasma treatment to improve the catalytic activity of the titanium oxide-based thin film. As this treatment method, a low-pressure and low-temperature inorganic gas plasma treatment method is particularly desirable.

In the low-pressure low-temperature inorganic gas plasma treatment method, a base material on which a titanium oxide-based thin film is formed is passed through a low-pressure plasma treatment device that can reduce the pressure, and the inside of the device is made into an atmosphere of inorganic gas, and the pressure is 0.001 to 10 Torr, preferably 0.01 to While holding at 1 Torr, apply power with a frequency of 50Hz to 13.6MHz between the electrodes. A low-temperature plasma of inorganic gas is generated by applying 0.1 to 50 kW of electric power and performing glow discharge. A base material on which a titanium oxide-based thin film is formed is placed therein and processed in sequence. When the base material is continuously treated, the surface of the titanium oxide thin film on the base material is plasma-treated while the base material is sequentially moved. As the inorganic gas, rare gases such as helium, neon and argon, oxygen, nitrogen, air, carbon dioxide gas, ammonia and the like can be used. These gases may be one type or a mixture of two or more types. The plasma processing time is usually 0.1 to 1,000 seconds, preferably 1 to 500 seconds.

Hereinafter, the present invention will be specifically described with reference to Examples.

In Examples and Comparative Examples, the titanium oxide-based photocatalyst thin film was evaluated as follows. [Evaluation method of photocatalytic activity] A methylene blue aqueous solution was applied to the sample, and the decrease in the absorbance of the blue dye was measured by the photocatalyst evaluation checker PCC-2 (trade name, manufactured by ULVAC).

[Examples 1 to 5 and Comparative Examples 1 to 2] A 25 μm-thick substrate film made of PET (polyethylene terephthalate) film was cut into 7 cm × 7 cm. The surface of the cut base film was coated with the following titanium oxide-based photocatalyst coating solution using the Depcoater MICRODIP MD0408 (trade name, manufactured by EINTESLA) at a pulling speed of 0.1 mm / sec to 1.0 mm / sec. .. A completely dried titanium oxide-based photocatalytic thin film was obtained by heating each of the air-dried thin films at 80 ° C. for 30 minutes. Next, the titanium oxide-based photocatalyst thin film surface was subjected to plasma treatment under the plasma treatment conditions shown below in Examples 1 to 5. The film thickness of the obtained titanium oxide-based photocatalytic thin film is measured as shown below, and the photocatalytic activity is measured by the above-mentioned photocatalytic activity evaluation method to determine the change in film thickness and the change in photocatalytic activity depending on the presence or absence of plasma treatment. evaluated. The results are shown in Table 1 below.

. Titanium oxide-based photocatalytic coating A commercially available Sagan coat (trade name: TPX sol, anatase-type peroxotitanium-containing titanium dioxide aqueous dispersion, peroxotitanium solid content concentration 0.85% by mass, manufactured by Saba Corporation) was used.

. Plasma treatment of titanium oxide-based photocatalytic thin film Plasma processing was performed using a small batch type plasma processing machine PC-300 (trade name, manufactured by SAMCO). High frequency power supply 13.56MHz / 250W, oxygen or nitrogen gas pressure 12Pa, processing time 60 seconds.

. Measurement of film thickness of titanium oxide-based photocatalyst thin film The film thickness of the photocatalytic thin film was measured using a thin film measuring device FILMETRICS F20 (trade name, manufactured by Matsushita Techno Trading) and a scanning electron microscope S-3400NX (trade name, Hitachi High-Technologies Corporation).

<tables num="1"><img file="JP2009106905A_D0002.tif" /></tables>* 1: Photocatalytic activity is the amount of change in methylene blue absorbance 10 minutes after the start of measurement x 10³。

[Examples 6 to 11 and Comparative Examples 2 to 3] The resin film shown in Table 2 was used as the base material, and in Examples 6 and 7, Tiosky Coat (trade name: TAK-A, an aqueous dispersion of peroxotitanium-containing titanium dioxide, peroxotitanium solid content) was used to form a titanium oxide-based thin film. A titanium oxide-based photocatalytic thin film was produced in the same manner as in Example 1 or Comparative Example 1 except that a concentration of 0.85% by mass (manufactured by Tiotechno) was used, and the photocatalytic activity thereof was measured in the same manner as in Example 1 to obtain a base material. Another photocatalytic activity and changes in photocatalytic activity with and without plasma treatment were evaluated. The results are shown in Table 2 below.

<tables num="2"><img file="JP2009106905A_D0003.tif" /></tables>* 1: In each substrate, PET = polyethylene terephthalate, PP = polypropylene, PVC = polyvinyl chloride, EVA = ethylene-vinyl acetate copolymer. * 2: Photocatalytic activity is the amount of change in methylene blue absorbance 10 minutes after the start of measurement x 10³。

[Example 12 and Comparative Examples 4 to 7] For the formation of titanium oxide-based thin films, in the comparative example, a 1.0% by mass aqueous dispersion of MPT-623 (trade name, manufactured by Ishihara Sangyo) that does not contain peroxotitanium, or a bistrator (trade name, manufactured by Nippon Soda) that does not contain peroxotitanium. ), Other than that, a titanium oxide-based photocatalytic thin film was produced in the same manner as in Example 1 or Comparative Example 1, and the photocatalytic activity thereof was measured in the same manner as in Example 1, and the titanium oxide-based thin film contained peroxotitanium. / The change in photocatalytic activity due to non-content was evaluated. The results are shown in Table 3 below.

<tables num="3"><img file="JP2009106905A_D0004.tif" /></tables>* 1: Photocatalytic activity is the amount of change in methylene blue absorbance 10 minutes after the start of measurement x 10³。

From the results in Tables 1 to 3, it can be seen that the photocatalytic activity is significantly improved when a titanium oxide-based material containing peroxotitanium is used for the formation of the titanium oxide-based thin film and plasma treatment is performed after the formation of the titanium oxide-based thin film. Understand.