JP4475594B2 - Method for forming coating film for titanium oxide photocatalyst - Google Patents

Description

  The present invention relates to a method for forming a coating film for a titanium oxide photocatalyst that is visible light responsive, has high photocatalytic activity, and is effective for decomposition of harmful substances and wet solar cells.

  Titanium oxide powder has long been used as a white pigment, and in recent years, it has been widely used in sintered materials used in electronic materials such as UV shielding materials for cosmetics, photocatalysts, capacitors, thermistors, and barium titanate materials. Has been. In particular, there have been many attempts to use it as a photocatalyst for several years. Titanium oxide is excited by irradiating titanium oxide with light having energy higher than its band gap, and electrons are generated in the conduction band. Holes are generated in the electric band, and development of applications for photocatalytic reactions using the reducing power of electrons or the oxidizing power of holes has been actively conducted. This titanium oxide photocatalyst has a wide variety of uses. Generation of hydrogen by water decomposition, decomposition of organic compounds using redox reaction, exhaust gas treatment, air purification, deodorization, sterilization, antibacterial, water treatment, lighting. Numerous applications have been developed, such as preventing contamination of equipment.

  However, since titanium oxide exhibits a large refractive index in the wavelength region near visible light, light absorption hardly occurs in the visible light region. This is because anatase-type titanium dioxide has a band gap of 3.2 eV and rutile-type titanium dioxide has a band gap of 3.0 eV. The wavelength of light that can be absorbed by titanium oxide is 385 nm or less for anatase-type titanium oxide. The rutile type titanium oxide has a thickness of 415 nm or less. Most of the light of these wavelengths falls in the ultraviolet region, and only a small portion is contained in infinite sunlight on the earth. Conventionally known titanium oxide photocatalysts are photocatalysts under ultraviolet irradiation. Although it exhibits the characteristics, only a part of its energy can be used under sunlight, and sufficient activity as a photocatalyst cannot be expected. Also, considering the use under fluorescent lamps indoors, since the spectrum of fluorescent lamps is almost 400 nm or more, sufficient characteristics as a photocatalyst cannot be expressed. Accordingly, development of highly active photocatalysts that exhibit catalytic activity in the visible light region and have higher utility is being carried out.

  In recent years, a titanium oxide dispersion comprising a sulfur-containing titanium oxide powder, a dispersant, and a solvent has been disclosed as an improvement in the insufficient catalytic activity of a conventional photocatalyst doped with titanium oxide with metal ions (Japanese Patent Laid-Open No. 2006-2006). -1774). According to this titanium oxide dispersion, the photocatalytic activity not only in the ultraviolet region but also in the visible light region is high, so that the photocatalytic action can be sufficiently exerted even in a room such as a fluorescent lamp not exposed to sunlight. .

  When the above titanium oxide dispersion is used as a photocatalyst, it is suspended and dispersed in a dispersion medium such as water or an organic solvent to prepare a coating agent or paint, which is applied to a substrate and dried, and then a titanium oxide coating film for photocatalyst Form. In this case, the dispersibility of the titanium oxide powder in the solvent becomes a problem. Specifically, after the titanium oxide powder is dispersed in the solvent, the titanium oxide powder aggregates and precipitates.

  Conventionally, in order to solve the problem related to the dispersibility of titanium oxide powder, a method of coating a surface of titanium oxide powder with a hydrophobic material having high dispersibility such as silica and alumina has been known. In No. 281726, an aluminum basic salt aqueous solution is adjusted to pH 10.5 to 12.0 with an acid, and a titanium dioxide slurry is mixed therewith, and then this is neutralized with an acid and oxidized to the surface of the titanium dioxide powder. A method for uniformly depositing aluminum hydrate is disclosed. JP-A-2001-220141 and JP-A-2001-262005 disclose a composition for forming a coating film for a titanium oxide dispersion or a titanium oxide photocatalyst obtained by uniformly dispersing a titanium oxide powder in a peroxotitanic acid-containing dispersion medium. Things are disclosed.

  However, these titanium oxide photocatalyst coating film forming compositions have improved dispersibility of the titanium oxide powder with respect to the dispersion medium, but actually, a composition having higher dispersibility is required. Moreover, these titanium oxide photocatalyst coating-film formation compositions also have the problem of causing gelation during storage. Furthermore, the hardness of the titanium oxide coating film formed using these compositions for forming a titanium oxide photocatalyst coating film is low, and the coating film is peeled off when a substrate coated with the titanium oxide coating film is processed. was there.

Further, at least one selected from the group consisting of (a) anatase-type titanium oxide, (b) silica fine particles, a silicone resin film precursor capable of forming a silicone resin film, and a silica film precursor capable of forming a silica film. And (c) a composition containing at least a solvent is disclosed (WO 98/03607). As the component (b) of this composition, a hydrolyzable silane derivative can be used, and it is disclosed that a titanium oxide powder is immobilized on a substrate surface. However, this composition for forming a titanium oxide photocatalyst coating film is dispersible to such an extent that aggregation does not occur after standing for 3 days, and does not satisfy the requirement for high dispersibility. Further, these prior documents do not disclose a composition for forming a photocatalytic coating film using the sulfur-containing titanium oxide powder used in the present invention.
JP 2006-1774 A JP-A-5-281726 JP 2001-220141 A JP 2001-262005 A WO98 / 03607

  Therefore, the purpose of the present invention is that when a coating film forming composition containing a sulfur-containing titanium oxide powder that expresses high light absorption characteristics in the visible light region is applied to a substrate, the titanium oxide powder is highly dispersed, Another object of the present invention is to provide a method for forming a coating film for a titanium oxide photocatalyst that is excellent in hardness and adhesion.

  In such a situation, the present inventors conducted extensive studies, and as a result, mixed a liquid containing an organosilane compound (liquid A) with a liquid containing sulfur-containing titanium oxide powder and peroxotitanic acid (liquid B). If a liquid mixture of the A liquid and the B liquid (hereinafter also referred to as “coating film forming composition”) is applied to a substrate within a predetermined time after mixing and dried to form a coating film, the A Since the dispersibility of the liquid and the liquid B is high, there is no risk of aggregation of the sulfur-containing titanium oxide powder, and the coating film obtained by applying to the substrate after mixing is excellent in the dispersibility of the titanium oxide powder. In addition, the inventors have found that the hardness is high and the adhesiveness is remarkably excellent, and that high catalytic activity is expressed in the visible light region, and the present invention has been completed.

  That is, the present invention mixes a liquid containing an organosilane compound (Liquid A) and a liquid containing sulfur-containing titanium oxide powder and peroxotitanic acid (Liquid B), and within 24 hours after mixing, the A The present invention provides a method for forming a coating film for a titanium oxide photocatalyst, which comprises applying a liquid mixture of the liquid and the liquid B to a substrate and drying to form a coating film.

  According to the method for forming a coating film for a titanium oxide photocatalyst of the present invention, the coated coating film for a photocatalyst has a titanium oxide powder uniformly dispersed, is excellent in hardness, does not easily peel off, and further in the visible light region. Expresses high light absorption characteristics.

In the liquid (solution A) containing the organosilane compound used in the method for forming a coating film for a titanium oxide photocatalyst of the present invention (hereinafter also simply referred to as “coating film forming method”), the organosilane compound is a coating film to be obtained. Used to increase the hardness. Examples of the organosilane compound include organosilane or an organosilane hydrolyzate. As the organosilane, alkylalkoxysilane, alkoxysilane, oligomers or polymers thereof are used. The organosilane compound is, for example, the general formula (1);
R ¹ _x Si (OR ² ) _4-x (1)
(In the formula, R ¹ represents a halogen atom, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group, a phenyl group, a vinyl group, an allyl group, in any of the aralkyl group may be the same or different, R ² Represents an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group, a phenyl group, a vinyl group, an allyl group, and an aralkyl group, which may be the same or different, and x is an integer of 0 ≦ x ≦ 3. General formula (2);

(Wherein R ³ and R ⁴ are an alkyl group having 1 to 6 carbon atoms, an alkoxy group, a hydroxyl group, or a halogen atom selected from a chlorine atom, a bromine atom and a fluorine atom, and R ³ and R ⁴ are the same or different. R ⁵ and R ⁶ are alkyl groups having 1 to 6 carbon atoms, R ⁵ and R ⁶ are the same or different, and m is a repeating number and is 2 to 20. A silane compound is mentioned.

  Specific examples of the organosilane compound include tetraalkoxysilane, tetraacetyloxysilane, tetraphenoxysilane, vinyltriethoxysilane, and chlorotriethoxysilane. As tetraalkoxysilane, tetraethoxysilane, tetramethoxysilane, trimethoxyethoxysilane and the like are preferable, and tetraethoxysilane is particularly preferable.

  As the hydrolyzate of organosilane, for example, a product obtained by adding and stirring organosilane in an aqueous solvent adjusted to pH 1 to 4 can be used, and among these, a hydrolyzate of tetraethoxysilane is suitable. is there.

  Liquid A is obtained by dissolving or suspending the organosilane compound in a solvent. This solvent is not particularly limited, and examples thereof include water and organic solvents. Examples of the organic solvent include alcohols such as methanol, ethanol, isopropanol, and ketones, and among these, water is preferable. A solvent can be used 1 type or in mixture of 2 or more types.

  The method for preparing the liquid A is not particularly limited. For example, tetraethoxysilane is added to pure water prepared with an acid to have a pH of 1 to 4, preferably 2 to 4, and the mixture is stirred and hydrolyzed with a stirrer overnight. The method of obtaining tetraethoxysilane hydrolyzate aqueous solution is mentioned. Examples of the acid include mineral acids and organic acids. Examples of mineral acids include hydrochloric acid, sulfuric acid, and nitric acid, and examples of organic acids include acetic acid, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, and the like. Of these, nitric acid or phosphoric acid is preferred because it does not affect the photocatalytic activity obtained.

  By further mixing one or more aggregation inhibitors selected from sodium phosphate, potassium phosphate and sodium hexametaphosphate into the tetraethoxysilane hydrolyzate aqueous solution (liquid A), a coating film forming composition is formed. This is preferable in that it can improve the dispersibility of the titanium oxide powder and prevent gelation. The blending amount of these anti-aggregation agents in the liquid A is not particularly limited, but is appropriately determined in the range of about 0.05 to 10% by weight.

  Furthermore, in the preparation of the liquid A, when the coating film forming composition (mixed liquid) is applied to a hydrophobic substrate, a sulfonic acid type compound can be added to improve the adhesion to the substrate. . Examples of the sulfonic acid type compounds include dialkyl sulfosuccinate, alkane sulfonate, alpha olefin sulfonate, alkyl benzene sulfonate, naphthalene sulfonate-formaldehyde condensate, and alkyl naphthalene sulfonate. The addition amount is 0.04 to 0.4% by mass, preferably 0.04 to 0.2% by mass in the composition for forming a coating film. When the amount is small, it is difficult to obtain an effect of improving wettability. On the other hand, when the amount is large, the photocatalytic performance tends to be adversely affected. Moreover, when a sulfonic acid type compound is mix | blended with B liquid, it will become difficult to disperse | distribute sulfur containing titanium oxide powder in B liquid.

  In this invention, it does not restrict | limit especially as a sulfur containing titanium oxide powder used with B liquid, It is a thing as described in Unexamined-Japanese-Patent No. 2006-1774, The thing containing a sulfur atom in titanium oxide, Furthermore, sulfur The thing by which the atom substituted the titanium atom in a titanium oxide, and was doped in the titanium oxide as a cation is mentioned. As a method for obtaining such a sulfur-containing titanium oxide powder, rutile or anatase type titanium oxide obtained by reacting titanium tetrachloride with oxygen or, if necessary, a combustible gas such as hydrogen gas or water vapor in a gas phase. Oxide and sulfur or sulfur-containing compound mixed and baked, titanyl sulfate, titanium sulfate and ammonium ammonium sulfate baked method, titanium oxide obtained by hydrolyzing titanium-containing aqueous solution such as titanyl sulfate, titanium sulfate and titanium ammonium sulfate A method of mixing and baking sulfur and a sulfur-containing compound, a method of mixing and baking titanium oxide obtained by hydrolyzing an organic titanium compound such as titanium alkoxide and a sulfur or sulfur-containing compound, and a solution or alkali of a titanium chloride aqueous solution In this stage, sulfur or By mixing sulfur compounds, and then and a method of firing a solid containing sulfur or sulfur-containing compounds. Of these, when obtaining a solid by hydrolyzing or neutralizing an aqueous solution of titanium chloride with alkali, sulfur or a sulfur-containing compound is mixed in any of these stages, and then the solid containing sulfur or the sulfur-containing compound is calcined. The sulfur-containing titanium oxide powder obtained by the method (hereinafter, also simply referred to as “method using a titanium chloride aqueous solution”) is preferable in that when it is used as a photocatalyst, photocatalytic activity is exhibited in the visible light region. Hereinafter, the method using the titanium chloride aqueous solution will be described in detail.

  The titanium chloride aqueous solution is a titanium trichloride aqueous solution or a titanium tetrachloride aqueous solution. The aqueous titanium trichloride solution can be obtained, for example, by dissolving titanium metal in hydrochloric acid. As the metal titanium, titanium powder, sponge-like titanium, or titanium scrap such as chips are used. The titanium tetrachloride aqueous solution can be obtained by dissolving titanium tetrachloride in water or hydrochloric acid. The titanium concentration in the aqueous titanium chloride solution is arbitrary, but considering the production efficiency and the particle size of the resulting titanium oxide powder, the titanium content is 1 to 20% by mass, preferably 1 to 10% by mass, particularly preferably 2 ˜5 mass%. In addition, it is desirable that the aqueous solution of titanium chloride has few impurity components and high purity. Specifically, aluminum, iron, and vanadium are each 1 ppm or less, and silicon and tin are each 10 ppm or less.

  The titanium chloride aqueous solution is hydrolyzed or neutralized with an alkali to obtain a solid, which is a rutile or anatase titanium oxide, orthotitanic acid, metatitanic acid, titanium hydroxide or titanium oxide water. Japanese and powdery or colloidal. Moreover, this solid substance is the same crystal | crystallization and form also when it contains sulfur or a sulfur compound. Specific examples of the method for obtaining such a solid material include the following methods.

(1) A method in which an aqueous titanium chloride solution is heated under reflux and hydrolyzed to precipitate a solid. Chlorine gas is generated at this time, but more fine titanium oxide powder can be obtained by suppressing the generation of hydrochloric acid gas by pressurizing or refluxing and hydrolyzing in a low pH region.
(2) A method in which an alkali such as ammonia is added to an aqueous titanium chloride solution to precipitate a solid. At this time, it is desirable to neutralize with ammonia or aqueous ammonia containing no metal component among these alkalis.
(3) A method in which a titanium chloride aqueous solution is added to an alkaline solution such as aqueous ammonia to precipitate a solid.

  After obtaining by hydrolyzing or neutralizing the aqueous titanium chloride solution as described above, orthotitanic acid or metatitanic acid is produced, but in order to improve the photocatalytic activity, titanium chloride is produced under conditions such that metatitanic acid is produced. It is desirable to hydrolyze or neutralize the aqueous solution. Thereafter, washing is performed to remove impurities such as hydrochloric acid and alkali components, and separation and drying are performed as necessary to form powder. Further, drying is performed as necessary to remove water such as crystal water. The solids are separated by filtration, decantation, centrifugation, or the like using a filter or filter press, and drying is preferably a method that can prevent aggregation of solid particles, and a spray dryer or a commercial dryer is used. Moreover, the obtained solid may be mixed with sulfur or a sulfur-containing compound in a suspended state without being dried, or may be subjected to a firing step.

Titanium oxide powder obtained by neutralizing an aqueous titanium chloride solution with a hydroxide of an alkali metal such as NaOH, KOH, Ca (OH) ₂ (slaked lime), or a metal such as an alkaline earth metal in the method of (2) above Even if these metal components remain, the properties of the photocatalyst finally obtained are not significantly affected. For example, a slaked lime solution is added to a titanium chloride aqueous solution and neutralized to precipitate titanium oxide hydrate, and a flocculant such as polyaluminum chloride is added to the suspension to precipitate and separate solids. Such a method is a process generally used for wastewater treatment such as acidic water, and it becomes possible to produce titanium oxide powder very efficiently on an industrial scale.

  In addition, by hydrolyzing an aqueous titanium chloride solution in the presence of ammonium sulfate to obtain a solid, it is possible to improve performance such as the activity of the finally obtained titanium oxide photocatalyst. Furthermore, the performance of the titanium oxide photocatalyst finally obtained can be improved also by hydrolyzing an aqueous titanium chloride solution in the presence of ammonium sulfate and then neutralizing with ammonia to obtain a solid.

  Furthermore, the crystal form of the titanium oxide of the finally obtained sulfur-containing titanium oxide powder can be controlled at the time of obtaining a solid by neutralizing or hydrolyzing the aqueous titanium chloride solution. The crystal form of titanium oxide is a rutile type, anatase type, or a mixed crystal thereof, and the crystal type (rutile ratio) of titanium oxide is controlled according to the use of the photocatalyst. The rutile ratio of the obtained titanium oxide powder can be controlled by the time or speed of hydrolysis or neutralization with the alkali of the above titanium chloride aqueous solution. For example, when neutralizing a titanium tetrachloride aqueous solution with ammonia water, etc., neutralization in a short time yields titanium oxide with a low anatase-rich rutile ratio, and slowing the neutralization reaction results in an oxidation with a high rutile ratio. Titanium can be obtained. The neutralization rate is preferably 50 to 500 g, more preferably 100 to 300 g, per minute in terms of titanium atoms. When it is slower than the rate of neutralizing 200 g of titanium atoms per minute, the rutile ratio becomes 50% or more. Also, the rutile rate of titanium oxide obtained can be controlled by the pH of the reaction system when the aqueous titanium chloride solution is neutralized or hydrolyzed. For example, when titanium oxide powder is precipitated, ripening reaction is performed in a low pH atmosphere. The rate is improved, and a rutile type and anatase type mixed crystal can be obtained.

The solid material obtained as described above can control the average particle size, specific surface area and crystal form depending on the conditions of hydrolysis or neutralization with alkali. A larger surface area is preferred. Specifically ^{50 m} 2 / g or more in BET specific surface area is preferably 100 m ² / g or more, particularly preferably 150 to 300 m ² / g. The crystal form is preferably a rutile type, anatase type, or a mixed crystal of rutile type and anatase type, and a fine titanium oxide having a specific surface area of 50 m ² / g or more.

  Any step of mixing sulfur or a sulfur-containing compound may be any of a step before preparing a solid, a step of precipitating a solid, or a step after precipitating a solid, Mixing with the titanium chloride aqueous solution as a raw material or mixing with a precipitated solid is desirable.

  The sulfur-containing compound used in the method using the titanium chloride aqueous solution is preferably a liquid or solid compound at room temperature, and examples thereof include a sulfur-containing inorganic compound, a sulfur-containing organic compound, and a metal sulfide. Specific examples include thioethers, thioureas, thioamides, thioalcohols, thioaldehydes, thiazyl, mercaptals, thiols, and thiocyanates. Specific compounds include thiourea and dimethylthiourea. , Sulfoacetic acid, thiophenol, thiophene, benzothiophene, dibenzothiophene, thiobenzophenone, bithiophene, phenothiazine, sulfolane, thiazine, thiazole, thiadiazole, thiazoline, thiazolidine, thianthrene, thiane, thioacetanilide, thioacetamide, thiobenzamide, thioanisole, Thionine, methylthiol, thioether, thiocyan, sulfuric acid, sulfonic acids, sulfonium salts, sulfonamides, sulfinic acids, sulfoxides, sulfines, sulfines Such as § emission class, and the like. These compounds can be used alone or in combination of two or more.

  Of these, sulfur-containing organic compounds are preferred, and organic compounds containing no sulfur and nitrogen atoms are particularly preferred. Specifically, thiourea and dimethylthiourea are preferred.

In the method using an aqueous titanium chloride solution, specific examples of the method for forming a mixture of solid and sulfur or a sulfur-containing compound include the following methods.
(1) A method in which sulfur or a sulfur-containing compound is mixed with an aqueous titanium chloride solution and then hydrolyzed or neutralized with an alkali to obtain a mixture of a solid and sulfur or a sulfur-containing compound,
(2) A method of obtaining a mixture by hydrolyzing or neutralizing an aqueous solution of titanium chloride with an alkali and then mixing the solid with sulfur or a sulfur-containing compound,
(3) A method in which a titanium chloride aqueous solution is hydrolyzed or neutralized with an alkali to obtain a solid, the obtained solid is calcined, and then the solid and sulfur or a sulfur-containing compound are mixed to obtain a mixture;
(4) After mixing sulfur or a sulfur-containing compound with an aqueous titanium chloride solution and then neutralizing with hydrolysis or alkali to form a solid, further mixing sulfur or a sulfur-containing compound with the solid to obtain a solid Examples thereof include a method for obtaining a mixture of sulfur or a sulfur-containing compound.

  The amount of sulfur or sulfur-containing compound to be mixed with the solid used in the method using the aqueous titanium chloride solution is usually 1% by mass or more, preferably 5% by mass or more, based on the solid when converted to the mass of sulfur atoms. More preferably, it is 10-30 mass%. If the amount of sulfur or sulfur-containing compound mixed is small, the amount of sulfur atoms contained in the photocatalytic titanium oxide will eventually decrease, and sufficient visible light absorption will not occur.

  Sulfur or a sulfur-containing compound may be mixed as it is in a solid or liquid form, but may be dissolved or suspended in a solvent such as pure water or alcohol. In this case, the sulfur or sulfur-containing compound may be mixed. As a result, it is possible to obtain a sulfur-containing titanium oxide powder having a good performance in which it is uniformly dispersed in a solid substance and sulfur atoms are uniformly doped in titanium oxide.

  Next, a mixture of the solid material obtained above and sulfur or a sulfur-containing compound is calcined to form a titanium oxide photocatalyst. The calcining temperature is 200 to 800 ° C., preferably 300 to 600 ° C., more preferably 400 to 500 ° C. It is. When a sulfur-containing organic compound is used, the reaction is performed at a temperature at which the compound is decomposed and sulfur atoms are liberated to replace titanium atoms in the solid. The firing atmosphere is performed in an oxidizing atmosphere such as air or oxygen, a reducing atmosphere such as hydrogen gas or ammonia gas, an inert atmosphere such as nitrogen gas or argon gas, or under vacuum. Although only a reducing gas such as hydrogen gas may be used, firing in an atmosphere of a mixed gas of hydrogen and oxygen or a mixed gas of hydrogen, oxygen and inert gas is also effective. Furthermore, it is important to maintain the firing atmosphere so that the partial pressure of the sulfur component is maintained to some extent so that sulfur does not evaporate during the firing or the sulfur-containing compound decomposes and the sulfur component is not discharged from the firing furnace. When a by-product gas such as carbon dioxide gas is generated by decomposition during firing, such as a sulfur-containing organic compound having a carbon atom, it is better to exhaust from the firing atmosphere to some extent. Therefore, the container for firing is not completely open or sealed, and the upper part is opened so that a certain amount of pressure is applied and the by-product gas can be discharged, and a non-fixed lid is placed on the upper part. A cylindrical, dished or rectangular container provided is preferred.

  The sulfur-containing titanium oxide powder obtained as described above is washed as necessary to remove free sulfur components and others. Moreover, in order to improve the dispersibility of particle | grains, it can also surface-treat with surfactant etc.

The sulfur-containing titanium oxide powder obtained as described above is a pale yellow or yellow powder containing sulfur atoms in the titanium oxide, and the sulfur atoms are substituted with titanium atoms in the titanium oxide. And those doped in titanium oxide as cations. Specifically, it can be represented by the chemical formula Ti _1-x S _x O ₂ , and x, which is the content of sulfur atoms with respect to titanium atoms, is 0.0001 or more, preferably 0.0005 or more, more preferably 0.001. ~ 0.008. The sulfur atoms include not only those contained in titanium oxide as cations, but also those adsorbed on the surface of titanium oxide particles as sulfur oxides or sulfur molecules, and those contained in the crystal grain boundaries of titanium oxide. The sulfur component finally contained in the titanium oxide photocatalyst is 0.01 mass% or more, preferably 0.01 to 3 mass%, particularly preferably 0.03 to 1 mass% as sulfur atoms. Further, the average particle diameter is 5 to 150 nm, preferably 5 to 100 nm, particularly preferably 10 to 80 nm, and the BET specific surface area is 30 to 250 m ² / g, preferably 50 to 50 nm as a primary particle diameter by SEM photograph image observation. 250 m ² / g, particularly preferably 100 to 200 m ² / g.

  Further, the sulfur-containing titanium oxide powder is excellent in visible light absorption characteristics, and an ultraviolet-visible diffuse reflection spectrum is measured, and an integrated value of absorbance at a wavelength of 300 to 350 nm is set to 1, usually, a wavelength of 350 to 400 nm. The integrated value of the absorbance at 0.3 to 0.9 and the integrated value of the absorbance at the wavelength of 400 to 500 nm is 0.3 to 0.9, and preferably the integrated value of the absorbance at the wavelength of 350 to 400 nm is 0. The integrated value of absorbance at a wavelength of 400 to 500 nm is 0.4 to 0.8, and more preferably, the integrated value of absorbance at a wavelength of 350 to 400 nm is 0.5 to 0.00. 7 and the integrated value of the absorbance at a wavelength of 400 to 500 nm is 0.5 to 0.75.

  In the sulfur-containing titanium oxide powder, the titanium oxide is a rutile type, anatase type, or a mixed crystal of a rutile type and an anatase type, and contains a sulfur atom, preferably a mixed crystal of a rutile type and an anatase type. The rutile ratio of titanium oxide is 5 to 99%, preferably 20 to 80%, more preferably 30 to 70%. The sulfur-containing titanium oxide powder is a mixed crystal of rutile type and anatase type, but may also contain amorphous titanium oxide.

The measurement method of the rutile ratio is the peak area (Ir) of the strongest interference line (surface index 110) of the rutile crystalline titanium oxide in the X-ray diffraction pattern according to ASTM D 3720-84, and the strongest interference line of the titanium oxide powder ( The peak area (Ia) of the plane index 101) can be obtained and obtained from the following formula.
Rutile conversion rate (mass%) = 100-100 / (1 + 1.2 × Ir / Ia)
In the formula, the peak area (Ir) and the peak area (Ia) refer to the area of the portion protruding from the base line in the corresponding diffraction line of the X-ray diffraction spectrum, and the calculation method may be performed by a known method. It can be obtained by methods such as computer calculation and approximate triangulation.

The peroxotitanic acid used in the liquid B of the coating film forming method of the present invention is used to suppress aggregation of the sulfur-containing titanium oxide powder and improve dispersibility. Peroxotitanic acid is also called peroxytitanic acid or titanium peroxide, and its structure is represented by H ₄ TiO ₅ , Ti (OOH) (OH) ₃ or TiO ₃ .2H ₂ O. Peroxotitanic acid is usually handled as a yellow, yellow-brown or red-brown transparent viscous aqueous solution (sol solution), and in the case of an aqueous solution, its pH is 5 to 8 and is almost in the neutral region. A commercially available peroxotitanic acid can be used, and examples thereof include “PTA-85” and “PTA-170” (both are peroxotitanic acid aqueous solutions manufactured by Sakai Corporation). It can also be prepared by a known method. For example, an aqueous solution of titanium tetrachloride is hydrolyzed with ammonia water to produce a slurry containing titanium hydroxide, which is washed and then added with hydrogen peroxide. A peroxytitanic acid aqueous solution can be obtained. Although it does not restrict | limit especially as a solvent of a peroxotitanic acid solution, For example, water and alcohols, such as ethanol and methanol, are mentioned, Among these, water is preferable. When using a peroxotitanic acid aqueous solution, a commercially available peroxotitanic acid aqueous solution can be used as it is. The concentration of the peroxotitanic acid solution used is appropriately determined depending on the addition concentration of the sulfur-containing titanium oxide powder, the use of the titanium oxide photocatalyst coating solution, and the like. Peroxotitanic acid is not limited to a simple substance, but includes a complex with a salt or chelating agent thereof. Examples of peroxotitanate include ammonium peroxotitanate, sodium peroxotitanate, potassium peroxotitanate, magnesium peroxotitanate, and calcium peroxotitanate. Examples of the complex with the chelating agent include a complex of the above-mentioned salt of peroxotitanic acid with a chelating agent such as tartaric acid and citric acid, and specifically, titanium peroxocitrate ammonium and the like.

  In the liquid B, the solvent for suspending or dissolving the sulfur-containing titanium oxide and peroxotitanic acid is not particularly limited, and examples thereof include water and organic solvents. Examples of the organic solvent include alcohols and ketones such as methanol, ethanol and isopropanol, and among these, water is preferable. A solvent can be used 1 type or in mixture of 2 or more types.

  Preparation of the B liquid includes, for example, a method in which the above-mentioned sulfur-containing titanium oxide is dispersed in a solvent, and a peroxotitanic acid aqueous solution is mixed with this in a predetermined ratio. As a dispersion method, it can be dispersed using a known means such as high-speed stirring, shaking, a bead mill such as a homogenizer, a Henschel mixer, and a super mixer. Further, the dispersion can be wet pulverized by a ball mill, a jet mill or the like.

  In preparing the liquid B, when dispersing the sulfur-containing titanium oxide powder in the solvent, a dispersing agent other than peroxytitanic acid can be used as appropriate. As the dispersing agent, one or two of polycarboxylate, polymer polycarboxylate, polyoxyethylene mono- or dialkyl ether, polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether It is preferable to use more than one species. Specific examples include sodium polyacrylate, ammonium polyacrylate, polymeric polyacrylate amine salt, polyoxyethylene distyrenated phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene polyoxypropylene alkyl ether, and the like. In particular, ammonium polyacrylate (“Poise 532A”; manufactured by Kao Corporation) and high molecular weight polyacrylate amine salt (“HIPLAAD ED214”; manufactured by Enomoto Kasei Co., Ltd.) are preferable. By combining the peroxotitanic acid and the dispersing material, the dispersibility of the sulfur-containing titanium oxide powder is further improved.

  In the coating film forming method of the present invention, the content of the sulfur-containing titanium oxide in the B liquid may be appropriately determined according to its use, but considering the transparency of the resulting titanium oxide coating film, the A liquid In the composition for forming a coating film after mixing B and B, titanium oxide is preferably 0.8 to 20% by mass, and more preferably 1.0 to 20% by mass. When the concentration of the titanium oxide powder is less than 0.8% by mass, the photocatalytic performance cannot be sufficiently exhibited. On the other hand, when the concentration of the titanium oxide powder exceeds 20% by mass, the dispersibility of the titanium oxide in the dispersion medium decreases. .

  The mixing ratio of the organosilane compound and the solvent in the liquid A is not particularly limited, and is appropriately determined depending on the addition concentration of the sulfur-containing titanium oxide powder in the liquid B. As a compounding quantity of the organosilane compound in A liquid, it is 0.37 to 2.2 times in the total density | concentration with a peroxotitanic acid with respect to a titanium oxide density | concentration on a mass reference | standard in the composition for coating-film formation, and 30% or more of the total concentration with peroxotitanic acid is suitable. If the total concentration with peroxotitanic acid is less than 0.37 times and less than 30% of the total concentration with peroxotitanic acid, the hardness of the coating film is lowered. On the other hand, when it exceeds 2.2 times, the coating film surface is cracked and the smoothness is impaired.

  As for the compounding quantity of peroxotitanic acid, 0.1-1.1 mass% in B liquid is preferable. Moreover, it is preferable that the mass ratio (peroxotitanic acid / sulphur-containing titanium oxide powder) of peroxotitanic acid and sulfur-containing titanium oxide powder is 0.01-1.0. In consideration of these conditions, the liquid B is produced, and in the mixing with the liquid A, the mixing satisfying all the characteristics of dispersibility, hardness and catalytic activity can be easily performed.

  In the liquid A thus prepared, the organosilane compound is stably dispersed. Further, in the liquid B, the sulfur-containing titanium oxide powder, or peroxotitanic acid and the sulfur-containing titanium oxide powder are stably dispersed. For this reason, A liquid and B liquid may be preserve | saved for a predetermined period, and you may use for a coating-film formation method after that. The storage period is 3 months or less, preferably 2 months or less at room temperature such as 15 to 25 ° C.

  In the coating film forming method of the present invention, the A liquid and the B liquid are mixed before coating. At this time, the total concentration of the organosilane compound and peroxotitanic acid is preferably 0.6 to 3.4% by mass, and the blending ratio of peroxotitanic acid and organosilane compound is 1:99 on a mass basis. ˜70: 30, preferably 3:97 to 70:30, from the viewpoints of the degree of coating film obtained, the degree of adhesion, the smoothness of the coating film surface, and the like.

  The titanium oxide photocatalyst coating film forming method of the present invention is a method in which liquid A and liquid B are mixed, and the composition for forming a titanium oxide photocatalyst coating film that is a mixed liquid is applied to a substrate within 24 hours after mixing, Preferably, after mixing the A liquid and the B liquid, the mixed liquid is applied to the substrate within 12 hours, particularly within 5 hours. According to this method, after mixing the liquid A and the liquid B, the titanium oxide powder in the coating composition can be prevented from agglomerating and excellent in dispersibility, and gelation of the composition can be prevented. In addition, after the coating film is formed, the titanium oxide photocatalyst coating film having a higher dispersion of the sulfur-containing titanium oxide powder, higher adhesion, and higher photocatalytic activity can be formed. In addition, the titanium oxide photocatalyst coating film obtained by the coating film forming method of the present invention, in particular, the one containing an anti-aggregation agent is mixed with the liquid A and liquid B, and even if stored for a long time, the titanium oxide powder Aggregation can be prevented, the dispersibility is excellent, and gelation of the composition can also be prevented. Examples of the aggregation inhibitor include sodium phosphate, potassium phosphate, and sodium hexametaphosphate, and one or more of these can be used. When the aggregation preventing agent is usually mixed with the liquid B, aggregation of the titanium oxide powder after mixing can be further suppressed.

  In the coating film forming method of the present invention, the mixed solution is applied to a substrate and dried to form a photocatalyst coating film. The application method is not particularly limited, and may be a known method, such as a spray coating method, a dip coating method, or a spin coating method. Drying conditions are not particularly limited, and for example, drying may be performed at room temperature to less than 100 ° C. without performing any special heat treatment. Thereby, the coating film which is strong and has high photocatalytic activity is formed. Moreover, a firmer coating film can be formed also by heat-processing in the range of 100 degreeC-500 degreeC. The thickness of the coating is not particularly limited as long as the photocatalytic activity can be exhibited and the strength of the coating can be ensured, but is usually 0.1 to 10 μm, preferably 0.5 to 2 μm. .

  In the method for forming a coating film for titanium oxide photocatalyst of the present invention, the substrate is not particularly limited, and examples thereof include metals such as stainless steel, carbon steel, aluminum, titanium, glass, concrete, asphalt, slate, stone, wood, Examples thereof include organic materials such as fibers and plastics, materials having no corrosion resistance and materials having no heat resistance in acidic regions such as paper. Moreover, the board | substrate by which the surface was hydrophobically processed may be sufficient. Examples of the hydrophobic treatment include coating with a silicone-based water repellent treatment agent.

  In the present invention, the composition for forming a titanium oxide photocatalyst coating film contains sulfur-containing titanium oxide having a high activity as a photocatalyst, and also contains peroxotitanic acid and an organosilane compound. When coated on a mirror, metal, lens, etc., a photocatalytic coating film having high hardness and adhesion as well as high photocatalytic activity can be obtained. In addition, since the coating composition for applying a titanium oxide photocatalyst of the present invention provides a photocatalytic coating having excellent absorption characteristics in the visible light region, sunlight or a fluorescent lamp in a room can be used without an ultraviolet light source. The photocatalytic activity is sufficiently reproduced with a light source of. In addition, since the photocatalyst coating film is excellent in hardness and adhesion, it is very advantageous in that the photocatalyst coating film is not destroyed even if the coated substrate is processed. It can be widely applied as a photocatalyst coating for the purpose of deodorization, sterilization, antibacterial, water treatment, prevention of stains on lighting equipment, and the like.

EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, this is merely an example and does not limit the present invention.

Evaluation of the sulfur-containing titanium oxide photocatalyst obtained in the examples was carried out as follows.
(1) Measurement of sulfur content in sulfur-containing titanium oxide photocatalyst Field emission scanning electron microscope (Field Emission-SEM: FE-SEM) with energy dispersive X-ray fluorescence spectrometer (EDX) (Hitachi Electronic Scanning) Quantitative analysis of sulfur atoms in titanium oxide was performed with a microscope S-4700).

(2) Measurement of the rutile ratio The peak area (Ir) of the strongest interference line (surface index 110) of rutile crystalline titanium oxide and the strongest interference line of titanium oxide powder (in the X-ray diffraction pattern according to ASTM D 3720-84) The peak area (Ia) of the plane index 101) was obtained and obtained from the above formula. The X-ray diffraction measurement conditions are as follows.

(X-ray diffraction measurement conditions)
Diffraction device RAD-1C (manufactured by Rigaku Corporation)
X-ray tube Cu
Tube voltage / tube current 40kV, 30mA
Slit DS-SS: 1 degree, RS: 0.15mm
Monochromator graphite measurement interval 0.002 degree counting method Constant clock number method

(4) Decomposition performance of isopropyl alcohol (IPA) A 10 ml glass flask equipped with a stirrer was charged with 5 ml of an acetonitrile solution of isopropyl alcohol having an initial concentration of 50 mmol / liter, and 0.1 g of a sulfur-containing titanium oxide photocatalyst powder was added thereto. Then, with stirring, irradiate a light source with a wavelength of 410 nm or less cut with a filter, and after 1 hour, 2 hours, and 5 hours, collect a small amount of isopropyl alcohol in acetonitrile, and use isopropyl alcohol by gas chromatography. The concentration of was measured. Degradation performance indicated the concentration at each time as a ratio (%) to the initial concentration.

(5) Decomposition performance of methylene blue (MB) A 150 ml glass flask equipped with a stirrer was charged with 100 ml of an aqueous methylene blue solution having an initial concentration of 50 μmol / liter, charged with 0.2 g of a sulfur-containing titanium oxide photocatalyst powder, and hydrochloric acid. The pH was adjusted to 3 with light shielding, and the mixture was left stirring for 12 hours or longer. A small amount of methylene blue aqueous solution was collected, and the concentration of methylene blue was measured with a spectrophotometer. Thereafter, a light source having a wavelength of 410 nm or less was cut with a filter while stirring, and a small amount of methylene blue solution was collected after 1 hour, 2 hours, and 5 hours, and the concentration of methylene blue was measured with a spectrophotometer. . Degradation performance indicated the concentration at each time as a ratio (%) to the initial concentration.

(Production of sulfur-containing titanium oxide powder)
297 g of a titanium tetrachloride aqueous solution having a titanium concentration of 4 mass% was inserted into a 1000-ml round bottom flask equipped with a stirrer, and then heated to 60 ° C. Next, ammonia water was added instantaneously to maintain the pH of the reaction system at 7.4 for neutralization, and the mixture was kept at 60 ° C. for 1 hour to obtain a metatitanic acid solid. The obtained solid was filtered and washed with pure water, and 9.7 g of thiourea dissolved in 100 ml of pure water was added thereto and stirred for 30 minutes. Thereafter, the solid was dried at 60 ° C. and pulverized with a ball mill to obtain a mixture of titanium oxide powder and thiourea. The mixture was filled in an alumina crucible without a lid, and was charged in a firing furnace, and fired at 400 ° C. for 3 hours in air mixed with 3% by volume of hydrogen. Thereafter, it was pulverized by a ball mill, washed with pure water, and then dried at 60 ° C. to obtain a pale yellow titanium oxide photocatalyst. When the sulfur content in the obtained titanium oxide photocatalyst was measured, it was 0.25% by mass, the rutile ratio was 10%, and the specific surface area was 180 m ² / g. The decomposition performance of isopropyl alcohol (IPA) and the decomposition performance of methylene blue (MB) are shown in Table 1. As is apparent from Table 1, this sulfur-containing titanium oxide photocatalyst has a photocatalytic action in the visible light region and is excellent in the decomposition performance of organic substances such as IPA and MB.

(Preparation of solution A)
Tetraethoxysilane was added to an aqueous solution adjusted to pH 3 with nitric acid so as to be 1.7% by mass, and the mixture was stirred with a stirrer all day and night for hydrolysis, and then alkanesulfonic acid sodium (trade name “hydrophilic accelerator”; (Clariant Japan Co., Ltd.) was added so that it might become 0.16 mass%, tetraethoxysilane hydrolyzate aqueous solution was produced, and A liquid was obtained.

(Method for preparing solution B)
With respect to pure water, the sulfur-containing titanium oxide powder obtained in Reference Example 1, a peroxotitanic acid aqueous solution, ammonium polyacrylate (trade name “Poise 2100”; manufactured by Kao Corporation), and sulfur-containing titanium oxide A powder water slurry was prepared. At this time, the components were mixed so that the titanium oxide concentration was 8.3% by mass, the peroxotitanic acid concentration was 0.28% by mass, and the ammonium polyacrylate concentration was 0.33% by mass. This water slurry was treated with a ball mill and a bead mill to prepare a mixed aqueous solution of peroxotitanic acid and a slurry containing sulfur-containing titanium oxide powder to obtain a liquid B. The operation conditions of the ball mill were a media diameter of 10 mmφ, a rotation speed of 60 rpm, a grinding time of 16 hours, and the bead mill operation conditions were a media diameter of 0.03 to 0.1 mmφ, a peripheral speed of 6 to 8 m / sec, and an operation time of 2 hours.

Examples 1 to 3 and Comparative Example (Production Method of Titanium Oxide Photocatalyst Coating Composition)
Said A liquid and B liquid were mixed by the ratio of 85:15, and the composition (coating liquid) for sulfur containing titanium oxide photocatalyst coating film formation was produced.

(Formation and evaluation of titanium oxide photocatalyst coating)
After mixing liquid A and liquid B, spraying was performed on the substrate surface with a spray gun for 2 hours (Example 1), 5 hours (Example 2), 24 hours (Example 3), and 48 hours (Comparative Example 1). It was. Thereafter, the film was dried at room temperature to obtain a film having a thickness of 1 μm. The above substrate is made by dipping an acrylic resin plate on an alkoxy oligomer (product name KR400) manufactured by Shin-Etsu Chemical Co., Ltd., whose main component is methyltrimethoxysilane, and drying it at room temperature for 24 hours to make the substrate surface hydrophobic. Is. Evaluation of the obtained titanium oxide photocatalyst coating film was performed by measuring its hardness, adhesion, coating property, and dispersibility. Hardness, adhesion, coatability, and dispersibility were measured as follows.

(5) Pencil hardness test A pencil hardness test was performed according to JIS-K5400 (hand-drawing method), and the tearing of the coating film was visually evaluated. ○ indicates no scratch, Δ indicates a slight scratch, and × indicates a clear scratch.
(6) Adhesion strength test An adhesion strength test was conducted in accordance with JIS-K5400 (tape peeling test). The glass slide coated with the photocatalyst coating is cut with a cutter knife in a grid pattern (10 × 10 = 100 squares), and the cellophane tape is attached, and then the cellophane tape is kept at a right angle to the coating surface and momentarily. It peeled off and the state of the damage | wound was observed visually, and the evaluation score (0-10) was attached. The evaluation score also conformed to JIS-K5400 (tape peeling test). For example, 10 is not peeled off at all, 8 is slightly peeled at the intersection of the cuts, there is no peeling at a glance, the area of the defect is within 5% of the total rectangular area, 2 is peeling due to the cuts The width is wide, the area of the defect portion is within 35 to 65% of the total rectangular area, and 0 indicates the peeling area of 65% or more of the total rectangular area.
(7) Evaluation of coatability A composition for forming a titanium oxide photocatalyst coating film was applied to a member to prepare a coating film. The coatability at this time was evaluated. ○ indicates that coating is possible, and × indicates that coating is impossible.
(8) Dispersibility evaluation The dispersibility of the composition for forming a sulfur-containing titanium oxide photocatalyst coating film (coating liquid) after mixing the liquid A and the liquid B was visually evaluated. ○ indicates that the dispersibility is good without separation / aggregation by the solid layer and the liquid layer. X indicates that there is clear separation / aggregation due to the solid layer and the liquid layer, and the dispersibility is poor.
(9) Storage stability Before mixing of liquid A and liquid B, the mixture was stored at 20 ° C. and the time for gelation was observed.

  It was confirmed that both A liquid and B liquid did not cause gelation even when stored for 3 months and had sufficient storage stability. Table 2 shows the results of pencil hardness, adhesion, coatability and dispersibility of the film. As shown in Table 2, in Examples 1 to 3, the coating properties and the dispersibility after mixing the liquid A and the liquid B were excellent, and the hardness and adhesion of the obtained coating film were also excellent. In Comparative Example 1, gelation occurred in a dispersed state, and sufficient coatability was not obtained.

Claims (6)

  The liquid containing the organosilane compound (liquid A) and the liquid containing sulfur-containing titanium oxide powder and peroxotitanic acid (liquid B) are mixed, and within 24 hours after mixing, the liquid A and the liquid B are mixed. A method of forming a coating film for a titanium oxide photocatalyst, which comprises applying a mixed solution to a substrate and drying to form a coating film.   The method for forming a coating film for a titanium oxide photocatalyst according to claim 1, wherein the organosilane compound is organosilane or a hydrolyzate of organosilane.   The formation of a coating film for a titanium oxide photocatalyst according to claim 2, wherein the hydrolyzate of the organosilane is hydrolyzed by adding an organosilane to an aqueous solvent adjusted to pH 1 to 4. Method.   The method for forming a coating film for a titanium oxide photocatalyst according to claim 2, wherein the organosilane is tetraethoxysilane.   The said A liquid further contains alkanesulfonic acid, The formation method of the coating film for titanium oxide photocatalysts of any one of Claims 1-4 characterized by the above-mentioned.   The method for forming a coating film for a titanium oxide photocatalyst according to claim 5, wherein the substrate is a hydrophobic substrate.