JP2005163050A - Liquid composition for forming titanium dioxide coating film for photocatalyst and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a liquid composition for forming a titanium dioxide coated coating film, and which composition can firmly cover and adhere the titanium oxide powder on the surface of a substrate, wherein the titanium dioxide has catalytic function of oxidizing and reducing organic matters by photoirradiation. <P>SOLUTION: The liquid composition comprises titanium dioxide having 0.001-0.5 μm average particle diameter, a hydrolysate of a hydrolyzable silicon compound represented by the formula (1): Si-X<SB>4</SB>(1) (wherein, X's are each a halogen or a 1-8C alkoxy and may be same or different) and of 50-1,500% hydrolysis rate, and a solvent, wherein the weight ratio of titanium to silicon is, when expressed in terms of TiO<SB>2</SB>and SiO<SB>2</SB>, (30-96):(70-4) (100 in total) and the solid content in the whole composition is less than 30 wt.%. The substrate applied with the liquid composition to impart its photocatalytic function to the surface thereof is provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid composition capable of forming a titanium oxide-containing coating film used as a photo-oxidation catalyst, and a method for producing the composition, such as glass, metal, cement, wallpaper, gypsum board, stone material, ceramics or plastic. It relates to a substrate applied to the surface.

  Titanium oxide itself is an optical semiconductor, and when irradiated with light having energy greater than its band gap, such as ultraviolet rays, electrons accumulate in the conduction band and holes are generated in the valence band. The photocatalytic activity of decomposing organic substances in the atmosphere by the redox action based on the electron transfer generated by these accumulated electrons and holes and showing a bactericidal effect is known, and various attempts to use this active action industrially have been made. It has been broken.

  It is quite difficult to form a titanium dioxide layer with high photocatalytic activity on the surface of the substrate. One of the conventional methods is to form a titanium oxide film by subjecting the surface of a pure titanium plate to air oxidation or anodization, but it is difficult to obtain a good function even though the oxidation method is difficult. . As another method, titanium oxide is vapor-deposited on the surface of the substrate by the CVD method or plasma spraying (Japanese Patent Laid-Open No. 6-210170) is known, but all are expensive and applied depending on the type of the substrate. I can't do it. In addition, attempts have been made to attach titanium dioxide powder to a substrate through an adhesive called a binder, but the binder is oxidized and decomposed by the photocatalytic action of titanium dioxide, and after a few months it falls off the substrate and is used for industrial purposes. It cannot withstand use.

  In recent years, a method for forming a titanium dioxide thin film on the surface of a glass tube by a sol-gel method from an alkoxide of titanium has been announced. In this method, a solution obtained by adding a certain organic polymer to an alcohol solution of alkoxide is applied to a substrate, the organic polymer is thermally decomposed and removed by heat treatment, and titanium oxide is crystallized. However, it is expensive and heat treatment at a high temperature is essential.

  Various attempts have been made to purify air pollution and wastewater using the photocatalytic action of titanium oxide, but all have problems, and no definitive method has yet been found. The present invention is intended to provide a titanium oxide coating film-forming liquid composition for photocatalysts that is economically applicable to various applications.

The present invention relates to a titanium oxide having an average particle diameter of 0.001 to 0.5 μm, the following general formula (1)
Si-X ₄ (1)
(However, X = halogen, it may be the same or different alkoxy group of C ₁ ~ _8.)

The hydrolyzable silicon compound represented by the above formula is composed of a hydrolyzate having a hydrolysis rate of 50 to 1500% and a solvent, and the weight ratio of titanium and silicon is 30 to 96:70 to 4 in terms of conversion to TiO ₂ and SiO ₂ , respectively. (Total 100), and the solid content concentration in the total composition is 30% by weight or less, and the titanium oxide coating film-forming liquid composition for photocatalyst, its production method, and the liquid composition as a base material Applied to a substrate having a photocatalytic function on the surface of the substrate.

  The composition of the present invention is capable of firmly coating and adhering fine titanium dioxide powder having a catalytic function for oxidation / reduction of organic substances by irradiation of light to the surface of the base material. It is possible to form a coating film having a high photoactivity that does not cause a decrease in adhesive strength over time due to the decomposition of. By selecting the ratio of film thickness and silica binder, a transparent film can be formed and applied to a wide range of applications.

The present invention will be described in detail below.
The titanium oxide used in the present invention exhibits a catalytic action for redox of organic matter by irradiation with light having a specific energy. In addition to pure titanium oxide, hydrous titanium oxide, hydrated titanium oxide, metatitanium. Includes what are called acids, orthotitanic acid, and titanium hydroxide. Titanium dioxide or a material in a lower oxidation state is particularly preferably used. The crystal form of titanium dioxide may be any of anatase type, rutile type, flukeite type, or a mixture thereof.

  These titanium dioxides are in the form of fine powder, and the particle size is preferably as fine as about 0.001 to 0.05 μm in view of the strength of the photocatalytic activity, but the particle size up to about 0.5 μm is larger than this. Can be used. This fine powder may be used as a dry powder, but it is desirable to prepare a dispersion in advance for uniform dispersion with a silica binder derived from a hydrolyzable silicon compound described below. Whether or not titanium dioxide is well dispersed in the composition of the present invention greatly affects the photocatalytic function when a coating film is formed.

  Titanium oxide is produced by various known methods. For example: 1. a method of hydrolyzing a titanium compound such as titanyl sulfate, titanium chloride, or an organic titanium compound in the presence of a nucleating species, if necessary; 2. A method of neutralizing a titanium compound such as titanyl sulfate, titanium chloride, or an organic titanium compound by adding an alkali in the presence of a nuclear forming species as necessary. 3. A method for vapor phase oxidation of titanium chloride, organic titanium compounds, etc. Examples thereof include a method of firing the titanium oxide obtained by the above methods 1 and 2. In particular, titanium oxide obtained by the methods 1 and 2 is preferable because of its high photocatalytic function. In order to further improve the photocatalytic function, the titanium oxide surface may be coated with a metal such as platinum, gold, silver, copper, palladium, rhodium or ruthenium, or a metal oxide such as ruthenium oxide or nickel oxide.

  These titanium oxides are used by being highly dispersed in a solvent such as water. In order to disperse the titanium oxide in ultrafine particles uniformly with a solvent such as water without secondary agglomeration, it is preferably stored as acidic or alkaline. When placed under acidic conditions, the pH is preferably 0.5 to 4, particularly 1 to 3.5. As a dispersion medium, a mixture of water and alcohol may be used in addition to water.

Examples of the hydrolyzable silicon compound represented by the general formula (1) used in the present invention include alkyl silicates, silicon halides, and partial hydrolysates thereof. As the alkyl silicate, methyl, ethyl, isopropyl silicate or the like is used. All of these silicates are used in the form of monomers or oligomers formed by partial hydrolysis, and the oligomers have the general formula Si _n O _n-1 (OR) _{2n + 2} (where n is 2-6, R is Alkyl silicate condensates represented by (C1-4 alkyl groups) are particularly preferred. These oligomers are also used in a mixture.

  Either acid or alkali can be used as the catalyst for partial hydrolysis. When the titanium oxide dispersion is acidic, an alkyl silicate hydrolyzed with an acid is preferred. Water or alcohol having 1 to 4 carbon atoms is used as a dispersion solvent for the hydrolyzed liquid. Esters such as ethyl acetate are not preferred because they make the composition liquid unstable. Since the silicon compound and its partial hydrolyzate used in the present invention are used for the purpose of binding titanium oxide, they are hereinafter referred to as a silica binder.

  Mixing of the titanium oxide and the silica binder can be performed as appropriate, but as an example, a predetermined amount of aqueous titanium dioxide dispersion under acidity is maintained at a liquid temperature of 10 to 50 ° C., and an alkyl silicate or The partial hydrolyzate is added dropwise over a period of time. After completion of the dropwise addition, a composition liquid is prepared by reacting with stirring for 1 to 5 hours. When adding an alkyl silicate or a partial hydrolyzate, the hydrolysis catalyst may be added at the same time, or the hydrolysis may be carried out using the acid present in the titanium dioxide dispersion. When an alcohol-based medium is used as the dispersion medium, a water / alcohol mixed medium dispersion of titanium dioxide and a liquid obtained by hydrolyzing 50 to 1500% of an alkyl silicate or a partial hydrolyzate in an alcohol medium are mixed with stirring. Thus, the present composition can also be obtained.

In the present specification, the hydrolysis rate is calculated based on the amount of water used, assuming that the hydrolysis rate is 100% when used at a ratio of 2 mol of water to 1 mol of alkyl silicate. When a partial hydrolyzate of the general formula Si _n O _n-1 (OR) _{2n + 2} is used, the case where it is used in a ratio of n + 1 mol of water to 1 mol of this condensate is regarded as a hydrolysis rate of 100%. Calculated.

The ratio of titanium and silica in the composition of the present invention needs to be 96/4 to 30/70 in terms of weight ratio (TiO ₂ / SiO ₂ ) converted to titanium dioxide and silicon dioxide, respectively. When the proportion of silica exceeds 70%, the photocatalytic function of titanium oxide becomes small and the practicality becomes poor. This is presumably because the proportion of silica covering the surface of the titanium oxide particles increases, preventing contact between the titanium oxide and the substance to be oxidatively decomposed. On the other hand, when the mixing ratio of silica is 4% or less, the adhesive strength between the base material and titanium oxide is not sufficient, and it easily falls off by finger touch or vibration, making it difficult to use industrially as a coating film. . A desirable ratio of silica is 10 to 50%.

The solid content concentration in the composition of the present invention is 30% or less by weight. Here, the solid content refers to the total amount of titanium oxide and silica in the entire composition, titanium oxide is titanium dioxide, silica is silicon (Si) content in the alkyl silicate or oligomer in the composition in SiO ₂ . The converted value is used. The other components are mainly water and / or an organic solvent, and should be substantially removed by drying after the composition is applied onto the substrate surface. The preferred solid content concentration is 5 to 20%, and if it is 5% or less, the adhesion to the substrate becomes strong, but the coating thickness is sufficient, that is, the amount of titanium dioxide is insufficient, so that the photocatalytic function can be sufficiently exerted. Can not form. Although it is possible to increase the thickness of the coating film by two-layer coating or three-layer coating, there is usually no merit of performing two-layer coating that takes a lot of time by reducing the solid content concentration. However, it can be used for special applications such as when a strong thin coating is required even at the expense of the photocatalytic function.

  On the other hand, when the solid content concentration exceeds 30%, the dispersibility of the solid matter in the composition is deteriorated, the storage stability of the composition is remarkably lowered, and gelation easily occurs in a few days. Further, such a high concentration is not preferable because the film formability is poor and the adhesion of the formed film to the base material is greatly reduced and the film peels off when rubbed with a finger.

  A small amount of titanium alkoxide or titanium tetrachloride may be added to the composition of the present invention. Further, titanium or a silane coupling agent may be added. Furthermore, various surfactants may be added to ensure the stability of the composition and improve the wetting characteristics. Further, a small amount of alkoxysilane or hydrosilane containing two or more alkoxy groups may be added, but these titanium and silane compounds are added in terms of silica when calculating the solid content.

  The composition of the present invention is applied to a substrate surface, dried, and optionally fired at a low temperature to form a coating film. As the coating method, spin coating, spray coating, bar coating, dip method or the like is appropriately used depending on the shape of the substrate to be coated. The thickness of the coating film is suitably 0.1 to 3 μm, particularly 0.3 to 2 μm. The photocatalytic activity of titanium dioxide is related to the amount of titanium dioxide that can be exposed to the surface and contacted with the compound to be oxidatively decomposed. It is uniform, and the dispersion of particles is not necessarily ideal, and if it is too thin, the amount of titanium dioxide on the surface of the coating film is small and the photocatalytic activity is not sufficient. With such a thickness, the coating film can be made transparent, and a coating film having photoactivity can be formed on the surface without impairing various structures and designs of the substrate.

  Examples of the substrate on which the film-forming liquid composition of the present invention is applied include glass, metal, cement concrete, slate, gypsum board, stone, wood, ceramics, plastics, and other tubular, plate-like, lattice-like, and spherical shapes. In addition, there are honeycomb-shaped members or molded products from these members, but it is preferable to dry sufficiently in order to remove the solvent, moisture and the like after application.

  The coating film from the composition of the present invention can form a fairly strong film that does not easily peel off when rubbed with a nail by drying at 100 ° C., but the silica binder is stronger by drying at a temperature of 100 ° C. or higher. A thin coating film can be formed, and may be dried or calcined at a low temperature of 100 to 300 ° C. as necessary. However, the catalytic activity of ultrafine titanium dioxide begins to gradually decrease after drying at 150 ° C. or higher, and may rapidly decrease when the temperature exceeds 400 ° C. In any case, drying at 480 ° C. or lower or low-temperature firing is preferable.

  The base material or member on which the coating film of the present invention is formed is used for a wide variety of applications. For example, a metal or plastic plate or grid is used as a sound insulation member for an expressway, and it is used for decomposing and removing organic substances and microorganisms adhering thereto. Or what coated the ceramic honeycomb is utilized as a catalyst for decomposition | disassembly of a toxic substance by making the gas or liquid containing a toxic substance, such as hydrogen sulfide, contact. In addition, when applied to a plastic decorative plate made of polyvinyl chloride, etc., when used as a wall material, it exhibits a function of automatically purifying the wall surface and can be used as having a sterilizing effect in hospitals. Those adhered to spherical glass, pumice, ceramics, etc. can be used as a purification material for waste water. In a conference room or the like, it can be used for decomposition of cigarette smoke simply by placing a member made of a base material coated and dried with the composition of the present invention, such as an ashtray or a screen. Furthermore, it can apply | coat to the inner side of a water tank and can be used for anti-algae.

  In the examples, the photocatalytic activity decomposition rate was determined by applying the composition of the present invention to a glass plate by the following method, using a test piece formed with a film, and subjecting the acetaldehyde to light irradiation while being in vapor phase contact with acetaldehyde. It is measured by the decomposition ratio.

1. Preparation of test piece (application condition of composition liquid)
Application piece: Glass plate 100 × 50 × 2t (mm)
Application method: Meyer bar # 3, # 5
Drying conditions: 100 ° C., 1 hour

2. Photocatalytic activity decomposition rate measurement method (1) Gas phase decomposition reaction apparatus A three-necked separable flask is assembled and set sideways so that a test piece can be placed inside.
(2) Light source Two black lights 4W manufactured by Toshiba Corporation are installed at a position about 8 cm from the coating surface of the test piece so that the amount of light (light intensity) is 1 mW / cm ² .
(3) Circulation device Using an air pump, the inside of the flask and the sampling three-way cock are connected to circulate through a Tygon tube, and circulate at 1 liter / min.
(4) Introduction of acetaldehyde and detector tube for concentration measurement A test piece is placed, and a silicone W cap is attached to one of the three necks of a flask filled with normal air, and acetaldehyde is introduced with a microsyringe. The amount introduced is 40 to 200 ppm. One of the sampling three-way cocks is provided with a gas detector tube for measuring the acetaldehyde concentration so that the concentration can be measured.
(5) Pretreatment of test piece and measurement of acetaldehyde decomposition rate Before measuring the photocatalytic activity of the test piece, it was pretreated with acetaldehyde. Pretreatment of the test piece is difficult because it is difficult to measure the correct decomposition rate of the introduced acetaldehyde because the organic substance is decomposed before or together with the start of the decomposition of acetaldehyde when residual organic substances are present in the test piece coating. This is done to minimize the impact. In the pretreatment, about 100 ppm of acetaldehyde is introduced into the flask, the circulation device is operated without irradiating light, and after circulating for 10 minutes, the concentration is measured with a gas detector tube. Thereafter, the light source switch is turned on and the acetaldehyde concentration is measured every 30 minutes after the start of light irradiation for a maximum of 3 hours. The decomposition rate was determined on the assumption that the reduced acetaldehyde was decomposed, and the pretreatment of the test piece was completed when the decomposition rate reached 85% or more or when light irradiation was performed for 3 hours.
About the test piece which completed pre-processing, the decomposition rate was measured with the following formula from the change of the acetaldehyde density | concentration before and behind light irradiation by the method similar to pre-processing, and it used for evaluation of the photocatalytic activity of a coating film.

The evaluation of the film-forming composition surface obtained in each example is shown in the table, and the hardness in the table is a measurement value relating to the strength of the coating film displayed in accordance with the standard below.
(1) Degree of destruction of paint film by finger touch (2) Degree of exfoliation when rubbed with nails (3) Degree of damage when rubbed with nails (4) (3) and (5) below Intermediate level (5) Nail scratches but nail mark remains (6) Intermediate level between (5) and (7) below (7) Nail mark level does not remain The reaction rate constants in the table are acetaldehyde Is calculated assuming that the decomposition of is linearly proportional to time, and its unit is min ⁻¹ .
In the examples, “parts” means parts by weight.

[Example 1]
An aqueous dispersion of titanium dioxide having an average particle size of 0.006 μm was adjusted to pH 1.5, and a predetermined amount of ethyl silicate was added dropwise with stirring while maintaining this at 30 ° C. The ratio of titanium and silica was adjusted as shown in Table 1 so that the solid concentration was 10%. Water (ion exchange water) was used for concentration adjustment. No particular addition was made as a hydrolysis catalyst. After completion of the dropwise addition, the mixture was reacted at 30 ° C. for 3 hours, and a film was formed on the glass plate of the test piece using the Mayer bar # 5 so that the film thickness was 0.75 μm. After drying at 100 ° C. for 1 hour, the appearance and hardness of the coating film and the photocatalytic activity were measured according to the method described above. The results are shown in Table 1. From this result, it can be seen that even if the proportion of SiO ₂ exceeds 50%, it still has acetaldehyde resolution.

[Example 2]
(1) Preparation of hydrolyzed liquid of silicon compound In a separable flask equipped with a stirrer, thermometer and reflux condenser, 223.5 parts of methyl alcohol, ethyl silicate 40 (ethyl silicate pentamer equivalent, Colcoat Co., Ltd.) (Product name, product name) 30 parts are charged, and uniformly stirred and maintained at 30 ° C. A mixed solution of 45 parts of ion-exchanged water and 1.5 parts of 60% nitric acid was added all at once so that the hydrolysis rate was about 1000%, and the mixture was hydrolyzed at 30 ° C. for 5 hours. The hydrolyzed solution thus prepared had a solid content concentration of 4% as SiO ₂ .

(2) Mixing method with TiO ₂ dispersion Into a separable flask equipped with a stirrer, thermometer and reflux condenser, 12.5 parts of the above hydrolyzed solution and 55.8 parts of isopropyl alcohol were charged and stirred uniformly. And maintain at 30 ° C. A predetermined amount of TiO ₂ dispersion having a particle size of 0.006 μm was added thereto, and the mixture was stirred at 30 ° C. for 1 hour. The TiO ₂ / SiO ₂ ratio of the obtained liquid was as described in Table 2, and the solid content concentration was adjusted to 10%.

(3) Film formation and photoactivity measurement The composition liquid obtained by the above mixing was applied to a test piece using a Mayer bar # 3, dried at 100 ° C. in the same manner as in Example 1, and the calculated film thickness. A 0.45 μm coating film was formed. The photocatalytic activity of the obtained test piece was measured. The results are shown in Table 2. The film thickness on the test piece used here is an extremely thin film from the viewpoint of actual use, and it is possible to withstand practical use because it shows a photocatalytic activity even though it is such a thin film. It will be a thing.

[Example 3]
The composition having a total solid content concentration of 10% obtained in Example 2 was applied to a test piece using a Mayer bar # 5, the coating film was dried at 150 ° C. for 30 minutes, and the calculated film thickness was 0. A 75 μm coating film was formed. The photocatalytic activity of the obtained test piece was measured. The results are shown in Table 3. When the coating film is dried at a high temperature, the coating film hardness is slightly improved, but the catalytic effect on acetaldehyde decomposition is not lowered, and it is recognized that the decomposition rate is improved by the increase in the film thickness.

[Example 4]
A composition of the present invention was prepared using a silica binder prepared by the following method in place of the silicon compound hydrolyzate used in Example 2.
A separable flask equipped with a stirrer, a thermometer and a reflux condenser was charged with 230.4 parts of methyl alcohol and methyl silicate 51 (methyl silicate tetramer equivalent, manufactured by Colcoat Co., Ltd., trade name) 23.4 parts. Stir uniformly and maintain at 30 ° C. A mixed solution of 44.7 parts of ion exchange water and 1.5 parts of 60% nitric acid was added all at once so that the hydrolysis rate was about 1000%, and the mixture was hydrolyzed at 30 ° C. for 5 hours. The hydrolyzed solution thus prepared had a solid content concentration of 4% as SiO ₂ .

  Various composition liquids obtained using the above silica binder were applied to a test piece using a Mayer bar # 5 and dried at 150 ° C. for 30 minutes in the same manner as in Example 3 (however, sample No. 14 was 200 And dried at 30 ° C. for 30 minutes to form a coating film having a calculated film thickness of 0.75 μm. The photocatalytic activity of the obtained test piece was measured. The results are shown in Table 4. It is recognized that the coating film using methyl silicate 51 tends to have high hardness as a whole.

Claims (4)

Titanium oxide having an average particle diameter of 0.001 to 0.5 μm, the following general formula (1)
[Chemical 1]
Si-X ₄ (1)
(However, X = halogen, it may be the same or different alkoxy group of C ₁ ~ _8.)
The hydrolyzable silicon compound represented by the above formula is composed of a hydrolyzate having a hydrolysis rate of 50 to 1500% and a solvent, and the weight ratio of titanium and silicon is 30 to 96:70 to 4 in terms of conversion to TiO ₂ and SiO ₂ , respectively. (Total 100) The solid content concentration in the total composition is 30% by weight or less, and the titanium oxide coating film-forming liquid composition for photocatalysts. An aqueous dispersion containing a titanium oxide having an average particle diameter of 0.001 to 0.5 μm is maintained at 10 to 50 ° C., and a hydrolyzable silicon compound represented by the following general formula (1) is stirred therein. In addition to the above, the reaction is performed for 1 hour or more to obtain a hydrolyzate having a hydrolysis rate of 50 to 1500%. The weight ratio of titanium and silicon is 30 to 96:70 to 4 in terms of conversion to TiO ₂ and SiO ₂ , respectively. (Total 100), The manufacturing method of the titanium oxide coating-film formation liquid composition for photocatalysts whose solid content concentration in all the compositions is 30 weight% or less.
[Chemical 2]
General formula (1)
Si-X ₄ (1)
(However, X = halogen, it may be the same or different alkoxy group of C ₁ ~ _8.) An aqueous dispersion containing a titanium oxide having an average particle size of 0.001 to 0.5 μm is maintained at 10 to 50 ° C., and a hydrolyzable silicon compound represented by the following general formula (1) is added to the alcohol. The alcoholic silica sol obtained by hydrolysis with water in such an amount that the hydrolysis rate is 50 to 1500% is added and mixed at 10 to 50 ° C., and the weight ratio of titanium and silicon is changed to TiO ₂ and SiO ₂ , respectively. The manufacturing method of the titanium oxide coating-film formation liquid composition for photocatalysts which is 30-96: 70-4 (total 100) by the conversion value of, and the solid content concentration in all the compositions is 30 weight% or less.
[Chemical formula 3]
General formula (1)
Si-X ₄ (1)
(However, X = halogen, it may be the same or different alkoxy group of C ₁ ~ _8.) Titanium oxide having an average particle diameter of 0.001 to 0.5 μm, the following general formula (1)
[Chemical formula 4]
Si-X ₄ (1)
(However, X = halogen, it may be the same or different alkoxy group of C ₁ ~ _8.)
The hydrolyzable silicon compound represented by the above formula is composed of a hydrolyzate having a hydrolysis rate of 50 to 1500% and a solvent, and the weight ratio of titanium and silicon is 30 to 96:70 to 4 in terms of conversion to TiO ₂ and SiO ₂ , respectively. A coating composition made of titanium oxide and silicon oxide having a thickness of 0.1 to 3 μm is applied by applying a liquid composition having a solid content concentration of 30% by weight or less in the total composition and drying. A substrate having a photocatalytic function formed on the surface.