JPH11171544A - Titanium-containing material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a titanium-contg. material and a titanium-contg. coating soln. giving a thin film excellent in transparency, photocatalytic action and adhesion to a substrate by imparting a specified light transmissivity at a specified wavelength in a specified thickness even after heating up to the boiling point. SOLUTION: An aq. soln. of titanium tetrachloride is hydrolyzed in the presence of a carboxylic acid, preferably citric acid to produce the objective titanium-contg. material and titanium-contg. coating soln. having >=85% light transmissivity at 450-700 nm wavelength in 10 mm thickness even after heating to the b.p. The concn. of the titanium tetrachloride in the aq. soln. is preferably 0.1-10 mol/l (expressed in terms of TiO2 ) and the amt. of the carboxylic acid added is preferably 0.1-10 mol/l and 0.01-10 mol per 1 mol Ti atom. After the hydrolysis, dechlorination is optionally carried out by electrodialysis or other method so as to attain 50-10,000 ppm Cl ion concn. and pH 0.5-5. The particle diameter in the material or soln. is 0.0008-0.015 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium-containing substance, a titanium-containing coating liquid suitable for forming a thin film on a substrate such as ceramics and synthetic resin, and a method for producing the same. The thin film formed from the liquid has excellent transparency, good photocatalysis, and good adhesion to the substrate. Further, the liquid has a high photocatalytic effect and a high ultraviolet absorbing function.

[0002]

2. Description of the Related Art It is well known that titanium oxide is produced by hydrolyzing an aqueous solution of titanium tetrachloride or titanium alkoxide, in which case a titanium oxide sol is produced. Recently, a titanium oxide sol is applied to a lighting device, for example, a glass tube or a cover of a fluorescent lamp to form a thin film, and when an organic substance such as oil smoke adheres to the glass tube or the cover by a photocatalytic action, it is decomposed, and the glass tube or the A method for preventing the cover from being stained has been proposed.

[0003]

When a titanium oxide thin film is formed on glass, plastic, or another substrate and used as a photocatalyst, the thin film is naturally required to have high catalytic activity. Is also required. Then, in order to further improve the transparency while maintaining the catalytic activity, it is an object of the present invention to produce finer particles by monodispersion of a titanium-containing substance.

[0004]

Means for Solving the Problems The present inventors hydrolyze titanium tetrachloride in the presence of a carboxylic acid to obtain an unprecedented titanium-containing substance or a titanium-containing substance containing fine particles of 2 to 5 nm. A coating liquid (sol) can be produced, and the resulting particles are fine and maintain catalytic activity, and have unprecedented transparency, ie, have a thickness of 450 to 700 nm even when heated to the boiling point. A titanium-containing substance or a titanium-containing coating liquid (sol) having a light transmittance of 85% or more at a thickness of 10 mm was obtained. Since the present invention also has a high photocatalytic effect and an ultraviolet absorbing function, it is also useful as a highly transparent photocatalytic effect material and an ultraviolet shielding and protecting material.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION If the concentration of titanium tetrachloride in an aqueous titanium tetrachloride solution to be hydrolyzed is too low, the productivity is poor, and if the concentration is too high, the reaction becomes violent, and the particles of the titanium-containing substance obtained are fine. And the dispersibility is also poor, so the preferred concentration range is TiO ₂ conversion,
0.1 to 10 mol / liter. The present invention is characterized in that titanium tetrachloride is hydrolyzed in the presence of a carboxylic acid, preferably a water-soluble carboxylic acid.

The preferred amount of carboxylic acid is 0.1 to 1
When the amount is less than 0.1 mol / L, the sol becomes turbid due to the progress of the hydrolysis reaction. On the other hand, when it exceeds 10 mol / L, the sol starts to precipitate as a carboxylic acid salt. Not preferred. As a preferred water-soluble carboxylic acid, oxalic acid, citric acid, malic acid, tartaric acid, succinic acid, and the like can be used, but citric acid is preferable in order to maximize the effect of addition in the smallest possible amount. . If it is not a water-soluble carboxylic acid, it may be dissolved in a lower or intermediate alcohol or ketone and added to water. The compound of the present invention can be obtained by adding a water-soluble carboxylic acid such as citric acid in a range of 0.01 mol or more and 10 mol or less with respect to 1 mol of titanium atom at the time of the reaction and performing a hydrolysis reaction. If the amount is less than 0.01 mol, it is difficult to obtain the desired effect, and the mixture becomes cloudy due to the progress of the hydrolysis reaction. On the other hand, if it exceeds 10 mol, it starts to precipitate as a carboxylic acid salt.

[0007] Hydrogen chloride generated by hydrolysis does not have to be completely prevented from escaping, as long as it is suppressed. The method is not particularly limited as long as the method can be suppressed.
For example, pressurization is possible, but the easiest and most effective method is to install a reflux condenser in the hydrolysis reaction tank to carry out hydrolysis. This device is shown in FIG. In FIG. 1, reference numeral 1 denotes a reaction tank filled with an aqueous solution 2 of titanium tetrachloride, in which a reflux condenser 3 is installed.
4 is a stirrer, 5 is a thermometer, and 6 is a device for heating the reaction tank. Although water and hydrogen chloride vapor are generated by the hydrolysis reaction, most of them are condensed by the reflux condenser and returned to the reaction tank, so that hydrogen chloride hardly escapes from the reaction tank.

In the present invention, a predetermined amount of a carboxylic acid is previously added to a solvent before the addition of titanium tetrachloride, and then sufficiently dissolved, and then the titanium tetrachloride is added. The temperature in the hydrolysis is preferably in the range of 50 ° C. or higher and up to the boiling point of the aqueous solution of titanium tetrachloride. If the temperature is lower than 50 ° C., a long time is required for the hydrolysis reaction. The hydrolysis is carried out by raising the temperature to the above-mentioned temperature and holding for about 10 minutes to 12 hours. This holding time may be shorter as the hydrolysis temperature is higher. For the hydrolysis of the aqueous solution of titanium tetrachloride, a mixed solution of titanium tetrachloride and water may be heated to a predetermined temperature in a reaction vessel, or water may be heated in advance in the reaction vessel, To a predetermined temperature.

When the sol obtained by hydrolysis is dried, it can be taken out as a dry powder.
This is not realistic because the effect of miniaturization is no longer recognized. When used as a sol, after the hydrolysis reaction, a dechlorination treatment can be performed if necessary. The dechlorination treatment can be performed by a commonly known means, such as electrodialysis, ion exchange resin, or electrolysis. The degree of dechlorination may be based on the pH of the sol, and the chlorine ion is 50 to 10,000 ppm.
In this case, the pH is about 0.5-5, a preferred range of 10
For 0 to 4,000 ppm, the pH is about 4-1.
An organic solvent can be added to the aqueous dispersion sol of the present invention and dispersed in a mixture of water and the organic solvent. When forming a thin film from the water-dispersed titanium-containing substance of the present invention, it is preferable to use the sol generated by the hydrolysis reaction as it is, to produce a powder from this sol, disperse it in water, and use it as a sol. This is not the preferred method. Titanium oxide particles have a high surface activity, and the finer the particles, the higher the activity, so it is very difficult to disperse them in water.In other words, they become agglomerates, and the thin films made therefrom have poor transparency. This is because the photocatalytic action is also reduced. The production method of the present invention is to suppress the escape of hydrogen chloride generated during the hydrolysis of the aqueous solution of titanium tetrachloride, and to add a stabilizer to prevent agglomeration. By dechlorinating into a sol, this method is capable of obtaining a thin film having high photocatalytic activity and high transparency when formed. When an organic solvent is used as the dispersion medium, it is produced by replacing the solvent into which titanium tetrachloride is charged with a water-soluble organic solvent.

The titanium-containing particles obtained by the production method of the present invention have not been sufficiently identified. Analysis has shown that the particles are not generally titanium oxide sol particles obtained by hydrolyzing titanium tetrachloride. The particle size of the present invention is from 0.0008 to 0.015 μm. Further, the titanium-containing substance or the coating liquid of the present invention,
Unlike conventional titanium oxide sols, they are not white turbid at room temperature, and are colorless and transparent even when heated to the boiling point. They are measured in a 10 mm × 10 mm square quartz cell having a height of 45 mm. At 10 mm, wavelength 4
A titanium-containing substance having a light transmittance of 85% or more at 50 to 700 nm, and a titanium-containing coating liquid.

In order to improve the film-forming property, a water-soluble polymer is added as required. Various materials such as polyvinyl alcohol, methylcellulose, ethylcellulose and nitrocellulose can be used for the one obtained in the present invention, but it is necessary to completely dissolve it in the sol. Therefore, it is desirable that the amount contained in the sol be 10 wt% or less in order to impart photocatalytic properties. The addition is preferably performed after the completion of the dechlorination treatment, but may be performed before the dechlorination treatment. The above describes the batch-type reaction. However, a continuous method in which the reaction vessel is continuously charged with titanium tetrachloride, the reaction liquid is taken out on the opposite side of the charging port, and the dechlorination treatment is subsequently performed is also possible. . When forming a transparent thin film from that obtained by the present invention, if the concentration of the particles in the sol is too high, the particles aggregate and the sol becomes unstable. Further, if the concentration is too low, for example, it takes a long time to apply the sol during the formation of a thin film.
The preferred concentration is 1 to 30 wt%.

The sol obtained by the present invention can be applied to a base material such as various materials and molded articles to form a thin film on the surface of the base material. As the base material, ceramics, metals, plastics, woods, papers, and the like can be used with almost no restrictions. The base material may be a catalyst carrier made of alumina, zirconia, or the like, and the thin film catalyst may be supported on the carrier and used as a catalyst. In addition, if a thin film is formed on a glass of a lighting device such as a fluorescent lamp or its plastic cover as a base material, the thin film is transparent and has a photocatalytic action, so that organic substances such as oil smoke can be decomposed without blocking light. It is effective in preventing stains on the glass and the cover. Also, if a thin film is formed on architectural glass or wall material, it will be possible to prevent dirt similarly, so it can be used for window materials and wall materials of high-rise buildings, etc., and cleaning work will not be required, so building management Helps reduce costs. To apply the monodisperse sol obtained by the present invention to a substrate, a method of immersing the substrate in the sol, a method of spraying the sol on the substrate, a method of applying the sol to the substrate with a brush, and the like are employed. . The appropriate amount of the sol to be applied is 0.01 to 0.2 mm as a liquid thickness. If the solvent is removed by drying after coating, a thin film can be obtained, which can be used as a catalyst or the like as it is.
When the substrate is heat-resistant such as metal or ceramics, for example, glass, it can be fired after forming the thin film, whereby the thin film adheres more strongly to the substrate and the hardness of the thin film increases. The firing temperature is preferably 200 ° C. or higher. The upper limit of the sintering temperature is not particularly limited and may be determined according to the heat resistance of the base material. However, if the temperature is too high, the hardness of the thin film and the adhesion to the base material do not increase. Up to is appropriate.
The firing atmosphere is not particularly limited, and may be in the air. The firing time is not particularly limited, and may be, for example, in the range of 1 to 60 minutes. The thickness of the thin film obtained by firing is about 0.02 to 1.0 μm in the case of the above-mentioned coating amount. The sol obtained by the present invention is completely transparent to visible light,
Further, the thin film produced using this sol exhibits high photocatalytic activity and high transparency, that the particles are very fine particles so as not to cause light scattering and absorption with respect to visible light. This is because the particles in the dispersed state do not agglomerate and exist as primary particles without limit.

[0013]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to the examples. Example 1 300 g of distilled water was charged into a reaction vessel equipped with a reflux condenser shown in FIG. 1, and the stirring speed was maintained at about 200 rpm.
8.4 g of citric acid was dissolved, and titanium tetrachloride (Ti content: 16.3%, specific gravity: 1.59, purity: 99.000 g) was dissolved therein.
63.4 g of an aqueous solution (9%) were added. After the addition was completed, the temperature of the solution was increased to about 100 ° C., and the reaction was maintained for 60 minutes to complete the reaction. After cooling, the residual chlorine generated in the reaction was subjected to electrodialysis to obtain a chlorine concentration of 600 ppm.
After the pH was adjusted to 2, a polyvinyl alcohol as a water-soluble polymer was used as a film-forming auxiliary at a concentration of 1.0 w
A titanium containing coating solution was made up to t%. Using a 10 mm × 10 mm × 45 mm quartz cell, this solution was measured with a spectrophotometer (JASCO Ubest300) to obtain a solution of 200 nm to 7 nm.
The transmission spectrum in the 00 nm region was measured. FIG. 2 shows the measurement results. It is apparent from FIG. 2 that the visible light region is 38.
It is clear that the absorbance is low at 0 nm to 700 nm and almost completely transparent, and 450 to 700 nm.
Has a light transmittance of 95%. At 380 nm or less, which is ultraviolet light, absorption of a specific ultraviolet ray observed in the case of titanium oxide was observed. Furthermore, the particle size distribution was measured by a particle size distribution analyzer (Otsuka Electronics DLS-7000), and as a result, the average particle size d ₅₀ was 2.56 nm. The coating liquid (titanium-containing substance) was very stable, and no sedimentation of the generated fine particles was observed even after one week or more. The particles were taken out using a vacuum dryer at 60 ° C. and subjected to electron beam diffraction with a transmission electron microscope, but could not be identified as a compound. The dried product was amorphous in terms of X-ray diffraction, and the product baked at 400 ° C. showed a peak of rutile titanium oxide.

Further, the above liquid was uniformly applied to a glass substrate using a spin coater, and dried at 100 ° C. to obtain a transparent film. FIG. 3 shows the transmission spectrum of this glass substrate with a thin film. FIG. 3 clearly shows that the visible portion has a transmittance of 97% or more, and is almost completely transparent. Further, absorption similar to that specific to titanium oxide was observed in the ultraviolet. In order to measure the photocatalytic ability, a red ink containing an organic dye was uniformly applied on the transparent thin film and irradiated with an ultraviolet irradiation lamp (black light) to perform a fading test. The test was performed at 550n, which is the center wavelength of red before and after fading.
It examined by comparing the absorptivity at m. Table 1 shows the results. As is clear from the table, red fading was observed, and the photocatalytic ability by ultraviolet absorption was confirmed.

Example 2 A titanium-containing coating liquid (titanium-containing substance) was prepared in the same manner as in Example 1 except that the amount of citric acid added was changed to 153.6 g. When the transmission spectrum of this sol-like liquid was measured, the absorbance was low and almost completely transparent in the visible light region. Further, absorption similar to titanium oxide was observed in the ultraviolet. The particle size distribution measured was 4.14 nm. Further, the sol-like liquid was uniformly applied to a glass substrate using a spin coater, and dried with a dryer at 100 ° C. to obtain a transparent film. Furthermore, it was baked at 400 ° C. for 30 minutes in an air atmosphere in an electric furnace, and was adhered to a glass substrate. When the transmission spectrum of this glass substrate with a thin film was measured, it showed a transmittance of 95% or more in the visible region, and was almost completely transparent. In addition, an absorption similar to absorption specific to titanium oxide was observed in the ultraviolet. In order to measure the photocatalytic ability of the titanium-containing substance, a red ink fading test was performed in the same manner as in Example 1. Table 1 shows the results. Table 1 clearly shows red fading,
It was confirmed to have photocatalytic ability.

Example 3 The procedure of Example 1 was repeated, except that 60 g of tartaric acid was added instead of citric acid. The absorbance of the sol was the same as in Example 1. The average particle size is 3.5n.
m. Further, a film was formed on a glass substrate using the sol liquid. This was dried in air at 200 ° C. and brought into close contact. The transmission spectrum and the photocatalytic activity of this glass substrate with a thin film were the same as those in Example 1.

Example 4 The transparent sol prepared in Example 1 was applied to a coated steel plate and sintered at 400 ° C. for 15 minutes to form a titanium oxide transparent film. The pencil hardness of this coating film was 5H, and the result of the stripping test was 90/100.

EXAMPLE 5 The concentration of titanium tetrachloride in an aqueous solution of titanium tetrachloride was adjusted to TiO ₂
The conversion ratio of citric acid was 0.01, 1.0 and 10 (citric acid concentration /
A titanium-containing substance was prepared as a concentration ratio (molar ratio in terms of TiO ₂ ). The operation such as other conditions is the same as that of the first embodiment. The average particle diameter d ₅₀ of the produced ones is 1.10 n each.
m, 4.4 nm and 12.5 nm.

Comparative Example 1 The same operation as in Example 1 was carried out except that citric acid was not added. About 5 after adding titanium tetrachloride
Although min was a transparent state, it gradually began to become cloudy as the liquid temperature became about 60 ° C. or higher, and became almost a white liquid at about 90 ° C. or higher. When the particle size distribution was measured, the average particle size of the particles was 65 nm.

Comparative Example 2 Anatase type titanium oxide particles having a particle diameter of 7 nm were dispersed in water using an ultrasonic disperser so that the titanium oxide concentration was 2%. At this time, hydrochloric acid was added as a deflocculant to adjust the pH to 1, thereby obtaining a titanium oxide sol. When the particle size distribution was measured, the average particle size of the particles was 35 nm, but the sol was white. Table 1 shows the results of the photocatalytic activity.

[0021]

[Table 1]

[0022]

According to the production method of the present invention, it is possible to provide a titanium-containing substance and a titanium-containing coating liquid (sol) having an unprecedented high transparency while maintaining photocatalysis and activity.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a reaction tank used in the method of the present invention.

FIG. 2 shows wavelengths 200 to 7 of a liquid prepared according to Example 1.
The transmittance at 00 nm is shown.

FIG. 3 shows the transmittance of a film prepared by applying the liquid prepared in Example 1 on a glass substrate and drying the liquid.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction tank 2 Titanium tetrachloride aqueous solution 3 Reflux cooler 4 Stirrer 5 Thermometer 6 Heating device

Claims (5)

[Claims] 1. Even when heated to the boiling point, the wavelength is 450 to 70
A titanium-containing substance having a light transmittance of 85% or more at a thickness of 10 mm at 0 nm. 2. Even when heated to the boiling point, the wavelength is 450-70.
A titanium-containing coating liquid having a light transmittance of 85% or more at 0 nm and a thickness of 10 mm. 3. A hydrolysis method, wherein the hydrolysis of titanium tetrachloride is performed in the presence of a carboxylic acid. 4. A method for producing a titanium-containing substance, comprising hydrolyzing titanium tetrachloride in the presence of a carboxylic acid. 5. A method for producing a titanium-containing coating liquid, comprising hydrolyzing titanium tetrachloride in the presence of a carboxylic acid.