Method for forming titanium dioxide membrane and catalyst or the like having the titanium dioxide membrane

The present invention relates to a water-dispersed titanium oxide sol, a thin film of titanium oxide formed on a base material such as ceramics or plastic using the sol, specific titanium oxide particles, and a method for producing a water-dispersed titanium oxide sol. This titanium oxide thin film is transparent, has excellent photocatalytic action, and has good adhesion to a base material.

It is known that titanium dioxide (hereinafter referred to as titanium oxide) has three crystal phases of anatase, blue kite, and rutile type. In the case of the vapor phase method produced by a mixed combustion method of titanium tetrachloride and oxygen, the anatase type is produced and stable at the lowest temperature. When this is heat-treated and calcined, titanium oxide having a blue kite type structure can be obtained at 816 to 1040 ° C, and a rutile type structure can be obtained in the temperature range higher than that (Physical and Chemical Dictionary, 3rd edition, P.514 to 515).

In the liquid phase method, for example, Koemon Funaki, Industrial Chemistry Vol. 59, No. 11, P.1295 et al. Report in detail the crystal phase of titanium oxide produced by hydrolysis of an aqueous solution of titanium tetrachloride. .. According to this, it is concluded that rutile-type titanium oxide is mainly produced from the high-concentration liquid, and anatase-type titanium oxide is produced from the low-concentration side. He states that it was impossible to produce fine particles of titanium oxide in the liquid phase, which was a blue kite type. From these reports, it has been difficult to stably produce blue kite-type titanium oxide by the liquid phase method. As described above, if titanium oxide by the vapor phase method is heat-treated at a high temperature, it becomes blue kite-type titanium oxide, but since the particles grow due to the heat treatment, it has been difficult to obtain blue kite-type crystals with fine particles. It was.

On the other hand, regarding the method for producing titanium oxide sol, either crystalline or amorphous titanium oxide particles are dispersed in a dispersion medium, or a precursor of titanium oxide such as titanium alkoxide, titanium sulfate, or titanium tetrachloride is mixed in the dispersion medium. It is common to form a sol by a method such as summing or hydrolysis. Titanium oxide sol is used for producing titanium oxide powder, or is used for applying the sol to glass, plastic, or the like to form a thin film of titanium oxide on their surfaces. Titanium oxide is a photosemiconductor, and it is known that the smaller the particle size, the more transparent the titanium oxide and the better the photocatalytic function. In recent years, active research and development has been carried out on the photocatalytic function of titanium oxide. Methods of using this photocatalyst include antifouling by removing harmful substances, deodorization of malodorous gases such as ammonia, and sterilization of bacteria, but the form of titanium oxide varies from bulk particles, thin films, and sol depending on the purpose of use. Is. This photocatalytic function is often made exclusively into a thin film when further transparency is to be added. Therefore, titanium oxide is used as a thin film forming material in the form of a sol.

Regarding the photocatalytic capacity of titanium oxide, it is recognized that the anatase type has a larger capacity than the rutile type. The reason is due to the energy gap between the two, and there is a difference of about 0.2 eV between the rutile type and 3.23 eV for the anatase type (Ceramics 31 (1996) No.10, P.817). Due to this energy difference, anatase-type titanium oxide having a high energy gap is preferably used as an optical semiconductor. However, with regard to the blue kite type, there have been few examples of extracting the elemental substance itself, and it has been conventionally possible to obtain it as fine particles having a high specific surface area that can be used as a photosemiconductor (photocatalyst) at a high temperature. It was impossible because the particles were sintered due to the production of.

Recently, as a form of use of a thin film, a titanium oxide sol is applied to a glass tube of a lighting fixture, for example, a fluorescent lamp or its cover to form a thin film, and when an organic substance such as oil smoke adheres to the glass tube or cover by photocatalysis, it is used. A method of disassembling and preventing the glass tube and the cover from becoming dirty has been proposed. However, when a thin film is formed using the sol obtained by the above method, there are few that can be made into a highly transparent thin film, and in particular, a blue kite type titanium oxide thin film is used as a photocatalyst for lighting equipment and the like. What was there has not been known in the past.

<p> When a titanium oxide thin film is formed on glass, plastic, or other base material and used as a photocatalyst, the thin film is required to have high catalytic activity. Since the photocatalytic action is a reaction on the surface of the particles, it is preferable that the particles have a high surface area and that the particles have good crystallinity in order to have high activity. Further, when forming a thin film on a lighting fixture or the like, the thin film needs to be transparent. In order to improve the transparency, it is desirable that the titanium oxide is fine particles and monodisperse as in the case of catalytic activity. Conventionally, these problems have been dealt with exclusively by refining anatase-type titanium oxide. Further, when the titanium oxide thin film is formed on the base material, the adhesion between the thin film and the base material must be improved so that the thin film does not easily peel off.</p><p> With the conventional method of hydrolyzing titanium tetrachloride, it has been difficult to produce a titanium oxide sol having very small particle size, good crystallinity, and good transparency when formed into a thin film. Titanium oxide in the sol is excellent in powder characteristics such as very small fine particles in the hydrolysis of the titanium alcoside compound, but alcohol is contained in the sol, and when it is made into a thin film and fired, it is safe for explosions and the like. There is a problem. In addition, large explosion-proof equipment is required to prevent explosion, which is economically disadvantageous. Moreover, the titanium alcoside compound is much more expensive than titanium tetrachloride. In the present invention, when water-dispersed titanium oxide sol is applied to various base materials to form a thin film of titanium oxide on the surface of the base material, the thin film has excellent photocatalytic function and transparency, and the adhesion between the thin film and the base material is good. It is an object of the present invention to provide a titanium oxide sol and fine blue kite type titanium oxide particles.</p>

<p> As a result of various studies on a thin film of titanium oxide formed from titanium oxide sol, the present inventors have identified chlorine ions contained in the titanium oxide sol as being involved in the transparency of the thin film, the adhesion between the base material and the thin film, and the like. It was found that the titanium oxide sol having a chlorine ion concentration improves these characteristics and that the blue kite type having a large energy gap is particularly excellent in the photocatalytic function of titanium oxide, and this invention was made.</p><p> The present invention basically comprises the following inventions. (1) Water-dispersed titanium oxide sol containing 50 to 10,000 ppm of chlorine ions as a chlorine element. (2) The average particle size is 0.5 μm or less and the specific surface area is 20 m.² Water-dispersed titanium oxide sol in which blue kite-type titanium oxide particles of / g or more are dispersed. (3) The water-dispersed titanium oxide sol according to (1) or (2) above, which contains an adhesive. (4) The average particle size is 0.5 μm or less and the specific surface area is 20 m.² Blue kite type titanium oxide particles of / g or more. (5) A titanium oxide thin film formed on the surface of a base material using the water-dispersed titanium oxide sol of (1) to (3) above. (6) A method for producing an aqueous-dispersed titanium oxide sol, which comprises producing an aqueous-dispersed titanium oxide sol by hydrolysis of titanium tetrachloride and adjusting chlorine ions in the sol to 50 to 10,000 ppm as a chlorine element. (7) A method for producing an aqueous dispersion sol of blue kite-type titanium oxide particles, which comprises adding titanium tetrachloride to hot water at 75 ° C to 100 ° C and hydrolyzing it in the temperature range of the boiling point of the solution at 75 ° C to solution. .. (8) A method for producing blue kite-type titanium oxide particles, which comprises filtering and drying the aqueous dispersion sol of titanium oxide particles according to (7) above.</p>

<p> The water-dispersed titanium oxide sol of the present invention is excellent in photocatalytic action by making the thin film transparent when it is applied to various substrates to form a thin film of titanium oxide. In particular, when titanium oxide is of the blue kite type, it has a high photocatalytic effect. Further, the thin film has high hardness and excellent adhesion to the base material. Therefore, the thin film on the base material is durable, and if this thin film is used for, for example, a glass tube of a luminaire or a cover of a luminaire, the photocatalytic action is maintained for a long period of time without blocking light. Since the water-dispersed titanium oxide sol of the present invention can be produced in an aqueous system using titanium tetrachloride as a raw material, the raw material is inexpensive, and the sol can easily form a thin film, which is economically advantageous.</p>

The first of the water-dispersed titanium oxide sol of the present invention is that the thin film formed from the sol not only has an excellent photocatalytic function, but also has particularly improved adhesion and transparency to the substrate. The water-dispersed titanium oxide sol contains chlorine. Ions are contained as a chlorine element in an amount of 50 to 10,000 ppm, preferably 100 to 4,000 ppm. In the method of hydrolyzing titanium tetrachloride to obtain an aqueous dispersion titanium oxide sol, hydrogen chloride is produced by the reaction. And in the sol, it is almost dissociated into chlorine ions and hydrogen ions. In general, most of this hydrogen chloride escapes to the outside of the system in the hydrolysis reaction under heating. In addition, if hydrogen chloride is contained in the sol, it is considered that various obstacles occur when titanium oxide powder is obtained from the sol or a titanium oxide thin film is obtained, and hydrogen chloride is contained in the sol to a certain extent or more by the hydrolysis reaction. If it remained, it was usually dechlorinated to prevent hydrogen chloride from being contained in the sol as much as possible. However, conventionally, the influence of chlorine ions in the sol on the thin film characteristics of titanium oxide has not been considered, and there has been no technique for controlling chlorine ions in the sol from this viewpoint.

In the water-dispersed titanium oxide sol, if the chlorine ion contained is less than 50 ppm as a chlorine element, the adhesion of the titanium oxide thin film formed on the base material to the base material is not sufficient. In particular, when the thin film is fired, the adhesion varies depending on whether or not chlorine ions are contained in an amount of 50 ppm or more. In the present invention, this adhesion is represented by the peel strength of the thin film from the substrate and the hardness of the thin film. On the contrary, the amount of chlorine ions in the sol increases, and if the chlorine element exceeds 10,000 ppm, the transparency of the thin film is inferior. A particularly preferable range in the above range is 100 to 4,000 ppm.

The action of the above chlorine ions is not clear, but since the electrical repulsion between the titanium oxide particles increases in the titanium oxide sol, the dispersibility of the particles is improved, and the transparency and peeling strength are improved. It is presumed that such a result was brought about. The finer the titanium oxide particles of the water-dispersed titanium oxide sol, the higher the photocatalytic action of the titanium oxide thin film and the better the transparency. Further, it is preferably crystalline from the viewpoint of catalytic action. However, since obtaining very fine titanium oxide particles is difficult in production, the average particle size of the titanium oxide particles in the sol is preferably in the range of 0.01 to 0.1 μm.

The second water-dispersed titanium oxide sol of the present invention enhances the photocatalytic function and transparency of the thin film formed from the sol, has an average particle size of 0.5 μm or less, preferably 0.01 to 0.1 μm, and a specific surface area. 20m² A sol in which blue kite-type titanium oxide particles of / g or more are dispersed in water. The blue kite type titanium oxide particles have an energy gap of 3.23 eV or more. Regarding the particle size of titanium oxide, it is preferable that the titanium oxide particles in the sol have an average particle size of 0.5 μm or less, more preferably 0.01 to 0.1 μm, in order to enhance the transparency of the titanium oxide thin film. Even if the specific surface area is large, if the primary particles are agglomerated in the sol, they will not become transparent when applied to form a thin film.

Conventionally, the only way to obtain a blue kite type is by heat treatment of anatase type titanium oxide as described above, and when the blue kite type titanium oxide particles obtained by heat treatment are to be made into a thin film, the particle size is determined by heat treatment. It was not used at all for thin film formation because it grew large due to sintering. The sol in which this blue kite-type titanium oxide is dispersed in water can also contain 50 to 10,000 ppm of chlorine ions as a chlorine element as described above. As a result, the thin film formed from the sol not only has an excellent catalytic function, but also has improved adhesion to the base material. In the sols of the first and second inventions described above, if the concentration of titanium oxide particles in the sol is too high, the particles aggregate and the sol becomes unstable. Further, if the concentration of the titanium oxide particles is too low, there arises a problem that, for example, it takes time to apply the sol when forming a thin film. From these facts, the concentration (content) of titanium oxide particles in the water-dispersed titanium oxide sol is particularly suitable at 0.05 to 10 mol / liter.

The water-dispersed titanium oxide sol of the present invention can obtain titanium oxide particles by filtering, washing with water, and drying the sol. The particles obtained from the blue kite-type titanium oxide sol have an average particle size of 5 μm or less, preferably 0.01 to 0.1 μm, and a specific surface area of 20 m.² It is more than / g. And the energy gap is more than 3.23 eV. When the water-dispersed titanium oxide sol is used for forming a thin film, it is preferable to add a small amount, for example, about 10 to 10,000 ppm of a water-soluble polymer to the sol in order to improve the film-forming property of the coating film. As the water-soluble polymer, polyvinyl alcohol, methyl cellulose, ethyl cellulose, CMC, starch and the like are suitable.

The water-dispersed titanium oxide sol of the present invention can be applied to a base material such as various materials and molded bodies to form a titanium oxide thin film on the surface of the base material. As the base material, ceramics, glass, metal, plastic, wood, paper and the like can be targeted with almost no restrictions. A catalyst carrier made of alumina, zirconia, or the like can be used as a base material, and a titanium oxide thin film catalyst can be supported on the catalyst carrier and used as a catalyst. Further, if a titanium oxide thin film is formed on the glass of a lighting fixture 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 removed without blocking light. It can be disassembled and is effective in preventing stains on the glass and cover. In addition, if a titanium oxide thin film is formed on building glass or wall material, it is possible to prevent stains in the same way, so it can be used for window materials and wall materials of high-rise buildings, etc., and cleaning work is not required. Helps reduce building management costs. To apply the water-dispersed titanium oxide sol to the base material, a method of immersing the base material in the sol, a method of spraying the sol on the base material, a method of applying the sol to the base material with a brush, or the like is adopted. The appropriate amount of sol applied is 0.01 to 0.2 mm in terms of liquid thickness. A thin film can be obtained by drying after coating to remove water, and the film can be used as it is as a catalyst or the like.

When the base material is heat-resistant such as metal or ceramics, for example, glass, a titanium oxide thin film can be formed and then fired, whereby the thin film adheres to the base material more strongly and the hardness of the thin film is increased. The firing temperature is preferably 200 ° C. or higher. The upper limit of the firing temperature is not particularly limited and may be set according to the heat resistance of the base material. However, even if the temperature is raised too high, the hardness of the thin film and the adhesion to the base material do not increase, so 800 ° C. Up to the rank is appropriate. In the case of blue kite type titanium oxide, it is preferable to sinter at a temperature of 700 ° C. or lower in order to maintain its crystal form. The firing atmosphere is not particularly limited and may be in the atmosphere. The firing time is not particularly limited, and may be, for example, in the range of 1 to 60 minutes. The thickness of the titanium oxide thin film obtained by firing is about 0.05 to 1.0 μm in the case of the above-mentioned coating amount. Further, in order to make the transparent thin film of the present invention stronger and to enhance the adhesive force to the substrate, an appropriate adhesive can be added to the water-dispersed titanium oxide sol. For example, an organic silica compound such as alkyl silicate is suitable. The amount added is SiO for titanium oxide in the titanium oxide sol of the present invention.₂ In terms of conversion, it may be about 1 to 50% by weight. When the addition amount is less than 1% by weight, the effect of adding the adhesive is low. On the other hand, if it exceeds 50% by weight, the adhesive strength to the substrate becomes very strong, but it is not preferable because the titanium oxide particles are completely wrapped in the adhesive and the photocatalytic ability is lost. In this case, the adhesive may be selected depending on the nature of the adhesive, whether it is mixed immediately before film formation or mixed with the sol in advance, and there is no problem in the effect of the present invention in either case. The thin film containing this adhesive does not have to be fired, but can be fired.

The titanium oxide thin film produced by using the titanium oxide sol according to the present invention is commonly crystalline, the titanium oxide fine particles are very fine particles, does not contain impurities, and the titanium oxide fine particles are Since it is dispersed as close as possible to the primary particles, it has high photocatalytic capacity and transparency, and especially when titanium oxide is of the blue kite type, the catalytic capacity is even higher.

Next, the invention of the method for producing a sol will be described. The first aqueous dispersion titanium oxide sol of the present invention may contain the above-mentioned amount of chlorine ions, and the production method thereof is not particularly limited. For example, it is also possible to hydrolyze the alkoxide compound of titanium to obtain an aqueous dispersion titanium oxide sol containing a small amount of alcohol, and add HCl or the like to the water-dispersed titanium oxide sol to bring the chlorine ion concentration within the above range. However, it is preferable to use titanium tetrachloride, which produces hydrogen chloride by hydrolysis. The second invention is obtained by hydrolyzing titanium tetrachloride under specific conditions. It is preferable that the hydrogen chloride produced in these hydrolysiss is prevented from escaping from the reaction vessel and remains in the sol as much as possible. When titanium tetrachloride is hydrolyzed while the generated hydrogen chloride is released, the particle size of titanium oxide in the sol does not easily decrease, and the crystallinity is not good.

Hydrogen chloride generated by hydrolysis may be suppressed even if its escape is not completely prevented. The method is not particularly limited as long as it can be suppressed, and for example, it can be pressurized, but the easiest and most effective method is to install a reflux condenser in the hydrolysis reaction vessel to hydrolyze. Is a way to do. This device is shown in Figure 1. In the figure, 1 is a reaction tank filled with an aqueous solution 2 of titanium tetrachloride, and a reflux condenser 3 is installed therein. 4 is a stirrer, 5 is a hygrometer, and 6 is a device for heating the reaction vessel. Water and hydrogen chloride vapor are generated by the hydrolysis reaction, but 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.

If the concentration of titanium tetrachloride in the aqueous solution of titanium tetrachloride to be hydrolyzed is too low, the productivity will be poor, the efficiency will be low when forming a thin film from the water-dispersed titanium oxide sol that is produced, and if the concentration is too high, the reaction will be intense. , The obtained titanium oxide particles are difficult to become fine and the dispersibility is also deteriorated, so that it is not suitable as a transparent thin film forming material. Therefore, it is not preferable to hydrolyze a sol having a high concentration of titanium oxide and dilute it with a large amount of water to adjust the concentration of titanium oxide to 0.05 to 10 mol / liter as described above. When the sol is formed, the concentration of titanium oxide should be in the above range, and for that purpose, the concentration of titanium tetrachloride in the aqueous solution of titanium tetrachloride to be hydrolyzed is not much different from the concentration of titanium oxide produced. That is, it may be approximately 0.05 to 10 mol / liter, and if necessary, the concentration may be adjusted to 0.05 to 10 mol / liter by adding or concentrating a small amount of water in the subsequent steps.

The temperature for hydrolysis is preferably 50 ° C. or higher, preferably in the range up to the boiling point of the titanium tetrachloride aqueous solution. Below 50 ° C, the hydrolysis reaction takes a long time. Hydrolysis is carried out by raising the temperature to the above temperature and holding it for about 10 minutes to 12 hours. This retention time may be shorter as the hydrolysis temperature is higher. To hydrolyze the aqueous solution of titanium tetrachloride, a mixed solution of titanium tetrachloride and water may be heated to a predetermined temperature in the reaction vessel, or water may be preheated in the reaction vessel, and titanium tetrachloride is added thereto. May be added to bring the temperature to a predetermined temperature. This hydrolysis generally gives titanium oxide, which is a mixture of blue kite type, anatase type and / or blue kite type. To increase the content of blue kite-type titanium oxide, water is preheated to 75 to 100 ° C in a reaction vessel, titanium tetrachloride is added to this, and the boiling point of the solution is 75 ° C to the boiling point of the solution. A method of hydrolysis in a temperature range is suitable. Of the total titanium oxide produced by this method, the amount of blue kite-type titanium oxide can be 70% by weight or more.

The rate of temperature rise of the titanium tetrachloride aqueous solution in hydrolysis is preferably 0.2 ° C / min or more, more preferably 0.5 ° C / min or more, because the obtained particles become finer as the rate of temperature rise is faster. By this method, the titanium oxide particles in the sol have an average particle size of 0.5 μm or less, preferably 0.01 to 0.1 μm, and have good crystallinity. The method for producing the water-dispersed titanium oxide sol of the present invention is not limited to the batch method, and the reaction solution is taken out on the opposite side of the charging port while continuously charging titanium tetrachloride and water in a continuous tank, and the dechlorination treatment is continued. A continuous method is also possible. In the first invention, the produced sol is adjusted so that chlorine ions become 50 to 10,000 ppm by dechlorination treatment or by adding water, dehydration, etc. within a range that does not hinder. Further, also in the second invention, if necessary, the chlorine ion can be adjusted to 50 to 10,000 ppm as described above.

The dechlorination treatment can be carried out by general known means, such as electrodialysis, ion exchange resin, and electrolysis. The degree of dechlorination may be based on the pH of the sol. When the chlorine ion is 50 to 10,000 ppm, the pH is about 5 to 0.5, and when the chlorine ion is 100 to 4,000 ppm, which is the preferable range, the pH is about 4-1. is there. It is also possible to add an organic solvent to the aqueous dispersion sol of the present invention and disperse the titanium oxide particles in a mixture of water and the organic solvent. When forming a thin film of titanium oxide from the water-dispersed titanium oxide sol of the present invention, it is preferable to use the sol produced by the hydrolysis reaction as it is, and a titanium oxide powder is produced from this sol, dispersed in water, and the sol is used. It is not a preferable method to use it. Titanium oxide particles have high surface activity, and the finer the particles, the higher the activity, making it extremely difficult to disperse in water, that is, they become aggregates, and the thin film produced from this is inferior in transparency. This is because the photocatalytic action is also reduced.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to the Examples. (Examples 1 to 6) Water was added to titanium tetrachloride (purity 99.9%), and the solution was adjusted so that the titanium tetrachloride concentration was 0.25 mol / liter (titanium oxide equivalent 2% by weight). At this time, an appropriate cooling device such as ice cooling was provided so that the temperature of the aqueous solution would not rise above 50 ° C. Next, 1 liter of this aqueous solution was placed in a reaction vessel equipped with a reflux condenser as shown in FIG. 1, heated to near the boiling point (104 ° C), and held for 60 minutes for hydrolysis. After cooling the obtained sol, residual chlorine generated in the reaction was removed by electrodialysis to obtain the chlorine ion concentration shown in Table 1. Electrodialysis was performed using an electrodialysis machine G3 manufactured by Asahi Kasei Kogyo Co., Ltd. while monitoring the pH of the sol solution. To each of the water-dispersed titanium oxide sol prepared with chlorine ions, 1,000 ppm of polyvinyl alcohol, which is a water-soluble polymer, was added as an auxiliary agent for film formation with respect to the weight of the sol solution. This sol was stable when the chlorine ion content was 50 to 10,000 ppm, and no precipitation of titanium oxide fine particles was observed even after 1 day or more. However, in the case of chlorine ion of 30 ppm, agglutination of titanium oxide was observed in the sol, and in the case of 15,000 ppm, the thin film using it showed a pale white color. When the particles in the sol were observed with a transmission electron microscope, the average particle size of the particles was 0.015 to 0.018 μm, and when the particles were identified by an X-ray diffractometer, they were crystalline titanium oxide.

(Comparative Examples 1 and 2) A sol was obtained in the same manner as in Examples except that the chlorine ion concentration in the water-dispersed titanium oxide sol was 30 ppm (Comparative Example 1) and 15,000 ppm (Comparative Example 2).

Using the sol of Examples and Comparative Examples, it was applied on a glass plate by dip coating, dried, and then heat-treated in air at 500 ° C. for 1 hour to obtain a titanium oxide thin film. The thickness of the titanium oxide thin film after the heat treatment was 0.15 μm. As a result of examining the crystal form of titanium oxide by Rietveld analysis of the powder X-ray diffraction pattern, the one before heat treatment was a mixture of about 50% by weight of anatase type and about 50% by weight of rutile type, and the temperature was 800 ° C or higher. When heated, it became a rutile type alone.

Evaluation of film formation The light transmittance, photocatalytic capacity, and adhesion to the quartz glass plate of the titanium oxide thin film obtained from the water-dispersed titanium oxide sol of each of the examples and comparative examples were measured. The light transmittance is measured by setting a titanium oxide thin film formed on a quartz glass plate in a spectrophotometer manufactured by JASCO Corporation and continuously changing the wavelength from 700 to 200 nm. It was measured. The light transmittance at 550 nm is expressed as the light transmittance in the present invention. The results are shown in Table 1. The method of decomposing oxalic acid is to prepare a reaction vessel from a fused silica glass plate with a titanium oxide thin film, put 5 mmol / liter of oxalic acid in it, irradiate it with a 100 W mercury lamp while blowing oxygen, and 4 The amount of oxalic acid decomposed after hours was determined by redox titration of potassium permanganate. The results are shown in Table 1. The adhesion between the quartz glass plate and the thin film after firing was determined by the pencil hardness test method and the goblin peeling test method (JIS K 5400). The results are shown in Table 1.

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(Examples 7 and 8, Comparative Examples 3 and 4) As in Examples 1 to 6 and Comparative Examples 1 and 2, a water-dispersed titanium oxide sol was used, and a plastic (polyethylene terephthalate (PET)) plate was used as a base material. A titanium oxide thin film was formed in the same manner as in the above Examples and Comparative Examples except that a coating film of the titanium oxide sol was formed and dried at 100 ° C. instead of firing, and the characteristics of the thin film were evaluated. The results are shown in Table 2.

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(Example 9) 954 ml of distilled water is placed in a reaction vessel equipped with a reflux condenser as shown in FIG. 1 and heated to 95 ° C. While maintaining the stirring speed at about 200 rpm, 46 ml of an aqueous solution of titanium tetrachloride (Ti content: 16.3%, specific gravity 1.59, purity 99.9%) was added dropwise to the reaction vessel at a rate of about 5 ml / min. At this time, care was taken not to lower the temperature of the reaction solution. As a result, the titanium tetrachloride concentration was 0.25 mol / l (titanium oxide equivalent 2% by weight). Immediately after the dropping, the reaction solution began to become cloudy in the reaction vessel, but it was kept at the same temperature, and after the dropping was completed, the temperature was further raised and heated to near the boiling point (104 ° C), and held in this state for 60 minutes. The reaction was completely terminated. After cooling, residual chlorine generated by the reaction is removed by electrodialysis to set pH = 2 (chlorine ion 600 ppm), and then polyvinyl alcohol, which is a water-soluble polymer, is added as a film-forming auxiliary to 0.1 with respect to the titanium oxide content. % Was added to obtain a titanium oxide sol. This sol was stable, and no sedimentation of the formed titanium oxide fine particles was observed even after 30 days or more.

After filtering the sol, it was taken out as a powder using a vacuum dryer at 60 ° C. As a result of identification by the above-mentioned X-ray diffraction method, titanium oxide was 96.7% by weight for blue kite type, 0.9% by weight for rutile type, and anatase type. Was 2.4% by weight. Moreover, when these fine particles were observed with a transmission electron microscope, the average particle size of the primary particles was 15 nm. Furthermore, the specific surface area of these fine particles is 100 m by the BET method.² It was / g. On the other hand, the sol was uniformly applied to a quartz glass substrate using a spin coater and dried in a 100 ° C dryer to obtain a transparent film. The transmittance of this quartz glass substrate with a thin film was 95% or more in the visible part and was completely transparent. Furthermore, absorption was observed in the ultraviolet, and the energy gap obtained from the basal absorption edge was 3.75 eV. The equation for obtaining the energy gap at this time is shown in Eq. (1). λ = 1239 / Eg (1) λ: Basic absorption edge (nm) Eg: Energy gap (eV)

(Example 10) Titanium oxide was precipitated in the same manner as in Example 9 except that the reaction temperature at which the aqueous titanium tetrachloride solution was dropped was set to 75 ° C. When these particles were similarly identified by an X-ray diffractometer, blue kite-type titanium oxide was 75% by weight, and rutile-type titanium oxide was 25% by weight. Moreover, when these fine particles were observed with a transmission electron microscope, the average particle size of the primary particles was 10 nm. Furthermore, the specific surface area of these fine particles is 120 m by the BET method.² It was / g. A transparent thin film was prepared by applying a titanium oxide sol having a pH of 1 (chlorine ion 3000 ppm) to a glass substrate by electrodialysis and firing at 500 ° C. When this thin film was measured by thin film X-ray diffraction, it was a mixed titanium oxide of blue kite type and rutile type as described above. Further, from the transmittance spectrum of the glass substrate with the thin film, the transmittance was 95% or more in the visible part, and it was completely transparent. Furthermore, the energy gap obtained from the basal absorption edge by ultraviolet rays was 3.30 eV.

(Example 11) In Example 9, the same was applied except that the amounts of water and the aqueous solution of titanium tetrachloride were 862 ml and 138 ml, respectively. After adjusting the pH to 2 by electrodialysis, an equal amount of ethyl alcohol was added to this sol to prepare an organic solvent mixed sol. This was applied onto a polyethylene sheet and dried to obtain a titanium oxide thin film. As a result of the analysis, the crystal form was a mixture of 85% by weight of the blue kite type and 15% by weight of the rutile type, and the particle size was 15 nm. The transmittance of the visible part was 80% or more, and the energy gap was 3.51 eV.

(Comparative Example 5) Anatase-type titanium oxide particles having a primary particle diameter of 7 nm were used and dispersed in water using an ultrasonic disperser so that the titanium oxide concentration became a 2% aqueous solution as in Example 9. It was. At this time, hydrochloric acid was added as a gelatinizing agent to adjust the pH to 1, and the same operation was performed thereafter to prepare a titanium oxide sol. Similarly, a transparent thin film was prepared by applying it on a glass substrate and drying it at 100 ° C.

(Comparative Example 6) A titanium oxide sol was obtained in the same manner as in Comparative Example 5 except that rutile-type titanium oxide particles having a primary particle size of 50 nm were used. As in Comparative Example 5, sedimentation of titanium oxide fine particles was observed in this sol, so that the sol was redispersed using hydrochloric acid as a defibrating agent to form a film. In this titanium oxide sol, fine particles of titanium oxide settled with the passage of time. Since the photocatalytic ability was not recognized in the film formed with the supernatant liquid after sedimentation, the sol was dispersed with an ultrasonic disperser immediately after preparation, and then the film was formed on the glass substrate by the same method as in Example 9, and the photocatalytic ability was obtained. Was evaluated.

Evaluation Results of Formed Thin Films The photocatalytic capacity of the titanium oxide thin films obtained from the titanium oxide sol of Examples 9 to 11 and Comparative Examples 5 and 6 was determined by the above-mentioned oxalic acid decomposition method. The results are shown in Table 3.

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In Comparative Example 5, agglomerates of titanium oxide were formed on the glass substrate and the surface was non-uniform. In Comparative Example 6, since a transparent titanium oxide thin film could not be obtained, the photocatalytic ability was not evaluated.

(Example 12) The same reaction as in Example 9 was carried out, and titanium tetrachloride (titanium oxide equivalent 2% by weight) having a concentration of 0.25 mol / l was hydrolyzed. Next, this reaction solution was concentrated to a titanium oxide concentration of 10% by weight, residual chlorine was removed by electrodialysis, pH = 2 (chlorine ion concentration of about 600 ppm), and then tetramethyl orthosilicate Si (OCH) was used as an adhesive.₃ )₄ The titanium oxide against SiO₂ It was added so as to be 5% by weight in terms of conversion to obtain a titanium oxide sol.

(Example 13) After performing the same operation as in Example 12 until concentration and electrodialysis, the mixture was diluted 5-fold with isopropyl alcohol, and then tetraethyl orthosilicate Si (OC) was used as an adhesive.₂ H₅ )₄ The titanium oxide against SiO₂ It was added so as to be 20% by weight in terms of conversion to obtain a titanium oxide sol mixed with an organic solvent.

(Example 14) In Example 12, tetrapropyl orthosilicate Si (OC) was used instead of tetraethyl orthosilicate.₃ H₇ )₄ The titanium oxide against SiO₂ It was added so as to be 35% by weight in terms of conversion to obtain a titanium oxide sol.

(Comparative Example 7) In Example 14, tetrapropyl orthosilicate Si (OC)₃ H₇ )₄ The titanium oxide against SiO₂ It was added so as to be 55% by weight in terms of conversion to obtain a titanium oxide sol.

Evaluation Results of the Formed Thin Film The titanium oxide sol of Examples 12 to 14 and Comparative Example 7 was uniformly applied to a quartz glass plate using a spin coater, left at room temperature, and dried to obtain a transparent film. The transmittance of this quartz glass plate with a film was 95% or more in the visible part and was completely transparent. Moreover, the pencil hardness test and the adhesion test of the quartz glass plate with a transparent film were evaluated by the above-mentioned method. The results are shown in Table 4.

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<figref num="1">It is the schematic sectional drawing of the reaction tank used in the method of this invention.</figref>

Code description

1 ... Reaction tank 2 ... Titanium tetrachloride aqueous solution 3 ... Reflux condenser 4 ... Stirrer 5 ... Thermometer 6 ... Heating device