Production of liquid dispersion of crystalline titanium dioxide grains

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a method for producing a crystalline titanium oxide particle dispersion liquid, and in particular, produces a crystalline titanium oxide particle dispersion liquid useful as a titanium oxide coating agent used for forming a titanium oxide film on a substrate. Regarding how to do it.

【0002】

[Conventional technology]

The titanium oxide film is formed by a coating method in which a titanium oxide powder slurry or an aqueous solution of titanium chloride or titanium sulfate is applied to a substrate and then fired, or a sol-gel method in which a sol prepared by hydrolysis of a metal alkoxide is applied to a substrate and then fired. , Sputtering method of sputtering an oxide target in a high vacuum to form a film on a substrate, CVD method of volatilizing an organic metal compound or halide and decomposing it in a heating furnace to form a film on the substrate, solid particles There is plasma firing which melts in plasma generated in the atmosphere and irradiates the surface of the substrate. Of these, the method of using a coating liquid as a method for forming the titanium oxide film is said to be simple and highly practical.

【0003】

Although the coating method using titanium oxide powder is simple, it is difficult to obtain a dense and good-adhesive film, and the formation of a titanium oxide film generally requires a high synthesis temperature, so that it has heat resistance to withstand the synthesis temperature. It is necessary to use the above-mentioned substrate, and there are restrictions on the types of substrates that can be applied. Further, an acid or an appropriate organic dispersant is generally used to obtain a dispersed liquid of the titanium oxide fine particles, and there is a drawback that a harmful halogen compound or the like is generated by firing. Further, the method of applying and firing an aqueous solution of titanium chloride, titanium sulfate or the like produces a harmful halogen compound, and the firing temperature also requires several hundred degrees or more.

【0004】

In addition, commercially available titanium oxide sol produced by the sol-gel method can be coated and impregnated, can be coated over a large area, and can be synthesized at low temperature, and has many industrial advantages. Since it had to be synthesized using a metal, the raw material was expensive, and the raw material was chemically unstable and was easily affected by temperature control and atmosphere, which made it difficult to handle. In addition, the sol-gel method contains acids and organic substances in the raw material sol, so heating at 400 ° C or higher is required to remove it by firing, which is not suitable for materials that are easily attacked by acids. There was a problem that it was easy to become.

【0005】

In addition, the sol-gel method is complicated and requires the use of an organic solvent, and acids, alkalis, or organic substances are added to the titanium oxide sol produced by the sol-gel method, which causes a problem of corrosion of the material to be coated. there were. In addition, a temperature of 400 ° C. or higher is required to decompose organic substances, and there are drawbacks such as the formation of harmful halides and nitrogen oxides during heating and firing.

【0006】

As described above, it is difficult to prepare a dense crystalline titania film at a low temperature by the conventional method, and it is necessary to decompose and eliminate organic substances, acids and the like by heat treatment in the sol-gel method which can be prepared at a relatively low temperature. This also causes the film to become more porous, and the heat treatment temperature had to be relatively high in order to produce a dense film. In addition, these auxiliaries have a drawback of producing harmful substances such as nitrogen oxides and organic gases by heat treatment.

【0007】

In contrast to these methods, it is known that when a titanium oxide film is formed from peroxotitanium hydrate, a film having good properties can be formed at a relatively low temperature. Peroxotitanium hydrate is produced in the form of solid precipitate by adding hydrogen peroxide solution directly to a solution of titanium tetrachloride, titanium sulfate, etc. to generate peroxotitanium hydrate ion, which is condensed to form a solid precipitate. Is known to be. In addition, peroxotitanium hydrate ions are generated as polynuclear ions containing two or more titanium atoms at a pH of 1 or higher, and gradually condense at room temperature to precipitate and precipitate. Therefore, it is difficult to use it as a coating agent for titanium oxide at a pH of 1 or more, and therefore, the types of substrates to which a strongly acidic coating agent having a pH of 1 or less can be applied are limited. In addition, there is also a problem that the contained halogen, sulfur and the like generate harmful substances such as hydrogen halide and sulfur oxide by heat treatment.

【0008】

Further, in order to prepare a high-purity titanium oxide film, hydrogen peroxide solution is directly added to or dissolved in titanium hydride or alkoxy titanium to dissolve it, and titanium hydrogen peroxide, that is, a substance considered to be peroxotitanium hydrate. Is proposed in Japanese Patent Application Laid-Open No. 62-252319. However, these titanium raw materials are not stable, and when a hydrogen peroxide solution is applied, a considerable exothermic reaction occurs, which has a drawback that adverse effects such as thermal decomposition of the raw materials and products occur. Therefore, when mass production is attempted, the peroxotitanic acid produced polymerizes and becomes extremely thickened due to insufficient cooling, and in extreme cases, the particles grow to the extent that they block the transmission of light. When used as a coating agent, it causes a decrease in film adhesion and density.

【0009】

Further, a method for producing an aqueous solution considered to be peroxotitanium hydrate described as a titanyl ion hydrogen peroxide complex or titanic acid by adding a hydrogen peroxide solution to a hydroxide-containing titanium gel or sol is described in JP-A. It is described in Japanese Patent Application Laid-Open No. 63-35419 and Japanese Patent Application Laid-Open No. 1-224220. However, when hydrogen peroxide solution is added directly to titanium hydroxide, peroxolation and solution formation occur at the same time, which causes a large amount of heat generation and requires sufficient stirring and cooling. If it cannot be cooled sufficiently, there is a problem that thickening occurs, condensation occurs, the polymer grows as particles, and the polymer may become turbid.

【0010】

In addition, when preparing a gel or sol of titanium hydroxide-containing, a basic substance such as ammonia is added, but since the adsorption of titanium hydroxide is instantaneously generated, cations such as ammonium ions and chlorine ions which are impurities are used. It becomes easier to take in and adsorb the anions of. In particular, the presence of anionic impurities such as chlorine ions and sulfate ions promotes the condensation of peroxotitanium hydrate produced after the addition of the hydrogen peroxide solution, and a transparent aqueous solution may not be obtained. Further, it is difficult to completely remove impurities even if the hydrous titanium is washed with distilled water, which has been a big problem for stable production of peroxotitanium hydrate.

【0011】

Further, in JP-A-9-71418 and JP-A-10-67516, the present inventor obtained a coating agent in which anatase ultrafine particles were precipitated by heating peroxotitanium hydrate, whereby adhesion was obtained. Proposes that it is possible to form a good crystalline titanium film. With these methods, it is possible to form a crystalline titania film with better adhesion than conventional methods, but when the residual amount of cations such as ammonium ions is large, peroxotitanium hydration When an aqueous solution of an aqueous solution is heated to prepare an anatase sol, decomposition of the peroxo group is less likely to occur, the size of the particles becomes large, and the adhesion or density may be inferior when used as a coating agent. It was.

【0012】

[Problems to be Solved by the Invention]

The present invention improves the conventional problems and provides a new method for producing crystalline titanium oxide particles, which is also useful as a coating agent for forming a titanium oxide film. That is, when an aqueous solution of peroxotitanium hydrate is prepared with hydrogen peroxide solution, the adhesion that occurs when used as a coating agent due to condensation due to thermal influence in the production process or excessive growth of particles, etc. An object of the present invention is to prevent a decrease in density, and an object of the present invention is to obtain crystalline titanium oxide particles capable of forming a titanium oxide coating film having good adhesion and a high density.

【0013】

[Means for solving problems]

In the present invention, in the method for producing crystalline titanium oxide particles, a peroxotitanium complex is formed by adding a hydrogen peroxide solution to a titanium-containing raw material aqueous solution, and then the solution obtained by adding a basic substance is left to stand. After forming a precipitate of a polymer of peroxotitanium hydrate, at least the dissolved components other than water derived from the aqueous solution of the titanium-containing raw material are removed, and then heated at a temperature of 70 ° C. or higher without separating water. This is a method for producing a crystalline titanium oxide particle dispersion liquid. This is the method for producing the above-mentioned crystalline titanium oxide particle dispersion liquid, which also removes dissolved components other than water derived from the basic substance added for hydrate formation. This is the method for producing the above-mentioned crystalline titanium oxide particle dispersion liquid, in which the dissolved components are removed by washing with water or an ion exchange reaction.

【0014】

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention removes factors that promote condensation and the like in the process of producing crystalline titanium oxide particles via peroxotitanium hydrate, and has excellent crystalline properties directly from the precipitated hydrate. The present invention has been made by finding that particles can be obtained.

【0015】

That is, the reaction product, which is a factor for promoting condensation or the like in the reaction process, or the impurities mixed in from the raw material are separated at an early stage to prevent the condensation or the like, and is composed of the following steps. (1) Precipitation step of polymer of peroxotitanium hydrate A soluble titanium compound such as titanium tetrachloride is diluted with water and an appropriate amount of aqueous hydrogen peroxide solution is added to form a brown peroxo complex, and then a basic substance such as ammonia is added to add yellow peroxotitanium water. An aqueous solution of a Japanese product is prepared, and the aqueous solution is left at room temperature or heated to precipitate and precipitate a polymer of peroxotitanium hydrate. (2) Removal process of ionic substances and impurities The liquid containing the precipitate and precipitate of the polymer of peroxotitanium hydrate is washed, or treated by filtration and washing to remove ammonium ions and chlorine ions contained in the liquid, or impurities derived from the raw materials. .. (3) Formation process of crystalline titanium oxide particles Heating the precipitate of peroxotitanium hydrate from which ionic substances and impurities have been removed by washing treatment in the state of a muddy substance that does not separate water or a dispersion liquid at 80 ° C or higher at normal pressure or in an autoclave. To form crystalline titanium oxide particles.

【0016】

By producing by the above steps, crystalline titanium oxide particles can be formed, and a dispersion of crystalline titanium oxide particles useful for forming a titanium oxide film having excellent characteristics at a low temperature can be obtained. Can be done.

【0017】

Examples of the soluble titanium compound used as a raw material in the method of the present invention include titanium tetrachloride, titanium sulfate, titanium nitrate, and alkoxytitanium. Further, the amount of hydrogen peroxide solution added to the aqueous solution of the soluble titanium compound needs to have a molar ratio of hydrogen peroxide / titanium of 1 or more, and if the amount is less than that, peroxolation is not completely completed. Moreover, since some of the added hydrogen peroxide solution decomposes without being involved in the reaction, it is preferable to add the hydrogen peroxide / titanium molar ratio in excess of 1.

【0018】

When hydrogen peroxide solution is added to a soluble titanium-containing solution, peroxolation occurs almost instantly, and when the pH is 3 or less, it is mainly dissolved as a cation, and when the pH is 3 or more, it is mainly an anion of peroxotitanium hydrate. Exists as. It is considered that this is because the higher the pH, the faster the condensation and the precipitation of the amorphous peroxotitanium hydrate polymer. Even when a basic substance is added, if the pH is low, the time for precipitating the polymer of peroxotitanium hydrate becomes long. Therefore, it is preferable to add the basic substance until the pH becomes 3 or more, and more preferably. It is better to adjust the pH to the neutral range. When a yellow precipitate is formed from the yellow transparent liquid of peroxotitanium hydrate produced by adding a basic substance, it may be left at room temperature, but the precipitation should be promoted by heating. Can be done. Precipitation becomes even faster with stirring.

【0019】

In the step of removing ammonium ions and chlorine ions contained in the liquid or impurities derived from the raw material from the liquid containing the precipitate, a method such as decantation, filtration washing, centrifugation, or an ion exchange reaction, reverse osmosis A method of removing an ionic substance by applying a penetration method can be used.

【0020】

If the residual amount of impurities is large, the stability and properties of the finally obtained aqueous solution of peroxotitanium hydrate will be adversely affected, so sufficient treatment is desirable. In particular, anions such as chlorine ions are considered to promote the condensation of peroxotitanium hydrate, and if their removal is insufficient, they may not be completely transparent and may become turbid. On the other hand, even if cations such as ammonium ions remain, a yellow transparent aqueous solution containing peroxotitanium hydrate can be obtained by sufficiently removing the anions.

【0021】

Next, the dispersion liquid containing the precipitate or the muddy substance is heat-treated. The heating temperature is preferably 70 ° C. or higher, and at a temperature lower than 70 ° C., the formation of crystalline titanium oxide particles of anatase is not sufficient. Further, the heating temperature is more preferably 80 ° C to 200 ° C. At 200 ° C or higher, precipitation of anatase occurs in a very short time, which makes it difficult to adjust the treatment time. The heating time is preferably 5 minutes to 20 hours. By heating in the autoclave, crystalline titanium oxide particles can be produced in a short time. The autoclave treatment is preferably carried out at 100 ° C to 200 ° C.

【0022】

Further, in the treatment of the precipitate, when the precipitate dries, it is dehydrated and solidified, which adversely affects the production process of the crystalline titanium oxide particle dispersion liquid, so it is necessary to prevent the precipitate from being dried. In the method of the present invention, when the precipitate is heated, crystalline particles are produced and a dispersed liquid of the particles is produced.

【0023】

Further, since the crystalline titanium oxide particle dispersion liquid of the present invention can form a crystalline titania film only by coating, it is useful as a coating agent for a material that cannot be heat-treated. Further, it can be used for various purposes such as a protective film, a photocatalyst, and a gas permeation blocking material for a synthetic resin film, and a material having a relatively high density and good adhesion can be obtained at a relatively low temperature.

【0024】

The liquid in which the crystalline titanium oxide particles of the present invention are dispersed can be mixed with various solid fine particles and dispersed by ultrasonic waves, a ball mill, or the like, and the titanium oxide film obtained by applying the liquid and drying and firing the film can be obtained. It is also possible to create a complex in which other substances are supported or dispersed. In addition, the substrate to be applied can be applied to any material such as ceramics, ceramics, metals, plastics, fibers, building materials, etc. that can withstand heat treatment according to the application, and can be applied to the inside of a porous body or powder. The titanium oxide coating agent produced in the present invention can be used for surface treatment of various materials such as protective coatings, photocatalytic films, ultraviolet blocking coatings, colored coating films, dielectric films, film-type sensors, and oxidation. It can be used in fields such as the production of titanium sol.

【0025】

[Example]

Hereinafter, the present invention will be described with reference to examples. Example 1 A brown transparent liquid was prepared by adding 20 ml of a 30% hydrogen peroxide solution to a solution obtained by diluting 5 ml of a 60% aqueous solution of titanium tetrachloride to 500 ml with distilled water, and adding ammonia water (1: 9) to this solution. Was added dropwise to adjust the pH to 7, and a transparent yellow solution was prepared. The obtained solution was left at 25 ° C for 24 hours to generate a yellow precipitate. After filtration and washing, the mixture was made into about 150 ml with distilled water, and 25 g each of a cation exchange resin and an anion exchange resin was added and left for 30 minutes to remove cation and anionic substances. As a cation exchange resin, Organo's Amberlite IR120B (Na)⁺Substitution type) was treated with 2N hydrochloric acid for 1 hour, washed, and H⁺ A substitution type resin is used, and the anion exchange resin is Organo's Amberlite IRA410 (Cl).^- Substitution type) was treated with 1N sodium hydroxide for 1 hour, then washed and OH.^- The replacement type was used.

【0026】

When the obtained liquid containing the yellow precipitate was made up to 150 ml, sealed in a glass container and heated at 100 ° C. for 5 hours, a pale yellow translucent liquid was produced. The powder obtained by drying the generated liquid was measured by an X-ray diffractometer (RAD-B manufactured by Rigaku Denki) using a copper target under the measurement conditions of an acceleration voltage of 30 kV and a current of 15 mA, and the results are shown in Fig. 1. Shown. In FIG. 1, a peak showing crystalline anatase was confirmed, and it was confirmed that crystalline anatase was present in the dried product of the pale yellow translucent liquid. The crystallite diameter obtained from the half width of the diffraction peak was 8 nm. Further, the produced liquid was applied onto a slide glass, dried at 60 ° C., and heat-treated to obtain a titanium oxide film.

【0027】

Example 2 A brown transparent liquid was prepared by adding 20 ml of a 30% hydrogen peroxide solution to a solution obtained by diluting 5 ml of a 60% aqueous solution of titanium tetrachloride to 500 ml with distilled water, and adding ammonia water (1: 9) to this solution. Was added dropwise to adjust the pH to 7, and a transparent yellow solution was prepared. The obtained solution was left at 25 ° C for 24 hours to generate a yellow precipitate. This was treated in the same manner as in Example 1 except that it was filtered and washed, made into about 150 ml with distilled water, sealed in a glass container and heated at 100 ° C. for 5 hours. A dispersion containing a crystalline titanium oxide was obtained.

【0028】

Comparative example 1 A brown transparent liquid was prepared by adding 20 ml of a 30% hydrogen peroxide solution to a solution obtained by diluting 5 ml of a 60% aqueous solution of titanium tetrachloride to 500 ml with distilled water, and adding ammonia water (1: 9) to this solution. Was added dropwise to bring the pH to 7, a transparent yellow solution was prepared, heated at 60 ° C. for 2 hours, and the obtained yellow precipitate was thoroughly filtered and washed. The liquid containing this yellow precipitate was made up to 150 ml, sealed in a glass container and heated at 75 ° C. for 12 hours to obtain a yellow translucent liquid. The result of measuring the powder obtained by drying this liquid by X-ray diffraction is shown in FIG. In FIG. 2, although there was a peak showing crystalline anatase, the peak was smaller than that in FIG. 1 showing the example, and the crystalline anatase was insufficient as compared with the example.

【0029】

Comparative example 2 A brown transparent liquid was prepared by adding 20 ml of a 30% hydrogen peroxide solution to a solution obtained by diluting 5 ml of a 60% aqueous solution of titanium tetrachloride to 500 ml with distilled water, and adding ammonia water (1: 9) to this solution. Was added dropwise to bring the pH to 7, a transparent yellow solution was prepared, heated at 60 ° C. for 2 hours, and the obtained yellow precipitate was thoroughly filtered and washed. A liquid containing this yellow precipitate was made up to 150 ml, sealed in a glass container and heated at 60 ° C. for 12 hours, and treated in the same manner as in Comparative Example 1 to obtain a yellow opaque liquid. The result of measuring the powder obtained by drying this liquid by X-ray diffraction is shown in FIG. In FIG. 3, no clear peak indicating the presence of crystalline substance was observed, confirming the absence of crystalline anatase in this liquid.

【0030】

[Effect of the invention]

According to the production method according to the present invention, condensation of peroxotitanium hydrate can be easily suppressed, and crystalline titanium oxide in which anatase having a small particle size is directly dispersed from the precipitate of peroxotitanium hydrate. A dispersion liquid can be obtained from the particles, and when used as a coating agent, a dense titanium oxide film can be formed.

[Simple explanation of drawings]

[Figure 1]

FIG. 1 is a diagram for explaining the X-ray diffraction result of the dried product of the pale yellow translucent liquid obtained in one embodiment of the present invention.

[Figure 2]

FIG. 2 is a diagram for explaining the X-ray diffraction result of the dried product of the pale yellow translucent liquid obtained in the comparative example of the present invention.

[Fig. 3]

FIG. 3 is a diagram for explaining the X-ray diffraction result of the dried product of the pale yellow opaque liquid obtained in another comparative example of the present invention.