Titanium oxide colloidal sol and process for the preparation thereof

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a titanium oxide sol and a method for producing the same. More specifically, the present invention relates to a colloidal sol of titanium dioxide mainly used as a semiconductor photocatalyst and a method for producing the same. The titanium oxide sol of the present invention can be mainly used as a raw material for various functional coating agents such as ultraviolet absorption, antifouling, hydrophilicity, antifogging, and antibacterial.

【0002】

[Conventional technology]

Conventionally, as ceramic paints that are superior in heat resistance and abrasion resistance to organic paints, paints such as alkali metal silicate-based, phosphate-based, silica sol-based, and metal oxide-based paints have been used. Are known.

【0003】

These paints have the characteristics of inorganic paints such as excellent heat resistance and wear resistance, but in recent years, attempts to equip ceramic coatings with new functions have been made to metal oxides. It is centered around the system.

【0004】

Among various ceramics, titanium oxide can exhibit an excellent photocatalytic effect, and when it is irradiated with ultraviolet rays, it exhibits high oxidizing power.

【0005】

For this reason, by allowing titanium oxide, which has excellent photocatalytic activity, to be present on the surface of objects to be coated such as metal, glass, and ceramics, it is possible to prevent the adhesion of dirt, decompose malodorous components, purify water quality, prevent rust, antibacterial, and algae. It is known to be effective in preventing the reproduction of algae and promoting the decomposition of persistent waste.

【0006】

Several various titanium oxide paints and methods for producing the same have been proposed so far for the purpose of forming a titanium oxide film having the above characteristics on the surface of the material.

【0007】

As a method for forming a titanium oxide film, a method of applying a hydrolyzed titanium alkoxide, that is, a sol-gel method is the most common, and a technique similar to this is described in, for example, Japanese Patent Application Laid-Open No. 4-83537. As shown, a method of adding amide or glycol to titanium alkoxide, and a method of adding alcohol amines to titanium alkoxide as shown in JP-A-7-100378 are known. ..

【0008】

In addition to the above method, as a method for producing a titanium oxide sol, as shown in JP-A-6-293519, titanium oxide fine particles crystallized by hydrothermal treatment are placed in an acid solution having a pH of 3 or less. There is known a method of dispersing in water and applying this dispersion.

【0009】

However, since the colloidal solution is acidic in the above sol-gel method and the method of thawing or dispersing with acid, there is a big problem that these materials are corroded or deteriorated when applied to the surface of metal or paper. there were. Further, even when the coating is applied to a material having good acid resistance such as resin, ceramic or glass, the coating equipment such as a coater, a printing machine and a spray gun is corroded, and the deterioration of the coating work environment for workers has been a problem. ..

【0010】

As means for solving these problems, as disclosed in Japanese Patent Application Laid-Open No. 9-71418, a sol solution containing a hydrogen peroxide solution and titanium oxide, and a method for producing the sol solution are known. .. This sol has the advantage that it can be neutral, but because it contains an oxidant, it is less effective in preventing metal corrosion and the sol turns yellow. There is a problem that it is colored and it is difficult to obtain a colorless film unless it is heated and dried.

【0011】

[Problems to be Solved by the Invention]

The present invention solves the problems of these conventional photocatalytic titanium oxide solutions, is stable even in neutral, can safely perform coating work, and obtains a colorless and transparent film even when dried at room temperature. It is an object of the present invention to provide a titanium oxide colloidal sol capable of producing the same.

【0012】

[Means for solving problems]

In order to solve the above problems, the present inventors first hydrolyzed an inorganic titanium salt such as titanium chloride and titanium sulfate or titanium alkoxide by reacting it with water in an acidic manner to prepare a titanium dioxide colloid solution. Furthermore, the inventors analyzed this acidic colloidal sol of titanium oxide, and the titanium oxide particles had a stable positive charge in acidity, but when this was neutralized with an alkaline solution, the pH became 3 to 5 It was confirmed that within the range of, the charge was almost lost, the colloid became extremely unstable, strongly aggregated and difficult to redisperse, and when the alkalinity was further increased, the aggregated particles were negatively charged.

【0013】

Therefore, the inventors have repeatedly studied a method for providing the titanium oxide colloidal particles with a stable charge and good dispersibility even in the neutral region. As a result, even if an alkali metal hydroxide or an aqueous ammonia solution is added to the titanium oxide acidic colloid sol solution to bring the pH of the sol solution to an alkaline range, the colloid does not redisperse and is strongly aggregated in a slurry-like suspension. The cause of the phenomenon of becoming a turbid liquid is Ti existing in the sol liquid.⁴⁺It was found that the ions become a glue-like titanium hydroxide, which binds the titanium dioxide particles to each other, and that the negative charge of the colloidal particles in the vicinity of neutrality is weak, so that the repulsive force between the particles is small.

【0014】

Then, in advance, add Ti to the acidic titanium oxide colloid sol.⁴⁺After surface modification of the surface of the titanium oxide colloidal particles by adding a complexing agent selected from condensed phosphoric acid such as pyrophosphate that can form a complex with ions, a sol solution is added with an alkaline component such as aqueous ammonia and morpholine. By increasing the pH of the material to adjust the pH value to a desired value, a titanium oxide colloidal sol stably dispersed by a negative charge can be obtained in the neutral to alkaline pH range, and this sol is applied to the object to be treated. As a result, it was found that a titanium dioxide film that is colorless and transparent and has excellent adhesion can be obtained.

【0015】

Further, as the composition of the titanium oxide sol, the neutral sol containing the negatively charged titanium oxide colloidal particle component, the complexing agent and the alkaline component has good stability and dispersibility, and satisfies the above performance. It was found to do. Further, as a result of further study on the method for producing the titanium oxide sol having the above composition, a specific alkaline component is added to the sol containing the titanium oxide colloidal particle component and the specific complexing agent component to make the sol solution neutral to alkaline. As a result, it was found that a titanium oxide sol with less impurities could be obtained, and the present invention was completed based on this.

【0016】

That is, the titanium oxide sol of the present invention contains 50 to 100 parts by weight of a negatively charged titanium oxide colloidal particle component, and 5 to 50 parts by weight of a complexing agent containing one or more selected from condensed phosphoric acid and condensed phosphate. It is characterized by containing 1 to 50 parts by weight of an alkaline component containing at least one selected from morpholine, piperidine and choline. The pH of the titanium oxide sol of the present invention is preferably 5 to 10. Further, the specific complexing agent used in the titanium oxide colloidal sol of the present invention may further contain at least one chelating compound having a carboxyl group. Further, the method for producing a titanium oxide sol of the present invention is a complexing agent containing 50 to 100 parts by weight of a titanium oxide colloidal sol particle component and 5 to 50 parts by weight of a complexing agent containing at least one selected from condensed phosphoric acid and condensed phosphate. To the acidic titanium oxide sol containing, an alkaline component containing at least one selected from morpholin, piperidine and choline is added to adjust the pH of the sol solution to 5 to 10, and the titanium oxide colloidal sol particles are negatively affected. It is characterized in that it is charged. In the method for producing a titanium oxide sol of the present invention, the complexing agent may further contain at least one chelating compound having a carboxyl group.

【0017】

BEST MODE FOR CARRYING OUT THE INVENTION

The titanium oxide sol of the present invention contains 50 to 100 parts by weight of the titanium oxide colloidal particles, and the titanium oxide colloidal particles are negatively charged in the neutral sol solution. If the titanium oxide particles are positively charged in the neutral region, the dispersion of the colloid becomes unstable, which is not preferable. The positive or negative of the charge of the particles can be easily known by a zeta potential measuring device or the like.

【0018】

As the type of titanium oxide used in the present invention, anatase-type titanium dioxide (including metatitanic acid) and ortho-titanium acid are most preferable, and then other titanium dioxide such as rutile-type is preferably used.

【0019】

The particle size of the titanium oxide colloidal particles is not particularly limited, but is generally preferably 1 nm to 500 nm, and more preferably 3 to 120 nm.

【0020】

These titanium dioxide colloidal particles are prepared by dissolving an inorganic titanium compound such as titanium chloride, titanium oxychloride, titanium sulfate and titanyl sulfate in water, adding a catalyst such as hydrochloric acid or nitric acid as needed, and adding water at room temperature or by heating. Obtained by disassembling. Alternatively, it can be obtained by hydrolyzing an organic titanium compound such as titanium alkoxide or titanium acetylacetonate. Since the titanium oxide particles obtained in the acidic solution as described above are positively charged, when an alkaline component is added to the sol solution to raise the pH to 6 or more, a complexing agent is added to the sol solution. It is necessary to make the charge of the titanium dioxide particles negative by adding.

【0021】

Further, the titanium oxide sol of the present invention needs to contain a complexing agent containing at least one selected from condensed phosphoric acids such as pyrophosphoric acid and tripolyphosphoric acid and salts thereof in a proportion of 5 to 50 parts by weight. There is. Further, the complexing agent used in the present invention may contain one or more chelating compounds containing at least one carboxyl group in its molecular skeleton. Moreover, Ti⁴⁺Those having a strong chelating effect on ions are preferable. Preferred types of chelating compounds include polyvalent carboxylic acids and hydroxycarboxylic acids, such as gluconic acid, glycolic acid, lactic acid, tartaric acid, citric acid, malic acid and succinic acid.

【0022】

In the titanium oxide sol of the present invention, in addition to the complexing agent, acidic ions such as hydrochloric acid ions or sulfate ions remaining in the sol solution are neutralized to give a stable negative charge to the titanium dioxide colloidal particles. Therefore, it is necessary that 1 to 50 parts by weight of a specific alkaline component is contained, and it is preferable that the pH of the sol solution is adjusted to the range of 5 to 9.

【0023】

The alkaline component used in the titanium oxide colloidal sol of the present invention contains at least one of morpholine, piperidine, and choline. When the titanium dioxide colloidal sol of the present invention is used as a coating agent, low molecular weight amines such as ammonium hydroxide and triethanolamine may be used in combination with morpholine and piperidine.

【0024】

As the complexing agent and the alkaline component, a compound having both components in the form of, for example, choline hydrogen tartrate can be added.

【0025】

Other components contained in the sol include chlorine ions, sulfate ions, alcohol, etc., depending on the titanium raw material used, but the remaining components are substantially composed of water. When the titanium dioxide colloidal sol of the present invention is used as a coating agent, it is also preferable to replace a part of water with a water-soluble solvent such as alcohol, glycol or ketone as an auxiliary solvent. Further, in this case, it is also possible to add a silane derivative such as silica sol or alkyltrimethoxysilane as a binder to improve the physical characteristics of the coating film.

【0026】

In the method of the present invention, if the weight ratio of the complexing agent to the weight of the titanium oxide colloidal particle component is too small, the dispersion of the colloid becomes insufficient and a stable sol cannot be obtained. Further, if the weight ratio of the complexing agent is excessive, the hardness of the obtained coating film is lowered, which is not preferable. Similarly, if the ratio of the alkaline component is too large, the hardness of the coating film is lowered, or it is corrosive to metals such as aluminum and zinc, which is not preferable. If it is too small, the sol solution is acidic. It is not preferable because it becomes.

【0027】

Further, in the method for producing a titanium oxide colloidal sol of the present invention, an acidic titanium oxide sol containing 50 to 100 parts by weight of titanium oxide colloidal particles and 5 to 50 parts by weight of a complexing agent is selected from morpholin, piperidine and choline. By adding an alkaline component containing at least one of the above, the pH of the sol solution is adjusted to 5 to 10, and the titanium oxide colloidal particles are negatively charged.

【0028】

The acidic titanium oxide sol component used in the method of the present invention dissolves an inorganic titanium compound such as titanium chloride, titanium oxychloride, titanium sulfate, or titanyl sulfate in water, and a catalyst such as hydrochloric acid or nitrate is added thereto as needed. It can be obtained by adding and hydrolyzing at room temperature or by heating, or by hydrolyzing an organic titanium compound such as titanium alkoxide or titanium acetylacetonate. Examples of the complexing agent used in the method of the present invention include those containing at least one selected from condensed phosphoric acids such as pyrophosphoric acid and tripolyphosphoric acid and salts thereof, and further, polyvalent carboxylic acid and hydroxycarboxylic acid. It is preferable that the molecular skeleton contains at least one chelating compound having at least one carboxyl group. This chelating compound includes, for example, gluconic acid, glycolic acid, lactic acid, tartaric acid, citric acid, malic acid, succinic acid and the like.

【0029】

Examples of the alkaline component that can be used in the method for producing the titanium oxide sol of the present invention include oxazine such as morpholine, piperidine, and choline. The amount of the alkaline component added is such that the pH of the sol solution is in the range of 5 to 10. The addition of the alkaline component causes the titanium dioxide colloidal particles to become negatively charged.

【0030】

Further, in the production method of the present invention, before adding the alkaline component, a silane derivative such as epoxysilane or methylsilane, or a partial hydrolysis product thereof is further added to the mixed solution of the titanium dioxide colloidal particles and the complexing agent. By adding the particles, the charge of the obtained titanium oxide colloidal particles is further stabilized, and the coatability when used as a coating agent is also improved, which is more preferable.

【0031】

In the production method of the present invention, after adding the alkaline component, the sol solution may be further subjected to a deionization treatment to remove excess ions in the sol solution.

【0032】

As the method of the deionization treatment, it is preferable to use diffusion dialysis with a semipermeable membrane, electrodialysis with an ion exchange membrane, or contact treatment with an ion exchange resin. Contaminated ions such as alkaline ions and acidic anions are removed, the purity of titanium oxide is increased, and a more practical sol with high coating performance can be obtained. The deionized titanium oxide sol has a pH of 5 to 9, more preferably 6 to 8.5.

【0033】

When the titanium oxide sol of the present invention is applied to the object to be treated, the amount of titanium dioxide adhered is 200 to 2000 mg / m.²It is most preferable to adjust so as to be. Drying can be performed not only by heating but also at room temperature. However, when the complexing agent contains an organic compound such as carboxylic acid and is dried at a temperature of 100 ° C. or lower, the coating layer may be dried. It is most preferable that the coating layer is irradiated with ultraviolet rays having a wavelength of less than 400 nm to decompose the organic compound during or after drying.

【0034】

The negatively charged titanium oxide sol of the present invention is a chelating compound containing condensed phosphoric acid or a salt thereof containing tetravalent titanium ions remaining as unreacted components in the conventional acidic titanium oxide sol, and if necessary, further having a carboxyl group. The complexing agent component containing the above masks, thereby preventing gelation and precipitation in the neutral region, and the negative charge of the complexing agent adsorbed on the titanium oxide colloidal particles negatively charges the positively charged titanium oxide colloidal particles. It works and thus provides a stable neutral titanium oxide sol. After the coating film is formed, the organic chelating agent component is decomposed into water and carbon dioxide gas by the photocatalytic effect of titanium dioxide, so that it does not have an adverse effect.

【0035】

In addition, the acidity of the carboxyl group and Cl derived from the raw material for producing titanium dioxide^-, SO₄^2-Contaminated acidic anions such as, can be neutralized by alkaline components such as morpholine and piperidine to a completely neutral sol.

【0036】

The negatively charged titanium oxide colloidal sol of the present invention can be produced by adding the above-mentioned alkaline component to an acidic titanium oxide sol containing a complexing agent, and is further removed by a method such as dialysis using a semipermeable membrane. By performing the ion treatment, a higher quality titanium oxide sol can be obtained.

【0037】

[Example]

The present invention will be further described with reference to the following examples, but the present invention is not limited to these examples.

【0038】

Examples 1 to 3 and Comparative Examples 1 to 6 The following materials were used in the following examples and comparative examples. (Titanium oxide colloid) One of the following two types (A, B) was used. A) In Comparative Examples 1, 2, 5 and 6, and Examples 1 and 2, the titanium oxide colloid prepared by the following method was used. Sumitomo Citix Co., Ltd. titanium chloride aqueous solution (Ti: 15 to 16%) is diluted with water and deionized with an ion exchange membrane to prepare an oxytitanium chloride aqueous solution, which is heated and hydrolyzed at 70 to 85 ° C. It was decomposed to obtain a titanium dioxide sol having a pH of 1 to 2. The crystal particle size of titanium dioxide measured by a transmission electron microscope was 0.002 to 0.01 μm. The concentration of the titanium oxide colloidal particles was 5.0% by dry weight. B) In Comparative Example 3, Comparative Example 4, and Example 2, titanium dioxide powder particles (particle size: 0.02 μm, anatase + rutile type) manufactured by Nippon Aerodil Co., Ltd. were dispersed in water and hydrochloric acid was added. The titanium dioxide sol obtained by adjusting the pH to 1.5 was used.

【0039】

(Coordinating agent) As the complexing agent, pyrophosphoric acid and tripoliphosphoric acid were selected and used as shown in Tables 1 and 2. For these chemicals, first-class reagents manufactured by Wako Junyaku Co., Ltd. were used.

【0040】

(Alkaline component) From among aqueous ammonia (ammonium hydroxide), sodium hydroxide, potassium hydroxide, lithium hydroxide, triethanolamine, triethylenetetramine, morpholine (tetrahydro-1,4-oxazine) and choline, use the amounts shown in Table 1. used. For these chemicals, first-class reagents or equivalents were used.

【0041】

Table 1 shows the composition of the titanium oxide sol used in Comparative Examples and Examples. The prepared sol was measured for positive and negative charges of titanium oxide particles by a zeta potential measuring device. Also, on the surface of aluminum, acid paper, galvanized steel sheet or stainless steel plate base material, 10 ml / m with a bar coater.² Appearance quality and photocatalytic activity (fatty acid decomposition rate: unit; mg / m) of the obtained coating film after coating at the coating amount of² Day) was measured.

【0042】

As the base material, an aluminum alloy was used in Comparative Example 1, acid paper was used in Comparative Example 2, a galvanized steel sheet was used in Comparative Examples 3 and 5, and a steel sheet was used in Comparative Examples 4 and 6, respectively. 1 used a stainless steel plate (SUS304). Further, in Examples 2 and 3, a polyester film coated with a silicone resin primer was used as a base material.

【0043】

As the raw material titanium oxide sol, the acidic sol of A) or B) was used, and in Comparative Example 1, an alkaline component was added without adding a complexing agent to adjust the pH to 7 to 8. Further, in Comparative Example 2, Comparative Example 4, Comparative Example 5, Comparative Example 6, and Examples 4 to 7, a complexing agent was added to the acidic sol, and then an alkaline component was added, and the results are shown in Table 1. The pH value was adjusted respectively.

【0044】

Further, in Comparative Example 3 and Example 3, similarly, the acidic sol of A) or B) was used, a complexing agent was added thereto, and an alkaline component was further added until the pH reached 6 to 12 to oxidize. Titanium particles were dispersed. In Example 3, instead of diffusion dialysis, a column containing an anion exchange resin and a cation exchange resin was passed through to perform deionization treatment.

【0045】

The coating film performance was evaluated by the following test methods and evaluation criteria. (Appearance of application) The presence or absence of rust or discoloration was visually evaluated. (Adhesion) Adhesion of the coating film The adhesion of the coating film was judged according to the JIS-K5400 grid tape method coating film adhesion test. (Film hardness) The coating film was scratched with a JIS-K5400 pencil scratch test pencil, and the hardness was measured by the pencil hardness. (Evaluation of base materials other than paper) (Photocatalytic activity) Stearic acid was diluted with ethanol and applied to the dried test piece, and the test piece was irradiated with ultraviolet rays with 20 W black light for 24 hours, and the fatty acid decomposition rate was determined per 24 hours from the weight difference before and after the irradiation.

【0046】

[table 1]

【0047】

As is clear from Table 1, the conventional titanium oxide sol or the titanium oxide sol of Comparative Examples 1 to 4 by the production method thereof could not obtain satisfactory results for the materials which are easily corroded or deteriorated. According to the methods for producing the titanium oxide sol and the titanium oxide sol of Examples 1 to 3 according to the present invention, good performance was obtained in each case.

【0048】

[Effect of the invention]

As described in detail above, according to the method for producing titanium oxide sol and titanium oxide sol of the present invention, a coating agent can be applied to easily corrosive metal materials and easily deteriorated organic materials, which have been difficult to use in the past. When a neutral photocatalytic titanium oxide sol with stable and good dispersibility is obtained, and titanium oxide is applied to various purposes such as stain decomposition, ultraviolet absorption, sterilization, gas decomposition and water purification. It can be applied to a wider range of materials and solves problems in terms of work environment and safety, so its practical value is great.