JP4026041B2 - Neutral titania sol - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a titania sol that is transparent and stable in a neutral region and a method for producing the same. This sol is mixed with a binder and applied to a substrate, and can be used, for example, to form a photocatalytic film, a semiconductor film, or an ultraviolet cut film.
[0002]
[Prior art and its problems]
The titania sol is useful for forming a photocatalyst film, a semiconductor film, an ultraviolet cut film and the like on the surface of a substrate. A general method for obtaining a titania sol is a method of peptizing hydrous titanium oxide with a strong acid such as hydrochloric acid or nitric acid. However, since the sol obtained by this method contains a strong acid of a peptizer, there are many restrictions on handling and use as it is. For example, transportation, storage and other handling equipment needs to be acid resistant, and the substrate on which the membrane is formed is also limited to acid resistant materials.
[0003]
Since the titania sol peptized with a strong acid is stable only in a strongly acidic region, when the acid component is removed from the sol, the dispersed particles aggregate and do not form a sol. For this reason, a method has been proposed in which an organic or inorganic compound that acts as a stabilizer is added to a strongly acidic titania sol and then neutralized by alkali neutralization or ion exchange (Japanese Patent Laid-Open No. 63-123815, Japanese Patent Laid-Open No. 63). -215520, Japanese Patent Publication No. 7-33255). In this case, since a relatively large amount of stabilizer is contained in the sol, the photocatalytic activity and transparency of the film formed from the sol are impaired.
[0004]
Accordingly, an object of the present invention is to provide a titania sol that does not have such disadvantages, that is, is stable in a neutral region without adversely affecting the high catalytic activity and transparency inherent in the titania sol, and a method for producing the same. .
[0005]
[Solutions to the problem]
The present invention provides a neutral titania sol composed of hydrated titanium phosphate compound-coated peptized titanium oxide particles having transparency and dispersion stability in the neutral region.
[0006]
The present invention also provides a process for producing the neutral titania sol described above. In this method, a titania sol obtained by peptizing hydrous titanium oxide with a monobasic strong acid such as hydrochloric acid or nitric acid is used as a starting material, and this is mixed with an aqueous solution of a water-soluble titanium compound and a phosphoric acid compound. Remove the acid. As a result, a titania sol having transparency and dispersion stability in the neutral region can be obtained.
[0007]
[Specific implementation method]
A method for producing a titania sol by hydrolyzing an aqueous solution of titanyl sulfate by heating, etc., neutralizing, filtering and washing the precipitated hydrous titanium oxide with a strong acid such as hydrochloric acid or nitric acid. Well known. It is also well known that titanium oxide particles having a crystalline form of rutile, anatase or amorphous can be obtained by selecting reaction conditions. In the present invention, the crystal form of the dispersed titanium oxide particles is not limited, but the anatase form is preferable for the photocatalyst application.
[0008]
The titania sol thus obtained is strongly acidic (pH 3 or less), transparent, and generally has an average primary particle diameter of 50 nm or less and an average micelle diameter in the range of 10 to 150 nm. As mentioned earlier, this sol is unstable in the neutral region. Therefore, in the present invention, an aqueous solution of a water-soluble titanium compound and an aqueous solution of a phosphoric acid compound are mixed with a sol, and the titanium oxide dispersed particles are coated with a hydrated titanium phosphate compound generated by the reaction of the aqueous titanium compound and the phosphoric acid compound. It is considered that this coating shifts the isoelectric point of the sol to the acidic side, resulting in a stable sol in the neutral region.
[0009]
Examples of water-soluble titanium compounds that can be used include titanium tetrachloride and titanyl sulfate. Examples of phosphoric acid compounds include various phosphorus oxygen acids such as orthophosphoric acid and metaphosphoric acid, and water-soluble salts thereof. Orthophosphoric acid or metaphosphoric acid is preferred. These compounds react either directly or by neutralizing the sol to produce a hydrated titanium phosphate compound that coats the dispersed titanium oxide in the sol. The order of mixing is arbitrary as long as the reaction between the titanium compound and the phosphate compound does not occur in the absence of the dispersed titanium oxide particles. However, it is preferable to sequentially add an aqueous solution of a water-soluble titanium compound and an aqueous solution of a phosphoric acid compound to the titania sol.
[0010]
At this point, the sol is still highly acidic. There are several methods for shifting the sol pH to the neutral range. For example, ion exchange method, ultrafiltration, dialysis including electrodialysis, and the like. The simplest and least expensive method is to wash the cake obtained by neutralizing and filtering the sol and then redispersing it in a neutral aqueous medium. An alkali such as sodium hydroxide can be used as the neutralizing agent, but it is preferable to use ammonia water that does not bring in contaminating metal ions. The redispersion can be performed using an apparatus such as a ball mill, a sand mill, a homomixer, or a paint shaker.
[0011]
In order to obtain a neutral titania sol that maintains the stability and transparency of the raw material titania sol in the present invention, the average primary particle diameter of the coated dispersed titanium oxide is 50 nm or less and the average dispersed particle diameter is in the range of 10 to 200 nm. It is preferable to stay. For this purpose, it is of course important to thoroughly redisperse the coated titanium oxide cake, but the coating amount and composition of the hydrated titanium phosphate compound are also important. The preferred coating amount is that titanium oxide and phosphorus of the hydrated titanium phosphate compound are converted to TiO ₂ and P ₂ O ₅ , respectively, with respect to titanium oxide converted to TiO ₂ in the sol of the raw material, and this total is 7 to 50 wt. % Range. As a matter of course, if the coating amount is too small, the effect is insufficient, and if it is excessive, the particles become enormous and the stability and transparency are impaired.
[0012]
The composition of the coated hydrated titanium phosphate compound is such that the weight ratio of TiO ₂ / P ₂ O _{5 in which} the titanium and phosphorus are converted to TiO ₂ and P ₂ O ₅ is 1.7 to 7.0. It is preferable. This ratio corresponds to an atomic ratio of Ti / P of about 1.3 to 6.2. On the other hand, known titanium phosphates such as Ti (HPO ₄ ) ₂ , TiP ₂ O ₇ , TiPO ₄ , Ti (H ₂ PO ₄ ) ₂ have an atomic ratio Ti / P of titanium and phosphorus of 1.0 or less. . Such a difference in composition is also considered to contribute to stability by a unique steric hindrance effect that is not found in the titanium compound and the phosphate compound alone and in the known titanium phosphate compound.
[0013]
Here, the transparency means an integral value of transmittance (% T · nm) over a wavelength range of 400 to 700 nm. Specifically, a sol having a solid content of 0.5% by weight in a quartz cell having a thickness of 1 mm and an optical path length of 10 mm. The transmittance integral value (% T · nm) when measured by putting in is evaluated as transmittance (% T) × (700−400 nm). In the neutral titania sol of the present invention, the initial value of the transmittance integral value and the value after storage at 25 ° C. for 2 months are both 4000% T · nm or more, and high transparency is maintained.
[0014]
Further, the neutral or neutral region here is not only strictly neutral (pH 7.0), but also a pH region in a range that does not require that the material to be contacted in handling and use is particularly acid-resistant, for example, It should be understood to include the region of pH 7.0 ± 1.5.
[0015]
The neutral titania sol of the present invention can be added to an appropriate binder and used to form a photocatalytic film, a semiconductor film, an ultraviolet cut film or the like on the surface of the substrate. In this case, the sol can be mixed with a binder after adjusting to a suitable solid content concentration or after replacing the dispersion medium with a water-miscible organic solvent such as methanol, ethanol, isopropanol, etc. It is also optional to add a dispersion stabilizer such as glycol and other conventional additives.
[0016]
【Example】
Hereinafter, the present invention will be described specifically by way of examples not intended to be limited.
[0017]
Example 1
Production of peptized anatase titania sol A hydrous titanium oxide slurry obtained by hydrolyzing a titanyl sulfate aqueous solution by a conventional method is neutralized to pH 7 with aqueous ammonia, filtered and washed with a cake. Peptide with 5% by weight (converted to HCl) hydrochloric acid with respect to titanium oxide (converted to TiO ₂ ) to obtain anatase titania sol having a concentration of 32% by weight converted to TiO ₂ . This sol had an average primary particle size of 7 nm and an average dispersed particle size of 50 nm. pH 1.1
[0018]
The anatase titania sol obtained by the manufacturing <br/> neutral coated titania sol diluted with water to a concentration of 50 g / L in terms of TiO _2, was added titanium tetrachloride aqueous solution of this in terms of TiO ₂ 15g to dilute sol 2L Subsequently, 5 g of normal phosphoric acid was added in terms of P ₂ O ₅ and reacted for 2 hours. The reaction solution was neutralized with ammonia water to pH 5.5, and the cake obtained by filtration was washed with water, water was added so that the solid content was 25% by weight, and a paint shaker (container: 400 mL mayonnaise bottle, medium) : Neutral titania sol having an average primary particle size of 7 nm, an average dispersed particle size of 60 nm, and a pH of 6.8. Got.
[0019]
Example 2
The same as Example 1, except that the amount of titanium tetrachloride aqueous solution added was changed to 6.5 g in terms of TiO _{2 and} orthophosphoric acid to 4 g in terms of P ₂ O ₅ . pH 6.6, average dispersed particle size 150 nm
[0020]
Example 3
The same as Example 1 except that the addition amount of the titanium tetrachloride aqueous solution was changed to 35 g in terms of TiO _{2 and} orthophosphoric acid was changed to 10 g in terms of P ₂ O ₅ . pH 6.9, average dispersed particle size 130 nm
[0021]
Example 4
The same as Example 1, except that the amount of titanium tetrachloride aqueous solution added was changed to 14 g in terms of TiO _{2 and} orthophosphoric acid was changed to 9 g in terms of P ₂ O ₅ . pH 6.9, average dispersed particle size 100 nm
[0022]
Example 5
The same as Example 1, except that the amount of titanium tetrachloride aqueous solution added was changed to 33 g in terms of TiO ₂ , and orthophosphoric acid to 5 g in terms of P ₂ O ₅ . pH 6.7, average dispersed particle size 110 nm
[0023]
Example 6
The same as Example 1 except that it was changed to 5 g of metaphosphoric acid in terms of P ₂ O ₅ instead of regular phosphoric acid. pH 6.7, average dispersed particle size 80 nm
[0024]
Example 7
The same as Example 1 except that the titanium tetrachloride aqueous solution was replaced with 15 g titanyl sulfate aqueous solution in terms of TiO ₂ . pH 6.5, average dispersed particle size 90 nm
[0025]
Example 8
Production of peptized amorphous titania sol An aqueous solution of titanyl sulfate was neutralized with aqueous ammonia to pH 7 and hydrolyzed, and the resulting hydrous titanium oxide slurry was filtered and washed with water. To the obtained cake, 25% by weight (in terms of HCl) of hydrochloric acid was added to titanium oxide (in terms of TiO ₂ ), heated at 85 ° C. for 30 minutes to pept, and converted to TiO ₂ of 50 g / L. Amorphous titania sol was obtained. This sol had an average primary particle size of 5 nm and an average dispersed particle size of 80 nm. pH 0.8
[0026]
Production of neutral coated titania sol 15 g of titanium tetrachloride aqueous solution in terms of TiO ₂ was added to ₂ L of the amorphous titania sol obtained above, and then ₅ g of orthophosphoric acid in terms of P ₂ O ₅ was added. Reacted for hours. The reaction solution was neutralized with aqueous ammonia to pH 5.5, the cake obtained by filtration was washed with water, added to water so that the solid content was 10% by weight, and a paint shaker (container: 400 mL mayonnaise bottle, medium) Using a glass bead of 1.5 mm in diameter, 300 g, sample: 100 g, rotation speed: 720 rpm, dispersion time: 10 minutes, re-dispersion was performed to obtain a neutral titania sol having a pH of 6.5. Average dispersed particle size 120nm
[0027]
Comparative Example 1
Same as Example 1 except that no orthophosphoric acid was added. The product was not a sol but a slurry. pH 6.7, average dispersed particle size 900 nm
[0028]
Comparative Example 2
The same as Example 1, except that the amount of titanium tetrachloride aqueous solution added was changed to 4 g in terms of TiO ₂ , and orthophosphoric acid was changed to 2 g in terms of P ₂ O ₅ . The product was not a sol but a slurry. pH 6.9, average particle dispersion diameter 700 nm
[0029]
Comparative Example 3
The same as Example 1 except that the addition amount of the titanium tetrachloride aqueous solution was changed to 10 g in terms of TiO ₂ , and orthophosphoric acid was changed to 20 g in terms of P ₂ O ₅ . The product was not a sol but a slurry. pH 6.7, average particle dispersion diameter 500 nm
[0030]
Comparative Example 4
The same as Example 1 except that the addition amount of the aqueous titanium tetrachloride solution was changed to 7 g in terms of TiO ₂ and the normal phosphoric acid was changed to 8 g in terms of P ₂ O ₅ . The product was not a sol but a slurry. pH 6.8, average dispersed particle size 320 nm
[0031]
Comparative Example 5
The same as Example 1 except that the addition amount of the titanium tetrachloride aqueous solution was changed to 25 g in terms of TiO ₂ , and orthophosphoric acid was changed to 3 g in terms of P ₂ O ₅ . The product was not a sol but a slurry. pH 6.7, average dispersed particle size 400 nm
[0032]
Comparative Example 6
Same as Example 1 except that no titanium tetrachloride aqueous solution and orthophosphoric acid were added. The product was not a sol but a slurry. pH 6.7, average dispersed particle size 1000 nm
[0033]
Comparative Example 7
Same as Example 6 except that no titanium tetrachloride aqueous solution was added. The product was not a sol but a slurry. pH 6.7, average dispersed particle size 400 nm
[0034]
Comparative Example 8
₂ L of titanyl sulfate aqueous solution diluted to a concentration of 50 g / L in terms of TiO ₂ was thermally hydrolyzed at 100 ° C. for 2 hours to obtain anatase type hydrous titanium oxide slurry. Average primary particle size 7nm, average dispersed particle size 500nm
[0035]
After adding 15 g of titanium tetrachloride aqueous solution in terms of TiO ₂ and 5 g of normal phosphoric acid in terms of P ₂ O ₅ to this slurry, the mixture was reacted for 2 hours and neutralized to pH 5.5 with aqueous ammonia. Filter and wash the resulting cake with water. Water was added to the cake so that the solid content was 25% by weight, and the cake was redispersed using a paint shaker under the same conditions as in Example 1. The product did not become a sol and remained in slurry form. pH 6.7, average particle dispersion diameter 700 nm
[0036]
Measurement of average dispersed particle diameter The sample was diluted to a solid dispersion concentration of 0.5 wt%, and the dispersed particle diameter (volume average diameter) was determined with a particle size distribution analyzer (Microtrac UPA Nikkiso Co., Ltd.).
[0037]
Measurement of transparency The sample was diluted to a solid concentration of 0.5% by weight, put into a cell having a thickness of 1 mm and an optical path length of 10 mm, and transmittance integration with a spectrophotometer (U-3300, Hitachi, Ltd.). Value (% T · nm) = transmittance (%) × (700 nm−400 nm) was determined. The measurement was performed twice after the initial value and storage at 25 ° C. × 2 months.
[0038]
Measurement of photocatalytic activity A sample was mixed with colloidal silica (Snowtex 30 manufactured by Nissan Chemical Co., Ltd.) at a solid content ratio of 1: 1, diluted with water to a total solid content of 5%, and 7. A 6 × 2.6 cm glass plate was coated using a bar coater # 5 and dried at 110 ° C. for 30 minutes to form a photocatalytic film. This film was placed in a 400 ml vessel, 5 ppm of nitric oxide was injected, and then irradiated with a mercury lamp (3.7 mW / cm ² ) for 5 minutes, and the reduction rate of nitric oxide was measured. The results are shown in Table 1.
[0039]
[Table 1]

Claims (5)

Neutral composed of hydrated titanium phosphate compound-coated peptized titanium oxide particles having transparency and dispersion stability in a neutral region having an average primary particle size of 50 nm or less and an average dispersed particle size in the range of 10 to 200 nm. Titania sol. _2. The titania sol according to claim 1, wherein a weight ratio TiO ₂ / P ₂ O ₅ converted to TiO ₂ and P ₂ O ₅ of the hydrated titanium phosphate compound is in a range of 1.5 to 7.0. The coating amount of the hydrated titanium phosphate compound is 7 to 50% of the total amount of TiO ₂ and P ₂ O ₅ converted to TiO ₂ of the peptized titanium oxide particles in the sol. Titani sol. A titania sol obtained by peptizing hydrous titanium oxide with a strong acid has a weight ratio of water-soluble titanium compound converted to TiO ₂ to phosphoric acid compound converted to P ₂ O ₅ and a weight ratio TiO ₂ / P ₂ O ₅ of 1.5 to It is characterized by coating dispersed titanium oxide particles with a hydrated titanium phosphate compound by mixing with an aqueous solution of a water-soluble titanium compound and a phosphoric acid compound within a range of 7.0 and removing the acid from the reaction solution. A method for producing a neutral titania sol having transparency and dispersibility in a neutral region .   5. The method according to claim 4, wherein the acid is removed from the reaction solution by neutralizing the reaction solution and washing the cake obtained by filtration and then redispersing in water.