JP5441264B2 - Ammonium niobate sol, process for producing the same, coating liquid for thin film formation, and thin film supporting substrate - Google Patents

Description

  The present invention relates to an ammonium niobate sol and a method for producing the same, and further relates to a coating solution for forming a thin film containing the ammonium niobate sol, and a thin film-supporting substrate having a coating formed by the coating solution for forming a thin film.

  In recent years, there is an increasing demand for niobium oxide having a high refractive index and dielectric constant in the fields of ceramic raw materials, electronic materials, surface treatment agents, and the like. In particular, in the fields of optoelectronic materials, semiconductor materials, surface protective agents, antireflection materials, refractive index modifiers, catalysts, etc., niobium raw materials having a small particle diameter and a uniform particle size distribution are required as raw materials. In the field of surface coating agents, there is a strong demand for niobium raw materials having these requirements and having strong adhesion to the substrate.

  Conventionally, titanium oxide has been used as a refractive index adjusting agent in a transparent thin film. However, since titanium oxide is a photocatalyst, in order to use it for an organic polymer substrate such as plastic, the surface of the substrate must be coated with an inert substance such as silica. There is a problem that the transparency is lowered. Moreover, even if it coat | covers with a silica etc., the effect of a photocatalyst is not lose | eliminated completely by this, and there still exists problems, such as a durable fall of a base material and discoloration. Thus, methods for utilizing niobium that have no photocatalytic action and have characteristics such as a high refractive index have been studied.

  As a method for forming a thin film containing niobium, a sputtering method, a vapor deposition method, a wet method, and the like are known. Among these, the wet method is a method that does not require a special apparatus and is simple and excellent in economic efficiency. In the wet method, alkoxides and sols are generally used. Not only are alkoxides expensive, but niobium alkoxides are very rarely used because they are very easy to decompose and difficult to handle.

  Therefore, niobium sol has recently attracted attention, and various niobium sols, for example, peroxyniobic acid sols prepared using hydrogen peroxide (for example, Patent Documents 1 and 2), oxalic acid stability that is stable against pH fluctuations. Type or citric acid-stabilized niobium oxide sols (for example, Patent Document 3 and Patent Document 4), and sols produced by electrolysis of niobium compounds (for example, Patent Document 5) have been developed. By the way, it has been known that niobic acid and niobium oxide fine particles themselves have no self-binding property, and thus it is usually difficult to obtain a transparent and strong film even when heated at a high temperature. In these niobium sols, since the fine particles have little or no self-binding property, in order to make a thin film made of niobium, it is necessary to add a binder for adhering the thin film to the substrate. (For example, Patent Document 6 and Patent Document 7). In a film containing a large amount of binder, the high refractive index, scratch resistance, chemical resistance, and the like, which are inherent characteristics of niobium, are hindered by the mixing of binder components, and it is difficult to obtain desired performance. In addition, the use of a sol with a stabilizer added to stabilize the sol is limited due to the stabilizer, especially when organic substances such as oxalic acid and citric acid remain in the thin film. This causes problems such as deterioration in color and coloring.

Japanese Patent Publication No. 8-701 JP2008-81378 Japanese Unexamined Patent Publication No. 8-143314 JP 2005-200235 A Japanese Patent Laid-Open No. 5-222562 JP 2008-114544 JP JP 2008-115323 A

  Therefore, the present inventors have been diligently studying a niobium sol that can obtain a transparent thin film with little or no use of a binder, and the ammonium niobate fine particles have self-binding properties. The present invention has been completed based on such findings. The self-binding property refers to a property of forming a strong and durable thin film having strong adhesion to the base material when the sol is formed alone.

In the ammonium niobate sol of the present invention, ammonia and niobic acid when the sol is dried at 100 ° C. for 10 hours is in a range of NH ₃ / Nb ₂ O ₅ (molar ratio) = 0.5 to 1.5, Is characterized by not containing an organic acid. In the present invention, “substantially free of organic acid” means that the amount of organic acid is 0.1 or less in terms of molar ratio to Nb ₂ O ₅ in the ammonium niobate sol. If the molar ratio exceeds 0.1, the self-binding property is lost and the object of the present invention cannot be achieved. The optical path when the average particle diameter of the ammonium niobate colloid is 100 nm or less and the niobium in the ammonium niobate sol is Nb ₂ O ₅ (hereinafter, niobium is expressed in terms of Nb ₂ O ₅ ) at 5% by mass. The total light transmittance at a length of 10 mm is 50% or more.

  In the method for producing an ammonium niobate sol of the present invention, an aqueous solution in which a niobium compound is dissolved in hydrofluoric acid or a mixed acid of hydrofluoric acid and sulfuric acid and an aqueous ammonia solution are mixed and reacted while maintaining the pH at 8 or more, A dispersion liquid containing fine particles of ammonium niobate is obtained, followed by filtration and washing.

Further, the present invention is characterized in that, in this production method, the Nb ₂ O ₅ concentration of the dispersion is 0.1 to 1.0% by mass.
Furthermore, the present invention is a coating solution for forming a thin film comprising the ammonium niobate sol of the present invention. In particular, this coating solution contains one or more organic polymer compounds or silica compounds in the range of 1 to 30% by mass as the solid content with respect to the amount of Nb ₂ O ₅ in the ammonium niobate sol. And Furthermore, the present invention is characterized in that it is a thin film-supporting substrate having a film formed by using a coating solution for forming a thin film on the surface of the substrate.

In the ammonium niobate sol of the present invention, since the ammonium niobate fine particles constituting the sol themselves have self-binding properties when dried, the sol alone or a small amount of an organic polymer and an auxiliary component such as silica are formed. By forming a film, it is possible to form a strong and durable thin film, particularly a thin film excellent in transparency, having strong adhesion to the substrate. That is, according to the sol of the present invention, the film strength, durability, refractive index, transparency and the like due to the use of the binder, which has been a conventional problem, are not reduced. In addition to this thin film forming function, the sol of the present invention is highly expected as a catalyst raw material because it is not necessary to use a dispersant or a stabilizer. Furthermore, the ammonium niobate sol of the present invention is produced by dissolving a niobium compound in hydrofluoric acid or a mixed acid of hydrofluoric acid and sulfuric acid, reacting with an aqueous ammonia solution, washing by filtration, and has a uniform and fine particle size. Excellent stability. Further, as described above, the sol of the present invention is extremely inexpensive because it can be produced by a simple process.

Below, the ammonium niobate sol of this invention and its manufacturing method are demonstrated.
The ammonium niobate sol of the present invention is an amorphous ammonium niobate fine particle, that is, an aqueous dispersion sol in which colloidal particles are dispersed. When the sol is dried at 100 ° C. for 10 hours, ammonia and niobic acid are NH. ₃ / Nb ₂ O ₅ (molar ratio) = 0.5 to 1.5. The ammonium niobate in the present invention is considered to have a structure in which ammonia is firmly adsorbed on the surface of the colloidal particles of amorphous niobic acid without ion dissociation like so-called salt. Therefore, although it may be originally called a niobate sol using ammonia as a dispersion stabilizer, it is referred to as an ammonium niobate sol in the present invention. The reason is that when the ammonium niobate sol of the present invention is sufficiently dried at 100 ° C. for 10 hours or more to form a solid, ammonia is NH ₃ / Nb ₂ O ₅ (molar ratio) = This is because it is considered that ammonia remains in the range of 0.5 to 1.5, and ammonia is bound to or strongly adsorbed to the niobic acid fine particles.
Therefore, the molar ratio in the present invention refers to the ammonia remaining in the solid after being dried at 100 ° C. for 10 hours, and does not include free ammonia present in the solution. This bound or adsorbed ammonia not only highly stabilizes the sol of the present invention, but is one of the important factors for obtaining a strong and durable high-quality film with strong adhesion to the substrate. ing. For example, even if ammonia is added to the sol of the present invention and apparently NH ₃ / Nb ₂ O ₅ (molar ratio) = 0.5 to 1.5 may be exceeded, the same effect can be obtained if it falls within this range during drying. Is obtained. However, when the molar ratio exceeds 1.5 in the dried state, ammonium niobate in the sol has a structure like a salt instead of amorphous fine particles, so a high adhesion and high strength film cannot be expected. . On the other hand, when the molar ratio is less than 0.5, the particle size is increased, and thus unstable properties such as generation of sediment and clouding of the film are exhibited.
From these facts, NH ₃ / Nb ₂ O ₅ (molar ratio) = 0.5 to 1.5 is an important factor in the sol of the present invention, and more preferably NH ₃ / Nb ₂ O ₅ (molar ratio) = 0.8 to 1.2. Range.

The average particle diameter of the colloidal particles in the ammonium niobate sol of the present invention is 100 nm or less, and the total light transmittance at an optical path length of 10 mm when Nb ₂ O ₅ in the ammonium niobate sol is 5% by mass is 50% or more. It is desirable to satisfy that at the same time. When the average particle diameter exceeds 100 nm, even if the total light transmittance is 50% or more, the self-binding property that is a feature of the sol of the present invention gradually decreases, and the scratch resistance and abrasion resistance of the thin film. , The smoothness decreases. Even when the average particle diameter is 100 nm or less, when the total light transmittance is less than 50%, precipitates are generated in the sol, the thin film becomes cloudy or spots are likely to occur. In addition, the above physical properties are also considerably reduced.
On the other hand, when the average particle size is smaller than 3 nm, the stability of the sol is reduced and the colloidal particles are not formed, but a salt-like structure is formed. Adhesiveness and strength with respect to are reduced. For these reasons, it is more preferable that the average particle diameter is 5 to 90 nm, more preferably 10 to 70 nm, and the total light transmittance is 70% or more.

  In addition, although the average particle diameter of the sol in this invention can also be measured with an electron microscope etc., it can be easily measured with the particle size distribution meter using a scattering theory. Further, the total light transmittance can be measured using a turbidity measuring device, for example, a chromaticity / turbidity measuring device manufactured by Nippon Denshoku Industries Co., Ltd. can be exemplified.

Next, the production method of the ammonium niobate sol of the present invention will be described in detail. Examples of the niobium raw material used in the present invention include niobium oxide and niobic acid. First, the niobium raw material is dissolved in hydrofluoric acid alone or in a mixed acid of hydrofluoric acid and sulfuric acid to produce a niobium solution. This niobium solution is mixed with an aqueous ammonia solution and reacted to obtain a dispersion containing fine particles of ammonium niobate. By-product salts and ionic substances produced at this time are removed by filtering and washing the dispersion, and further concentrated to obtain the ammonium niobate sol of the present invention.
By the way, the aqueous solution produced by the mixing reaction of the niobium solution and the aqueous ammonia solution is a dispersion that is difficult to say a sol containing fine particles of ammonium niobate (note that it may exhibit a sol-like state depending on the composition and the like). In order to distinguish from the ammonium niobate sol of the present invention obtained after filtration and washing, this dispersion is hereinafter referred to as a dispersion containing fine particles of ammonium niobate.

As the acid for dissolving the niobium raw material, hydrofluoric acid is optimal, but a mixed acid containing sulfuric acid may be used. The amount of acid used is preferably HF / Nb ₂ O ₅ (molar ratio) = 6 to 12 and H ₂ SO ₄ / Nb ₂ O ₅ (molar ratio) = 0 to 6 with respect to Nb ₂ O ₅ in the niobium raw material, More preferably, HF / Nb ₂ O ₅ (molar ratio) = 8 to 10 and H ₂ SO ₄ / Nb ₂ O ₅ (molar ratio) = 0 to 3, as necessary for complete dissolution in a short time. The heat treatment can also be performed. As ammonia used in the aqueous ammonia solution, ammonium bicarbonate, ammonium carbonate, ammonia, and the like are suitable. However, even if alkali metal hydroxides such as sodium hydroxide and potassium hydroxide are contained, cleaning described later is performed. A similar effect can be obtained by sufficiently removing cations.

The temperature at which the niobium solution and the aqueous ammonia solution are reacted is not particularly limited, but is preferably in the range of 10 to 90 ° C. The Nb ₂ O ₅ concentration of the niobium solution and the concentration of the aqueous ammonia solution are not particularly limited, but the Nb ₂ O ₅ concentration in the dispersion containing the ammonium niobate fine particles obtained after the reaction of both is 0.1 to 1.0% by mass. It is preferable to set it so that it is 0.2 to 0.6% by mass.
When the Nb ₂ O ₅ concentration in the dispersion is less than 0.1% by mass, the concentration is too low to be economical in production, and when it exceeds 1.0% by mass, the average particle size becomes too large and unstable, and the object of the present invention is It is difficult to obtain a sol to be used. Moreover, regarding the method of making both react, either the method of adding a niobium melt | dissolution solution to ammonia aqueous solution, or the method of adding both in a container simultaneously may be sufficient.
What is important is that the two are allowed to react while the pH is constantly maintained at 8.0 or higher. When an aqueous ammonia solution is added to the niobium solution, or when the pH of the reaction solution becomes less than 8.0, fluorine is taken into the ammonium niobate fine particles or the particle diameter increases, so the object of the present invention is finally achieved. An ammonium niobate sol cannot be obtained.

The amount ratio between the niobium solution and the aqueous ammonia solution is preferably in the range of 1.0 to 1.5 in terms of an equivalent ratio of the ammonia amount of the aqueous ammonia solution to the acid amount of the niobium solution. When the equivalence ratio exceeds 1.5, a partly soluble niobate is formed by excess ammonia, so that not only a long time is required for the subsequent filtration and washing, but it becomes difficult to obtain a sol at the designed concentration. .
Regarding the ammonium niobate sol of the present invention obtained after filtration and washing, the solid dried at 100 ° C. for 10 hours is in the range of NH ₃ / Nb ₂ O ₅ (molar ratio) = 0.5 to 1.5. This is due to the fact that ammonium niobate that is insoluble, that is, present as colloidal fine particles, has NH ₃ / Nb ₂ O ₅ (molar ratio) within the above range. In addition, the present inventors have discovered for the first time an ammonium niobate sol in which such ammonium niobate is present as colloidal fine particles having a specific composition and a specific binding form of niobic acid and ammonium. On the other hand, if the equivalent ratio is less than 1.0, the pH of the reaction solution is naturally less than 8.0, and it becomes difficult to obtain the ammonium niobate sol of the present invention. That is, an unreacted niobium component remains, which not only inhibits the stability of the colloidal fine particles of the present invention, but also reduces the self-binding property. The more preferable range of the equivalent ratio is 1.1 to 1.3, and the pH at the end of the neutralization reaction is particularly preferably 8.0 to 9.0.

The dispersion containing the ammonium niobate fine particles thus obtained is then subjected to filtration and washing to remove by-product salts such as ammonium fluoride and ammonium sulfate produced by the neutralization reaction. Among the remaining impurities, alkali metals, fluoride ions, sulfate ions, and the like are factors that inhibit the stability of the ammonium niobate sol of the present invention, and the use is limited.
The filtration washing means is not particularly limited, but usually ultrafiltration is the simplest. It is preferable to remove impurities such as by-product salts until the electrical conductivity of the filtrate is 1.0 mS / cm or less, and more preferably 0.5 mS / cm or less. The dispersion after filtration and washing has an appearance as a sol in which colloidal fine particles are uniformly dispersed, and has a pH of about neutral. When a neutral or higher pH is required depending on the application, the pH can be adjusted by adding an alkaline agent within a range that does not impair the dispersion state of the sol.
Examples of the alkaline agent include ammonia, and primary to quaternary amines such as methylamine, diethylamine, trimethylamine, ethylenediamine, and tetramethylammonium hydroxide, and alkanolamines such as methanolamine, ethanolamine, and propanolamine. The concentrations and types of ammonia and amines are not particularly limited, and commercially available ammonia water and various amines can be used directly or as an aqueous solution. If it is necessary to make it acidic, carboxylic acids such as glycolic acid, oxalic acid, malic acid, citric acid, and tartaric acid can be added. Undesirable because sex is inhibited.

The ammonium niobate sol of the present invention can be further stabilized by further heating. The heat treatment method may be heating at 100 ° C. or lower, or hydrothermal treatment at 100 ° C. or higher, and the treatment may be performed under any conditions for about 1 to 10 hours. The longer the treatment time, the more uniform the particle size of the ammonium niobate fine particles, the better the storage stability and viscosity stability, and the higher the refractive index of the transparent thin film obtained by the progress of crystallization of niobic acid. Is done. From an economical point of view, it is usually desirable to stabilize by treating at about 100 to 150 ° C. for about 3 to 10 hours.
In addition, it is desirable that the ammonium niobate sol of the present invention is usually produced at 3 to 20% by mass as Nb ₂ O ₅ . If it is less than 3% by mass, it is difficult to say that the concentration is sufficient for use as a coating solution, and it is not economical in terms of production and transportation. On the other hand, if it exceeds 20% by mass, the viscosity becomes high and handling properties are impaired, which is not preferable. Usually, it is preferable to manufacture and use at about 7 to 15% by mass.

Since the ammonium niobate sol of the present invention itself has self-binding properties, it can directly and firmly adhere to ceramics such as glass, tile, and alumina, and a glaze-coated surface, thereby forming a transparent thin film. Further, by drying at about 100 ° C., a hard film having a pencil hardness exceeding 9H can be obtained. In particular, glass and tile exhibit strong adhesion, and a hard film of niobium alone containing no binder can be formed. In addition, the coating liquid in which additives such as organic polymer compound and silica compound of 30% by mass or less as solid content with respect to Nb ₂ O ₅ in the sol are plastics such as acrylic, PET, polycarbonate, vinyl chloride, Improves wettability to metals such as iron, stainless steel, and aluminum.
A film formed using such an ammonium niobate sol of the present invention as a coating solution for thin film formation improves adhesion, prevents cracking of the film, improves scratch resistance by improving smoothness, and has uneven appearance. An effect such as reduction of Furthermore, since the adhesiveness with the material applied on such a film is also improved, it is suitable for multilayering of the film. Examples of the organic polymer compound that brings about these effects include various aqueous resin emulsions, polyvinyl alcohol, polyethylene oxide, polyethylene glycol, and the like, and examples of the silica compound include silica sol, silicon alkoxide, and silane coupling agent.
One or more types of these additives can be added according to the type and shape of the base material, the heat treatment temperature, and the expected film properties, and the addition amount may be determined according to the expected characteristics and the like. What is important is that the amount of these additives is 30% by mass or less as a solid content with respect to the amount of Nb ₂ O ₅ in the ammonium niobate sol. When an amount larger than this is added, the properties of niobic acid are no longer inhibited, and the self-binding properties of the sol of the present invention are not exhibited, resulting in a fragile film. Further, if the content of the organic polymer compound is increased, the durability of the film is lost accordingly. Therefore, the amount of these additives is more preferably 20% by mass or less. As for the lower limit, 1% by mass or more is necessary. If it is less than 1% by mass, the effect of the additive cannot be expected.

  In addition to these additives, it is preferable to add a small amount of a surfactant, a lower alcohol or the like as a film-forming aid in terms of improving the adhesion and smoothness of the film. In addition to the properties of ammonium niobate, in addition to the properties of antibacterial properties, conductivity, photocatalytic activity, etc., oxide sols such as Si, Ti, Sn, Zr, Ce, Ag, Cu, alkoxides, It is also possible to form a film by mixing a complex or the like, or to form a composite film depending on the purpose.

  There are various known methods for forming a thin film containing ammonium niobate by applying a coating solution for forming a thin film onto a substrate, such as brush coating, spray coating, spin coating, dip coating, roll coating, gravure coating, and bar coating. The coating method can be selected in consideration of the shape of the substrate. Although drying of a coating liquid changes with kinds of base material, it is preferable to heat-process normally at 300 degrees C or less. However, when glass or ceramics is used as a base material, high temperature treatment is desirable from the viewpoint of improving adhesion, and heat treatment at 500 ° C. or higher is desired, in which ammonia is completely decomposed and niobium oxide is generated by sintering of niobic acid. . On the other hand, when the substrate is a plastic such as acrylic, PET, polycarbonate, or vinyl chloride, the heat treatment temperature is 150 ° C. or less due to the heat resistance of the substrate. If the adhesion between the base material such as plastic or metal and the ammonium niobate thin film is insufficient, other metal oxide thin film or film made of silane coupling agent, resin film between the base material and ammonium niobate thin film Etc. can also be provided as a primer layer.

EXAMPLES Hereinafter, although an Example is given and the detail of this invention is demonstrated, this invention is not limited by those Examples. In addition, unless otherwise indicated, all% shows the mass%.
The physical properties of the ammonium niobate sol of the present invention were measured by the following methods.
[Measurement of average particle size]
The average particle size was measured using a dynamic light scattering particle size distribution analyzer LB-500 (manufactured by Horiba, Ltd.).

[Measurement of total light transmittance of sol]
The total light transmittance was measured using a chromaticity / turbidity measuring device COH-300A (manufactured by Nippon Denshoku Industries Co., Ltd.). As measurement conditions, an ammonium niobate sol adjusted to Nb ₂ O ₅ = 5.0% was placed in a glass cell having an optical path length of 10 mm and measured.

(Example 1)
Dissolve 50 g of niobium pentoxide (manufactured by Taki Chemical Co., Ltd.) in 480 mL of 10% aqueous hydrofluoric acid solution, and add 8.8 L of ion-exchanged water to obtain an aqueous niobic fluoride solution of Nb ₂ O ₅ = 0.54%. Obtained. Slowly constant the pH of the reaction solution so that the pH of the reaction solution does not fall below 8.0 against 4.9 L of aqueous ammonia (NH ₃ = 1%) adjusted to 30 ° C. The mixture was added at a rate of about 60 minutes to obtain a dispersion containing fine particles of ammonium niobate having a pH of 8.3 containing a by-product salt and an Nb ₂ O ₅ content of 0.35%. This dispersion showed sol properties, and the fine particles were uniformly dispersed. Next, this dispersion is filtered and washed with ion-exchanged water using an ultrafiltration device (Microza UF: Model SLP-1053; manufactured by Asahi Kasei Corporation) until the electrical conductivity of the filtrate is 0.4 mS / cm or less. By removing ammonium fluoride and the like, 600 g of ammonium niobate sol having a pH of 7.5 was obtained. When the composition analysis of the obtained sol was performed, the Nb ₂ O ₅ content was 8.0% and F = 32 ppm, and the ammonia amount after drying this sol at 100 ° C. for 10 hours was NH ₃ / Nb ₂ O ₅ (Molar ratio) = 1.0. The average particle diameter determined by the dynamic scattering method was 20 nm, and the total light transmittance at Nb ₂ O ₅ = 5.0% was 75%. This sol was stable over a long period of time, and no change in average particle size, transmittance, pH and viscosity was confirmed even after 1 month storage at room temperature.
The obtained ammonium niobate sol was diluted with ion-exchanged water to Nb ₂ O ₅ = 5.0%, then used as a coating solution, spin-coated on a slide glass, and dried at 100 ° C. for 10 minutes to form a thin film-supporting substrate Got.

(Example 2)
50 g of niobium pentoxide (manufactured by Taki Chemical Co., Ltd.) is dissolved in 380 mL of 10% hydrofluoric acid aqueous solution, and 6.5 L of ion-exchanged water is added to obtain an aqueous solution of niobic fluoride of Nb ₂ O ₅ = 0.72%. Obtained. Slowly constant the pH of the reaction solution so that the pH of the reaction solution does not fall below 8.0 against 2.6L of aqueous ammonia (NH ₃ = 1.5%) adjusted to 30 ° C. The mixture was added at a rate of about 60 minutes to obtain a dispersion containing fine particles of ammonium niobate having a pH of 8.5 containing a by-product salt and an Nb ₂ O ₅ content of 0.52%. The dispersion was cloudy, and the fine particles easily aggregated and exhibited sedimentation properties. Next, this dispersion is filtered and washed with ion-exchanged water using an ultrafiltration device (Microza UF: Model SLP-1053; manufactured by Asahi Kasei Corporation) until the electrical conductivity of the filtrate is 0.4 mS / cm or less. Then, by removing ammonium fluoride and the like, 500 g of ammonium niobate sol having a pH of 7.5 was obtained. When the composition analysis of the obtained sol was performed, the Nb ₂ O ₅ content was 10.0% and F = 27 ppm. The amount of ammonia after the sol was dried at 100 ° C. for 10 hours was NH ₃ / Nb ₂ O ₅ (Molar ratio) = 1.0. The average particle diameter by dynamic scattering was 90 nm, and the total light transmittance was 55% when Nb ₂ O ₅ = 5.0%. This sol was stable over a long period of time, and no change in average particle size, transmittance, pH and viscosity was confirmed even after 1 month storage at room temperature.
The obtained ammonium niobate sol was diluted with ion-exchanged water to Nb ₂ O ₅ = 5.0%, then used as a coating solution, spin-coated on a slide glass, and dried at 100 ° C. for 10 minutes to form a thin film-supporting substrate Got.

(Example 3)
7 mL of aqueous ammonia (NH ₃ = 18%) was added to 500 g of ammonium niobate sol having an Nb ₂ O ₅ content of 8.0% obtained in Example 1, and subjected to hydrothermal treatment at 140 ° C. for 6 hours to grow grains. It was. Further, by using an ultrafiltration device (Microza UF: Model SLP-1053; manufactured by Asahi Kasei Co., Ltd.), the filtrate is washed with ion-exchanged water until the electric conductivity of the filtrate becomes 0.2 mS / cm or less, thereby obtaining a pH of 8. 320 g of 0 ammonium niobate sol was obtained. When the composition analysis of the obtained sol was performed, the Nb ₂ O ₅ content was 12.0% and F = 19 ppm. The amount of ammonia after the sol was dried at 100 ° C. for 10 hours was NH ₃ / Nb ₂ O ₅ (Molar ratio) = 0.9. The average particle diameter by dynamic scattering was 30 nm, and the total light transmittance was 70% when Nb ₂ O ₅ = 5.0%. This sol was stable over a long period of time, and no change in average particle size, transmittance, pH and viscosity was confirmed even after 1 month storage at room temperature.
The obtained ammonium niobate sol was diluted with ion-exchanged water to Nb ₂ O ₅ = 5.0%, then used as a coating solution, spin-coated on a slide glass, dried at 100 ° C. for 10 minutes, and then at 500 ° C. A heat treatment for 5 minutes was performed to obtain a thin film-supporting substrate. As shown in Table 1, the refractive index of the thin film was improved from that of Example 1 by hydrothermal treatment.

(Example 4)
The ammonium niobate sol having a pH of 8.0 was obtained in the same manner as in Example 1 except that the aqueous alkaline solution used for the neutralization reaction was a mixed solution of aqueous ammonia and aqueous sodium hydroxide (NH ₃ = 0.5%, NaOH = 1.2%). 700 g was obtained. Composition analysis of the obtained ammonium niobate sol showed that the Nb ₂ O ₅ content was 7.0%, Na / Nb ₂ O ₅ (molar ratio) = 0.2, and F = 8 ppm. The amount of ammonia after drying for hours was NH ₃ / Nb ₂ O ₅ (molar ratio) = 0.7. The average particle diameter by dynamic scattering was 30 nm, and the total light transmittance was 65% when Nb ₂ O ₅ = 5.0%. This sol was stable over a long period of time, and no change in average particle size, transmittance, pH and viscosity was confirmed even after 1 month storage at room temperature.
The obtained ammonium niobate sol was diluted with ion-exchanged water to Nb ₂ O ₅ = 5.0%, then used as a coating solution, spin-coated on a slide glass, and dried at 100 ° C. for 10 minutes to form a thin film-supporting substrate Got.

(Example 5)
Dissolve 50 g of niobium pentoxide (manufactured by Taki Chemical Co., Ltd.) in 480 mL of 10% aqueous hydrofluoric acid solution, and add 8.8 L of ion-exchanged water to obtain an aqueous niobic fluoride solution of Nb ₂ O ₅ = 0.54%. Obtained. Slowly constant the pH of the reaction solution so that the pH of the reaction solution does not fall below 8.0 against 6.1 L of aqueous ammonia (NH ₃ = 1%) adjusted to 30 ° C. The mixture was added at a rate of about 60 minutes to obtain a dispersion containing fine particles of ammonium niobate having a pH of 9.5 containing a by-product salt and an Nb ₂ O ₅ content of 0.32%. This dispersion showed sol properties, and the fine particles were uniformly dispersed. Next, this dispersion is filtered and washed with ion-exchanged water using an ultrafiltration device (Microza UF: Model SLP-1053; manufactured by Asahi Kasei Corporation) until the electrical conductivity of the filtrate is 0.2 mS / cm or less. Then, 450 g of ammonium niobate sol having a pH of 9.0 was obtained by removing ammonium fluoride and the like. Composition analysis of the obtained ammonium niobate sol showed Nb ₂ O ₅ content of 8.0% and F = 8 ppm, and the amount of ammonia after drying this sol at 100 ° C. for 10 hours was NH ₃ / Nb ₂ O ₅ (molar ratio) = 1.3. The average particle diameter determined by the dynamic scattering method was 10 nm, and the total light transmittance was 95% when Nb ₂ O ₅ = 5.0%. This sol was stable over a long period of time, and no change in average particle size, transmittance, pH and viscosity was confirmed even after 1 month storage at room temperature.
The obtained ammonium niobate sol was diluted with ion-exchanged water to Nb ₂ O ₅ = 5.0%, then used as a coating solution, spin-coated on a slide glass, and dried at 100 ° C. for 10 minutes to form a thin film-supporting substrate Got.

(Example 6)
By dissolving 50 g of niobium pentoxide (manufactured by Taki Chemical Co., Ltd.) in a mixed solution of 300 mL of 10% hydrofluoric acid aqueous solution and 550 mL of 10% sulfuric acid aqueous solution and adding 8.4 L of ion-exchanged water, Nb ₂ O ₅ = A 0.54% aqueous solution of niobic fluoride was obtained. Compared to 5.4 L of aqueous niobic acid solution adjusted to 30 ° C and ammonia water adjusted to 30 ° C (NH ₃ = 1%), slowly and at a constant rate so that the pH of the reaction solution does not fall below 8.0. The mixture was added over about 60 minutes to obtain a dispersion containing fine particles of ammonium niobate having a pH of 8.2 containing a by-product salt and an Nb ₂ O ₅ content of 0.34%. This dispersion showed sol properties, and the fine particles were uniformly dispersed. Next, this dispersion is filtered and washed with ion-exchanged water using an ultrafiltration device (Microza UF: Model SLP-1053; manufactured by Asahi Kasei Corporation) until the electrical conductivity of the filtrate is 0.4 mS / cm or less. Then, 700 g of ammonium niobate sol having a pH of 7.5 was obtained by removing ammonium fluoride and the like. The composition analysis of the obtained sol revealed that the Nb ₂ O ₅ content was 7.0% and F = 26 ppm, and the ammonia amount after the sol was dried at 100 ° C. for 10 hours was NH ₃ / Nb ₂ O ₅ (Molar ratio) = 1.0. The average particle diameter determined by the dynamic scattering method was 20 nm, and the total light transmittance at Nb ₂ O ₅ = 5.0% was 75%. This sol was stable over a long period of time, and no change in average particle size, transmittance, pH and viscosity was confirmed even after 1 month storage at room temperature.
The obtained ammonium niobate sol was diluted with ion-exchanged water to Nb ₂ O ₅ = 5.0%, then used as a coating solution, spin-coated on a slide glass, and dried at 100 ° C. for 10 minutes to form a thin film-supporting substrate Got.

(Example 7)
In 500 g of ammonium niobate sol having a Nb ₂ O ₅ content of 8.0% obtained in Example 1, ₂ g of polyvinyl alcohol (PVA) (GOHSENOL GH-17 manufactured by Nippon Synthetic Chemical Co., Ltd.) was dissolved to obtain a coating solution. It was. The amount of PVA added at this time is 5% with respect to Nb ₂ O ₅ in the ammonium niobate sol, and the PVA content in the coating solution is 0.4%.
The obtained coating solution was diluted with ion-exchanged water to Nb ₂ O ₅ = 5.0%, bar-coated on a commercially available PET film, and dried at 100 ° C. for 10 minutes to obtain a thin film supporting substrate.

(Example 8)
To 500 g of ammonium niobate sol having an Nb ₂ O ₅ content of 8.0% obtained in Example 1, ₂ g of polyethylene glycol (PEG) (PEG # 4000 manufactured by Nippon Oil & Fats Co., Ltd.) and silica sol (Asahi Denka Kogyo Co., Ltd.) Adelite AT-20Q (20 g) was mixed to obtain a coating solution. The total solid content of PEG and silica sol at this time is 15% with respect to Nb ₂ O ₅ in the ammonium niobate sol, the PEG content in the coating solution is 0.4%, and the SiO ₂ content is 0.8%.
The obtained coating solution was diluted with ion-exchanged water to Nb ₂ O ₅ = 5.0%, bar-coated on a commercially available PET film, and dried at 100 ° C. for 10 minutes to obtain a thin film supporting substrate.

(Comparative Example 1)
36 mL of 1% hydrofluoric acid aqueous solution was added to 100 g of ammonium niobate sol having an Nb ₂ O ₅ content of 8.0% obtained in Example 1, and the electrical conductivity of the filtrate was 0.2 mS using an ultrafiltration device. When the ammonia component in the sol was removed by washing with ion-exchanged water until it became less than / cm, a sol with high turbidity and high viscosity was obtained. When the composition analysis of the obtained sol was performed, the Nb ₂ O ₅ content was 5.0% and F = 40 ppm. The amount of ammonia after the sol was dried at 100 ° C. for 10 hours was NH ₃ / Nb ₂ O ₅ (Molar ratio) = 0.4. The average particle diameter determined by the dynamic scattering method was 200 nm, and the total light transmittance when Nb ₂ O ₅ = 5.0% was 20%. In addition, precipitation was observed after 1 month of storage at room temperature.
The obtained ammonium niobate sol (Nb ₂ O ₅ = 5.0%) was directly used as a coating solution, spin-coated on a slide glass, and dried at 100 ° C. for 10 minutes to obtain a thin film-supporting substrate.

(Comparative Example 2)
Dissolve 50 g of niobium pentoxide (manufactured by Taki Chemical Co., Ltd.) in 480 mL of 10% aqueous hydrofluoric acid solution, and add 9.9 L of ion-exchanged water to obtain an aqueous solution of niobic fluoride of Nb ₂ O ₅ = 0.48%. Obtained. Add the niobic fluoride aqueous solution adjusted to 30 ° C to ammonia water (NH ₃ = 1%) adjusted to 30 ° C slowly at a constant rate over about 60 minutes, pH 6.5 A dispersion containing ammonium niobate fine particles having an Nb ₂ O ₅ content of 0.35% was obtained. The dispersion was cloudy, and the fine particles easily aggregated and exhibited sedimentation properties. Next, this dispersion is filtered and washed with ion-exchanged water using an ultrafiltration device (Microza UF: Model SLP-1053; manufactured by Asahi Kasei Corporation) until the electrical conductivity of the filtrate is 0.4 mS / cm or less. Then, ammonium fluoride and the like were removed, but a uniformly dispersed sol state was not obtained, and 500 g of ammonium niobate sedimentary slurry having a pH of 7.0 was obtained. When the composition analysis of the obtained slurry was performed, the Nb ₂ O ₅ content was 8.0% and F = 900 ppm, and the ammonia amount after drying this slurry at 100 ° C. for 10 hours was NH ₃ / Nb ₂ O _5. (Molar ratio) = 0.9. Although the strength of the filtration washing judged from the electrical conductivity of the filtrate was the same as in Example 1, much fluorine remained in the sol. The average particle diameter measured by a dynamic scattering method is _{120nm, Nb 2 O 5 = 5.0} % total light transmittance when it than it was 40%, fluorine aggregates of ammonium niobate produces captured within the particles It was thought that The reason why the sol was not obtained is that the mixture was not mixed and reacted while maintaining the pH at 8 or more.
The obtained slurry (Nb ₂ O ₅ = 5.0%) was directly used as a coating solution, spin-coated on a slide glass, and dried at 100 ° C. for 10 minutes to obtain a thin film supporting substrate.

(Comparative Example 3)
Dissolve 50 g of niobium pentoxide (manufactured by Taki Chemical Co., Ltd.) in 480 mL of 10% aqueous hydrofluoric acid solution, and add 2.5 L of ion-exchanged water to obtain an aqueous solution of niobic fluoride of Nb ₂ O ₅ = 1.6%. Obtained. Slowly constant the pH of the reaction solution so that the pH of the reaction solution does not fall below 8.0 against 1.6 L of aqueous ammonia (NH ₃ = 3%) adjusted to 30 ° C. The mixture was added at a rate of about 60 minutes to obtain a dispersion containing fine particles of ammonium niobate having a pH of 8.3 containing a by-product salt and a Nb ₂ O ₅ content of 1.1%. The dispersion was cloudy, and the fine particles easily aggregated and exhibited sedimentation properties. Next, using an ultrafiltration device (Microza UF: Model SLP-1053; manufactured by Asahi Kasei Co., Ltd.), the filtrate is filtered and washed with ion-exchanged water until the electric conductivity of the filtrate is 0.4 mS / cm or less. Although ammonium and the like were removed, a uniformly dispersed sol state was not obtained, and 400 g of ammonium niobate sedimentary slurry having a pH of 8.5 was obtained. The composition analysis of the resulting slurry revealed that the Nb ₂ O ₅ content was 12.0% and F = 30 ppm. The ammonia amount after drying this slurry at 100 ° C. for 10 hours was NH ₃ / Nb ₂ O ₅ ( Molar ratio) = 1.0. The average particle diameter determined by the dynamic scattering method was 280 nm, and the total light transmittance was 5% when Nb ₂ O ₅ = 5.0%. The reason why the sol was not obtained is that the Nb ₂ O ₅ content after the reaction exceeded 1.0% and the average particle size became 100 nm or more. Therefore, the Nb ₂ O ₅ content after the reaction is an important management factor.
The obtained slurry was diluted with ion-exchanged water to Nb ₂ O ₅ = 5.0% and sufficiently dispersed, then used as a coating solution, spin-coated on a slide glass, and dried at 100 ° C. for 10 minutes to form a thin film supporting substrate. The material was obtained.

(Comparative Example 4)
Dissolve 50 g of niobium pentoxide (manufactured by Taki Chemical Co., Ltd.) in 480 mL of 10% aqueous hydrofluoric acid solution, and add 8.8 L of ion-exchanged water to obtain an aqueous niobic fluoride solution of Nb ₂ O ₅ = 0.54%. Obtained. Slowly constant the pH of the reaction solution so that the pH of the reaction solution does not fall below 8.0 against 6.8 L of aqueous ammonia (NH ₃ = 1%) adjusted to 30 ° C. The mixture was added at a rate of about 60 minutes to obtain a dispersion containing fine particles of ammonium niobate having a pH of 9.5 containing a by-product salt and an Nb ₂ O ₅ content of 0.31%. When this dispersion was concentrated to Nb ₂ O ₅ = 5.0% using an evaporator, it became cloudy and thickened and a sol could not be obtained. Composition analysis of the resulting thickened liquid revealed that the Nb ₂ O ₅ content was 1.5% and F = 12000 ppm, and the ammonia amount after drying this thickened liquid at 100 ° C. for 10 hours was NH ₃ / Nb ₂ O. ₅ (molar ratio) = 4.2. The average particle diameter by dynamic scattering was 300 nm, and the total light transmittance was 5% when Nb ₂ O ₅ = 1.5%.
The resulting thickening solution is diluted with ion-exchanged water to Nb ₂ O ₅ = 1.0%, then used directly as a coating solution, spin-coated on a slide glass, and dried at 100 ° C for 10 minutes to form a uniform thin film I could not.

(Comparative Example 5)
Based on Example 2 of Patent Document 4 (Japanese Patent Laid-Open No. 2005-200235) previously filed by the present applicant, oxalic acid / Nb ₂ O ₅ (molar ratio) = 0.15, citric acid / Nb ₂ O ₅ (molar) An acidic niobium oxide sol with a pH of 4.5 containing a ratio) = 0.35 was obtained. Ammonia water was added to the obtained niobium oxide sol until the pH reached 8.5 to obtain an alkaline niobium oxide sol. When the composition analysis of the obtained sol was performed, the Nb ₂ O ₅ content was 10.0% and F = 30 ppm. The amount of ammonia after the sol was dried at 100 ° C. for 10 hours was NH ₃ / Nb ₂ O ₅ (Molar ratio) = 0.6. The average particle diameter determined by the dynamic scattering method was 15 nm, and the total light transmittance was 90% when Nb ₂ O ₅ = 5.0%.
The obtained niobium oxide sol was diluted with ion-exchanged water to Nb ₂ O ₅ = 5.0%, then used as a coating solution, spin-coated on a slide glass, and dried at 100 ° C. for 10 minutes to obtain a thin film supporting substrate. It was. However, as shown in Table 1, this organic acid-containing sol did not exhibit self-binding properties.

(Comparative Example 6)
To 500 g of ammonium niobate sol having an Nb ₂ O ₅ content of 8.0% obtained in Example 1, 22 g of 25% tetramethylammonium hydroxide and 500 g of ion-exchanged water were added, and ammonia was added by heat treatment under reduced pressure. The niobium sol stabilized with tetramethylammonium hydroxide was obtained by removing and concentrating to 500 g. When the composition analysis of the obtained sol was performed, the Nb ₂ O ₅ content was 8.0% and F = 32 ppm, and the ammonia amount after drying this sol at 100 ° C. for 10 hours was NH ₃ / Nb ₂ O ₅ (Molar ratio) = 0.3. The average particle size determined by the dynamic scattering method was 15 nm, and the total light transmittance was 85% when Nb ₂ O ₅ = 5.0%. This sol was stable over a long period of time, and no change in average particle size, transmittance, pH and viscosity was confirmed even after 1 month storage at room temperature.
The obtained sol was diluted with ion-exchanged water to Nb ₂ O ₅ = 5.0%, spin-coated on a slide glass as it was, and dried at 100 ° C. for 10 minutes to obtain a thin film supporting substrate. However, as shown in Table 1, this sol stabilized with tetramethylammonium hydroxide instead of ammonia showed almost no self-binding property.

(Comparative Example 7)
Using the ultrafiltration device (Microza UF: Model SLP-1053; manufactured by Asahi Kasei Co., Ltd.) for the dispersion of ammonium niobate fine particles obtained in Example 1, the electrical conductivity of the filtrate is 1.0 mS / cm or less. After filtering and washing with ion-exchanged water until it became, a part of ammonium niobate fine particles were dissolved by adding ammonia to the dispersion with NH ₃ / Nb ₂ O ₅ (molar ratio) = 2.0. Further, by using a similar ultrafiltration device to filter and wash with ion exchange water until the electrical conductivity of the filtrate was 0.2 mS / cm or less, a dissolved ammonium niobate salt was obtained as a filtrate. The obtained aqueous ammonium niobate solution was concentrated using an evaporator. When the composition analysis of the obtained aqueous solution was performed, the Nb ₂ O ₅ content was 5.0% and F = 150 ppm, and the ammonia amount after drying this aqueous solution at 100 ° C. for 10 hours was NH ₃ / Nb ₂ O _5. (Molar ratio) = 1.8. The average particle diameter by the dynamic scattering method could not be measured, and the total light transmittance at Nb ₂ O ₅ = 5.0% was 95%.
The obtained ammonium niobate aqueous solution was directly used as a coating solution, spin-coated on a slide glass and dried at 100 ° C. for 10 minutes, and a uniform thin film could not be formed.

(Evaluation of thin film substrate)
The thin film-supporting substrates prepared in the above examples and comparative examples were evaluated by the following methods.
[Measurement of refractive index]
The refractive index of the thin film supporting substrate was measured using a thin film measuring apparatus F-20 (manufactured by FILMETRICS).

[Evaluation of self-binding properties (film strength)]
Evaluated by repeated scratching of # 0000 steel wool with a load of 400 g / cm ² applied to the thin film substrate, ◎ for scratches that do not occur at all, ◎ for slight scratches, severely scratches The case where the film was removed was indicated by Δ, and the case where the film disappeared was indicated by x.

[Evaluation of transparency]
The thin film-supported substrate was measured using a chromaticity / turbidity measuring device COH-300A (manufactured by Nippon Denshoku Industries Co., Ltd.).
The results are shown in Table 1.

＊；Nb₂O₅＝1.5％時の全光線透過率

*: Total light transmittance when Nb ₂ O ₅ = 1.5%

Claims (9)

Ammonium niobate sol containing ammonia and niobic acid when dried at 100 ° C. for 10 hours in a range of NH ₃ / Nb ₂ O ₅ (molar ratio) = 0.5 to 1.5 and substantially free of organic acid. _2. The total light transmittance at an optical path length of 10 mm when the average particle diameter of the ammonium niobate colloid is 100 nm or less and Nb ₂ O ₅ in the ammonium niobate sol is 5 mass% is 50% or more. Ammonium niobate sol. The manufacturing method of the ammonium niobate sol of Claim 1 or 2 manufactured by the following process.
(1) Dispersion containing ammonium niobate fine particles by mixing and reacting an aqueous solution in which a niobium compound is dissolved in hydrofluoric acid or a mixed acid of hydrofluoric acid and sulfuric acid and an aqueous ammonia solution while maintaining the pH at 8 or more. A step of obtaining a liquid.
(2) A step of filtering and washing the dispersion liquid of (1). The method for producing an ammonium niobate sol according to claim 3, wherein the Nb ₂ O ₅ concentration of the dispersion is 0.1 to 1.0 mass%. A method for producing an ammonium niobate sol, wherein the ammonium niobate sol obtained by the production method according to claim 3 or 4 is hydrothermally treated at 100 to 150 ° C for 3 to 10 hours. A coating solution for forming a thin film comprising the ammonium niobate sol according to claim 1 or 2. The coating for forming a thin film according to claim 6, wherein the amount of Nb ₂ O ₅ in the ammonium niobate sol contains at least one of an organic polymer compound and a silica compound in a range of 1 to 30% by mass as a solid content. liquid. A thin film-supporting substrate having a film formed on the surface of the substrate using the coating liquid for forming a thin film according to claim 6 or 7. The thin film-supporting substrate according to claim 8, wherein the substrate or the surface of the substrate is ceramics.