JP5582999B2 - Method for producing aqueous solution containing alumina colloid and aqueous solution containing alumina colloid obtained by the production method - Google Patents

Description

The present invention was obtained by a method for producing a colloid composed of alumina hydrate or the like (hereinafter referred to as alumina colloid) and an aqueous solution containing alumina colloid having a pH of 5.5 to 9 containing an ionic aluminum compound, and the production method thereof. The present invention relates to an aqueous solution containing alumina colloid having excellent storage stability.

  A sol in which an alumina colloid is dispersed in a solution (hereinafter sometimes referred to as an alumina sol) or an aqueous solution in which an aluminum salt is dissolved (hereinafter sometimes referred to as an alumina aqueous solution) is an optical material, an electronic material, or a catalyst carrier. It is widely used as a wide variety of materials such as ceramics, heat-resistant binders, cosmetics, and ointments in pharmaceuticals.

  Various techniques have been disclosed in the past regarding alumina sol and aqueous alumina solutions and methods for producing the same. For example, as an acidic alumina sol, an acidic alumina sol composed of pseudoboehmite crystals (Patent Document 1), or an alumina gel obtained from a water-soluble basic aluminum salt is hydrothermally treated in the presence of an organic acid to form a boehmite crystal lattice. And a method for producing an acidic alumina sol (Patent Document 2). Further, as the alkaline alumina sol, an alkaline alumina sol containing an anionic colloidal hydrated alumina (Patent Document 3) or an acidic alumina hydrate sol using an anion exchanger in the presence of an alkali is used. A method for producing an alkaline alumina sol composed of a hydrate (Patent Document 4) is mentioned.

On the other hand, Patent Document 5 discloses that a stable alumina sol can be obtained even in a neutral region by adding an aqueous solution of an organic hydroxyl acid dropwise to an aqueous solution of an alkali metal aluminate salt.
Further, the applicant of the present application discloses a method for producing an acidic aqueous alumina solution made of basic aluminum having an acid amount per equivalent equivalent to that of a normal salt (Patent Documents 6 and 7).

JP 59-78925 A JP 53-112299 A JP 59-195527 A JP-A-8-322010 JP 59-223223 A Japanese Patent Publication No.58-5174 Japanese Patent Publication No.59-40381

However, since acidic alumina sol is composed of a cationic aluminum compound, when it is mixed with anionic fine particles such as colloidal silica, it agglomerates violently, thus limiting the application and restrictions on use. Moreover, it is difficult to say that alkaline alumina sol is sufficient in terms of transparency and stability over time. Furthermore, the alumina sol described in Patent Document 3 has a high pH of 10 to 14, and in the production method, alumina trihydrate is calcined to form a monohydrate, which is kneaded in an alkaline solution. The method described in Patent Document 4 uses an anion exchanger, which requires a long time for production and is not economical.
On the other hand, in the method for producing a neutral alumina sol described in Patent Document 5, it is necessary to add a large amount of an organic acid in order to neutralize a strong alkaline alkali metal aluminate aqueous solution, which is not economical.

  In addition, many literatures disclosing technologies related to alumina sol and aqueous alumina solutions are said to be excellent in stability, but commercially available alumina sol and aqueous alumina solutions are about several weeks to several months after production. In many cases, long-term storage stability such as precipitation is observed in many cases, and there is almost no alumina sol or aqueous alumina solution in the neutral region. Therefore, a neutral region and excellent long-term storage stability have been strongly desired.

  In light of the current situation as described above, the present inventors have made extensive studies on neutral alumina sol and aqueous alumina solution with a low organic acid content, and as a result, skillfully set the blending amount of the organic acid and aluminum. By adjusting to a specific pH, an alumina colloid-containing aqueous solution containing an alumina colloid and an ionic aluminum compound and having a long-term storage stability including a neutral region of pH 5.5-9 can be obtained. The present invention has been completed based on the finding and the findings.

That is, the present invention relates to a method for producing an aqueous solution containing alumina colloid having a pH of 5.5 to 9, characterized by mixing and heating an organic acid, alumina hydrate and an alkali agent. However, the product (A) of the number of moles of the organic acid and the number of carboxyl groups in the organic acid and the number of moles (B) of Al ₂ O _{3 in} the aqueous solution containing alumina colloid is A / B = 1.0. It is in the range of ~ 2.0.
Moreover, this invention relates to the manufacturing method of the alumina colloid containing aqueous solution of pH5.5-9 characterized by mixing basic organic acid aluminum aqueous solution and an alkali agent. However, the product (A) of the number of moles of the organic acid and the number of carboxyl groups in the organic acid and the number of moles (B) of Al ₂ O _{3 in} the aqueous solution containing alumina colloid is A / B = 1.0. It is in the range of ~ 2.0.
Furthermore, the present invention relates to a method for producing an alumina colloid-containing aqueous solution, wherein the alumina colloid-containing aqueous solution obtained by the above production method is further heated at 70 to 200 ° C.
Moreover, this invention relates to the alumina colloid containing aqueous solution manufactured by one of the said manufacturing methods.
Furthermore, the present invention, the alumina colloid-containing aqueous solution, when filtered through a ultrafiltration membrane with molecular weight cut off 10,000, the Al ₂ O ₃ in the filtrate, the Al ₂ O ₃ in the aqueous solution before filtration On the other hand, it relates to an alumina colloid-containing aqueous solution of 5 to 50% by mass.

In the aqueous solution containing alumina colloid obtained by the production method of the present invention, (1) the content of the organic acid relative to aluminum is less than the amount of the organic acid constituting the normal salt of aluminum, and (2) the pH is 5.5-9. That is, it is in the range of weakly acidic to neutral to weakly alkaline, (3) excellent in long-term storage stability, and (4) substantially containing only aluminum as a metal element, that is, derived from impurities in the raw material. Since it has the property of not containing any metal element other than aluminum except for the metal element to be used, it can be widely used for various applications. In particular, by including a neutral region, it can be mixed with various metal salts and sols, and exhibits excellent characteristics in various applications. Furthermore, it has the advantage that the production method is simple, and its industrial significance is tremendous.

Hereinafter, the manufacturing method of the alumina colloid containing aqueous solution of this invention is demonstrated in detail.
The first production method of the present invention is a method for producing an aqueous solution containing alumina colloid having a pH in the range of 5.5 to 9, characterized by mixing and heating an organic acid, alumina hydrate, and an alkaline agent. . However, the product (A) of the number of moles of the organic acid and the number of carboxyl groups in the organic acid and the number of moles (B) of Al ₂ O _{3 in} the aqueous solution containing alumina colloid is A / B = 1.0. It is in the range of ~ 2.0.

  Here, with regard to the A / B value, when the A / B value is less than 1.0, an unreacted aluminum component remains, making it difficult to obtain a uniform solution state. On the other hand, if the A / B value exceeds 2.0, even if a solution is obtained once, it is likely to be an unstable solution due to the generation of precipitates or gelation after storage for several days. There is a tendency for the binder performance to decrease because the components are produced in excess. In addition, in the use which performs a baking process, the one where content of an organic acid is small is preferable, However, The alumina colloid containing aqueous solution obtained by the method of this invention can be said to be the optimal thing also in this point.

As the organic acid used in the present invention, oxycarboxylic acid is preferable. Examples of the oxycarboxylic acid include lactic acid, citric acid, malic acid, tartaric acid, glycolic acid and the like. Of these, only one kind or two or more kinds may be used.
As the alumina hydrate, commercially available aluminum hydroxide or aluminum oxide hydrate, or alumina hydrate gel obtained by neutralization of an aluminum salt or the like can be suitably used. Of these, those that are easily soluble are particularly preferred.
Alkali agents include alkali metal hydroxides (sodium hydroxide, potassium hydroxide, etc.), carbonates, bicarbonates, ammonia, ammonium hydroxides, carbonates, bicarbonates, amines, and urea. But you can use it. Among these, in the use of the alumina colloid-containing aqueous solution of the present invention, when used after drying or baking, it is possible to use ammonia, ammonium hydrogen carbonate, urea, or amines that can be removed during the treatment. preferable. The alkali agent may be used alone or in combination of two or more. The concentration in the case of using the alkaline agent as an aqueous solution varies depending on the type of the alkaline agent, but is generally preferably about 0.2 to 30% by mass.

  The mixing method of the organic acid, the alumina hydrate and the alkali agent, and the heating method are not particularly limited. For example, a solution in which an organic acid dissolved in water and an aqueous solution of an alumina hydrate and an alkali agent are mixed. Alternatively, after adding alumina hydrate to an organic acid aqueous solution and heating, an alkali agent may be added while maintaining the temperature of the heated state so as not to decrease. The mode of addition may be continuous or intermittent, and the rate of addition is not particularly limited, but it is desirable to avoid adding a large amount at once. The mixing mode may be a normal stirring method, and the mixing time may be set as appropriate. The purpose of heating in the present invention is dissolution of alumina hydrate, and the heating temperature is preferably 50 to 200 ° C, more preferably 70 to 140 ° C, and still more preferably 90 to 120 ° C. There is no restriction | limiting in particular in a heating method, A normal heating method, an autoclave, etc. can be illustrated.

The second production method of the present invention is a method for producing an alumina colloid-containing aqueous solution having a pH in the range of 5.5 to 9, characterized by mixing an aqueous basic organic acid aluminum solution and an alkaline agent. However, the product (A) of the number of moles of the organic acid and the number of carboxyl groups in the organic acid and the number of moles (B) of Al ₂ O _{3 in} the aqueous solution containing alumina colloid is A / B = 1.0. It is in the range of ~ 2.0.

The basic organic aluminum acid aqueous solution is an aqueous solution containing an ionic aluminum compound, and examples thereof include a basic aluminum lactate aqueous solution. For these, commercially available industrial chemicals may be used, or those obtained by known production methods may be used. For example, as a commercially available industrial chemical, a basic aluminum lactate aqueous solution (Taxelum (registered trademark): manufactured by Taki Chemical Co., Ltd., pH 4-5, A / B = 1.5-1.6, Al ₂ O ₃ concentration : 8-9 mass%). As known production methods, Patent Document 6 (Japanese Patent Publication No. 58-5174) and Patent Document 7 (Japanese Patent Publication No. 59-40181) disclosing methods for producing basic aluminum lactate can be exemplified. Among these, those having A / B = 1.0 to 2.0 have high stability as basic salts, and therefore can be suitably used in the present invention. In addition, when the A / B value of the alumina colloid-containing aqueous solution, which is the final product, exceeds 2.0, the same phenomenon as described in the first manufacturing method occurs.
In the present invention, the basic organic acid aluminum aqueous solution may contain an inorganic acid radical derived from the production raw material or an inorganic acid group added for stabilization of the basic organic acid aluminum aqueous solution. .
About the kind of alkaline agent, it is the same as that of said 1st manufacturing method. Further, the mode of addition and the mode of mixing are the same as in the first production method.
In the second production method, since the basic organic acid aluminum aqueous solution having the A / B value and the alkaline agent are mixed, the A / B value in the alumina colloid-containing aqueous solution that is the final product is the base that is the raw material. This is the same as the A / B value of the aqueous organic organic acid solution.

Next, among the A / B value and pH common to the first production method and the second production method, since the A / B value is as described above, the pH will be described. In both of the above production methods, it is important to mix the raw materials so that the pH of the alumina colloid-containing aqueous solution, which is the final product, is in the range of 5.5-9. When the pH is less than 5.5 or more than 9, precipitates are generated or gelled regardless of the storage period, and the object of the present invention cannot be achieved. If it is in this range, it can sufficiently withstand long-term storage, but the aqueous solution tends to have a slight pH decrease with time. Therefore, the pH range immediately after the production is preferably 6.0 to 9, more preferably 6.5 to 9.
In the first production method, the pH of the mixed solution is acidic to neutral because unreacted organic acid and alkaline agent are present in the solution, but the reaction between aluminum and organic acid proceeds by heat treatment. Therefore, the pH increases due to the influence of the remaining alkaline agent. Therefore, in the first production method, it is desirable to appropriately set the amounts of the organic acid and the alkali agent so that the pH after heating falls within the above range in consideration of heating conditions such as heating temperature and time.

Further, the concentration of Al ₂ O ₃ alumina colloid-containing aqueous solution of the present invention, it is preferable upper limit is 20 mass% or less. When it exceeds 20% by mass, the viscosity increases and the handling property tends to deteriorate. The lower limit of the concentration of Al ₂ O ₃ is not particularly limited, it is preferable from an economical point of view is 1% by mass or more. A more preferred range of concentration of _Al 2 _{O 3} is 3 to 15 mass%.

In the present invention, since the raw material to be mixed is contained in the final product as it is without being lost outside the system except for volatile substances such as ammonia, the mixing ratio of the raw material contains the alumina colloid that is the final product. What is necessary is just to set suitably according to the design value in aqueous solution. In addition, in the second production method, when a commercially available basic organic acid aluminum acid aqueous solution of about 1 to 10% by mass is used as Al ₂ O ₃ , it can be used as a raw material as it is or diluted.

The alumina colloid-containing aqueous solution of the present invention obtained by such a production method is highly transparent in appearance, and can be used particularly as a coating agent. In addition, since it contains an appropriate amount of an organic acid as a dispersant, it is excellent in miscibility with an acid-alkaline solution and is particularly useful for applications in which an organic acid is removed by firing.
In addition, the alumina colloid-containing aqueous solution of the present invention is excellent in long-term storage stability with little change in appearance and viscosity for 6 months or more even at room temperature storage as well as storage at room temperature.

  Also, when using the alumina colloid-containing aqueous solution of the present invention as a coating agent to prevent cracking of the film during relatively strong heat drying, or when using it as a catalyst, optical material, etc., to further improve its performance The object can be achieved by further grain growth of the alumina colloid in the aqueous solution. That is, the purpose can be achieved by heating the aqueous solution. The heating referred to here is different from the heating for dissolving the alumina hydrate in the first production method, and is the reheating of the aqueous solution containing the alumina colloid produced by the method of the present invention. The heating temperature may be appropriately set depending on the desired particle size, but the temperature range is preferably 70 to 200 ° C. Similarly, the heating time may be appropriately set depending on the desired particle size. In general, the higher the heating temperature, the faster the grain growth, and the longer the heating time, the larger the grains. A heating method is not particularly limited, and a normal heating method, an autoclave, or the like may be used. In addition, since pH falls by heating, when heating, it is desirable to set pH value before a heating so that pH after a heating may be in the range of 5.5-9.

The mixing ratio of the ionic aluminum compound and the alumina colloid in the alumina colloid-containing aqueous solution of the present invention is not particularly limited, but when the aqueous solution is filtered through an ultrafiltration membrane having a molecular weight cut off of 10,000, of _Al 2 _{O 3} is, with respect to _Al 2 _{O 3} in an aqueous solution before filtration, which is one of it is desirable embodiments to be 5 to 50 mass%. At this time, it can also be considered that the ionic aluminum compound and the alumina colloid exist as Al ₂ O _{3 in} a mass ratio of 5:95 to 50:50.

By the way, when the alumina colloid-containing aqueous solution of the present invention is compared with the basic organic acid aluminum aluminum solution that is the raw material of the second production method, the alumina colloid-containing aqueous solution of the present invention is the basic material that is the raw material of the second production method. Whereas an aqueous solution containing both an alumina colloid and an ionic aluminum compound is obtained by a neutralization reaction between an organic acid aluminum aqueous solution and an alkaline agent, the basic organic acid aluminum aqueous solution is mostly in the solution as an ionic aluminum compound. Exists. This is due to, for example, the filtration leakage rate (mass% of Al ₂ O ₃ in the filtrate with respect to Al ₂ O _{3 in} the aqueous solution before filtration) when filtering using an ultrafiltration membrane with a molecular weight cut off of 10,000. Can be explained. That is, the basic organic acid aluminum aqueous solution has different filtration leakage rates depending on the type of organic acid and the abundance ratio of the organic acid and aluminum. For example, the filtration is performed when the basic aluminum lactate aqueous solution has an A / B value of 1.0. There is a difference that the leakage rate is 55% by mass and the filtration leakage rate in the case of 1.6 is 65% by mass, whereas the alumina colloid-containing aqueous solution of the present invention is 5 to 50% by mass. Moreover, in the result of the powder X-ray diffraction analysis of the dried product dried at 100 ° C. for the alumina colloid-containing aqueous solution of the present invention and the basic organic acid aluminum solution, the former shows a pseudo-boehmite crystal form. The latter is different in that it shows an irregular shape (amorphous). The reason why such a difference occurs is that, in the present invention, by raising the pH of the aqueous solution of the basic organic acid aluminum, a part of the ionic aluminum compound is precipitated and dispersed as a colloid. It is presumed that this is due to the fact that the abundance of the colloidal alumina produces a skillful equilibrium.

Since the alumina colloid-containing aqueous solution of the present invention has excellent stability, it can be used by being concentrated by ultrafiltration or heating, or can be diluted with water or the like. However, since ultrafiltration cannot recover all the aluminum components as described above, heat concentration is preferred. When concentrating by heating or the like, the concentration of Al ₂ O _{3 in} the aqueous solution after concentration is preferably 20% by mass or less from the viewpoint of stability and handling properties.

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. In Examples, “%” means “% by mass” unless otherwise specified.
The raw materials used in the examples were those available as reagents or industrial chemicals.

<analysis>
(1) The Al ₂ O ₃ concentration was calculated from the firing residue after firing the alumina colloid-containing aqueous solution at 1000 ° C./5 h in accordance with the old JIS K-5407-8. The iron concentration was calculated from the iron oxide concentration.
(2) The crystal structure was analyzed by measuring an aqueous solution dried at 100 ° C. with an X-ray diffractometer XRD-7000 (manufactured by Shimadzu Corporation).
(3) The electric conductivity was measured using an electric conductivity meter CM-14S (manufactured by TOA ELECTRON Ltd.).
(4) The viscosity was measured with an E-type viscometer after setting the temperature of the aqueous solution to 25 ° C.
(5) transmittance, and the aqueous solution was measured which was adjusted to 7.5 wt% as Al ₂ O ₃ on the side colorimeter ND-300A (manufactured by Nippon electric decoration Kogyo Co.). However, when the Al ₂ O ₃ content in the aqueous solution was less than 7.5% by mass, the measurement was performed with the stock solution.
(6) The average particle size was measured using a dynamic light scattering color particle size distribution analyzer LB-500 (manufactured by Horiba, Ltd.).

<Storage stability test>
The sample was sealed in a 50 mL sample bottle and stored in a 50 ° C. constant temperature bath for 6 months, and the long-term storage stability was evaluated by measuring pH, EC, viscosity, and transmittance before and after storage, and visual observation. .
<Filtration leakage rate>
Filtration leakage rate is calculated by the percentage of the mass of the aluminum component in the filtrate with respect to the mass of the aluminum component before filtration when filtered through an ultrafiltration membrane with a molecular weight cut off of 10,000 (ADVANTEC ultra filter unit USY-1). did.
<A/B value>
The product of the number of moles of organic acid and the number of carboxyl groups in the organic acid is A, and A / B when the number of moles of Al ₂ O ₃ is B is the A / B value.

[Example 1]
Ion exchange water was added to aluminum hydroxide to obtain a 10% slurry as Al ₂ O ₃ . To 100 parts by mass of the slurry, 12 parts by mass of 88% lactic acid and 10 parts by mass of 20% aqueous ammonia were added (pH 6.8 at this time). This was heated at 100 ° C. for 3 hours to obtain an alumina colloid-containing aqueous solution having an Al ₂ O ₃ concentration of 8.2% and a pH of 8.5. The obtained aqueous solution had an A / B value of 1.2 and an average particle size of 11 nm. The analytical values immediately after production and after storage at 50 ° C./6 months are shown in Table 1. Although a slight decrease in pH was observed after storage, gelation and precipitation were not observed, and the stability was maintained. Further, the aqueous solution obtained by concentrating the Al ₂ O ₃ concentration to 15% using an evaporator maintained a stable state even after a storage stability test for 6 months. The powder X-ray diffraction of the dried product of the aqueous solution immediately after concentration showed a pseudoboehmite diffraction pattern, confirming that the resulting aqueous solution contained alumina colloid.

[Example 2]
Ion exchange water was added to aluminum hydroxide to obtain a 10% slurry as Al ₂ O ₃ . To 100 parts by mass of the slurry, 12 parts by mass of 88% lactic acid and 27 parts by mass of 10% aqueous sodium hydroxide solution were added (pH 3.7 at this time). This was heated at 100 ° C. for 3 hours to obtain an alumina colloid-containing aqueous solution having an Al ₂ O ₃ concentration of 7.2% and a pH of 7.3. The obtained aqueous solution had an A / B value of 1.2 and an average particle size of 11 nm. The analytical values immediately after production and after storage at 50 ° C./6 months are shown in Table 1. After storage, gelation and precipitate generation were not observed, and stability was maintained. An aqueous solution obtained by diluting this aqueous solution with ion-exchanged water to an Al ₂ O ₃ concentration of 1% remained stable even after a 6-month storage stability test. The powder X-ray diffraction of the dried product of the aqueous solution immediately after dilution showed a pseudoboehmite diffraction pattern, confirming that the aqueous solution obtained contained alumina colloid.

Example 3
After slowly reacting an aqueous solution of aluminum sulfate (10% as Al ₂ O ₃ ) with an aqueous solution of ammonium hydrogen carbonate (5% as NH ₃ ) until the pH reaches 8.0, it was converted to 10 as Al ₂ O ₃ by ultra-cleaning. % Alumina hydrate gel was obtained. By reacting 10 parts by mass of 88% lactic acid with 100 parts by mass of this gel, a basic aluminum lactate aqueous solution (Al ₂ O ₃ concentration = 9.1%, lactic acid / Al ₂ O ₃ molar ratio = 1.0, pH 5.7) Produced. To 100 parts by mass of this basic aluminum lactate aqueous solution, 2 parts by mass of 20% aqueous ammonia was gradually added with stirring to obtain an aqueous solution containing alumina colloid having a pH of 6.7. The obtained aqueous solution had an A / B value of 1.0, an Al ₂ O ₃ concentration of 8.9%, and an average particle diameter of 6 nm. When this solution was hydrothermally treated at 100, 120, and 140 ° C. for 3 hours, the average particle size was 8, 15, and 31 nm, respectively, confirming the growth of alumina colloid particles. The analysis values immediately after the production of the aqueous solution before hydrothermal treatment and after storage at 50 ° C./6 months are shown in Table 1. After storage, gelation and precipitate generation were not observed, and stability was maintained. The powder X-ray diffraction of the dried product of this aqueous solution immediately after production showed a pseudoboehmite diffraction pattern, confirming that the obtained aqueous solution contained alumina colloid.

Example 4
After slowly reacting an aqueous solution of aluminum sulfate (10% as Al ₂ O ₃ ) with an aqueous solution of ammonium hydrogen carbonate (5% as NH ₃ ) until the pH reaches 8.0, it was converted to 10 as Al ₂ O ₃ by ultra-cleaning. % Alumina hydrate gel was obtained. A basic aluminum lactate aqueous solution (Al ₂ O ₃ concentration = 8.6%, lactic acid / Al ₂ O ₃ molar ratio = 1.6, pH 4.5) is reacted with 100 parts by mass of the gel and 88% lactic acid. Produced. After gradually adding 7 parts by mass of 20% aqueous ammonia to 100 parts by mass of this basic aluminum lactate aqueous solution with stirring, it was heated at 140 ° C. for 3 hours to obtain an alumina colloid-containing aqueous solution having a pH of 7.8. The obtained aqueous solution had an A / B value of 1.6, an Al ₂ O ₃ concentration of 8.0%, and an average particle diameter of 33 nm. Table 1 shows analytical values immediately after production of the obtained aqueous solution and after storage at 50 ° C for 6 months. After storage, gelation and precipitate generation were not observed, and stability was maintained. The powder X-ray diffraction of the dried product of this aqueous solution immediately after production showed a pseudoboehmite diffraction pattern, confirming that the obtained aqueous solution contained alumina colloid.

Example 5
Ion exchange water was added to aluminum hydroxide to obtain a 20% slurry as Al ₂ O ₃ . To 100 parts by mass of the slurry, 125 parts by mass of 20% malic acid and 21 parts by mass of 20% aqueous ammonia were added (pH 4.6 at this time). This was heated at 140 ° C. for 3 hours to obtain an alumina colloid-containing aqueous solution having an Al ₂ O ₃ concentration of 8.1% and a pH of 8.1. The obtained aqueous solution had an A / B value of 1.9 and an average particle size of 9 nm. Table 1 shows analytical values immediately after production of the obtained aqueous solution and after storage at 50 ° C for 6 months. After storage, gelation and precipitate generation were not observed, and stability was maintained. The powder X-ray diffraction of the dried product of this aqueous solution immediately after production showed a pseudoboehmite diffraction pattern, confirming that the obtained aqueous solution contained alumina colloid.

[Comparative Example 1]
After slowly reacting an aqueous solution of aluminum sulfate (10% as Al ₂ O ₃ ) with an aqueous solution of ammonium hydrogen carbonate (5% as NH ₃ ) until the pH reaches 8.0, it was converted to 10 as Al ₂ O ₃ by ultra-cleaning. % Alumina hydrate gel was obtained. By reacting 15 parts by mass of 88% lactic acid with 100 parts by mass of this gel, a basic aluminum lactate aqueous solution (Al ₂ O ₃ concentration = 8.7%, lactic acid / Al ₂ O ₃ molar ratio = 1.5, pH 4.6) Produced. To 100 parts by mass of this basic aluminum lactate aqueous solution, 15 parts by mass of 2% aqueous ammonia was gradually added with stirring to obtain an alumina colloid-containing aqueous solution having a pH of 5.2. The obtained aqueous solution had an A / B value of 1.5 and an Al ₂ O ₃ concentration of 7.6%. However, in the obtained aqueous solution, generation of precipitate was observed after storage at 50 ° C./1 month.

[Comparative Example 2]
After slowly reacting an aqueous solution of aluminum sulfate (10% as Al ₂ O ₃ ) with an aqueous solution of ammonium hydrogen carbonate (5% as NH ₃ ) until the pH reaches 8.0, it was converted to 10 as Al ₂ O ₃ by ultra-cleaning. % Alumina hydrate gel was obtained. By reacting 15 parts by mass of 88% lactic acid with 100 parts by mass of this gel, a basic aluminum lactate aqueous solution (Al ₂ O ₃ concentration = 8.7%, lactic acid / Al ₂ O ₃ molar ratio = 1.5, pH 4.6) Produced. To 100 parts by mass of this basic aluminum lactate aqueous solution, 17 parts by mass of a 24% sodium hydroxide aqueous solution was gradually added with stirring to obtain an alumina colloid-containing aqueous solution having a pH of 10.5. The A / B value of the obtained aqueous solution was 1.5, and the Al ₂ O ₃ concentration was 7.4%. However, the obtained aqueous solution was gelled after storage at 50 ° C./1 month.

[Comparative Example 3]
Ion exchange water was added to aluminum hydroxide to obtain a 10% slurry as Al ₂ O ₃ . When 5 parts by weight of 88% lactic acid and 5 parts by weight of 10% ammonia water were added to 100 parts by weight of this slurry (pH 4.7 at this time, A / B value was 0.5) and heated at 100 ° C. for 3 hours, An undissolved aluminum hydroxide was observed in the inside, and an alumina colloid-containing aqueous solution was not obtained with a good yield.

[Comparative Example 4]
According to JP 59-223223 (Example 4), 100 parts by mass of an aqueous potassium aluminate solution (Al ₂ O ₃ = 8.0%, K ₂ O / Al ₂ O ₃ molar ratio 1.63) was stirred with a homomixer. Below, 130 parts by mass of a 20% aqueous lactic acid solution was gradually added dropwise to obtain an aqueous solution having a pH of 8.0. The A / B value of this aqueous solution was 3.7, and the Al ₂ O ₃ concentration was 3.5%. When this aqueous solution was stored at 50 ° C., an increase in viscosity was observed over time.

[Comparative Example 5]
Commercially available basic aluminum chloride ("Tan White" manufactured by Taki Chemical Co., Ltd. Al ₂ O ₃ concentration = 23%, Cl = 12%, pH 2.5. Does not contain organic acids. Cl / Al ₂ O ₃ (mol Ratio) = 1.5.) Was diluted to 10% as Al ₂ O ₃ . When 4 parts by mass of 20% aqueous ammonia was added to 100 parts by mass of this diluted product, white turbidity occurred immediately after the addition. After completion of the addition, a few minutes after standing, generation of precipitates was observed at the bottom of the reaction vessel, and an alumina colloid-containing aqueous solution was not obtained.

[Reference example]
In the same manner as in Example 4, an aqueous ammonium hydrogen carbonate solution (5% as NH ₃ ) was slowly added to an aluminum sulfate aqueous solution (10% as Al ₂ O ₃ ) until the pH reached 8.0, and then subjected to ultracleaning. Thereby obtaining 10% alumina hydrate gel as Al ₂ O ₃ . 16 parts by mass of 88% lactic acid is reacted with 100 parts by mass of this gel, and a basic aluminum lactate aqueous solution (Al ₂ O ₃ concentration = 8.6%, lactic acid / Al ₂ O ₃ molar ratio = 1.6, pH 4.5, EC1 0.5 mS / cm, viscosity 3.4 mPa · s, transmittance 99%). From the powder X-ray diffraction analysis of the dried product of this aqueous solution, it was confirmed to be amorphous. Moreover, the filtration leakage rate when this aqueous solution was filtered with an ultrafiltration membrane was 65 mass%. Further, when the basic aluminum aqueous solution before filtration was stored at 50 ° C., generation of precipitates was observed at the bottom of the reaction vessel in about 2 weeks.

Claims (5)

A method for producing an aqueous solution containing alumina colloid having a pH of 5.5 to 9, wherein an organic acid, an alumina hydrate and an alkali agent are mixed and heated.
However, the product (A) of the number of moles of the organic acid and the number of carboxyl groups in the organic acid and the number of moles (B) of Al ₂ O _{3 in} the aqueous solution containing alumina colloid is A / B = 1.0. It is in the range of ~ 2.0. A method for producing an aqueous solution containing alumina colloid having a pH of 5.5 to 9, comprising mixing an aqueous aluminum salt of a basic organic acid and an alkaline agent.
However, the product (A) of the number of moles of the organic acid and the number of carboxyl groups in the organic acid and the number of moles (B) of Al ₂ O _{3 in} the aqueous solution containing alumina colloid is A / B = 1.0. It is in the range of ~ 2.0. A method for producing an alumina colloid-containing aqueous solution, wherein the alumina colloid-containing aqueous solution obtained by the production method according to claim 1 or 2 is further heated at 70 to 200 ° C. Alumina colloid-containing aqueous solution produced by the production method according to claim 1. Alumina colloid-containing aqueous solution according to claim 4, when filtered through a ultrafiltration membrane with molecular weight cut off 10,000, the _Al 2 _{O 3} in the filtrate, relative to _Al 2 _{O 3} in the aqueous solution before filtration, Alumina colloid-containing aqueous solution of 5 to 50% by mass.