JP6253178B2 - Method for producing alumina dispersion - Google Patents

Description

The present invention relates to a method for producing an alumina dispersion.
In the following, “aluminum oxide” is synonymous with alumina whose composition formula is represented by Al ₂ O ₃ .

  With respect to the alumina sol, various techniques have been conventionally disclosed. For example, acidic alumina sol (for example, Patent Document 1) and alkaline alumina sol (for example, Patent Document 2 and Patent Document 3) are disclosed.

  On the other hand, regarding an alumina sol that is stable in an acidic to alkaline region including a neutral region, for example, in Patent Document 4, an aqueous solution of an organic hydroxyl acid is added dropwise to an aqueous solution of an alkali metal aluminate salt and neutralized. Discloses a method for producing an alumina sol that is stable in the pH range of 4-11. Patent Document 5 discloses that a dibasic hydroxycarboxylic acid and a dialkali metal hydrogen phosphate and / or an alkali metal dihydrogen phosphate are added to a liquid in which an aluminum oxide powder produced by a thermal decomposition method is dispersed in an aqueous phase. After adding a solution containing at least one kind of salt, and further adding the aluminum oxide powder, the mixture is stirred with a predetermined shearing force to obtain a stable dispersion of aluminum oxide in a pH range of 5 to 9. A method of manufacturing is disclosed.

JP 59-78925 A JP 59-195527 A JP-A-8-322010 JP 59-223223 A Japanese Patent No. 4778779

However, the method for producing an alumina sol described in Patent Document 4 is not economical because it requires the addition of a large amount of organic hydroxyl acid in order to neutralize the strongly alkaline alkali metal aluminate aqueous solution. In addition, the aluminum compound obtained by neutralization of an aqueous solution of alkali metal aluminate and organic hydroxyl acid is not alumina whose composition formula is represented by Al ₂ O ₃ but boehmite or pseudoboehmite represented by AlOOH. Since it is an alumina hydrate, the resulting sol was more appropriately referred to as an alumina hydrate sol.

  On the other hand, since the aluminum oxide dispersion described in Patent Document 5 contains phosphorus as an essential component, for example, when used for an application involving a baking treatment, the possibility that phosphorus scatters and reacts with other materials, Further, when used as a catalyst material, there is a concern that phosphorus may become a catalyst poison, and there are cases where the use is restricted.

Accordingly, the present invention provides a method for easily producing a solution in which the alumina represented by the composition formula Al ₂ O ₃ is stably dispersed in an acidic to alkaline region including a neutral region without using phosphorus as an essential constituent. Development is a challenge.

  As a result of intensive studies on the above problems, the inventors of the present invention have excellent storage stability by mixing an acidic aluminum oxide dispersion, an organic acid, and an alkali agent, and then heating at 50 to 200 ° C. The inventors have found that an alumina dispersion having a pH of 5 to 14 can be obtained, and have completed the present invention based on such knowledge.

That is, the present invention is as follows.
[1] including a first step of mixing an acidic aluminum oxide dispersion, an organic acid, and an alkali agent, and a second step of heating the mixture obtained in the first step at 50 to 200 ° C., and having a pH of A method for producing an alumina dispersion characterized by being in the range of 5-14.
[2] Alumina in the alumina dispersion exhibits one or more crystal structures selected from the group consisting of ρ, χ, κ, η, pseudo γ, γ, δ, θ, and α types The method for producing an alumina dispersion according to the above [1].
[3] When the ratio of the organic acid in the alumina dispersion is A when the product of the number of moles of organic acid and the number of carboxyl groups in the organic acid is A and the number of moles of Al ₂ O ₃ is B, A / B = The manufacturing method of the alumina dispersion liquid of the said [1] or [2] description which is the range of 0.01-1.0.
[4] Any one of [1] to [3] above, wherein the addition amount of the alkaline agent in the first step is such an addition amount that the pH of the mixed solution obtained in the first step is 4 or more. The manufacturing method of the alumina dispersion liquid of description.
[5] Further, in order to remove excess organic acid and alkali agent, a third step of washing the alumina dispersion obtained by the production method according to any one of [1] to [4] above. A method for producing an alumina dispersion.
[6] An alumina dispersion produced by the production method according to any one of [1] to [5].

  The production method of the present invention has the advantage of being simple. And the alumina dispersion obtained by the production method of the present invention has the characteristics that the pH is 5 to 14, that is, the range of weak acidity to alkalinity covering the neutral region, and the long-term storage stability is high. Furthermore, since the content of the organic acid relative to the aluminum in the alumina dispersion liquid can be significantly less than the amount of the organic acid constituting the normal salt of aluminum, there are a variety of applications including applications involving firing treatment. It can be used widely for various purposes.

2 is a particle size distribution diagram of a mixed liquid and an alumina dispersion liquid 1 in Example 1. FIG.

  Hereinafter, the method for producing an alumina dispersion of the present invention (hereinafter sometimes referred to as “the present production method”) will be described in detail.

  The production method includes a first step of mixing an acidic aluminum oxide dispersion, an organic acid, and an alkali agent, and a second step of heating the mixed liquid obtained in the first step at 50 to 200 ° C. The present invention relates to a method for producing an alumina dispersion (hereinafter sometimes referred to as “the present dispersion”) having a pH in the range of 5 to 14.

  Examples of a method for preparing an acidic aluminum oxide dispersion include, for example, (i) a method in which a commercially available easily dispersible aluminum oxide powder is dispersed in water, and (ii) an aluminum oxide powder and a dispersant (hydrochloric acid). , Nitric acid, acetic acid and other inorganic acids or organic acids) is dispersed in water by a dispersion treatment. Other methods include, for example, the method described in JP-A-7-89717.

  The easily dispersible aluminum oxide powder in the above (i) is preferably an aluminum oxide powder produced by a thermal decomposition method, and as a production method, for example, a method described in the example of Japanese Patent No. 4141386. Is mentioned. Specific examples of the easily dispersible aluminum oxide powder include AEROXIDE Alu 130, AEROXIDE Alu C, AEROXIDE Alu 65 manufactured by EVONIC, and SpectrAl 100, SpectrAl 51, and SpectrAl 81 manufactured by Cabot. In general, a readily dispersible aluminum oxide powder often contains a small amount of acid as a dispersant in order to facilitate dispersibility.

  Examples of the aluminum oxide powder in (ii) above include those generally marketed as reagents or industrial aluminum oxide. Moreover, as a dispersion process, the method of disperse | distributing a liquid mixture using pressure type dispersers, such as a heating, wet grinding, an ultrasonic device, a homogenizer, can be illustrated. However, in said (ii), the inorganic acid or organic acid added as a dispersing agent is contained as an impurity in an alumina dispersion liquid. The impurities can be removed by ultra-cleaning or the like, but considering the ease of production, the preparation method (i) above, which basically does not require the addition of a dispersant, is preferred.

  The alumina crystal structure in the dispersion is preferably one or more selected from the group consisting of ρ, χ, κ, η, pseudo-γ, γ, δ, θ, and α types. In this production method, since the treatment to change the crystal structure of alumina in the acidic aluminum oxide dispersion is not performed, the crystal structure of alumina in this dispersion is the crystal structure of alumina in the acidic aluminum oxide dispersion. It can be said that it is derived from. Therefore, it is preferable that the alumina used for the preparation of the acidic aluminum oxide dispersion has one of the above crystal structures, and a plurality of types may be mixed.

  As the organic acid, hydroxycarboxylic acid is preferable. Examples of the hydroxycarboxylic 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.

  Examples of alkaline agents include alkali metal (preferably sodium or potassium) hydroxide, carbonate, bicarbonate, ammonia, ammonium hydroxide, carbonate, bicarbonate, amines, urea, and the like. Of these, only one type or two or more types may be used. Among the above examples, when this dispersion is used for an application involving a drying treatment or a baking treatment, it can be appropriately selected from ammonia, ammonium hydrogen carbonate, urea, or amines that can be removed during the treatment. preferable. Examples of amines include primary amines, secondary amines, tertiary amines, quaternary ammonium hydroxides, aromatic amines, and alicyclic amines. Examples of the primary amine include methylamine, ethylamine, butylamine, monoethanolamine, and isopropanolamine. Examples of the secondary amine include dimethylamine, diethylamine, diethanolamine, diisopropanolamine and the like. Examples of the tertiary amine include trimethylamine, triethanolamine, triisopropanolamine and the like. Examples of the quaternary ammonium hydroxide include, for example, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethylethylammonium hydroxide, tetratrimethylpropylammonium hydroxide, dimethylhydroxide Examples include diethylamine and choline. Examples of aromatic amines include benzylamine and phenethylamine. Examples of alicyclic amines include piperidine.

  The addition ratio of the organic acid and the alkali agent is not particularly limited as long as the stability of the dispersion can be obtained and the pH of the dispersion is set to be in the range of 5-14. Since the organic acid greatly contributes to the stabilization of the dispersion, if the amount of organic acid added is determined, the pH of the dispersion will be adjusted in consideration of the content of the dispersant in the acidic aluminum oxide dispersion. It is convenient to set the addition amount of the alkaline agent so as to be within the above range.

The addition amount of the organic acid in this dispersion is A / B value when the product of the number of moles of organic acid and the number of carboxyl groups in the organic acid is A and the number of moles of Al ₂ O ₃ is B. May be greater than 1.0. The upper limit of the A / B value is, for example, preferably 6.0, and more preferably 3.0. However, even if a large amount of organic acid is added, the effect corresponding to the added amount may not be obtained and it may not be economical, and if a large amount of organic acid and alkaline agent are contained, inconvenience may occur depending on the application. In some cases.

  Therefore, it is preferable that the amount of the organic acid added is such that A / B = 0.01 to 1.0 in the present dispersion. When the A / B value is less than 0.01, long-term storage stability may be difficult to obtain due to a shortage of organic acid necessary for stabilizing the aluminum component. The A / B value is more preferably in the range of 0.01 to 0.5. In addition, when using this dispersion for the use accompanying a baking process, the one where content of an organic acid is as little as possible is preferable.

  In this production method, since the pH tends to increase due to the heating in the second step, the amount of the alkali agent added may be an amount such that the pH of the mixed solution obtained in the first step is 4 to 5. .

  Moreover, although the density | concentration when using an alkali agent as aqueous solution changes with kinds of alkali agent, generally it is preferable that it is a density | concentration of about 0.2-30 mass%.

  There are no particular restrictions on the form of mixing the acidic aluminum oxide dispersion, the organic acid, and the alkali agent. For example, a method of adding an aqueous solution of an organic acid and an alkaline agent to the acidic aluminum oxide dispersion, acidic aluminum oxide Examples include a method of adding an aqueous solution of an organic acid to an aqueous solution obtained by mixing a dispersion and an alkaline agent, and a method of adding a mixed aqueous solution of an organic acid and an alkaline agent to an acidic aluminum oxide dispersion. In any of the above methods, the order of addition may be changed. Further, 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. Moreover, what is necessary is just to mix by a normal stirring method, and what is necessary is just to set mixing time suitably.

  In the second step, the mixed solution obtained in the first step is heated at 50 to 200 ° C. In general, the heat treatment in the second step shows a phenomenon in which the average particle size is reduced and a phenomenon in which the uniformization of the particle size of the alumina particles is promoted. These phenomena are presumed to be caused by an accelerated reaction between alumina and organic acid on the surface of the alumina particles. In addition, the heat treatment tends to improve long-term storage stability. The heating temperature is preferably 70 to 140 ° C, more preferably 80 to 120 ° C. There is no restriction | limiting in particular in a heating method, A normal heating method, an autoclave, etc. can be illustrated.

  Although this manufacturing method makes the heat processing in a 2nd process essential, it does not exclude the aspect which heat-processes in another process. Accordingly, for example, an embodiment in which heat treatment is performed as necessary in the first step is naturally included in the present manufacturing method. By performing the heat treatment in the first step, the long-term storage stability of the dispersion tends to be further improved, which is considered to be because the reaction between alumina and the organic acid is further promoted. As one aspect of heating in the first step, after adding an acidic aluminum oxide dispersion to an organic acid aqueous solution and heating, an alkali agent is added while maintaining the temperature of the heated state so as not to decrease. is there. In addition, about heating temperature, it is preferable to set it as the range of 50-200 degreeC similarly to the heating temperature of a 2nd process.

  By this production method, the present dispersion having a pH in the range of 5 to 14 can be obtained. When the pH of the present dispersion is less than 5, the viscosity tends to increase and long-term storage stability is difficult to obtain. Considering the safety of the user, the pH range is preferably a weakly acidic to weakly alkaline region, and is approximately 5 to 9 when the region is indicated by pH.

  When this dispersion is used, for example, for applications involving baking treatment, it is preferable that the contents of the organic acid and the alkali agent are small. Therefore, as a third step, this dispersion may be washed to remove excess organic acid and alkali agent. There is no restriction | limiting in particular in the washing | cleaning method, Ultrafiltration, Nutsche filtration, a filter press, etc. which add water can be illustrated, Of these, ultrafiltration is especially preferable. The washing strength may be appropriately set in consideration of the allowable amount of the organic acid and the alkali agent in the intended use within the range not impairing the effects of the present invention.

The cleaning in the third step is generally in the direction of convergence to the neutral region because the excess organic acid and alkali agent are removed as the cleaning strength is increased. Therefore, since the alumina dispersion obtained after washing can be regarded as having a pH within the range of 5 to 14, the alumina dispersion is also referred to as the present dispersion for convenience below.
In addition, generally this dispersion liquid has a low possibility of becoming unstable even if it carries out an overwash. This may be because the organic acid is firmly attached to the alumina surface by the heat treatment in the second step, so that the stability is hardly impaired.

The upper limit of the Al ₂ O ₃ concentration of this dispersion is preferably 30% by mass or less from the viewpoint of stability and handling properties. When it exceeds 30% 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 preferable range of the Al ₂ O ₃ concentration is 3 to 25% by mass. The dispersion may be concentrated by ultrafiltration, heating, or the like, but the Al ₂ O ₃ concentration is preferably not more than the above upper limit. Further, it may be diluted with water or the like.

  This dispersion has high 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. A slight amount of precipitation may occur after long-term storage at room temperature or after storage at 50 ° C for 6 months, but this precipitation is thought to originate from the original aluminum oxide powder with poor dispersibility. There is almost no gradual increase. If it is necessary to remove the precipitate during use, it can be removed by filtration or the like, and there is no particular problem.

  In addition, the dispersion liquid contains substantially only aluminum as a metal element, that is, does not contain any metal element other than aluminum except for metal elements derived from impurities in the raw material. desirable. However, as long as the effects of the present invention are not impaired, elements other than metal elements other than aluminum, such as phosphorus, silicon, and sulfur, and compounds containing these elements as constituents are contained as necessary. It doesn't matter.

In addition to organic acids and alkaline solutions, this dispersion is excellent in mixing properties with anionic sols that exhibit anionic properties, water-soluble organic polymers, resin emulsions, etc., and is also mixed with silica sols in any composition ratio. And has the advantage of excellent dispersibility.
Due to the above advantages, this dispersion can be used in various applications, for example, optical materials, electronic materials, catalyst carriers, coated steel sheets such as zinc, coating agents such as electromagnetic steel sheets, or additives thereof, and ink jet recording. Applications such as an ink receiving layer of a medium can be mentioned. Further, it can be suitably used as a binder for binding inorganic materials to each other. For example, in the ceramics field (ceramic fiber molding, phosphor, refractory, earthenware, cement, etc.) The form of the inorganic material shown on the left includes powder), and uses for binding a ceramic substrate and a catalyst carrier or catalyst carrier in an automobile exhaust gas purification catalyst.
In addition, as this dispersion liquid, it is preferable to use the thing (composition of organic acid content, pH etc.) according to a use. In particular, in applications involving a baking treatment, it is preferable to use one having a low organic acid content in the dispersion.

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.

[Example 1]
To a solution obtained by adding 636 g of ion exchange water to 100 g of “AEROXIDE Alu 130” manufactured by EVONIC, 28 g of 20% citric acid and 235 g of 1% NaOH were added and mixed. This mixed solution had an Al ₂ O ₃ concentration of 10%, pH of 7.9, electric conductivity (EC) of 4.5 mS / cm, and an average particle size of 590 nm. This mixture was heated at 100 ° C. for 3 hours to obtain an alumina dispersion 1 having an Al ₂ O ₃ concentration of 10%, pH 9.2, EC 3.9 mS / cm, average particle size 581 nm, and A / B = 0.09.
In the above A / B, A is the product of the number of moles of the organic acid and the number of carboxyl groups in the organic acid, and B is the number of moles of Al ₂ O ₃ .
The particle size distribution of the mixed solution and alumina dispersion 1 is shown in FIG. In the mixed liquid, there were two peaks, but it can be seen that by heating, the alumina dispersion 1 has one peak, and the uniformization of the particle diameter was promoted.
Table 1 shows the results immediately after the production of the alumina dispersion 1 and after the storage stability test at 50 ° C./6 months. As a result of visual observation, although slight precipitation was observed after storage at 50 ° C. for 6 months, other properties were not changed and kept stable.
Alumina dispersion liquid 1 ′ was prepared by concentrating alumina dispersion liquid 1 to an Al ₂ O ₃ concentration of 20% using an evaporator. As a result of analyzing the crystal structure of the alumina dispersion 1 ′, the presence of γ, δ and θ type alumina was confirmed. In addition, although the alumina dispersion liquid 1 ′ showed a slight precipitation after being stored at 50 ° C. for 6 months, the other properties remained unchanged and remained stable.

[Example 2]
To a solution obtained by adding 139 g of ion exchange water to 100 g of “AEROXIDE Alu C” manufactured by EVONIC, 188 g of 20% citric acid and 572 g of 25% TMAH were added and mixed. This mixed solution had an Al ₂ O ₃ concentration of 10%, pH 13.9, EC 136.3 mS / cm, and an average particle size of 1.7 μm. This mixture was heated at 80 ° C. for 5 hours to obtain an alumina dispersion 2 having an Al ₂ O ₃ concentration of 10%, pH 13.8, EC 111.4 mS / cm, average particle size 1.1 μm, and A / B = 0.6.
The results immediately after the production of the alumina dispersion 2 and after the storage stability test at 50 ° C./6 months are shown in Table 1. As a result of visual observation, although slight precipitation was observed after storage at 50 ° C. for 6 months, other properties were not changed and kept stable.
The alumina dispersion liquid 2 ′ was prepared by diluting the alumina dispersion liquid 2 with ion-exchanged water to an Al ₂ O ₃ concentration of 1%. Alumina dispersion 2 ′ had a slight precipitation after storage at 50 ° C./6 months, but remained stable with no other changes in properties.
The alumina dispersion liquid 2 ″ was prepared by concentrating the alumina dispersion liquid 2 to an Al ₂ O ₃ concentration of 20% using an evaporator. As a result of analyzing the crystal structure of the alumina dispersion 2 ″, the presence of γ, δ and θ type alumina was confirmed. In addition, although the alumina dispersion 2 ″ showed a slight precipitation after storage at 50 ° C./6 months, the other properties remained unchanged and remained stable.

Example 3
To a solution obtained by adding 581 g of ion-exchanged water to 100 g of “AEROXIDE Alu C” manufactured by EVONIC, 283 g of 20% citric acid and 36 g of 28% aqueous ammonia were added and mixed. This mixture had an Al ₂ O ₃ concentration of 10%, pH 6.1, EC 37.3 mS / cm, and an average particle size of 760 nm. This mixture was heated at 120 ° C. for 1 hour to obtain an alumina dispersion 3 having an Al ₂ O ₃ concentration of 10%, pH 8.4, EC 33.4 mS / cm, an average particle size of 533 nm, and A / B = 0.9.
The results immediately after the production of the alumina dispersion 3 and after the storage stability test at 50 ° C./6 months are shown in Table 1. As a result of visual observation, although slight precipitation was observed after storage at 50 ° C. for 6 months, other properties were not changed and kept stable.
As a result of analyzing the crystal structure of the alumina dispersion 3, the presence of γ, δ and θ type alumina was confirmed.

Example 4
To a solution obtained by adding 148 g of ion-exchanged water to 100 g of “AEROXIDE Alu C” manufactured by EVONIC, 942 g of 20% citric acid and 60 g of 28% aqueous ammonia were added and mixed. This mixture had an Al ₂ O ₃ concentration of 8%, a pH of 4.1, an EC of 42.3 mS / cm, and an average particle size of 4.9 μm. This mixed solution was heated at 140 ° C. for 1 hour to obtain an alumina dispersion 4 having an Al ₂ O ₃ concentration of 8%, pH 5.2, EC 40.4 mS / cm, an average particle size of 2.2 μm, and A / B = 3.0.
The results immediately after the production of the alumina dispersion 4 and after the storage stability test at 50 ° C./6 months are shown in Table 1. As a result of visual observation, although slight precipitation was observed after storage at 50 ° C. for 6 months, other properties were not changed and kept stable.
As a result of analyzing the crystal structure of the alumina dispersion 4, it was confirmed that γ, δ, and θ type alumina was present.

[Comparative Example 1]
“DISPERAL D” manufactured by SASOL (Al ₂ O ₃ concentration: 72.4%, crystal structure: boehmite) 599 g of ion-exchanged water was added to 138 g and dispersed. When 20 g of 20% citric acid and 235 g of 1% NaOH were added to this dispersion, gelation occurred. Next, even when heated at 100 ° C. for 3 hours, a dispersion was not obtained.

[Comparative Example 2]
To a solution obtained by adding 860 g of ion exchange water to 100 g of “Alu 130” manufactured by EVONIC, 28 g of 20% citric acid and 12 g of 1% NaOH were added and mixed. This mixture had an Al ₂ O ₃ concentration of 10%, pH 2.7, and EC 1.4 mS / cm. When this mixed solution was heated at 100 ° C. for 3 hours, it gelled and no dispersion was obtained.

<analysis>
(1) The Al ₂ O ₃ concentration was calculated from the firing residue after firing the alumina dispersion at 1200 ° C./1 h according to the old JIS K-5407-8.
(2) The crystal structure was analyzed by measuring an alumina dispersion dried at 100 ° C. with an X-ray diffractometer XRD-7000 (manufactured by Shimadzu Corporation).
(3) EC was measured using a conductivity meter CM-14S (manufactured by TOA ELECTRON Ltd.) without adjusting the concentration of the mixed solution or alumina dispersion.
(4) The average particle size (particle size distribution) is a dynamic light scattering color particle size distribution analyzer LB-500 (Horiba, Ltd.) adjusted to 8% Al ₂ O ₃ concentration in the mixed solution or alumina dispersion. ).

<Storage stability test>
The alumina dispersion was sealed in a 50 mL sample bottle and stored for 6 months in a 50 ° C. constant temperature bath, and then the long-term storage stability was evaluated by measuring pH and EC, and visually observing.

Claims (3)

A first step of mixing an acidic aluminum oxide dispersion, an organic acid and an alkali agent;
A method for producing an alumina dispersion, comprising a second step of heating the mixed liquid obtained in the first step at 50 to 200 ° C., wherein the pH is in the range of 5 to 14.
However,
The organic acid is one or more of lactic acid, citric acid, malic acid, tartaric acid and glycolic acid,
When the product of the number of moles of organic acid and the number of carboxyl groups in the organic acid is A and the number of moles of Al ₂ O ₃ is B, the ratio of the organic acid in the alumina dispersion is A / B = Range from 0.01 to 1.0,
The alumina in the alumina dispersion exhibits one or more crystal structures selected from the group consisting of ρ, χ, κ, η, pseudo γ, γ, δ, θ and α types,
The alumina dispersion does not contain a compound containing phosphorus as a constituent element . The method for producing an alumina dispersion according to claim 1, wherein the addition amount of the alkaline agent in the first step is such that the pH of the mixed liquid obtained in the first step is 4 or more. Furthermore, in order to remove excess organic acids and alkali agents,
A method for producing an alumina dispersion, comprising a third step of washing the alumina dispersion obtained by the production method according to claim 1.

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