Alumina aqueous dispersion and method for producing same

Abstract

The present invention provides a neutral to alkaline aqueous alumina dispersion that can be obtained in a stable pH range without using an alkaline earth metal compound as an alkaline agent, and that has good emulsion stability as a Pickering adjustment material, and also provides a method for producing the same. [Solution] The present invention provides an alumina aqueous dispersion that is alkaline earth metal-free, contains 1 to 30 mass% Al2O3, has a pH of 6 to 9.5, has an average particle size of 5 to 1,000 nm converted into number as measured by dynamic light scattering particle size distribution measurement, has a zeta potential of -20 to 10 mV, and is amorphous, pseudo-boehmite, or boehmite when dried at 100°C; the alumina aqueous dispersion is characterized in that, when the alumina aqueous dispersion is mixed and homogenized with liquid paraffin in a weight ratio of 1:1, a W / O type emulsion is formed that does not undergo phase separation even after 72 hours, and has a micelle size range of 50 to 600 μm; and a method for producing the same.

Description

[Technical Field]

[0001] The present invention relates to an aqueous alumina dispersion and a method for producing the same. [Background technology]

[0002] Aqueous dispersions of alumina particles are currently used in a variety of applications. Conventionally, they have been used as binders for forming refractories by firing ceramics and as film fillers for surface coatings. In recent years, numerous research results have been reported on the preparation of Pickering emulsions that can be stabilized by interfacial adsorption without using surfactants (see, for example, B. Binks et al., Advances in Colloid and Interface Science 100-102 (2003) (Non-Patent Document 1)). Their applications are expanding as functional raw materials for cosmetic materials, emulsion polymerization resin materials, aqueous coating agents, adhesives, porous materials, microcapsule materials, and the like.

[0003] Meanwhile, various technologies have been disclosed for aqueous alumina dispersions, including acidic aqueous alumina dispersions and neutral to alkaline aqueous alumina dispersions (e.g., Patent Documents 1, 2, and 3). Of these, many acidic aqueous alumina dispersions have been commercially available, but neutral to alkaline aqueous alumina dispersions, taking into account alumina hydrate or aluminum oxide, have an isoelectric point (pH at which the zeta potential becomes 0) between approximately 7 and 9, making them unstable in terms of potential, and therefore the design conditions are very strict, making them difficult to handle.

[0004] As described above, there has been a need for neutral to alkaline alumina aqueous dispersions as materials for preparing Pickering emulsions in recent years, for use in formulations that cannot be used in acidic solutions due to reactions or deterioration, and improved formulations have been desired. Furthermore, the use of alkaline earth metal compounds in these preparation materials is undesirable because impurity elements can cause the potential to become unstable or, depending on the application, can prevent the desired performance from being achieved. Furthermore, there has traditionally been an issue of poor stability during emulsification, and improvements have been desired.

[0005] Patent No. 3708985 (Patent Document 1) discloses that crystalline alumina is subjected to an acidic alumina dispersion treatment and then converted into an alkaline dispersion using an anion exchange resin. First, for crystalline alumina, the entire process is very long and complicated, as it involves synthesizing a calcined product, dispersing it in water again, acidifying it and deflocculating it, and then using ion exchange to remove impurities and make it alkaline, resulting in issues of high cost and low productivity.

[0006] Japanese Patent No. 6598377 (Patent Document 2) discloses an alumina colloidal dispersion containing only lactic acid as an organic acid, containing no alkali metal or ammonia compounds, and having a pH of 5 to 8. This alumina colloidal dispersion contains an alkaline earth metal substance as an essential component, which can lead to impurities and quality defects in firing applications, and therefore has significant limitations on its use.

[0007] Japanese Patent No. 7308650 (Patent Document 3) discloses an aqueous alumina dispersion containing lactic acid and / or malic acid as an organic acid, ammonia and / or alkali metal, and having an average particle size of 50 to 3000 nm at a pH of 5.5 to 9. This document does not mention impurity elements, nor does it mention the preparation of Pickering emulsions, and does not consider emulsifying performance. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 3708985 [Patent Document 2] Patent No. 6598377 [Patent Document 3] Patent No. 7308650 [Non-patent literature]

[0009] [Non-Patent Document 1] B. Binks et. Al, Advances in Colloid and Interface Science 100-102(2003) Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to provide a neutral to alkaline aqueous alumina dispersion that can be obtained in a stable pH range without using an alkaline earth metal compound as an alkaline agent, and that has good emulsion stability as a Pickering adjustment material, and also to provide a production method that allows for easy synthesis. [Means for solving the problem]

[0011] Conventionally, neutral to alkaline aqueous alumina dispersions tend to aggregate and become unstable when the particle surface potential approaches a neutral state (neutral). Therefore, a method of maintaining dispersion stability by adjusting the potential to a significantly negative value using an alkaline agent has been used. As a result of extensive research, the inventors have discovered a method that allows a stable, uniform dispersion to be obtained by using a specific component blend and conditions without necessarily adjusting the potential to a positive or negative direction. This finding led to the completion of the present invention, which allows a Pickering emulsion to be formed by mixing with an oily material without the need for an alkaline agent containing an alkaline earth metal, and further improves emulsion stability.

[0012] That is, the present invention provides the following aspects: [1] The aqueous alumina dispersion is free of alkaline earth metals, contains 1 to 30 mass% Al2O3, exhibits a pH of 6 to 9.5, exhibits an average particle size of 5 to 1000 nm converted into number as measured by dynamic light scattering particle size distribution measurement, exhibits a zeta potential of -20 to 10 mV, and is either amorphous, pseudo-boehmite, or boehmite in crystallinity when dried at 100°C, characterized in that when the aqueous alumina dispersion is mixed and homogenized with liquid paraffin in a weight ratio of 1:1, a W / O type emulsion is formed that does not undergo phase separation even after 72 hours, and exhibits a micelle size range of 50 to 600 μm. [2] 1. A method for producing an aqueous alumina dispersion by heating and concentrating an aqueous solution containing aluminum lactate, a basic amino acid, and water, When the number of moles of aluminum converted to Al2O3 in the obtained alumina aqueous dispersion is [A], the number of moles of lactic acid is [B], and the number of moles of basic amino acid is [C], the following formula can be calculated: [B] / [A]=1.0~2.0 [C] / [A]=0.1~2.0 and The method for producing an aqueous alumina dispersion according to [1], wherein the heat concentration is performed at 90 to 130°C for 5 to 36 hours to concentrate the dispersion to 5 to 50% by mass of the initial weight, and to achieve an Al2O3 equivalent of 0.1 to 3.5% by mass and a pH of 6 to 9.5. [3] The method for producing an aqueous alumina dispersion according to [2], further comprising adjusting the pH of the obtained aqueous alumina dispersion to 6 to 9.5 with an alkaline agent not containing alkaline earth metals. [4] The method for producing an aqueous alumina dispersion according to [2], wherein, during the heating and concentration, the pH is adjusted to 6 to 9.5 with an alkaline agent not containing alkaline earth metals. [5] The method for producing an aqueous alumina dispersion according to [2], wherein the basic amino acid is at least one selected from the group consisting of lysine, arginine, and histidine. [6] The method for producing an alumina aqueous dispersion according to [2], characterized in that the alumina aqueous dispersion contains a sugar alcohol as a stabilizer, and the sugar alcohol is one or more selected from sorbitol, erythritol, and pentaerythritol. [7] The method for producing an aqueous alumina dispersion according to [3] or [4], wherein the alkaline agent not containing an alkaline earth metal is one or more selected from the group consisting of ammonia, ethylenediamine, monoethanolamine, diethanolamine, dimethylacetamide, and 1-methyl-2-pyrrolidinone. [Effects of the Invention]

[0013] In the present invention, since an alkaline earth metal compound is not used as an alkaline agent, it is applicable to a wide range of fields and formulation systems, and since the alumina particles are protected with lactic acid and a basic amino acid, the particle state is highly stable, so that it can be used as a material for preparing Pickering emulsions and has the desired effect as alumina particles. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is an X-ray diffraction image of the alumina aqueous dispersion obtained in Example 1 dried at 100°C. [Figure 2] 1 is a graph showing the particle size distribution, based on the number of particles, of the aqueous alumina dispersion obtained in Example 1, determined by dynamic light scattering. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below based on preferred embodiments, but the present invention is not limited to the following embodiments and various modifications are possible within the scope of the claims. Furthermore, in the present invention, the expression "numeric value 1 to numerical value 2" in a numerical range indicates that numerical value 1 is the lower limit and numerical value 2 is the upper limit. This means a range including numerical values ​​1 and 2 at both ends, and is synonymous with "numerical value 1 or more and numerical value 2 or less."

[0016] In the alumina aqueous dispersion of the present invention, the alumina may be in the form of ionic aluminum or colloidal aluminum. Because it is an aqueous dispersion, the term "alumina hydrate" in the broad sense encompasses alumina n-hydrate, aluminum hydroxide, pseudoboehmite, and boehmite. There are no restrictions on the proximity of the alumina particles and the organic acid, and the entire dispersion must be in a uniform sol state. Regarding the contained alumina, the Al concentration is expressed in terms of Al2O3.

[0017] Hereinafter, when describing alkaline agents, hydroxides, carbonates, and bicarbonates of alkaline earth metals will be referred to as "alkaline earth metal compounds."

[0018] Hereinafter, the method for producing the aqueous alumina dispersion of the present invention will be described. The alumina aqueous dispersion of the present invention is produced by heating and concentrating an aqueous solution containing aluminum lactate, a basic amino acid, and water, and the alumina aqueous dispersion can be calculated by the following formula, where the number of moles of aluminum in terms of Al2O3 in the obtained alumina aqueous dispersion is [A], the number of moles of lactic acid is [B], and the number of moles of basic amino acid is [C]. [B] / [A]=1.0~2.0 [C] / [A]=0.1~2.0 and The heat concentration is carried out at 90 to 130°C for 5 to 36 hours to concentrate the alumina to 5 to 50% by mass of the initial weight, to 0.1 to 3.5% by mass in terms of Al2O3, and to a pH of 6 to 9.5. The method for producing the alumina aqueous dispersion can be obtained by adjusting the pH with an alkaline agent other than alkaline earth metal compounds, as needed, either at this initial stage or when adjusting the pH of the alumina aqueous dispersion obtained at the end.

[0019] <Aluminum lactate First, aluminum lactate will be described. Aluminum lactate can be produced by known methods, such as neutralizing inorganic aluminum hydroxide or the like with an alkaline agent, desalting and washing the resulting aluminum hydroxide gel, and then heating and dissolving it in lactic acid; dissolving metallic aluminum in the form of ingots, shot, rolled rods, chips, etc., in lactic acid in the presence of a catalyst; or adding lactic acid to aluminum sulfate and an alkaline earth metal to precipitate and remove by-product salts. Lactic acid has two optical isomers, L- and D-, and either can be used. The L-isomer, which can be fermented from plant materials, is readily available and economically advantageous. Commercially available products can be used. Powdered products can be dissolved and used as an aqueous solution. The Al2O3-equivalent concentration can be adjusted as desired by adjusting the amount of dilution water. The number of moles of [B] lactic acid and the number of moles of [A] Al2O3 are in the range of [B] / [A] = 1.0 to 2.0.

[0020] <Basic amino acids> Amino acids have amino and carboxyl groups and form zwitterions in water. The isoelectric points of acidic and neutral amino acids are acidic to neutral, but basic amino acids have many amino groups and therefore have an isoelectric point of approximately 10. The basic amino acid can be one or more selected from lysine, arginine, and histidine. Commercially available products may be purchased and used. They can be dissolved and used as an aqueous solution. Lysine and arginine, which have excellent water solubility, are preferred. Basic amino acids include L- and D-isomers, and either can be used. Like lactic acid, the L-isomer is easily available and is therefore economically advantageous.

[0021] <Method of manufacturing alumina aqueous dispersion> (1) Preparation of alumina aqueous dispersion A homogeneous aqueous solution is prepared by mixing aluminum lactate, a basic amino acid, water, etc. Regarding the component ratio, when the number of moles of aluminum converted to Al2O3 in the alumina aqueous dispersion is [A], the number of moles of lactic acid is [B], and the number of moles of basic amino acid is [C], [B] / [A]=1.0~2.0 [C] / [A]=0.1~2.0 The ratio is adjusted so that the solution is stable. If the ratio [B] / [A] is less than 1.0, the solution will tend to solidify and become unstable. If it exceeds 2.0, the solubility of the aluminum compound will decrease and the solution will tend to precipitate, making it unstable. If the ratio [C] / [A] is less than 0.1, the dispersion will be poor and the quality will be unstable. If it exceeds 2.0, the aluminum concentration will decrease, making it uneconomical.

[0022] When preparing the aqueous alumina dispersion, it is preferable to stir at room temperature for 0.5 to 3 hours. Heating may be performed in winter. Preferably, the temperature is 10 to 35°C and the time is 1 to 2 hours. During this process, hydrolysis may gradually progress at the interface, resulting in the formation of fine precipitates and forming a slurry, but either state can be used without any problems.

[0023] The aqueous solution is prepared so that the components are 0.1 to 3.5 mass% in terms of Al2O3 and the pH is 6 to 9.5. If the Al2O3 content is less than 0.1%, the effective amount of Al is insufficient, and if it exceeds 3.5%, solidification tends to occur before sol formation, resulting in a deterioration in quality. If the pH is below 6, sol formation becomes difficult, and if it exceeds 9.5, the viscosity becomes high and the solution tends to become unstable. If necessary, the aforementioned stabilizer and / or initial alkali agent can be added at this point. The amount added is determined according to the pH setting range of the product of the present invention.

[0024] The stabilizer used is a sugar alcohol, specifically one or more selected from sorbitol, erythritol, and pentaerythritol, dissolved in water. The incorporation of the stabilizer supplies a large number of hydroxyl groups from the stabilizer, which improves the retention of the alumina hydrate form and further improves dispersibility and storage stability.

[0025] The alkaline agent added at this stage is called the initial alkaline agent. As described below, the alkaline agent may be added in the final step of the production method for an aqueous alumina dispersion (step (3) described below) to adjust the pH. The term "initial alkaline agent" is used to distinguish it from the alkaline agent used at that stage (sometimes referred to as a "later alkaline agent"). The initial alkaline agent may include a basic compound such as ammonia and / or an amine compound. The amine compound may be, for example, one or more selected from ethylenediamine, monoethanolamine, diethanolamine, dimethylacetamide, and 1-methyl-2-pyrrolidinone. In addition to adjusting the pH, the initial alkaline agent can enhance the dispersion stability of the alumina hydrate through the amino groups provided by these materials.

[0026] (2) Heat concentration process of alumina aqueous dispersion Next, the aqueous alumina dispersion obtained in the above step is concentrated to 5 to 50% by mass of the initial weight at 90 to 130°C for 5 to 36 hours. The heating method is not particularly limited, and electrical heating or steam heating at normal atmospheric pressure, or the use of an autoclave, etc., is possible. Stirring during heating is not particularly limited; the mixture may be left unstirred, or may be stirred or sheared using a stirring blade equipped with a propeller, anchor, or disperser, etc., and there are no particular restrictions. The reaction temperature is preferably 95 to 130°C. The reaction time is preferably 5 to 24 hours. If the temperature is below 90°C, the reaction will not proceed sufficiently to produce an aqueous alumina dispersion. On the other hand, if the temperature exceeds 130°C, a special high-temperature, high-pressure reaction environment is required to raise the temperature, which reduces productivity. If the heating time is less than 5 hours, concentration will be insufficient and an aqueous alumina dispersion may not be produced. If the heating time exceeds 36 hours, the heating and concentration time will be too long, resulting in reduced productivity. Heating and concentration is performed to reduce the concentration to 5 to 50% by mass of the initial weight. If the concentration is less than 5%, the aqueous alumina dispersion will gel or solidify, making the dispersion unstable. On the other hand, if the concentration exceeds 50%, the heat concentration will be insufficient and the desired aqueous alumina dispersion will not be obtained. After the concentration, the aqueous alumina dispersion can be diluted to any desired concentration. Water is preferably used as the dilution solvent, but water-soluble solvents such as alcohols, ketones, esters, and amides can also be used depending on the application. Depending on the application, the aqueous alumina dispersion of the present invention may be thermally dried at 40 to 250°C and used as a powder. In this specification, the term "aqueous alumina dispersion" is intended to include a thermally dried dispersion.

[0027] (3) Final adjustment process of alumina aqueous dispersion Next, the pH of the resulting aqueous alumina dispersion can be adjusted to a final pH of 6 to 9.5, as needed. The alkaline agent used here can be any agent other than an alkaline earth metal compound. As mentioned above, the alkaline agent used here is sometimes referred to as a "later alkaline agent." Examples of late alkaline agents include alkali metal compounds, water-soluble amine compounds, basic amino acids, and nitrogen-containing heterocyclic compounds, but compounds containing alkaline earth metals are not used.

[0028] Examples of alkali metal compounds include sodium hydroxide, sodium bicarbonate, sodium carbonate, potassium hydroxide, and lithium hydroxide. Examples of water-soluble amine compounds include ammonia, trimethylamine, triethylamine, ethylenediamine, triethylenetetramine, monoethanolamine, diethanolamine, triethanolamine, hexamethylenetetramine, dimethylformamide, dimethylacetamide, and urea. Examples of basic amino acids include lysine, arginine, and histidine. Examples of nitrogen-containing heterocyclic compounds include imidazole, morpholine, piperidine, pyridine, N-methyl-2-pyrrolidone, γ-butyrolactam, and ε-caprolactam. Examples of late-stage alkali agents include sodium hydroxide, potassium hydroxide, ammonia, ethylenediamine, monoethanolamine, diethanolamine, lysine, arginine, histidine, and pyridine. One or more of each can be selected as appropriate.

[0029] The amount of the alkaline agent at this stage (later alkaline agent) depends on the pH of the resulting aqueous alumina dispersion, and an amount that will give the desired pH is used.

[0030] <Features of alumina aqueous dispersion> The alumina aqueous dispersion of the present invention has the following characteristics. (a) The amount of aluminum (Al) is 1 to 30% by mass, preferably 4 to 28% by mass, and more preferably 4 to 26% by mass, calculated as Al2O3. The pH of the aqueous dispersion is preferably 6 to 9.5, more preferably 6.5 to 9.5, and even more preferably 6.5 to 9.2. If the amount of Al2O3 is less than 1%, the effective amount of Al is insufficient, and if it exceeds 30%, the viscosity increases and handling becomes difficult. The final pH is 6 to 9.5. If the pH is below 6, corrosion may occur depending on the application, making it difficult to use, and if the pH is above 9.5, the viscosity increases and the dispersion is prone to instability.

[0031] (b) The average particle size of the dispersed particles in the alumina aqueous dispersion is 5 to 1000 nm. The average particle diameter calculated by number as determined by dynamic light scattering particle size distribution measurement is 5 to 1000 nm, preferably 5 to 800 nm, and more preferably 5 to 600 nm. If the average particle diameter is less than 5 nm, the physical properties of alumina particles are insufficient, and if it exceeds 1000 nm, the particles tend to settle and are unstable.

[0032] (c) The zeta potential of the aqueous alumina dispersion is -20 to 10 mV, preferably -18 to 10 mV, and more preferably -15 to 10 mV. If the zeta potential is below -20, the amount of alkaline agent is too high, which is uneconomical, while if it exceeds 10, the potential is unstable and changes such as gelation are likely to occur. In either case, if the potential is outside this range, the potential deviation is too large, and depending on the compound, the compound becomes significantly unstable and cannot be incorporated. The zeta potential is measured by electrophoretic light scattering.

[0033] (d) When the aqueous alumina dispersion is dried at 100°C, the alumina particles are composed of one or more of amorphous, pseudo-boehmite, and boehmite. [Example]

[0034] The present invention will be described in more detail with reference to examples. The present invention should not be construed as being limited to these examples. In the examples, parts and percentages are by weight unless otherwise specified.

[0035] In the examples, the aluminum concentration at the time of preparation and blending of the alumina aqueous dispersion is expressed as % by mass in terms of Al2O3. The number of moles of aluminum in terms of Al2O3 is [A], the number of moles of lactic acid is [B], and the number of moles of basic amino acid is [C], and these are expressed as [B] / [A] and [C] / [A], respectively.

[0036] Example 1 A 500 mL separable flask was charged with 17.0 g of basic aluminum lactate aqueous solution (Al2O3 equivalent = 8.0%) and 250.0 g of water, and while stirring at 200 rpm, 7.6 g of arginine was gradually added to obtain a solution adjusted to pH = 8.0. At this time, the Al2O3 equivalent was 0.5 mass%, and the [B] / [A] ratio was 2.0 and [C] / [A] ratio was 1.6. The resulting solution was heated and concentrated at 200 rpm at 120 °C for 12 hours to obtain an alumina aqueous dispersion. The resulting alumina aqueous dispersion was weighed to be 8 mass% of the initial weight.

[0037] An X-ray diffraction image of the alumina aqueous dispersion obtained in Example 1 dried at 100°C is shown in Figure 1. A graph showing the particle size distribution of the alumina aqueous dispersion obtained in Example 1, determined by dynamic light scattering, on a number basis is shown in Figure 2. Figure 1 shows that the crystallinity of the alumina aqueous dispersion dried at 100°C is amorphous and pseudo-boehmite. Figure 2 shows that the average particle size calculated as a number is 21 nm, falling within the range of 5 to 1000 nm.

[0038] Example 2 85.0 g of basic aluminum lactate aqueous solution (Al2O3 equivalent = 8.0%) and 250.0 g of water were added to a 500 mL separable flask and stirred at 200 rpm. 17.2 g of arginine was gradually added to obtain a pH-adjusted solution of 7.9. At this time, the Al2O3 equivalent was 2.0 mass%, and the [B] / [A] ratio was 2.0 and [C] / [A] ratio was 1.5. The resulting solution was heated and concentrated at 200 rpm at 120 °C for 12 hours to obtain an alumina aqueous dispersion. The resulting alumina aqueous dispersion was weighed to be 9 mass% of the initial weight.

[0039] Example 3 85.0 g of basic aluminum lactate aqueous solution (Al2O3 equivalent = 8.0%) and 250.0 g of water were added to a 500 mL separable flask and stirred at 200 rpm. 17.2 g of arginine was gradually added to obtain a pH-adjusted solution of 7.9. At this time, the Al2O3 equivalent was 2.0 mass%, and the [B] / [A] ratio was 2.0 and [C] / [A] ratio was 1.5. The resulting solution was heated and concentrated at 200 rpm at 95 °C for 18 hours to obtain an aqueous alumina dispersion. The resulting aqueous alumina dispersion was weighed to be 36 mass% of the initial weight.

[0040] Example 4 85.0 g of basic aluminum lactate aqueous solution (Al2O3 equivalent = 8.0%) and 250.0 g of water were added to a 500 mL separable flask and stirred at 200 rpm. 17.2 g of arginine was gradually added to obtain a solution adjusted to pH = 8.0. At this time, the Al2O3 equivalent was 2.0 mass%, and [B] / [A] = 2.0, [C] / [A] = 1.5. The resulting solution was heated and concentrated at 200 rpm at 120 °C for 9 hours to obtain an alumina aqueous dispersion. The resulting alumina aqueous dispersion was weighed to be 42 mass% of the initial weight.

[0041] Example 5 A 500 mL separable flask was charged with 17.0 g of a basic aluminum lactate aqueous solution (equivalent to 8.0% Al2O3) and 250.0 g of water, and while stirring at 200 rpm, 3.8 g of lysine was gradually added to obtain a solution adjusted to pH 8.1. At this time, the Al2O3 equivalent was 0.5 mass%, and the [B] / [A] ratio was 2.0 and [C] / [A] ratio was 2.0. The resulting solution was heated and concentrated at 200 rpm at 120°C for 12 hours to obtain an alumina aqueous dispersion. The resulting alumina aqueous dispersion was weighed to be 11 mass% of the initial weight.

[0042] Example 6 A 500 mL separable flask was charged with 17.0 g of basic aluminum lactate aqueous solution (Al2O3 equivalent = 8.0%) and 250.0 g of water, and while stirring at 200 rpm, 0.2 g of arginine and 0.9 g of ethylenediamine (initial alkaline agent) were gradually added to obtain a solution adjusted to pH = 7.2. At this time, the Al2O3 equivalent was 0.5 wt%, and the [B] / [A] ratio was 1.0 and [C] / [A] ratio was 0.1. The resulting solution was heated and concentrated at 200 rpm at 120 °C for 12 hours to obtain an alumina aqueous dispersion. The resulting alumina aqueous dispersion was weighed to be 10 wt% of the initial weight. The pH was 5.5, and the final pH was 8.4 after adding 0.3 g of 25% ammonia (later alkaline agent) water.

[0043] Example 7 A 500 mL separable flask was charged with 17.0 g of basic aluminum lactate aqueous solution (Al2O3 equivalent = 8.0%) and 250.0 g of water, and while stirring at 200 rpm, 2.3 g of arginine, 1.7 g of D-sorbitol (stabilizer), and 0.9 g of diethanolamine (initial alkali agent) were gradually added to obtain a solution adjusted to pH = 9.0. At this time, the Al2O3 equivalent was 0.5 wt%, and the [B] / [A] ratio was 1.0, and the [C] / [A] ratio was 1.0. The resulting solution was heated and concentrated at 200 rpm at 120 °C for 12 hours to obtain an alumina aqueous dispersion. The resulting alumina aqueous dispersion was weighed to be 13 wt% of the initial weight.

[0044] Example 8 A 500 mL separable flask was charged with 17.0 g of basic aluminum lactate aqueous solution (Al2O3 equivalent = 8.0%) and 250.0 g of water, and while stirring at 200 rpm, 3.4 g of arginine and 1.7 g of D-sorbitol were gradually added to obtain a solution adjusted to pH = 9.1. At this time, the Al2O3 equivalent was 0.5 mass%, and the [B] / [A] ratio was 1.0 and [C] / [A] ratio was 1.5. The resulting solution was heated and concentrated at 200 rpm at 120 °C for 12 hours to obtain an alumina aqueous dispersion. The resulting alumina aqueous dispersion was weighed to be 13 mass% of the initial weight.

[0045] (Comparative Example 1) A 1L jacketed GL stirring vessel was used, with 5°C cooling water circulating through the jacket. 153.2 g of tap water was added to the vessel and stirred. 190.9 g of an aluminum chloride aqueous solution (10.0% Al2O3 equivalent) and 155.9 g of a sodium aluminate aqueous solution (20.0% Al2O3 equivalent, 18.9% Na2O equivalent) were simultaneously added, yielding 500 g of aluminum hydroxide gel solution. The temperature at this time was 21-30°C. The resulting gel solution was then dehydrated using a centrifugal dehydrator, and water was added and stirred seven times. The resulting washed gel weighed 192.0 g. The gel was measured using an infrared moisture meter at 105°C for 30 minutes, and the volatile content was 70.0%.

[0046] A 500 mL separable flask was charged with 8.0 g of the aluminum hydroxide wash gel (Al2O3 equivalent = 16.5%) and 250.0 g of water to form a slurry. While stirring at 200 rpm, 4.6 g of arginine was gradually added to obtain a pH-adjusted solution of 9.0. The Al2O3 equivalent was 0.5 mass%, and no lactic acid was used, resulting in a [B] / [A]=0, [C] / [A]=2.0. The resulting solution was heated and concentrated at 200 rpm at 120 °C for 12 hours, resulting in a large amount of precipitated sediment, and no dispersion was obtained.

[0047] (Comparative Example 2) A 500 mL separable flask was charged with 17.0 g of basic aluminum lactate aqueous solution (equivalent to 8.0% Al2O3) and 250.0 g of water, and while stirring at 200 rpm, 12.2 g of 25% aqueous ammonia was gradually added to obtain a solution adjusted to pH = 9.0. The Al2O3 equivalent was 0.5 wt%. Furthermore, since no basic amino acid was used, the [B] / [A] ratio was 2.0, and [C] / [A] ratio was 0.0. The resulting solution was heated and concentrated at 200 rpm at 120 °C for 12 hours to obtain an aqueous alumina dispersion. The resulting aqueous alumina dispersion was weighed to be 17% by weight of its initial weight. The pH was 5.8, and the final pH was 8.2 after adding 0.2 g of 25% aqueous ammonia. After one week of storage at 40 °C, the solution significantly thickened and solidified.

[0048] (Comparative Example 3) A 500 mL separable flask was charged with 17.0 g of basic aluminum lactate aqueous solution (Al2O3 equivalent = 8.0%) and 250.0 g of water, and while stirring at 200 rpm, 9.2 g of arginine was gradually added to obtain a solution adjusted to pH = 9.5. At this time, the Al2O3 equivalent was 0.5 mass%, and the [B] / [A] ratio was 2.0 and [C] / [A] ratio was 4.0. The resulting solution was heated and concentrated at 200 rpm at 120 °C for 12 hours, but became cloudy and non-fluid, resulting in a heterogeneous dispersion.

[0049] Comparative Example 4 A 500 mL separable flask was charged with 170.0 g of an aqueous solution of aluminum tris-lactate (4.0% Al2O3 equivalent) and 250.0 g of water, and while stirring at 200 rpm, 24.0 g of 25% aqueous ammonia was gradually added to obtain a solution adjusted to pH = 8.8. The Al2O3 equivalent was 0.6 mass %, and since no basic amino acid was used, [B] / [A] = 6.0, [C] / [A] = 0. The resulting solution was heated and concentrated at 200 rpm at 120 °C for 12 hours to obtain an aqueous alumina dispersion. The resulting aqueous alumina dispersion was weighed to be 25 mass % of its initial weight. After 3 weeks of storage at 40 °C, whitening of the solution and particle settling were observed.

[0050] (Comparative Example 5) A 500 mL separable flask was charged with 170.0 g of basic aluminum lactate aqueous solution (Al2O3 equivalent = 11.0%) and 250.0 g of water, and while stirring at 200 rpm, 34.8 g of arginine was gradually added to obtain a solution adjusted to pH = 8.0. At this time, the Al2O3 equivalent was 4.1 mass%, and the [B] / [A] ratio was 2.0 and [C] / [A] ratio was 1.1. The resulting solution was heated and concentrated at 200 rpm at 120 °C for 12 hours, but became a non-fluid, heterogeneous mass and did not form a dispersion.

[0051] (Comparative Example 6) 85.0 g of basic aluminum lactate aqueous solution (Al2O3 equivalent = 8.0%) and 250.0 g of water were added to a 500 mL separable flask and stirred at 200 rpm. 17.2 g of arginine was gradually added to obtain a pH-adjusted solution of 8.0. At this time, the Al2O3 equivalent was 2.0 mass%, and the [B] / [A] ratio was 2.0 and [C] / [A] ratio was 1.6. The resulting solution was heated and concentrated at 200 rpm at 120 °C for 4 hours, resulting in an opaque, cloudy liquid that did not form a dispersion. The resulting alumina aqueous dispersion was weighed to be 60 mass% of the initial weight.

[0052] For the alumina aqueous dispersions of Examples 1 to 8 and Comparative Examples 1 to 6, the average particle size (nm) of the alumina particles, the zeta potential (mV), the crystal system when dried at 100°C, the pH and Al2O3 equivalent concentration (mass%) of the alumina aqueous dispersion, and the storage stability are shown in Table 1. In Comparative Examples 1, 3, 5, and 6, the formation state of the alumina aqueous dispersion was insufficient, and the final state is shown in the table.

[0053] (Average particle size of alumina particles (nm) and (Zeta potential of alumina particles (mV)) The average particle diameters of Examples 1 to 7 and Comparative Examples 2 and 4 were measured by dynamic light scattering in an aqueous solvent using a Zetasizer Nano ZS (manufactured by Spectris Inc.), and the average particle diameters measured on a number basis, and the zeta potentials were calculated by electrophoretic light scattering, and are shown in Table 1.

[0054] (Crystalline system when dried at 100℃) The crystal systems of Examples 1 to 8 and Comparative Examples 2 and 4 when dried at 100° C. were measured using an X-ray diffractometer (Smartlab9kw: manufactured by Rigaku Corporation). The results are shown in Table 1.

[0055] (pH) Measurements were performed using a portable pH meter "HM-40P" and a pH combination electrode "GST-2739C" manufactured by Toa DKK Corporation, and the results are shown in Table 1.

[0056] (Al2O3 equivalent concentration) The Al2O3 equivalent concentrations of Examples 1 to 8 and Comparative Examples 2 and 4 were calculated by first calculating the aluminum concentration. Measurements were carried out using an optical emission spectrometer (Agilent 5110 ICP-OCS, manufactured by Agilent Technologies), and the aluminum concentration was converted to Al2O3 concentration using the following formula, and the results are shown in Table 1. Al2O3 equivalent concentration (mass%) = Al concentration (mass%) × (102 / 27)

[0057] (Storage stability) The alumina aqueous dispersions of Examples 1 to 8 and Comparative Examples 1 to 6 were placed in airtight containers and placed in a constant temperature incubator DKN402 (Yamato Scientific Co., Ltd.) at 40° C. for one month, after which the appearance was visually evaluated. 〇: Liquid and no change. ×: Significant thickening or solidification occurs, or precipitation or particle sedimentation occurs.

[0058] (Pickering emulsion formation test) The alumina aqueous dispersions prepared from Examples 1 and 2 and Comparative Example 2 were diluted with water to an Al2O3-equivalent concentration of 2.5% by mass and mixed with the target solvents (i.e., liquid paraffin, linseed oil, and pentaerythritol (tri / tetra)acrylate) in a weight ratio of 1:1. W / O Pickering emulsions were formed by shearing the emulsions at 18,000 rpm for 1 minute using a homogenizer T10 (manufactured by IKA). After allowing the emulsions to stand at room temperature for 72 hours, the appearance and micelle size were measured. Table 2 shows the results.

[0059] For comparison, similar experiments were carried out using acidic colloidal silica (particle size = 12 nm, SiO2 = 20%, pH = 2.0) and alkaline colloidal silica (particle size = 12 nm, SiO2 = 20%, pH = 8.3).

[0060] (Target solvent) [Liquid paraffin] Fujifilm Wako Pure Chemical Industries, Ltd., Reagents (Wako First Grade) [Linseed oil] Fujifilm Wako Pure Chemical Industries, Ltd., Reagents (Wako First Grade) [Pentaerythritol (tri / tetra)acrylate] Merck, reagents. PTA / TMPTA mixture, pentaerythritol acrylate mixture

[0061] (exterior) The formed W / O type emulsion state was observed, and the appearance was evaluated as follows. ◯: The emulsion is uniform. ▲: Partially emulsified, but some emulsification was disrupted and phase separation occurred. ×: Almost no emulsion was formed, and phase separation occurred.

[0062] (micelle size (μm)) The W / O emulsion was dispensed onto a slide and observed using the VIEWTY autofocus microscope manufactured by 3R Solutions, Inc. Thirty micellar particles were randomly measured, and the minimum to maximum values ​​(μm) were recorded. Note that (*) in the table indicates that significant emulsification occurred during sampling and measurement.

[0063] [Table 1]

[0064] [Table 2]

[0065] As shown in Table 1, in all of Examples 1 to 8, alumina aqueous dispersions were stably prepared, and the average particle size, zeta potential, Al2O3-equivalent concentration, pH, and crystalline structure of the 100°C dried product were within the ranges of the present invention. On the other hand, in Comparative Examples 1 and 3, the molar ratio of lactic acid or basic amino acid to Al2O3-equivalent concentration was outside the range, resulting in insoluble matter and solidification, and no dispersion was obtained. Furthermore, in Comparative Examples 2 and 4, when ammonia was used without a basic amino acid, even if an aqueous dispersion was prepared, it thickened and solidified over time, or precipitation and particle sedimentation occurred. Furthermore, in Comparative Examples 5 and 6, the Al2O3-equivalent concentration during blending or the heat treatment time was outside the range, resulting in thickening, solidification, and clouding, and no dispersion was obtained.

[0066] As shown in Table 2, in Examples 1 and 2, stable W / O emulsions were formed with oil-based solvents, and the micelle size was maintained within a certain range. It is believed that a Pickering emulsion was formed. On the other hand, in Comparative Example 2, even after emulsion formation, stability was poor, and the emulsion dissolved over time, resulting in phase separation. In the colloidal silica reference material, emulsion formation was either not observed or was minimal. In Comparative Example 2 and the colloidal silica material, the zeta potential exceeded -20 mV (the zeta potential (mV) of each sample was -33.18 for Comparative Example 2, -51.81 for acidic colloidal silica, and -23.24 for alkaline colloidal silica). This made emulsion formation unstable, and the micelle size range tended to be broad, resulting in an unstable emulsion.

[0067] The present invention does not use an alkaline earth metal compound as an alkaline agent and can be applied to a wide range of fields as an aqueous alumina dispersion. In addition, because the alumina particles are protected with lactic acid and a basic amino acid, the particle state is highly stable, and the present invention can provide excellent effects in emulsion formation and stability as a Pickering emulsion preparation material. [Industrial Applicability]

[0068] The aqueous dispersion of alumina particles of the present invention can be used as a Pickering emulsion-forming material in functional raw materials such as cosmetic materials, emulsion polymerization resin materials, water-based coating agents, adhesives, porous materials, and microcapsule materials. In cosmetic materials, alumina is expected to be used as a heat resistance, hardness, refractive index, and stability agent, and to adjust micelle size to enhance brightness and brightness, or as a color fixative. It can also be used as a nanofiller in emulsion polymerization systems, or in materials containing reactive groups such as hydroxyl groups. Furthermore, due to the high heat resistance and stability of the nanoparticles, the product of the present invention has a wide range of potential applications, including as a refractory binder for ceramics and other materials, as a density improver, an additive for forming inorganic sintered films, a catalyst support, and for the production of porous bodies.

[0069] The following aspects of the invention are added: [1] The aqueous alumina dispersion is free of alkaline earth metals, contains 1 to 30 mass% Al2O3, exhibits a pH of 6 to 9.5, exhibits an average particle size of 5 to 1000 nm converted into number as measured by dynamic light scattering particle size distribution measurement, exhibits a zeta potential of -20 to 10 mV, and is either amorphous, pseudo-boehmite, or boehmite in crystallinity when dried at 100°C, characterized in that when the aqueous alumina dispersion is mixed and homogenized with liquid paraffin in a weight ratio of 1:1, a W / O type emulsion is formed that does not undergo phase separation even after 72 hours, and exhibits a micelle size range of 50 to 600 μm. [2] 1. A method for producing an aqueous alumina dispersion by heating and concentrating an aqueous solution containing aluminum lactate, a basic amino acid, and water, When the number of moles of aluminum converted to Al2O3 in the obtained alumina aqueous dispersion is [A], the number of moles of lactic acid is [B], and the number of moles of basic amino acid is [C], the following formula can be calculated: [B] / [A]=1.0~2.0 [C] / [A]=0.1~2.0 and The method for producing an aqueous alumina dispersion according to [1], wherein the heat concentration is performed at 90 to 130°C for 5 to 36 hours to concentrate the dispersion to 5 to 50% by mass of the initial weight, and to achieve an Al2O3 equivalent of 0.1 to 3.5% by mass and a pH of 6 to 9.5. [3] The method for producing an aqueous alumina dispersion according to [2], further comprising adjusting the pH of the obtained aqueous alumina dispersion to 6 to 9.5 with an alkaline agent not containing alkaline earth metals. [4] The method for producing an aqueous alumina dispersion according to [2] or [3], wherein, during the heating and concentration, the pH is adjusted to 6 to 9.5 with an alkaline agent containing no alkaline earth metal. [5] 5. The method for producing an aqueous alumina dispersion according to any one of [2] to 4, wherein the basic amino acid is at least one selected from the group consisting of lysine, arginine, and histidine. [6] The method for producing an alumina aqueous dispersion according to any one of [2] to [5], characterized in that the alumina aqueous dispersion contains a sugar alcohol as a stabilizer, and the sugar alcohol is one or more selected from sorbitol, erythritol, and pentaerythritol. [7] The method for producing an aqueous alumina dispersion according to any one of [3] to [6], wherein the alkaline agent not containing an alkaline earth metal is one or more selected from ammonia, ethylenediamine, monoethanolamine, diethanolamine, dimethylacetamide, and 1-methyl-2-pyrrolidinone.

Claims

1. Contains no alkaline earth metals, ２ O ３ the aqueous alumina dispersion contains 1 to 30% by mass in terms of crystalline alumina, has a pH of 6 to 9.5, has an average particle size of 5 to 1,000 nm in terms of number as measured by dynamic light scattering particle size distribution measurement, has a zeta potential of -20 to 10 mV, and is in the form of amorphous, pseudo-boehmite, or boehmite when dried at 100°C; the aqueous alumina dispersion is characterized in that, when the aqueous alumina dispersion is mixed and homogenized with liquid paraffin in a weight ratio of 1:1, a W / O type emulsion is formed that does not undergo phase separation even after 72 hours, and has a micelle size range of 50 to 600 μm.

2. 1. A method for producing an aqueous alumina dispersion by heating and concentrating an aqueous solution containing aluminum lactate, a basic amino acid, and water, comprising: The Al content in the obtained aqueous alumina dispersion was ２ O ３ When the converted number of moles of aluminum is [A], the number of moles of lactic acid is [B], and the number of moles of basic amino acid is [C], the following formula is used: [B] / [A]=1.0~2.0 [C] / [A]=0.1 to 2.0 and The heat concentration is performed at 90 to 130° C. for 5 to 36 hours to concentrate the mixture to 5 to 50% by mass of the initial weight, and Al ２ O ３ 2. The method for producing an aqueous alumina dispersion according to claim 1, wherein the pH is adjusted to 6 to 9.5 at a concentration of 0.1 to 3.5 mass % in terms of converted amount.

3. 3. The method for producing an aqueous alumina dispersion according to claim 2, further comprising adjusting the pH of the resulting aqueous alumina dispersion to 6 to 9.5 with an alkaline agent containing no alkaline earth metal.

4. 3. The method for producing an aqueous alumina dispersion according to claim 2, wherein the pH of the aqueous alumina dispersion is adjusted to 6 to 9.5 with an alkaline agent containing no alkaline earth metal during the heating and concentration.

5. 3. The method for producing an aqueous alumina dispersion according to claim 2, wherein the basic amino acid is at least one selected from the group consisting of lysine, arginine, and histidine.

6. 3. The method for producing an alumina aqueous dispersion according to claim 2, wherein the alumina aqueous dispersion contains a sugar alcohol as a stabilizer, and the sugar alcohol is at least one selected from the group consisting of sorbitol, erythritol, and pentaerythritol.

7. 5. The method for producing an aqueous alumina dispersion according to claim 3, wherein the alkaline agent not containing an alkaline earth metal is at least one selected from the group consisting of ammonia, ethylenediamine, monoethanolamine, diethanolamine, dimethylacetamide, and 1-methyl-2-pyrrolidinone.

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