Alumina gel and manufacturing method thereof

Abstract

To provide a gel material that enables rapid gel formation using aluminum without using silica or calcium materials and exhibits excellent shape retention, and a manufacturing method thereof.SOLUTION: In an alumina gel containing 5 to 25 mass% of Al2 O3, 1 to 8 mass% of alkali metal atoms, 5 to 20 mass% of hydroxy acid and 55 to 85 mass% of water and having a pH of 8 to 12, a 2 mm coating film of the alumina gel shows color coordinates L* of 90 to 100, a* of -0.5 to 0.5, and b* of 0 to 1.0 when measured with a haze meter, and when the 2 mm coating film of the alumina gel is sandwiched by a stainless steel jig having a surface #400 finish and having a diameter of 30 mm and subjected to a tensile test at 10 mm / sec by a tensile testing machine, the maximum stress value shows 5 N or greater.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an alumina gel, particularly an alumina gel that does not use silica or calcium materials, and a method for making the same. [Background technology]

[0002] Gels containing aluminum are used in the construction and ceramics industries, as well as in moldings, fibers, catalysts, and other surface treatments. However, many conventional materials require elements such as silica and calcium, and depending on the application, these elements can result in insufficient performance in the final composition, such as heat resistance, hardness, and strength.

[0003] Japanese Patent No. 6503129 (Patent Document 1) discloses a powdered quick-setting admixture used in wet spraying of refractories, which comprises an additive and a refractory material, the additive comprising calcium hydroxide, at least one hardening accelerator selected from alumina cement and silicates, and at least one specific powder material selected from sulfates, carbonates, citric acid, citrates, boric acid, and borates, wherein the ratio of the calcium hydroxide content to the hardening accelerator content (calcium hydroxide content / hardening accelerator content) is 0.7 to 4, and the ratio of the total amount of the calcium hydroxide and hardening accelerator to the content of the specific powder material (total amount of the calcium hydroxide and hardening accelerator / specific powder material content) is 1 to 10. While this refractory is well used, the high silica or calcium content is undesirable because it reduces the heat resistance of the composition. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6503129 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a gel material that can quickly form a gel using aluminum without using silica or calcium materials and has excellent shape retention, and a method for producing the same. [Means for solving the problem]

[0006] That is, the present invention provides the following aspects: [1] An alumina gel having a pH of 8 to 12, containing 5 to 25% by mass of Al2O3, 1 to 8% by mass of alkali metal atoms, 5 to 20% by mass of hydroxy acid, and 55 to 85% by mass of water, When a 2 mm coating film of the alumina gel is measured with a haze meter, the color coordinates are L* of 90 to 100, a* of -0.5 to 0.5, and b* of 0 to 1.0, and When a 2 mm coating of the alumina gel is clamped between a 30 mm diameter stainless steel jig with a surface finish of #400 and subjected to a tensile test at 10 mm / sec using a tensile tester, the maximum stress value is 5 N or more. 1. Alumina gel characterized by: [2] The alumina gel according to [1], wherein the content of silicon atoms or calcium atoms is 0 to 100 ppm. [3] The alumina gel according to [1] or [2], wherein the alumina gel contains a stabilizer, and the stabilizer is one or more of a polysaccharide of three or more sugars, a sugar alcohol, ammonia, or a water-soluble amine. [4] A method for producing an alumina gel, comprising mixing (A) an aluminum hydroxylate and (B) an alkali aluminate or an alkali aluminate hydroxylate, and gelling the mixture. [5] The method for producing an alumina gel according to [4], wherein the aluminum hydroxylate (A) is aluminum lactate or aluminum glycolate. [6] The method for producing an alumina gel according to [4] or [5], wherein the aluminum hydroxylate (A) has a ratio (I) of the product of the number of moles of hydroxy acid in the aluminum hydroxylate (A) and the number of carboxyl groups in the hydroxy acid, to the number of moles of Al2O3 (II) calculated from the number of moles of aluminum in the aluminum hydroxylate (A), in the range of I / II = 1.0 to 2.0. [7] The method for producing an alumina gel according to [4], wherein the alkali aluminate or alkali hydroxyaluminate (B) is one or more of sodium aluminate, sodium lactate aluminate, and sodium glycolate aluminate. [8] The method for producing an alumina gel according to [4] or [5], wherein a stabilizer (C) is added during mixing, and the stabilizer (C) is one or more of a polysaccharide of three or more sugars, a sugar alcohol, ammonia, or a water-soluble amine. [9] The obtained alumina gel contains 5 to 25 mass% of Al2O3, 1 to 8 mass% of alkali metal atoms, 5 to 20 mass% of hydroxy acid, and 55 to 85 mass% of water; It has a pH of 8 to 12. When a 2 mm coating film of the alumina gel is measured with a haze meter, the color coordinates are L* of 90 to 100, a* of -0.5 to 0.5, and b* of 0 to 1.0, and When a 2 mm coating of the alumina gel is clamped between a 30 mm diameter stainless steel jig with a surface finish of #400 and subjected to a tensile test at 10 mm / sec using a tensile tester, the maximum stress value is 5 N or more. [4] or [5], the method for producing the alumina gel.

[10] An alumina gel obtained by reacting and gelling (A) an aluminum hydroxy acid with (B) an alkali aluminate or an alkali aluminate hydroxy acid, The alumina gel has a pH of 8 to 12 and contains 5 to 25 mass% of Al2O3, 1 to 8 mass% of alkali metal atoms, 5 to 20 mass% of hydroxy acid, and 55 to 85 mass% of water. [Effects of the Invention]

[0007] The alumina gel and its manufacturing method of the present invention enable the rapid formation of an alumina gel containing almost no silica or calcium. The alumina gel of the present invention can be powdered by drying at 20 to 200°C, and is characterized in that the crystalline system of the product dried at 100°C is mainly amorphous, and furthermore, it exhibits the same gelling effect when water is added. DETAILED DESCRIPTION OF THE INVENTION

[0008] 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."

[0009] The alumina gel of the present invention is produced by mixing and gelling (A) aluminum hydroxylate and (B) alkali aluminate or alkali hydroxylate aluminate, and an alumina gel having a pH of 8 to 12 and a composition of 5 to 25 mass% Al2O3, 1 to 8 mass% alkali metal atoms, 5 to 20 mass% hydroxylate, and 55 to 85 mass% water is obtained. The manufacturing method will be explained first.

[0010] (A) Aluminum hydroxylate (hereinafter sometimes referred to as "component (A)") Examples of hydroxy acids used in the aluminum hydroxylate include lactic acid, citric acid, tartaric acid, malic acid, gluconic acid, and glycolic acid, with lactic acid, gluconic acid, and glycolic acid being preferred. The aluminum hydroxylate may be one of these or two or more. The product (I) of the number of moles of hydroxy acid and the number of carboxyl groups in the hydroxy acid and the number of moles of aluminum in component (A) calculated as Al2O3 (II) is in the range of I / II = 1.0 to 2.0. If the ratio is less than 1.0, the solution will tend to solidify and become unstable. If the ratio exceeds 2.0, the solubility of the aluminum compound will decrease and precipitation will occur, making the solution unstable.

[0011] Aluminum hydroxylate can be produced by a variety of well-known methods, including neutralizing inorganic aluminum hydroxide with an alkaline agent to obtain an aluminum hydroxide gel, desalting and washing it, and then dissolving it in hydroxy acid by heating; dissolving metallic aluminum in the form of ingots, shot, rolled rods, chips, etc., in hydroxy acid in the presence of a catalyst; or adding hydroxy acid to aluminum sulfate and an alkaline earth metal to precipitate and remove by-product salts. Commercially available products may also be used. The form of aluminum hydroxylate can be either a powder or an aqueous solution. The powder may be used as is, or the aluminum may be dissolved in an aqueous solution and the concentration adjusted in terms of Al2O3. For example, when used as an aqueous solution, the Al2O3-equivalent concentration should be 1 to 25% by mass. A concentration less than 1% by mass is uneconomical due to its low concentration, while a concentration greater than 25% by mass results in high viscosity and poor handleability.

[0012] (B) Alkali aluminate or alkali hydroxyaluminate (hereinafter sometimes referred to as "component (B)") The alkali agent used in the alkali aluminate includes alkali metals, ammonia, and water-soluble amines, and preferably sodium and potassium salts. These may be used alone or in combination of two or more.

[0013] Alkali aluminate can be produced by adding caustic alkali to aluminum hydroxide and dissolving it under heat, or by dissolving metallic aluminum in the form of ingots, shot, rolling rods, chips, etc. in an alkali solution in the presence of a catalyst. It can also be purchased commercially. Carbonate may optionally be included as an additional ingredient. There are no restrictions on the form of the solution, whether it is a powder or an aqueous solution; powder products can be used as is. For example, in the case of an aqueous solution, the Al2O3-equivalent concentration is 1-30%. A concentration less than 1% is uneconomical due to its low concentration, while a concentration greater than 30% is prone to crystallization and becomes highly viscous, making it difficult to handle.

[0014] The alkali hydroxyaluminate can be prepared by adding a hydroxy acid such as lactic acid, citric acid, tartaric acid, malic acid, gluconic acid, or glycolic acid to the alkali aluminate, or by dissolving aluminum hydroxide gel in the alkali hydroxyaluminate, but the method is not particularly limited.

[0015] (C) Stabilizers (polysaccharides of three or more sugars, sugar alcohols, ammonia, water-soluble amines) A stabilizer may be added to improve the uniformity and stability of the alumina gel. Specifically, one or more of the following stabilizers can be used: trisaccharide or higher polysaccharides, sugar alcohols, ammonia, and water-soluble amines. Among polysaccharides, monosaccharides and disaccharides, which exhibit strong reducing properties, are excluded. More specific examples of stabilizers include starch, glycogen, celluloses, sucrose, sorbitol, erythritol, pentaerythritol, ammonia, trimethylammonia, ethylenediamine, and triethanolamine. Preferred stabilizers are D-sorbitol, erythritol, and triethanolamine. Commercially available stabilizers can be used. These stabilizers may be added in advance to the aluminum hydroxylate (A), alkali aluminate, or alkali hydroxylate aluminate (B). The amount of stabilizer used is 1 to 30% by mass, preferably 3 to 15% by mass, based on the mass of Al2O3.

[0016] Among the above-mentioned components (B), aqueous solutions of alkali aluminates have poor long-term stability, especially at high temperatures, and have problems such as crystallization over time, causing blockages in pipes, and making storage difficult. Therefore, high stability can be achieved by blending a stabilizer in advance with the alkali aluminate or alkali hydroxyaluminate (B). This is because the hydroxyl groups supplied by the stabilizer are converted into Al(OH) 4― This is thought to be because it stabilizes the structure of the aluminate complex ion represented by

[0017] Furthermore, the aqueous alkali aluminate solution of component (B) is expressed as sodium tetrahydroxoaluminate (Na[Al(OH)4]) and free sodium hydroxide as its constituents, but because it contains 5% or more by mass of this free sodium hydroxide, it is highly corrosive and poses safety concerns. However, by blending a hydroxy acid and a stabilizer (i.e., a polysaccharide of three or more sugars, a sugar alcohol, ammonia, or a water-soluble amine) into the aqueous alkali aluminate solution, the free sodium hydroxide content can be reduced to 5% by mass or less, thereby improving safety. Note that the absence of free sodium hydroxide is undesirable because it results in a shortage of alkali necessary for gelation in the present invention and also reduces the Al2O3 concentration.

[0018] Alumina gel manufacturing method Alumina gel is obtained by adding alkali aluminate and / or alkali hydroxy aluminate (component (B)) to aluminum hydroxylate (component (A)). If necessary, stabilizer (C) can be mixed with component (A) and / or component (B) beforehand. These various materials are mixed uniformly with the required amount of water using a method or device such as stirring or pressure feeding. The various materials can be used in any form, such as powder or aqueous solution, but because gelation begins immediately upon mixing, rapid mixing is required immediately after adding water to ensure uniformity.

[0019] It is also possible to mix various materials in the presence of the required amount of water to form a gel, then dry the powder and add a specified amount of water as needed to form a gel again. The drying temperature to obtain the dried product is 20 to 200°C. Temperatures below 20°C require a long drying time and are uneconomical, while temperatures above 200°C are undesirable because they cause yellowing and reduce water retention. Furthermore, no temperature or pressure control is required during gel formation, and the process can be carried out at room temperature and pressure.

[0020] Alumina gel is formed by blending hydroxyaluminum acid (A) with alkali aluminate and / or alkali hydroxyaluminate (B) (together with a stabilizer (C) as needed) in water. The resulting alumina gel contains 5-25% by mass of Al2O3, 5-20% by mass of hydroxy acid, 1-8% by mass of alkali metal atoms, and 55-85% by mass of water, and the ratio of each material is adjusted to have a pH of 8-12.

[0021] The amount of Al2O3 is calculated assuming that all of the aluminum in the aluminum hydroxylate (A) and the aluminum in the alkali hydroxylate aluminate (B) is Al2O3. An amount of Al2O3 less than 5% by mass has the drawback of inability to gel in a short time, while an amount greater than 25% by mass results in a hard gel with gaps and prone to crumbling. The amount of Al2O3 is preferably 5 to 23% by mass, more preferably 5 to 20% by mass. The amount of hydroxy acid is calculated based on the amounts at the time of blending. If the amount of hydroxy acid is less than 5% by mass, stability decreases and precipitation is likely to occur. If the amount is greater than 20% by mass, water solubility decreases and gelation tends to become uneven. The amount of hydroxy acid is preferably 5 to 19% by mass, more preferably 5 to 18% by mass. The amount of alkali metal atoms is similarly calculated based on the amounts at the time of blending. If the amount of alkali metal atoms is less than 1% by mass, stability decreases and precipitation is likely to occur, while if it exceeds 8% by mass, by-products increase, making gelation difficult. The amount of alkali metal atoms is preferably 1 to 7% by mass, more preferably 1 to 6% by mass. The amount of water is also calculated from the blending ratio; if the amount of water is less than 55% by mass, the gel becomes hard and easily cracked, while if it exceeds 85% by mass, the gelation rate slows and the gel strength is low. The amount of water is preferably 55 to 80% by mass, more preferably 55 to 75% by mass. The obtained alumina gel exhibits an alkaline pH of 8 to 12. If the pH of the alumina gel is less than 8, it will be non-uniform and its shape retention will be poor, while if it is higher than 12, the gel strength will tend to be weak. The pH of the alumina gel is preferably 8.5 to 11, more preferably 9 to 11.

[0022] The crystalline phase of the dried alumina gel of the present invention can be confirmed by X-ray diffraction, and is usually mainly amorphous. The reason why the alumina gel water-retaining material can be instantly formed in the present invention is not clear, but it is presumed that the hydrolysis during neutralization of the aluminum salt is suppressed by the chelating action of the hydroxy acid, resulting in the formation of self-peptized fine particles of amorphous material, which exhibit high water retention.

[0023] The alumina gel obtained by the present invention is characterized in that, when a 2 mm thick coating film of the alumina gel is measured using a haze meter, it exhibits color coordinates of L* of 90 to 100, a* of -0.5 to 0.5, and b* of 0 to 1.0. Furthermore, when the 2 mm thick coating film of the alumina gel is clamped between 30 mm diameter stainless steel jigs with a #400 surface finish and subjected to a tensile test at 10 mm / sec using a tensile tester, it exhibits a maximum stress value of 5 N or more. This indicates that the color of the alumina gel is nearly transparent and uniform when measured using a haze meter. Furthermore, the fact that the alumina gel is clamped between stainless steel jigs indicates good adhesion to inorganic materials. For example, shape-retaining applications in sprayed refractories require adhesion to steel and aggregates. The upper limit of the maximum stress value can be 100 N. If the maximum stress in the tensile test is less than 5 N, the gel tends to peel off easily from the object, and if it exceeds the upper limit of 100 N, the gel tends to be too hard, causing gaps between the gels and resulting in insufficient shape retention. The maximum stress value in the tensile test is preferably 5 to 90 N, and more preferably 7 to 90 N.

[0024] The alumina gel of the present invention is characterized by being essentially free of silicon atoms or calcium atoms. However, silicon atoms or calcium atoms are present as impurities in the raw materials. In the alumina gel of the present invention, the content of silicon atoms or calcium atoms is 0 to 100 ppm, preferably 0 to 80 ppm, and more preferably 0 to 60 ppm. If the content of silicon atoms or calcium atoms exceeds 100 ppm, the heat resistance of the alumina gel tends to be insufficient.

[0025] (Example) The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0026] Example 1 A 1-liter kneader was charged with 100 g of a basic aluminum lactate solution (Al2O3 = 6.8%, lactic acid / Al2O3 molar ratio: 2.0), and 26 g of a sodium aluminate lactate solution (Al2O3 = 16.1%) containing 0.78 g of D-sorbitol was added in equal amounts while stirring to form an alumina gel. The gel appeared transparent and uniform, and exhibited good shape retention after 3 minutes. The Al2O3 content in the alumina gel was 8.6% by mass, and the pH was 8.5. The alumina gel was applied to a glass plate at a thickness of 2 mm. The resulting coating film was measured using a haze meter, yielding color coordinates of L* 97.97, a* -0.05, and b* 0.34. The alumina gel was dried at 100°C for 2 hours and was found to be amorphous by X-ray diffraction. As an example of typical use, 100g of easily sintered alumina powder (LS-711C, manufactured by Nippon Light Metal Co., Ltd., average particle size: 0.6μm) used as aggregate was used as a base, and equal amounts of the basic aluminum lactate aqueous solution and sodium aluminate lactate aqueous solution with D-sorbitol dissolved therein were mixed and stirred to create an alumina gel containing aggregate, and a 2mm coated film was clamped between a 30mm diameter stainless steel jig with a #400 surface finish in a tensile testing machine (universal testing machine manufactured by MinebeaMitsumi Inc.), and the maximum stress value when pulled at 10mm / sec was 10.5N.

[0027] Example 2 The gel from Example 1 was dried at 100°C for 8 hours to obtain a dried product containing 33.1% Al2O3. This was then pulverized using a hammer mill (8,000 rpm) and recovered. 30 g of the recovered product was mixed with 100 g of water and the resulting gel was evaluated for its physical properties in the same manner as in Example 1. The gel's appearance was transparent and uniform, and its shape retention after 3 minutes was good. The alumina gel contained 9.9% Al2O3 and had a pH of 9.5. A 2 mm coating film on a glass plate was measured using a haze meter to obtain color coordinates of L* 97.22, a* -0.07, and b* 0.42. X-ray diffraction analysis of the gel dried at 100°C for 2 hours revealed that it was amorphous. Furthermore, a tensile test was performed using a sinterable alumina powder base in the same manner as in Example 1, and the maximum stress was 6.4 N.

[0028] Example 3 A 1-liter kneader was charged with 100 g of a basic aluminum glycolate solution (Al2O3 = 6.0%, glycolic acid / Al2O3 molar ratio: 2.0), and 20.2 g of a sodium aluminate lactate solution (Al2O3 = 16.1%) containing 0.78 g of D-sorbitol was added in equal amounts while stirring to form a gel. The gel appeared transparent and uniform, and exhibited good shape retention after 3 minutes. The alumina gel contained 8.2% Al2O3 and a pH of 9.5. A 2 mm coating on a glass plate was measured using a haze meter to obtain color coordinates of L* 95.60, a* -0.03, and b* 0.28. X-ray diffraction analysis of the alumina gel dried at 100°C for 2 hours revealed it to be amorphous. A tensile test was also performed using a sinterable alumina powder base, as in Example 1, and the maximum stress was 6.7 N.

[0029] Example 4 A 1-liter kneader was charged with 100 g of basic aluminum lactate aqueous solution (Al2O3 = 6.8%, lactic acid / Al2O3 molar ratio: 2.0), and 20 g of sodium aluminate aqueous solution (Al2O3 = 20.1%) was added in equal amounts while stirring to form a gel. The gel appeared transparent and uniform, and its shape was well retained after 3 minutes. The alumina gel contained 9.0% Al2O3 and had a pH of 10.5. A 2 mm coating film on a glass plate was measured with a haze meter to obtain color coordinates of L* 97.63, a* -0.07, and b* 0.38. X-ray diffraction analysis of the gel, which was dried at 100°C for 2 hours, revealed it to be amorphous. A tensile test was also conducted using a sinterable alumina powder base, as in Example 1, and the maximum stress was 9.2 N.

[0030] Example 5 A 1-liter kneader was charged with 100 g of basic aluminum lactate solution (Al2O3 = 6.8%, lactic acid / Al2O3 molar ratio: 2.0), and 17 g of powdered sodium aluminate (Al2O3 = 52.9%) dissolved in 13 g of water was added in equal amounts while stirring to form a gel. The gel appeared transparent and uniform, and its shape was well retained after 3 minutes. The gel contained 12.1% Al2O3 and a pH of 11.1. A 2 mm coating on a glass plate was measured with a haze meter to obtain color coordinates of L* 98.80, a* -0.06, and b* 0.31. X-ray diffraction analysis of the gel, which was dried at 100°C for 2 hours, revealed it to be amorphous. A tensile test was also conducted using a sinterable alumina powder base, as in Example 1, and the maximum stress was 14.4 N.

[0031] (Comparative Example 1) 68.0 g of 90% lactic acid was placed in a 1-liter kneader, and 100 g of sodium aluminate aqueous solution (Al2O3 = 16.1%) was added in equal amounts while stirring. The resulting mixture was a white slurry, but did not gel. The Al2O3 content of the slurry was 11.9%, and the pH was 9.8. The slurry was dried at 100°C for 2 hours, and X-ray diffraction showed an undefined impurity peak. Furthermore, a tensile test was performed using a sinterable alumina powder base, as in Example 1, and the maximum stress was 0.2 N.

[0032] (Comparative Example 2) 100g of basic aluminum lactate solution (Al2O3 = 6.8%, lactic acid / Al2O3 molar ratio: 2.0) was placed in a 1-liter kneader, followed by 400g of purified water. 26g of sodium aluminate lactate solution (Al2O3 = 16.1%) with 0.78g of D-sorbitol dissolved in it was added in equal amounts to the 400g of purified water while stirring, and the mixture was mixed and stirred. The mixture gradually thickened, and it took more than 4 hours for it to gel. The resulting mixture had an Al2O3 of 2.1% and a pH of 9.0.

[0033] (Comparative Example 3) 100g of basic aluminum lactate aqueous solution (Al2O3 = 6.8%, lactic acid / Al2O3 molar ratio: 2.0) was placed in a 1 liter kneader, and 19.9g of sodium aluminate lactate aqueous solution (Al2O3 = 16.1%) with 0.6g of D-sorbitol dissolved in it was added in equal amounts while stirring. The mixture gradually thickened with scattered aggregates, but did not gel. The resulting mixture had an Al2O3 of 8.5% and a pH of 6.1.

[0034] Comparative Example 4 100g of basic aluminum lactate solution (Al2O3 = 8.4%, lactic acid / Al2O3 molar ratio: 1.9) was placed in a 1 liter kneader, and 22.4g of 48% sodium hydroxide solution was added in equal amounts while stirring, and the mixture was mixed and stirred. The mixture remained liquid and did not gel. The resulting product had an Al2O3 content of 6.9% and a pH of 9.5.

[0035] (Comparative Example 5) 50g of aluminum sulfate aqueous solution (Al2O3 = 8.0%) was placed in a 1-liter kneader, followed by 50g of purified water. 50g of sodium aluminate aqueous solution (Al2O3 = 20.1%) was added in equal amounts to the 50g of purified water while stirring, and the mixture was mixed and stirred. The mixture separated from the water and solidified into a mass, without gelling. The resulting mixture had an Al2O3 content of 9.3% and a pH of 11.0.

[0036] Table 1 lists the components (A), (B), and stabilizer used to form the materials obtained in the examples and comparative examples. Table 1 also lists the measured values ​​for Al2O3 content, hydroxy acid content, alkali metal atom content, water content, and pH. The pH value was measured at 20°C using a portable pH meter HM-40P manufactured by Toa DKK Corporation. Table 1 also lists the gel state, the crystallinity after 3 minutes, and the crystallinity of the dried product. The measurement methods are described below.

[0037] The gel state was evaluated by visually observing the appearance and was recorded in Table 1 according to the following criteria: ○: Uniform gel △: Uniform gel after 3 hours or more ×: Liquid or powder

[0038] The shape retention after 3 minutes was evaluated by tilting the container 90 degrees after 3 minutes from the time the gel was formed, and visually observing for 30 seconds whether or not dripping occurred. ○: No dripping occurs. ×: Dripping occurred.

[0039] The crystalline phase was described based on the results of X-ray diffraction (SmartLab 9kW; Rigaku Corporation).

[0040] [Table 1]

[0041] Table 2 shows the color coordinates measured by a haze meter for the alumina gels obtained in Examples 1 to 5. The alumina gels were coated on a glass plate to a thickness of 2 mm, and the color coordinates were measured using a haze meter SH-7000 manufactured by Nippon Denshoku Industries Co., Ltd.

[0042] [Table 2]

[0043] Table 3 shows the maximum stress values ​​obtained by tensile testing of Examples 1 to 5, Comparative Example 1, and Reference Example (a slurry prepared by adding 100 g of purified water to 100 g of sinterable alumina powder). The test material was prepared by applying a 2 mm thick layer of alumina gel to a 30 mm diameter stainless steel jig with a #400 surface treatment and clamping the jig. A tensile test was then carried out at 10 mm / sec using a universal testing machine manufactured by MinebeaMitsumi Inc.

[0044] [Table 3]

[0045] As shown in Table 1, in Examples 1 to 5, the Al2O3 content was 5 to 25 mass%, the hydroxy acid content was 5 to 20 mass%, the alkali metal atom content was 1 to 8 mass%, the moisture content was 55 to 85 mass%, and the pH was 8 to 12, which enabled rapid gel formation and good shape retention after 3 minutes. Furthermore, as shown in Table 2, the alumina gel of the present invention exhibited color coordinates of L* of 90 to 100, a* of -0.5 to 0.5, and b* of 0 to 1.0, measured using a haze meter for a 2 mm coating film. This indicates a very bright, achromatic color due to the high L* value of 90 or more and the a* and b* values ​​approaching 0. Furthermore, as shown in Table 3, in the sinterable alumina powder base, the water slurry of the Reference Example exhibited a stress value of less than 0.1 N, whereas Examples 1 to 5 all exhibited a stress value of 5 N or more, indicating good adhesion to steel materials.

[0046] On the other hand, as shown in Table 1, the desired alumina gel cannot be obtained when the material of the present invention is not used, as in Comparative Examples 1, 4, and 5. Furthermore, when the Al2O3 concentration or pH range is outside the range of the present invention, such as Al2O3 = 2.1% in Comparative Example 2 and pH = 6.1 in Comparative Example 3, rapid gelation cannot be achieved.

[0047] The alumina gels obtained in Examples 1 to 5 dried at 100°C showed amorphous properties in X-ray diffraction, but the alumina gel obtained in Comparative Example 1 dried at 100°C showed an indefinite impurity peak, which was different from the alumina gels shown in the Examples.

[0048] As described above, the alumina gel and its manufacturing method of the present invention do not require silica or calcium materials, and can quickly form an aluminum gel (specifically, within 3 minutes) with excellent shape retention. The product of the present invention is a water-based, homogeneous aluminum material, and the alumina gel of the present invention can be powdered and re-gelled when water is added, making it suitable for use as a binder for conventional fired products. Since the product does not contain silica or calcium, improved heat resistance can be expected. [Industrial Applicability]

[0049] The alumina gel of the present invention can be suitably used as a binder for monolithic refractories, an accelerator, for the surface treatment of alumina fibers, for the treatment of composite minerals such as zeolites, and for catalyst carriers. In addition, it can be used in the fields of cosmetics and healthcare, such as for use as a moisture-retaining gel for cosmetics, a pigment fixing agent, toothpaste, and antiperspirant.

[0050] The following aspects of the invention are added: [1] An alumina gel having a pH of 8 to 12, containing 5 to 25% by mass of Al2O3, 1 to 8% by mass of alkali metal atoms, 5 to 20% by mass of hydroxy acid, and 55 to 85% by mass of water, When a 2 mm coating film of the alumina gel is measured with a haze meter, the color coordinates are L* of 90 to 100, a* of -0.5 to 0.5, and b* of 0 to 1.0, and When a 2 mm coating of the alumina gel is clamped between a 30 mm diameter stainless steel jig with a surface finish of #400 and subjected to a tensile test at 10 mm / sec using a tensile tester, the maximum stress value is 5 N or more. 1. Alumina gel characterized by: [2] The alumina gel according to [1], wherein the content of silicon atoms or calcium atoms is 0 to 100 ppm. [3] The alumina gel according to [1] or [2], wherein the alumina gel contains a stabilizer, and the stabilizer is one or more of a polysaccharide of three or more sugars, a sugar alcohol, ammonia, or a water-soluble amine. [4] A method for producing an alumina gel according to [1], characterized in that (A) an aluminum hydroxylate and (B) an alkali aluminate or an alkali aluminate hydroxylate are mixed and gelled. [5] The method for producing an alumina gel according to [4], wherein the aluminum hydroxylate (A) is aluminum lactate or aluminum glycolate. [6] The method for producing an alumina gel according to [4] or [5], wherein the aluminum hydroxylate (A) has a ratio (I) of the product of the number of moles of hydroxy acid in the aluminum hydroxylate (A) and the number of carboxyl groups in the hydroxy acid, to the number of moles of Al2O3 (II) calculated from the number of moles of aluminum in the aluminum hydroxylate (A), in the range of I / II = 1.0 to 2.0. [7] The method for producing an alumina gel according to any one of [4] to [6], wherein the alkali aluminate or alkali hydroxyaluminate (B) is one or more of sodium aluminate, sodium lactate aluminate, and sodium glycolate aluminate. [8] The method for producing an alumina gel according to any one of [4] to [7], wherein a stabilizer (C) is added during mixing, and the stabilizer (C) is one or more of a polysaccharide of three or more sugars, a sugar alcohol, ammonia, or a water-soluble amine. [9] The obtained alumina gel contains 5 to 25 mass% of Al2O3, 1 to 8 mass% of alkali metal atoms, 5 to 20 mass% of hydroxy acid, and 55 to 85 mass% of water; It has a pH of 8 to 12. When a 2 mm coating film of the alumina gel is measured with a haze meter, the color coordinates are L* of 90 to 100, a* of -0.5 to 0.5, and b* of 0 to 1.0, and When a 2 mm coating of the alumina gel is clamped between a 30 mm diameter stainless steel jig with a surface finish of #400 and subjected to a tensile test at 10 mm / sec using a tensile tester, the maximum stress value is 5 N or more. The method for producing an alumina gel according to any one of [4] to [8].

[10] An alumina gel obtained by reacting and gelling (A) an aluminum hydroxy acid with (B) an alkali aluminate or an alkali aluminate hydroxy acid, The alumina gel has a pH of 8 to 12 and contains 5 to 25 mass% of Al2O3, 1 to 8 mass% of alkali metal atoms, 5 to 20 mass% of hydroxy acid, and 55 to 85 mass% of water.

Claims

1. Al ２ O ３ an alumina gel having a pH of 8 to 12, containing 5 to 25% by mass of hydroxy acid, 1 to 8% by mass of alkali metal atoms, 5 to 20% by mass of hydroxy acid, and 55 to 85% by mass of water, When a 2 mm coated film of the alumina gel is measured with a haze meter, the color coordinates are L* of 90 to 100, a* of −0.5 to 0.5, and b* of 0 to 1.0, and When a 2 mm thick coating film of the alumina gel is sandwiched between a 30 mm diameter stainless steel jig with a surface finish of #400 and subjected to a tensile test at 10 mm / sec using a tensile tester, the maximum stress value is 5 N or more. Alumina gel characterized by:

2. 2. The alumina gel according to claim 1, wherein the content of silicon atoms or calcium atoms is 0 to 100 ppm.

3. 3. The alumina gel according to claim 1, wherein the alumina gel contains a stabilizer, and the stabilizer is one or more of a trisaccharide or higher polysaccharide, a sugar alcohol, ammonia, or a water-soluble amine.

4. A method for producing an alumina gel, comprising mixing (A) an aluminum hydroxylate and (B) an alkali aluminate or an alkali aluminate hydroxylate, and gelling the mixture.

5. 5. The method for producing an alumina gel according to claim 4, wherein the aluminum hydroxy acid (A) is aluminum lactate or aluminum glycolate.

6. The aluminum hydroxy acid (A) has an Al content calculated from the product (I) of the number of moles of hydroxy acid in the aluminum hydroxy acid (A) and the number of carboxyl groups in the hydroxy acid, and the number of moles of aluminum in the aluminum hydroxy acid (A). ２ O ３ The method for producing an alumina gel according to claim 4 or 5, wherein the ratio of the number of moles (II) of I to II is in the range of 1.0 to 2.

0.

7. 5. The method for producing an alumina gel according to claim 4, wherein the alkali aluminate or alkali hydroxyaluminate (B) is one or more of sodium aluminate, sodium lactate aluminate, and sodium glycolate aluminate.

8. 6. The method for producing an alumina gel according to claim 4, wherein a stabilizer (C) is added during mixing, and the stabilizer (C) is one or more of a polysaccharide of three or more sugars, a sugar alcohol, ammonia, or a water-soluble amine.

9. The resulting alumina gel was ２ O ３ 5 to 25% by mass of an aqueous solution of hydroxyl group-1, 1 to 8% by mass of an alkali metal atom, 5 to 20% by mass of a hydroxy acid, and 55 to 85% by mass of water; having a pH of 8 to 12; When a 2 mm coated film of the alumina gel is measured with a haze meter, the color coordinates are L* of 90 to 100, a* of −0.5 to 0.5, and b* of 0 to 1.0, and When a 2 mm thick coating film of the alumina gel is sandwiched between a 30 mm diameter stainless steel jig with a surface finish of #400 and subjected to a tensile test at 10 mm / sec using a tensile tester, the maximum stress value is 5 N or more. The method for producing the alumina gel according to claim 4 or 5.

10. An alumina gel obtained by reacting and gelling (A) an aluminum hydroxy acid with (B) an alkali aluminate or an alkali aluminate hydroxy acid, The alumina gel has a pH of 8 to 12 and Al ２ O ３ 1 to 8 mass% of alkali metal atoms, 5 to 20 mass% of a hydroxy acid, and 55 to 85 mass% of water.

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