Plate-shaped boehmite aggregate and method for manufacturing the same

Abstract

This invention provides a plate-shaped boehmite aggregate with low impurities and high specific surface area, and an efficient method for producing the same. [Solution] The present invention relates to an aggregate of plate-shaped boehmite in which the length of the short axis (α) of the primary particles is 0.01 to 0.5 μm, the length of the long axis (β) is 0.1 to 3 μm, the thickness (γ) is 0.005 to 0.05 μm, the ratio of the short axis to the long axis is (β) / (α) = 1.2 to 80, and the ratio of the long axis to the thickness is (β) / (γ) = 20 to 400, with a specific surface area of ​​5 to 120 m². 2 The present invention provides a plate-shaped boehmite aggregate characterized by having / g and a method for producing the same.

Description

[Technical Field]

[0001] The present invention relates to plate-shaped boehmite aggregates, particularly plate-shaped boehmite aggregates with low impurity content and high specific surface area, and to a method for producing the same. [Background technology]

[0002] Boehmite is produced by various methods. For example, Japanese Patent Publication No. 2023-47346 (Patent Document 1) describes a method for producing plate-shaped pseudo-boehmite by adding an organic acid to an aqueous solution of an aluminum precursor to produce an acidic solution, and reacting it at 160-250°C at 2-100 bar for 6-25 hours. Japanese Patent Publication No. 4181777 (Patent Document 2) describes a method for producing plate-shaped boehmite with an aspect ratio of 3-12 by using aluminum hydroxide powder with a particle size of 0.8-2 μm and drying and curing it in a pressure vessel under a steam atmosphere at 150-180°C while heating.

[0003] Furthermore, Japanese Patent Publication No. 4938318 (Patent Document 3) describes a method for obtaining boehmite with a thickness of 50 to 100 nm and an external dimension of 200 to 1500 nm by hydrothermal synthesis of a reaction mixture containing a basic aluminum salt and sulfate ions, with the pH adjusted to 8 to 13. Japanese Patent Publication No. 6786104 (Patent Document 4) describes a method for hydrothermally reacting two types of aluminum hydroxide powders in the presence of sodium hydroxide to obtain a specific surface area of ​​2 to 10 m². 2 A method for producing boehmite having a particle shape in which multiple plate-like portions are connected in one direction in the in-plane direction is disclosed.

[0004] Japanese Patent Publication No. 2009-292698 (Patent Document 5) discloses a method for producing needle-shaped boehmite by hydrothermally reacting gibbsite-type aluminum hydroxide in the presence of an aromatic carboxylic acid. Japanese Patent Publication No. 2009-155116 (Patent Document 6) discloses a method for producing boehmite particles with an average primary particle diameter of 0.6 μm or less, in which the primary particles have a hexahedral shape, characterized by adding a basic magnesium compound to an acidic solution containing aluminum sulfate to precipitate aluminum hydrolysates, and then hydrothermally treating the obtained aluminum hydrolysates by heating them to 150°C or higher. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-47346 [Patent Document 2] Patent No. 4181777 [Patent Document 3] Patent No. 4938318 [Patent Document 4] Patent No. 6786104 [Patent Document 5] Japanese Patent Publication No. 2009-155116 [Patent Document 6] Patent No. 5530672 [Overview of the project] [Problems that the invention aims to solve]

[0006] The method described in Patent Document 1 involves adding an organic acid to an aqueous solution of an aluminum precursor to produce an acidic solution, and then reacting it at 160-250°C at 2-100 bar for 6-25 hours. Because this method involves high temperature and pressure, the internal pressure increases, requiring a pressure vessel, which presents the challenge of requiring large-scale manufacturing equipment. Patent Document 2 also presents the challenge of requiring a pressure vessel because the internal pressure increases in order to create a water vapor atmosphere at 150-180°C, thus requiring large-scale manufacturing equipment.

[0007] The method described in Patent Document 3 involves obtaining boehmite by hydrothermally reacting a reaction stock solution containing a basic aluminum salt and sulfate ions, adjusted to a pH of 8-13. However, since sulfate ions are used as raw materials, it is predicted that sulfur elements will remain in the boehmite. This presents challenges such as sulfur remaining as an impurity when boehmite is used as a synthesis raw material, and the generation of SOx such as sulfur monoxide and sulfur dioxide when used as a calcination raw material. Furthermore, since hydrothermal synthesis is performed, it is reasonable to assume that the synthesis is carried out under high temperature and high pressure conditions using a pressure vessel. As the internal pressure increases during synthesis, it is necessary to prepare a pressure vessel, which presents challenges as it results in large-scale manufacturing equipment.

[0008] The method described in Patent Document 4 involves a hydrothermal reaction of two or more types of aluminum hydroxide powders in the presence of sodium hydroxide. This method presupposes the inclusion of sodium hydroxide in the reaction system during synthesis, and it is predicted that sodium will remain in the resulting boehmite. When boehmite is used for firing purposes, this is expected to cause sintering defects due to melting point depression, etc. In the field of electronic materials, alkali metals such as sodium are expected to ionize when electricity is applied, causing insulation defects, thus limiting its applications. Furthermore, since the reaction is hydrothermal, it is reasonable to assume that the synthesis is carried out under high temperature and high pressure conditions using a pressure vessel. As the internal pressure increases during synthesis, it is necessary to prepare a pressure vessel, which presents the challenge of requiring large-scale manufacturing equipment.

[0009] The method described in Patent Document 5 involves adding a basic magnesium compound to an acidic aqueous solution containing aluminum sulfate to precipitate aluminum hydrolysates, and then hydrothermally synthesizing the resulting aluminum hydrolysates at 150°C or higher. This method presents challenges such as the presence of sulfur as an impurity when using boehmite as a synthesis raw material, and the generation of SOx (sulfur monoxide, sulfur dioxide, etc.) when used as a calcination raw material. Furthermore, because a basic magnesium salt compound is used, magnesium remains in the resulting boehmite, which can remain as an impurity when used as a reaction raw material, potentially resulting in the appearance of different crystalline phases and causing defects. Moreover, since the hydrothermal reaction is performed, it is reasonable to assume that the synthesis is carried out under high temperature and high pressure conditions using a pressure vessel. As the internal pressure increases during synthesis, it is necessary to prepare a pressure vessel, which presents challenges in terms of the large scale of the manufacturing equipment.

[0010] Patent Document 6 describes a hydrothermal reaction in which aluminum hydroxide powder is used as a nucleating agent along with a metal oxide sol or metal salt. Since a hydrothermal reaction is performed, it is reasonable to assume that the synthesis is carried out under high temperature and high pressure conditions using a pressure vessel. As the internal pressure rises during synthesis, it is necessary to prepare a pressure vessel, which presents the challenge of requiring large-scale manufacturing equipment.

[0011] In view of the above-mentioned problems, the object of the present invention is to provide a plate-shaped boehmite aggregate with few impurities and a high specific surface area, and an efficient method for producing the same. [Means for solving the problem]

[0012] In other words, the present invention provides the following aspects: [1] The primary particles have a short axis length (α) of 0.01 to 0.5 μm, a long axis length (β) of 0.1 to 3 μm, and a thickness (γ) of 0.005 to 0.05 μm, with a ratio of short axis to long axis (β) / (α) = 1.2 to 80, and a ratio of long axis to thickness (β) / (γ) = 20 to 400. This aggregate consists of plate-like boehmite with a specific surface area of ​​15 to 120 m². 2 A plate-shaped boehmite aggregate characterized by having / g. [2] The plate-like boehmite aggregate according to [1], characterized in that the iron (Fe) contained in the plate-like boehmite aggregate is 0 to 0.08% by mass, calcium (Ca) is 0 to 0.08% by mass, magnesium (Mg) is 0 to 0.08% by mass, chlorine (Cl) is 0 to 0.08% by mass, sulfur (S) is 0 to 0.05% by mass, and sodium (Na) is 0 to 0.08% by mass. [3] (1) A step of dissolving aluminum nitrate and at least one urea compound selected from urea, methylurea, and ethylurea in water to prepare an aqueous solution; (2) A step of heating and concentrating the aqueous solution described in step (1) at 90 to 120 °C for 24 to 120 hours; (3) A step of filtering the concentrated solution heated and concentrated in step (2) and washing the cake with water; (4) A step of drying the cake filtered in step (3) at 50 to 90 °C for 1 to 10 hours; The method for producing a plate-like boehmite aggregate according to [1], characterized by including the above steps. [4] Furthermore, (5) The method for producing a plate-like boehmite aggregate according to [3], characterized by including a step of adjusting the particle size by pulverizing the dried plate-like boehmite aggregate obtained in the above step (4). [5] The method for producing a plate-like boehmite aggregate according to [3] or [4], characterized in that the ratio (A) / (B) of the number of moles (A) of aluminum in aluminum nitrate to the number of moles (B) of at least one selected from urea, methylurea, and ethylurea is 0.15 to 0.45. [6] The method for producing a plate-like boehmite aggregate according to [3] or [4], characterized in that the pH after heating and concentration in the above step (2) is 5.0 to 8.3. [7] The method for producing the plate-shaped boehmite aggregate according to [3] or [4], characterized in that iron (Fe) contained in the plate-shaped boehmite aggregate is controlled to 0 to 0.08% by mass, calcium (Ca) is controlled to 0 to 0.08% by mass, magnesium (Mg) is controlled to 0 to 0.08% by mass, chlorine (Cl) is controlled to 0 to 0.06% by mass, sulfur (S) is controlled to 0 to 0.06% by mass, and sodium (Na) is controlled to 0 to 0.08% by mass. [8] The method for producing the plate-shaped boehmite aggregate according to [3] or [4], characterized in that when the pulverized plate-shaped boehmite aggregate is measured with a dynamic light scattering particle size distribution meter, the particle size distribution measurement based on the number is controlled such that D50 is 0.1 to 0.8 μm. [9] The method for producing the plate-shaped boehmite aggregate according to [3] or [4], characterized in that the device for drying in the step (4) is any one of a hot air circulation dryer, a shelf dryer, a vacuum dryer, and a vibration dryer. [Advantages of the Invention]

[0013] The plate-shaped boehmite aggregate of the present invention contains almost no impurities (for example, elements such as Fe, Ca, Mg, Cl, S, Na, etc.), the length of the short axis (α) of the primary particle is 0.01 to 0.5 μm, the length of the long axis (β) is 0.1 to 4 μm, the thickness of the plate-shaped boehmite (γ) is 0.005 to 0.1 μm, the ratio of the short axis to the long axis is (β) / (α)=1.2 to 80, and the ratio of the long axis to the thickness (β) / (γ)=20 to 400. It is an aggregate of plate-shaped boehmite having a specific surface area of 5 to 120 m 2 / g. It has been confirmed that the plate-shaped boehmite aggregate of the present invention can be produced by preparing an aqueous solution using aluminum nitrate and at least one selected from urea, methylurea, and ethylurea with low contents of Fe, Ca, Mg, Cl, S, Na as main raw materials, and optimizing the heating and concentration process, the pH after the heating and concentration process, the washing process, the drying conditions, and the pulverization conditions. [Brief Description of the Drawings]

[0014] [Figure 1]This is a 100,000x magnification SEM (Field Emission Scanning Electron Microscope) image of the boehmite particle aggregate obtained in Example 1. [Figure 2] This is a 10,000x magnification SEM (Field Emission Scanning Electron Microscope) image of the boehmite particle aggregate obtained in Example 1. [Figure 3] This is an X-ray diffraction pattern of the plate-like boehmite aggregate obtained in Example 1. [Figure 4] This is an X-ray diffraction pattern of the plate-like boehmite aggregate obtained in Comparative Example 4. [Figure 5] This graph shows the particle size distribution of the plate-like boehmite aggregate obtained in Example 1. [Figure 6] This graph shows the particle size distribution of the plate-like boehmite aggregate obtained in Comparative Example 2. [Modes for carrying out the invention]

[0015] (definition) In this specification, a numerical range, specifically "x~y," represents a range of x or greater and y or less (where both x and y represent numerical values).

[0016] (Explanation of plate-like boehmite aggregates) In this invention, the aggregate of plate-shaped boehmite contains almost no impurities (e.g., elements such as Fe, Ca, Mg, Cl, S, and Na), the primary particles have a short axis length (α) of 0.01 to 0.5 μm, a long axis length (β) of 0.1 to 3 μm, and a thickness (γ) of 0.005 to 0.05 μm, with a ratio of short axis to long axis (β) / (α) = 1.2 to 80 and a ratio of long axis to thickness (β) / (γ) = 20 to 400, and the aggregate of plate-shaped boehmite has a specific surface area of ​​15 to 120 m². 2 We provide products that have / g.

[0017] The plate-like boehmite aggregate of the present invention is an aggregate (aggregate or secondary particle) formed by aggregation of plate-like boehmite (primary particles). Since the primary particles are plate-like, they have a long axis and a short axis. The length (α) of the short axis of the primary particle is 0.01 to 0.5 μm, preferably 0.05 to 0.4 μm, more preferably 0.08 to 0.35 μm. The length (β) of the long axis is 0.1 to 3 μm, preferably 0.15 to 2.5 μm, more preferably 0.18 to 2.0 μm. The thickness (γ) of the plate-like boehmite is 0.005 to 0.05 μm, preferably 0.007 to 0.04 μm, more preferably 0.009 to 0.035 μm. The ratio of the short axis to the long axis is (β) / (α) = 1.2 to 80, preferably 1.3 to 95, more preferably 1.4 to 90, and the ratio of the long axis to the thickness (β) / (γ) = 20 to 400, preferably 25 to 350, more preferably 30 to 300.

[0018] The specific surface area of the plate-like boehmite aggregate in the present invention is 15 to 120 m 2 / g, preferably 16 to 110 m 2 / g, more preferably 18 to 105 m 2 / g. When the specific surface area is 15 m 2 / g, there is a problem of poor reaction activity. On the other hand, if it is larger than 120 m 2 / g, the activity is too high, and there is a problem of change during storage. The specific surface area is the surface area per unit mass of an object. The specific surface area in the examples and comparative examples of the present invention was measured with N2 using a specific surface area measuring device (manufactured by Shimadzu Corporation, Gemini VII 2390a).

[0019] The aggregate of the plate-like boehmite of the present invention can be produced by the following steps: (1) A step of dissolving aluminum nitrate and one or more urea compounds selected from urea, methylurea, and ethylurea in water to prepare an aqueous solution; (2) A step of heating and concentrating the aqueous solution described in step (1) at 90 to 120 °C for 24 to 120 hours; (3) A step of filtering the concentrated solution heated and concentrated in step (2) and washing the cake with water; (4) A step in which the cake filtered in step (3) is dried at 50-90°C for 1-10 hours, Includes. The above process further includes (5) a step of pulverizing the dried plate-shaped boehmite aggregate obtained in step (4) to standardize the particle size.

[0020] In synthesizing the plate-shaped boehmite aggregates in the present invention, (1) an aqueous solution is prepared by dissolving aluminum nitrate and one or more urea compounds selected from urea, methylurea, and ethylurea in water. The ratio (A) / (B) of the number of moles of aluminum in aluminum nitrate (A) to the number of moles of one or more urea compounds selected from urea, methylurea, and ethylurea (B) must be 0.15 to 0.45, preferably 0.18 to 0.40, and more preferably 0.20 to 0.38. When the molar ratio (A) / (B) is less than 0.15, the amount of urea, methylurea, and ethylurea is too high, resulting in unreacted urea, methylurea, and ethylurea remaining in the system, causing stickiness in the plate-shaped boehmite and making it difficult to handle. On the other hand, when (A) / (B) exceeds 0.45, the amount of aluminum is too high, resulting in the formation of a large amount of aluminum hydroxide instead of boehmite.

[0021] In synthesizing the plate-shaped boehmite aggregates in the present invention, (2) it is necessary to heat and concentrate the aqueous solution obtained in step (1) above at 90 to 120°C for 24 to 120 hours. If the temperature is below 90°C, the water will not boil sufficiently, and the reaction and concentration will not proceed. On the other hand, if the temperature exceeds 120°C, unless the heating and concentration is carried out in a dedicated closed system container, the water will volatilize before the reaction can occur, and plate-shaped boehmite cannot be obtained. Next, if the heating and concentration time is less than 24 hours, the heating and concentration time is too short, and the reaction will not proceed sufficiently, and plate-shaped boehmite cannot be obtained. On the other hand, if it exceeds 120 hours, the heating and concentration time is too long, and productivity will be reduced. The heating temperature is preferably 95 to 120°C, and more preferably 98 to 118°C. The heating time is preferably 40 to 120 hours, and more preferably 80 to 115 hours.

[0022] In synthesizing the plate-shaped boehmite aggregates in this invention, (3) it is necessary to filter the concentrated liquid heated and concentrated in step (2) and wash the cake with water. The pH after heating and concentration must be between 5.0 and 8.3. If the pH after heating and concentration is less than 5.0, the reaction will be insufficient, resulting in the problem of excessive aluminum hydroxide production. On the other hand, if the pH exceeds 8.3, the viscosity of the heated and concentrated liquid will become very high, making filtration impossible. The pH in this step is preferably between 5.1 and 8.0, more preferably between 5.2 and 7.8.

[0023] In synthesizing the plate-shaped boehmite aggregate in the present invention, (4) the cake filtered in step (3) is dried at 50 to 90°C for 1 to 10 hours. If the drying temperature is below 50°C, it takes a very long time to reach the desired moisture content, resulting in poor productivity. On the other hand, if it exceeds 90°C, the moisture content decreases excessively, resulting in poor reactivity of the plate-shaped boehmite. If the drying time is less than 1 hour, the drying is insufficient and the moisture content becomes excessive, causing stickiness in the plate-shaped boehmite and creating handling problems. On the other hand, if the drying time exceeds 10 hours, the drying is excessive, the moisture content decreases excessively, resulting in poor reactivity of the plate-shaped boehmite. The temperature in the drying process is preferably 55 to 85°C, more preferably 60 to 80°C, and the drying time is preferably 2 to 8 hours, more preferably 3 to 7 hours.

[0024] In synthesizing the plate-shaped boehmite aggregates in the present invention, (5) the particle size may be standardized by grinding the dried plate-shaped boehmite aggregates obtained in step (4) above. Grinding can be done using a hammer mill, a stone mill type grinder, an automatic mortar and pestle, or a vibratory mill, and the grinding conditions should be set to achieve the desired particle size.

[0025] In the present invention, when the particle size distribution of the pulverized plate-shaped boehmite aggregate is measured on a number basis using a dynamic light scattering particle size distribution analyzer, the D50 is preferably 0.1 to 0.8 μm, more preferably 0.15 to 0.75 μm, and more preferably 0.17 to 0.7 μm. If D50 is less than 0.1 μm, the size of the plate-shaped boehmite aggregate is small, and the primary particles are too fine, which makes handling difficult. On the other hand, if it exceeds 0.8 μm, the size of the plate-shaped boehmite aggregate is too large, and when used for thin-layer coating or filter applications for electronic materials, the plate-shaped boehmite aggregate protrudes from the coating film, resulting in problems where the coating film does not function properly. Also, when used in filter applications, the target material is finer, resulting in problems where the filter does not perform its filtration function.

[0026] The plate-shaped boehmite aggregate of the present invention reduces impurities from the raw materials used in plate-shaped boehmite production and from manufacturing equipment, resulting in a very low level of impurities (e.g., elements such as Fe, Ca, Mg, S, Cl, and Na) in the alumina itself. The amount of impurities in the plate-shaped boehmite is measured using an energy-dispersive X-ray fluorescence analyzer mounted on a benchtop scanning electron microscope (JCM-7000, manufactured by JEOL Ltd.).

[0027] In the present invention, the plate-shaped boehmite aggregate is controlled to contain 0-0.08 mass% Fe, 0-0.08 mass% Ca, 0-0.08 mass% Mg, 0-0.08 mass% Cl, 0-0.08 mass% S, and 0-0.08 mass% Na. In particular, it is important to have Fe content of 0-0.07 mass%, Ca content of 0-0.07 mass%, Mg content of 0-0.07 mass%, Cl content of 0-0.07 mass%, S content of 0-0.04 mass%, and Na content of 0-0.07 mass%. More specifically, it is preferable to limit these elements (Fe, Ca, Mg, Cl, S, and Na) to 0.06% or less, and more preferably to 0.05% or less. If plate-shaped boehmite contains more than 0.08% of Fe, Ca, Mg, or Cl as impurities, it can cause the formation of undesirable crystalline phases or defects such as discoloration during firing to synthesize compounds. If plate-shaped boehmite contains more than 0.05% of S as an impurity, it can generate chlorine gas or SOx gas during firing to synthesize compounds such as aluminum composite oxides, causing corrosion in the firing furnace. If plate-shaped boehmite contains more than 0.08% of Na as an impurity, it can ionize when used in electronic materials such as resin-based conductor materials, causing short circuits between wiring.

[0028] In the wetted and powdered parts of the various equipment used in the method for manufacturing plate-shaped boehmite according to the present invention, materials that do not release impurity metals and impurity elements are used to reduce or eliminate impurities (for example, metals such as Fe, Ca, Mg, and elements such as Cl, S, and Na). Specifically, materials such as borosilicate glass, Pyrex glass, fiber-reinforced plastic (FRP), stainless steel (SUS316 or SUS316L), corrosion-resistant metals (such as Hastelloy), heat-resistant polyvinyl chloride, high-density polyethylene (HDPE), polypropylene, polyvinylidene fluoride, polyfluorotetraethylene, alumina, zirconia, zirconia thermal spraying, alumina thermal spraying, and Teflon lining are used. [Examples]

[0029] The present invention will be described in more detail by reference to examples. The present invention should not be construed as being limited to these examples. In the examples, percentages, parts, etc., are based on mass unless otherwise specified.

[0030] The Al2O3 equivalent concentrations of basic aluminum lactate, aluminum chloride, and aluminum sulfate listed in the comparative examples below are calculated based on JIS K1450, and the aluminum concentration is calculated based on these values.

[0031] (Example 1) 40 g of aluminum nitrate nonahydrate, 25.6 g of urea, and 342.0 g of water were weighed into a 500 ml separable flask and stirred at 150 rpm for 10 minutes using a stirrer equipped with a Teflon stirring blade to dissolve. The ratio (A) / (B) at this time was 0.26. Next, the 500 ml separable flask was placed on a mantle heater and heated at 115°C for 96 hours, then allowed to cool naturally. The pH at this time was 7.3. The heated and concentrated liquid was removed and filtered by suction using 5C filter paper. Then, the cake was washed twice using 1000 g of water and filtered by suction. After that, it was dried in a hot air circulating dryer at 80°C for 5 hours, and the dried material was pulverized at 8000 rpm using a hammer-type pulverizer to obtain plate-like boehmite aggregates.

[0032] The pH of the heated and concentrated liquid was measured using a portable pH meter (HM-40P: manufactured by Toa DKK Co., Ltd.).

[0033] The particle size distribution of the obtained plate-like boehmite aggregates was measured as described below, and the D50 values ​​are listed in Table 1. The specific surface area of ​​the plate-like alumina aggregates was also measured as described below. The results are shown in Table 1. The crystalline phase is also listed in Table 1. The crystalline phase is described based on the results of X-ray diffraction (Mini Flex; manufactured by Rigaku Corporation).

[0034] The particle size distribution of the plate-like boehmite aggregate is shown as D50 data, measured at 25°C with water as the solvent using a dynamic light scattering particle size analyzer (Zetasizer Pro).

[0035] The specific surface area shown is data measured in N2 using a specific surface area measuring device (Gemini72390a; manufactured by Shimadzu Corporation).

[0036] The amounts of Fe, Mg, Ca, Cl, S, and Na in plate-like boehmite aggregates were measured using energy-dispersive X-ray fluorescence (X-ray) mounted on a scanning electron microscope (JCM-7000: manufactured by JEOL Ltd.).

[0037] The shape of the plate-like boehmite aggregates was confirmed at 10,000x magnification using a scanning electron microscope (JCM-7000: manufactured by JEOL Ltd.), and the long axis, short axis, and thickness were measured from images at 10,000x and 100,000x magnification using a field emission scanning electron microscope (JSM-7610F).

[0038] SEM (Field Emission Scanning Electron Microscope) images of the plate-like boehmite particle aggregate obtained in Example 1 are shown (Figure 1 is a 100,000x SEM image, Figure 2 is a 10,000x SEM image).

[0039] (Example 2) 40 g of aluminum nitrate nonahydrate, 19.2 g of urea, and 620.0 g of water were weighed into a 1000 ml separable flask and stirred at 150 rpm for 10 minutes using a stirrer equipped with a Teflon stirring blade to dissolve. The ratio (A) / (B) at this time was 0.34. Next, a 500 ml separable flask was set on a mantle heater and heated at 115°C for 115 hours, after which it was allowed to stand and cool naturally. The pH at this time was 7.3. The heated and concentrated liquid was removed and filtered by suction using 5C filter paper. Then, the cake was washed twice using 1000 g of water and filtered by suction. After that, it was dried in a hot air circulating dryer at 80°C for 5 hours, and the dried material was pulverized at 8000 rpm using a hammer-type pulverizer to obtain plate-like boehmite aggregates.

[0040] (Example 3) 90 g of aluminum nitrate nonahydrate, 43.2 g of urea, and 697.6 g of water were weighed into a 500 ml separable flask and stirred at 150 rpm for 10 minutes using a stirrer equipped with a Teflon stirring blade to dissolve. The ratio (A) / (B) at this time was 0.33. Next, the 500 ml separable flask was placed on a mantle heater and heated at 115°C for 96 hours, then allowed to cool naturally. The pH at this time was 7.2. The heated and concentrated liquid was removed and filtered by suction using 5C filter paper. Then, the cake was washed twice using 1000 g of water and filtered by suction. After that, it was dried in a hot air circulating dryer at 80°C for 5 hours, and the dried material was pulverized at 8000 rpm using a hammer-type pulverizer to obtain plate-like boehmite aggregates.

[0041] (Example 4) 40 g of aluminum nitrate nonahydrate, 9.6 g of N-methylurea, 9.6 g of urea, and 310.0 g of water were weighed into a 500 ml separable flask and stirred at 150 rpm for 10 minutes using a stirrer equipped with a Teflon stirring blade to dissolve. The ratio (A) / (B) at this time was 0.34. Next, the 500 ml separable flask was placed on a mantle heater and heated at 115°C for 96 hours, then allowed to cool naturally. The pH at this time was 7.6. The heated and concentrated liquid was removed and filtered by suction using 5C filter paper. Then, the cake was washed twice using 1000 g of water and filtered by suction. After that, it was dried in a hot air circulating dryer at 80°C for 5 hours. The dried material was then pulverized at 8000 rpm using a hammer-type pulverizer to obtain plate-like boehmite aggregates.

[0042] (Example 5) 35 g of aluminum nitrate nonahydrate, 24.7 g of N-ethylurea, and 263.3 g of water were weighed into a 500 ml separable flask and stirred at 150 rpm for 10 min using a stirrer equipped with a Teflon stirring blade to dissolve. The ratio (A) / (B) at this time was 0.32. Next, the 500 ml separable flask was placed on a mantle heater and heated at 115°C for 96 hours, then allowed to cool naturally. The pH at this time was 7.5. The heated and concentrated solution was removed and filtered by suction using 5C filter paper. After that, the cake was washed and filtered by suction twice using 1000 g of water, and then dried in a hot air circulating dryer at 80°C for 5 hours. The dried material was then pulverized at 8000 rpm using a hammer-type pulverizer to obtain plate-like boehmite aggregates.

[0043] (Example 6) 40 g of aluminum nitrate nonahydrate, 19.2 g of urea, 310 g of water, and 10.1 g of nitric acid were weighed into a 500 ml separable flask and stirred at 150 rpm for 5 minutes using a stirrer equipped with a Teflon stirring blade to dissolve. The ratio (A) / (B) at this time was 0.34. Next, the 500 ml separable flask was placed on a mantle heater and heated at 115°C for 94 hours, then allowed to cool naturally. The pH at this time was 5.1. The heated and concentrated solution was removed and filtered by suction using 5C filter paper. After that, the cake was washed and filtered by suction twice using 1000 g of water, and then dried in a hot air circulating dryer at 60°C for 4 hours. The dried material was then pulverized at 8000 rpm using a hammer-type pulverizer to obtain plate-like boehmite aggregates.

[0044] (Comparative Example 1) 40 g of aluminum nitrate nonahydrate, 12.8 g of urea, and 278 g of water were weighed into a 1000 ml separable flask and stirred at 150 rpm for 5 minutes using a stirrer equipped with a Teflon stirring blade to dissolve. The ratio (A) / (B) at this time was 0.52. Next, a 500 ml separable flask was set on a mantle heater and heated at 115°C for 115 hours, after which it was allowed to stand and cool naturally. The pH at this time was 7.1. The heated and concentrated liquid was removed and filtered by suction using 5C filter paper. After that, the cake was washed and filtered by suction twice using 1000 g of water, and then dried in a hot air circulating dryer at 60°C for 3 hours. After that, the dried material was pulverized at 8000 rpm using a hammer-type pulverizer to obtain plate-like boehmite aggregates.

[0045] (Comparative Example 2) 40 g of aluminum nitrate nonahydrate, 19.2 g of urea, and 500.0 g of water were weighed into a 1000 ml separable flask and stirred at 150 rpm for 10 minutes using a stirrer equipped with a Teflon stirring blade to dissolve. The ratio (A) / (B) at this time was 0.34. Next, the 1000 ml separable flask was placed on a mantle heater and heated at 125°C for 23 hours, then allowed to cool naturally. The pH at this time was 7.4. The heated and concentrated solution was removed and filtered by suction using 5C filter paper. Then, the cake was washed twice using 1000 g of water and filtered by suction. After that, it was dried in a hot air circulating dryer at 80°C for 5 hours, and the dried material was pulverized at 8000 rpm using a hammer-type pulverizer to obtain plate-shaped boehmite aggregates.

[0046] (Comparative Example 3) 40 g of aluminum lactate (8.7% Al2O3 equivalent), 24.5 g of urea, and 282.5 g of water were weighed into a 500 ml separable flask and stirred at 150 rpm for 5 minutes using a stirrer equipped with a Teflon stirring blade to dissolve. The ratio (A) / (B) at this time was 0.08. Next, the 500 ml separable flask was placed on a mantle heater and heated at 115°C for 67 hours, after which it was allowed to stand and cool naturally. The pH at this time was 8.5. The heated and concentrated solution was taken out and filtered by suction using 5C filter paper.

[0047] (Comparative Example 4) 80.8g of 8.1% aluminum chloride (based on Al2O3 concentration), 28.8g of urea, and 289.2g of water were weighed into a 500ml separable flask and stirred at 150rpm for 10 minutes using a stirrer equipped with a Teflon stirring blade to dissolve. The ratio (A) / (B) at this time was 1.33. Next, the 500ml separable flask was placed on a mantle heater and heated at 115°C for 96 hours, then allowed to cool naturally. The pH at this time was 7.4. The heated and concentrated solution was removed and filtered by suction using 5C filter paper. Then, the cake was washed twice using 500g of water and filtered by suction. After that, it was dried in a hot air circulating dryer at 80°C for 5 hours, and the dried material was pulverized at 8000rpm using a hammer-type pulverizer to obtain plate-shaped boehmite aggregates.

[0048] (Comparative Example 5) 66.7 g of 10.0% aluminum sulfate (based on Al2O3 concentration), 19.2 g of urea, and 283.3 g of water were weighed into a 500 ml separable flask and stirred at 150 rpm for 10 minutes using a stirrer equipped with a Teflon stirring blade to dissolve. The ratio (A) / (B) at this time was 0.41. Next, the 500 ml separable flask was placed on a mantle heater and heated at 115°C for 96 minutes, then allowed to cool naturally. The pH at this time was 7.4. The heated and concentrated solution was removed and filtered by suction using 5C filter paper. Then, the cake was washed twice using 500 g of water and filtered by suction. After that, it was dried in a hot air circulating dryer at 80°C for 5 hours, and the dried material was pulverized at 8000 rpm using a hammer-type pulverizer to obtain plate-shaped boehmite aggregates.

[0049] (Comparative Example 6) 40 g of aluminum nitrate nonahydrate, 44.8 g of hexamethylenetetramine, and 384.2 g of water were weighed into a 500 ml separable flask and stirred at 150 rpm for 5 minutes using a stirrer equipped with a Teflon stirring blade to dissolve. The ratio (A) / (B) at this time was 0.34. Next, the 500 ml separable flask was placed on a mantle heater and heated at 115 °C for 96 hours, after which it was allowed to stand and cool naturally. The pH at this time was 7.8. The heated and concentrated liquid was removed and filtered by suction using 5C filter paper. Then, the cake was washed twice using 1000 g of water and filtered by suction. After that, it was dried in a hot air circulating dryer at 80 °C for 4 hours, and the dried material was pulverized at 8000 rpm using a hammer-type pulverizer to obtain plate-like boehmite aggregates.

[0050] The dried samples obtained in the examples were observed using SEM to confirm the short axis, long axis, and thickness. Table 1 shows the number of moles of aluminum during synthesis, the number of moles of the urea compound consisting of urea, methylurea, and ethylurea, the molar ratio of aluminum to the urea compound (A) / (B), and the pH after maturation during synthesis. In addition, Table 1 also shows information on the crystalline phase identified by X-ray diffraction, the D50 particle size distribution of the boehmite particle aggregate measured by a dynamic light scattering particle size analyzer, and the specific surface area.

[0051] The dried samples obtained in the comparative example were observed using SEM to confirm the short axis, long axis, and thickness. Table 2 shows the number of moles of aluminum during synthesis, the number of moles of one or more urea compounds (urea, methylurea, or ethylurea), the molar ratio of aluminum to urea compounds (A) / (B), and the pH after maturation during synthesis. In addition, Table 2 also shows information on the crystalline phase identified by X-ray diffraction, the D50 particle size distribution of the boehmite particle aggregate measured by a dynamic light scattering particle size analyzer, and the specific surface area.

[0052] The values ​​(% = mass%) of Fe, Mg, Ca, Cl, S, and Na content in the dried material obtained in the examples were measured using energy-dispersive X-ray fluorescence on a scanning electron microscope (JCM-7000: manufactured by JEOL Ltd.) and are listed in Table 3.

[0053] The Fe, Mg, Ca, Cl, S, and Na content in the dried products obtained in the comparative examples was measured using energy-dispersive X-ray fluorescence (X-ray fluorescence) on a scanning electron microscope (JCM-7000: manufactured by JEOL Ltd.) and is shown in Table 4.

[0054] [Table 1]

[0055] [Table 2]

[0056] [Table 3]

[0057] [Table 4]

[0058] As shown in Table 1, it was confirmed that all of Examples 1 to 6 exhibited a boehmite crystalline phase. In all of Examples 1 to 6, the long axis, short axis, thickness, (β / α) value, and (β / γ) value all met the target values. In all of Examples 1 to 6, the specific surface area ranged from 5 to 120 m². 2 It was confirmed that the levels were within the range of / g, and the particle size distribution also confirmed that the desired boehmite particle aggregates were formed. Furthermore, as shown in Table 3, the amounts of Fe, Mg, Ca, Cl, S, and Na in the boehmite particle aggregates were also controlled to a low level, confirming that the desired boehmite particle aggregates were formed.

[0059] Furthermore, as can be seen in the field emission scanning electron microscope images in Figures 1 and 2, it was confirmed that the primary particles are plate-like, and aggregates of primary particles are formed as secondary particles.

[0060] Figures 3 and 4 show the results of X-ray diffraction (MiniFlex: manufactured by Rigaku Corporation) measurements performed on Example 1 and Comparative Example 5.

[0061] Table 2 shows the formulation design and molar ratio of aluminum to urea, etc., for Comparative Examples 1 to 6, the general shape confirmed at 10,000x magnification with a scanning electron microscope (JCM-7000: JEOL Ltd.), the values ​​of the short axis α, long axis β, and thickness γ confirmed at 10,000x and 100,000x magnification with a field emission scanning electron microscope, the D50 value measured with a dynamic light scattering particle size distribution analyzer, and the specific surface area. Table 4 shows the measurement results of the Fe, Mg, Ca, Cl, S, and Na content in the dried products obtained by measuring with energy-dispersive fluorescent X-rays mounted on a scanning electron microscope (JCM-7000: JEOL Ltd.) for the synthesized products in Comparative Examples 1 to 6.

[0062] Comparative Example 1 successfully synthesized plate-like boehmite, but the plate-like size did not grow, and the (β / γ) value did not meet the target value. Comparative Example 3 could not be recovered as powder. Comparative Example 2 produced boehmite, but its shape was irregular. Comparative Example 4 showed that boehmite was the main phase from X-ray diffraction, but different crystalline phases were formed around 2θ=23 and 32 degrees, and the shape was spherical or spiky. Furthermore, as shown in Table 4, the Fe and Cl content was high and the target Fe and Cl concentrations were not met. Comparative Example 5 produced plate-like boehmite aggregates, but as shown in Table 4, the S content was high and the target S concentration was not met. Comparative Example 6 produced boehmite, but only particles with irregular primary particle shapes could be synthesized.

[0063] Figure 5 shows the particle size distribution results for Example 1. The plate-shaped boehmite particle aggregate showed a D50 of 0.35 μm in the measurement using a dynamic light scattering particle size analyzer. On the other hand, the particle size distribution measurement results for Comparative Example 2, shown in Figure 6, showed an irregular shape rather than a plate-shaped boehmite aggregate, resulting in a D50 of 0.087 μm, indicating a very small particle size and a peak shape with two peaks. [Industrial applicability]

[0064] According to the present invention, by using aluminum nitrate, one or more urea compounds selected from urea, methylurea, and ethylurea as the main raw materials, and water, and by controlling the molar ratio (A) / (B) during blending, as well as the temperature and heating time during synthesis, it is possible to provide a plate-like boehmite particle aggregate with a low content of impurity elements (Fe, Mg, Ca, Cl, S, Na), and by optimizing the grinding conditions, it is possible to provide a plate-like boehmite particle aggregate consisting of primary particles that are plate-like boehmite and secondary particles formed by the aggregation of primary particles. Furthermore, it has been confirmed that the plate-like boehmite particle aggregate of the present invention has the characteristic of having a very high specific surface area for boehmite.

[0065] The plate-shaped boehmite particle aggregate according to the present invention has a thin, plate-like primary particle shape and contains few impurities. Therefore, when mixed with various solvents and resins and coated onto films, metals, etc., it is expected to be used as a filler that exhibits gas barrier properties or as a filler for electronic materials. Furthermore, because it has a large specific surface area, a plate-like shape, and is made of boehmite, it can be used as a catalyst support, an adsorbent for various materials such as fragrances, and as a raw material for synthesizing composite oxides with other materials such as spinel. Other expected applications include use as a filter for various purposes (gas separation, solid separation, sterilization, dust removal, etc.).

[0066] The present invention also includes the following embodiments: [1] The primary particles have a short axis length (α) of 0.01 to 0.5 μm, a long axis length (β) of 0.1 to 3 μm, and a thickness (γ) of 0.005 to 0.05 μm, with a ratio of short axis to long axis (β) / (α) = 1.2 to 80, and a ratio of long axis to thickness (β) / (γ) = 20 to 400. This aggregate consists of plate-like boehmite with a specific surface area of ​​5 to 120 m². 2 A plate-shaped boehmite aggregate characterized by having / g. [2] The plate-shaped boehmite aggregate according to [1] is characterized in that the plate-shaped boehmite aggregate contains 0-0.08% by mass of iron (Fe), 0-0.08% by mass of calcium (Ca), 0-0.08% by mass of magnesium (Mg), 0-0.08% by mass of chlorine (Cl), 0-0.05% by mass of sulfur (S), and 0-0.08% by mass of sodium (Na). [3] (1) A step of preparing an aqueous solution by dissolving aluminum nitrate and one or more urea compounds selected from urea, methylurea, and ethylurea in water, (2) A step of heating and concentrating the aqueous solution described in step (1) at 90 to 120°C for 24 to 120 hours. (3) The process of filtering the concentrated liquid heated and concentrated in step (2), and washing the cake with water, (4) A step in which the cake filtered in step (3) is dried at 50-90°C for 1-10 hours, A method for producing a plate-shaped boehmite aggregate according to [1], characterized by containing the following: [4] Furthermore, the method for producing a plate-shaped boehmite aggregate according to [3] is characterized by including (5) a step of pulverizing the dried plate-shaped boehmite aggregate obtained in step (4) to standardize the particle size. [5] A method for producing plate-shaped boehmite aggregates according to [3] or [4], characterized in that the ratio (A) / (B) = 0.15 to 0.45 between the number of moles of aluminum in aluminum nitrate (A) and the number of moles of one or more selected from urea, methylurea, and ethylurea (B). [6] A method for producing a plate-shaped boehmite aggregate according to [3]-[5], characterized in that the pH after heating and concentration in step (2) is 5.0 to 8.3. [7] A method for producing plate-shaped boehmite aggregates according to [3]-[6], characterized in that the iron (Fe) contained in the plate-shaped boehmite aggregate is controlled to be 0-0.08% by mass, calcium (Ca) to be 0-0.08% by mass, magnesium (Mg) to be 0-0.08% by mass, chlorine (Cl) to be 0-0.06% by mass, sulfur (S) to be 0-0.06% by mass, and sodium (Na) to be 0-0.08% by mass. [8] A method for producing a plate-shaped boehmite aggregate according to [3]-[7], characterized in that when the crushed plate-shaped boehmite aggregate is measured with a dynamic light scattering particle size distribution analyzer, the D50 is controlled to 0.1-0.8 μm in the particle size distribution measurement based on the number of particles. [9] A method for producing a plate-shaped boehmite aggregate according to [3] to [8], characterized in that the apparatus used for drying in step (4) is one of a hot air circulation dryer, a shelf dryer, a vacuum dryer, and a vibratory dryer.

Claims

1. The aggregate consists of plate-like boehmite particles with a primary particle length (α) of 0.01–0.5 μm, a major axis length (β) of 0.1–3 μm, a thickness (γ) of 0.005–0.05 μm, a ratio of minor axis to major axis (β) / (α) = 1.2–80, and a ratio of major axis to thickness (β) / (γ) = 20–400, with a specific surface area of ​​15–120 m². 2 A plate-shaped boehmite aggregate characterized by having / g, A plate-shaped boehmite aggregate characterized by containing 0 to 0.08% by mass of iron (Fe), 0 to 0.08% by mass of calcium (Ca), 0 to 0.08% by mass of magnesium (Mg), 0 to 0.08% by mass of chlorine (Cl), 0 to 0.05% by mass of sulfur (S), and 0 to 0.08% by mass of sodium (Na).

2. (1) A step of preparing an aqueous solution by dissolving aluminum nitrate and one or more urea compounds selected from urea, methylurea, and ethylurea in water, (2) A step of heating and concentrating the aqueous solution described in step (1) at 90 to 120°C for 24 to 120 hours. (3) The process of filtering the concentrated liquid heated and concentrated in step (2), and washing the cake with water, (4) A step in which the cake filtered in step (3) is dried at 50 to 90°C for 1 to 10 hours, A method for producing a plate-shaped boehmite aggregate according to claim 1, comprising: In step (1) above, the ratio (A) / (B) of the number of moles of aluminum in aluminum nitrate (A) to the number of moles of one or more selected from urea, methylurea, and ethylurea (B) is 0.15 to 0.

45. The iron (Fe) content within the plate-shaped boehmite aggregate is controlled to be 0-0.08% by mass, calcium (Ca) to be 0-0.08% by mass, magnesium (Mg) to be 0-0.08% by mass, chlorine (Cl) to be 0-0.06% by mass, sulfur (S) to be 0-0.06% by mass, and sodium (Na) to be 0-0.08% by mass. A method for producing a plate-shaped boehmite aggregate according to claim 1, characterized by its features.

3. Furthermore, the method for producing a plate-shaped boehmite aggregate according to claim 2, characterized in that it includes a step of pulverizing the dried plate-shaped boehmite aggregate obtained in step (4) to standardize the particle size.

4. A method for producing a plate-shaped boehmite aggregate according to claim 2 or 3, characterized in that the pH after heating and concentration in step (2) is 5.0 to 8.

3.

5. A method for producing a plate-shaped boehmite aggregate according to claim 2 or 3, characterized in that when the crushed plate-shaped boehmite aggregate is measured using a dynamic light scattering particle size distribution analyzer, the D50 is controlled to 0.1 to 0.8 μm in the particle size distribution measurement based on the number of particles.

6. The method for producing a plate-shaped boehmite aggregate according to claim 2 or 3, characterized in that the drying apparatus in step (4) is one of a hot air circulation dryer, a shelf dryer, a vacuum dryer, and a vibratory dryer.

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