Amorphous aluminum hydroxide composed of highly spherical particles

Abstract

The challenge is to develop amorphous aluminum hydroxide composed of highly spherical particles. [Solution] The amorphous aluminum hydroxide satisfies requirement (1): the average circularity obtained by the following procedure is 0.6 or higher, and requirement (2): the SEM image for calculating circularity obtained in the following procedure [3] does not contain any isolated particles with a maximum length exceeding 50 μm. The procedure is as follows: [1] Prepare an analytical sample from the amorphous aluminum hydroxide for analysis by scanning electron microscopy (SEM); [2] Subject the analytical sample to scanning electron microscopy (SEM) analysis to obtain an SEM image; [3] The SEM image containing 40 to 200 isolated particles with a maximum length of 1 to 50 μm is used as the SEM image for calculating circularity; [4] For all isolated particles with a maximum length of 1 to 50 μm in the SEM image for calculating circularity, the circularity is calculated as circularity = 4πS / L 2 The mean circularity is calculated using the formula, and its arithmetic mean is taken as the mean circularity.

Description

Technical Field

[0001] The present invention relates to amorphous aluminum hydroxide composed of highly spherical particles.

Background Art

[0002] Aluminum hydroxide is used in a wide range of fields as a flame retardant and filler. It is known that a shape closer to a perfect sphere is preferable from the viewpoints of fluidity, filling property, abrasion resistance, etc.

[0003] Patent Document 1 discloses a method for producing α-alumina with high sphericity by an explosion combustion method or a melting method.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to develop amorphous aluminum hydroxide composed of particles with high sphericity.

Means for Solving the Problems

[0006] The present invention is as follows. 〔1〕Amorphous aluminum hydroxide satisfying the following requirements (1) to (2). (1) The average circularity obtained by the following procedure is 0.6 or more. (2) There are no isolated particles with a maximum length exceeding 50 μm in the SEM image for circularity calculation in the following procedure [3]. 〔Procedure〕 [1] Prepare an analytical sample for analysis by a scanning electron microscope (SEM) from the above amorphous aluminum hydroxide. [2] The sample for analysis is subjected to SEM analysis to obtain an SEM image. [3] Among the SEM images, the SEM image containing 40 to 200 isolated particles with a maximum length of 1 to 50 μm is used as the SEM image for calculating circularity. [4] In the SEM image for calculating circularity, the circularity of each isolated particle with a maximum length of 1 to 50 μm is determined, and the arithmetic mean of these is taken as the average circularity. Here, the circularity is calculated from the following formula, where S is the projected area of ​​the isolated particle and L is its perimeter. Circularity = 4πS / L 2 [2] A method for producing amorphous aluminum hydroxide as described in [1] above, comprising the following steps. (1) The first step involves adding an aqueous solution of basic aluminum chloride with a basicity of 60-85% and an aqueous solution of a carbonate-containing alkaline compound, so as to maintain the pH of the mixture of the two solutions within the range of 6-7.5, and reacting them to produce gel-like aluminum hydroxide, thereby obtaining a crude slurry containing gel-like aluminum hydroxide. However, the Al2O3 concentration in the crude slurry shall be 3% by mass or more. (2) A second step in which the crude slurry obtained in the first step is washed to obtain an aluminum hydroxide-containing slurry. (3) A third step in which the aluminum hydroxide-containing slurry obtained in the second step is dried. [3] A slurry containing amorphous aluminum hydroxide that satisfies the following requirements (1) to (2). (1) The average circularity obtained by the following procedure is 0.6 or higher. (2) The SEM images used for calculating circularity in the following procedure [3] do not contain any isolated particles with a maximum length exceeding 50 μm. 〔procedure〕 [1] The amorphous aluminum hydroxide-containing slurry is allowed to stand and dry to prepare an analytical sample for analysis using a scanning electron microscope (SEM). [2] The sample for analysis is subjected to SEM analysis to obtain an SEM image. [3] Among the SEM images, the SEM image containing 40 to 200 isolated particles with a maximum length of 1 to 50 μm is used as the SEM image for calculating circularity. [4] In the SEM image for calculating circularity, the circularity of each isolated particle with a maximum length of 1 to 50 μm is determined, and the arithmetic mean of these is taken as the average circularity. Here, the circularity is calculated from the following formula, where S is the projected area of ​​the isolated particle and L is its perimeter. Circularity = 4πS / L 2 [4] A method for producing the amorphous aluminum hydroxide-containing slurry described in [3] above, comprising the following steps. (1) The first step involves adding an aqueous solution of basic aluminum chloride with a basicity of 60-85% and an aqueous solution of a carbonate-containing alkaline compound, so as to maintain the pH of the mixture of the two solutions within the range of 6-7.5, and reacting them to produce gel-like aluminum hydroxide, thereby obtaining a crude slurry containing gel-like aluminum hydroxide. However, the Al2O3 concentration in the crude slurry shall be 3% by mass or more. (2) A second step in which the crude slurry obtained in the first step is washed to obtain an aluminum hydroxide-containing slurry. [Brief explanation of the drawing]

[0007] [Figure 1] These are X-ray diffraction patterns of the dried powders obtained in Examples 1 to 4. [Figure 2] These are SEM images used for calculating the circularity of Examples 1-4. [Figure 3] These are SEM images used for calculating the circularity of Comparative Examples 1-4. [Modes for carrying out 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. In this invention, the notation "value 1 to value 2" in relation to a numerical range means a numerical range that includes both values ​​1 and 2, with value 1 as the lower limit and value 2 as the upper limit, and is synonymous with "value 1 or greater and value 2 or less".

[0009] The amorphous aluminum hydroxide of the present invention satisfies the following requirements (1) to (2). (1) The average circularity obtained by the following procedure is 0.6 or more. (2) In the SEM image for calculating circularity in the following procedure [3], there are no isolated particles having a maximum length exceeding 50 μm. [Procedure] [1] Prepare an analytical sample for analysis by a scanning electron microscope (SEM) from the above amorphous aluminum hydroxide. [2] Subject the analytical sample to SEM analysis to obtain an SEM image. [3] Among the SEM images, an SEM image containing 40 to 200 isolated particles with a maximum length of 1 to 50 μm is used as the SEM image for calculating circularity. [4] In the SEM image for calculating circularity, for all isolated particles with a maximum length of 1 to 50 μm, determine the circularity of each, and take their weighted average as the average circularity. Here, the circularity is calculated from the following formula when the projected area of the isolated particle is S and the perimeter is L. Circularity = 4πS / L 2

[0010] Amorphous aluminum hydroxide refers to aluminum hydroxide that does not have an ordered crystal structure. Specifically, it refers to aluminum hydroxide in a state where the presence of crystal peaks is not recognized or is substantially equivalent to not being recognized in a powder X-ray diffraction pattern.

[0011] The measurement procedure for the average circularity is as described above, and supplementary explanations will be given below. Procedure [1] is a conventional method for preparing an analytical sample for SEM analysis. When it contains moisture, it is dried to remove moisture. A preferred example is static drying at 100°C. Thereafter, the dried product may be appropriately loosened as necessary.

[0012] The SEM image in procedure [2] is a two-dimensional projection image.

[0013] In procedure [3], an isolated particle refers to an independent particle in the SEM image that does not overlap with other particles. In other words, the entire outer edge of each particle is bordered by the background color of the SEM image. By appropriately adjusting the magnification and field of view of the SEM image, an SEM image containing 40 to 200 isolated particles with a maximum length of 1 to 50 μm is selected as the SEM image for calculating circularity. It is also preferable to select a magnification that makes the shape of isolated particles around 1 μm in maximum length clear. For example, a magnification of 1000 to 3000x is preferable. Figure 2 shows a good example of an SEM image for calculating circularity.

[0014] In procedure [4], the projected area S and perimeter L are determined for all isolated particles with a maximum length of 1 to 50 μm. It is preferable to use image analysis software for this purpose, one example being "A-zo-kun" (manufactured by Asahi Kasei Engineering Corporation).

[0015] The particles constituting the amorphous aluminum hydroxide of the present invention have an average circularity of 0.6 or higher, calculated from all isolated particles with a maximum length of 1 to 50 μm in the SEM image used for calculating circularity, and the three-dimensional shape of the isolated particles in the SEM image is spherical (including shapes close to spherical; the same applies hereinafter), thus indicating a high degree of sphericity.

[0016] As mentioned above, the SEM image used for calculating circularity contains 40 to 200 isolated particles with a maximum length of 1 to 50 μm, but the presence of isolated particles with a maximum length of less than 1 μm does not cause any problems. If even one isolated particle with a maximum length exceeding 50 μm is present in the SEM image used for calculating circularity, requirement (2) will no longer be met. Requirement (2) is set particularly from the viewpoint of packing ability as a filler. To determine the maximum length of isolated particles, it is preferable to use image analysis software as described above. The maximum length specified in requirement (2) is preferably 40 μm, and more preferably 30 μm.

[0017] The amorphous aluminum hydroxide of the present invention also includes, for example, the following particles, insofar as requirements (1) to (2) are met: particles obtained by spray drying, in which case the particles are aggregates of single particles, and when these particles are separated into single particles by appropriate means such as crushing, the single particles satisfy requirements (1) to (2).

[0018] A preferred method for producing amorphous aluminum hydroxide according to the present invention includes the following steps. (1) The first step involves adding an aqueous solution of basic aluminum chloride with a basicity of 60-85% and an aqueous solution of a carbonate-containing alkaline compound, so as to maintain the pH of the mixture of the two solutions within the range of 6-7.5, and reacting them to produce gel-like aluminum hydroxide, thereby obtaining a crude slurry containing gel-like aluminum hydroxide. However, the Al2O3 concentration in the crude slurry shall be 3% by mass or more. (2) A second step in which the crude slurry obtained in the first step is washed to obtain an aluminum hydroxide-containing slurry. (3) A third step in which the aluminum hydroxide-containing slurry obtained in the second step is dried.

[0019] In the first step, a basic aluminum chloride aqueous solution with a basicity of 60-85% and an aqueous solution of a carbonate-containing alkaline compound are added and reacted while maintaining the pH of the mixture of both solutions within the range of 6-7.5 to produce gel-like aluminum hydroxide, and a crude slurry containing gel-like aluminum hydroxide (hereinafter referred to as "crude slurry") is obtained. However, the Al2O3 concentration in the crude slurry shall be 3% by mass or more. Note that the crude slurry does not necessarily exclude trace amounts of AlOOH, Al2O3, etc.

[0020] Basic aluminum chloride aqueous solutions with a basicity of 60-85% can be produced by known manufacturing methods. Alternatively, "Takibain #1500" manufactured by Taki Chemical Co., Ltd., can be used as a commercially available basic aluminum chloride aqueous solution with a basicity of 83%. Here, "Takibain #1500" is substantially sulfate-free, and apart from other unavoidable impurities, its components are Al and Cl. To produce a low-basicity product from an 83% basic aluminum chloride aqueous solution, hydrochloric acid can be added. Heating may also be performed after adding hydrochloric acid if necessary. On the other hand, to produce a high-basicity product from an 83% basic aluminum chloride aqueous solution, for example, an aluminum hydroxide-containing slurry can be added to the 83% basic aluminum chloride aqueous solution and dissolved. Here, basicity is given by the general formula: Al2(OH) n Cl 6-n Therefore, the basicity is calculated using the formula: Basicity = n / 6 × 100. Note that n is within the range satisfying 60 ≤ n / 6 × 100 ≤ 85.

[0021] Examples of carbonate-containing alkaline compounds used in aqueous solutions of carbonate-containing alkaline compounds include sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, and sodium sesquicarbonate. These may be used individually or in combination of two or more. Of these, sodium carbonate is particularly preferred.

[0022] The method for mixing a basic aluminum chloride aqueous solution with a basicity of 60-85% with an aqueous solution of a carbonate-containing alkaline compound is designed so that the pH of the mixed solution is maintained within the range of 6-7.5, and the mixture is added and reacted to produce a gel-like aluminum hydroxide. The mixing method is not particularly limited as long as the mixture is mixed within the above pH range. One example is to continuously inject both solutions into the reaction vessel simultaneously. A metering pump is preferred for continuous injection. However, as long as the pH remains within the above range, the solutions may be injected intermittently, or only one of the solutions may be injected intermittently. Although not essential, it is preferable to pre-fill the reaction vessel with water. Another good example is to mix both solutions using a line mixer such as a static mixer. The concentrations of each solution are not particularly limited, but the pH of the mixed solution should be within the above pH range, and the Al2O3 concentration in the crude slurry should be 3% by mass or more. The upper limit of the Al2O3 concentration is not particularly limited, but a guideline is 20% by mass. Therefore, the Al2O3 concentration in the crude slurry is preferably in the range of 3 to 20% by mass. The lower limit of the above range is more preferably 5% by mass, and even more preferably 7% by mass. Therefore, a more preferable range for the Al2O3 concentration in the crude slurry is 5 to 20% by mass, and even more preferably 7 to 20% by mass.

[0023] In the second step, alkali metal ions, chloride ions, and other substances contained in the crude slurry, as well as excess carbonate ions, are removed by washing to obtain an aluminum hydroxide-containing slurry. The degree of removal is preferably designed so that the alkali metal content is in the range of greater than 0 and 1000 ppm or less, the Cl content is in the range of greater than 0 and 1000 ppm or less, and the carbonate content is in the range of 0.2 to 1 in the molar ratio of CO2 / Al2O3. The upper limit of the alkali metal content is more preferably 800 ppm, even more preferably 500 ppm, and even more preferably 300 ppm. The upper limit of the Cl content is more preferably 800 ppm, even more preferably 500 ppm, even more preferably 300 ppm, and particularly preferably 150 ppm. Good examples of washing methods include ultrafiltration, microfiltration (MF), Nutsche filtration, and filter pressing. As an example of a guideline for washing intensity in ultrafiltration, washing is performed until the EC of the filtrate is 1.0 mS / cm or less. Furthermore, it is preferable that the aluminum hydroxide-containing slurry is substantially sulfate-free. Here, substantially sulfate-free means that, apart from sulfate rhizates derived from impurities in the raw materials, it contains no sulfate rhizates. Even more preferably, it contains no sulfate rhizates at all.

[0024] In the third step, the aluminum hydroxide-containing slurry obtained in the second step is dried. The drying method is not particularly limited and can be, for example, spray drying or static drying. The drying conditions (temperature, time) are preferably set as appropriate.

[0025] The second invention, which falls under the category of amorphous aluminum hydroxide of the present invention, is an amorphous aluminum hydroxide-containing slurry that satisfies the following requirements (1) to (2). (1) The average circularity obtained by the following procedure is 0.6 or higher. (2) The SEM images used for calculating circularity in the following procedure [3] do not contain any isolated particles with a maximum length exceeding 50 μm. 〔procedure〕 [1] The amorphous aluminum hydroxide-containing slurry is allowed to stand and dry to prepare an analytical sample for analysis using a scanning electron microscope (SEM). [2] The sample for analysis is subjected to SEM analysis to obtain an SEM image. [3] Among the SEM images, the SEM image containing 40 to 200 isolated particles with a maximum length of 1 to 50 μm is used as the SEM image for calculating circularity. [4] In the SEM image for calculating circularity, the circularity of each isolated particle with a maximum length of 1 to 50 μm is determined, and the arithmetic mean of these is taken as the average circularity. Here, when the projected area of ​​the isolated particle is S and its perimeter is L, the circularity = 4πS / L 2 It is calculated from the formula.

[0026] As a supplement, the static drying in step [1] only needs to remove moisture, and it is preferable to dry the material at 100°C, for example, and then loosen the dried material appropriately as needed. Also, steps [2] to [4] are the same as steps [2] to [4] in the amorphous aluminum hydroxide of the present invention.

[0027] The amorphous aluminum hydroxide-containing slurry of the present invention may be the aluminum hydroxide-containing slurry obtained in the second step of the above-mentioned method for producing amorphous aluminum hydroxide of the present invention, or it may be the amorphous aluminum hydroxide of the present invention dispersed in water. The Al2O3 concentration in the amorphous aluminum hydroxide-containing slurry of the present invention is preferably in the range of 3 to 20% by mass. More preferably, this range is 5 to 20% by mass, and even more preferably 7 to 20% by mass.

[0028] A preferred method for producing the amorphous aluminum hydroxide-containing slurry of the present invention includes the following steps. Steps (1) and (2) below are the same as the above-described method for producing amorphous aluminum hydroxide of the present invention. (1) The first step involves adding an aqueous solution of basic aluminum chloride with a basicity of 60-85% and an aqueous solution of a carbonate-containing alkaline compound, so as to maintain the pH of the mixture of the two solutions within the range of 6-7.5, and reacting them to produce gel-like aluminum hydroxide, thereby obtaining a crude slurry containing gel-like aluminum hydroxide. However, the Al2O3 concentration in the crude slurry shall be 3% by mass or more. (2) A second step in which the crude slurry obtained in the first step is washed to obtain an aluminum hydroxide-containing slurry. [Examples]

[0029] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0030] As a basic aluminum chloride aqueous solution with a basicity of 83%, we used "Takibain #1500" (Al2O3 = 23.2% by mass, Cl = 8.3% by mass) manufactured by Taki Chemical Co., Ltd.

[0031] [Example 1] To a reaction vessel containing 128.5 g of water, 203.4 g of an 83% basic aluminum chloride aqueous solution and 124.3 g of a 15.0% by mass sodium carbonate aqueous solution were simultaneously added and mixed in a pH range of 6 to 7 to produce gel-like aluminum hydroxide, yielding a crude slurry containing gel-like aluminum hydroxide. The Al2O3 concentration in the crude slurry was 9.5% by mass. Next, the obtained crude slurry was washed with an MF membrane until the filtrate EC ≤ 1 mS / cm to obtain an aluminum hydroxide-containing slurry (hereinafter referred to as "Slurry A"). Slurry A was allowed to stand and dry at 100°C to obtain the dried powder of Example 1.

[0032] [Example 2] A basic aluminum chloride aqueous solution with a basicity of 83% was mixed with a normal salt aluminum chloride aqueous solution, and then heated at 100°C for 1 hour to prepare a basic aluminum chloride aqueous solution with a basicity of 60% (Al2O3 = 18% by mass). 275 g of a 60% basic aluminum chloride aqueous solution and 414.7 g of a 15.0% by mass sodium carbonate aqueous solution were simultaneously added to a reaction vessel containing 210.3 g of water, and the mixture was maintained at a pH of 6-7 to produce a gel-like aluminum hydroxide, yielding a crude slurry containing the gel-like aluminum hydroxide. The Al2O3 concentration in the crude slurry was 5.5% by mass. Next, the obtained crude slurry was washed with an MF membrane until the filtrate EC ≤ 1 mS / cm to obtain an aluminum hydroxide-containing slurry. This aluminum hydroxide-containing slurry was allowed to stand and dry at 100°C to obtain the dried powder of Example 2.

[0033] [Example 3] Slurry A was added to a basic aluminum chloride aqueous solution with a basicity of 83% to prepare a basic aluminum chloride aqueous solution with a basicity of 85% (Al2O3 = 20.6% by mass). To a reaction vessel containing 155.5 g of water, 237.5 g of an 85% basic aluminum chloride aqueous solution and 96.5 g of a 15.0% by mass sodium carbonate aqueous solution were simultaneously added and mixed in a pH range of 6 to 7 to produce gel-like aluminum hydroxide, yielding a crude slurry containing gel-like aluminum hydroxide. The Al2O3 concentration in the crude slurry was 9.5% by mass. Next, the obtained crude slurry was washed with an MF membrane until the filtrate EC ≤ 1 mS / cm to obtain an aluminum hydroxide-containing slurry. This aluminum hydroxide-containing slurry was allowed to stand and dry at 100°C to obtain the dried powder of Example 3.

[0034] [Example 4] In a reaction vessel containing 64.3 g of water, 406.8 g of an 83% basic aluminum chloride aqueous solution and 156.6 g of a 30.0% by mass sodium carbonate aqueous solution were simultaneously added and mixed in a pH range of 6 to 7 to produce a gel-like aluminum hydroxide, yielding a crude slurry containing the gel-like aluminum hydroxide. The Al2O3 concentration in the crude slurry was 15.0% by mass. Next, the obtained crude slurry was washed with an MF membrane until the filtrate EC ≤ 1 mS / cm to obtain an aluminum hydroxide-containing slurry. This aluminum hydroxide-containing slurry was allowed to stand and dry at 100°C to obtain the dried powder of Example 4.

[0035] [Comparative Example 1] In a reaction vessel containing 166.7 g of water, 482.7 g of an aluminum sulfate aqueous solution with an Al2O3 concentration of 8.1% by mass and 1050.6 g of a 15.0% by mass sodium carbonate aqueous solution were simultaneously added and mixed in a pH range of 6 to 7 to produce gel-like aluminum hydroxide, yielding a crude slurry containing gel-like aluminum hydroxide. The Al2O3 concentration in the crude slurry was 2.3% by mass. Next, the obtained crude slurry was washed with an MF membrane until the filtrate EC ≤ 1 mS / cm to obtain an aluminum hydroxide-containing slurry. This aluminum hydroxide-containing slurry was allowed to stand and dry at 100°C to obtain the dried powder of Comparative Example 1.

[0036] [Comparative Example 2] Slurry A was added to a basic aluminum chloride aqueous solution with a basicity of 83% to prepare a basic aluminum chloride aqueous solution with a basicity of 86% (Al2O3 = 5% by mass). 980.0 g of a basic aluminum chloride aqueous solution with a basicity of 86% and 104.8 g of a 15.0% by mass sodium carbonate aqueous solution were simultaneously added to a reaction vessel containing 315.2 g of water, and the mixture was stirred in the pH range of 6 to 7 to produce gel-like aluminum hydroxide, yielding a crude slurry containing gel-like aluminum hydroxide. The Al2O3 concentration in the crude slurry was 3.5% by mass. Next, the obtained crude slurry was washed with an MF membrane until the filtrate EC ≤ 1 mS / cm to obtain an aluminum hydroxide-containing slurry. This aluminum hydroxide-containing slurry was allowed to stand and dry at 100°C to obtain the dried powder of Comparative Example 2.

[0037] [Comparative Example 3] In a reaction vessel containing 354.8 g of water, 409.4 g of an 83% basic aluminum chloride aqueous solution and 235.6 g of a 7.3% by mass sodium hydroxide aqueous solution were simultaneously added and mixed in a pH range of 6 to 7 to produce a gel-like aluminum hydroxide, yielding a crude slurry containing the gel-like aluminum hydroxide. The Al2O3 concentration in the crude slurry was 9.5% by mass. Next, the obtained crude slurry was washed with an MF membrane until the filtrate EC ≤ 1 mS / cm to obtain an aluminum hydroxide-containing slurry. This aluminum hydroxide-containing slurry was allowed to stand and dry at 100°C to obtain the dried powder of Comparative Example 3.

[0038] [Comparative Example 4] To a reaction vessel containing 3638g of water, 162.7g of an 83% basic aluminum chloride aqueous solution and 99.4g of a 15.0% by mass sodium carbonate aqueous solution were simultaneously added and mixed in a pH range of 6-7 to produce a gel-like aluminum hydroxide, yielding a crude slurry containing the gel-like aluminum hydroxide. The Al2O3 concentration in the crude slurry was 1.0% by mass. Next, the obtained crude slurry was washed with an MF membrane until the filtrate EC ≤ 1 mS / cm to obtain an aluminum hydroxide-containing slurry. This aluminum hydroxide-containing slurry was allowed to stand and dry at 100°C to obtain the dried powder of Comparative Example 4.

[0039] <Powder X-ray Diffraction> The crystal structure of each dried powder obtained in the above examples was analyzed by powder X-ray diffraction. The analytical conditions were as follows: • Powder X-ray diffractometer: Rigaku MiniFlex600-C ·Tube: CuKα ray Output: Voltage 40kV, Current 15mA • Step width: 0.01° (diffraction angle 15°~85°) • Measurement speed: 10° / min

[0040] <SEM analysis> [1] After the dried powders obtained in the above examples and comparative examples were allowed to dry at 100°C, they were loosened appropriately using a mortar and pestle or the like to prepare samples for SEM analysis. [2] The analytical sample was subjected to analysis using a scanning electron microscope (SEM) model JSM-6010LA manufactured by JEOL Ltd., and SEM images were obtained. [3] Of the SEM images, those containing 40 to 200 isolated particles with a maximum length of 1 to 50 μm were used as SEM images for calculating circularity. [4] In the SEM images for calculating circularity, the circularity of each isolated particle was determined, and the arithmetic mean of these was taken as the average circularity. Here, when the projected area of ​​the isolated particle is S and its perimeter is L, the circularity = 4πS / L 2 The values ​​were calculated from the formula shown. The projected area, perimeter, and maximum length of the isolated particle were determined using "A-Image-kun" (manufactured by Asahi Kasei Engineering Corporation).

[0041] (component analysis) The component values ​​shown in the examples and comparative examples were measured as follows. • Al2O3: Analyzed by chelation titration. • Cl: Analyzed using the Forhardt method.

[0042] Figure 1 shows the powder X-ray diffraction patterns for Examples 1 to 4. Figure 2 shows SEM images used for calculating the circularity of the examples. (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Example 4. Figure 3 shows SEM images used for calculating the circularity of the comparative examples. (e) is Comparative Example 1, (f) is Comparative Example 2, (g) is Comparative Example 3, and (h) is Comparative Example 4.

[0043] Table 1 shows the average circularity, maximum length, and number of isolated particles for the examples and comparative examples. "Maximum length" refers to the longest length among the isolated particles, and "Number of isolated particles" refers to the number of isolated particles with a maximum length of 1 to 50 μm counted in the SEM images used for calculating circularity.

[0044] [Table 1]

[0045] From the powder X-ray diffraction pattern in Figure 1, it can be seen that the aluminum hydroxides in Examples 1 to 4 are all amorphous. Examples 1 to 4 satisfy requirements (1) to (2) as shown in Table 1, and are spherical as is clear from the SEM image for calculating circularity in Figure 2, so they can be evaluated as having high sphericity. On the other hand, Comparative Examples 1-4 all failed to meet requirement (1) as shown in Table 1, and Comparative Example 3 also failed to meet requirement (2). Furthermore, as is clear from the SEM image used for calculating circularity in Figure 3, they could not be described as spherical.

Claims

1. Amorphous aluminum hydroxide that satisfies the following requirements (1) to (2). (1) The average circularity obtained by the following procedure is 0.6 or higher. (2) The SEM images used for calculating circularity in the following procedure [3] do not contain any isolated particles with a maximum length exceeding 50 μm. 〔procedure〕 [1] Prepare an analytical sample from the amorphous aluminum hydroxide described above for analysis using a scanning electron microscope (SEM). [2] The sample for analysis is subjected to SEM analysis to obtain an SEM image. [3] SEM images containing 40 to 200 isolated particles with a maximum length of 1 to 50 μm are used as SEM images for calculating circularity. [4] In the SEM image for calculating circularity, the circularity of each isolated particle with a maximum length of 1 to 50 μm is determined, and the arithmetic mean of these is taken as the average circularity. Here, the circularity is calculated from the following formula, where S is the projected area of ​​the isolated particle and L is its perimeter. Circularity = 4πS / L 2

2. A method for producing amorphous aluminum hydroxide according to claim 1, comprising the following steps. (1) A first step in which an aqueous solution of basic aluminum chloride with a basicity of 60-85% and an aqueous solution of a carbonate-containing alkaline compound are added and reacted so as to maintain the pH of the mixture of the two solutions within the range of 6-7.5 to produce gel-like aluminum hydroxide, thereby obtaining a crude slurry containing gel-like aluminum hydroxide. However, Al in the crude slurry 2 O 3 The concentration shall be 3% by mass or higher. (2) A second step in which the crude slurry obtained in the first step is washed to obtain an aluminum hydroxide-containing slurry. (3) A third step in which the aluminum hydroxide-containing slurry obtained in the second step is dried.

3. A slurry containing amorphous aluminum hydroxide that satisfies the following requirements (1) to (2). (1) The average circularity obtained by the following procedure is 0.6 or higher. (2) The SEM images used for calculating circularity in the following procedure [3] do not contain any isolated particles with a maximum length exceeding 50 μm. 〔procedure〕 [1] The amorphous aluminum hydroxide-containing slurry is allowed to stand and dry to prepare an analytical sample for analysis using a scanning electron microscope (SEM). [2] The sample for analysis is subjected to SEM analysis to obtain an SEM image. [3] SEM images containing 40 to 200 isolated particles with a maximum length of 1 to 50 μm are used as SEM images for calculating circularity. [4] In the SEM image for calculating circularity, the circularity of each isolated particle with a maximum length of 1 to 50 μm is determined, and the arithmetic mean of these is taken as the average circularity. Here, the circularity is calculated from the following formula, where S is the projected area of ​​the isolated particle and L is its perimeter. Circularity = 4πS / L 2

4. A method for producing an amorphous aluminum hydroxide-containing slurry according to claim 3, comprising the following steps. (1) A first step in which an aqueous solution of basic aluminum chloride with a basicity of 60-85% and an aqueous solution of a carbonate-containing alkaline compound are added and reacted so as to maintain the pH of the mixture of the two solutions within the range of 6-7.5 to produce gel-like aluminum hydroxide, thereby obtaining a crude slurry containing gel-like aluminum hydroxide. However, Al in the crude slurry 2 O 3 The concentration shall be 3% by mass or higher. (2) A second step in which the crude slurry obtained in the first step is washed to obtain an aluminum hydroxide-containing slurry.

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