JP7680899B2 - Aluminum hydroxide powder and its manufacturing method - Google Patents

Description

This disclosure relates to aluminum hydroxide powder and a method for producing the same.

Demand for aluminum hydroxide powder is increasing as a filler for resin molded products (sealants, thermal interface materials (TIM), artificial marble, etc.).
For example, Patent Document 1 discloses a method for producing aluminum hydroxide for use as a filler, which is characterized in that raw aluminum hydroxide is pulverized in a screw-type kneader having a compression capacity of 5 to 500 kgf/ ^cm2 .

JP 2001-322813 A

However, it has been found that conventional techniques such as those disclosed in Patent Document 1 may lead to increased viscosity when aluminum hydroxide powder is added to the resin.

The present invention was made in consideration of these circumstances, and one of its objectives is to provide an aluminum hydroxide powder that can sufficiently suppress viscosity increase when added to a resin, and a method for producing the same.

Aspect 1 of the present invention is
The density when molded at 10 MPa is 1.59 to 2.00 g/ ^cm3 ,
The aluminum hydroxide powder has an XRD pattern in which the ratio of the diffraction intensity of the (002) plane to the diffraction intensity of the (110) plane is 2.0 to 7.5.

Aspect 2 of the present invention is
The aluminum hydroxide powder according to aspect 1, wherein the 90% by mass particle size (D90) is less than 100 μm.

Aspect 3 of the present invention is
The mass standard particle size distribution has one or two peaks in the particle size range of 1 to 200 μm,
When there is one peak, the frequency of the peak is 4.0% by mass or more,
In the case where there are two peaks, the frequency of one peak is 4.0 mass% or more, and the frequency of the other peak is more than 0 mass% and 4.0 mass% or less, in the aluminum hydroxide powder according to aspect 1 or 2.

Aspect 4 of the present invention is
The method for producing aluminum hydroxide powder comprises crushing aluminum hydroxide powder having a 50% mass particle size (D50) of 10 to 200 μm and a cumulative volume of pores with a radius of 0.05 to 1 μm of 0.01 to 1 mL/g under a pressure of 49.0 to 294.0 MPa, and then disintegrating the powder at a collision speed of 92 m/sec or less.

According to an embodiment of the present invention, it is possible to provide an aluminum hydroxide powder that can sufficiently suppress an increase in viscosity when added to a resin, and a method for producing the same.

The present inventors have conducted research from various angles in order to realize an aluminum hydroxide powder that can sufficiently suppress an increase in viscosity (hereinafter also referred to as "resin viscosity") when added to a resin. As a result, they have found that an increase in resin viscosity can be sufficiently suppressed by controlling, within a predetermined range, the density when molded at 10 MPa (hereinafter also referred to as "molded density") and the ratio of the diffraction intensity of the (002) plane to the diffraction intensity of the (110) plane in the XRD pattern (hereinafter also referred to as "(002)/(110) diffraction intensity ratio").
It has been found that in order to control the molding density and the (002)/(110) diffraction intensity ratio within a predetermined range, it is important to control the particle size and pore volume of the raw aluminum hydroxide powder within a predetermined range, to crush the powder at a pressure greater than that of the conventional technology (500 to 3000 kgf/ ^cm2 , i.e., 49.0 to 294.0 MPa), and to disintegrate the powder at a relatively low impact speed of 92 m/sec or less.

The following provides details of each requirement stipulated by the embodiment of the present invention.

<1. Aluminum hydroxide powder>
The aluminum hydroxide powder according to the embodiment of the present invention has a density of 1.59 to 2.00 g/ ^cm3 when molded at 10 MPa, and a ratio of the diffraction intensity of the (002) plane to the diffraction intensity of the (110) plane in the XRD pattern of 2.0 to 7.5. This makes it possible to sufficiently suppress an increase in the resin viscosity.

If the molding density is less than 1.59 g/ ^cm3 , the resin viscosity increases. There is no particular upper limit to the molding density, but to make it exceed 2.00 g/ ^cm3 , for example, more detailed manufacturing conditions must be set, and it is preferable to keep it at 2.00 g/cm3 or ^less in consideration of productivity.

The molding density is determined as follows.
3.00 g of aluminum hydroxide powder is placed in a cylindrical uniaxial molding die having an inner diameter of 20.0 mm, and the aluminum hydroxide powder is compressed and packed at a compression speed of 1 mm/min to a pressure of 10 MPa using a universal material testing machine (e.g., TENSILON RTG-1310 manufactured by A&D Corporation), and the weight/volume ratio is defined as the molding density.

If the (002)/(110) diffraction intensity ratio exceeds 7.5, the aluminum hydroxide powder, which may normally have a shape close to a sphere, will become distorted, for example, into a plate-like shape, and the resin viscosity will increase. Preferably, the (002)/(110) diffraction intensity ratio is 6.0 or less. There is no particular lower limit to the (002)/(110) diffraction intensity ratio, but in order to make the (002)/(110) diffraction intensity ratio less than 2.0, more detailed manufacturing conditions must be set, and it is preferable to set it to 2.0 or more in consideration of productivity.

The (002)/(110) diffraction intensity ratio is determined as follows.
The aluminum hydroxide powder is compacted and packed into a glass cell for measurement, and then an XRD pattern is measured using a powder X-ray diffraction measuring device (e.g., Rigaku Corporation, RINT-2000) with a step width of 0.02 deg, a scan speed of 0.04 deg/sec, an acceleration voltage of 40 kV, and an acceleration current of 30 mA. Cu-Kα is used as the X-ray source. In the obtained XRD pattern, the peak appearing at 2θ=18.3° is taken as the peak of the (002) plane, and the peak appearing at 2θ=20.3° is taken as the peak of the (110) plane, and the ratio of the diffraction intensity (peak height) of the peak of the (002) plane to the diffraction intensity (peak height) of the peak of the (110) plane is taken as the (002)/(110) diffraction intensity ratio.

The aluminum hydroxide powder according to the embodiment of the present invention preferably has a 90% by mass particle size (i.e., the particle size at which the cumulative frequency from the fine particle side in the mass-based particle size distribution is 90% by mass, also referred to as D90) of less than 100 μm. This makes it possible to sufficiently suppress poor appearance when the aluminum hydroxide powder is filled into a resin molded body, and also makes it easier to ensure sufficient strength of the resin molded body. Preferably, D90 is 90 μm or less, more preferably 65 μm or less, and even more preferably 45 μm or less.
The aluminum hydroxide powder according to the embodiment of the present invention preferably has a D90 of 20 μm or more, which can suppress poor dispersion when dispersing the aluminum hydroxide powder in a liquid.

The aluminum hydroxide powder according to the embodiment of the present invention preferably has one or two peaks in the particle size range of 1 to 200 μm in the mass-based particle size distribution. This can suppress poor appearance when the aluminum hydroxide powder is filled into a resin molded body, and can also suppress poor dispersion when the aluminum hydroxide powder is dispersed in a liquid. When there is one peak, the frequency of the peak may be 4.0 mass% or more. When there are two peaks, the frequency of one peak may be 4.0 mass% or more, and the frequency of the other peak may be more than 0 mass% and 4.0 mass% or less. In this case, it is preferable that there is only one peak in the particle size range of 1 to 200 μm in the mass-based particle size distribution. This can further suppress poor appearance and poor dispersion of the resin molded body.

The aluminum hydroxide powder according to the embodiment of the present invention may have one or more peaks in the mass-based particle size distribution in one or both of the particle size ranges of less than 1 μm and more than 200 μm, and the frequency of the peaks may be greater than 0 mass% and less than 0.5 mass%, or may have no peaks in the particle size ranges of less than 1 μm and more than 200 μm.

The aluminum hydroxide powder according to the embodiment of the present invention preferably has a 50% by mass particle size (i.e., the particle size at which the cumulative frequency from the fine particle side in the mass-based particle size distribution is 50% by mass, also referred to as D50) of 30 μm or less, which can suppress poor appearance when the aluminum hydroxide powder is filled into a resin molded body, and also makes it easier to ensure the strength of the resin molded body.
The aluminum hydroxide powder according to the embodiment of the present invention preferably has a D50 of 7 μm or more, which can suppress poor dispersion when dispersing the aluminum hydroxide powder in a liquid.

The mass-based particle size distribution (including D50 and D90) is determined as follows.
Aluminum hydroxide powder is added to a 0.2% by mass aqueous solution of sodium hexametaphosphate, and ultrasonic waves of 25 W are applied for 120 seconds to disperse the aluminum hydroxide powder in the aqueous solution. The mass-based particle size distribution (including D50 and D90) of the aluminum hydroxide powder is determined using a laser scattering particle size distribution measuring device. The particle size distribution is determined by dividing the particle size range of 0.02 μm to 2000 μm into 132 parts on a logarithmic scale and measuring the mass of aluminum hydroxide having a particle size in each section. In addition, as the laser scattering particle size distribution measuring device, it is preferable to use a Microtrac MT-3300EXII (manufactured by Nikkiso Co., Ltd.) or a device equivalent thereto, taking into consideration the difference between devices and the consistency with the present embodiment and the like. In addition, when measuring the particle size distribution, it is preferable to appropriately adjust the concentration of the aluminum hydroxide powder to a measurable concentration of the measuring device before measurement.

The aluminum hydroxide powder according to the embodiment of the present invention preferably has a BET specific surface area of 2.0 m ² /g or less. This makes it possible to suppress poor dispersion when dispersing the aluminum hydroxide powder in a liquid. The BET specific surface area is determined by a nitrogen adsorption method using a fully automatic specific surface area measuring device (e.g., Macsorb HM-1201 manufactured by Mountech) in accordance with the method specified in JIS-Z-8830:2013.

The aluminum hydroxide powder according to the embodiment of the present invention may contain Na ₂ O as an impurity. The content of Na ₂ O is preferably, for example, 0.13 mass% or less. This can suppress deterioration of the resin and decrease in insulation when filled into a resin molded body. Here, the Na ₂ O content is determined by dissolving the aluminum hydroxide powder in an aqueous solution of an inorganic acid to prepare an aqueous solution, and then using an ICP emission spectrometer. Specifically, the intensity of the wavelength of sodium (589.592 nm) is measured, converted into Na ₂ O, the mass of Na ₂ O is calculated, and the ratio of the mass of the Na ₂ O to the mass of the dissolved aluminum hydroxide powder is the Na ₂ O content (mass%). In addition to Al(OH) ₃ and Na ₂ O, the aluminum hydroxide powder according to the embodiment of the present invention may contain inevitable impurities. As inevitable impurities, the inclusion of elements brought in due to the conditions of raw materials, materials, manufacturing equipment, etc. is permitted.

The aluminum hydroxide powder according to the embodiment of the present invention can sufficiently suppress the increase in viscosity when added to a resin, and is suitable as a filler for resin molded bodies (sealing materials, thermal interface materials (TIM), artificial marble, etc.). Applicable resins include, for example, thermosetting resins such as unsaturated polyester resins, epoxy resins, phenolic resins, and polyurethane resins, and thermoplastic resins such as polyethylene, polypropylene, copolymers of ethylene and propylene, copolymers of ethylene and/or propylene with other α-olefins such as butene-1, pentene-1, hexene-1, heptene-1, octene-1, nonene-1, 4-methylpentene-1, and decene-1, tyrenic (co)polymers, methyl methacrylate (co)polymers, polyamides, polycarbonates, ethylene-vinyl acetate copolymers, polyacetals, acrylonitrile-butadiene-styrene copolymers, polyphenylene oxides, polyethersulfones, polyarylates, polyetheretherketones, and polymethylpentenes. The aluminum hydroxide powder according to the embodiment of the present invention is not limited to the above resins, but can also be used as a filler for other synthetic resins, natural resins, paper, etc.

2. Method for producing aluminum hydroxide powder
The method for producing an aluminum hydroxide powder according to an embodiment of the present invention includes the steps of (a) preparing an aluminum hydroxide powder having a 50% by mass particle size (D50) of 10 to 200 μm and a cumulative volume of pores with a radius of 0.05 to 1 μm of 0.01 to 1 mL/g, (b) pulverizing the powder at a pressure of 49.0 to 294.0 MPa, and (c) disintegrating the powder at a collision speed of 92 m/sec or less. Each step will be described in detail below.

[(a) Step of preparing aluminum hydroxide powder]
First, aluminum hydroxide powder (hereinafter also referred to as "raw aluminum hydroxide powder") is prepared as a raw material. The raw aluminum hydroxide powder must have a 50% mass particle size (D50) of 10 to 200 μm and a cumulative volume of pores with a radius of 0.05 to 1 μm (hereinafter also referred to as "accumulated pore volume") of 0.01 to 1 mL/g. This makes it easier to obtain a desired molding density. Preferably, the cumulative pore volume is 0.02 to 1 mL/g. This makes it easier to obtain a desired D90 and also makes it easier to obtain aluminum hydroxide powder with a desired mass-based particle size distribution.

If D50 is less than 10 μm or more than 200 μm, and/or the cumulative pore volume is less than 0.01 mL/g or more than 1 mL/g, it will be difficult to obtain the desired molding density.

The cumulative pore volume is determined as follows.
The aluminum hydroxide powder is dried at 120°C for 4 hours to remove adsorbed moisture. Then, about 0.5 to 0.6 g is weighed out using a precision balance and filled into a measurement cell with a diameter of 15 mm and a height of 24 mm. This measurement cell is set in an automatic porosimeter (e.g., Autopore III9420, manufactured by Micromeritics), and measurements are performed separately on the low pressure side (1 to 10,000 psi) and the high pressure side (10,000 to 60,000 psi). These measurement data are added together to determine the pore volume distribution in the region of pore radius of 0.002 μm to 100 μm, and the cumulative volume in the region of pore radius of 0.05 μm to 1.0 μm is calculated.

The crystal structure of the raw aluminum hydroxide powder may be, for example, gibbsite type or bayerite type, and is preferably gibbsite type.

The raw aluminum hydroxide powder can be produced by adding seed crystals to a supersaturated sodium aluminate solution, hydrolyzing with stirring to precipitate aluminum hydroxide, and filtering, washing, and drying the resulting aluminum hydroxide. Here, the raw aluminum hydroxide powder having the above particle size and cumulative pore volume can be obtained by appropriately adjusting the precipitation conditions (and/or partially dissolving the precipitate, and/or crushing or crushing the precipitate). Note that commercially available aluminum hydroxide powders may be used as long as they satisfy the above particle size and cumulative pore volume.

[(b) Crushing at a pressure of 49.0 to 294.0 MPa]
Next, the raw aluminum hydroxide powder is pulverized at a pressure of 49.0 to 294.0 MPa. Here, "pulverization" refers to an operation of applying some energy to solid particles of a certain size (e.g., primary particles) to make them smaller than their original size.

If the pressure during grinding is less than 49.0 MPa, the desired molding density cannot be obtained. It is preferably more than 49.0 MPa, and more preferably 68.6 MPa or more. There is no particular upper limit to the pressure during grinding, but considering productivity, it is preferable to keep it at 294.0 MPa or less.

Examples of mills that mill at the above pressure include co-kneaders, onlators, self-cleaning kneaders, gear compounders, single-shaft screw kneaders, and twin-shaft screw kneaders. These devices may be used alone or in combination of two or more. Either batch or continuous mills can be used, but continuous mills are preferred from the viewpoint of reducing the milling energy per unit weight. When using a continuous mill, it is not necessary for the raw aluminum hydroxide in the mill to be milled entirely, and it is sufficient to make the degree of milling gradually increase in the direction of transport (axial direction) of the raw aluminum hydroxide. In the case of a screw kneader, the compression capacity can be adjusted by, for example, the shape, length, and rotation speed of the screw, and the rotation speed of the rotor (which acts to transport the raw material to the screw).

In the grinding mill, raw aluminum hydroxide powder is present as the solid phase, and in addition, air, etc. is usually present as the gas phase, and water, etc. is present as the liquid phase. Since the state of the inside of the grinding mill during grinding can affect the physical properties of the aluminum hydroxide powder obtained by grinding, grinding is preferably performed in a state where the solid, liquid, and gas phases are packed in (i) a dry state in which the solid and gas phases are continuous and the liquid phase is substantially absent, (ii) a pendular state in which the solid and gas phases are continuous and the liquid phase is discontinuous, or (iii) a funicular I state in which the solid, gas, and liquid phases are continuous. Such a packing form constitutes a mixture system that is smooth or dry in appearance.

It is preferable to adjust the liquid content of the raw aluminum hydroxide powder before grinding so that a dry state, a pendular state, or a funicular I state is achieved during grinding. The liquid content can be adjusted, for example, by drying the raw aluminum hydroxide powder or adding a liquid such as water or alcohol. The preferred liquid content varies depending on the particle size distribution of the raw aluminum hydroxide and is not unambiguous, but is, for example, 30% by weight or less, more preferably 10% by weight or less, and 1% by weight or more, more preferably 5% by weight or more. If the liquid content is too high, it becomes difficult to grind the raw aluminum hydroxide efficiently.

When liquid such as water is added during grinding, or when raw aluminum hydroxide powder containing water is ground, the aluminum hydroxide powder after grinding is usually dried. Drying can be performed, for example, by using a known dryer, or by heating part of a continuous grinder when grinding is performed with the grinder.

[(c) Crushing at a collision speed of 92 m/s or less]
After the step (b), the mixture is crushed at a collision speed of 92 m/s or less. Here, "crushing" refers to a process of breaking down agglomerates of fine particles (e.g., secondary particles) into smaller particles (e.g., primary particles).

If the impact speed during crushing exceeds 92 m/sec, the desired (002)/(110) diffraction intensity ratio cannot be obtained. For example, by using an impact crusher, it is possible to crush at the above impact speed.

The method for producing aluminum hydroxide powder according to an embodiment of the present invention may include other steps (e.g., a surface treatment step, etc.) within the scope of achieving the object of the present invention.

The following provides a more detailed explanation of the embodiments of the present invention, using examples. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the intent described above and below, and all such modifications are within the technical scope of the embodiments of the present invention.

The raw aluminum hydroxide powder (D50: 81 μm, pore cumulative volume: 0.09 mL/g) was adjusted to a moisture content of 5 wt % and continuously fed into a grinder (single-screw type kneader) for grinding. The grinder pressure was set to 196.0 MPa by adjusting the feeding speed. Regarding the grinder pressure, the same raw aluminum hydroxide powder was separately compressed and ground using a cold isostatic press to investigate the relationship between the pressing pressure and D90, and the grinder pressure was simply calculated from the D90 of the ground aluminum hydroxide powder.
The obtained pulverized product was dried at 120° C. and then charged into an impact pulverizer (Jiyuu pulverizer, manufactured by Nara Kikai) and pulverized to obtain the aluminum hydroxide powder of Example 1. The impact speed of the impact pulverizer was set to 46 m/sec.
Moreover, the various conditions were changed from the production method of Example 1 as shown in Table 1 below to obtain aluminum hydroxide powders of Examples 2 to 4 and Comparative Examples 1 and 2. Furthermore, commercially available aluminum hydroxide powders were set as Comparative Example 3 (manufactured by Sumitomo Chemical, CW-308), Comparative Example 4 (manufactured by Sumitomo Chemical, C-305), and Comparative Example 5 (manufactured by Sumitomo Chemical, CM-3080).

For the aluminum hydroxide powders of Examples 1 to 4 and Comparative Examples 1 to 5, the compact density, (002)/(110) diffraction intensity ratio, mass-based particle size distribution (including D50 and D90), BET specific surface area and Na ₂ O content were determined by the following methods.

[Molding density]
3.00 g of aluminum hydroxide powder was placed in a cylindrical uniaxial molding die having an inner diameter of 20.0 mm, and the aluminum hydroxide powder was compressed and packed at a compression speed of 1 mm/min to a pressure of 10 MPa using a universal material testing machine (TENSILON RTG-1310, manufactured by A&D Corporation), and the weight/volume ratio was defined as the molding density.

[(002)/(110) diffraction intensity ratio]
The aluminum hydroxide powder was compacted and packed into a glass cell for measurement, and then the XRD pattern was measured using a powder X-ray diffraction measuring device (Rigaku Corporation, RINT-2000) with a step width of 0.02 deg, a scan speed of 0.04 deg/sec, an acceleration voltage of 40 kV, and an acceleration current of 30 mA. Cu-Kα was used as the X-ray source. In the obtained XRD pattern, the peak appearing at 2θ=18.3° was taken as the peak of the (002) plane, and the peak appearing at 2θ=20.3° was taken as the peak of the (110) plane, and the ratio of the diffraction intensity (peak height) of the peak of the (002) plane to the diffraction intensity (peak height) of the peak of the (110) plane was taken as the (002)/(110) diffraction intensity ratio.

[Mass-based particle size distribution (including D50 and D90)]
Aluminum hydroxide powder was added to a 0.2% by mass aqueous solution of sodium hexametaphosphate, and ultrasonic waves of 25 W were applied for 120 seconds to disperse the aluminum hydroxide powder in the aqueous solution. The mass-based particle size distribution (including D50 and D90) of the dispersion was determined using a laser scattering particle size distribution analyzer. The particle size distribution was determined by dividing the particle size range of 0.02 μm to 2000 μm into 132 ranges on a logarithmic scale and measuring the mass of aluminum hydroxide having a particle size in each range. As the laser scattering particle size distribution analyzer, a Microtrac MT-3300EXII (manufactured by Nikkiso Co., Ltd.) was used. In addition, when measuring the particle size distribution, the concentration of the aluminum hydroxide powder was appropriately adjusted to a concentration measurable by the above-mentioned measuring device before measurement.

[BET specific surface area]
According to the method specified in JIS-Z-8830:2013, the BET specific surface area was determined by the nitrogen adsorption method using a fully automatic specific surface area measuring device (Macsorb HM-1201, manufactured by Mountech).

[Na ₂ O content]
After preparing an aqueous solution by dissolving aluminum hydroxide powder in an aqueous solution of an inorganic acid, the Na ₂ O content was determined using an ICP atomic emission spectrometer. Specifically, the intensity of the wavelength of sodium (589.592 nm) was measured and converted into Na ₂ O to calculate the mass of Na ₂ O, and the ratio of the mass of the Na ₂ O to the mass of the dissolved aluminum hydroxide powder was defined as the Na ₂ O content (mass%).

Furthermore, the resin viscosity was determined by the following method.
5.59 parts by mass of aluminum hydroxide powder and 1.86 parts by mass of bisphenol A type epoxy resin mixture (AQ010-8140, room temperature curing resin 53 type base agent) were mixed at 1000 rpm for 3 minutes using a planetary mixer (Thinky Corporation, Awatori Rentaro ARV-310) to obtain a compound. A 30 mm diameter parallel plate was attached to a dynamic viscoelasticity measuring device (Rheosol-G3000), and the compound was set on it. After leaving it for 10 minutes under the conditions of a parallel plate gap of 0.50 mm and a temperature of 100°C, the resin viscosity at a shear rate of 40 s ^-1 was measured.
The results are summarized in the following Table 2. In Table 2, "-" in the "second peak" column means that the second peak was not present.

From the results in Table 2, the following can be considered. All of Examples 1 to 4 in Table 2 are examples that satisfy all of the requirements stipulated in the embodiments of the present invention, and the resin viscosity was 10 Pa·s or less, so that an increase in the resin viscosity could be sufficiently suppressed. Of these, Examples 1 to 3 were preferable examples in that they had a D90 of less than 100 μm, so that poor appearance when filled into a resin molded body could be sufficiently suppressed and the strength of the resin molded body could be easily ensured. In Example 4, the cumulative pore volume of the raw aluminum hydroxide powder was less than 0.02 mL/g, so that D90 was 100 μm or more.
On the other hand, Comparative Examples 1 to 5 are examples that do not satisfy the requirements defined in the embodiment of the present invention, and the resin viscosity exceeded 10 Pa·s, so that the increase in the resin viscosity could not be sufficiently suppressed.

In Comparative Example 1, the impact speed during disintegration was greater than 92 m/s, so the (002)/(110) diffraction intensity ratio was greater than 7.5 and the resin viscosity was greater than 10 Pa·s.

In Comparative Example 2, the pressure during crushing was less than 49.0 MPa, so the molding density was less than 1.59 g/cm ³ and the resin viscosity exceeded 10 Pa·s.

In Comparative Examples 3 and 4, the molded density was less than 1.59 g/cm ³ , and therefore the resin viscosity exceeded 10 Pa·s.

In Comparative Example 5, the (002)/(110) diffraction intensity ratio was greater than 7.5, and the resin viscosity was greater than 10 Pa·s.

Claims (4)

The density when molded at 10 MPa is 1.59 to 2.00 g/ ^cm3 ,
the ratio of the diffraction intensity of the (002) plane to the diffraction intensity of the (110) plane in the XRD pattern is 2.0 to 7.5;
The 50% by mass particle size (D50) is 33 μm or less,
The BET specific surface area is 2.0 m ² /g or less;
The mass standard particle size distribution has one or two peaks in the particle size range of 1 to 200 μm,
The aluminum hydroxide powder has no peak or one or more peaks having a frequency of more than 0 mass% and not more than 0.5 mass% below 1 μm in the mass-based particle size distribution . The aluminum hydroxide powder according to claim 1, having a 90% by mass particle size (D90) of less than 100 μm. When the mass-based particle size distribution has one peak in the particle size range of 1 to 200 μm , the frequency of the peak is 4.0 mass% or more,
3. The aluminum hydroxide powder according to claim 1, wherein, when the mass-based particle size distribution has two peaks in the particle size range of 1 to 200 μm , the frequency of one peak is 4.0 mass% or more, and the frequency of the other peak is more than 0 mass% and 4.0 mass% or less. A method for producing aluminum hydroxide powder, comprising crushing aluminum hydroxide powder having a 50% by mass particle size (D50) of 10 to 200 μm and a cumulative volume of pores with a radius of 0.05 to 1 μm of 0.01 to 1 mL/g at a pressure of 49.0 to 294.0 MPa, and then disintegrating the powder at a collision speed of 92 m/sec or less.