JP2008303110A - Low-soda fine particle aluminum hydroxide and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide gibbsite-type aluminum hydroxide having ≤2 μm average particle diameter, ≤0.04 mass% total soda (T-Na<SB>2</SB>O) content and ≤10 m<SP>2</SP>/g BET specific surface area, and its production method. <P>SOLUTION: The low-soda fine particle aluminum hydroxide having ≤2 μm particle diameter, ≤0.04 mass% total soda (T-Na<SB>2</SB>O) content and ≤10 m<SP>2</SP>/g BET specific surface area, is produced by the Bayer process. The process is carried out by preparing an initial solution by adding aluminum hydroxide having ≤0.05 mass% total soda (T-Na<SB>2</SB>O) content and ≤1 μm average particle diameter as a seed into an initial medium having ≤30 g/L Na<SB>2</SB>O concentration and ≤30 g/L Al<SB>2</SB>O<SB>3</SB>concentration; preparing a precipitation solution by continuously or intermittently adding an addition solution composed of a sodium aluminate solution to the initial solution; and precipitating the aluminum hydroxide from the precipitation solution at 60-90°C precipitation temperature under an average supersaturation Al<SB>2</SB>O<SB>3</SB>concentration in the range of not exceeding 15 g/L from starting to completion of the precipitation, followed by optionally disintegrating thereof. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

This invention is produced by the Bayer method, has a very low content of total soda (T-Na ₂ O), and is composed of gibbsite crystals (Al ₂ O ₃ .3H ₂ O) having an extremely small average particle diameter. Although it relates to soda fine aluminum hydroxide and its manufacturing method, it is not particularly limited, but it is used for applications such as electrical / electronic materials such as printed wiring boards, wire coating materials, insulation materials, architectural interior materials and exterior materials. The present invention relates to a low soda fine aluminum hydroxide that is blended in various polymer materials such as synthetic rubber, natural rubber, and synthetic resin, and is particularly useful as a flame retardant for imparting heat resistance and flame retardancy, and a method for producing the same.

Conventionally, there have been many proposals for this type of aluminum hydroxide. For example, US Pat. No. 4,014,985 discloses an Al ₂ O ₃ / Na ₂ O ratio in a sodium aluminate solution obtained by the Bayer method. 1.04 or less, seeds with an average particle size of 55 μm were added, and 0.03 g-Al ₂ O ₃ / m ² -seed · h or less was precipitated very slowly, with a total soda content of 0.1% by weight. The production of the following aluminum hydroxide is described.

JP-A-59-204,632 discloses gibbsite-type aluminum hydroxide having an average particle size of 0.5 to 60 μm and a total soda content of 0.1% or less, preferably 0.07% or less. The heat-resistant resin moldings obtained by addition are described, and in the examples and comparative examples, the center particle size is 8.0 to 8.5 μm and the total soda content (T-Na ₂ O). Describes that 0.06 to 0.21% of gibbsite type aluminum hydroxide is used.

Furthermore, Japanese Patent Application Laid-Open No. 62-246,961 discloses an average particle size of 0.5 to 15 μm and a BET specific surface area by nitrogen gas adsorption method of 2.8 m ² / g or more, preferably 3 to 4.5 m ² / g. , And a heat-resistant resin composition obtained by adding gibbsite-type aluminum hydroxide having a total soda content of 0.08% by weight or less, and examples and comparative examples show average particles. It is described that gibbsite type aluminum hydroxide having a diameter of 0.8 to 14.3 μm, a BET specific surface area of 1.5 to 4.5 m ² / g, and a total soda content of 0.015 to 0.21 wt% is used. .

  Furthermore, Japanese Patent Application Laid-Open No. 2-74,521 discloses an average particle size of 10 μm or less, preferably 5 μm or less, a total soda content of 0.10% by weight or less, and low temperature dehydration at a temperature of 200 ° C. or less. Gibbsite-type heat-resistant aluminum hydroxide having a low reaction rate and a low boehmite transfer reaction rate is described. In Example 1, the average particle size is 1.7 μm and the total soda content is 0.06 wt. % Aluminum hydroxide is obtained.

  Japanese Patent Laid-Open No. 3-28,121 discloses an average particle size of 5 μm or less and a total soda content of 0.10% by weight or less, excellent heat resistance, and reduced strength when filled in rubber or plastic. The heat-resistant aluminum hydroxide with a small particle size is described, and in Example 1, the average particle size is 1.5 μm, the primary particle size is 0.5 μm, and the total soda content is 0.06 wt. % Heat-resistant aluminum hydroxide is described.

  Further, JP-A-11-278,829 discloses high-purity aluminum hydroxide having an average particle size of 1 to 6 μm and a total soda content of 0.1% by mass or less, an average particle size of 15 to 40 μm and a total soda content of 0.1 mass. % Of high-purity aluminum hydroxide is described, and comparative examples and examples thereof have an average particle size of 1.8 to 42.2 μm and a total soda content of 0.05 to 0.31% by mass or less. Aluminum hydroxide is described.

Furthermore, JP-A-2002-348,408 discloses that the SiO ₂ content is less than 0.02% by weight, the BET specific surface area is less than 3 m ² / g, and the temperature is raised from 110 ° C. to 210 ° C. An aluminum hydroxide powder for resin filling having a weight reduction rate of 0.3% or less when held is described, and the example has an Na ₂ O content of 0.04% by weight and an average particle size Obtained 5 μm gibbsite-type aluminum hydroxide.

By the way, when examining gibbsite type aluminum hydroxide used as a flame retardant for imparting heat resistance and flame retardancy to such various polymer materials, the average particle diameter thereof is, for example, semiconductor components. From the standpoint of responding to miniaturization and thinning of laminated plates and the like, the thickness should be 3 μm or less, preferably 0.5 μm or more and 3 μm or less in consideration of the viscosity of the compound and molding workability. As for the content of T-Na ₂ O), the higher the content, the easier the initial dehydration reaction due to the boehmite transition starting from around 200 ° C. does not occur and the heat resistance decreases, so 0.1% by mass or less, preferably The BET specific surface area should be as small as possible. Further, as the value increases, the kneadability and moldability with the resin deteriorate, so 10 m ² / g or less, preferably 5 m ² / g or less.

However, there is no known method for producing gibbsite-type aluminum hydroxide by the Bayer method, which has an extremely small average particle diameter of 2 μm or less and a very small content of soda of 0.04% by mass or less. In addition, a gibbsite-type low soda fine aluminum hydroxide that has not been pulverized and satisfies the conditions of an average particle diameter of 2 μm or less, a total soda content of 0.04 mass% or less, and a BET specific surface area of 10 m ² / g or less has been produced. Not.

  By the way, a gibbsite-type aluminum hydroxide having a total soda content of 0.04% by mass or less and an average particle size exceeding 2 μm is produced, and then the average particle size is reduced by grinding by known means. Thus, it is possible to produce gibbsite type aluminum hydroxide having an average particle diameter of 2 μm or less and a total soda content of 0.04% by mass or less. However, the gibbsite-type sodium hydroxide produced by such a method is damaged by the crystal itself by pulverization, is likely to generate chipping, and further increases the BET specific surface area. Kneadability and moldability also deteriorate.

U.S. Pat.No. 4,014,985 JP 59-204,632 A JP-A-62-246,961 Japanese Patent Laid-Open No. 2-74,521 JP-A-3-28,121 Japanese Patent Laid-Open No. 11-278,829 JP 2002-348,408

Therefore, as a result of earnestly examining the development of gibbsite-type aluminum hydroxide in which the average particle size, the total soda (T-Na ₂ O) content, and the BET specific surface area are all small, surprisingly, The initial solution is prepared by adding aluminum hydroxide having a total soda content of 0.05% by mass or less and an average particle diameter of 1 μm or less as seeds to an initial medium having an Na ₂ O concentration of 30 g / L or less and an Al ₂ O ₃ concentration of 30 g / L or less. In this initial solution, a sodium aluminate solution obtained by the Bayer method as an additive solution is added continuously or intermittently to form a precipitation solution, and the precipitation temperature when aluminum hydroxide is precipitated from this precipitation solution And the average supersaturated Al ₂ O ₃ concentration from the start of precipitation to the end of precipitation within a predetermined range, and if necessary, by crushing the aluminum hydroxide recovered from the precipitation solution, the target average particle Diameter 2 m or less, the total soda content 0.04 wt% or less, and ascertained that can produce a BET specific surface area of 10 m ² / g or less of gibbsite type aluminum hydroxide, and have completed the present invention.

Accordingly, an object of the present invention is to provide a gibbsite-type aluminum hydroxide having an average particle diameter of 2 μm or less, a total soda (T—Na ₂ O) content of 0.04% by mass or less, and a BET specific surface area of 10 m ² / g or less. It is in.

Another object of the present invention is to provide a gibbsite-type low particle having an average particle size of 2 μm or less, a total soda (T—Na ₂ O) content of 0.04% by mass or less, and a BET specific surface area of 10 m ² / g or less. An object of the present invention is to provide a method for producing low-soda fine aluminum hydroxide, which can easily produce soda-fine aluminum hydroxide.

That is, the present invention is a gibbsite-type aluminum hydroxide produced by the Bayer method, having an average particle size of 2 μm or less and a total soda (T—Na ₂ O) content of 0.04% by mass or less, A low soda fine aluminum hydroxide characterized by having a BET specific surface area of 10 m ² / g or less.

In addition, when producing low-soda fine aluminum hydroxide by the Bayer method, the present invention provides all soda as seeds in an initial medium having a Na ₂ O concentration of 30 g / L or less and an Al ₂ O ₃ concentration of 30 g / L or less. An initial solution is prepared by adding aluminum hydroxide having a Na ₂ O content of 0.05% by mass or less and an average particle size of 1 μm or less, and then an added solution comprising a sodium aluminate solution is continuously or intermittently added to the initial solution. To prepare a precipitation solution of aluminum hydroxide, and from this precipitation solution, the average supersaturated Al ₂ O ₃ concentration from the start of precipitation to the end of precipitation at a precipitation temperature of 60 to 90 ° C. does not exceed 15 g / L. In this method, aluminum hydroxide is precipitated by crushing and, if necessary, aluminum hydroxide recovered from the precipitation solution is crushed.

In the present invention, the initial medium used to prepare the initial solution may be any Na ₂ O concentration of 30 g / L or less and Al ₂ O ₃ concentration of 30 g / L or less, but most preferably pure water. There should be. When the Na ₂ O concentration and Al ₂ O ₃ concentration of the initial medium are higher than 30 g / L, aluminum hydroxide is difficult to precipitate. Even if the supply flow rate of the additive solution is increased in order to obtain a constant deposition rate, the concentration of supersaturated Al ₂ O _{3 in} the deposition solution increases, so that the deposition conditions for depositing aluminum hydroxide from the deposition solution, that is, deposition from the start of deposition Production of gibbsite-type aluminum hydroxide having a target average particle size, total soda content, and BET specific surface area becomes difficult to maintain the average supersaturated Al ₂ O ₃ concentration in the range not exceeding 15 g / L until completion. Becomes difficult.

  In addition, regarding aluminum hydroxide used as a seed in preparing the initial solution, at least the total soda content is 0.05% by mass or less, preferably 0.04% by mass or less, and the average particle size is 1 μm or less, preferably Needs to be 0.9 μm or less. When the total soda content of aluminum hydroxide used as seed exceeds 0.05% by mass, a portion exceeding 0.04% by mass of total soda content is locally generated in the particles of low soda fine aluminum hydroxide obtained. There is a risk that the thermal decomposition starting temperature may be lowered, and when the average particle diameter exceeds 1 μm, it is difficult to prepare fine aluminum hydroxide having an average particle diameter of 2 μm or less and a total soda content of 0.04% by mass or less. Become. Aluminum hydroxide used as such seeds is prepared by preparing aluminum hydroxide having a total soda content of 0.05% by mass or less by the Bayer method and wet-pulverizing the resulting aluminum hydroxide to an average particle size of 1 μm or less. can do.

Furthermore, the aluminum hydroxide as the seed in the initial solution has a BET specific surface area of 10 m ² / g or more, preferably 10 m ² / g or more and 20 m ² / g or less. The amount added is usually 300 m ² / L or more, preferably 300 m ² / L or more and 1000 m ² / L or less, in terms of seed addition rate (m ² / L). If the BET specific surface area of aluminum hydroxide used as the seed is lower than 10 m ² / g, it is necessary to add a large amount of seed in order to increase the seed addition rate to 300 m ² / L or more. when the seed addition rate is less than 300 meters ² / L, when productivity is reduced by, or caused a problem that the particle size becomes coarse, also be more than 1000 m ² / L, seed amount split However, the production volume does not increase and the cost becomes high.

In the present invention, the additive solution used to prepare the precipitation solution by continuously or intermittently adding to the initial solution is a sodium aluminate solution obtained by the Bayer method, and the Al ₂ O ₃ concentration is about There is no particular limitation as long as it can be added to the above initial solution to achieve a concentration sufficient to precipitate aluminum hydroxide. For example, it is usually 100 g / L or more and 200 g / L or less, preferably 140 g / L or more and 170 g. The molar ratio of dissolved Na ₂ O and dissolved Al ₂ O ₃ (Na ₂ O / Al ₂ O ₃ ) is, for example, usually 3.0 or less, preferably Those of 1.4 or more and 1.7 or less are used. If the molar ratio of the additive solution is lower than 1.4, there is a problem that the additive solution becomes unstable.

  Further, for this added solution, it is desirable that the total organic matter concentration (TOC) in the solution is 1 g / L or less, preferably as low as possible. When this total organic matter concentration (TOC) exceeds 1 g / L, it becomes difficult to precipitate and the total soda content tends to increase.

When preparing the aluminum hydroxide precipitation solution by continuously or intermittently adding the additive solution to the initial solution, at least the precipitation conditions for precipitation of aluminum hydroxide from the precipitation solution, that is, the precipitation temperature is 60. The average supersaturated Al ₂ O ₃ concentration from the start of precipitation to the end of precipitation is 15 g / L, preferably 10 g / L, more preferably 5 g / L. There is no limitation on the method of adding the additive solution to the initial solution as long as the deposition conditions are maintained. When the precipitation temperature is lower than 60 ° C., there is a problem that the total soda content of the precipitated aluminum hydroxide is increased. On the other hand, when the precipitation temperature is higher than 90 ° C., the productivity is deteriorated, and the average supersaturated Al ₂ O _{3 When the} concentration is higher than 15 g / L, there arises a problem that the total soda content of the precipitated aluminum hydroxide is increased. Here, the average supersaturated Al ₂ O ₃ concentration from the start of the precipitation to the end of the precipitation means that the addition of the additive solution to the initial solution starts the precipitation of the aluminum hydroxide and then finishes the addition of the additive solution, and then finishes the aluminum hydroxide. The supersaturated Al ₂ O ₃ concentration of the precipitation solution gradually rises until the precipitation is completed, and it is obtained as a simple average value of a plurality of supersaturated Al ₂ O ₃ concentrations measured over time during this period.

  In addition, in the precipitation operation in which the additive solution is added to the initial solution to prepare a precipitation solution and aluminum hydroxide is precipitated, the solution temperature of the initial solution is preferably 70 ° C. or higher, preferably 70 ° C. or higher before the addition solution is added. The temperature is adjusted to 90 ° C. or less, and the solution temperature of the precipitation solution is preferably maintained within the range of 60 to 90 ° C. immediately after the addition solution is added. When the solution temperature is lower than 60 ° C., the solution is precipitated. This is not preferable because the total soda content of aluminum hydroxide tends to increase.

In addition, during the precipitation of aluminum hydroxide, the supersaturated Al ₂ O ₃ concentration in the precipitation solution changes temporarily depending on the addition of the additive solution and the precipitation of aluminum hydroxide. _{Although the} case where the ₂ O ₃ concentration exceeds 15 g / L may occur, preferably, the average supersaturated Al ₂ O ₃ concentration from the start of precipitation to the end of precipitation so that the supersaturated Al ₂ O ₃ concentration does not exceed 15 g / L. Is preferably maintained at 15 g / L or less, and the average supersaturated Al ₂ O ₃ concentration from the start of precipitation to the end of precipitation is adjusted to 15 g / L or less by adjusting the temperature drop rate during the precipitation operation to the end of the precipitation operation. May be maintained.

  This precipitation operation is not particularly different from that in the conventional method, and an initial solution is prepared in a precipitation tank, and then the added solution is continuously or intermittently added to the initial solution in the precipitation tank with stirring. Then, aluminum hydroxide is precipitated under a predetermined precipitation condition while forming a precipitation solution in the precipitation tank. When the inside of the precipitation tank reaches a predetermined liquid amount, the addition of the addition solution is stopped, and then the precipitation temperature is 60 to 90. Precipitation for a predetermined time at ℃, usually about 0.02 to 0.25 times the time required for the addition of the addition solution, for about 0 to 2 hours, and finally maintaining the precipitation temperature of 60 to 90 ° C End the operation.

In this way, after the precipitation operation is completed, solid-liquid separation is performed by means such as filtration with a filter press or centrifugal separation with a screw decanter, etc., and then repulped with pure water at a temperature of about 70 to 90 ° C. from room temperature to solid-liquid again. Repeat the washing operation several times to separate the free soda (f-Na ₂ O) content that can be removed by washing (measure the content of free soda (f-Na ₂ O) content by immersing the sample in warm water and eluting it). After that, the atomic absorption method according to JIS R9301-3-9 is performed. ] Is 0.002% by mass or less, preferably as much as possible.

  In the present invention, the aluminum hydroxide obtained by the precipitation operation is loosely agglomerated. Therefore, if necessary, the aluminum hydroxide obtained by the precipitation operation is partially dissolved, or the water obtained by the precipitation operation by wet crushing before or after the above water washing, preferably after water washing. The secondary particles of aluminum oxide are crushed to primary particles. Specifically, the crushing operation for crushing the secondary particles into primary particles is, for example, preparing a slurry by adding pure water to the obtained aluminum hydroxide, and then removing the slurry from a wet crusher (bead mill, etc.) It is done by feeding in.

As described above, the aluminum hydroxide obtained by crushing the secondary particles as necessary is dried with a drier or the like, and then used as the low-soda fine aluminum hydroxide of the product. This low soda fine aluminum hydroxide usually has an average particle size of 2 μm or less, preferably 1.0 μm or more and 2.0 μm or less, and a total soda content of 0.04% by mass or less. The surface area is 10 m ² / g or less.

  The low soda fine aluminum hydroxide may be subjected to a surface treatment with a surface treatment agent such as a silane coupling agent, a titanate coupling agent, or stearic acid, if necessary.

The low soda fine aluminum hydroxide of the present invention is a gibbsite type aluminum hydroxide having an average particle size of 2 μm or less, a total soda content of 0.04% by mass or less, and a BET specific surface area of 10 m ² / g or less. It exhibits excellent performance as a flame retardant for imparting heat resistance and flame resistance to the polymer material.

  In addition, according to the method for producing low-soda fine aluminum hydroxide of the present invention, the average particle diameter, the total soda content, and the BET specific surface area are all small and excellent as a flame retardant for various polymer materials. Gibbsite-type aluminum hydroxide exhibiting excellent performance can be easily produced by the Bayer method.

  Hereinafter, preferred embodiments of the present invention will be described in detail based on examples and comparative examples.

[Example 1]
[Preparation of aluminum hydroxide for seeds]
An aluminum hydroxide having an average particle diameter of 1.2 μm, a soda (T—Na ₂ O) content of 0.040% by mass and a BET specific surface area of 12 m ² / g prepared by the Bayer method was mixed with pure water to give 500 g / L. A slurry was prepared, and wet pulverized using a wet pulverizer (Dynomill KDL-PILOT manufactured by WAB). The average particle size was 1.0 μm, the total soda content was 0.047% by mass, and the BET specific surface area was 14.8 m ² / g. Aluminum hydroxide was prepared and used as seed aluminum hydroxide.

(Preparation of initial solution)
Pure water was used as an initial medium, and 120 g of the above-mentioned aluminum hydroxide for seeds was mixed with pure water heated to 70 ° C. in a precipitation tank having a volume of 5 L and the above-mentioned aluminum hydroxide for seeds to give a slurry concentration of 60 g / 2 L of an initial solution of L was prepared.

(Preparation of additive solution)
According to the Bayer method, dissolved Na ₂ O content (Na ₂ O concentration) 148 g / L, dissolved Al ₂ O ₃ content (Al ₂ O ₃ concentration) 149 g / L, and these dissolved Na ₂ O content and dissolved Al ₂ O ₃ content A sodium aluminate solution having a molar ratio (Na ₂ O / Al ₂ O ₃ ) of 1.6 was prepared, and this was heated to 70 ° C. to obtain an added solution.

(Deposition operation)
The additive solution is continuously added to the initial solution in the precipitation tank with stirring to prepare a precipitation solution of aluminum hydroxide in the precipitation tank, and the supersaturated Al ₂ O ₃ concentration of the precipitation solution is 15 g / While maintaining below L, aluminum hydroxide is precipitated. When 2 L of additive solution is added, the addition of the additive solution is terminated, and subsequently maintained at 70 ° C. for 2 hours to precipitate aluminum hydroxide. The operation has ended.

During this precipitation operation, the precipitation solution in the precipitation tank was always maintained at 70 ° C., and the average supersaturated Al ₂ O ₃ concentration from the start of precipitation of aluminum hydroxide to the end of precipitation was 4.5 g / L. Furthermore, the precipitation rate calculated | required as the amount of aluminum hydroxide (alumina conversion) precipitated per 1L of addition solutions was 74 g / L.

[Washing and crushing operation]
After completion of the precipitation operation, solid-liquid separation was performed using a centrifuge, and the obtained solid was repulped with 4.8 m ³ of pure water at 70 ° C. and then subjected to a water-washing operation for solid-liquid separation 5 times to cause precipitation. Aluminum hydroxide was recovered.

  Next, with respect to the recovered aluminum hydroxide, pure water was added to prepare a slurry having a slurry concentration of 300 g / L, and pulverized so that the average particle diameter became 1.3 μm.

  Next, the obtained aluminum hydroxide was dried for about 1 hour under heating at 130 ° C. to obtain low soda fine aluminum hydroxide of Example 1.

With respect to the low soda fine aluminum hydroxide obtained in Example 1, the average particle size, the total soda content, the free soda (f-Na ₂ O) content, and the BET specific surface area were measured. The average particle size was measured using a laser diffraction type particle size distribution device (Microtrack X100 manufactured by Nikkiso Co., Ltd.), the total soda content and the free soda content were measured by an atomic absorption method according to JIS R9301-3-9, The BET specific surface area was measured using a specific surface area automatic measuring device (Microsorbex, Flowsorb II2300 type).
The results are shown in Table 1.

[Example 2]
Average particle diameter of aluminum hydroxide used as seed, total soda content, BET specific surface area, addition amount and addition rate, dissolved sodium aluminate solution used as additive solution, Na ₂ O content (Na ₂ O concentration), dissolution Al ₂ O ₃ minutes (Al ₂ O ₃ concentration), molar ratio of dissolved Na ₂ O components (Na ₂ O concentration) to dissolved Al ₂ O ₃ minutes (Al ₂ O ₃ concentration) (Na ₂ O / Al ₂ O) ₃ ) A low-soda fine aluminum hydroxide of Example 2 was obtained in the same manner as in Example 1 except that the addition amount was adjusted to the value shown in Table 1.

During this precipitation operation, the precipitation solution in the precipitation tank was always maintained at 70 ° C., and the average supersaturated Al ₂ O ₃ concentration from the start of precipitation of aluminum hydroxide to the end of precipitation was 3.3 g / L. The precipitation rate was 69 g / L.

For the low soda fine aluminum hydroxide obtained in Example 2, the average particle diameter, the total soda content, the free soda content, and the BET specific surface area were measured in the same manner as in Example 1.
The results are shown in Table 1.

[Comparative Example 1]
Average particle diameter of aluminum hydroxide used as seed, total soda content, BET specific surface area, addition amount and addition rate, dissolved sodium aluminate solution used as additive solution, Na ₂ O content (Na ₂ O concentration), dissolution Al ₂ O ₃ minutes (Al ₂ O ₃ concentration), molar ratio of dissolved Na ₂ O components (Na ₂ O concentration) to dissolved Al ₂ O ₃ minutes (Al ₂ O ₃ concentration) (Na ₂ O / Al ₂ O) ₃ ) A low soda fine aluminum hydroxide of Comparative Example 1 was obtained in the same manner as in Example 1 except that the addition amount was adjusted to the value shown in Table 1.

During this precipitation operation, the precipitation solution in the precipitation tank was always maintained at 50 ° C., and the average supersaturated Al ₂ O ₃ concentration from the start of precipitation of aluminum hydroxide to the end of precipitation was 7.1 g / L. Moreover, the precipitation rate was 98 g / L.
The results are shown in Table 1.

[Comparative Example 2]
As an initial medium, a sodium aluminate solution having a Na ₂ O concentration of 134 g / L, an Al ₂ O ₃ concentration of 86 g / L, a molar ratio (Na ₂ O / Al ₂ O ₃ ) of 2.6 and an addition amount of 2 L was used. The average particle diameter, total soda content, BET specific surface area, addition amount and addition rate shown in Table 1 are used, and the dissolved Na ₂ O content (Na ₂ O concentration) shown in Table 1 is used as the addition solution. , Dissolved Al ₂ O ₃ minutes (Al ₂ O ₃ concentration), molar ratio of dissolved Na ₂ O components (Na ₂ O concentration) to dissolved Al ₂ O ₃ minutes (Al ₂ O ₃ concentration) (Na ₂ O / Al ₂ O ₃ ), a low soda fine aluminum hydroxide of Comparative Example 2 was obtained in the same manner as in Example 1 except that the added amount of sodium aluminate solution was used.

During this precipitation operation, the precipitation solution in the precipitation tank was always maintained at 70 ° C., and the average supersaturated Al ₂ O ₃ concentration from the start of precipitation of aluminum hydroxide to the end of precipitation was 13.7 g / L. The precipitation rate was 58 g / L.
The results are shown in Table 1.

As is apparent from the results shown in Table 1, in both cases of Example 1 and Example 2, the average particle size after pulverization was 2 μm or less, and total soda (T-Na ₂ O) was used. In the case of Comparative Example 1, the precipitation temperature was 50 ° C. and the total soda content (T-Na) was 0.04% by mass or less and the BET specific surface area was 10 m ² / g or less. ₂ O) is as high as 0.074%, and in the case of Comparative Example 2, the Na ₂ O concentration of the initial medium is 134 g / L, the Al ₂ O ₃ concentration is 86 g / L, and the total soda content (T- Na ₂ O) is as high as 0.049%, and the precipitation rate is 58 g / L, which is lower in productivity than those in Examples 1 and 2 and Comparative Example 1.

  The present invention provides a gibbsite-type low soda fine aluminum hydroxide having an extremely small average particle size and total soda, and if necessary, a BET specific surface area, which is extremely small. It is extremely useful for uses such as flame retardants for imparting heat resistance and flame retardancy to various polymer materials, and has high industrial value.

Claims (6)

Gibbsite-type aluminum hydroxide produced by the Bayer method, having an average particle size of 2 μm or less, a total soda (Na ₂ O) content of 0.04 mass% or less, and a BET specific surface area of 10 m ² / g A low soda fine aluminum hydroxide characterized by:   The low-soda fine aluminum hydroxide according to claim 1, which has been subjected to a surface treatment with a surface treatment agent.   The low soda fine aluminum hydroxide according to claim 2, wherein the surface treatment agent is a silane coupling agent, a titanate agent, or stearic acid. When producing low-soda fine aluminum hydroxide by the Bayer process, total soda (Na ₂ O) content of 0.05 as seeds in an initial medium having a Na ₂ O concentration of 30 g / L or less and an Al ₂ O ₃ concentration of 30 g / L or less Aluminum hydroxide having a mass% or less and an average particle size of 1 μm or less is added to prepare an initial solution, and then an additive solution comprising a sodium aluminate solution is added continuously or intermittently to the initial solution to form aluminum hydroxide. In addition to preparing a precipitation solution, aluminum hydroxide is precipitated from this precipitation solution at a precipitation temperature of 60 to 90 ° C. so that the average supersaturated Al ₂ O ₃ concentration from the start of precipitation to the end of precipitation does not exceed 15 g / L. A process for producing low-soda fine-grain aluminum hydroxide characterized by 5. The low soda fine aluminum hydroxide according to claim 4, wherein the precipitation solution has a molar ratio (Na ₂ O / Al ₂ O ₃ ) of dissolved Na ₂ O and dissolved Al ₂ O ₃ of 5.0 or less. Manufacturing method. The method for producing low-soda fine aluminum hydroxide according to claim 4 or 5, wherein, during the precipitation operation of aluminum hydroxide, the temperature drop rate is adjusted to maintain the average supersaturated Al ₂ O ₃ concentration of the precipitation solution at 15 g / L or less.