JP2003095645A - Aluminum hydroxide and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide aluminum hydroxide which is pulverised to a single granular state without generation of unevenness of the grain surface, chipping of the grain, etc. SOLUTION: A slurry is prepared by suspending aluminum hydroxide, which is obtained by a Bayer method, in a solution of sodium aluminate. The temperature of the slurry is raised from <=70 deg.C to >=85 deg.C within 15 min and after the temperature reaches >=85 deg.C, the temperature is kept >=80 deg.C at least for 15 min from the start of the temperature raise. The ratio A/C [aluminum concentration A (unit g/L) and sodium hydroxide concentration C (unit g/L) of the sodium aluminate solution before the temperature raise] is made <=0.45.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to aluminum hydroxide used as a flame-retardant filler for plastics, rubber and the like, and a method for producing the same. More specifically, the present invention relates to aluminum hydroxide crushed into single particles without causing surface roughness of the particles, chipping of the particles, and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, aluminum hydroxide has been widely used as a filler for filling rubbers and plastics. For example, it is used as a flame retardant for thermoplastic resins, rubbers, and epoxy resins, and as a toning filler for thermosetting resins such as unsaturated polyester resins and acrylic resins.

When used as a flame retardant, the more flame retardant performance is improved by filling aluminum hydroxide more, but the addition of a large amount increases the kneading torque and the molding temperature. However, there is a problem that aluminum hydroxide is partially dehydrated and foams. Also, when the thermosetting resin is filled, the material cost is reduced by increasing the filling amount, but there is a problem that the material strength is lowered.

In order to suppress the decrease in material strength, it is desired to make the particle diameter as fine as possible. It is also possible to obtain aluminum hydroxide having a small particle size by precipitation, but since aluminum hydroxide has a form of secondary agglomerated particles in which a large number of primary particles are agglomerated, the oil absorption is very large and a large amount as a filler. It is difficult to fill.
For this reason, generally, aluminum hydroxide having a particle size of about 50 to 150 μm is crushed by a ball mill or other crusher into primary particles.

However, a great amount of energy is required to pulverize to a predetermined particle size by pulverization. In the crushed aluminum hydroxide, the primary particles thereof are destroyed, the surface is roughened, chipping of the particles occurs, and the BET specific surface area of the powder is increased. As a result, the compatibility with the resin is poor and the viscosity increases, making it difficult to highly fill the resin. Further, in the case of a thermosetting resin, the curing time becomes long.

[0006] From the above, it can be said that the ideal aluminum hydroxide for a filler is one in which the surface is not rough, that is, the BET specific surface area is low and the aluminum hydroxide is in the form of a single grain.

[0007] Japanese Patent Publication No. 5-4336 discloses that a continuous type centrifugal separator applies a large centrifugal force to crush secondary agglomerated particles without destroying primary particles, thereby suppressing particle roughness. Although proposed, it was a limited method for specific raw materials and was not a method that could be widely applied.

Further, Japanese Patent Publication No. 62-9256 proposes that aluminum hydroxide having a single crystal or a rounded shape is obtained by bringing a temperature-increased Bayer extract into contact with solid aluminum hydroxide. However, there are drawbacks that a long contact time is required and that the production efficiency is deteriorated because the aluminum hydroxide is dissolved during the contact.

Further, in Japanese Patent Application Laid-Open No. 9-208740, after secondary agglomerated particles of aluminum hydroxide are crushed by a dry impact crusher in advance, they are slurried in a sodium aluminate solution having a specific alkali concentration to raise the temperature. Therefore, a method of dissolving the surface to reduce the BET specific surface area is proposed, but since the aluminum hydroxide needs to be filtered and dried once for dry pulverization in advance, the process is long and the manufacturing cost is high. There is a problem of becoming.

[0010]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide an ideal aluminum hydroxide for filler as a single particle having a low BET specific surface area over a wide range of particle diameters and an efficient production method thereof. is there.

[0011]

In view of such circumstances, the inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, suspended aluminum hydroxide in a specific sodium aluminate solution. Heating the slurry under specific conditions,
The inventors have found that a single granular ideal aluminum hydroxide having a low specific surface area suitable for a filler can be obtained by holding it thereafter under a specific condition, and have completed the present invention.

That is, the present invention provides the following means. [1] A slurry in which aluminum hydroxide obtained by the Bayer method is suspended in a sodium aluminate solution,
The aluminum hydroxide is heated from 70 ° C. or lower to 85 ° C. or higher within 15 minutes, and after the temperature is raised, the solution temperature is kept at 80 ° C. or lower for 15 minutes from the start of temperature rising. Production method. [2] Alumina concentration A (unit g / liter) and sodium hydroxide concentration C of the sodium aluminate solution before heating
The method for producing aluminum hydroxide according to item 1 above, wherein the ratio A / C (in g / liter) is 0.45 or less.

[3] The dissolution rate of aluminum hydroxide when the temperature of the slurry is raised is represented by the following general formula: Dissolution rate (%) = C before temperature rise × (after temperature rise A / C−before temperature rise A /
C) × 1.53 / slurry concentration before temperature increase × 100 (in the formula, A represents the alumina concentration of the sodium aluminate solution (unit g / liter), and C represents the sodium hydroxide concentration (unit g / liter)) And less than 15%, the method for producing aluminum hydroxide according to the above item 1 or 2. [4] The method for producing aluminum hydroxide as described in any one of the aforementioned Items 1 to 3, wherein the slurry temperature raising device is a double-tube heat exchanger.

[5] Average particle diameter D is 1 to 25 μm, BE
T specific surface area S is 1.5 m ² / g or less, particle diameter Dbet calculated from S by sphere approximation (where Dbet is Dbet = 6 / (S
× ρ) is calculated. ρ is the specific gravity of aluminum hydroxide. ) To D (cohesion degree) D / Dbet is less than 3, the aluminum hydroxide obtained by the method according to any one of items 1 to 4 above. [6] An aluminum hydroxide-containing composition containing the aluminum hydroxide according to item 5 as a filler. [7] The aluminum hydroxide-containing composition according to the above item 6, wherein the matrix material of the aluminum hydroxide-containing composition is rubber or plastic.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. In the present invention, aluminum hydroxide obtained by the Bayer method is used as a ratio of alumina (Al ₂ O ₃ ) concentration A (unit g / liter) and sodium hydroxide (NaOH) concentration C (unit g / liter) A / The slurry prepared by suspending the sodium aluminate solution in which C is 0.45 or less in 15
Within a minute, the temperature is raised from 70 ° C. or lower to 85 ° C. or higher, and after the temperature is raised to 85 ° C., the liquid temperature is maintained without lowering from 80 ° C. for at least 15 minutes from the start of temperature rise. A method for manufacturing aluminum is provided. The aluminum hydroxide obtained by this production method can be suitably used as a filler.

In the above-mentioned manufacturing method, aluminum hydroxide is subjected to a thermal shock to selectively dissolve only the grain boundaries of the secondary agglomerated grains having a weak crystallographically bonding force, and the subsequent reaggregation or the like. By suppressing the diameter change, it has the effect of crushing the secondary agglomerated particles.

By this method, the average particle diameter D is 1 to 25.
μm, specific surface area S measured by nitrogen adsorption method (BET method)
Of 1.5 m ² / g or less, and aluminum hydroxide having a ratio of the particle diameters Dbet and D calculated from S by the sphere approximation, that is, an aggregation degree D / Dbet of less than 3 is obtained. Where Dbet = 6 /
(S × ρ), where ρ is the specific gravity of aluminum hydroxide.

It is essential that the temperature rise in this method is 85 ° C. or higher. If the temperature is lower than 85 ° C, sufficient thermal shock for selectively melting only the grain boundaries is not given, and dissolution from the particle surface proceeds, resulting in poor production efficiency and rough surface of the particle. Therefore, it is not preferable.

Incidentally, the boiling point of the sodium aluminate solution cannot be limited because it changes depending on the sodium hydroxide concentration, but it is about 104 ° C. in the case of the sodium aluminate solution used in the Bayer process. The temperature rising time in this method is within 15 minutes. If it is longer than 15 minutes, sufficient thermal shock is not given to selectively dissolve only the grain boundaries, and the dissolution of the entire particles proceeds, which is not preferable.

The temperature of the slurry before heating in this method is 70 ° C. or lower, preferably 65 ° C. or lower. 70 ° C
When the temperature is higher, a sufficient thermal shock to selectively dissolve only the grain boundaries is not given at the time of temperature rise, which is not preferable. The holding temperature after temperature rise in this method is 80 ° C. or higher, preferably 85 ° C. or higher. If the holding temperature is lower than 80 ° C., the crushed particles reaggregate, which is not preferable.

The sodium aluminate solution before temperature increase used in this method is such that A is the concentration of alumina (unit: g / liter) and C is the concentration of sodium hydroxide (unit: g / liter). Ratio of sodium oxide concentration, that is, A / C is 0.45 or less, preferably 0.4
It is 0 or less. When A / C is higher than 0.45, the alumina component necessary for loosening the grain boundaries due to the temperature rise is not dissolved, which is not preferable.

The dissolution rate of aluminum hydroxide due to the temperature rise in this method is less than 15%, preferably less than 13%. If the dissolution rate is more than 15%, the yield of aluminum hydroxide will be low, resulting in poor production efficiency. Here, the dissolution rate of aluminum hydroxide due to temperature rise, the following general formula,

Dissolution rate (%) = C before temperature rise × (A / C after temperature rise)
-A / C before temperature rise x 1.53 / slurry concentration before temperature rise x 1
00 (in the formula, A represents the concentration of alumina in the sodium aluminate solution (unit: g / liter), and C represents the concentration of sodium hydroxide (unit: g / liter)).

In the present invention, the BET specific surface area is low at the desired particle size by selecting the primary particle size of the secondary agglomerated particles as the starting material in consideration of the desired particle size after dissolution.
It is possible to obtain a single granular aluminum hydroxide for resin filler. The aluminum hydroxide produced in the present invention is suitable for various fillers. For example, rubber or a plastic such as a thermoplastic resin, an epoxy resin, a thermosetting resin (unsaturated polyester resin, acrylic resin, etc.) can be preferably used as the matrix material of the aluminum hydroxide-containing composition contained as a filler.

When the aluminum hydroxide obtained by this method is filled in a resin or the like, it may be used alone or in combination with several other types of aluminum hydroxide having different particle diameters in order to lower the compound viscosity. You may mix and use.

Further, the aluminum hydroxide obtained by this method may be surface-treated with a conventionally known surface-treating agent before use. The surface treatment agent is not particularly limited, silane coupling agents, various coupling agents such as titanate coupling agents, fatty acids such as oleic acid and stearic acid, and fatty acid esters thereof, methyl silicate,
Examples thereof include silicates such as ethyl silicate.

[0027]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples. The physical properties in the present invention were measured by the following methods.

(Average particle diameter D) The average particle diameter D of aluminum hydroxide was measured by a laser scattering diffraction method. (BET specific surface area S) Specific surface area S of aluminum hydroxide
Was measured by the nitrogen adsorption method (BET method). (Cohesion degree D / Dbet) The cohesion degree of aluminum hydroxide is
The particle diameter Dbet calculated from S by sphere approximation (where Dbet is calculated as Dbet = 6 / (S × ρ). Ρ is the specific gravity of aluminum hydroxide) and the ratio D / Dbet of D And estimated.

(Dissolution Rate of Aluminum Hydroxide) The dissolution rate of aluminum hydroxide due to temperature increase was calculated by the following formula. Dissolution rate (%) = C before temperature rise × (after temperature rise A / C−before temperature rise A /
C) × 1.53 / slurry concentration before temperature increase × 100 (In the formula, A represents the alumina concentration of the sodium aluminate solution (unit g / liter), and C represents the sodium hydroxide concentration (unit g / liter).)

(Example 1) Water obtained by the Bayer method
Aluminum oxide slurry (average of aluminum hydroxide
Particle size 110.9 μm, sodium hydroxide concentration 149 g
/ Liter, A / C = 0.37, slurry concentration 175 g
/ Liter, slurry temperature 38 ° C) double tube heat exchanger
(Inner tube side volume 0.019m³, Heat transfer area 3.2m²) Of
3m on the tube side ³/ Hr (residence time in heat exchanger 23 seconds)
Then, steam is put into the outer tube, and the temperature is raised to 96 ° C.
Was held at 85 ° C for 15 minutes. A / C of slurry is
0.46, the dissolution rate was 11.7% Solid aluminum hydroxide was washed from the slurry and separated by filtration
And then dried. Average particle size of the obtained aluminum hydroxide
Child diameter D is 22.2 μm, BET specific surface area S is 0.2 m²/
g, and the degree of aggregation was 1.8.

(Example 2) The same aluminum hydroxide slurry as in Example 1 was charged into a SUS tank having a volume of 1 m ³ , and the tank temperature was raised to 85 ° C in 15 minutes while stirring. The slurry A / C was 0.48, and the dissolution rate was 14.
It was 3%. Solid aluminum hydroxide was washed from the slurry, filtered, and dried. The average particle diameter D of the obtained aluminum hydroxide was 21.6 μm, the BET specific surface area S was 0.3 m ² / g, and the degree of aggregation was 2.6.

Example 3 Aluminum hydroxide slurry obtained by the Bayer method (aluminum hydroxide average particle size 76.8 μm, sodium hydroxide concentration 146 g /
Liter, A / C = 0.38, slurry concentration 190 g /
Liter and a slurry temperature of 65 ° C.) are the same as S in Example 2.
Add to a US tank and stir to increase the tank temperature to 15
The temperature was raised to 85 ° C in minutes. A / C of slurry is 0.4
8, the dissolution rate was 11.8%. Solid aluminum hydroxide was washed from the slurry, filtered, and dried. The average particle diameter D of the obtained aluminum hydroxide is 13.4μ.
m, BET specific surface area S is 0.3 m ² / g, aggregation degree is 1.6
Met.

(Example 4) Water obtained by the Bayer method
Aluminum oxide slurry (average of aluminum hydroxide
Particle size 20.8 μm, sodium hydroxide concentration 154 g /
Liter, A / C = 0.35, slurry concentration 230g
/ Liter, slurry temperature 64 ° C.) as in Example 2.
Put in a SUS tank and set the tank temperature to 1 while stirring.
Raised to 85 ° C in 5 minutes. A / C of slurry is 0.4
9, the dissolution rate was 14.3%. Solid from the slurry
The aluminum hydroxide was washed, filtered and dried. Profit
The obtained aluminum hydroxide average particle diameter D is 2.9 μm,
BET specific surface area S is 1.2 m ²/ g, cohesion is 1.4
It was.

(Comparative Example 1) The same aluminum hydroxide slurry as in Example 1 was placed in the same SUS tank as in Example 2, and the tank temperature was raised to 80 ° C in 15 minutes while stirring. A / C of slurry is 0.45, dissolution rate is 1
It was 0.4%. Solid aluminum hydroxide was washed from the slurry, filtered, and dried. The obtained aluminum hydroxide had an average particle diameter D of 46.5 μm, a BET specific surface area S of 0.2 m ² / g, and an aggregation degree of 3.8.

(Comparative Example 2) The same aluminum hydroxide slurry as in Example 1 was placed in the same SUS tank as in Example 2, and the tank temperature was raised to 85 ° C in 30 minutes while stirring. A / C of slurry is 0.51, dissolution rate is 1
It was 8.2%. Solid aluminum hydroxide was washed from the slurry, filtered, and dried. The average particle diameter D of the obtained aluminum hydroxide was 25.4 μm, the BET specific surface area S was 0.2 m ² / g, and the degree of aggregation was 2.0.

(Comparative Example 3) Water obtained by the Bayer method
Aluminum oxide slurry (average of aluminum hydroxide
Particle size 76.8μ, sodium hydroxide concentration 147g / liter
Attle, A / C = 0.47, slurry concentration 210 g /
Liter, slurry temperature 63 ° C.) is the same as S in Example 2.
Add to a US tank and stir to increase the tank temperature to 15
The temperature was raised to 85 ° C in minutes. A / C of slurry is 0.5
1, the dissolution rate was 4.3%. Solid water from the slurry
The aluminum oxide was washed, filtered, and dried. Got
The average particle diameter D of the formed aluminum hydroxide is 35.5μ.
m, BET specific surface area S is 0.2 m ²/ g, degree of aggregation 2.9
Met.

The summary of the results of Examples and Comparative Examples is summarized in Table 1 above.

[0038]

[Table 1]

[0039]

INDUSTRIAL APPLICABILITY In the production method of the present invention, aluminum hydroxide is subjected to thermal shock to selectively dissolve only the grain boundaries of secondary agglomerates having a weak crystallographically bonding force, and reaggregation thereafter. The effect of crushing the secondary agglomerated particles is obtained by suppressing changes in particle diameter such as. Therefore, the method for producing aluminum hydroxide of the present invention uses a conventional grinding method utilizing impact force due to collision between media, milling grinding such as Raymond mill, and collision between particles such as jet mill. Unlike the pulverization method described above, it is epoch-making in that it does not roughen the primary particle surface during crushing.As a result, the resulting aluminum hydroxide has a low specific surface area and is a single particle, so it is used as a filler. It is suitable and its industrial value is enormous.

Continued front page    (72) Inventor Takahashi Seisuke             8 Ebisu-cho, Kanagawa-ku, Yokohama-shi, Kanagawa             Showa Denko Co., Ltd. Yokohama Production & Engineering Department F-term (reference) 4G076 AA10 AB02 AC01 BA27 BD02                       CA02 CA15 CA26 CA28 DA02                       DA05                 4J002 AA011 AA021 AC001 CD001                       CF211 DE146 FD016 FD136                 4J037 AA24 DD05 DD07 EE25 EE28                       EE43 EE47

Claims (7)

[Claims] 1. A slurry obtained by suspending aluminum hydroxide obtained by the Bayer method in a sodium aluminate solution is heated from 70 ° C. or lower to 85 ° C. or higher within 15 minutes, and then heated to a solution temperature. The method for producing aluminum hydroxide, characterized in that the temperature is maintained for 15 minutes from the start of the temperature increase without lowering the temperature to 80 ° C. or lower. 2. The ratio A / C of the alumina concentration A (unit g / liter) and the sodium hydroxide concentration C (unit g / liter) of the sodium aluminate solution before heating is 0.45 or less. The method for producing aluminum hydroxide according to claim 1, which is characterized in that. 3. The dissolution rate of aluminum hydroxide when the temperature of the slurry is raised is expressed by the following general formula: Dissolution rate (%) = C before temperature rise × (after temperature rise A / C−before temperature rise A /
C) × 1.53 / slurry concentration before temperature increase × 100 (In the formula, A represents the alumina concentration of the sodium aluminate solution (unit g / liter), and C represents the sodium hydroxide concentration (unit g / liter).) The method for producing aluminum hydroxide according to claim 1 or 2, wherein the content is less than 15%. 4. The method for producing aluminum hydroxide according to claim 1, wherein the temperature raising device for the slurry is a double-tube heat exchanger. 5. An average particle diameter D of 1 to 25 μm, a BET specific surface area S of 1.5 m ² / g or less, and a particle diameter Dbet calculated from S by a sphere approximation (where Dbet is Dbet = 6 / (S × ρ)
It is calculated by. ρ is the specific gravity of aluminum hydroxide. 5. The aluminum hydroxide obtained by the method according to any one of claims 1 to 4, wherein the ratio (cohesion degree) D / Dbet of D) to D is less than 3. 6. An aluminum hydroxide-containing composition containing the aluminum hydroxide according to claim 5 as a filler. 7. The aluminum hydroxide-containing composition according to claim 6, wherein the matrix material of the aluminum hydroxide-containing composition is rubber or plastic.