JPH03197314A - Growth of magnesium hydroxide crystal - Google Patents

Abstract

PURPOSE:To readily obtain a hexagonal plate crystal with only slight secondary aggregation by adding ground light burnt magnesia to a solution containing organic acid and Mg salt thereof in a given ratio, irradiating the solution with ultrasonic wave to carry out hydration reaction as a first process and effecting a second process following the first process. CONSTITUTION:A solution containing 0.01-1wt.% organic acid and/or Mg salt thereof is poured to a stirring warm water tank with an ultrasonic wave generator and maintained at >=50 deg.C. Ground light burnt magnesia is thrown into the warm water tank and hydration reaction is done while irradiating the solution with ultrasonic wave. Then, 1/2-3 times the amount of ground light burnt magnesia of the first process is added to Mg hydroxide slurry obtained by this first process and hydration reaction is caused while irradiating with ultrasonic wave.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for growing magnesium hydroxide crystals, and more specifically, to grow magnesium hydroxide in the form of hexagonal plate-like crystals with excellent dispersibility at low cost and industrially. The present invention relates to a method for growing magnesium hydroxide crystals that can be advantageously produced.

[Prior Art] Magnesium hydroxide has a wide range of uses in various fields. As one of these, the use of thermoplastic resins as non-halogen flame retardants is attracting attention. When using magnesium hydroxide as such a flame retardant filler, it is desired that the magnesium hydroxide has a large crystal size and is free from secondary agglomeration. In other words, crystals with small crystal diameters tend to form secondary aggregates, and when kneaded with resin, have extremely poor dispersibility in the resin, resulting in poor processability and
It has an adverse effect on various physical properties such as flame retardancy, MA mechanical strength, and water resistance and insulation properties.

Conventionally, the following methods (1) to (2) have been proposed as methods for producing highly dispersible magnesium hydroxide with a large crystal size.

■ Add magnesium hydroxide with a specific surface area of 30 to 60 d/g to a 10 to 40% by weight calcium chloride aqueous solution,
A method for producing magnesium hydroxide having a specific surface area of 10 m'/g or less by autoclave curing under high temperature and high pressure (Japanese Patent Application Laid-Open No. 57-100918).

■ After heating basic magnesium chloride or basic magnesium nitrate in an alkaline solution at 10 to 20°C, it is cured in an autoclave under high temperature and high pressure.
A method for producing magnesium hydroxide having a specific surface area of /g (Japanese Patent Application Laid-open No. 115799/1983).

■ Magnesium oxide calcined at 1400°C or higher is converted into acid or magnesium by the total amount of acid groups corresponding to an equivalent number of 0.5% or more of the equivalent number of raw material magnesium oxide and acid groups corresponding to the equivalent number of raw material calcium oxide. Method of hydration in a slurry state of water suspension containing salt (Japanese Patent Application Laid-Open No. 56-1098
No. 20).

■ The crystallite diameter in the <200> direction obtained by calcining and pulverizing magnesium hydroxide at 1150-1350℃ is 800.
BET specific surface area is 0.7 to 2 Go/in the range of ~1500A
A method of hydrating fine magnesium oxide powder in the range of g and average particle diameter of 2 to 5 μm in the coexistence of a magnesium salt (Japanese Unexamined Patent Publication No. 1-131022).

[Problems to be Solved by the Invention] Among the conventional methods described above, methods (1) and (2) have a problem in that the autoclave is likely to corrode because the treatment uses a highly concentrated calcium chloride aqueous solution or the like. In addition, in methods ① and ①, magnesium oxide (magnesia clinker) fired at high temperature is finely pulverized and subjected to a hydration reaction, so calcination and pulverization steps are required, which makes the processing operations complicated, and the manufacturing process is complicated. There is a problem that the cost is high.

The present invention eliminates the firing and pulverizing steps of the conventional method, alleviates corrosion of the equipment, and uses magnesium hydroxide, which has hexagonal plate-shaped crystals with large particle diameters and improves the problem of secondary aggregation. An object of the present invention is to provide a method for growing magnesium hydroxide crystals that can produce magnesium hydroxide having a large crystal size at low cost and industrially advantageously.

[Means for Solving the Problems] The method for growing magnesium hydroxide crystals of the present invention comprises:
A predetermined amount of pulverized light-burnt magnesia was put into a stirring hot water tank equipped with an ultrasonic generator containing a solution of an organic acid and/or its magnesium salt with a concentration of 0.01 to 1% by weight held above, and ultrasonic waves were applied. A first step of causing a hydration reaction without irradiating the
A second step in which 1/3 to 3 times the amount of crushed light-burned magnesia added in the previous step is added to the magnesium hydroxide slurry obtained in the previous step, and a hydration reaction is carried out while irradiating ultrasonic waves. It is characterized by consisting of the above-mentioned higher-order processes.

The present invention will be explained in detail below.

Examples of the organic acids and/or magnesium salts thereof used in the present invention include organic acids such as acetic acid, formic acid, butyric acid, and propionic acid, and magnesium salts thereof.
The species can be used alone or in combination of two or more species. Magnesium acetate is particularly suitable as the organic acid or its magnesium salt.

Such an organic acid and/or its magnesium salt may contain 0
．． It is used as a solution with a concentration of 0.01 to 1% by weight. If this concentration is less than 0.01% by weight, particles that are likely to form secondary agglomerations are produced, which is undesirable, and if it exceeds 1% by weight, the produced particles become flaky, which is not desirable. In the present invention, the organic acid and/or its magnesium salt is particularly
．． Preferably, the aqueous solution has a concentration of 0.05 to 0.1% by weight.

The temperature of the stirring hot water tank equipped with an ultrasonic generator into which the solution of the organic acid and/or its magnesium salt is placed is 50° C. or higher and lower than the boiling temperature of the reaction slurry. If the temperature is less than 50°C, the hydration reaction takes a long time, which is industrially disadvantageous. When considering the hydration reaction rate, the temperature is 60~
Most preferably, the temperature is in the range of 80°C.

On the other hand, the crushed light calcined magnesia used in the present invention is
In terms of hydration reaction rate, the specific surface area is 3 to 20rrl"/
A powder form of H is preferable. If the specific surface area of the crushed light calcined magnesia is less than 3 m''/g, the hydration rate of magnesia is extremely slow and it takes a long time to complete the hydration reaction, which is industrially disadvantageous. On the other hand, the specific surface area of magnesia is 2om”/
If it exceeds g, it will not be possible to obtain magnesium hydroxide with good dispersibility and less secondary agglomeration, which is the objective of the present invention.The main reason for this is that the hydration rate of magnesia is too fast, resulting in irregular crystal shapes This is thought to be because the particles become uniform and form aggregates.

In the present invention, as a first step, a solution of an organic acid and/or its magnesium salt with a concentration of 0.01 to 1% by weight, maintained at 50°C or higher, is placed in a stirring hot water tank equipped with an ultrasonic generator. A certain amount of pulverized light-burned magnesia is added while irradiating with ultrasonic waves to complete the hydration reaction. In this first step, the amount of pulverized light calcined magnesia to be added is 5 to 50% by weight based on the weight of the organic acid and/or its magnesium salt contained in the solution of the organic acid and/or its magnesium salt.
It is preferable to set it to about 50 times.

The time required to complete the hydration reaction after the first step and second step varies depending on the reaction temperature, etc., but the specific surface area is 2 to 12 tr.
? /g of crushed light calcined magnesia, hydration reaction temperature 60
When carried out in the preferred range of -80°C, the reaction time is usually 2 to 6 hours.

Next, in the second step, the magnesium hydroxide slurry obtained in the first step is added with an amount equivalent to yJ to 3 times the amount of crushed light calcined magnesia input in the first step, preferably the same as the amount of crushed light calcined magnesia input in the first step. Approximately the same amount of pulverized light-burned magnesia is added and the hydration reaction is completed without irradiation with ultrasonic waves.

Furthermore, as a third step, if necessary, the magnesium hydroxide slurry obtained in the second step is added with an amount equivalent to yJ to 3 times the amount of pulverized light-burned magnesia input in the second step, preferably pulverized light-burnt magnesia in the second step. Approximately twice the amount of pulverized light calcined magnesia input is added, and the hydration reaction is completed while irradiating with ultrasonic waves.

Thereafter, in the same manner, the fourth, fifth and subsequent steps are performed as necessary, that is, in the fourth step, 1/3 to 3 times the amount of crushed light burnt magnesia input in the third step, and in the fifth step In this step, the hydration reaction is completed by adding 1 to 3 times the amount of pulverized light-burned magnesia as the amount of pulverized light-burned magnesia added in the previous step, such as y1 to 3 times the amount of pulverized light-burned magnesia input in the fourth step. .

In particular, in the present invention, it is preferable that the total amount of pulverized light-burned magnesia immersed into the slurry in each step is twice the total amount of pulverized light-burned magnesia input in the previous step. When the input amount of pulverized light calcined magnesia in one step is defined as X, each input amount is optimally set as follows.

In addition, in the present invention, an organic acid and/or its magnesium salt may be replenished into the slurry before adding the pulverized light-burned magnesia in each step, if necessary.

In the present invention, such reaction steps include two or more steps,
Preferably, by carrying out 2 to 5 steps, good magnesium hydroxide crystals can be obtained.

In addition, in the present invention, the magnesium hydroxide slurry concentration obtained in the final step is 3 to 70% by weight, particularly 20 to 5% by weight.
Preferably it is 0% by weight. When the magnesium hydroxide slurry concentration exceeds 70% by weight, the fluidity of the slurry decreases, causing problems in the operation of equipment such as agitators and pump transportation, and when the concentration is low, below 3% by weight, production efficiency is low. .

Magnesium hydroxide crystals obtained through a series of reactions are
For example, it is made into a product through treatments such as filtration, drying, and pulverization.

[Function] Although the details of the reason why hexagonal plate-shaped magnesium hydroxide crystals with excellent dispersibility are produced by the method of the present invention are not clear, Fine particles of magnesium hydroxide with good dispersibility become seeds, and in the next step, the dissolution of the hydrated magnesia and the precipitation of the generated magnesium hydroxide act subtly to form hexagonal particles that are substantially free of secondary agglomerated particles. This is thought to be due to the growth of good plate-shaped crystals. In particular, in the present invention, the generation of secondary agglomerated particles can be almost completely prevented by irradiating ultrasonic waves during this reaction and the generation and growth of crystals.

[Examples] The present invention will be described in more detail with reference to Examples and Comparative Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

Example 1 Ultrasonic waves (42 kHz, 600 W) were applied to 1.5 kg of hot water in a beaker 21 held at 80°C, and 0.48 g of magnesium acetate tetrahydrate was added to form an aqueous solution with a concentration of 0.02% by weight. did. Further, ultrasonic oscillation was continued, and pulverized light calcined magnesia 75 with a specific surface area of 7.2 d/g was added to this aqueous solution.
g was added and stirred with a Chemister stirrer for 6 hours to perform a hydration reaction (1st step).Next, ultrasonic oscillation was continued and 1.
92 g of magnesium acetate tetrahydrate was added to the slurry at 80°C obtained in the first step to reduce the amount of magnesium acetate to 0.
．． After adjusting the concentration to 1% by weight, 75 g of pulverized light calcined magnesia with a specific surface area of 7.2 d/g was added, and the mixture was stirred for 6 hours using a Chemistry stirrer to perform a hydration reaction (second step). The second step was completed. After that, the slurry was filtered, washed and dried to obtain magnesium hydroxide powder.

Figure 1 shows an electron micrograph of the obtained magnesium hydroxide powder. As is clear from Figure 1, hexagonal plate-shaped crystals with uniform particle size and good dispersibility with little secondary aggregation were obtained. . The specific surface area value of this magnesium hydroxide by the BET method was Bd/g. Further, the particle size distribution was as shown in Table 1.

Example 2 Ultrasonic waves (45 kHz, 35 W) were oscillated into 500 g of warm water in an In beaker held at 80° C., and 0.16 g of magnesium acetate tetrahydrate was added to make an aqueous solution with a concentration of 0.02% by weight. Further, ultrasonic oscillation was continued, and 25 grams of pulverized light calcined magnesia with a specific surface area of 3 and 7 g was added to the aqueous solution.
g was added and stirred for 8 hours in a Chemister stirrer to perform a hydration reaction (first step). Next, ultrasonic oscillation was performed [M,
．． 64 g of magnesium acetate tetrahydrate was added to the slurry at 80°C obtained in the first step to reduce the amount of magnesium acetate to 0.
．． After setting the concentration to 1% by weight, the specific surface area was further increased to 3. am"7g
25g of crushed light calcined magnesia was added and stirred in a Chemister stirrer for 8 hours to perform a hydration reaction (second step).
After completing the process, the slurry was filtered, washed and dried to obtain magnesium hydroxide powder.

The obtained magnesium hydroxide has a specific surface area value of 10rr? according to the BET method. /g, and the particle size distribution was as shown in Table 1. Furthermore, as is clear from the electron microscope shown in FIG. 2, this product had hexagonal plate-shaped crystals and had good dispersibility.

Comparative Example 1 75 g of pulverized light calcined magnesia with a specific surface area of 7.2 d/g was added to 1.5 kg of hot water in a 21 beaker kept at 80°C, and the mixture was stirred in a Chemister stirrer for 6 hours to carry out a hydration reaction. Step 1) Next, 75 g of pulverized light calcined magnesia with a specific surface area of 7.2 m"/H was put into the slurry at 80°C obtained in the first step, and stirred with a Chemister stirrer for 6 hours to cause a hydration reaction. After completing the second step, the slurry was filtered, washed and dried to obtain magnesium hydroxide powder.

The obtained magnesium hydroxide had a specific surface area value of 7rn'/g by the BET method, and its particle size distribution was as shown in Table 1. Further, as is clear from the electron micrograph shown in FIG. 3, aggregates were formed in this product.

Comparative Example 2 25 g of pulverized light calcined magnesia with a specific surface area of 3.0 m'/g was added to 500 kg of hot water in a beaker 11 kept at 80°C, and the mixture was stirred in a Chemister stirrer for 8 hours to perform a hydration reaction (1st Further, 25 g of crushed light calcined magnesia with a specific surface area of 3 and Or'7 g was added to the slurry at 80°C obtained in the first step, and the mixture was stirred for 8 hours using a Chemister stirrer to perform a hydration reaction ( After completing the second step, the slurry was filtered, washed and dried to obtain magnesium hydroxide powder.

The obtained magnesium hydroxide had a specific surface area value of 14 m'/g by the BET method, and its particle size distribution was as shown in Table 1. Moreover, as is clear from the electron micrograph shown in FIG. 4, aggregates were formed in this product.

Table 1 [Effects of the Invention] As detailed above, according to the method for growing magnesium hydroxide crystals of the present invention, there is no need to undergo a calcination step or a pulverization step, and the problem of corrosion of equipment such as an autoclave does not occur. Magnesium hydroxide crystals with excellent dispersibility, which have hexagonal plate-like crystals with little secondary agglomeration and a regular lattice arrangement under an electron microscope, can be produced easily, efficiently, and at low cost under normal pressure without any problems. .

Thus, the obtained magnesium hydroxide can be effectively used as a filler of the above-mentioned non-halogen flame retardant for thermoplastic resins.

[Brief explanation of drawings]

Figures 1, 2, 3 and 4 are examples 1 and 2, respectively.
and a micrograph (10,000 times magnification) showing the particle structure of magnesium hydroxide obtained in Comparative Example 1.2.

Claims (1)

[Claims] (1) A predetermined amount of pulverized light calcined magnesia is put into a stirring hot water tank equipped with an ultrasonic generator and containing a solution of an organic acid and/or its magnesium salt with a concentration of 0.01 to 1% by weight held at 50°C or higher. The first step is to carry out a hydration reaction while irradiating ultrasonic waves, and the magnesium hydroxide slurry obtained in the previous step is mixed with 1/3 to 3 of the amount of pulverized light-burned magnesia input in the previous step.
A method for growing magnesium hydroxide crystals, which comprises a second or higher-order step in which twice the amount of pulverized light-burned magnesia is introduced and a hydration reaction is carried out while irradiating ultrasonic waves.