JPS63277511A - Production of magnesium hydroxide and surface-treated magnesium hydroxide - Google Patents

Abstract

PURPOSE:To obtain Mg(OH)2 having excellent dispersibility, by hydrating MgO in a slurry containing an Mg salt of a carboxylic acid having a specific number or more of carbon atoms. CONSTITUTION:An aqueous slurry of an Mg salt of a carboxylic acid expressed by the formula CnH2n+1COOH (provided that n is 2<=n) is prepared. For example, propionic acid or n-butyric acid or a mixture thereof may be used as the above- mentioned carboxylic acid. The concentration of the afore-mentioned Mg salt is preferably about 0.01-0.5mol./l. MgO is then added into the above-mentioned slurry to provide about 50-300g concentration and hydrothermally reacted while stirring to afford the aimed Mg(OH)2. The afore-mentioned reaction temperature is room temperature - about 50 deg.C in the case of the MgO fired at, e.g. about 800-1,000 deg.C. The Mg(OH)2 obtained by the above-mentioned method is even directly used as a filler for synthetic resins, sizing agents, etc. In use especially as the filler for synthetic resins, the surface can be treated with a metal carboxylate to further improve compatibility with the resins and dispersibility therein.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing magnesium hydroxide, particularly magnesium hydroxide having a desired particle size and good dispersibility, and a method for producing surface-treated magnesium hydroxide.

[Prior Art] Magnesium hydroxide has excellent properties as a flame retardant for thermoplastic resins. That is, the resin begins to decompose at a relatively low temperature of around 400° C., thereby inhibiting the combustion of the resin. Therefore, it has recently begun to be used as a flame retardant for coating electric wires. One of the most important properties when using magnesium hydroxide as a flame retardant for resins is its dispersibility in the resin. If the dispersibility in the resin deteriorates, the inherent impact strength of the resin, especially the brittleness and tensile strength at low temperatures, will become extremely poor. Therefore, strongly agglomerated magnesium hydroxide, which has been conventionally used as a raw material for magnesia clinker, tongue fertilizer, or flue gas desulfurization, is generally not suitable for use as a flame retardant. Therefore, the following proposals have been made as magnesium hydroxide with good dispersibility for fine chemical applications such as synthetic resin fillers such as flame retardants, paper sizing agents and fillers, and annealing separators for electrical steel sheets. .

For example, in JP-A No. 52-5963, the bulk density is 0.3.
Specific surface area is 10-3077f/5-0.70g/cl
g, and the ratio of the crystallite thickness in the direction perpendicular to the (110) plane in the crystal lattice to that of the (001) plane is 1.7 to 2.
．． The use of magnesium hydroxide, which is No. 7, has been proposed.

Furthermore, for example, in Japanese Patent Publication No. 60-57457, BET
The use of magnesium hydroxide with a specific surface area ratio in the range of 1 to about 3 has been proposed.

Furthermore, for example, in JP-A-56-109820,
Magnesium oxide calcined at 1,400°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 calcium oxide in the raw material. A method for producing magnesium hydroxide has been proposed, which is characterized by hydration in the form of a water-suspended slurry containing it as a salt.

[Problems to be Solved by the Invention] The magnesium hydroxide synthesized by the above-mentioned proposed method or the surface-treated magnesium hydroxide has improved dispersibility. However, there is still a problem with low-temperature brittleness of the resin composition when kneaded into a resin, and this is thought to be caused by insufficient dispersion of magnesium hydroxide in the resin. Furthermore, in the magnesia hydration method of JP-A-56-109820@, 1q of magnesium hydroxide with small particle size (high specific surface area) to large particle size (low specific surface area) is produced.
With this method, there is still room for improvement in terms of aggregation and the like.

[Means for Solving the Problems] The present inventors continued their earnest efforts to easily obtain magnesium hydroxide with a desired particle size and good dispersibility by improving the magnesia hydration method, and as a result, they succeeded in producing magnesium hydroxide. Completely new knowledge regarding the production method and surface treatment of magnesium hydroxide was obtained.

Therefore, in the present invention, as a method for obtaining magnesium hydroxide with excellent dispersibility and surface-treated magnesium hydroxide,
It has the following configuration.

That is, the general formula CnH2゜+1COOH (however, 2
A method for producing magnesium hydroxide in which magnesia is hydrated in a slurry containing a magnesium salt of a carboxylic acid represented by ≦n), and a surface-treated water in which the magnesium hydroxide is further surface-treated with a carboxylic acid metal salt. This is a method for producing magnesium oxide.

In order to have a magnesium salt present in the reaction system in the method of the present invention, an acid may be added to generate the magnesium salt by reaction with the raw material magnesia, or a magnesium salt may be added.

As the acid, for example, organic acids such as propionic acid, n-butyric acid, isobutyric acid, and valeric acid, or mixtures thereof can be used.

As the magnesium salt, organic acid salts such as magnesium propionate, magnesium n-butyrate, magnesium imbutyrate, and magnesium valerate, which are salts of the above acids, or mixtures thereof can be used. Use of this acid (or its salt) improves the dispersibility of the produced magnesium hydroxide, but if the acid has 5 or more carbon atoms, it will not dissolve in water and will not be effective.

The higher the concentration of acid or salt added, the faster the reaction. Therefore, their concentration can be determined based on the operability and economy of the reaction, but generally 0.01 to 0.5 mol.
/I is preferable, more preferably 0.05 to 0.
It is 2mof/I. However, in the case where the raw material magnesia contains an acid-soluble component such as CaO as an impurity in a reaction method using an acid, it is preferable to use an acid or salt concentration equal to or higher than the equivalent amount.

Water needs to be present in the slurry for hydration of the magnesia. Therefore, it is most convenient to use a water suspension slurry. However, the reaction rate and dispersibility can also be adjusted by adding alcohol or the like to the slurry.

The reaction temperature may be selected depending on the activity of the magnesia used. In general, in the case of magnesia fired at a temperature of about 800 to 1000°C, the temperature is from room temperature to about 50°C,
For magnesia fired at temperatures above ℃, 90-100℃
It is preferable to carry out the reaction at a temperature of about 100%.

In the case of magnesia fired at 1400° C. or higher, the particle size of magnesia is preferably 100 μm or less, more preferably 50 μm or less, from the viewpoint of reaction time.

In order to disperse the raw material magnesia well in the solution and to prevent the produced magnesium hydroxide from agglomerating, the reaction is preferably carried out under stirring. The concentration of the raw material magnesia may be any value as long as it can be stirred, but from the viewpoint of operability and economy, it is preferably about 50 to 300 g/l.
Particularly preferred is 100 to 200 g/I.

Magnesium hydroxide obtained by the above method can be used as it is as a filler for synthetic resins, a sizing agent, etc., and can also be lightly calcined to produce magnesium oxide and used as an annealing agent for electrical steel sheets.

For these uses, magnesium hydroxide obtained by this method has a specific surface area of 1 to 15rd/9 and crystallites in the direction perpendicular to the (011) plane by X-ray diffraction of 200 to 150.
0A, the particle size measured by centrifugal sedimentation is 0.5 to 3 μm, and particularly suitable as a flame retardant for synthetic resins is 3 to 15-IIi/g, 300 to 1000 particles, and 1.8 to 2.5 μm.

When used as a filler for synthetic resins, compatibility with the resin and dispersibility in the resin are further improved by surface treatment with a metal carboxylate.

The surface treatment is performed by dissolving a carboxylic acid metal salt in a magnesium hydroxide slurry, which is simple and efficient. Although organic solvents such as alcohol and xylene can be used as the slurry solvent, it is preferable to use water because it is convenient. For example, the surface treatment may be performed by adding an aqueous solution of a carboxylic acid metal salt to a stirred aqueous magnesium hydroxide slurry. In this case, the concentration of carboxylic acid metal salt is
From the point of view of surface treatment effect and economy, 0゜1~1g/l
, more preferably 0.2 to 0.5 g/l. Also,
The concentration of magnesium hydroxide is preferably 50 to 2009/l.

The reaction is completed in several minutes to several tens of minutes by heating to about 50 to 100°C. As carboxylic acid metal salts,
unsaturated carboxylic acids, saturated carboxylic acids, monocarboxylic acids,
Although metal salts of various carboxylic acids such as dicarboxylic acids can be used, it is preferable to use an alkali metal salt having 8 or more carbon atoms, and more preferably an alkali metal salt having 12 or more carbon atoms. Among these, potassium stearate, sodium stearate, potassium oleate, sodium oleate, and the like are particularly preferred because they are inexpensive and easily soluble in water.

[Examples] Hereinafter, the present invention will be specifically explained using Examples and Comparative Examples.

Example 1 The magnesia clinker shown in Table 1 was mixed with 2009/I and propionic acid at a ratio of 0.2511101/l to form a water slurry, and the mixture was reacted at 100'C with stirring for 24 hours.

The resulting magnesium hydroxide slurry was sieved through a 16 μm mesh, filtered, washed with water, and dissolved in condensate to give a concentration of 100 g/l.

About 99% or more of the solid content in this slurry was magnesium hydroxide. Specific surface area of magnesium hydroxide and X
Table 2 shows the crystallite size (referred to as ε001) in the direction perpendicular to the (001) plane as determined by line diffraction.

This magnesium hydroxide slurry was heated to 80° C., and while stirring, sodium oleate was added to the slurry at a concentration of 0.49/l, and surface treatment was carried out for 1 hour. After filtering the slurry, 1
Dry at 20'C for 12 hours.

This surface-treated magnesium hydroxide was crushed, magnesium hydroxide 130 type RIBU, ethylene vinyl acetate 10
0 parts by weight at 140°C in a Banbury mixer.
The mixture was kneaded for 0 minutes to form pellets. This beret weighs 40kg
/cr/l, and molded into a sheet having a thickness of 2IrIIr1 at 160°C. JI using cut pieces from this sheet
A low temperature brittleness test was conducted according to S6301, and a tensile test was conducted according to JIS7113. Further, dispersibility was observed using an electron microscope.

These results are shown in Table 2. As a measure of the torque at the time of crosstalk, Table 2 shows the difference (A>) between the current value when the mixer is running idly and the current value 10 minutes after crosstalk.

Example 2 A water slurry was prepared by mixing 2009/l of the magnesia clinker shown in Table 1 and 0.5 mol/l of isobutyric acid, and the mixture was reacted at 100° C. for 24 hours with stirring.

The obtained magnesium hydroxide slurry was sieved through a 16 μm mesh, filtered, washed with water, and then dissolved in water to prepare a concentration of 100 g/l. About 99% or more of the solid content in this slurry was magnesium hydroxide.

Thereafter, surface treatment and tests were performed in the same manner as in Example 1. Table 2 shows the results of each measurement and test.

Example 3 A water slurry was prepared by mixing 2009/l of the magnesia clinker shown in Table 1 and 0.5 mol/l of n-butyric acid, and the mixture was reacted at 100° C. for 24 hours with stirring.

The obtained magnesium hydroxide slurry was sieved through a 16 μm mesh, filtered, washed with water, and then dissolved in water to prepare a slurry of 100 g/I. About 99% or more of the solid content in this slurry was magnesium hydroxide.

Thereafter, surface treatment and tests were performed in the same manner as in Example 1. Table 2 shows the results of each measurement and test.

Example 4 The magnesia clinker shown in Table 1 was mixed at a ratio of 2009/l and valeric acid at a ratio of 0.5 mol/I to form a water slurry, and the mixture was reacted at 100°C for 24 hours with stirring.

The obtained magnesium hydroxide slurry was sieved through a 16 μm mesh, filtered, washed with water, and then dissolved in water to prepare a concentration of 100 g/l. About 99% or more of the solid content in this slurry was magnesium hydroxide.

Thereafter, surface treatment and tests were performed in the same manner as in Example 1. Table 2 shows the results of each measurement and test.

Example 5 Magnesium hydroxide was synthesized in the same manner as in Example 2, and 0.4 g/l of sodium stearate was used instead of sodium oleate in Example 2, and the surface was treated in the same manner as in Example 2. I did this. The test results are shown in Table 2.

Comparative Example 1 Table 1. Magnesia clinker 2009/I and magnesium chloride were mixed at a ratio of 0.1 mol/I to form a water slurry, and the mixture was reacted at 100° C. for 24 hours with stirring.

The obtained magnesium hydroxide slurry was sieved through a 16 μm mesh, filtered, washed with water, and then dissolved in water to prepare a concentration of 100 g/l. About 99% or more of the solid content in this slurry was magnesium hydroxide.

Thereafter, surface treatment and tests were performed in the same manner as in Example 1. Table 2 shows the results of each measurement and test.

Comparative Example 2 The magnesia clinker shown in Table 1 was mixed with 200 CJ/I and formic acid at a ratio of 0.1 mol/l to form a water slurry, and the mixture was reacted at 100° C. for 24 hours with stirring.

The obtained magnesium hydroxide slurry was sieved through a 16 μm mesh, filtered, washed with water, and then dissolved in water to prepare a concentration of 100 g/l. About 99% or more of the solid content in this slurry was magnesium hydroxide.

Thereafter, surface treatment and tests were performed in the same manner as in Example 1. Table 2 shows the results of each measurement and test.

Table 1 Table 2 ■ Low-temperature embrittlement is F2O value [Effects of the invention] As explained above, the magnesium hydroxide produced by the method of the present invention has good dispersibility when kneaded into a resin, and the embrittlement of the resin composition. temperature becomes lower. That is, by the method of the present invention, magnesium hydroxide which is extremely excellent as a flame retardant for resins can be produced.

Claims (4)

[Claims] (1) A method for producing magnesium hydroxide, which comprises hydrating magnesia in a slurry in which a magnesium salt of a carboxylic acid represented by the general formula C_nH_2_n_+_1COOH (2≦n) is present. (2) The method for producing magnesium hydroxide according to claim (1), wherein in the general formula, 2≦n≦4. (3) Surface treatment of magnesium hydroxide obtained by hydrating magnesia in a slurry containing a magnesium salt of a carboxylic acid represented by the general formula C_nH_2_n_+_1COOH (where 2≦n) with a carboxylic acid metal salt. A method for producing surface-treated magnesium hydroxide, characterized by: (4) The method for producing surface-treated magnesium hydroxide according to claim (3), wherein in the general formula, 2≦n≦4.