JPH01320220A - Magnesium hydroxide and its production - Google Patents

Abstract

PURPOSE:To obtain powdered Mg(OH)2 useful flame retardant for resin, having specified physical properties by heating and aging fine Mg(OH)2 obtd. by adding an aq. soln. of Mg salt to an aq. alkali soln., in an autoclave. CONSTITUTION:The very fine Mg(OH)2 obtd. by adding the aq. soln. of Mg salt, preferably the aq. 8-35wt.% soln. of MgCl2, in 2-10wt.% in excess of NaOH to the aq. alkali soln., preferably 10-50wt.% NaOH soln., is heated preferably at 120-210 deg.C and aged in the autoclave to obtain the thick and roundish Ma(OH)2 particles having 0.7-1.3 the ratio of intensity between diffraction patterns of [001] face and [101] face by a powder X-ray diffraction method, 1-20m<2>/g BET specific surface area and 0.1-2.5mu mean particle size of primary particles.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to powdered magnesium hydroxide that is blended into a resin and used to make the resin composition flame retardant, and a method for producing the same.

[Prior art 1] At present, there is a strong demand for flame retardant properties for various synthetic resins due to their various fields of use. Among these, harmless and inexpensive flame retardants such as magnesium hydroxide and aluminum hydroxide are metal hydroxides are used.

However, magnesium hydroxide -i is agglomerated with a large number of fine particles, and even if it is blended into a synthetic resin, the dispersibility is extremely poor, so it cannot be used.

For this reason, magnesium hydroxide as a flame retardant is used in the form of crystalline, grain-grown hexagonal plates.

There are various methods for producing magnesium hydroxide used as a flame retardant, and a typical method consists of adding an alkali to an aqueous solution of a water-soluble magnesium salt. Industrially, magnesium chloride containing seawater or bittern is used as a magnesium source, and magnesium hydroxide obtained through a neutralization reaction using calcium hydroxide, sodium hydroxide, etc. as an alkali is used under pressure. It is matured and made into a product. According to powder X-ray diffraction, the magnesium hydroxide product thus obtained was [001
Intensity ratio of peaks between plane 1 and plane [1011 [001/[
101] is in the range of 1.6 to 8 and is recognized to be a thin plate-like crystal. By the way, the magnesium hydroxide kneaded into the resin changes to basic magnesium carbonate or magnesium carbonate under the action of moisture in the air and carbon dioxide gas, and not only does it no longer function as a flame retardant, but it also deteriorates on the surface of the wire. Phenomenon where white powder blows out (
There is an inherent drawback that chalking occurs which detracts from the appearance.

[Problems to be Solved by the Invention] However, even though the crystalline magnesium hydroxide is said to have good dispersibility as an additive for synthetic resins, the existing crystalline magnesium hydroxide is a plate-like crystal.
The dispersibility is insufficient, and there is still room for improvement.

By the way, the magnesium hydroxide kneaded into the resin changes to basic magnesium carbonate or magnesium carbonate under the action of moisture in the air and carbon dioxide gas, and not only does it no longer function as a flame retardant, but it also deteriorates on the surface of the wire. It has the inherent disadvantage that it causes a phenomenon in which white powder blows out (chalking), which impairs the appearance.

Since it is an inherent drawback, it cannot be avoided in principle, but it is possible to minimize this drawback as much as possible.

In other words, if the surface area per unit volume of magnesium hydroxide is small, the ratio of exposure to the outside air is small, and the Rt is also small. If magnesium hydroxide is made as close to a sphere as possible, the influence from the outside world will be reduced. This results in improved carbonation resistance and improved dispersibility.

Therefore, in magnesium hydroxide as a flame retardant,
In line with the demand for improved stability and dispersibility, crystal grains are required to be as thick or round as possible.

[Means for Solving the Problems] The present inventors have completed the present invention as a result of intensive research in view of the above-mentioned problems.

That is, the present invention is based on the intensity ratio [001]/[1011] of the diffraction lines of the [001] plane and the [101] plane in the powder X-ray diffraction method.
is in the range of 0.7 to 1.3 and the BET specific surface area is 1
It relates to magnesium hydroxide characterized in that it is ~20 m'/g.

Furthermore, the present invention provides powder
The intensity ratio [001]/[101,1 of the diffraction lines of the [001] plane and the [1011 plane] in the line diffraction method is in the range of 0.7 to 1.3, and the BET specific surface area is 1 to 20 m / g. Relates to a method for producing magnesium hydroxide.

[Function] As mentioned above, the magnesium hydroxide of the present invention has an intensity ratio of [0011 plane and [] of the diffraction line of the 011 plane, [001]/[101], or 0.7 to 13 in the X-ray diffraction method. and is characterized by a BET specific surface area of 1 to 20 m2/g.

Magnesium hydroxide having such characteristics is different from conventional thin hexagonal plate-shaped particles, and is a thick or rounded crystalline particle, which can be easily identified by electron term W1 mirror observation.

Therefore, the dispersibility is better than the conventional one.

To explain in more detail the method for producing magnesium hydroxide of the present invention, a sodium hydroxide aqueous solution is used as an alkaline aqueous solution, and an extremely fine magnesium hydroxide obtained by adding a magnesium chloride aqueous solution is heated and aged in an autoclave. It can be obtained by

The basic reaction formula of sodium hydroxide and magnesium chloride is as follows: 2NaOH + MgCb → 2NaOH + Mg (○H) 2 Sodium hydroxide is preferably used as an aqueous solution with a concentration of 10 to 50%, and magnesium chloride has a concentration of 8 to 35% as MgCl2. % aqueous solution.

When producing the magnesium hydroxide of the present invention, first,
An alkaline aqueous solution, such as sodium hydroxide, is placed in a container equipped with a stirring device, and a magnesium salt aqueous solution, such as magnesium chloride, is added over a period of 20 minutes to 2 hours at a temperature of 0 to 100°C. Preferably, the amount of indigo is in excess of 2 to 10% by weight relative to sodium hydroxide.

The fine gel-like magnesium hydroxide slurry obtained by the above reaction is heated and aged in an autoclave at a temperature of 120 to 210° C. for 1 to 8 hours without separating the mother liquor.

The specific surface area of magnesium hydroxide treated in an autoclave decreases as the aging temperature increases. Although the influence of time is relatively small, the specific surface area tends to decrease as the time increases.

In addition, the [001] plane and [101
] The peak intensity ratio [001]/[101] of the plane is 1.0±
It is in the range of 0.3, resulting in thick crystal grains.

After aging, the mother liquor of magnesium hydroxide is separated according to the usual method, washed with water, and then surface treated as necessary. filtration, drying,
It can be crushed into products.

When the crystal particles of the magnesium hydroxide of the present invention obtained in this way are observed with an electron microscope, it is found that conventional crystalline magnesium hydroxide has plate-like crystals, whereas the magnesium hydroxide of the present invention has a thick and round shape. It was observed that the primary particles had a certain average particle diameter in the range of approximately 0.1 to 2.5 μI, and the dispersibility in resin compositions etc. was also good.
Even when blended into resin compositions, etc., the yoking resistance is better than that of conventional products, making it suitable.

EXAMPLES] The magnesium hydroxide of the present invention will be further explained with reference to Examples below.

6.08 ky of 50% liquid caustic soda was placed in a 2.5N reaction vessel equipped with a stirrer. When 6.08 kg of water was added to this, the liquid temperature rose to 43°C. 6 Next, industrial magnesium chloride (Mg
C12・6H20) 70% aqueous solution L2.1.0kg
was added dropwise over about 30 minutes to prepare a fine magnesium hydroxide gel. This slurry was then transferred to a pressure vessel, heated to 170°C, and aged for 6 hours under a pressure of 8ky/an2. After cooling, the mother liquor was separated and washed until the amount of Cl ions in the P solution became less than sp ppm.

After passing through and washing, dry at 120℃ and crush with a swing hammer type crusher to powder magnesium hydroxide.
．． I got 14ky. For this magnesium hydroxide, B
Specific surface area measured by ET method was 6.1 m"/g
As measured by powder X-ray diffraction, it is a well-developed crystal grain, and the intensity of the peak due to the [001,] plane and [
101,] Ratio of the intensity of the peak due to the plane [001]/
[101] was 1.05.

Therefore, compared to conventional magnesium hydroxide, it was observed that it had characteristics as crystalline particles, but when it was observed with an electron microscope, it was found that the average particle diameter was approximately 0.5 μm with a thickness and roundness.
It was recognized that the particles were primary particles in the range of m.

Pour 304g of 50% by weight liquid caustic soda into a 2R container equipped with a stirring device, and add Mg while stirring at room temperature.
1.655 g of bittern liquid containing 11.51% by weight as Cβ2 was added over 45 minutes to prepare a fine gel-like magnesium hydroxide.Next, this gel-like magnesium hydroxide was transferred to a pressure vessel, and the following settings were made. Aging was carried out using a program in which the temperature was raised for 3 hours to reach the pressure, the set pressure was maintained for 6 hours, and then the heat source was turned off and the temperature was left to cool.
Next, after cooling in a conventional manner, the contents were taken out, and ta was separated, washed with water, filtered, dried, and ground to obtain magnesium hydroxide. Table 1 below shows the relationship between aging pressure, specific surface area of magnesium hydroxide, and peak intensity ratio of [001] plane and [101] plane by powder X-ray diffraction for samples obtained under each condition. do.

/' Chopsticks--L-j tense 2 2 106.6 13.2
0.803 4 107.2
10.5 0.824 6
107.6 7.3 0.865
8 1.04.5 6.5
0.966 10 106.9 4
．． 5 1.017 12 1.0
6.3 3.5 1.068 1
4 106.0 2.9 1.1
605.1 g of a commercially available 70% by weight aqueous solution of magnesium chloride was placed in a 21 reaction vessel equipped with a 4 m stirrer, and 20 g was added to the magnesium chloride aqueous solution while stirring at room temperature.
Using a metering pump, 760 g of a wt % aqueous sodium hydroxide solution was added dropwise over 56 minutes. The obtained magnesium hydroxide precipitate was transferred to an autoclave, and 8,5
Aged for 4 hours at a pressure of kg/am2. After cooling, remove the contents from the autoclave, separate the mother liquor, wash with water,
Filtration, drying and pulverization yielded 106.5 g of magnesium hydroxide powder. The specific surface area of the obtained powder was measured by the BET method and was found to be 8.6 aa2/g, and the measurement by the powder
The peak intensity ratio [001,]/[101] with respect to the 011 plane was 2.37.

When this material was observed using an electronic microscope, it was found that it was a very thin plate-like particle.

11.51% by weight of bittern 1655 was charged into a reaction vessel equipped with a stirring device, and 304 g of 50% by weight liquid caustic soda was quantitatively added to this bittern while stirring at room temperature. The mixture was dripped using a pump over a period of 41 minutes. The obtained precipitate of magnesium hydroxide is charged into a crepe together with the mother liquor and aged at a pressure of 1.0 kg/cm2 for 4 hours. After cooling, take out the contents and separate the mother liquor.
Washing with water, filtration, drying and pulverization yielded 105.3y of magnesium hydroxide powder. The specific surface area of this powder by BET method is 6.3 m2/g, and the peak intensity ratio of [001] plane and [101] plane by powder X-ray diffraction method is [00
1]/[101] was 1.88.

[Effects of the Invention] As can be seen from the above-mentioned Examples and Comparative Examples, conventional magnesium hydroxide produced by adding a sodium hydroxide aqueous solution to a magnesium chloride aqueous solution has a [001] plane as measured by powder X-ray diffraction. It was observed that many of the particles were oriented, the peak intensity was high, and the thickness of the magnesium hydroxide particles was not relative to the diameter.

On the other hand, in the case of passing through very fine magnesium hydroxide obtained by adding a magnesium salt aqueous solution to an alkaline aqueous solution as in the present invention, the [0011 plane and [101] plane measured by powder X-ray diffraction method. As can be seen from the peak intensity ratio, thick and well-developed crystal grains are obtained.

When the magnesium hydroxide of the present invention is blended into a resin composition or the like, it has good dispersibility, acts suitably as a flame retardant, and eliminates problems such as chalking.

Patent applicant Nihon Kagaku Kogyo Co., Ltd. Procedural amendment damage July 25, 1988 [1

Claims (1)

[Claims] 1. [001] plane and [101] in powder X-ray diffraction method
The intensity ratio [001]/[101] of the surface diffraction line is 0.7 to
1.3 and the BET specific surface area is 1 to 20 m^
2/g of magnesium hydroxide. 2. The magnesium hydroxide according to claim 1, wherein the magnesium hydroxide has an average primary particle diameter of 0.1 to 2.5 μm based on electron microscopic observation, and is thick and rounded. 3. Diffraction lines of [001] plane and [101] plane in powder X-ray diffraction method, which involves heating and aging very fine magnesium hydroxide obtained by adding a magnesium salt aqueous solution to an alkaline aqueous solution in an autoclave. The intensity ratio of [
001]/[101] is in the range of 0.7 to 1.3, and the BET specific surface area is in the range of 1 to 20 m^2/g. 4. Add 8-35% by weight of magnesium chloride as MgCl_2 into a 10-50% by weight sodium hydroxide solution in an amount such that magnesium chloride is in excess of 2-10% by weight relative to the sodium hydroxide to form a very fine particle. The method for producing magnesium hydroxide according to claim 3, wherein a magnesium hydroxide slurry is obtained, and then the slurry is heated and aged in an autoclave at a temperature of 120 to 210°C.