JPWO2008120746A1 - Magnesium hydroxide powder and method for producing the same - Google Patents

Abstract

Magnesium hydroxide powder composed of spherical secondary particles formed from scale-like primary particles and having an average particle diameter in the range of 1.0 to 4.8 μm and a BET specific surface area in the range of 1 to 10 m 2 / g is It has low hygroscopicity and is suitable for use as a flame retardant for resins.

Description

  The present invention relates to a magnesium hydroxide powder having a low BET specific surface area and a method for producing the same.

  Magnesium hydroxide powder is used in various applications, and one of its uses is as a flame retardant for resins, particularly resin compositions used as coating materials for electric wires and cables. Examples of flame retardant resins include polyethylene, polypropylene, ethylene-propylene rubber (EPM), ethylene-propylene-diene terpolymer blend (EPDM), ethylene-ethyl acrylate copolymer (EEA), ethylene -Polyolefins such as vinyl acetate copolymers.

As an industrial production method of magnesium hydroxide powder, it was formed from scaly primary particles by introducing an alkali source such as lime milk into seawater and reacting magnesium ions in the seawater with an alkali source. In general, a magnesium hydroxide slurry in which spherical secondary particles are dispersed is obtained, and then the magnesium hydroxide slurry is subjected to treatments such as washing and dehydration, and then dried to obtain a powder. This method for producing magnesium hydroxide powder using seawater as the magnesium source (hereinafter sometimes referred to as the seawater method) is an advantageous method in terms of production cost. However, the magnesium hydroxide powder obtained by the seawater method is generally composed of spherical secondary particles formed from scale-like primary particles and having an average particle diameter in the range of 1.0 to 4.8 μm, and has a BET specific surface area. Is as high as 11 to 50 m ² / g, so that the hygroscopicity tends to be high. When moisture-absorbed magnesium hydroxide powder is used as a flame retardant for resin compositions such as wire and cable coating materials, moisture absorbed in magnesium hydroxide powder is evaporated and foamed by heat during kneading with resin. It may become a factor which impairs the external appearance of the resin composition obtained. For this reason, the development of magnesium hydroxide powder having low hygroscopicity, that is, low specific surface area is underway.

Patent Document 1 discloses a magnesium hydroxide powder having a specific surface area of 10 m ² / g or less, comprising spherical secondary particles having an average particle diameter of 5 to 500 μm formed by agglomeration of flaky magnesium hydroxide primary particles. It is disclosed. According to this Patent Document 1, the magnesium hydroxide powder comprises an aqueous solution containing a water-soluble magnesium salt and ammonia, a crystallization load of magnesium hydroxide of 500 kg / m ³ · h or less, and a crystallization apparatus. It is said that it can be produced by reacting under a condition that the magnesium hydroxide slurry concentration is 1 to 60 wt%.

In Patent Document 2, the BET specific surface area is less than about 10 m ² / g, the average particle size is about 0.5 to 10.0 microns, and the number of particles exceeding 10 microns is less than about 0.5%. Discloses a flame retardant magnesium hydroxide powder having an approximately oval cross section. According to Patent Document 2, the above magnesium hydroxide powder is obtained by adding an excess ammonia raw material in terms of molecular weight to a magnesium chloride solution to form a magnesium hydroxide precipitate. It is said that it can manufacture by the method including the process to make.
JP-A 61-168522 Special table 2001-508015 gazette

Magnesium hydroxide powder having a spherical or oval particle shape and a BET specific surface area of 10 m ² / g or less is disclosed in Patent Document 1 and Patent Document 2 described above. Among these, since the magnesium hydroxide powder described in Patent Document 1 has a large average particle diameter of secondary particles, when used as a flame retardant, the resulting resin composition has a rough appearance and stress is concentrated. It tends to be weak and weak. Further, the magnesium hydroxide powder described in Patent Document 2 is fine but not spherical, so there is a problem in dispersibility in the resin, and it requires hot water treatment for its production, and the production process is complicated. Manufacturing costs tend to be high.
Accordingly, an object of the present invention is to provide a magnesium hydroxide powder comprising fine spherical particles having a low BET specific surface area, which is particularly suitable for use as a flame retardant for resins.

The present inventor has prepared a magnesium hydroxide slurry obtained as an intermediate product in a seawater method, or a hydrous magnesium hydroxide solid having a water content of 10 to 50% by mass obtained by dehydrating the magnesium hydroxide slurry. After drying gently under drying conditions that require a time of 2 hours or more until the rate becomes 5% by mass to obtain a hydrous magnesium hydroxide powder having a moisture content of 1 to 5% by mass, the moisture content becomes 0.5% by mass or less. It was found that a magnesium hydroxide powder having a BET specific surface area as low as 1 to 10 m ² / g and a spherical shape can be obtained by drying to a low temperature. In addition, the present inventor used magnesium hydroxide powder (water content: 0.5% by mass or less) having a BET specific surface area of 11 to 50 m ² / g obtained by the seawater method until the water content became 1% by mass. By contacting with water vapor under moisture absorption conditions that require more than a minute, and gradually setting the moisture content of the magnesium hydroxide powder to 1% by mass or more, and then drying until the moisture content is 0.5% by mass or less, It has been found that magnesium hydroxide powder having a BET specific surface area as low as 1 to 10 m ² / g and having a spherical shape can be obtained.

Therefore, the present invention comprises spherical secondary particles formed from scale-like primary particles and having an average particle diameter in the range of 1.0 to 4.8 μm, and a BET specific surface area in the range of 1 to 10 m ² / g. In the magnesium hydroxide powder.

Preferred embodiments of the magnesium hydroxide powder of the present invention are as follows.
(1) When the length of the longest diameter among the diameters of the spherical secondary particles in three directions orthogonal to each other is 1, the lengths of the other two diameters are in the range of 0.6 to 1, respectively. .
(2) The maximum value of the log differential pore volume in pores having a pore diameter in the range of 3 to 5 nm is in the range of 0.001 to 0.14 cm ³ / g.
(3) The surface is treated with a fatty acid, a fatty acid soap, or a silane coupling agent.
(4) The above fatty acid, fatty acid soap or silane coupling agent is contained in a range of 0.1 to 10 parts by mass with respect to 100 parts by mass of magnesium hydroxide.

  The magnesium hydroxide powder of the present invention can be used particularly advantageously as a flame retardant for resins. Therefore, the present invention also resides in a resin composition in which the magnesium hydroxide powder of the present invention is kneaded.

  The present invention also provides a magnesium hydroxide slurry in which spherical secondary particles formed from scale-like primary particles obtained by reacting magnesium ions in seawater with an alkali source are dispersed, or the hydroxide A water-containing magnesium hydroxide solid substance having a water content of 10 to 50% by mass obtained by dehydrating the magnesium slurry is dried under a drying condition that requires 2 hours or more until the water content becomes 5% by mass, The magnesium hydroxide powder of the present invention, comprising obtaining a water-containing magnesium hydroxide powder having a water content of 1 to 5% by mass, and then drying the water-containing magnesium hydroxide powder until the water content becomes 0.5% by mass or less. There is also a manufacturing method.

  In the manufacturing method of the magnesium hydroxide powder of the present invention, the drying conditions of the magnesium hydroxide slurry or the hydrated magnesium hydroxide solid are that the temperature is 50 to 100 ° C. and the relative humidity is 50 to 85% RH. preferable.

The present invention is further produced from a magnesium hydroxide slurry obtained by reacting magnesium ions in seawater with an alkali source, in which spherical secondary particles formed from scaly primary particles are dispersed, It consists of spherical secondary particles formed from scale-like primary particles and having an average particle diameter in the range of 1.0 to 4.8 μm, and has a BET specific surface area in the range of 11 to 50 m ² / g, and has a water content The magnesium hydroxide powder having a water content of 0.5% by mass or less is brought into contact with water vapor under moisture absorption conditions that require a time of 30 minutes or more until the water content becomes 1% by mass. The magnesium hydroxide of the present invention is obtained by drying a hydrous magnesium hydroxide powder until the water content becomes 0.5% by mass or less. There is also the end of the manufacturing method.

  In the manufacturing method of the magnesium hydroxide powder of the said invention, it is preferable that the moisture absorption conditions of a magnesium hydroxide powder are conditions whose temperature is 10-100 degreeC and relative humidity is 50-98% RH.

Since the magnesium hydroxide powder of the present invention has a low BET specific surface area and low hygroscopicity, it is stable with little hygroscopicity over a long period of time, and is composed of fine spherical secondary particles, so that it can be dispersed in a resin. Is expensive. Therefore, the magnesium hydroxide powder of the present invention is particularly suitable as a flame retardant for resins.
Further, by using the production method of the present invention, magnesium hydroxide powder produced by an industrially inexpensive seawater method, or magnesium hydroxide slurry or hydrous magnesium hydroxide solid product obtained as an intermediate product in the seawater method As a raw material, it is possible to produce a magnesium hydroxide powder composed of fine spherical secondary particles having a low BET specific surface area and suitable for use as a flame retardant for resins.

The magnesium hydroxide powder of the present invention comprises spherical secondary particles formed from scale-like primary particles and having an average particle diameter in the range of 1.0 to 4.8 μm, and has a BET specific surface area of 1 to 10 m ² / It is in the range of g. The average particle diameter of the spherical secondary particles is preferably in the range of 1.0 to 4.5 μm, and particularly preferably in the range of 1.2 to 4.0 μm. The BET specific surface area is preferably in the range of 2-9 m ² / g.

  In the magnesium hydroxide powder of the present invention, the secondary particles of magnesium hydroxide are spherical when the length of the longest diameter among the diameters of the secondary particles in three directions orthogonal to each other is set to 1. The lengths of the two diameters are in the range of 0.6 to 1, preferably 0.8 to 1.

The magnesium hydroxide powder of the present invention can be produced, for example, by the following method (1) or (2).
(1) Magnesium hydroxide slurry obtained by dispersing spherical secondary particles formed from scaly primary particles obtained as an intermediate product in the seawater method, or obtained by dehydrating the magnesium hydroxide slurry A water-containing magnesium hydroxide solid having a water content of 10 to 50% by mass is dried under drying conditions that require 2 hours or more until the water content reaches 5% by mass, and a water-containing hydroxide having a water content of 1 to 5% by mass. A method comprising obtaining a magnesium powder and then drying the hydrated magnesium hydroxide powder until the moisture content is 0.5% by mass or less.
(2) It consists of spherical secondary particles having an average particle diameter in the range of 1.0 to 4.8 μm, formed from scale-like primary particles produced by the seawater method, and a BET specific surface area of 11 to 50 m ^2. / G or less and a moisture content of 0.5% by mass or less is brought into contact with water vapor under moisture absorption conditions that require 30 minutes or more until the moisture content becomes 1% by mass. A method comprising obtaining a hydrous magnesium hydroxide powder having a rate of 1% by mass or more (particularly, 5% by mass or less) and then drying the hydrous magnesium hydroxide powder until the water content becomes 0.5% by mass or less.

  In the method (1), first, a mixed solution of seawater and an alkali source is prepared, and magnesium ions in the seawater and an alkali source are reacted to precipitate magnesium hydroxide scaly primary particles. The precipitated flaky primary particles are circulated in the mixed solution, and the flaky primary particles are aggregated and grown as spherical secondary particles, thereby obtaining a magnesium hydroxide slurry in which spherical secondary particles are dispersed. be able to.

  The seawater used as the magnesium source is preferably decarboxylated in advance so that the dissolved carbonate ion concentration is 20 mass ppm or less (in terms of carbon dioxide). As the decarboxylation method, lime milk (calcium hydroxide slurry) is added to seawater to fix carbonate ions as calcium carbonate, or an acidic solution such as hydrochloric acid or sulfuric acid is added to seawater to adjust the pH of the seawater. After setting to 4 or less, a method of removing carbonate ions as carbon dioxide gas by aeration treatment of seawater can be used. Note that the former decarboxylation method using lime milk is a more preferable method because silicon and aluminum components in seawater are adsorbed on the generated calcium carbonate and the content thereof is reduced.

Lime milk can be used as an alkali source mixed with seawater.
The mixing ratio of the seawater and the alkali source is such that the reaction rate of magnesium ions in the seawater (molar percentage of magnesium ions in the seawater that reacts with the alkali source and precipitates as magnesium hydroxide particles) is 50 to 110%. It is preferable that the ratio is 70 to 90%. If the reaction rate is too low, it is economically disadvantageous from the viewpoint of the yield of magnesium hydroxide powder.

  In the method (1), the magnesium hydroxide slurry produced as described above is used as it is, or by subjecting it to normal dehydration treatment such as filtration, Then, it is put in a drying apparatus and dried under a drying condition that requires 2 hours or more, preferably 4 hours or more, more preferably 24 hours or more and 200 hours or less until the water content becomes 5% by mass. A hydrous magnesium hydroxide powder having a rate of 1 to 5% by mass is obtained. The time until the moisture content reaches 5% by mass can be adjusted by the temperature and relative humidity in the drying apparatus. The temperature in the drying apparatus is generally in the range of 50-100 ° C, preferably in the range of 60-90 ° C, and the relative humidity is generally in the range of 50-85% RH. The concentration of the magnesium hydroxide slurry before drying is generally in the range of 10 to 45 mass%. Rather than drying the magnesium hydroxide slurry as it is, it is preferable to dry it after making it into a hydrous magnesium hydroxide solid.

  The water-containing magnesium hydroxide powder having a water content of 1 to 5% by mass obtained as described above is then heated in a hot air dryer (for example, a box dryer, a flash dryer, a band-type aeration dryer, a fluidized bed dryer). , Rotary drier) and conduction heat transfer drier (for example, cylindrical drier, disk drier) and the like, and dried until the water content is 0.5 mass% or less. The drying temperature is generally 100 ° C. or higher, preferably 110 to 150 ° C. Although there is no restriction | limiting in particular in drying time, Generally it is 0.01 to 2 hours.

In the method (2), spherical secondary particles having an average particle diameter in the range of 1.0 to 4.8 μm formed from magnesium hydroxide powder produced by the seawater method, that is, scaly primary particles. A magnesium hydroxide powder having a BET specific surface area of 11 to 50 m ² / g and a water content of 0.5% by mass or less is used as a starting material.

  As the magnesium hydroxide powder used as a raw material, the scale-like primary particles of magnesium hydroxide precipitated by reacting magnesium ions in seawater with an alkali source in the same manner as in the above method (1), spherical secondary After agglomerating and growing into particles to obtain a magnesium hydroxide slurry, this is treated with washing, dehydration, etc. to obtain a hydrous magnesium hydroxide solid having a water content of 10 to 50% by mass, and then a hot air dryer and a conductive What put water content into 0.5 mass% or less by putting in normal drying equipments, such as a heat transfer drier, and drying for 0.01 to 2 hours at the temperature of 100 ° C or more, preferably 110 to 150 ° C. It can be preferably used.

  In the method (2), the raw material magnesium hydroxide powder (water content: 0.5% by mass or less) is used for 30 minutes or more, preferably 2 hours or more, more preferably, until the water content becomes 1% by mass. By contact with water vapor under moisture absorption conditions requiring a time of 24 hours or more and 200 hours or less, a water-containing magnesium hydroxide powder having a water content of 1% by mass or more, preferably 2% by mass or more, more preferably 5% by mass or less is obtained. Specifically, a raw magnesium hydroxide powder having a water content of 1% by mass or more is brought into contact with a gas containing water vapor in a state suspended in an air stream or in a fluidized bed or in a stationary state. Get. The time until the water content becomes 1% by mass or more can be adjusted by the relative humidity or temperature of the water vapor-containing gas (usually air) brought into contact with magnesium hydroxide. The conditions for absorbing the magnesium hydroxide powder are as follows. The temperature is generally 10 to 100 ° C., preferably 50 to 90 ° C., and the relative humidity is generally 50 to 98% RH.

  The water-containing magnesium hydroxide powder having a water content of 1% by mass or more obtained as described above is then placed in a normal drying apparatus such as a hot air dryer or a conductive heat transfer dryer, so that the water content is 0.5. Dry until mass% or less. The drying temperature is generally 100 ° C. or higher, preferably 110 to 150 ° C. Although there is no restriction | limiting in particular in drying time, Generally it is 0.01 to 2 hours.

The magnesium hydroxide powder of the present invention obtained by the above method has a log differential pore volume in pores having a pore diameter in the range of 3 to 5 nm as compared with magnesium hydroxide powder produced by a normal seawater method. The maximum value of is low. Since the pores having a pore diameter in the range of 3 to 5 nm correspond to pores formed between the primary particles of magnesium hydroxide, the magnesium hydroxide powder of the present invention was produced by a normal seawater method. Compared to magnesium hydroxide powder, the BET specific surface area is low and the hygroscopicity is low because the fine pore volume between primary particles is small. In the magnesium hydroxide powder of the present invention, the maximum value of the log differential pore volume in the pores having a pore diameter in the range of 3 to 5 nm is generally in the range of 0.001 to 0.14 cm ³ / g, preferably 0.00. It is in the range of 005 to 0.10 cm ³ / g.

  The magnesium hydroxide powder of the present invention itself has a characteristic of low hygroscopicity compared to magnesium hydroxide powder produced by a normal seawater method, but in order to further reduce the hygroscopicity The surface may be treated with a fatty acid, a fatty acid soap or a silane coupling agent. The fatty acid, the fatty acid soap and the silane coupling agent are preferably contained in a range of 0.1 to 10 parts by mass with respect to 100 parts by mass of magnesium hydroxide. Examples of fatty acids include stearic acid and oleic acid. The fatty acid soap is preferably a sodium salt or a potassium salt.

  The magnesium hydroxide powder of the present invention can be advantageously used as a flame retardant for a resin composition used as a coating material for resins, particularly electric wires and cables. Examples of flame retardant resins include polyethylene, polypropylene, ethylene-propylene rubber (EPM), ethylene-propylene-diene terpolymer blend (EPDM), and ethylene-ethyl acrylate copolymer (EEA). And polyolefins such as ethylene-vinyl acetate copolymer. The compounding quantity of the magnesium hydroxide powder to these resins is generally in the range of 10 to 150 parts by mass, preferably in the range of 30 to 100 parts by mass with respect to 100 parts by mass of the resin.

  The resin composition containing magnesium hydroxide powder of the present invention kneads the resin and magnesium hydroxide powder using a conventional kneader such as a Banbury mixer, tumbler, pressure kneader, kneading extruder, twin screw extruder or the like. Can be manufactured. The resin composition containing the magnesium hydroxide powder of the present invention may optionally contain an inorganic filler such as talc, a lubricant such as silicone oil or fatty acid, a surfactant such as silane coupling agent or fatty acid soap, a plasticizer, and a softening agent. Various additives used for usual resin compositions such as an agent, an antioxidant, a colorant, an antioxidant, an ultraviolet absorber, a stabilizer, and a crosslinking agent can be included.

  In this example, the moisture content, the average secondary particle diameter, the sphericity of the secondary particles, the maximum value of the log differential pore volume and the moisture absorption characteristics in the pores having a pore diameter in the range of 3 to 5 nm are as follows. It was measured.

[Moisture content]
5 g of a sample is put into a moisture meter (MX-50, manufactured by A & D Co., Ltd.), heated at a temperature of 180 ° C., and the mass reduction rate when the mass reduction reaches equilibrium is calculated as the moisture content. .

[Average secondary particle size]
0.5 g of a sample is put into 50 mL of ethanol, and a dispersion treatment is performed for 2 minutes under the condition of an output of 200 μA using an ultrasonic homogenizer to prepare a magnesium hydroxide suspension. Next, the volume-based average particle diameter of the magnesium hydroxide particles contained in the magnesium hydroxide suspension is determined by a laser diffraction scattering method particle size distribution analyzer (Microtrac particle size distribution measuring device 9320HRA (X-100), manufactured by Nikkiso Co., Ltd.). ) To measure.

[Sphericality of secondary particles]
The sample stage angle of the scanning electron microscope (SEM) is set to 0 degree (horizontal), the magnesium hydroxide secondary particles are photographed, the diameter of the secondary particles is determined, and the length thereof is measured. Taking the direction in which the diameter is measured as the rotation axis, the sample stage angle is inclined +45 degrees from the horizontal position, and the magnesium hydroxide secondary particles are photographed, and the diameter of the secondary particles in the direction perpendicular to the rotation axis is measured. Next, the sample stage angle is tilted by −45 degrees from the horizontal position, the magnesium hydroxide secondary particles are photographed, and the diameter of the secondary particles in the direction perpendicular to the rotation axis is measured. Among the diameters of the magnesium hydroxide secondary particles measured at sample stage angles of 0 °, + 45 °, and −45 °, the longest diameter is X = 1, the next longest length Y, and the shortest diameter. Is calculated as a relative value.

[Maximum log differential pore volume]
A desorption isotherm was measured by a nitrogen gas adsorption method using a fully automatic gas adsorption amount measuring device (Autosorb-3B) manufactured by Quantachrome Co., Ltd. The log differential pore volume of pores having a pore diameter in the range of 3 to 5 nm based on the above is calculated, and the maximum value is obtained.

[Hygroscopic properties]
Magnesium hydroxide powder is put into a thermo-hygrostat set at a temperature of 30 ° C. and a relative humidity of 80% RH. The mass of the magnesium hydroxide powder is measured every 30 minutes until 180 minutes immediately after the addition and every 60 minutes thereafter. Measure and calculate the mass increase rate as the moisture absorption rate.

[Example 1]
(1) Production of hydrous magnesium hydroxide solid matter Lime milk is added to seawater having a dissolved carbonate ion concentration of 80 mass ppm in terms of carbon dioxide, and the dissolved carbonate ions are precipitated as calcium carbonate. After reducing to 10 mass ppm in terms of conversion, it was filtered with a sand filter to remove calcium carbonate. Lime milk is added to seawater in which the content of dissolved carbonate ions is reduced to a rate at which the reaction rate of magnesium hydroxide ions contained in the seawater is 80% to prepare a mixed solution. I put it in thickener. In the thickener, the precipitated magnesium hydroxide scaly primary particles were circulated, and the scaly primary particles were agglomerated and grown into spherical secondary particles to obtain a magnesium hydroxide slurry in which the spherical secondary particles were dispersed. . This magnesium hydroxide slurry was extracted from the bottom of the thickener, washed with water to remove residual salt, and then suction filtered with Nutsche to obtain a hydrous magnesium hydroxide solid having a water content of 33.5% by mass.

(2) Production of magnesium hydroxide powder The hydrous magnesium hydroxide solid was placed in a thermo-hygrostat set at a temperature of 85 ° C. and a relative humidity of 65% RH and allowed to stand for 48 hours. % Hydrous magnesium hydroxide powder was obtained (the time until the water content became 5% by mass was about 30 hours). Next, the hydrous magnesium hydroxide powder was placed in a box dryer set at a temperature of 120 ° C. and dried for 2 hours. The obtained magnesium hydroxide powder had a water content of 0.5% by mass or less.

  The particle shape of the obtained magnesium hydroxide powder was observed using a scanning electron microscope (SEM). FIG. 1 shows an SEM photograph. From the photograph in FIG. 1, it was confirmed that the magnesium hydroxide powder was composed of spherical secondary particles formed by agglomeration of scaly primary particles.

  The chemical component of the obtained magnesium hydroxide powder, the BET specific surface area, the average secondary particle diameter, the maximum value of the log differential pore volume in the pores having a pore diameter in the range of 3 to 5 nm, and the sphericity of the secondary particles Table 1 shows. The measurement result of the hygroscopic property of the magnesium hydroxide powder is shown in FIG.

[Example 2]
A water-containing magnesium hydroxide solid product having a water content of 33.5% by mass produced in the same manner as in Example 1 (1) was placed in a box-type dryer set at a temperature of 120 ° C. and dried for 1 hour to obtain a water content. Was made into magnesium hydroxide powder of 0.5 mass% or less. This magnesium hydroxide powder was placed in a thermo-hygrostat set at a temperature of 80 ° C. and a relative humidity of 80% RH, and allowed to stand for 24 hours. The magnesium hydroxide powder after standing was a water-containing magnesium hydroxide powder having a water content of 2.1% by mass. Next, the hydrous magnesium hydroxide powder was placed in a box dryer set at a temperature of 120 ° C. and dried for 2 hours. The obtained magnesium hydroxide powder had a water content of 0.5% by mass or less.

  As a result of observing the particle shape of the obtained magnesium hydroxide powder using a scanning electron microscope (SEM), it was confirmed that spherical secondary particles formed by aggregation of scaly primary particles were formed.

  The chemical component of the obtained magnesium hydroxide powder, the BET specific surface area, the average secondary particle diameter, the maximum value of the log differential pore volume in the pores having a pore diameter in the range of 3 to 5 nm, and the sphericity of the secondary particles Table 1 shows. Moreover, the measurement result of the moisture absorption characteristic of magnesium hydroxide powder is shown in FIG.

[Comparative Example 1]
(1) Manufacture of hydrous magnesium hydroxide solids Water contained in seawater in which the dissolved carbonate ion concentration was reduced to 10 mass ppm in terms of carbon dioxide in the same manner as in Example 1 (1) Lime milk was added at a rate that the reaction rate of magnesium oxide ions was 90% to prepare a mixed solution, and the mixed solution was put into a thickener. In the thickener, the precipitated magnesium hydroxide scaly primary particles were circulated, and the scaly primary particles were agglomerated and grown into spherical secondary particles to obtain a magnesium hydroxide slurry in which the spherical secondary particles were dispersed. . The magnesium hydroxide slurry was extracted from the bottom of the thickener, washed with water to remove residual salt, and then suction filtered with Nutsche to obtain a water-containing magnesium hydroxide solid having a water content of 38.5% by mass.

(2) Production of Magnesium Hydroxide Powder The hydrous magnesium hydroxide solid was placed in a box dryer set at a temperature of 120 ° C. and dried for 1 hour. The obtained magnesium hydroxide powder had a water content of 0.5% by mass or less.

  As a result of observing the particle shape of the obtained magnesium hydroxide powder using a scanning electron microscope (SEM), it was confirmed that spherical secondary particles formed by aggregation of scaly primary particles were formed.

  The chemical component of the obtained magnesium hydroxide powder, the BET specific surface area, the average secondary particle diameter, the maximum value of the log differential pore volume in the pores having a pore diameter in the range of 3 to 5 nm, and the sphericity of the secondary particles Table 1 shows. Moreover, the measurement result of the moisture absorption characteristic of magnesium hydroxide powder is shown in FIG.

  As can be seen from the results of FIG. 2, the magnesium hydroxide powder having a BET specific surface area within the range of the present invention has low hygroscopicity.

[Example 3]
In a 3 L glass beaker, 2000 g of pure water was added and heated to 70 ° C., and then 2.5 g of sodium stearate (Non-Sal SN-15, manufactured by NOF Corporation) was added as a surface treatment material. After that, it was dissolved by stirring. Into this sodium stearate aqueous solution, 100 g of the magnesium hydroxide powder produced in Example 2 was added and stirred for 1 hour while maintaining the temperature at 70 ° C. to disperse the magnesium hydroxide powder in the sodium stearate aqueous solution. The surface of the magnesium hydroxide powder was treated with stearic acid.
The magnesium hydroxide dispersion was suction filtered with a Nutsche, and the obtained magnesium hydroxide-containing solid content was washed with 20 times the water of the solid content. Next, the solid content after washing was dried for 12 hours at a temperature of 120 ° C. in a box dryer, and then crushed by a sample mill. In the obtained magnesium hydroxide powder, 2.3 parts by mass of the surface treatment agent was adhered to 100 parts by mass of magnesium hydroxide.
The moisture absorption characteristics of the surface treated magnesium hydroxide powder are shown in FIG. The moisture absorption after 360 minutes was 0.5% by mass, which was about 40% of the magnesium hydroxide powder before the surface treatment (Example 2).

[Example 4]
The condition of a rotation speed of 60 rpm in a Brabender plastograph in which 100 parts by mass of the surface-treated magnesium hydroxide obtained in Example 3 and 100 parts by mass of an ethylene-ethyl acrylate copolymer (EEA) were heated to a temperature of 170 ° C. And kneading for 5 minutes with a roll heated to a temperature of 150 ° C., and further kneading with a kneader at a temperature of 160 ° C. to obtain a resin composition. The obtained resin composition was pressure-molded at a temperature of 160 ° C. to obtain resin composition sheets having a thickness of 1 mm and 3 mm.

  The resin composition sheet obtained as described above was measured for melt flow index (MFI), tensile stress at break, elongation and oxygen index. As a result, MFI was 0.25 g / 10 min (measurement temperature 190 ° C., measurement load 2.16 kg), breaking tensile stress was 9.0 MPa, elongation was 850%, and oxygen index was 26.0.

  A 1 mm thick resin composition sheet was used for measurement of MFI, breaking tensile stress and elongation, and a 3 mm thick resin composition sheet was used for measurement of oxygen index. The breaking tensile stress and elongation were measured by a method based on JIS-K-7113 (using test piece No. 1 dumbbell). The oxygen index was measured by a method based on JIS-K-7201.

2 is a scanning electron micrograph of magnesium hydroxide powder produced in Example 1. FIG. It is a graph which shows the measurement result of the moisture absorption characteristic of the magnesium hydroxide powder manufactured in Examples 1-3 and Comparative Example 1.

Claims (12)

Magnesium hydroxide powder comprising spherical secondary particles having an average particle diameter in the range of 1.0 to 4.8 μm and a BET specific surface area in the range of 1 to 10 m ² / g, formed from scale-like primary particles. .   2. The spherical secondary particles have a length of the other two diameters in the range of 0.6 to 1, respectively, when the length of the longest diameter among the diameters in three directions orthogonal to each other is 1. 2. Magnesium hydroxide powder described in 1. 2. The magnesium hydroxide powder according to claim 1, wherein the maximum value of the log differential pore volume in pores having a pore diameter in the range of 3 to 5 nm is in the range of 0.001 to 0.14 cm ³ / g.   The magnesium hydroxide powder according to any one of claims 1 to 3, wherein the surface is treated with a fatty acid, a fatty acid soap, or a silane coupling agent.   The magnesium hydroxide powder of Claim 4 which contains a fatty acid, fatty acid soap, or a silane coupling agent in the range of 0.1-10 mass parts with respect to 100 mass parts of magnesium hydroxide.   The magnesium hydroxide powder according to any one of claims 1 to 5, which is used for a flame retardant for a resin.   A resin composition in which the magnesium hydroxide powder according to claim 1 is kneaded.   Magnesium hydroxide slurry in which spherical secondary particles formed from scaly primary particles obtained by reacting magnesium ions in seawater with an alkali source are dispersed, or the magnesium hydroxide slurry is dehydrated The water-containing magnesium hydroxide solid substance having a water content of 10 to 50% by mass obtained by drying under a drying condition requiring 2 hours or more until the water content becomes 5% by mass is obtained. The method for producing a magnesium hydroxide powder according to claim 1, comprising obtaining a magnesium hydroxide powder containing 5% by mass, and then drying the magnesium hydroxide powder until the moisture content becomes 0.5% by mass or less. .   The method for producing a magnesium hydroxide powder according to claim 8, wherein the drying conditions of the magnesium hydroxide slurry or the hydrated magnesium hydroxide solid are a temperature of 50 to 100 ° C and a relative humidity of 50 to 85% RH. Scale-like primary particles produced from magnesium hydroxide slurry in which spherical secondary particles formed from scale-like primary particles obtained by reacting magnesium ions in seawater with an alkali source are dispersed. Formed from spherical secondary particles having an average particle diameter of 1.0 to 4.8 μm, a BET specific surface area of 11 to 50 m ² / g, and a water content of 0.5 mass. % Of the magnesium hydroxide powder is brought into contact with water vapor under moisture absorption conditions that require a time of 30 minutes or more until the water content becomes 1% by mass to obtain a hydrous magnesium hydroxide powder having a water content of 1% by mass or more. The method for producing magnesium hydroxide powder according to claim 1, wherein the water-containing magnesium hydroxide powder is then dried until the water content becomes 0.5 mass% or less.   The method for producing a magnesium hydroxide powder according to claim 10, wherein the water content of the hydrous magnesium hydroxide powder is 5% by mass or less.   The method for producing a magnesium hydroxide powder according to claim 10, wherein the moisture absorption conditions of the magnesium hydroxide powder are a temperature of 10 to 100 ° C and a relative humidity of 50 to 98% RH.

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