KR101369121B1 - Magnesium hydroxide powder and method for producing the same - Google Patents

Abstract

Magnesium hydroxide powder formed of flaky primary particles and composed of spherical secondary particles having an average particle diameter in the range of 1.0 to 4.8 μm and having a BET specific surface area in the range of 1 to 10 m 2 / g is hygroscopic. It is low and suitable for using resin as a flame retardant.

Magnesium hydroxide powder

Description

Magnesium hydroxide powder and its manufacturing method {MAGNESIUM HYDROXIDE POWDER AND METHOD FOR PRODUCING THE SAME}

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

Although magnesium hydroxide powder is used for various uses, there exists one use as a flame retardant of the resin composition used as a coating material of resin, especially an electric wire and a cable. Examples of the resin to be flame retarded include polyethylene, polypropylene, ethylene-propylene rubber (EPM), ethylene-propylene-diene terpolymer (EPDM), ethylene-ethyl acrylate copolymer (EEA), ethylene-vinyl acetate air Polyolefins such as coalescing.

As an industrial production method of magnesium hydroxide powder, spherical secondary particles formed of flaky primary particles are prepared by adding an alkali source such as lime oil to seawater and reacting magnesium ions in the seawater with an alkali source. It is common to obtain a dispersed magnesium hydroxide slurry, and then, the magnesium hydroxide slurry is subjected to a treatment such as washing and dehydration, followed by drying to form a powder. The manufacturing method (henceforth a seawater method) of the magnesium hydroxide powder which used seawater for this magnesium source is an advantageous method from a manufacturing cost viewpoint. However, the magnesium hydroxide powder obtained by this seawater method generally consists of spherical secondary particles in the range of 1.0-4.8 micrometers in average particle diameter formed from the flaky primary particle, and the BET specific surface area is 11-. Since it is high at 50 m <2> / g, there exists a tendency for high hygroscopicity. When moisture-absorbed magnesium hydroxide powder is used as a flame retardant in resin compositions such as coating materials for electric wires and cables, moisture absorbed by the magnesium hydroxide powder is evaporated by heat during kneading with the resin, which damages the appearance of the resin composition obtained by foaming. It may be a factor. For this reason, development of magnesium hydroxide powder with low hygroscopicity, ie, low specific surface area, is advanced.

Patent Literature 1 discloses a magnesium hydroxide powder having a specific surface area of 10 m 2 / g or less, consisting of spherical secondary particles having an average particle diameter of 5 to 500 µm formed by aggregation of flaky magnesium hydroxide primary particles. According to this patent document 1, the said magnesium hydroxide powder is the crystallization apparatus of the aqueous solution containing a water-soluble magnesium salt, and ammonia, and the crystallization load of magnesium hydroxide is 500 kg / m <3> * h or less, Furthermore, the crystallization apparatus It is disclosed that it can be manufactured by making it react on the conditions which the magnesium hydroxide slurry concentration in will be 1-60 wt%.

Patent Document 2 has a BET specific surface area of less than about 10 m 2 / g, an average particle diameter of about 0.5 to 10.0 microns, less than about 0.5% of particles exceeding 10 microns, and many crystals have a flame-retardant hydroxide having almost an egg-shaped cross section. Magnesium powder is disclosed. According to this patent document 2, the said magnesium hydroxide powder is manufactured by the method containing the process of adding the excess ammonia raw material in molecular weight to a magnesium chloride solution, forming precipitation of magnesium hydroxide, and recrystallizing magnesium hydroxide hydrothermally. It is disclosed that it can be done.

Patent Document 1: Japanese Patent Application Laid-Open No. 61-168522

Patent Document 2: Japanese Patent Application Publication No. 2001-508015

DISCLOSURE OF INVENTION

Problems to be solved by the invention

Magnesium hydroxide powder whose particle shape is spherical or oval, and whose BET specific surface area is 10 m <2> / g or less is disclosed by the said patent document 1 and patent document 2. Among these, the magnesium hydroxide powder described in Patent Literature 1 has a large average particle diameter of secondary particles, and when used as a flame retardant, the resin composition obtained has a rough appearance, stresses tend to be concentrated, and strength is weak. There is a tendency to lose. Further, the magnesium hydroxide powder described in Patent Literature 2 is fine but not spherical, so there is a problem in dispersibility in the resin, and also requires hydrothermal treatment at the time of manufacture, which makes the manufacturing process complicated and the production cost is high. Tends to be high.

Therefore, an object of the present invention is to provide a magnesium hydroxide powder composed of low BET specific surface area and fine spherical particles, which is particularly suitable for using a resin as a flame retardant.

Means for solving the problem

The inventors of the present invention provide a magnesium hydroxide slurry obtained as an intermediate product in the seawater method, or a water-containing magnesium hydroxide solid having a water content of 10 to 50 mass% obtained by dehydrating the magnesium hydroxide slurry for at least 2 hours until the water content becomes 5 mass%. After drying slowly in the drying condition which needs to make water-containing magnesium hydroxide powder of 1-5 mass% of water content, and drying until it becomes 0.5 mass% or less of water content, BET specific surface area is low as 1-10 m <2> / g, It was also found that a magnesium hydroxide powder having a spherical shape was obtained. In addition, the present inventors require a time of 30 minutes or more for a magnesium hydroxide powder having a BET specific surface area of 11 to 50 m 2 / g (water content: 0.5 mass% or less) obtained by the seawater method until the water content becomes 1 mass%. The BET specific surface area is low at 1 to 10 m 2 / g even when the moisture content of magnesium hydroxide powder is made to be 1 mass% or more, and then dried until it becomes 0.5 mass% or less. It was found that a magnesium hydroxide powder having a spherical shape was obtained.

Accordingly, the present invention is made of magnesium hydroxide powder having spherical secondary particles having an average particle diameter in the range of 1.0 to 4.8 μm, formed of flaky primary particles, and having a BET specific surface area in the range of 1 to 10 m 2 / g. Is in.

The preferable aspect of the magnesium hydroxide powder of this invention is as follows.

(1) When spherical secondary particles make the length of the longest diameter one among the diameters in the three directions orthogonal to each other, the length of another two diameter exists in the range of 0.6-1, respectively.

(2) The maximum value of the log differential pore volume in the pores in the pore 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, fatty acid soap, or a silane coupling agent.

(4) The fatty acid, fatty acid soap or silane coupling agent is contained in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of magnesium hydroxide.

The magnesium hydroxide powder of this invention can be used especially advantageously as a flame retardant of resin. Therefore, this invention also exists in the resin composition which knead | mixed the magnesium hydroxide powder of the said this invention.

The present invention also provides a water content 10 obtained by dehydrating a magnesium hydroxide slurry or a magnesium hydroxide slurry in which spherical secondary particles formed of flaky primary particles obtained by reacting magnesium ions in seawater with an alkali source are dispersed. The water-containing magnesium hydroxide solid of -50 mass% is dried under the drying conditions which require time of 2 hours or more until a water content becomes 5 mass%, and the water-containing magnesium hydroxide powder of 1-5 mass% of water content is obtained, and then the water content is It also exists in the manufacturing method of the magnesium hydroxide powder of this invention which consists of drying magnesium hydroxide powder until water content becomes 0.5 mass% or less.

In the manufacturing method of the magnesium hydroxide powder of the said invention, it is preferable that the drying conditions of a magnesium hydroxide slurry or a hydrous magnesium hydroxide solid are conditions of 50-100 degreeC, and 50-85% RH of relative humidity.

The present invention is also formed of flaky primary particles made of magnesium hydroxide slurry in which spherical secondary particles formed of flaky primary particles obtained by reacting magnesium ions in seawater with an alkali source are dispersed. Magnesium hydroxide powder having an average particle diameter of 1.0 to 4.8 µm and having a BET specific surface area in the range of 11 to 50 m 2 / g, and a water content of 0.5% by mass or less, has a water content of 1% by mass. Contact with water vapor under moisture absorption conditions that require a time of 30 minutes or more to obtain a water-containing magnesium hydroxide powder having a water content of 1% by mass or more (particularly 5% by mass or less), and then the water-containing magnesium hydroxide powder has a water content of 0.5 It also exists in the manufacturing method of the magnesium hydroxide powder of the said invention which consists of drying until it becomes mass% or less.

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

Effects of the Invention

Since the magnesium hydroxide powder of this invention is low in BET specific surface area and low hygroscopicity, since it has little hygroscopicity over a long period of time, it is stable, and is comprised from the fine spherical secondary particle, dispersibility to resin is high. Therefore, the magnesium hydroxide powder of this invention is especially suitable as a flame retardant of resin.

In addition, by using the production method of the present invention, a magnesium hydroxide powder produced by an industrially inexpensive seawater method, or a magnesium hydroxide slurry obtained as an intermediate product in the seawater method, or a hydrous magnesium hydroxide solid is used as a raw material. Magnesium hydroxide powder made of fine spherical secondary particles having a low BET specific surface area suitable for use as a flame retardant can be produced.

1 is a scanning electron micrograph of the magnesium hydroxide powder prepared 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. FIG.

Carrying out the invention  Best form for

The magnesium hydroxide powder of this invention consists of spherical secondary particle which the average particle diameter formed from flaky primary particle in the range of 1.0-4.8 micrometer, and has a BET specific surface area in the range of 1-10 m <2> / g. have. It is preferable to exist in the range of 1.0-4.5 micrometers, and, as for the average particle diameter of spherical secondary particle, it is especially preferable to exist in the range which is 1.2-4.0 micrometers. It is preferable that BET specific surface area exists in the range of 2-9 m <2> / g.

In the magnesium hydroxide powder of the present invention, the fact that the secondary particles of magnesium hydroxide are spherical is the other two when the length of the longest diameter is 1 out of the diameters in three directions orthogonal to each other. It means that the length of the diameter is in the range of 0.6 to 1, preferably 0.8 to 1, respectively.

The magnesium hydroxide powder of this invention can be manufactured by the following (1) or (2) method, for example.

(1) A water content of 10 to 50 mass% of water content obtained by dehydrating a magnesium hydroxide slurry or a magnesium hydroxide slurry in which spherical secondary particles formed from flaky primary particles are obtained as an intermediate product in a seawater method. The magnesium hydroxide solids are dried under dry conditions requiring a time of at least 2 hours until the water content becomes 5% by mass to obtain a water-containing magnesium hydroxide powder having a water content of 1 to 5% by mass, and then the water-containing magnesium hydroxide powder is The method made by drying until it becomes 0.5 mass% or less.

(2) The average particle diameter formed by the scale-shaped primary particle manufactured by the seawater method consists of spherical secondary particle which exists in the range of 1.0-4.8 micrometers, and BET specific surface area is 11-50 m <2> / g or less And 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 requiring a time of 30 minutes or more until the water content is 1% by mass, and the water content is 1% by mass or more (in particular, 5% by mass or less). A water-containing magnesium hydroxide powder is obtained, and then the water-containing magnesium hydroxide powder is dried 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 allowed to react to precipitate flake primary particles of magnesium hydroxide. The magnesium hydroxide slurry in which spherical secondary particles are disperse | distributed can be obtained by making the precipitated flaky primary particle circulate in a liquid mixture, and coagulating and growing a flaky primary particle as spherical secondary particle.

It is preferable that the seawater used as a magnesium source is previously decarboxylated and the dissolved carbonate ion concentration is 20 mass ppm or less (carbon dioxide equivalent). In the decarbonation treatment method, lime oil (calcium hydroxide slurry) is added to seawater to fix carbonate ions with calcium carbonate, or an acidic solution such as hydrochloric acid or sulfuric acid is added to the seawater to make the pH of the seawater 4 or less. A method of removing carbonate ions with carbon dioxide gas can be used by aeration treatment of seawater. In addition, the decarbonation treatment method using electrolyzed oil is a more preferable method because silicon and aluminum components in seawater are adsorbed to the resulting calcium carbonate and the content thereof is reduced.

As an alkali source mixed with seawater, lime oil can be used.

The mixing ratio of the seawater and the alkali source is preferably such that the reaction rate of the magnesium ions in the seawater (mole percentage of magnesium ions in the seawater that reacts with the alkali source and precipitates as magnesium hydroxide particles) is 50 to 110%, and is 70 to 110%. It is especially preferable that it is the ratio which becomes 90%. If the reaction rate is too low, it is economically disadvantageous in view of the yield of magnesium hydroxide powder.

In the above method (1), the magnesium hydroxide slurry produced as described above is subjected to a conventional dehydration treatment such as filtration or the like to form an aqueous magnesium hydroxide solid having a water content of 10 to 50% by mass, followed by a drying apparatus. To 2 hours or more, preferably 4 hours or more, more preferably 24 hours or more, and 200 hours or less until the water content is 5% by mass, followed by drying under dry conditions requiring a water content of 1 to 5 A mass% hydrous magnesium hydroxide powder is obtained. The time until a moisture content becomes 5 mass% can be adjusted with the temperature and relative humidity in a drying apparatus. The temperature in the drying apparatus is generally in the range of 50 to 100 ° C, preferably in the range of 60 to 90 ° C, and the relative humidity is generally in the range of 50 to 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 make it dry as a hydrous magnesium hydroxide solid.

The hydrous magnesium hydroxide powder having a water content of 1 to 5% by mass as described above is then subjected to a hot air dryer (for example, a box type dryer, an air flow dryer, a band type air dryer, a fluidized bed dryer, a rotary dryer) and a conductive electrothermal dryer ( For example, it puts into normal drying apparatuses, such as a cylinder dryer and a disk dryer, and it dries until a moisture content becomes 0.5 mass% or less. Drying temperature is generally 100 degreeC or more, Preferably it is the range of 110-150 degreeC. There is no restriction | limiting in particular in drying time, Generally, it is 0.01 to 2 hours.

In the method (2), the magnesium hydroxide powder produced by the seawater method, ie, spherical secondary particles having a mean particle diameter of 1.0 to 4.8 µm, formed of flaky primary particles, is formed of BET. Magnesium hydroxide powder whose specific surface area is 11-50 m <2> / g, and whose water content is 0.5 mass% or less is used as a starting material.

As a magnesium hydroxide powder used as a raw material, in the same manner as in the above method (1), flake primary particles of magnesium hydroxide precipitated by reacting magnesium ions in the seawater with an alkali source are aggregated and grown as spherical secondary particles to be hydrated. A magnesium slurry was obtained, and then treated with washing, dehydration, and the like to form a hydrous magnesium hydroxide having a water content of 10 to 50% by mass, and then put into a conventional drying apparatus such as a hot air dryer and a conductive electrothermal dryer, at least 100 ° C, Preferably, the thing which made water content 0.5 mass% or less by drying at the temperature of 110-150 degreeC for 0.01 to 2 hours can be used preferably.

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

The water-containing magnesium hydroxide powder having a water content of 1% by mass or more is then placed in ordinary drying equipment such as a hot air dryer and a conductive heat transfer dryer, and dried until the water content becomes 0.5% by mass or less. Drying temperature is generally 100 degreeC or more, Preferably it is the range of 110-150 degreeC. 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 is the maximum of the log fine pore volume in the pores having a pore diameter in the range of 3 to 5 nm as compared with the magnesium hydroxide powder produced by a conventional seawater method. The value is low. Since the pores in the pore diameter 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 is compared with the magnesium hydroxide powder produced by a conventional seawater method. In addition, since there are few fine pore volumes between primary particles, it is thought that BET specific surface area is low and hygroscopicity is low. 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 0.005 to 0.10 cm 3 / It is in the range of g.

The magnesium hydroxide powder of the present invention, by itself, has a property of low hygroscopicity compared to magnesium hydroxide powder prepared by a conventional seawater method, but in order to further reduce the hygroscopicity, the surface of the magnesium hydroxide powder or You may process with a silane coupling agent. It is preferable to contain a fatty acid, fatty acid soap, and a silane coupling agent in 0.1-10 mass parts with respect to 100 mass parts of magnesium hydroxide. Examples of the fatty acid include stearic acid and oleic acid. It is preferable that fatty acid soap is a sodium salt or a potassium salt.

The magnesium hydroxide powder of this invention can be advantageously used as a flame retardant of the resin composition used for resin, especially the coating material of electric wire or a cable. Examples of the resins to be flame retarded include polyethylene, polypropylene, ethylene-propylene rubber (EPM), ethylene-propylene-diene terpolymer copolymer (EPDM), ethylene-ethyl acrylate copolymer (EEA), ethylene-vinyl acetate Polyolefins such as copolymers. The compounding quantity of magnesium hydroxide powder with respect to these resin is generally in the range of 10-150 mass parts with respect to 100 mass parts of resin, Preferably it exists in the range of 30-100 mass parts.

The resin composition containing the magnesium hydroxide powder of this invention can be manufactured by kneading resin and magnesium hydroxide powder using conventional kneading machines, such as a Banbury mixer, a tumbler, a pressurized kneader, a kneading extruder, and a twin screw extruder. The resin composition containing the magnesium hydroxide powder of the present invention may, if desired, include inorganic fillers such as talc, lubricants such as silicone oil and fatty acids, surfactants such as silane coupling agents and fatty acid soaps, and plasticizers, softeners and anti-aging agents. And various additives used in conventional resin compositions such as colorants, antioxidants, ultraviolet absorbers, stabilizers, and crosslinking agents.

Example

In this example, the maximum value and hygroscopic characteristics of the log differential pore volume in the pores in which the water content, the average secondary particle diameter, the sphericity of the secondary particles, and the pore diameter are in the range of 3 to 5 nm are as described below. Measured by

[Water content]

5 g of samples were put into a moisture meter (MX-50, manufactured by A & D), and heated at a temperature of 180 ° C. to calculate the mass reduction rate when the mass reduction reached equilibrium as a moisture content.

[Mean Secondary Particle Diameter]

0.5 g of a sample is added to 50 ml of ethanol, and it disperse | distributes for 2 minutes on the conditions of 200 microA of outputs using an ultrasonic homogenizer, and prepares a magnesium hydroxide suspension. Subsequently, the average particle diameter of the magnesium hydroxide particles contained in the magnesium hydroxide suspension was measured using a laser diffraction scattering method particle size distribution meter (Mike track particle size distribution measuring device 9320HRA (X-100), manufactured by Nikkiso Co., Ltd.). Measure

[Sphericalness of Secondary Particles]

The sample stand angle of a scanning electron microscope (SEM) shall be 0 degree (horizontal), the magnesium hydroxide secondary particle | grains are imaged, the diameter of a secondary particle is determined, and the length is measured. The direction which measured this diameter is made into the rotating shaft, and the sample stand angle is inclined +45 degree | times from a horizontal position, image | photographing magnesium hydroxide secondary particles, and the diameter of the secondary particle in the direction orthogonal to a rotating axis is measured. Next, the magnesium hydroxide secondary particles are photographed by tilting the sample stage angle from the horizontal position by -45 degrees, and the diameter of the secondary particles in the direction orthogonal to the rotation axis is measured. The length of the longest diameter of the magnesium hydroxide secondary particles measured at the sample angle of 0 degrees, +45 degrees, and -45 degrees is X = 1, the length of the longest diameter Y, and the length of the shortest diameter Z is calculated as a relative value.

[Maximum value of log differential pore volume]

Using a Quantachrome Co., Ltd., fully automatic gas adsorption measurement device (Autosorb-3B), the desorption isotherm was measured by nitrogen gas adsorption method, and the pores based on the specific surface area by BJH method from the data of the desorption isotherm The log differential pore volume of the pores in the range of 3 to 5 nm in diameter is calculated and the maximum value is obtained.

Hygroscopic properties

The magnesium hydroxide powder was added to a constant temperature thermostat set at a temperature of 30 ° C. and a relative humidity of 80% RH, and the mass of the magnesium hydroxide powder was measured every 30 minutes from immediately after the injection to 180 minutes, thereafter every 60 minutes, and the mass increase rate Is calculated as the moisture absorption rate.

Example 1

(1) Preparation of hydrous magnesium hydroxide solids

Lime oil is added to 80 mass ppm of seawater with dissolved carbonate ions in carbon dioxide, the dissolved carbonate is precipitated with calcium carbonate, and the dissolved carbonate concentration is reduced until it becomes 10 mass ppm in carbon dioxide, and then the sand filter Calcium carbonate was removed by filtration. Lime oil was added to the seawater which reduced content of dissolved carbonate ion in the ratio which the reaction rate of the magnesium hydroxide ion contained in the seawater becomes 80%, the liquid mixture was prepared, and the liquid mixture was thrown into the Seeker. In a thinner, the precipitated magnesium hydroxide primary particles were circulated, and the aggregated primary particles were aggregated and grown into spherical secondary particles to obtain a magnesium hydroxide slurry in which spherical secondary particles were dispersed. The magnesium hydroxide slurry was taken out from the bottom of the thinner, washed with water to remove residual salts, and filtered by suction with a liquid to obtain a hydrous magnesium hydroxide having a water content of 33.5% by mass.

(2) Preparation of Magnesium Hydroxide Powder

Water-containing magnesium hydroxide solids were placed in a constant temperature thermostat set at a temperature of 85 ° C. and a relative humidity of 65% RH, and allowed to stand for 48 hours to obtain a water-containing magnesium hydroxide powder having a water content of 1.1% by mass (time until the water content becomes 5% by mass). Was about 30 hours). Subsequently, the hydrous magnesium hydroxide powder was placed in a box-type drier set at a temperature of 120 ° C. and dried for 2 hours. The obtained magnesium hydroxide powder was 0.5 mass% or less in water content.

The particle shape of the obtained magnesium hydroxide powder was observed using the scanning electron microscope (SEM). A SEM photograph is shown in FIG. It was confirmed from the photograph of FIG. 1 that the magnesium hydroxide powder was composed of spherical secondary particles formed by aggregation of flaky primary particles.

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

[Example 2]

Example 1 The moisture content magnesium hydroxide solid of 33.5 mass% of moisture content manufactured by the method similar to (1) was put into the box type dryer set to the temperature of 120 degreeC, and it was made to dry for 1 hour, and the water content was made into the magnesium hydroxide powder of 0.5 mass% or less. . This magnesium hydroxide powder was put into the constant temperature thermostat set to the temperature of 80 degreeC, and 80% RH of relative humidity, and it was left to stand for 24 hours. The magnesium hydroxide powder after standing was a hydrous magnesium hydroxide powder having a water content of 2.1% by mass. Subsequently, the hydrous magnesium hydroxide powder was placed in a box-type drier set at a temperature of 120 ° C. and dried for 2 hours. The obtained magnesium hydroxide powder was 0.5 mass% or less in water content.

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 primary particles formed spherical secondary particles.

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

Comparative Example 1

(1) Preparation of hydrous magnesium hydroxide solids

Example 1 Lime oil was added to the 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), so that the reaction rate of magnesium hydroxide ions contained in the seawater became 90%. The mixture was added to prepare a mixed liquid, and the mixed liquid was added to the Seeker. In a thinner, the precipitated magnesium hydroxide primary particles were circulated, and the aggregated primary particles were aggregated and grown into spherical secondary particles to obtain a magnesium hydroxide slurry in which spherical secondary particles were dispersed. The magnesium hydroxide slurry was taken out from the bottom of the thinner, washed with water to remove residual salts, and filtered by suction with a liquid to obtain a hydrous magnesium hydroxide having a water content of 38.5% by mass.

(2) Preparation 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 was 0.5 mass% or less in water content.

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 primary particles formed spherical secondary particles.

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

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

[Example 3]

After putting 2000 g of pure water into the glass beaker of capacity 3L, and heating at 70 degreeC, after adding 2.5 g of sodium stearate (made by Nippon Oil Holdings Co., Ltd., editorial SN-15) as a surface treatment material, It was stirred and dissolved. 100 g of the magnesium hydroxide powder prepared in Example 2 was added to the aqueous sodium stearate solution, the mixture was stirred for 1 hour while maintaining the temperature at 70 ° C, the magnesium hydroxide powder was dispersed in the aqueous sodium stearate solution, and the surface of the magnesium hydroxide powder was dispersed. Was treated with stearic acid.

Magnesium hydroxide dispersion liquid was suction-filtered with nutchite, and the obtained magnesium hydroxide containing solid content was wash | cleaned with 20 times of water with respect to solid content. Subsequently, the solid content after washing was dried in a box dryer at a temperature of 120 ° C. for 12 hours, and then pulverized with a sample mill. 2.3 mass parts of surface treating agents were affixed to the obtained magnesium hydroxide powder with respect to 100 mass parts of magnesium hydroxide.

The moisture absorption characteristic of the surface-treated magnesium hydroxide powder is shown in FIG. The moisture absorption rate after 360 minutes was 0.5 mass%, and was about 40% of the magnesium hydroxide powder (Example 2) before surface treatment.

Example 4

100 mass parts of surface-treated magnesium hydroxide obtained in Example 3 and 100 mass parts of ethylene-ethyl acrylate copolymer (EEA) were kneaded for 15 minutes under conditions of a rotational speed of 60 rpm in a Brabender Plus graph heated at a temperature of 170 ° C. Then, after kneading for 5 minutes with the roll heated to the temperature of 150 degreeC, it knead | mixed again by the kneading machine at the temperature of 160 degreeC, and obtained the resin composition. The obtained resin composition was pressure-molded at the temperature of 160 degreeC, and it was set as the resin composition sheet of thickness 1mm and 3mm.

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

In addition, the resin composition sheet of thickness 1mm was used for the measurement of MFI, breaking tensile stress, and elongation, and the resin composition sheet of thickness 3mm was used for the measurement of an oxygen index. Breaking tensile stress and elongation were measured by the method according to JIS-K-7113 (test piece No. 1 dumbbell). Oxygen index was measured by the method based on JIS-K-7201.

Claims (12)

The average particle diameter formed from the flaky primary particle consists of spherical secondary particle in the range of 1.0-4.8 micrometers, BET specific surface area exists in the range of 1-10 m <2> / g, When the length of the longest diameter is 1 among the diameters in the three directions orthogonal to each other, the lengths of the other two diameters are in the range of 0.6 to 1, respectively, and the pores are in the range of 3 to 5 nm. Magnesium hydroxide powder whose maximum value of the log fine pore volume in the range is 0.001-0.14 cm <3> / g. delete delete The method of claim 1, Magnesium hydroxide powder whose surface is treated with fatty acid, fatty acid soap, or a silane coupling agent. 5. The method of claim 4, Magnesium hydroxide powder 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 method according to any one of claims 1, 4, and 5, Magnesium hydroxide powder for flame retardant of resin. The resin composition in which the magnesium hydroxide powder according to any one of claims 1, 4 and 5 is kneaded. 10-50 mass% of water content obtained by dehydrating the magnesium hydroxide slurry or the magnesium hydroxide slurry in which the spherical secondary particles formed from the flaky primary particles obtained by reacting magnesium ions in the seawater with the alkali source are dispersed. The water-containing magnesium hydroxide solid is dried under dry conditions requiring a time of 2 hours or more until the water content becomes 5% by mass to obtain a water-containing magnesium hydroxide powder having a water content of 1 to 5% by mass, and then the water-containing magnesium hydroxide powder is dried. The manufacturing method of the magnesium hydroxide powder of Claim 1 which consists of drying until it becomes 0.5 mass% or less. 9. The method of claim 8, The manufacturing method of the magnesium hydroxide powder whose conditions of drying of a magnesium hydroxide slurry or hydrous magnesium hydroxide solid are conditions of 50-100 degreeC of temperature, and 50-85% RH of relative humidity. The average particle diameter formed by the flaky primary particle made from the magnesium hydroxide slurry disperse | distributed to the spherical secondary particle formed from the flaky primary particle obtained by making magnesium ion in seawater react with an alkali source is 1.0 Magnesium hydroxide powder composed of spherical secondary particles in the range of ˜4.8 μm, having a BET specific surface area in the range of 11 to 50 m 2 / g and having a water content of 0.5% by mass or less until the water content is 1% by mass Contacting with water vapor at a moisture absorption condition requiring a time of at least minutes to obtain a hydrous magnesium hydroxide powder having a moisture content of 1% by mass or more, and then drying the hydrous magnesium hydroxide powder until the moisture content is 0.5% by mass or less. The manufacturing method of the magnesium hydroxide powder of Claim. 11. The method of claim 10, The manufacturing method of the magnesium hydroxide powder whose water content is 1 mass% or more and 5 mass% or less. 11. The method of claim 10, The manufacturing method of the magnesium hydroxide powder whose moisture absorption conditions of magnesium hydroxide powder are conditions of 10-100 degreeC of temperature, and 50-98% RH of relative humidity.

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