Magnesium hydroxide, resin composition containing magnesium hydroxide, and method for producing magnesium hydroxide

Abstract

To provide magnesium hydroxide particles which are easier to handle.SOLUTION: The loose bulk density of the magnesium hydroxide is 0. 28g / ml or more and less than 0. 55g / ml. The volume average diameter in the wet particle size distribution may be 0.55 μm or more and 1.30 μm or less. The volume fraction of particles greater than or equal to 250 μm in the dry particle size may be less than 35%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to magnesium hydroxide, a resin composition comprising magnesium hydroxide, and a method for producing magnesium hydroxide. [Background technology]

[0002] Inorganic particles are used in a variety of applications, including industrial and medical applications. Examples of inorganic particle materials include magnesium hydroxide. Industrial uses of magnesium hydroxide include flame retardants, flue gas desulfurization agents, and soil conditioners, while pharmaceutical and food additive applications include gastrointestinal medicines, antacids, and laxatives.

[0003] For example, Patent Document 1 discloses a resin composition containing compressed magnesium hydroxide granules (hereinafter simply referred to as "compressed granules"). The loose bulk density of the compressed granules is 0.55 to 0.80 g / ml. With regard to the dry particle size of the compressed granules, 850 μm or more is 0 to 20 mass %. 500 μm or more and less than 850 μm is 5 to 35 mass %. 250 μm or more and less than 500 μm is 15 to 35 mass %. Less than 250 μm is 30 to 65 mass %. A method for producing compressed granules includes a step of passing magnesium hydroxide powder between at least one pair of rolls set at a roll pressure of 1 to 10 MPa to obtain compressed granules having a loose bulk density of 0.55 to 0.80 g / ml. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-137185 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent document 1 states that pressed granular materials having bulk density and particle size distribution characteristics within a specified range have the effects of maintaining their function as a flame retardant, improving handleability (ease of adhesion to objects), and maintaining dispersibility in resin.

[0006] However, the granular material of Patent Document 1 leaves room for improvement in terms of handling.

[0007] Therefore, an object of the present invention is to provide magnesium hydroxide that is easier to handle, a resin composition containing magnesium hydroxide, and a method for producing magnesium hydroxide. [Means for solving the problem]

[0008] The present disclosure includes the following aspects.

[0009] (First Disclosure) The first disclosure relates to magnesium hydroxide particles, which have a loose bulk density of 0.28 g / ml or more and less than 0.55 g / ml.

[0010] (Second Disclosure) In the second disclosure, in the first disclosure, the magnesium hydroxide has a volume average diameter in a wet particle size distribution of 0.55 μm or more and 1.30 μm or less.

[0011] (Third Disclosure) In the third disclosure, in the first disclosure, the volume ratio of particles having a dry particle size of 250 μm or more of the magnesium hydroxide is less than 35%.

[0012] (Fourth Disclosure) The fourth disclosure relates to a resin composition, which includes the magnesium hydroxide disclosed in any one of the first to third disclosures and a resin.

[0013] (Fifth Disclosure) The fifth disclosure relates to a method for producing magnesium hydroxide particles, which includes a forming step of dry-pressing a magnesium hydroxide raw material to form magnesium hydroxide having a loose bulk density of 0.28 g / ml or more and less than 0.55 g / ml.

[0014] (Sixth Disclosure) In the sixth disclosure, in the fifth disclosure, the magnesium hydroxide raw material has a loose bulk density of 1.0 g / ml or less.

[0015] (7th Disclosure) In this seventh disclosure, in the fifth disclosure, the forming step includes a step of pressing the magnesium hydroxide raw material so that the volume average diameter in the wet particle size distribution of the magnesium hydroxide is 0.55 μm or more and 1.30 μm or less.

[0016] (Eighth Disclosure) In this eighth disclosure, in the fifth disclosure, the forming process includes a process of pressing the magnesium hydroxide raw material so that the volume ratio of particles of 250 μm or more in the dry particle size of the magnesium hydroxide is less than 35%. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide magnesium hydroxide that is easier to handle, a resin composition containing magnesium hydroxide, and a method for producing magnesium hydroxide. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, preferred embodiments of the magnesium hydroxide, the resin composition containing magnesium hydroxide, and the method for producing magnesium hydroxide of the present invention will be described.

[0019] [Magnesium hydroxide] The magnesium hydroxide according to this embodiment is in the form of particles. The loose bulk density of the magnesium hydroxide is 0.28 g / ml or more and less than 0.55 g / ml. The loose bulk density is preferably 0.32 g / ml or more, and more preferably 0.35 g / ml or more. The loose bulk density is preferably 0.52 g / ml or less, and more preferably 0.50 g / ml or less.

[0020] Patent Document 1 does not mention improving the feedability (ease of supply) of granular materials or achieving both feedability and adhesiveness (ease of adhering to objects). If granular materials have the properties described in Patent Document 1, the feedability of the granular materials may be reduced. Changing the properties of the granular materials in an attempt to improve feedability may adversely affect adhesiveness. In such a case, when the granular materials are used in a product, they may become difficult to handle. Therefore, in this embodiment, by setting the loose bulk density of the magnesium hydroxide to a value within the above-mentioned numerical range, it is possible to improve and achieve both feedability and adhesiveness of the magnesium hydroxide. This makes it possible to provide magnesium hydroxide that is easier to handle.

[0021] In a preferred aspect of this embodiment, the volume mean diameter (MV) in the wet particle size distribution of the magnesium hydroxide is 0.55 μm or more and 1.30 μm or less. The volume mean diameter in the wet particle size distribution is preferably 0.60 μm or more, and more preferably 0.65 μm or more. When the volume mean diameter in the wet particle size distribution is 0.55 μm or more, fine particles are less likely to be mixed into the magnesium hydroxide particles, and the loose bulk density described above is less likely to exceed the upper limit. The volume mean diameter in the wet particle size distribution is preferably 1.20 μm or less, and more preferably 1.10 μm or less. When the volume mean diameter in the wet particle size distribution is 1.30 μm or less, the magnesium hydroxide is less likely to aggregate strongly, and the dispersibility when blended into a resin is less likely to be impaired. The loose bulk density of the magnesium hydroxide can be easily adjusted to the above-mentioned numerical range, and the dispersibility can be easily improved.

[0022] In a preferred aspect of this embodiment, the volume ratio of particles of 250 μm or more in the dry particle size of magnesium hydroxide is less than 35%. The volume ratio of particles of 250 μm or more in the dry particle size is preferably less than 33%. The volume ratio of particles of 250 μm or more in the dry particle size is more preferably less than 30%. By making the volume ratio of particles of 250 μm or more in the dry particle size less than 35%, the feedability of the magnesium hydroxide can be improved, and the dispersibility when the magnesium hydroxide is blended into a resin can be improved. Note that there is no particular restriction on the lower limit of the volume ratio of particles of 250 μm or more in the dry particle size. The lower limit of the volume ratio of particles of 250 μm or more in the dry particle size is, for example, 10% or more, and preferably 13% or more.

[0023] In a preferred aspect of this embodiment, the packed bulk density of the magnesium hydroxide is 0.50 g / ml or more and less than 0.90 g / ml. When the packed bulk density is within this range, the magnesium hydroxide can be well dispersed when blended into a resin.

[0024] [Resin composition] The resin composition according to this embodiment includes the magnesium hydroxide described above and a resin. In this embodiment, the resin includes a synthetic resin and a synthetic rubber. Examples of the synthetic resin include polystyrene, polypropylene, polyethylene, copolymers of ethylene and other α-olefins, copolymers of ethylene and vinyl acetate, ethyl acrylate, or methyl acrylate, copolymers of propylene and other α-olefins, polybutene-1, 4-methylpentene-1, copolymers of styrene and acrylonitrile, copolymers of styrene and acrylonitrile and butadiene, copolymers of ethylene and propylene diene rubber or butadiene, thermoplastic resins such as polyvinyl acetate, polyacrylate, polymethacrylate, polyurethane, polyester, polyether, polyamide, polyvinyl chloride, and chlorinated polyethylene, and thermosetting resins such as phenolic resin, melamine resin, epoxy resin, unsaturated polyester resin, and alkyd resin. Examples of synthetic rubbers include EPDM (ethylene propylene diene rubber), SBR (styrene butadiene rubber), NBR (acrylonitrile butadiene rubber), butyl rubber, isoprene rubber, chlorosulfonated polyethylene, silicone rubber, fluororubber, urethane rubber, and acrylic rubber.

[0025] The amount of magnesium hydroxide in the resin composition is, for example, 0.5 to 400 parts by mass per 100 parts by mass of synthetic resin or synthetic rubber. The amount of magnesium hydroxide in the resin composition is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more. The amount of magnesium hydroxide in the resin composition is preferably 380 parts by mass or less, more preferably 350 parts by mass or less.

[0026] The resin composition may contain other agents. Examples of the other agents include crosslinking aids, crosslinking agents, softeners, antioxidants, weathering agents, lubricants, antistatic agents, antioxidants, foaming agents, colorants, flame retardants, and flame retardant aids. One or more of these agents may be blended. The amount of these agents blended may be, for example, 35 parts by mass or less per 100 parts by mass of the synthetic resin or synthetic rubber.

[0027] The resin composition can be obtained, for example, by blending magnesium hydroxide particles and particles of other agents into a resin. Methods for dispersing such particles in a resin include mixing using a single-screw kneader, a twin-screw kneader, a kneader, a roll kneader, or the like. Furthermore, a molded article of the resin composition can be molded using a press molding machine, a calendar molding machine, or the like.

[0028] [Magnesium hydroxide manufacturing method] The above-mentioned method for producing magnesium hydroxide involves dry pressing a magnesium hydroxide raw material. Dry pressing improves the dispersibility of the resulting magnesium hydroxide when blended with a resin. The production method is characterized by including a forming step of dry pressing a magnesium hydroxide raw material to form magnesium hydroxide particles having a loose bulk density of 0.28 g / ml or more and less than 0.55 g / ml. The lower limit of the loose bulk density is preferably 0.32 g / ml, more preferably 0.35 g / ml. The upper limit of the loose bulk density is preferably 0.52 g / ml, more preferably 0.50 g / ml. This is from the viewpoint of improving both the feedability and adhesiveness of the magnesium hydroxide, while achieving both.

[0029] Dry pressing is carried out using a roll molding machine, a press molding machine, or the like. When a roll molding machine is used, the physical properties of the magnesium hydroxide can be adjusted by the roll rotation speed, roll diameter, roll surface shape, roll clearance, and the like. The physical properties of the magnesium hydroxide can also be adjusted by the amount of magnesium hydroxide raw material supplied, the presence or absence and conditions of degassing after pressing, and the presence or absence and conditions of a crusher. An example of a roll molding machine is the Roller Compactor RC-156 (manufactured by Freund Corporation). When the Roller Compactor RC-156 is used, the roll rotation speed is preferably 4 to 16 rpm and the feed screw rotation speed is preferably 10 to 30 rpm, from the viewpoint of achieving an appropriate degree of compaction.

[0030] Magnesium hydroxide raw material particles having various loose bulk densities can be used for the production of magnesium hydroxide. The upper limit of the loose bulk density of the magnesium hydroxide raw material is 1.0 g / ml or less, preferably 0.7 g / ml or less, and more preferably 0.4 g / ml or less. This is from the viewpoint of making it easier to obtain an appropriate loose bulk density and an appropriate volume average diameter for the magnesium hydroxide produced. On the other hand, the lower limit of the loose bulk density of the magnesium hydroxide raw material is 0.05 g / ml or more, preferably 0.07 g / ml or more, and more preferably 0.1 g / ml or more. This is from the viewpoint of the workability of the pressing process during the production of magnesium hydroxide.

[0031] The method for producing the magnesium hydroxide raw material is not particularly limited. Examples of production methods include a method using bittern, seawater, or dolomite as a magnesium (Mg) source and lime or caustic soda as an alkali source, a method using a magnesium oxide (MgO) hydration reaction, and a method of reacting a magnesium salt with ammonia (NH3) to crystallize magnesium hydroxide (Mg(OH)2). Any of these methods may be used as the method for producing the magnesium hydroxide raw material of this embodiment.

[0032] In a preferred aspect of this embodiment, the forming step includes a step of pressing the magnesium hydroxide raw material so that the volume average diameter in the wet particle size distribution of the magnesium hydroxide is 0.55 μm or more and 1.30 μm or less. The volume average diameter in the wet particle size distribution is preferably 0.60 μm or more, and more preferably 0.65 μm or more. The volume average diameter in the wet particle size distribution is preferably 1.20 μm or less, and more preferably 1.10 μm or less. This is from the viewpoint of making it easier to obtain the above-mentioned loose bulk density and improving dispersibility when the magnesium hydroxide is blended into a resin.

[0033] In a preferred aspect of this embodiment, the forming step includes a step of pressing the magnesium hydroxide raw material so that the volume ratio of particles of 250 μm or larger in the dry particle size of the magnesium hydroxide is less than 35%. The volume ratio of particles of 250 μm or larger in the dry particle size is preferably less than 33%. The volume ratio of particles of 250 μm or larger in the dry particle size is more preferably less than 30%. The lower limit of the volume ratio of particles of 250 μm or larger in the dry particle size is not particularly limited, but may be, for example, 10%, and preferably 13%. This is from the viewpoint of improving the feedability of the magnesium hydroxide and improving the dispersibility when blended into a magnesium hydroxide resin.

[0034] [Surface treatment] The magnesium hydroxide according to this embodiment is preferably coated with a surface treatment agent. That is, the magnesium hydroxide according to this embodiment is preferably surface-treated. When the magnesium hydroxide raw material is dry-pressed, the timing of the surface treatment may be before or after pressing. From the viewpoint of uniform treatment, the timing of the surface treatment is preferably before pressing.

[0035] Examples of surface treatment agents include higher fatty acids having 10 or more carbon atoms, such as stearic acid, erucic acid, palmitic acid, lauric acid, and behenic acid; alkali metal salts of the above higher fatty acids; sulfate salts of higher alcohols, such as stearyl alcohol and oleyl alcohol; anionic surfactants, such as sulfate salts of polyethylene glycol ether, amide-bonded sulfate salts, ester-bonded sulfate salts, ester-bonded sulfonates, amide-bonded sulfonates, ether-bonded sulfonates, ether-bonded alkylaryl sulfonates, ester-bonded alkylaryl sulfonates, and amide-bonded alkylaryl sulfonates; phosphate esters, such as mono- or diesters of orthophosphoric acid and oleyl alcohol, stearyl alcohol, or a mixture of both, in the acid form, alkali metal salts, or amine salts thereof; vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxy ... silane coupling agents such as nitris(β-methoxyethoxy)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, and γ-mercaptopropyltrimethoxysilane;Isopropyl triisostearoyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, isopropyl tri(N-aminoethyl-aminoethyl) titanate, isopropyl tridecylbenzenesulfonyl titanate, tetraoctyl bis(ditridecyl phosphite) titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, isopropyl tridodecylbenzenesulfonyl titanate, tetraisopropyl bis(dioctyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, bis(dioctyl pyrophosphate)ethylene titanate, isopropyl trioctanoyl titanate, isopropyl dimethacrylisostearoyl titanate, isopropyl isopropyl Titanate-based coupling agents such as isostearoyl diacryl titanate, isopropyl tri(dioctylphosphate) titanate, isopropyl tricumyl phenyl titanate, dicumyl phenyloxyacetate titanate, and diisostearoyl ethylene titanate; aluminum-based coupling agents such as acetoalkoxyaluminum diisopropylate; triphenyl phosphite, diphenyl tridecyl phosphite, phenyl ditridecyl phosphite, phenyl isodecyl phosphite, tri-nonylphenyl phosphite, 4,4'-butylidene-bis(3-methyl-6-t-butylphenyl)-ditridecyl phosphite, trilauryl thiophosphite; and esters of polyhydric alcohols and fatty acids such as glycerin monostearate and glycerin monooleate. Among these, aminosilanes such as N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane, and anionic surfactants such as amide-bonded alkylarylsulfonates are preferably used because of their good compatibility with certain resins;

[0036] The surface treatment method is not particularly limited, and examples include known wet and dry methods in which magnesium hydroxide particles are surface-coated using the above-mentioned surface treatment agent. Examples of wet methods include adding the above-mentioned surface treatment agent in liquid or emulsion form to a slurry of magnesium hydroxide particles and thoroughly mixing them mechanically at a temperature of up to about 100°C. Examples of dry methods include adding the above-mentioned surface treatment agent in liquid, emulsion, or solid form to magnesium hydroxide particles using a mixer such as a Henschel mixer while thoroughly stirring, and thoroughly mixing with or without heating. The amount of surface treatment agent added can be selected as appropriate, but is preferably about 10% by mass or less based on the mass of the magnesium hydroxide particles. The surface-treated magnesium hydroxide particles can be optionally subjected to a suitable process, such as washing with water, dehydration, granulation, drying, pulverization, or classification, to form the final product.

[0037] [Measurement method] <Loose bulk density> The loose bulk density of magnesium hydroxide particles is measured as follows. (1) Weigh 10.0 g of sample using an electronic top-loading balance and pour it gently into a 100 ml glass measuring cylinder from the top. (2) Read the number of ml at the top of the sample in the measuring cylinder. (3) Calculate the loose bulk density (g / ml) according to the following formula. Loose bulk density (g / ml) = (10(g)) / (sample volume (ml))

[0038] <D50, D10, D90, MV in wet particle size distribution> The methods for measuring D50, D10, D90, and MV in the wet particle size distribution of magnesium hydroxide particles are as follows. (1) A particle size distribution analyzer MT-3000II (manufactured by Microtrac Bell Co., Ltd.) is prepared as a measuring device. (2) Weigh out 0.700 g of sample. (3) Add 70 ml of 0.2 W / V% sodium hexametaphosphate solution to the sample to make a mixed solution. (4) The mixture is subjected to ultrasonic treatment for 3 minutes, and this is used as the sample solution. (5) Add the solvent to the sample supply of the measuring device. (6) The solvent is circulated in the sample supply device, and a predetermined amount of sample solution is added. (7) After one minute, take two 30-second measurements. (8) The average of two measurements is used as the measurement results for D50, D10, D90, and MV in the wet particle size distribution.

[0039] <Dry particle size distribution> The dry particle size distribution of magnesium hydroxide particles is measured as follows. (1) A laser micron sizer LMS-3000 (manufactured by Seishin Enterprise Co., Ltd.) is prepared as a measuring device. (2) Install the dry unit in the measuring device. (3) Set the refractive index of the sample. (4) After placing a specified amount of sample into the sample hopper of the measuring device, turn on the suction of the measuring device and perform three 5-second measurements. (5) The average value of the three measurements is used as the measurement result of the dry particle size distribution.

[0040] <Packed bulk density> The method for measuring the packed bulk density of magnesium hydroxide particles is as follows. (1) Prepare a multi-tester MT-02 (manufactured by Seishin Enterprise Co., Ltd.) as a measuring device. (2) Place the sample in the measuring device. (3) The value measured by the measuring device is taken as the measurement result of the packed bulk density.

[0041] <Feedability> Feedability is evaluated by the mass of particles that can be fed per unit time in a specific device. The method for measuring the feedability of magnesium hydroxide particles is as follows. (1) Prepare a 1-liter capacity feeder (manufactured by Technovel Co., Ltd.). (2) The sample to be measured is placed in the hopper of the volumetric feeder. (3) The spring-loaded screw of the volumetric feeder is operated at 25 rpm for 30 seconds. (4) The mass of the sample discharged from the volumetric feeder is measured five times. (5) The average value of the five measurements was used to confirm the feedability of the sample. A value of 3 g / 30 sec or more was considered to be acceptable.

[0042] <Adhesion> Adhesion is assessed by the amount of particles remaining adhered to a particular particle storage container after the particles are dispensed from the storage container. (1) Implement the above-mentioned method for measuring feedability. (2) After that, the amount of particles remaining in the hopper of the volumetric feeder is visually observed and recorded. However, the visual observation results are evaluated in two stages: "A lot" if the powder appears to be stuck and adheres thickly, and "A little" if there is no adhesion or if it adheres thinly. A little is considered to be a pass. [Example]

[0043] The present embodiment will be described below using examples, but the present embodiment is not limited to these examples.

[0044] (i) Example 1 Magnesium hydroxide raw material particles with a loose bulk density of 0.26 g / ml were prepared by surface treatment with 0.5% by mass of aminosilane attached to the magnesium hydroxide. The magnesium hydroxide raw material was placed in a roller compactor RC-156 (roll rotation speed: 8 rpm, feed screw rotation speed: 20 rpm) and compressed at a roll pressure of 10 MPa to produce magnesium hydroxide particles. (ii) Example 2 Magnesium hydroxide particles were prepared in the same manner as in Example 1, except that the roll rotation speed was 10 rpm and the supply screw rotation speed was 15 rpm. (iii) Comparative example 1 Magnesium hydroxide particles were prepared in the same manner as in Example 1, except that the roll rotation speed was 20 rpm and the supply screw rotation speed was 5 rpm.

[0045] The magnesium hydroxide particles of Examples 1 and 2 and Comparative Example 1 were evaluated for loose bulk density (g / ml), D50 (μm), D10 (μm), and D90 (μm) in the wet particle size distribution, volume mean diameter MV, the volume ratio (%) of particles 250 μm or larger in the dry particle size, packed bulk density (g / ml), feedability (g / 30 sec.), and adhesion. The evaluation results are shown in Table 1.

[0046] [Table 1]

[0047] It was found that the samples of Examples 1 and 2 had higher and better feedability than Comparative Example 1.

[0048] Furthermore, it was found that the samples of Examples 1 and 2 had lower and better adhesion than Comparative Example 1.

[0049] Although Examples 1 and 2 have smaller particles than Comparative Example 1, they have good adhesion, which is thought to be due to their high loose bulk density.

[0050] As shown in the examples, by setting the loose bulk density of magnesium hydroxide to a value within a specific range, it was possible to improve the feedability and adhesion of the magnesium hydroxide, while achieving both.

[0051] The magnesium hydroxide of the present invention, the resin composition containing that magnesium hydroxide, and the method for producing that magnesium hydroxide are not limited to the above-mentioned embodiments and examples, and can be appropriately combined or modified with other technologies within the scope that does not deviate from the purpose, intent, etc. of the present invention.

Claims

1. The loose bulk density is equal to or greater than 0.28 g / ml and less than 0.55 g / ml. Magnesium hydroxide.

2. The volume average diameter in the wet particle size distribution is 0.55 μm or more and 1.30 μm or less. The magnesium hydroxide of claim 1.

3. The volume fraction of particles of 250 μm or more in dry particle size is less than 35%; The magnesium hydroxide of claim 1.

4. Magnesium hydroxide according to any one of claims 1 to 3; Resin and Equipped with Resin composition.

5. a forming step of dry pressing a magnesium hydroxide raw material to form magnesium hydroxide having a loose bulk density of 0.28 g / ml or more and less than 0.55 g / ml; How to make magnesium hydroxide.

6. The magnesium hydroxide raw material has a loose bulk density of 1.0 g / ml or less. The method of claim 5.

7. the forming step includes a step of pressing the magnesium hydroxide raw material so that the volume average diameter in a wet particle size distribution of the magnesium hydroxide is 0.55 μm or more and 1.30 μm or less. The method of claim 5.

8. the forming step includes a step of pressing the magnesium hydroxide raw material so that a volume ratio of particles having a size of 250 μm or more in a dry particle size of the magnesium hydroxide is less than 35%. The method of claim 5.

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