JP2005247604A - Magnesium hydroxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide magnesium hydroxide which can be formulated with a thermoplastic polymer to impart sufficient flame retardancy thereto without causing a discoloration problem. <P>SOLUTION: The magnesium hydroxide has a calcium content of 1/100 or smaller and a content of a metallic element of group 14 in the periodic table of 0.2/100 to 20/100, the contents being expressed in terms of a numerical ratio of the related atoms to the magnesium atoms, a BET specific surface area of 100 m<SP>2</SP>/g or larger as measured by nitrogen adsorption. This is produced by dissolving a magnesium compound in water and hydrolyzing the compound in the presence of an element of group 14 in the periodic table. A flame-retardant polymer composition prepared by formulating a synthetic polymer with the magnesium hydroxide exhibits sufficient flame retardancy and does not discolor even when heated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to magnesium hydroxide, and more particularly to magnesium hydroxide used as a flame retardant in a synthetic polymer.

Magnesium hydroxide is blended and used as a flame retardant in a synthetic polymer, and the higher the specific surface area, the higher the flame retardancy. For this reason, magnesium hydroxide having a high specific surface area is required. As magnesium hydroxide having a high specific surface area, one obtained by reacting magnesium chloride with slaked lime [Ca (OH) ₂ ] in water is known [Patent Document 1: Japanese Patent Laid-Open No. 48-43088].

JP-A-48-43088

However, the magnesium hydroxide obtained by the method described in Patent Document 1 has a problem that a composition in which this is blended with a synthetic polymer is easily discolored under heating.

Therefore, the present inventor has intensively studied to develop magnesium hydroxide that does not cause discoloration even when blended with a synthetic polymer and can impart sufficient flame retardancy. Magnesium hydroxide having a high specific surface area with a content of 1/100 or less and a metal element content of Group 14 of the Periodic Table is 0.2 / 100 to 20/100. Has been found to give sufficient flame retardancy, and the present invention has been achieved.

That is, according to the present invention, the atomic ratio to magnesium is such that the calcium content is 1/100 or less and the content of the metal element belonging to Group 14 of the periodic table is 0.2 / 100 to 20/100. Magnesium hydroxide having a BET specific surface area of 100 m ² / g or more is provided.

The magnesium hydroxide of the present invention is useful as a flame retardant used in a synthetic polymer because it provides sufficient flame retardancy when blended with a synthetic polymer and does not discolor under heating. is there.

The magnesium hydroxide of the present invention has a calcium content of 1/100 or less, preferably 0.7 / 100 or less in terms of the number ratio of magnesium, and substantially does not contain calcium, and its content is 0/100. There may be.

The magnesium hydroxide of the present invention contains a metal element belonging to Group 14 of the Periodic Table, such as silicon (Si), tin (Sn), and the like. The content of the metal element of Group 14 of the periodic table is 0.2 / 100 to 20/100, preferably 1/100 to 15/100, in terms of the atomic ratio with respect to magnesium. If the content is less than 0.2 / 100, the flame retardancy tends to be insufficient, and if it exceeds 20/100, there is no effect commensurate with this, which is uneconomical.

The magnesium hydroxide of the present invention has a BET specific surface area of 100 m ² / g or more, preferably 150 m ² / g or more, usually 400 m ² / g or less, preferably 300 m ² / g or less as measured by a nitrogen adsorption method. When the BET specific surface area is less than 100 m ² / g, sufficient flame retardancy tends not to be imparted.

The magnesium hydroxide of the present invention can be produced, for example, by hydrolyzing a magnesium compound with water in water in the presence of a metal element belonging to Group 14 of the periodic table.

As the magnesium compound, water-soluble compounds are used, and specific examples include magnesium inorganic salts such as magnesium chloride, magnesium nitrate and magnesium sulfate, and magnesium organic salts such as magnesium acetate. The amount of water used may be an amount sufficient to dissolve the magnesium compound and can be hydrolyzed by the base, and is usually about 1 to 100 times, preferably 1 times the weight of the magnesium compound. It is about 20 mass times.

In order to hydrolyze in the presence of a metal element belonging to Group 14 of the Periodic Table, for example, a water-soluble compound of the metal element may be used and dissolved or dispersed in water. Examples of such compounds include inorganic silicon compounds such as sodium silicate (water glass), potassium silicate, ammonium silicate, and silicic acid, tin chloride [Sn (II) Cl ₂ , Sn (IV) Cl ₄ ], Tin inorganic salts such as tin sulfate [Sn (II) SO ₄ , Sn (IV) (SO ₄ ) ₂ ], tin nitrate [Sn (II) (NO ₃ ) ₂ , Sn (IV) (NO ₃ ) ₄ ] And tin compounds. The amount of the group 14 metal element compound in the periodic table is usually 0.2 / 100 to 20/100, preferably 1/100 to 15 / in terms of the atomic ratio of the group 14 metal element to the magnesium compound. 100.

As the base, those not containing calcium are used. For example, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia and the like can be used.

For the hydrolysis, for example, a base and a compound of an element belonging to Group 14 of the periodic table may be dissolved in water in advance and mixed with a magnesium compound. The magnesium compound is preferably mixed as an aqueous solution previously dissolved in water. Further, a base may be dissolved in water in advance and mixed with a magnesium compound and a compound of an element belonging to Group 14 of the periodic table. It is preferable that the magnesium compound and the compound of the element belonging to Group 14 of the periodic table are each alone or mixed in advance and then mixed with a base, dissolved in water in advance and mixed as an aqueous solution.

The hydrolysis temperature is usually in the range of 0 ° C to 100 ° C, preferably 10 ° C to 50 ° C. The time required for the hydrolysis may be a time sufficient for the magnesium compound to hydrolyze and precipitate, and is usually 3 hours or less, and may be completed simultaneously with the mixing.

The magnesium hydroxide of the present invention can be obtained by taking out the precipitate from the hydrolysis mixture after hydrolysis and drying it. The resulting magnesium hydroxide is in the form of a powder and is usually crystalline showing a peak of magnesium oxide by powder X-ray diffraction.

The magnesium hydroxide of the present invention is useful as a flame retardant used by blending with a synthetic polymer. The synthetic polymer may be a synthetic rubber. Examples of the synthetic rubber include styrene-butadiene rubber (SBR), neoprene rubber, isoprene rubber, butyl rubber, chloroprene rubber, butadiene rubber, acrylonitrile / butadiene rubber, and ethylene / propylene rubber.

Further, it may be a synthetic resin, a thermoplastic synthetic resin that is plasticized by heating, or a thermosetting synthetic resin that is cured by heating. Examples of the thermoplastic synthetic resin include polyolefin resins such as polyethylene resin and polypropylene resin, styrene resins such as polystyrene and acrylonitrile-styrene-butadiene copolymer resin (ABS resin), ethylene-vinyl acetate copolymer resin, and polyethylene terephthalate resin. (PET). Examples of the thermosetting synthetic resin include an epoxy resin and a urethane resin.

The amount of magnesium hydroxide blended varies depending on the type of synthetic polymer and the desired degree of flame retardancy, but is usually about 1 to 150 parts by weight, preferably 2 parts by weight per 100 parts by weight of the synthetic polymer. Part to about 50 parts by mass. If the amount is less than 1 part by mass, sufficient flame retardancy tends not to be exhibited.

In order to mix the magnesium hydroxide of the present invention with a synthetic polymer, for example, when using an emulsion dispersed in water as a synthetic polymer, the magnesium hydroxide of the present invention is added to the emulsion, and then the mixture is made acidic. A synthetic polymer and magnesium hydroxide may be precipitated by adding a salt. In addition to the magnesium hydroxide of the present invention, additives such as processing oils, stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, reinforcing agents, dyes and pigments may be added to the emulsion.

In order to make it acidic, an acid may be added. As the acid, for example, an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid is used. As the salt, a water-soluble salt is used, and examples thereof include sodium chloride, potassium chloride, potassium nitrate, sodium nitrate, sodium sulfate, and potassium sulfate. These acids and salts are each alone or in combination of two or more. Used.

By adding salt after acidification, the synthetic polymer in the emulsion is precipitated together with magnesium hydroxide by salting out. A flocculant may be added together with the salt. A precipitated polymer is taken out from the mixture after salting out, washed with water if necessary, and dried to obtain a powdery polymer composition in which a synthetic polymer and magnesium hydroxide are mixed. This composition is flame retardant. The flame retardant polymer composition may be molded by a usual method such as a hot press molding method. In molding, a crosslinking agent and a vulcanization accelerator may be added as necessary.

When the synthetic polymer is thermoplastic, it may be melted by heating and mixed with the magnesium hydroxide of the present invention while kneading to obtain a flame retardant polymer composition. In addition to the magnesium hydroxide of the present invention, additives such as a lubricant, an antioxidant, an antioxidant, an ultraviolet absorber, an antistatic agent, a reinforcing agent, a dye, and a pigment may be added. In order to melt by heating and knead, a kneader such as a normal uniaxial kneader or biaxial kneader may be used.

When the synthetic polymer is thermosetting, the precursor before thermosetting and the magnesium oxide of the present invention may be mixed and polymerized and cured. In addition to the magnesium hydroxide of the present invention, additives such as lubricant antioxidants, dyes and pigments may be added.

Thus, the flame retardant polymer composition obtained by mixing the magnesium hydroxide of the present invention with a synthetic polymer exhibits sufficient flame retardancy and does not discolor even when heated.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by this Example.

In addition, the magnesium hydroxide and flame retardant polymer composition obtained in each Example were evaluated by the following methods.
The content of Si, Sn and Ca in magnesium hydroxide was determined as the atomic ratio with respect to magnesium by fluorescent X-ray analysis.
The BET specific surface area of magnesium hydroxide was determined by a nitrogen adsorption method.
The discoloration of the flame retardant polymer composition was determined by first obtaining the color coordinates L, a and b according to the UCS color system with a formula difference meter (“Z-300A” manufactured by Nippon Denshoku Industries Co., Ltd.) for the test piece. , Which are respectively L ₀ , a ₀ and b _0, and then the test piece is kept in an air bath at 60 ° C. for 93 hours to obtain the color coordinates L, a and b in the same manner, and these are respectively determined as L ₉₃ , a ₉₃ and b ₉₃ and the formula (1)
ΔE = {(L ₀ −L ₉₃ ) ² + (a ₀ −a ₉₃ ) ² + (b ₀ −b ₉₃ ) ² } ^1/2 (1)
Thus, the color difference ΔE was obtained and evaluated. A smaller ΔE indicates a smaller color change.
The flame retardancy of the flame retardant polymer composition is the maximum heat generation per unit area under the condition of a heat flow rate of 35 kW / m ^{2 with} a cone calorimeter [Toyo Seiki Co., Ltd., “Cone Calorimeter III”] for the test piece. The speed was determined and evaluated. A smaller maximum heat generation rate indicates flame retardancy.

Example 1
345 g of sodium hydroxide was dissolved in 3600 g of water, and 22.5 g of water glass (JIS No. 1) was further dissolved to obtain an aqueous solution. While stirring this aqueous solution at room temperature (about 25 ° C.), an aqueous solution in which 786 g of magnesium chloride hexahydrate was dissolved in 1500 g of water was added dropwise to cause hydrolysis to precipitate the precipitate. Stirring was continued for 10 minutes after completion of the dropping, and then the stirring was stopped. The precipitate was removed by centrifugation, dispersed in water, centrifuged again, and dried with an air dryer to obtain a powder. . This powder was confirmed to be magnesium hydroxide crystals by powder X-ray diffraction. This powder has an atomic ratio of calcium (Ca) content to magnesium (Mg) of less than 0.1 / 100 (lower detection limit), silicon (Si) content of 5/100, and tin (Sn) content of 0. It was less than 1/100 (detection lower limit), and the BET specific surface area was 172 m ² / g.

100 parts by mass of a polyethylene resin (manufactured by Sumitomo Chemical Co., Ltd., “FS-240”) was melted at 160 ° C. with a kneader (manufactured by Toyo Seiki Co., Ltd., “Lab Plast Mill”) and kneaded while kneading. 100 parts by mass of magnesium was added, and the mixture was further mixed for 10 minutes to obtain a flame retardant polymer composition. This composition was pressed at 160 ° C. for 10 minutes to obtain a plate-like polypropylene press-molded body having a length of 40 mm, a width of 40 mm and a thickness of 3 mm. When this press-molded body was used as a test piece and the discoloration was evaluated, ΔE was 4.2.

45 parts by mass of magnesium hydroxide obtained above and 38 parts by mass of processing oil (aromatic oil, “JOMO Process X”, manufactured by Japan Energy Co., Ltd.), SBR [“# HS-1”, Sumitomo Chemical Co., Ltd. Manufactured) In addition to an emulsion in which 100 parts by mass are dispersed in 310 parts by mass of water, 16 parts by mass of 1N sulfuric acid (containing 0.5 mol of H ₂ SO ₄ in 1 L) and 25% aqueous sodium chloride solution [NaOH in 1 kg 250 g included] 200 parts by mass were added to precipitate the precipitate. The precipitate was taken out by filtration, washed with water, and dried to obtain a flame retardant polymer composition. Using a lab plast mill, 53 parts by mass of this composition was added to a vulcanization accelerator ["Soccinol CZ", manufactured by Sumitomo Chemical Co., Ltd.] 0.28 parts by mass, a vulcanization accelerator ["Soccinol D", 0.28 parts by mass and 0.39 parts by mass of a vulcanizing agent [sulfur] were added and hot-pressed at 170 ° C. for 20 minutes to obtain a 3 mm thick SBR press molded product. When this molded body was cut into a length of 100 mm × 100 mm to obtain a test piece and the flame retardancy was evaluated, the maximum heat generation rate per unit area was 615 kW / m ² .

Example 2
An aqueous solution prepared by dissolving 115 g of sodium hydroxide in 1200 g of water and dissolving 249 g of magnesium chloride hexahydrate and 3 g of tin (II) chloride dihydrate in 500 g of water while stirring at room temperature (about 25 ° C.). It was added dropwise and hydrolyzed to precipitate the precipitate. Stirring was continued for 10 minutes after completion of dropping, and then stirring was stopped. The precipitate was removed by centrifugation, dispersed in water, centrifuged again, and dried at 120 ° C. to obtain a powder. This powder was confirmed to be magnesium hydroxide crystals by powder X-ray diffraction. The calcium (Ca) content of this powder was less than 0.1 / 100 (lower detection limit) with respect to magnesium (Mg) in atomic ratio. The silicon (Si) content was less than 01/100 (lower detection limit) and the tin (Sn) content was 5.3 / 100 in terms of the atomic ratio relative to magnesium. The BET specific surface area was 118 m ² / g.

The polypropylene press-molded product obtained in the same manner as in Example 1 except that the magnesium hydroxide obtained above was used in place of the magnesium hydroxide obtained in Example 1 was the same as the polypropylene press obtained in Example 1. Discoloration (ΔE) comparable to that of the molded product is exhibited.

In addition, the SBR press molded body obtained in the same manner as in Example 1 except that the magnesium hydroxide obtained above was used in place of the magnesium hydroxide obtained in Example 1 was the SBR press obtained in Example 1. The maximum heat generation rate is the same as that of the molded body.

Comparative Example 1
A slurry obtained by dispersing 300 g of calcium hydroxide (manufactured by Suzuki Kogyo Co., Ltd., “Caltech LT”) in 2 kg of water and an aqueous solution in which 890 g of magnesium chloride hexahydrate was dissolved in 8.4 kg of water were stirred at room temperature. At about 25 ° C., it was added dropwise to 1000 g of water over 20 minutes, and stirring was further continued for 10 minutes after completion of the dropwise addition. The solid content in the mixture after stirring was removed by centrifugation, dispersed in water, further centrifuged to remove the solid content, and then dried at 120 ° C. to obtain a powder. This powder was confirmed to be magnesium hydroxide crystals by powder X-ray diffraction. This powder has a calcium (Ca) content of 20/100 with respect to magnesium (Mg) by atomic ratio, a silicon (Si) content of less than 0.1 / 100, and a tin (Sn) content of 0.1 / 100. (Detection lower limit) and the BET specific surface area was 58 m ² / g.

When the discoloration property of the polypropylene press-molded article obtained by operating in the same manner as in Example 1 was evaluated except that the magnesium hydroxide obtained above was used instead of the magnesium hydroxide obtained in Example 1, ΔE was 6.2.

Comparative Example 2
Instead of the magnesium hydroxide obtained in Example 1, commercially available magnesium hydroxide [manufactured by Kyowa Chemical Co., Ltd., “Kisuma 5”, the atomic ratio of calcium (Ca) content to magnesium (Mg) is 0.1 / 100 (Detection lower limit), silicon (Si) content is less than 0.1 / 100, tin (Sn) content is less than 0.1 / 100 (detection lower limit), and BET specific surface area is 7 m ² / g] 45 The SBR press-molded body was obtained by operating in the same manner as in Example 1 except that the parts by mass were used, and when the flame retardancy was evaluated, the maximum heat generation rate per unit area was 898 kW / m ² .

Claims (3)

The atomic ratio with respect to magnesium, the calcium content is 1/100 or less, the content of the metal element of Group 14 of the periodic table is 0.2 / 100 to 20/100, and the BET specific surface area by the nitrogen adsorption method is 100 m. Magnesium hydroxide which is ² / g or more. The method for producing magnesium hydroxide according to claim 1, wherein the magnesium compound is dissolved in water and hydrolyzed with a base in the presence of a metal element belonging to Group 14 of the periodic table. A flame retardant polymer composition comprising the magnesium hydroxide according to claim 1 blended with a synthetic polymer.