JP2009155116A - Method for producing acicular boehmite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing acicular boehmite having less than 1 μm major axial length with high productivity in a simple operation. <P>SOLUTION: The method for producing boehmite is characterized in that a basic magnesium compound in a solid state is added to an acidic aqueous solution of aluminum sulfate until hydrogen ion concentration reaches pH 4 or higher so as to precipitate an aluminum hydrolyzate, which is then subjected to a hydrothermal process by heating to 150°C or higher. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a method for producing acicular boehmite having a major axis of less than 1 μm.

Acicular boehmite [AlOOH] is known as a filler for improving the rigidity and impact resistance of a resin material. As a method for producing such acicular boehmite, Patent Document 1 (Japanese Patent Laid-Open No. 2000-239014) discloses that a long axis length is obtained by adding aluminum hydroxide to an aqueous solution in which magnesium acetate is dissolved and hydrothermally treating it in an autoclave. However, it is difficult to produce acicular boehmite having a major axis length of less than 1 μm. As a method for producing acicular boehmite having a major axis length of less than 1 μm, an alkaline aqueous solution in which sodium hydroxide or the like is dissolved in an aluminum salt aqueous solution is added to Patent Document 2 (Japanese Patent Laid-Open No. 2006-56739). The aluminum hydrolyzate is precipitated by adjusting the hydrogen ion concentration to pH 4.5, and then kept at 120 ° C. for 24 hours, kept at 180 ° C. for 20 minutes, and then rapidly cooled to 10 ° C. or lower and then heated again to 140 A method of hydrothermal treatment under the condition of holding at 1 ° C. for 1 week is disclosed.

In such a conventional production method, acicular boehmite having a major axis length of less than 1 μm is obtained by adding an alkaline aqueous solution, but a method that can be produced by a simpler method has been desired.

JP 2000-239014 A JP 2006-56739 A

Therefore, the present inventor has intensively studied to develop a method capable of producing acicular boehmite having a major axis length of less than 1 μm with a simple operation and using a cheap aluminum salt aqueous solution, and as a result, the present invention has been achieved. .

That is, the present invention adds an aluminum hydrolyzate by adding a solid basic magnesium compound to an acidic aqueous solution containing aluminum sulfate at a temperature of 100 ° C. or lower and a hydrogen ion concentration of pH 4 or higher. An object of the present invention is to provide a method for producing acicular boehmite, characterized in that a product is heated to 150 ° C. or higher and hydrothermally treated.

According to the method of the present invention, acicular boehmite having a major axis length of less than 1 μm can be produced in an extremely short time by using an inexpensive aluminum salt aqueous solution by a simple operation.

The aluminum sulfate [Al ₂ (SO ₄ ) ₃ ] used in the production method of the present invention may be a solid solution dissolved in water or a liquid solution prepared by dissolving aluminum hydroxide in a sulfuric acid aqueous solution. Aluminum sulfate is an aluminum metal salt that is sold and used in large quantities for wastewater treatment as an inorganic flocculant under the name of “sulfuric acid band” or “sulfuric acid vane”, and is available at a very low cost.

The concentration of the aluminum salt per liter of the acidic aqueous solution containing aluminum sulfate is usually 0.05 mol / L or more in terms of volume efficiency in terms of Al ₂ O ₃ , and the precipitated aluminum hydrolyzate can be handled. In terms of ease, it is usually 5 mol / L or less.

The aqueous solution containing aluminum sulfate usually shows acidity with a hydrogen ion concentration of less than pH 4, but an acid may be further added to adjust the hydrogen ion concentration to pH 1-2. Specific examples of the acid include inorganic acids such as sulfuric acid and nitric acid, and organic acids such as acetic acid.

A basic magnesium compound is added to the acidic aqueous solution. The basic magnesium compound may be added in the form of a powder, or it may be dispersed alone in water or the like, or may be added as a sol by pulverizing a slurry containing the basic magnesium compound with a wet pulverizer. Add in the form. Thereby, since the melt | dissolution process for preparing the aqueous alkali solution conventionally required can be skipped, it leads to simplification of a manufacturing process.

Examples of basic magnesium compounds include those having low solubility in neutral water, such as magnesium hydroxide, magnesium oxide, magnesium carbonate, basic magnesium sulfate [MgSO ₄ .5Mg (OH) ₂ .3H ₂ O]. It is done. Of these, magnesium hydroxide is preferred.

The basic magnesium compound has a particle size of 10 μm or less, preferably 5 μm or less, as an aggregated particle size. When the aggregated particle diameter is 10 μm or more, the basic magnesium compound is difficult to dissolve during mixing with an acidic aqueous solution containing aluminum sulfate and during hydrothermal treatment, which is not preferable. The aggregate particle diameter means a particle diameter measured by a laser diffraction method.

The concentration of the basic magnesium compound is determined from the aluminum salt concentration and the pH for obtaining the hydrolyzate, but is usually 0.1 mol / L or more. In addition, when a large amount of the basic magnesium compound is added, it takes time to dissolve the basic magnesium compound in the aqueous solution, and therefore it is usually 10 mol / L or less.

The basic magnesium compound is added until the hydrogen ion concentration reaches pH 4 or higher. By adding a basic magnesium compound, the acidic aqueous solution containing aluminum sulfate is neutralized, the hydrogen ion concentration gradually decreases, and an aluminum hydrolyzate is formed, usually in the form of a slurry or gel. To do. The basic magnesium compound is added until the hydrogen ion concentration becomes pH 4 or higher. However, it is preferable to add the basic magnesium compound so that the device used for the reaction is less likely to corrode, and pH 9 or lower. It is preferable to add so that it may become pH 7 or less at the point obtained easily.

The temperature at which the basic magnesium compound is added to precipitate the hydrolyzate is 100 ° C. or lower, preferably 50 ° C. or lower, and is usually higher than the freezing temperature of the aqueous solution. Since heat of neutralization reaction occurs when adding a basic magnesium compound to an acidic aqueous solution containing aluminum sulfate, the basic magnesium compound is added while cooling so that the above temperature is not exceeded. It is preferable.

Thus, by adding the basic magnesium compound until the hydrogen ion concentration becomes pH 4 or more, the aluminum salt in the acidic aqueous solution containing aluminum sulfate is hydrolyzed to produce an aluminum hydrolyzate, usually in a slurry or gel form To be deposited.

Only the basic magnesium compound may be added until the pH becomes 4 or more, but it is also possible to make the pH 4 or more by adding a base not containing a metal component such as ammonia. For example, when ammonia is used, it may be added in a gaseous state, but it is preferably added as an aqueous ammonia solution.

Next, the hydrolysis mixture after the aluminum hydrolyzate is deposited is heated to 150 ° C. or higher, usually 250 ° C. or lower. Heating is performed under pressure in a pressure vessel such as an autoclave. The pressurization may be performed by steam generated by heating the hydrolysis mixture in a sealed pressure vessel, or may be performed by supplying compressed nitrogen, compressed air, or the like from the outside.

The heating of the hydrolysis mixture is usually performed over 10 minutes after the temperature of the mixture reaches a predetermined temperature. By heating to such a temperature, the precipitated aluminum hydrolyzate undergoes a structural transition to boehmite, and a slurry containing the desired acicular boehmite can be obtained.

The heating time is 10 minutes or more, usually less than 24 hours. After the above hydrothermal treatment, it is preferable to collect the slurry, solid-liquid separate by a known method such as vacuum filtration and centrifugation, and then wash with water or a water / methanol mixed solution to remove impurities such as by-product salts. .

Thus, the desired acicular boehmite can be obtained. The major axis length of this acicular boehmite is usually less than 1 μm, and the aspect ratio (major axis length / minor axis length) is 10 or more.

The acicular boehmite obtained by the method of the present invention has a high aspect ratio and is useful as a filler for resin. The resin composition obtained by filling the acicular boehmite of the present invention into a resin is excellent in mechanical strength.

Examples of the resin include thermoplastic resins such as olefin resin, aromatic polyester resin, aliphatic polyester resin, aromatic polyamide resin, and methacrylic resin, epoxy resin, vinyl ester resin, phenol resin, unsaturated polyester resin, polyimide resin, and polyurethane. Examples thereof include thermosetting resins such as resins and melamine resins.

Examples of the olefin resin include polyolefin homopolymers such as polyethylene, polypropylene, and polybutene. Examples of the olefin resin include polyolefin copolymers such as ethylene-propylene copolymer and ethylene-butene copolymer. The polyolefin copolymer may be a random copolymer or a block copolymer. May be.

Examples of the aromatic polyester resin include polyethylene terephthalate and polybutylene terephthalate.

Examples of the aliphatic polyester resin include polycaprolactone and polyhydroxybutyrate.

As an aromatic polyamide resin, nylon-6, nylon-10, nylon-12, nylon-46 etc. are mentioned, for example.

In order to fill the resin with the acicular boehmite obtained by the method of the present invention, for example, when a thermoplastic resin is used as the resin, the thermoplastic resin may be melt-kneaded together with the acicular boehmite of the present invention. Examples of the melt kneading include a Banbury mixer, a plast mill, a Brabender plastograph, a single screw extruder, a twin screw extruder, and the like. In addition, the acicular boehmite of the present invention is added to a monomer such as the thermoplastic resin, a polymerization method, or the acicular boehmite of the present invention is added to a solvent in which the thermoplastic resin is dissolved, and the solvent is added. It can also be filled by removing.

When a thermosetting resin is used as the resin, the uncured resin before thermosetting may be mixed with the acicular boehmite obtained by the method of the present invention and then cured by heating. For mixing, for example, a Henschel mixer, a ribbon blender, or the like is used.

The filling amount of acicular boehmite is usually 0.1 parts by mass or more, preferably 1 part by mass or more with respect to 100 parts by mass of the resin, and the resin composition obtained by filling is easy. It is 100 parts by mass or less, preferably 50 parts by mass or less in that it is easy to mold.

The resin composition obtained by filling the resin with the acicular boehmite of the present invention includes, for example, a dispersant, a lubricant, a plasticizer, a flame retardant, an antioxidant, an antistatic agent, a light stabilizer, an ultraviolet absorber, and crystallization. It may contain colorants such as accelerators (nucleating agents), pigments, dyes and the like. Further, fillers other than the acicular boehmite of the present invention, for example, particulate fillers such as carbon black, titanium oxide, talc, calcium carbonate, mica, clay, short fiber fillers such as wollastonite, potassium titanate, etc. No whiskers.

Such a resin composition is usually used after being molded into a molded body. Examples of the molding method include an injection molding method, a compression molding method, and an extrusion molding method.

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

In addition, the powder obtained in each Example was evaluated by the following method.
(1) The powder X-ray diffraction spectrum obtained by using a main crystal phase X-ray diffractometer [manufactured by Rigaku Corporation, “RINT2000”] was identified by comparing it with JCPDS (Joint Committee on Powder Diffraction Standards).
(2) BET specific surface area It was determined by a nitrogen gas adsorption method using a specific surface area measuring device ["Macsorb HMModel-1208" manufactured by Mountec Co., Ltd.].
(3) The particle size was determined by observing with a transmission electron microscope having a long diameter and a short diameter.
(4) Magnesium hydroxide is dispersed in a 0.1% sodium hexametaphosphate aqueous solution using an agglomerated particle size laser scattering type particle size distribution measuring apparatus (Microtrac HRA, manufactured by Reed and North Co.) as D50 on a weight basis. Asked.

Example 1
242 g of liquid aluminum sulfate containing aluminum sulfate in an amount equivalent to 0.19 mol in terms of Al ₂ O ₃ [Aluminum sulfate aqueous solution “JIS waterworks standard product” manufactured by Sumitomo Chemical Co., Ltd.] was diluted with 397 g of pure water. To this, 33.8 g (0.58 mol) of powdered magnesium hydroxide [aggregated particle diameter 0.83 μm] was added in powder form at room temperature [25 ° C.] with stirring, and further stirred for 1 hour. The mixture after 1 hour had a hydrogen ion concentration of pH 4.8, and a gelled aluminum hydrolyzate was precipitated. Thereafter, the temperature was raised to 200 ° C. over 90 minutes while stirring at 500 rpm in an autoclave having an internal volume of 1 L, and hydrothermal treatment was performed while maintaining the same temperature for 4 hours. After cooling, the contents are taken out, mixed with 2 L of water, and then the washing operation of collecting the solid content by centrifugation is repeated three times. The washed solid content is heated to 120 ° C. and dried to obtain a white powder. Got.

This white powder had a main crystal phase of boehmite, a BET specific surface area of 180 m ² / g, a major axis length of 100 nm to 200 nm, a minor axis length of 5 nm to 10 nm, and an aspect ratio of 10 to 20. A transmission electron micrograph of this white powder is shown in FIG.

Comparative Example 1
Example in place of magnesium hydroxide except that 200 mL (0.72 mol) of an aqueous solution having a concentration of 3.6 mol / L obtained by dissolving sodium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd., reagent grade) in water was added. The same operation as in 1 was performed. The hydrogen ion concentration after addition of this aqueous solution and stirring for 1 hour was pH 4.2. The obtained white powder had a main crystal phase of soda alum [NaAl ₃ (SO ₄ ) ₂ (OH) ₆ ] and an angular shape of 1 to 3 μm. A scanning electron micrograph of this white powder is shown in FIG.

2 is a transmission electron micrograph of the white powder obtained in Example 1. FIG. 2 is a scanning electron micrograph of the white powder obtained in Comparative Example 1.

Claims (2)

A basic magnesium compound in a solid state is added to an acidic aqueous solution containing aluminum sulfate until the hydrogen ion concentration becomes pH 4 or higher to precipitate an aluminum hydrolyzate, and the obtained aluminum hydrolyzate is heated to 150 ° C. or higher. A method for producing acicular boehmite, which is hydrothermally treated. The production method according to claim 1, wherein the magnesium compound is magnesium hydroxide.