JP2005060164A - Hydrotalcite particle, and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide hydrotalcite particles with a new, special shape having excellent characteristics such as a high specific surface area, a high pore volume, a low bulk density and high liquid absorbability, and to provide a production method therefor. <P>SOLUTION: The hydrotalcite particles have a tubular structure, and are produced, in a process of adding alkali aluminate to a water base suspension of tubular flocks consisting of the flakelike fine crystals of basic magnesium carbonate, by: (1) regulating the pH of the water base suspension before the addition of the alkali aluminate to 7.0 to 9.5; (2) holding its temperature under the addition of the alkali aluminate to the range of 10 to 25°C; and (3) controlling the amount of the alkali aluminate to be added to 40 to 65g expressed in terms of Al<SB>2</SB>O<SB>3</SB>per 100g of MgO contained in the basic magnesium carbonate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a hydrotalcite particle having a novel and special shape and a method for producing the same. More specifically, the present invention relates to a hydrotalcite particle having a tubular structure and having excellent characteristics such as a high specific surface area, a high pore volume, a low bulk density, and a high liquid absorbency, and a method for producing the same.

Technical background

Hydrotalcite is a layered mineral of basic magnesium aluminum carbonate hydrate, [Mg _1-x Al _x (OH) ₂ ] _x · [(CO ₃ ) _{x / 2} · yH ₂ O] _x (x is Usually 0.2 to 0.33).
Specific compositions include Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O, Mg ₅ Al ₂ (OH) ₁₄ CO ₃ .4H ₂ O, or Mg _4.3 Al ₂ (OH) _12.6 CO ₃ .4H _2. O and the like are known.
Further, Co ²⁺ to Mg sites, Ni ^2+, divalent metal ions such as Zn ^2+, Fe ³⁺ to Al sites, trivalent metal ions such as Cr ^3+, CO ₃ sites Also known are those in which anions such as OH ⁻ , Cl ⁻ and SO 4 ²⁻ are dissolved.

Hydrotalcite is characterized by having anion exchange ability and acid neutralization ability. Utilizing these performances, etc., pharmaceuticals such as anion exchanger, adsorbent, deodorant, antacid and gastric ulcer treatment It is used as a stabilizer for olefinic and chlorinated resins.
Hydrotalcite is naturally produced, but many synthetic methods are currently being developed.
As a method for producing the hydrotalcite, for example, a mixture of aluminum hydroxide and magnesium hydroxide described in Patent Document 1 is prepared in the presence of carbon dioxide in an aqueous medium containing ammonia or a water-soluble organic nitrogen-containing base. There is a method of heating at 100 ° C.

  Further, a method of solid-liquid reaction between basic magnesium carbonate and alkali aluminate in the alkaline region described in Patent Document 2, aluminum hydroxide described in Patent Document 3, completely or partially changed to magnesium oxide. A method of hydrothermally synthesizing magnesium hydroxide and basic magnesium carbonate at 50 to 100 ° C. under the action of shearing force and then spray drying, a specific amount of hydroxylation in the water-soluble magnesium salt aqueous solution described in Patent Document 4 A method has been proposed in which magnesium is added and then a mixed solution of a water-soluble aluminum salt and sodium carbonate is added dropwise to boil reduction at pH 8 or higher.

  Many proposals have also been made on modified hydrotalcite products or applications. For example, hydrotalcite-containing antacids described in Patent Document 5 and hydrotalcites described in Patent Document 6 and Patent Document 7 are used. Photochromic material in which photochromic molecules are intercalated between talcite layers, stabilizer for resin described in Patent Document 8, hydrotalcite ion-exchanged perchlorate ion described in Patent Document 9, and halogen containing the same There are a resin composition, a hydrotalcite-based compound in which silicic acid or the like is held between layers described in Patent Document 10, and an infrared absorber that is used therefor.

[Prior art documents]
Japanese Patent No. 14334678 Japanese Patent No. 1546644 Japanese Patent No. 1573376 JP-A-6-329410 Japanese Patent No. 1573376 JP-A-6-95288 JP-A-6-95289 Japanese Patent No. 2925857 JP-A-6-219732 JP 2001-2408 A

As for the hydrotalcite, many studies have been made as described above, but there are few things related to the particle shape, and it is new for expanding applications to other fields, improving performance, enhancing functionality, etc. A hydrotalcite having a shape and exhibiting excellent characteristics derived from the shape is desired.
The present inventors have been studying basic magnesium carbonate that can be used as one of the raw materials for hydrotalcite, and among them, a novel and unique base of tubular aggregated particles composed of flaky fine crystals. Patent application has already been filed (Japanese Patent Application Nos. 2002-179462 and 2002-220768).

Then, when this unique shaped basic magnesium carbonate was treated with an aqueous alkali aluminate solution, etc., it was also found that surface-treated basic magnesium carbonate coated with a coating such as alumina having characteristics before coating was obtained. A patent application has already been filed for this (Japanese Patent Application No. 2002-376709).
Furthermore, the knowledge that tubular particles of magnesium aluminum double hydroxide can be produced by performing treatment with an aqueous alkali aluminate solution under specific conditions has been obtained, and a patent application has also been filed (Japanese Patent Application No. 2002-380092).

Based on these experiences, the present inventors paid attention to the unique shape of the basic magnesium carbonate tubular aggregated particles, and produced hydrotalcite using the basic magnesium carbonate tubular aggregated particles as a raw material. As a result of diligent research and development regarding the possibility, the present invention has been successfully developed.
That is, the subject of this invention is providing the hydrotalcite particle | grains which have a novel shape, and express the various outstanding characteristic derived from the shape, and its manufacturing method.

The present invention provides hydrotalcite particles and a method for producing the same in order to solve the above-mentioned problems. Among them, the hydrotalcite particles have a tubular structure.
Further, the method for producing hydrotalcite particles having a tubular structure of the present invention includes the step of adding an alkali aluminate to an aqueous suspension of tubular aggregated particles composed of flaky fine crystals of basic magnesium carbonate.
(1) pH of aqueous suspension before addition of alkali aluminate is 7.0 to 9.5,
(2) Keeping the temperature during alkali aluminate addition in the range of 10 to 25 ° C.
(3) The addition amount of alkali aluminate is 40 to 65 g in terms of Al ₂ O ₃ per 100 g of MgO contained in basic magnesium carbonate.

The hydrotalcite particles of the present invention have a novel and unique shape called a tubular shape, and the high specific surface area, high pore volume, high oil absorption, high water absorption, low bulk density and porosity are derived from the shape. It has various excellent characteristics.
In addition to these properties, it also has excellent properties such as flame retardancy, acid neutralization ability, and anion exchange performance.

  As a result, the hydrotalcite particles of the present invention make use of these properties, various fillers for rubber, resin or paper, heat insulating materials, sound absorbing materials, heat insulating materials, filters, medical pesticides and cosmetic carriers, Medical pesticides and cosmetics including it, catalyst carrier, microbial carrier, biological carrier, plant growth agent, olefin absorbent, liquid absorbent, oil absorbent, desiccant, fragrance, deodorant, sealing agent, rust preventive, It can be used as a food additive, a filter agent, a filter aid, an abrasive, or a column filler, and exhibits excellent effects.

For example, as a filler for rubber, not only is it effective for reducing the weight of rubber products due to the above-mentioned property of low bulk density, but also the unevenness on the particle surface improves adhesion to the matrix, resulting in high strength. It is also possible to obtain a rubber product.
Furthermore, when it is used as a filler for resin, it has the same effect of reducing weight or improving strength, and is effective in imparting flame retardancy because it has crystal water. It has an anion scavenging ability as a property of, and when used as a flame retardant, it also has an effect of suppressing halogen ion release during combustion and resin degradation caused by free halogen ions.

In addition, the paper filler is derived from a tubular shape having an extensibility, and is effective in improving the strength of the paper. In addition, the paper has improved printability due to its properties of high oil absorption and high water absorption, and Due to its low density, it is effective for reducing the weight of paper products.
In addition, coated paper using the hydrotalcite particles as a coating pigment for paper becomes a lightweight coated paper, and has excellent ink acceptability, opacity after printing, printability, etc. For example, it can be used for ink jet recording paper, thermal recording paper, and the like.

Furthermore, when it is used as a carrier for medicines, agricultural chemicals, cosmetics, etc., it has a space that can contain an active ingredient inside the tubular structure and has a high pore volume and high specific surface area, thereby increasing the amount of impregnation of drugs and the like In addition, it is possible to obtain medical and agrochemicals and cosmetics having controlled release characteristics such as controlled release characteristics and selective removal characteristics for adsorbing and removing specific substances.
In particular, when an active ingredient is impregnated into the tubular structure of the tubular particles of the hydrotalcite to make an antacid, the hydrotalcite itself has an antacid effect, so that the hydrotalcite itself can be taken by taking it. At the same time as the antacid effect is exerted, the active ingredient impregnated in the tubular structure is released, and the effect by the ingredient is also expressed, so that an antacid having a plurality of effects can be obtained.

The molded product or granulated product obtained by molding the hydrotalcite of the present invention using a binder or the like not only has excellent lightness due to the property of low bulk density, but also has heat insulation properties due to the property of porosity. It also exhibits effects such as sound absorption, adsorbability, and filterability, and can be used as, for example, a heat insulating material, a sound absorbing material, a heat insulating material, and a filter.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the best mode for carrying out the present invention will be described in detail. However, the present invention is not limited thereby, but is specified by the description of the scope of claims. Not too long.
The hydrotalcite particles of the present invention are characterized by having a tubular structure, and the structure is a new and unique shape.
The hydrotalcite in the present invention are those represented by _{[Mg 1-x Al x (} OH) 2] x · [(CO 3) x / 2 · yH 2 O] x, the values of x and y Although there is no special restriction, there is Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O, which is generally known as hydrotalcite.

The hydrotalcite particles of the present invention are obtained by collecting the plate-like and / or irregular fine particles of hydrotalcite into a tubular shape.
The fine particles forming the tubular particles are indefinite shapes having a diameter of 0.05 to 0.5 μm, or plate-like ones having a thickness of 0.02 to 0.2 μm and a diameter of 0.2 to 5 μm.
The hydrotalcite particles of the present invention have various excellent effects due to the unique shape of a tubular structure in which such fine particles are aggregated.
Specifically, the reinforcing shape is expressed as a filler such as a resin or rubber by a tubular shape having extensibility.

In addition, due to the irregularity of the particle surface due to the tubular structure in which the fine particles are aggregated, when used as various fillers, the adhesion with the matrix substance is improved, and the performance as a porous material is also excellent. It is also effective for adsorbents and carriers.
Furthermore, since a space exists inside the particles in accordance with the tubular shape, it has an excellent effect as a carrier that can enclose an active ingredient therein.
Not only that, it has excellent heat insulation properties due to increased voids, and the space inside the tube can be used as a reaction field in the synthesis of fine containers and fine particles, and it can also be used for the synthesis of microtubes using a tubular structure as a template. it can.

In the present invention, the hydrotalcite particles having a tubular structure have an outer diameter of 1 to 20 μm, an inner diameter of 0.5 to 5 μm, a length of 5 to 200 μm, and a length / outer diameter ratio of 2 to 50, The length / outer diameter ratio is preferably 4-50.
As a result, the above-described characteristics are more effectively expressed.
Further, in the pore distribution measured by the BET method with a specific surface area of 150 to 300 m ² / g or mercury intrusion method, the pore volume (A) having a pore diameter of 0.01 to 100 μm is 6000 to 12000 mm ³ / g. It is desirable that B / A, which is a ratio with a pore volume (B) having a pore diameter of 0.5 to 5 μm, is 0.45 to 0.70. It is more desirable that both be in the above-mentioned range, whereby the characteristic derived from the shape of the tubular structure described above can be expressed more effectively.

The present inventors presume that such a specific surface area and pore distribution are derived from a unique shape of a tubular shape.
In other words, the shape of the tube increases the specific surface area due to the space inside the particle, and the ratio of the pore volume of 0.5-5 μm pores corresponding to the inner diameter of the tube increases. Yes.
As for this tubular form, there are not only those in which both ends of the tube are open but also those in which the ends are closed.

Next, the manufacturing method of the hydrotalcite particle | grains which have the tubular structure of this invention is described.
In the present invention, in the step of using as a raw material tubular aggregated particles composed of flaky fine crystals of basic magnesium carbonate, and adding an alkali aluminate to the aqueous suspension of basic magnesium carbonate,
(1) The pH of the aqueous suspension before addition of alkali aluminate is 7.0 to 9.5.
(2) Maintaining the temperature during alkali aluminate addition in the range of 15 to 25 ° C.
(3) The amount of alkali aluminate added is 40 to 65 g in terms of Al ₂ O ₃ per 100 g of MgO contained in basic magnesium carbonate.
Thus, hydrotalcite particles having a tubular structure are produced.

The tubular aggregated particles made of flaky fine crystals of basic magnesium carbonate used as a raw material in the production method of the present invention have a flaky fine crystal having a thickness of 0.005 to 0.5 μm and a diameter of 0.1 to 10 μm in a card house structure. It is a collection of shapes.
The method for preparing the tubular aggregated particles can be used without any particular limitation as long as the above-mentioned shape can be obtained. For example, Japanese Patent Application Nos. 2002-179462 and 2002-1992, which were developed and patented by the present inventors, are available. It is preferable to use the method of 220768.

The shape of the tubular agglomerated particles is as described above, and the outer diameter is 1 to 20 μm, the length is 5 to 200 μm, the length / outer diameter ratio is 2 to 50, and the inner diameter is 0.5. It is preferable that the ratio of the inner diameter / outer diameter is 0.1 to 0.95, the specific surface area by the BET method is 70 to 200 m ² / g, and the fine pore distribution measured by the mercury intrusion method is fine. The pore volume (A) having a pore diameter of 0.01 to 100 μm is 3000 to 6000 mm ³ / g, and B / A, which is the ratio to the pore volume (B) having a pore diameter of 0.5 to 5 μm, is 0.45. A value of ˜0.85 can be preferably used.

The above-described manufacturing method for which a patent application has been made will be described in detail as follows.
In the method of the former Japanese Patent Application No. 2002-179462, a water-soluble magnesium salt and a water-soluble carbonate are mixed in an aqueous solution, and the diameter is 0.5 to 10 μm and the length is 5 to 5 at a temperature of 25 to 55 ° C. A first step of producing 500 μm normal magnesium carbonate columnar particles; and a temperature of the suspension of the normal magnesium carbonate columnar particles that is higher than the temperature at which normal magnesium carbonate was generated in the first step; A basic magnesium carbonate of tubular aggregated particles made of flaky fine crystals is prepared by a second step of heat treatment at a temperature of 80 ° C. and a pH of 9.5 to 11.5.

As the water-soluble magnesium salt used in the first step, various water-soluble magnesium salts can be used without particular limitation, and examples thereof include magnesium chloride, magnesium sulfate, magnesium nitrate, and magnesium acetate.
Water-soluble carbonates can also be used without particular limitation, and examples thereof include sodium carbonate, potassium carbonate, ammonium carbonate, etc., but strong alkali carbonates, specifically, sodium carbonate, potassium carbonate should be used. However, the tubular aggregated particles of basic magnesium carbonate can be prepared more efficiently, which is preferable.

In the first step, the water-soluble magnesium salt and the water-soluble carbonate as described above are reacted in an aqueous solution to precipitate the columnar particles of normal magnesium carbonate. Conditions in which water-soluble magnesium salt and water-soluble carbonate are mixed in the solution and magnesium ions and carbonate ions react, such as a method of adding a magnesium chloride aqueous solution to a solution and a method of adding ammonium carbonate to a magnesium sulfate aqueous solution If it is.
In that case, it is preferable to stir the reaction solution in order to ensure the uniformity of the reaction.

About the shape of the normal magnesium carbonate produced | generated in a 1st step, it is desirable that it is columnar, the diameter is 0.5-10 micrometers, and length is 5-500 micrometers.
The reason is that it is assumed that a unique shape called a tube is formed when basic magnesium carbonate is generated from the surface of columnar particles of normal magnesium carbonate.
That is, it can be said that the shape of normal magnesium carbonate, which is an intermediate product, greatly affects the shape of basic magnesium carbonate.

Therefore, the shape of the basic magnesium carbonate tubular aggregated particles produced in the second step is determined according to the desired shape according to the size of the hydrotalcite tubular particles, which is the production purpose, particularly the diameter and length. It is important to adjust the synthesis conditions of magnesium carbonate to obtain an appropriately shaped normal magnesium carbonate.
In the case of normal magnesium carbonate other than the above-mentioned shape, when the basic magnesium carbonate is generated in the second step, the time required for the generation becomes extremely long and the production efficiency decreases, or the desired tubular aggregated particles are formed. It may not be obtained.
The normal magnesium carbonate produced in the first step is a magnesium carbonate hydrate represented by the chemical formula MgCO ₃ .nH ₂ O, and is generally n = 3, but other than n = 3 Even if it is a thing, if it is a shape as mentioned above, it will not be restrict | limited.

As such, in order to generate columnar particles of normal magnesium carbonate that can efficiently obtain the tubular aggregated particles of basic magnesium carbonate of the desired shape in the second step, The temperature at which the magnesium salt reacts with the water-soluble carbonate is preferably 25 to 55 ° C, and more preferably 28 to 50 ° C.
If the temperature at that time is less than 25 ° C., the production rate of magnesium carbonate as an intermediate product becomes extremely slow, and the production efficiency is lowered, which is not realistic.
On the other hand, if the temperature exceeds 55 ° C., the desired shape of normal magnesium carbonate cannot be obtained, or the tubular aggregated particles of basic magnesium carbonate cannot be obtained in the subsequent second step.

In addition, by adjusting the shape of the normal magnesium carbonate produced in the first step, the shape of the tubular aggregated particles of basic magnesium carbonate produced in the second step is taken into account the dimensions of the hydrotalcite tubular particles, which is the production purpose. When it is desired to control, the shape of the normal magnesium carbonate can be adjusted within the above-mentioned range by appropriately controlling the reaction conditions in the first step.
For example, regarding the diameter of the columnar particles of normal magnesium carbonate, the columnar particles having a smaller diameter can be obtained by relatively increasing the temperature at which the normal magnesium carbonate is generated.
About pH, the one where the pH when the production | generation of normal magnesium carbonate is started in a 1st step is higher can produce | generate the columnar particle | grains of a normal magnesium carbonate with a smaller diameter.

  Thus, the suspension of columnar particles of normal magnesium carbonate having a diameter of 0.5 to 10 μm and a length of 5 to 500 μm obtained in the first step may be directly used for the second step. However, if you want to recover the anionic component of soluble magnesium salt or the cationic component of soluble carbonate dissolved as an impurity in the suspension, or if these impurities are contained in the basic magnesium carbonate that is the final product. If it is not desirable to remain, the liquid may be replaced with water or the like to remove impurities.

Subsequently, in the second step, the suspension of columnar particles of magnesium carbonate obtained in the first step is preferably 40 to 70 ° C., more preferably 45 to 65 ° C., and higher than the first step. To produce basic magnesium carbonate.
It is important that the heat treatment temperature in the second step is higher than the temperature at which normal magnesium carbonate is generated in the first step, and the temperature difference between the first step and the second step is 2 to 35. It is good to set it as 0 degreeC, It is 2-25 degreeC desirably, It is good to set it as 2-20 degreeC more desirably.

  In addition, regarding this temperature difference, there is a more appropriate range depending on the temperature at which columnar particles of normal magnesium carbonate are generated in the first step and the pH when heat treating the normal magnesium carbonate in the second step. When the pH of the second step is 10.5, the temperature difference is 20 to 35 ° C. when the first step is 25 to 35 ° C., and the temperature difference is 5 to 5 when the first step is 35 to 45 ° C. When the temperature in the first step is 25 to 55 ° C., the temperature difference is preferably 2 to 15 ° C.

If the temperature is lower than the first step or less than 40 ° C., the desired tubular aggregated particles of basic magnesium carbonate cannot be obtained, or the reaction time becomes extremely long and the production efficiency decreases, which is not realistic. .
When the temperature exceeds 70 ° C., the uniformity of the basic magnesium carbonate particles to be produced deteriorates, and the mixing of irregular to spherical aggregated particles becomes remarkable.
Also in the second step, as in the case of the first step, it is preferable to stir the reaction solution in order to ensure the uniformity of the reaction.

Further, the pH of the normal magnesium carbonate suspension during the heat treatment is preferably 9.5 to 11.5, and more preferably 10.0 to 11.5.
That is, when the pH is less than 9.5, the rate of production of basic magnesium carbonate from the normal magnesium carbonate is slowed, and not only the production efficiency is lowered, but also the normal magnesium carbonate may remain in the product. But there is.
On the other hand, when the pH exceeds 11.5, the uniformity of the basic magnesium carbonate particles is impaired, and amorphous or spherical particles are likely to be mixed.

In order to adjust the pH within this range, the amount ratio between the water-soluble magnesium salt and the water-soluble carbonate in the first step may be adjusted, or an acidic substance or an alkaline substance may be added and adjusted in the second step. .
In the former case, the amount can be adjusted to the acidic side by increasing the amount of the water-soluble magnesium salt, and conversely to the alkaline side by increasing the amount of the water-soluble carbonate.
In the latter case, hydrochloric acid, sulfuric acid, nitric acid or the like can be used as the acidic substance to be added, and sodium hydroxide, potassium hydroxide, aqueous ammonia or the like can be used as the alkaline substance.

In the second step, it is preferable to continue heating and stirring until the production of basic magnesium carbonate is completed.
The termination of the production of basic magnesium carbonate can be determined by measuring the pH and conductivity of the suspension.
For example, regarding the pH, when the production of basic magnesium carbonate continues, the pH of the suspension gradually decreases, whereas when the production is completed, the pH remains almost constant. .
In this manner, in the method of Japanese Patent Application No. 2002-179462, tubular aggregated particles of basic magnesium carbonate, which is a raw material for the hydrotalcite particles of the present invention, are prepared.

  Next, the method of the latter Japanese Patent Application No. 2002-220768 includes a first step of preparing a magnesium hydrogen carbonate solution by introducing a carbon dioxide-containing gas into the magnesium hydroxide suspension, and the magnesium hydrogen carbonate solution is adjusted to pH 7. A second step of producing columnar particles of normal magnesium carbonate by adjusting to 5 to 11.0, and a suspension of the columnar particles of normal magnesium carbonate at a pH of 9.0 to 12.0 and a temperature of 30 to 75 ° C. A third step of producing basic magnesium carbonate by adjusting the temperature range after adjustment.

The first step is a step of preparing a magnesium hydrogen carbonate solution by introducing a carbon dioxide-containing gas into a magnesium hydroxide suspension, and the raw material magnesium hydroxide used here is particularly limited. In addition, magnesium hydroxide produced by the so-called seawater method, in which calcium hydroxide is precipitated by adding calcium hydroxide to seawater, can be used.
There are no particular restrictions on the carbon dioxide-containing gas, and carbon dioxide supplied from a cylinder or the like, diluted with air or the like, or containing carbon dioxide such as combustion exhaust gas can be used.

In the first step, 90% or more of the magnesium hydroxide used as a raw material, preferably the total amount is preferably changed to magnesium hydrogen carbonate.
The reason is that when the amount of magnesium hydroxide that has not changed to magnesium hydrogen carbonate is large, in the subsequent second step and third step, the uniform reaction is hindered, and the tubular aggregation of the basic product, basic magnesium carbonate, occurs. This is because the uniformity of the particle shape of the particles may deteriorate.

The change from magnesium hydroxide to magnesium hydrogen carbonate can be confirmed by measuring the pH and conductivity of the liquid.
For example, regarding the pH of the liquid, the magnesium hydroxide suspension before introducing the carbon dioxide-containing gas is about 9 to 11, whereas the total amount of magnesium hydroxide is changed to magnesium hydrogen carbonate. For example, the pH of the liquid becomes almost neutral.
In the first step, it is desirable to introduce the carbon dioxide-containing gas until the pH of the liquid is 8 or less, and it is more desirable to introduce until the pH is 7.5 or less.

There is no particular restriction on the liquid temperature when introducing the carbon dioxide-containing gas into the magnesium hydroxide suspension, but if the liquid temperature is too high, the solubility of magnesium hydrogen carbonate will decrease, and the liquid temperature will be adjusted accordingly. Not only is the amount of unreacted magnesium hydroxide remaining in the magnesium hydrogen carbonate solution increased, but also a phenomenon in which the magnesium hydrogen carbonate decomposes before the completion of the first step reaction is observed.
Therefore, when introducing the carbon dioxide-containing gas into the magnesium hydroxide suspension, it is desirable to maintain the liquid temperature at 35 ° C. or lower, and more desirably at 30 ° C. or lower.

  In addition, after introducing the carbon dioxide-containing gas into the magnesium hydroxide suspension, it is preferable to remove undissolved residues such as unreacted magnesium hydroxide and other impurities, so that the impurities can be removed. A small amount of magnesium hydrogen carbonate solution can be prepared, and basic magnesium carbonate with high purity and high particle uniformity can be obtained in the third step.

In the subsequent second step, the magnesium hydrogen carbonate solution prepared in the first step is adjusted to pH 7.5 to 11.0 to produce columnar particles of normal magnesium carbonate.
Also in this second step, it is preferable to stir the reaction solution in order to ensure the uniformity of the reaction as in the case of the first step.
In this second step, it is necessary to adjust the pH shifted to the neutral range in the first step to the alkali side. For this purpose, an appropriate amount of alkaline substance is added to the magnesium hydrogen carbonate solution prepared in the first step. The pH is adjusted by adding.
Moreover, after adjustment, the pH needs to be in the range of 7.5 to 11.0.

In the second step, it is necessary to adjust the pH as described above, because when the pH is less than 7.5, tubular aggregated particles of basic magnesium carbonate cannot be obtained in the subsequent third step. is there.
On the contrary, when the pH exceeds 11.0, the normal magnesium carbonate becomes unstable, and basic magnesium carbonate is generated before the formation of normal magnesium carbonate is completed. Magnesium carbonate is generated and the uniformity of the basic magnesium carbonate particles is notably deteriorated, and the required amount of alkaline substance used for pH adjustment increases, which is not economical.

In order to produce the columnar particles of normal magnesium carbonate in the second step, the magnesium hydrogen carbonate solution prepared in the first step is adjusted to pH 7.5 to 11.0, and then the reaction is continued until the production of normal magnesium carbonate is completed. It is preferable to continue.
The completion of the production of normal magnesium carbonate can be confirmed by measuring the pH or conductivity of the liquid and observing that the value has stabilized.
Moreover, about the temperature in that case, it is good to set it as 20-55 degreeC, and it is desirable to set it as 30-55 degreeC.
When the temperature is lower than 20 ° C., in the third step, amorphous aggregated particles are easily mixed in addition to the basic aggregated tubular magnesium carbonate particles. Conversely, even in the case of a temperature exceeding 55 ° C., the uniformity of particles tends to deteriorate in the third step.

In the second step, the pH is adjusted as described above, and the temperature is preferably adjusted as described above, and the reaction is continued until the formation of normal magnesium carbonate is completed, thereby generating columnar particles of normal magnesium carbonate. The columnar particles preferably have a diameter of 0.5 to 10 μm and a length of 5 to 500 μm.
In particular, when the diameter of the columnar particles is less than 0.5 μm or exceeds 10 μm, the target tubular aggregated particles of basic magnesium carbonate may not be obtained in the subsequent third step.

In addition, the shape, particularly the diameter and length, of the basic magnesium carbonate tubular aggregated particles produced in the third step is affected by the diameter and length of the normal magnesium carbonate columnar particles produced in the second step. It is desirable to adjust the diameter and length of the normal magnesium carbonate produced in the second step in accordance with the shape of the tubular aggregated particles of basic magnesium carbonate.
In order to adjust the diameter and length of the columnar particles of normal magnesium carbonate, the pH and temperature for generating normal magnesium carbonate may be appropriately controlled in the second step.

For example, regarding the pH in the second step, within the above-mentioned range, columnar particles of normal magnesium carbonate having a small diameter can be obtained by setting the pH higher, and conversely by setting the pH to a lower value, Magnesium carbonate columnar particles can be obtained.
Further, regarding the temperature in the second step, columnar particles of normal magnesium carbonate having a small diameter can be obtained by setting the temperature to a higher temperature within the above-described range. Magnesium carbonate columnar particles can be obtained.

The formed magnesium carbonate columnar particles may be filtered and washed once, so that the alkaline substances added in the second step can be removed and contained in the product. This is preferable in that the impurity content can be further reduced.
In this way, in the second step, columnar particles of normal magnesium carbonate can be generated from the magnesium hydrogen carbonate solution.

In the third step, which is the last step following the second step, the suspension of columnar particles of magnesium carbonate obtained in the second step is subjected to pH 9.0 to 12.0 at a temperature of 30 to 75 ° C. To produce basic magnesium carbonate.
Also in the third step, as in the case of the first step and the second step, it is preferable to stir the reaction liquid to ensure the uniformity of the reaction.

About the temperature at the time of producing | generating basic magnesium carbonate by a 3rd step, it is necessary and important that it is 30-75 degreeC.
If the temperature is less than 30 ° C., the desired tubular basic magnesium carbonate cannot be obtained, or the reaction time becomes extremely long, resulting in a decrease in production efficiency, which is not realistic.
At a temperature exceeding 75 ° C., the uniformity of the basic magnesium carbonate particles to be produced is deteriorated, and mixing of irregular to spherical aggregated particles becomes remarkable.

About pH in this step, it is necessary to set it as 9.0-12.0.
The reason is that if the pH is less than 9.0, the rate of production of basic magnesium carbonate from normal magnesium carbonate is slowed down and the production efficiency is lowered, and the normal magnesium carbonate may remain in the product. Because.
On the other hand, if the pH exceeds 12.0, the uniformity of the product particles is impaired, and irregular or spherical particles are likely to be mixed.

Furthermore, the pH in the third step is preferably higher than the pH at which the columnar particles of normal magnesium carbonate are generated in the second step, and preferably 0.3 or more.
By doing so, it becomes possible to efficiently prepare the tubular aggregated particles of basic magnesium carbonate having high uniformity and excellent various powder properties.
In order to adjust the pH within this range, an acidic substance or an alkaline substance may be added and adjusted in the third step.

In addition, it is desirable to adjust the temperature and pH in the third step according to the shape of the normal magnesium carbonate produced in the second step, particularly the diameter and length. Magnesium carbonate tubular aggregated particles can be obtained.
Specifically, when the diameter of the normal magnesium carbonate is small, the pH and temperature in the third step are preferably lower, and conversely, when the diameter of the normal magnesium carbonate is large, the pH and temperature in the third step are higher. Is preferred.

In the third step, it is preferable to continue stirring while maintaining the temperature in the above-described range until the production of basic magnesium carbonate is completed.
In this case, it is not necessary to maintain the temperature immediately after the temperature is adjusted to 30 to 75 ° C., and the temperature may fluctuate in the temperature range, but it is preferable that the fluctuation is as small as possible. is there. The completion of the production of the basic magnesium carbonate can be confirmed by measuring the pH and conductivity of the suspension.
For example, with respect to pH, when the production of basic magnesium carbonate continues, the pH of the suspension decreases, whereas when the production is completed, the pH changes to be substantially constant.
Thus, in the method of Japanese Patent Application No. 2002-220768, the tubular aggregated particles of basic magnesium carbonate, which is the raw material of the hydrotalcite particles of the present invention, are prepared.

By the method as described above, tubular aggregated particles made of flaky fine crystals of basic magnesium carbonate can be prepared.
Subsequently, in the step of adding alkali aluminate to the aqueous suspension of the tubular aggregated particles composed of the flaky fine crystals of the basic magnesium carbonate,
(1) pH of aqueous suspension before addition of alkali aluminate is 7.0 to 9.5,
(2) Keeping the temperature during addition of alkali aluminate in the range of 15 to 25 ° C.,
(3) The amount of alkali aluminate added is 40 to 65 g in terms of Al ₂ O ₃ per 100 g of MgO contained in basic magnesium carbonate,
Thus, hydrotalcite particles having a tubular structure are produced.

The temperature of the suspension at the time of adding the alkali aluminate aqueous solution is in the range of 10 to 25 ° C., preferably 10 to 20 ° C. as described above.
If the temperature is less than 10 ° C., the hydrotalcite formation reaction tends to hardly occur, the production efficiency is low and it is not practical, and it is not preferable in terms of equipment such as requiring equipment for cooling other than water cooling.
The temperature of the suspension is preferably adjusted as appropriate depending on the basic magnesium carbonate as a raw material and the amount of alkali aluminate to be added. When the amount of alkali aluminate added is relatively small, the temperature is It is desirable to raise it.

The dimensions such as the inner diameter, outer diameter, and length of the basic magnesium carbonate tubular agglomerated particles used as a raw material can be appropriately adjusted in consideration of the dimensions of the hydrotalcite tubular particles that are the production objective.
The size of the hydrotalcite particles is substantially the same as the size of the tubular aggregated particles of basic magnesium carbonate as a raw material.
The adjustment of the size of the tubular aggregated particles has already been described. For example, in the method of Japanese Patent Application No. 2002-220768, the inner diameter of the tubular aggregated particles is adjusted by adjusting the pH when generating normal magnesium carbonate in Step 2. can do.

As the suspension of the basic aggregated tubular particles of magnesium carbonate, the suspension of the prepared basic magnesium carbonate may be used as it is or after adjusting the concentration appropriately, or once dried, water may be used. You may use what was disperse | distributed to.
The concentration of the suspension is not particularly limited and can be appropriately adjusted in consideration of the amount of hydrotalcite particles to be produced.
However, if the concentration is too low, the amount of hydrotalcite particles obtained in one production is small and the production efficiency deteriorates. Conversely, if the concentration is too high, the reaction tends not to occur uniformly. The concentration of the suspension of basic magnesium carbonate is preferably 1 to 50 g / L.

The pH of the basic magnesium carbonate suspension before addition of alkali aluminate is 7.0 to 9.5.
When the pH of the suspension exceeds 9.5, hydrotalcite is hardly generated even when alkali aluminate is added.
Usually, when basic magnesium carbonate is suspended in water, the pH of the suspension is about 10.5 to 12.
Therefore, in this case, an appropriate amount of acid, specifically, carbonic acid (gas), acetic acid, hydrochloric acid, sulfuric acid, nitric acid, other organic acids, etc. are added to adjust the suspension pH to 7.0 to 9.5. And

Moreover, the suspension of the tubular aggregated particles of basic magnesium carbonate immediately after the preparation is in a state where carbonic acid generated by the production of basic magnesium carbonate is dissolved, and the pH thereof is 8.0 to 9.5.
In this case, it is not necessary to adjust the pH by adding an acid, and it can be used as it is. Therefore, it is desirable to use a basic magnesium carbonate suspension immediately after preparation because pH adjustment is not necessary.

When alkali aluminate is added to this basic magnesium carbonate suspension, the pH of the suspension gradually rises, but alkali aluminate may be added until the pH reaches 10.5 to 11.5. desirable.
As the alkali aluminate to be added, sodium aluminate, potassium aluminate or the like can be used, and it is desirable to add these aqueous solutions to a suspension of basic magnesium carbonate from the viewpoint of maintaining the uniformity of the reaction.
In addition, it is preferable to perform addition of alkali aluminate aqueous solution under stirring in order to raise | generate the production | generation reaction of hydrotalcite uniformly.

Regarding the addition amount of alkali aluminate, the addition amount of alkali aluminate needs to be 40 to 65 g in terms of Al ₂ O ₃ per 100 g of MgO contained in the basic magnesium carbonate, desirably 42 to 50 g. Good.
At that time, if the addition amount is less than 40 g, the hydrotalcite which is the object of the present invention is hardly formed.
If it is an addition amount of 40 to 65 g or more, the composition of the hydrotalcite particles to be produced, specifically, the ratio of magnesium to aluminum may be adjusted as appropriate.

In addition, when the amount of alkali aluminate added is small, formation of hydrotalcite may be difficult to occur. In this case, by increasing the temperature at the time of alkali aluminate addition, the hydrotalcite particles Can be obtained.
Specifically, when the amount of alkali aluminate added is relatively low, 40-50 g in terms of Al ₂ O ₃ , per 100 g of MgO contained in the basic magnesium carbonate, the temperature during addition is set to 15 ° C. or higher. It is desirable to do.

The concentration of the alkali aluminate aqueous solution to be added may be adjusted to an appropriate concentration based on the amount of alkali aluminate added and the amount of basic aggregated magnesium carbonate particles used as a raw material. The stability of the acid-alkali aqueous solution is lowered, and it may be decomposed by being left for a long time or by heating.
On the other hand, if the concentration is too low, the time required to add the required amount of alkali aluminate becomes extremely long and the production efficiency deteriorates.
From these facts, the concentration of the alkali aluminate aqueous solution to be added is preferably 5 to 250 g / L.

The addition rate of the alkali aluminate aqueous solution may be adjusted according to the addition amount of the alkali aluminate and the concentration of the aqueous solution. Preferably, the alkali aluminate aqueous solution is used with respect to 100 g of MgO contained in the basic magnesium carbonate. The addition rate is preferably 0.2 to 10 g / min in terms of Al ₂ O ₃ .
By making it in this range, the hydrotalcite formation reaction can be caused uniformly, and the basic magnesium carbonate as a raw material can be prevented or suppressed from remaining in the product.

As described above, the addition of the alkali aluminate aqueous solution is preferably continued until the pH of the suspension becomes 10.5 to 11.5.
If the reaction is terminated at a stage where the pH is less than 10.5, the formation of hydrotalcite, which is the object of the present invention, may be incomplete, and the basic magnesium carbonate as a raw material may remain. On the contrary, even if the alkali aluminate aqueous solution is added until the pH exceeds 11.5, the total amount of the added alkali aluminate does not participate in the hydrotalcite formation reaction, and only part of the alkali aluminate is wasted. In addition, the single particles of alumina precipitated from the alkali aluminate are mixed in the product, which may adversely affect the quality of the product.

After the addition of the aqueous alkali aluminate is completed, stirring is preferably continued until the hydrotalcite formation reaction is completed.
The completion of the reaction can be determined by measuring the pH and conductivity of the suspension.
While the reaction is progressing, the pH and conductivity of the suspension change, whereas when the reaction is completed, the pH and conductivity change to be substantially constant.
The hydrotalcite which is the tubular particles thus obtained can be used in the form of a suspension or dried and in the form of a dry powder depending on the application.

When used in the form of a suspension, the suspension after the reaction may be used as it is, but in applications where impurities such as by-products contained in the suspension have an adverse effect, The minutes may be replaced with a solvent such as water and removed.
When using in the state of dry powder, the dry powder may be obtained through a dehydration process or a drying process.
In this case as well, when higher purity hydrotalcite is required, it is desirable to remove impurities by washing solids.
In addition, dry agglomeration may occur in the drying process, and crushing may be necessary in the subsequent process. In some cases, a phenomenon in which the particle shape is destroyed by crushing is also observed.

Therefore, a more desirable method for obtaining a dry powder is to replace the solvent of the hydrotalcite particle suspension after production with an organic solvent such as alcohol, or to perform a washing step with an organic solvent such as alcohol after dehydration. The method of providing and drying after that is good.
By performing substitution or washing of the solvent with an organic solvent such as alcohol, a dry powder in which aggregation due to drying is suppressed can be obtained.
In addition, as an organic solvent used here, the thing with the low solubility of a hydrotalcite is suitable, for example, methyl alcohol, ethyl alcohol, propanol, acetone etc. can be used.

Further, it is possible to adopt a drying method that does not easily cause dry aggregation without replacing or washing the solvent with an organic solvent as described above. For example, spray dryer, fluidized bed dryer, vacuum dryer, vacuum freeze drying If a dryer or a stirrer / dryer is used, a dry powder in which dry agglomeration is suppressed can be obtained.
Furthermore, the obtained hydrotalcite particles are converted into organic surface treatment agents such as various surfactants including fatty acid salts and resinate coupling agents, or inorganic surface treatment agents such as phosphates and sulfates. Can be used in various fields.

The hydrotalcite produced by the above method exhibits a novel shape called a tube, and due to the unique shape of the tube, it has a high specific surface area, a high pore volume, a high oil absorption, a high water absorption, a low bulk density, and a porosity. It has various excellent characteristics.
Furthermore, the hydrotalcite has an anion scavenging ability as an inherent property, and when used as a flame retardant, it suppresses halogen ion release during combustion and resin degradation caused by free halogen ions. Also has an effect.
Utilizing such a unique shape and excellent characteristics, the hydrotalcite particles of the present invention can be used in various fields.

Various fillers are mentioned as one of the application fields of the hydrotalcite particles of the present invention. For example, as a filler for rubber, not only is it effective for reducing the weight of rubber products due to the above-mentioned property of low bulk density, but also the unevenness on the particle surface improves adhesion to the matrix, resulting in high strength. It is also possible to obtain a rubber product.
In addition to the effects of weight reduction or strength improvement, the filler for resin is effective for imparting flame retardancy because it has crystal water as well as rubber.

As a filler for paper, it is derived from a tubular shape with an extensibility, and is effective in improving the strength of the paper. In addition, it has high oil absorbency and high water absorbency to improve paper printability and low density. This is also effective for reducing the weight of paper products.
Furthermore, the hydrotalcite particles of the present invention can also be used as a coating pigment for paper, and the coated paper used becomes a lightweight coated paper, ink acceptability, post-printing opacity, printability, etc. For example, it can be used for ink jet recording paper, thermal recording paper, and the like.

And the molded object or granulated material obtained by shape | molding the hydrotalcite particle | grains of this invention using a binder etc. not only can be excellent in the lightness by the characteristic of low bulk density, but is called porosity. Effects such as heat insulating properties, sound absorbing properties, adsorptive properties, and filterability are also manifested depending on the characteristics, and can be used as, for example, heat insulating materials, sound absorbing materials, heat insulating materials, filters, and the like.
In addition to these, medical and agrochemical carriers, cosmetic carriers, catalyst carriers, microbial carriers, biological carriers, plant growth agents, olefin absorbents, liquid absorbents, oil absorbents, desiccants, fragrances, deodorants, It can also be used as a sealing agent, rust inhibitor, food additive, filter agent, filter aid, abrasive, column filler, and the like.

  When used as a carrier for pharmaceuticals, agrochemicals, cosmetics, etc., the amount of impregnation with drugs, etc. is increased by having a space that can contain active ingredients inside the tubular structure and having a high pore volume and specific surface area. In addition, it can be used as medicines, agricultural chemicals, cosmetics, etc. that have controlled release characteristics such as controlled release and selective removal properties that remove specific substances by adsorption. .

An antacid is described as a specific example of the medicine.
The hydrotalcite tubular particles of the present invention impregnated with an active ingredient in the tubular structure of the hydrotalcite itself have an antacid effect. At the same time, the active ingredient impregnated in the tubular structure is released, and the effect of the ingredient is also expressed, so that an antacid having a plurality of effects can be obtained.

[Examples and Comparative Examples]
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples, and is specified by the scope of claims. Needless to say.

7. A carbon dioxide-containing gas composed of 25 vol% carbon dioxide and 75 vol% air is added to 2.0 L of a magnesium hydroxide suspension (30 g / L) while stirring at a temperature of 20 ° C. After introducing at a rate of 0 L / min for 30 minutes, the insoluble residue was removed to prepare a magnesium hydrogen carbonate solution (pH 7.3) (first step).
Following this step, an appropriate amount of aqueous sodium hydroxide solution is added to the magnesium hydrogen carbonate solution to adjust the pH of the solution to 9.0, and the temperature of the solution is raised to 35 ° C. by heating. While maintaining the temperature, the mixture was stirred for 60 minutes to prepare a suspension of normal magnesium carbonate (second step).
When this normal magnesium carbonate was observed by SEM, it was a columnar particle having a diameter of 1 to 3 μm and a length of 20 to 50 μm.

Subsequently, an appropriate amount of aqueous sodium hydroxide solution is added to the suspension of columnar particles of magnesium carbonate to adjust the pH of the solution to 10.5, and the temperature of the solution is increased to 50 ° C. by heating. While maintaining the same temperature, the mixture was stirred for 120 minutes to prepare basic magnesium carbonate (third step).
When this basic magnesium carbonate was observed with an SEM, the inner diameter was 1-2 μm, the outer diameter was 2-3 μm, and the length was made of flaky fine crystals having a thickness of 0.01-0.05 μm and a diameter of 0.2-1 μm. They were 5-30 μm tubular aggregated particles.
Further, chemical analysis revealed that the MgO content was 43% by weight.

A suspension of the basic magnesium carbonate tubular aggregated particles was diluted with ion-exchanged water immediately after preparation to prepare 2.0 L of a suspension having a concentration of 20 g / L and pH 8.5.
Subsequently, while maintaining the temperature of the suspension at 18 ° C. and stirring, 250 mL of an aqueous sodium aluminate solution (29 g / L in terms of Al ₂ O ₃ ) was dropped at a rate of 5 mL / min, and the dropping was completed (suspension After pH 10.7), stirring was continued for 5 minutes.
The amount of sodium aluminate added was 42.5 g in terms of Al ₂ O _{3 with} respect to 100 g of MgO contained in the basic magnesium carbonate.

When the obtained product was subjected to chemical analysis and powder X-ray diffraction, a diffraction peak of hydrotalcite (Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O) was confirmed.
Further, when SEM observation was performed, the product had an inner diameter in which plate-shaped fine particles having a diameter of 0.2 to 1 μm and a thickness of 0.02 to 0.05 μm and irregular fine particles having a diameter of 0.1 to 0.3 μm were assembled. Tubular particles having an outer diameter of 2 to 4 μm and a length of 5 to 30 μm were 0.8 to 1.5 μm.

Basic magnesium carbonate was prepared in the same manner as in Example 1 except that the pH of the second step was 8.0 and the temperature of the third step was 55 ° C.
In addition, when the normal magnesium carbonate produced | generated at the 2nd step was observed in SEM, it was confirmed that it is a columnar particle | grain with a diameter of 5-10 micrometers and length of 30-100 micrometers.
Further, when the basic magnesium carbonate obtained in the third step was observed with an SEM, the inner diameter was 2 to 5 μm consisting of flaky fine crystals having a thickness of 0.02 to 0.1 μm and a diameter of 0.5 to 2 μm. It was a tubular aggregated particle having an outer diameter of 5 to 10 μm and a length of 20 to 50 μm. When chemical analysis was performed, the MgO content was 43% by weight.

A suspension of basic aggregated tubular magnesium carbonate particles was diluted with ion-exchanged water, and an appropriate amount of carbon dioxide gas was blown to prepare 2.0 L of a suspension having a concentration of 10 g / L and pH 7.5.
Subsequently, while maintaining the temperature of the suspension at 15 ° C. and stirring, 150 mL of an aqueous sodium aluminate solution (29 g / L in terms of concentration Al ₂ O ₃ ) was dropped at a rate of 3 mL / min to complete the dropping (suspension) After the solution pH 11.2), stirring was continued for 5 minutes (the amount of sodium aluminate added was 52 g in terms of Al ₂ O _{3 with} respect to 100 g of MgO contained in basic magnesium carbonate).

When the obtained product was subjected to chemical analysis and powder X-ray diffraction, a diffraction peak of hydrotalcite (Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O) was confirmed.
Further, when SEM observation was performed, the product was a collection of plate-shaped fine particles having a diameter of 0.2 to 1 μm and a thickness of 0.02 to 0.05 μm, an inner diameter of 1.5 to 4 μm, an outer diameter of 5 to 12 μm, and a long length. It was a tubular particle having a thickness of 20 to 50 μm.

0.50 L of anhydrous sodium carbonate aqueous solution (220 g / L) was gradually added to 2.0 L of magnesium sulfate heptahydrate aqueous solution (125 g / L) adjusted to 40 ° C. while maintaining the temperature at 40 ° C., and stirred for 50 minutes. Thus, normal magnesium carbonate was obtained (first step).
When this normal magnesium carbonate was observed by SEM, it was a columnar particle having a diameter of 1 to 3 μm and a length of 10 to 50 μm.

Subsequently, the suspension of regular magnesium carbonate columnar particles (pH 10.2) obtained in the first step is heated and stirred for 120 minutes while maintaining the temperature at 55 ° C. to produce basic magnesium carbonate. (Second step).
When the obtained product was observed with an SEM, it was an aggregated particle composed of flaky primary particles having a thickness of 0.01 to 0.04 μm and a diameter of 0.2 to 2 μm. It was a tubular aggregated particle of basic magnesium carbonate having a length of 0.5 to 3 μm and a length of 5 to 20 μm.
Moreover, when the chemical analysis was conducted, MgO content was 43 weight%.

Immediately after the preparation, a suspension of basic magnesium carbonate tubular aggregated particles was diluted with ion-exchanged water to prepare 2.0 L of a suspension having a concentration of 20 g / L and pH 8.8.
Subsequently, while maintaining the temperature of the suspension at 18 ° C. and stirring, 265 mL of an aqueous sodium aluminate solution (29 g / L in terms of concentration Al ₂ O ₃ ) was dropped at a rate of 4 mL / min to complete the dropping (suspension) After the solution pH was 10.8), stirring was continued for 5 minutes (the amount of sodium aluminate added was 45 g in terms of Al ₂ O _{3 with} respect to 100 g of MgO contained in the basic magnesium carbonate).

When the obtained product was subjected to chemical analysis and powder X-ray diffraction, a diffraction peak of hydrotalcite (Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O) was confirmed.
Moreover, when SEM observation was performed, the product had an inner diameter in which plate-shaped fine particles having a diameter of 0.2 to 1 μm and a thickness of 0.02 to 0.05 μm and irregular fine particles having a diameter of 0.1 to 0.2 μm were assembled. Tubular particles having a diameter of 0.5 to 2.5 μm, an outer diameter of 1 to 7 μm, and a length of 5 to 20 μm.

[Comparative Example 1]
Carbon dioxide gas was introduced into 2.0 L of a suspension of industrial basic magnesium carbonate (5 to 20 μm amorphous particles, MgO content 46 wt%) at a concentration of 20 g / L to adjust the pH to 8.5.
Subsequently, while maintaining the temperature of the suspension at 18 ° C. and stirring, 285 mL of an aqueous sodium aluminate solution (29 g / L in terms of concentration Al ₂ O ₃ ) was added dropwise at a rate of 5 mL / min to complete the addition (suspension) After the solution pH was 10.7), the stirring was continued for 5 minutes (the amount of sodium aluminate added was 45 g in terms of Al ₂ O _{3 with} respect to 100 g of MgO contained in the basic magnesium carbonate).
When the obtained product was subjected to chemical analysis and powder X-ray diffraction, it was confirmed that the product was Mg ₆ Al ₂ (OH) ₁₆ CO ₃ .4H ₂ O.
Moreover, when SEM observation was performed, the product was 5-30 micrometers irregular shaped particle | grains.

[Comparative Example 2]
In the same manner as in Example 1, a suspension of basic magnesium carbonate tubular aggregated particles was prepared.
Immediately after preparation, this suspension was diluted with ion-exchanged water to prepare 2.0 L of a suspension having a concentration of 20 g / L and pH 8.5.
Subsequently, while maintaining the temperature of the suspension at 50 ° C. and stirring, 400 mL of an aqueous sodium aluminate solution (29 g / L in terms of Al ₂ O ₃ ) was added dropwise at a rate of 10 mL / min to complete the addition (suspension) After pH 10.8), stirring was continued for 5 minutes.

In this case, the amount of sodium aluminate added was 68 g in terms of Al ₂ O _{3 with} respect to 100 g of MgO contained in the basic magnesium carbonate.
When SEM observation of the obtained product was performed, it was tubular particles having an inner diameter of 0.8 to 1.5 μm, an outer diameter of 2 to 4 μm, and a length of 5 to 30 μm, in which fine particles of 20 to 100 nm were gathered.
When this was subjected to chemical analysis and powder X-ray diffraction, the product was Mg ₂ Al (OH) ₇ and no hydrotalcite was produced.

[Evaluation of the physical properties]
The specific surface area by the BET method and the pore distribution by the mercury intrusion method of the basic magnesium carbonate obtained in Examples and Comparative Examples were measured.
The specific surface area was measured with an automatic surface area meter Macsorb (HM model-1201) manufactured by Mountec, and the pore distribution was measured with a mercury intrusion porosimeter (series 140 type, 440 type) manufactured by CE Instruments.
The results are shown in Table 1. As is clear from the table, the hydrotalcite particles of the examples had a specific surface area and a pore volume higher than those of the amorphous particles of Comparative Example 1, and corresponded to the inner diameter of the tubular particles. It can be seen that a unique pore distribution with a high proportion of 5-5 μm pores is shown.

2 is a SEM photograph (× 10,000) showing the morphology of tubular particles of hydrotalcite obtained in Example 1. FIG.

Claims (5)

Hydrotalcite particles characterized by having a tubular structure. The hydrotalcite particle according to claim 1, wherein the tubular structure has an outer diameter of 1 to 20 µm, an inner diameter of 0.5 to 5 µm, a length of 5 to 200 µm, and a length / outer diameter ratio of 2 to 50. The hydrotalcite particles according to claim 1 or 2, wherein the BET method has a specific surface area of 150 to 300 m ² / g. In the pore distribution measured by the mercury intrusion method, the pore volume (A) having a pore diameter of 0.01 to 100 μm is 3000 to 6000 mm ³ / g and the pore volume having a pore diameter of 0.5 to 5 μm (B The hydrotalcite particles according to any one of claims 1 to 3, wherein B / A, which is a ratio to (A), is 0.45 to 0.70. In the step of adding alkali aluminate to an aqueous suspension of tubular aggregated particles made of flaky fine crystals of basic magnesium carbonate, (1) pH of aqueous suspension before addition of alkali aluminate is 7.0- 9.5, (2) Maintaining the temperature during addition of alkali aluminate in the range of 10-25 ° C., (3) Al ₂ O ₃ conversion per 100 g of MgO contained in basic magnesium carbonate with addition amount of alkali aluminate A method for producing hydrotalcite particles having a tubular structure, characterized by being 40 to 65 g.

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