JP2005103345A - Method for taking out inorganic particle synthesized in aqueous system as single-particle powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for economically and efficiently manufacturing a single-particle powder of inorganic particles of calcium carbonate or the like dispersed as single particles excellent in the improving effect of physical constitution and plysical properties. <P>SOLUTION: This method for taking out the inorganic particles synthesized in the aqueous system as the single-particle powder is composed of a process (1) for preparing an aqueous suspension of inorganic particles in the aqueous system, a process (2) for substituting a water medium with an organic solvent immediately after the process for preparing the aqueous suspension of the inorganic particles in the aqueous system and a process (3) for separating the single-particle powder of the inorganic particles from the organic solvent suspension of the inorganic particles obtained in the process (2). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a method for producing an inorganic powder such as a calcium carbonate powder excellent in dispersibility dispersed in a single particle.
More specifically, the present invention can be formulated in a monodispersed state when blended with rubber, resin, paint, ink, etc., and can be improved in physical properties. The present invention relates to a novel method for producing a single particle powder composed of agglomerated inorganic particles.

  Synthetic calcium carbonate can be mentioned as a typical example of inorganic particles, and the synthetic calcium carbonate is widely known for its synthesis in an aqueous system in which carbon dioxide gas is introduced into an aqueous suspension of calcium hydroxide (lime milk). It has been.

At this time, the following two types of calcium carbonate can be synthesized roughly by selecting the synthesis conditions.
(1) By setting the conditions such that the concentration of lime milk is low (3 to 6%), the amount of carbon dioxide gas introduced is large (the reaction rate is increased), and the reaction temperature is lowered (30 ° C. or lower). .. Colloidal calcium carbonate (colloidal calcium carbonate) of 1 μm or less can be synthesized.
(2). By setting the conditions such that the lime milk concentration is high (10% or more), the amount of carbon dioxide introduced is small (reaction rate is slow), and the reaction temperature is high (30 ° C. or more). It is possible to synthesize light calcium carbonate (light calcium carbonate) of 0 μm or more.

  In addition, the above-mentioned synthetic calcium carbonate, for example, calcium carbonate having a particle size of 1.0 μm or less, aggregates particles due to the relationship between surface energy and aggregation energy, and this tendency becomes stronger as the particle size of the particles becomes smaller. It is also widely known that even if it is dispersed again in water, it does not return to its original state (a state in which particles immediately after synthesis are well dispersed).

The cohesiveness of the synthetic calcium carbonate described above can also be explained from the following points.
That is, although calcium carbonate is a hardly soluble substance, it is slightly soluble in water suspension but dissolves in water (solubility: 0.82 g / dm ³ , 25 ° C. Chemical Handbook Basic Edition 3rd revised edition, Nippon Chemical Co., Ltd.) Ed., II-167). Therefore, when the calcium carbonate is dried from the aqueous suspension, the dissolved calcium carbonate acts as a binder between the calcium carbonate particles to aggregate the calcium carbonate particles.

In the industry, when using the above-mentioned cohesive calcium carbonate, a utilization method with improved cohesiveness is employed. For example, the following usage is adopted.
(1). Calcium carbonate having a particle size of 0.1 μm or more is used for the purpose of improving whiteness and ink acceptability as a paper coating agent. In this case, in order to prepare an aqueous dispersion of calcium carbonate, a method of treating the surface of the calcium carbonate particles with an acrylic acid-based organic substance having a carboxyl group or a condensed phosphoric acid-based compound is employed.

  (2). Calcium carbonate having a particle size of 0.04 μm or more is used as a filler, extender pigment, etc. for rubber, resin, ink and the like. In this case, in order to achieve dispersion in these organic substances (medium), the surface of calcium carbonate is treated with an organic substance such as a fatty acid or resin acid to make the surface of calcium carbonate oleophilic and improve dispersibility. The method is adopted.

However, there is a limit to the measures for improving the dispersion of the cohesive calcium carbonate described above.
Generally, the average particle diameter (of secondary particles) of a powder obtained by treating colloidal calcium carbonate (particle diameter of 0.1 μm or less) with a fatty acid or resin acid is 5 to 10 μm.
The theoretical specific surface area of calcium carbonate having a particle size of 0.04 μm is 55.6 (m ² / g), but a commercially available product is 20 to 30 (m ² / g).
This means that only 10-20 particles of 0.04 μm aggregated can be obtained even if dispersion is achieved by surface treatment with the above-described conventional fatty acids and resin acids.

  For this reason, in order to further enhance dispersibility when filling and blending calcium carbonate into rubber, resin, ink, etc., for example, a banbury mixer in the rubber industry, a pelletizer in the resin industry, and a sand grind mill or dissolver in the paint industry. In the ink industry, the agglomerates are brought close to monodispersion using strong energy such as three rolls.

The present invention has been devised to eliminate the above-mentioned drawbacks of the prior art.
That is, the object of the present invention is to provide a simple substance that does not require excessive energy for dispersion during filling and blending in various inorganic particles such as calcium carbonate that are filled and blended in various base materials for the purpose of improving the constitution. It is an object of the present invention to provide a novel and efficient method for producing a single particle powder of inorganic particles having excellent dispersibility and dispersed in particles.

If the present invention is outlined, the present invention is a method for taking out inorganic particles synthesized in an aqueous system as a single particle powder.
(1). A step of preparing an aqueous suspension of inorganic particles in an aqueous system;
(2). A step of immediately replacing the aqueous medium with an organic solvent after the step of preparing an aqueous suspension of inorganic particles in the aqueous system,
(3). A step of separating single particle powder of inorganic particles from an organic solvent suspension of inorganic particles obtained by the step (2).
It is related with the method of taking out the inorganic particle | grains synthesize | combined by the aqueous system characterized by comprising as a single particle powder.

  According to the present invention, it is possible to economically and efficiently produce a single particle powder of inorganic particles such as calcium carbonate, which is dispersed in single particles having an average particle size of 1.0 μm or less and has a high degree of dispersibility.

  In addition, since the single particle powder of inorganic particles such as calcium carbonate dispersed in the single particles of the present invention has excellent dispersibility, it is excellent in dispersibility in various base materials such as rubber, resin, paint, and ink. When manufacturing products such as rubber, resin, paint and ink, no special disperser is required for filling and blending, and the energy consumption required for production can be greatly reduced.

  Furthermore, the single particle powder of inorganic particles such as calcium carbonate dispersed in the single particles of the present invention has excellent dispersibility with respect to various substrates. It is possible to provide various products excellent in improving the constitution and physical properties.

  The technical configuration and embodiments of the present invention will be described in detail below.

The method for taking out the inorganic particles synthesized in the aqueous system of the present invention as a single particle powder will be described in detail below, taking a case where the inorganic particles are calcium carbonate particles as a typical example.
The method of taking out the calcium carbonate particles synthesized in the aqueous system of the present invention as a single particle powder,
1). Synthetic calcium carbonate prepared by introducing carbon dioxide into a calcium hydroxide aqueous suspension (lime milk) containing water, for example, synthetic calcium carbonate having a particle size of 1 μm or less, aggregates due to the surface energy of the particles at the same time as the formation. That begins,
2). Calcium carbonate is a poorly soluble substance, but if there is water on the particle surface, a very small amount dissolves. Therefore, when water is lost in the drying process, the dissolved matter precipitates and acts as a binder between the particles. Promoting aggregation,
3). The dissolution and elution described above can be prevented by medium conversion simultaneously with the production of synthetic calcium carbonate, that is, by converting the aqueous medium to the organic medium, thus preventing aggregation between the particles,
It was completed based on this knowledge.

  In the preparation step of the aqueous calcium carbonate suspension in the step (1) of the present invention, it is preferable that calcium carbonate having an average particle size of 1 μm or less is obtained from the viewpoint of utilization of the synthetic calcium carbonate. However, the step (1) of the present invention is not limited to the step of obtaining the average particle size.

  The step of substituting the aqueous medium in the step (2) of the present invention with an organic solvent (organic medium) includes the preparation of the aqueous calcium carbonate suspension in the step (1), Since aggregation due to surface energy or the like starts, it is preferably performed immediately after the step (1).

In the present invention, the method of replacing the aqueous medium with an organic solvent (organic medium) may be performed in a desired manner. For example, dialysis or replacement may be performed.
As the dialysis method, for example, an aqueous suspension of synthetic calcium carbonate may be placed in a cellophane dialysis tube and dialyzed in an organic solvent such as methyl alcohol. At this time, the replacement efficiency may be increased by exchanging the alcohol several times to increase the dialysis rate, or by adding biolite or activated carbon that adsorbs or dehydrates water into the alcohol.

  In the present invention, as the organic solvent, alcohols such as methyl alcohol, ethyl alcohol, butyl alcohol, and propyl alcohol, ketones such as acetone, pentanone, and ethyl methyl ketone may be used.

Needless to say, those used in the synthesis of calcium carbonate can be used as the organic solvent.
For example, examples of using an organic solvent in the synthesis of calcium carbonate include JP-A-4-31315, JP-A-4-31316, Open / Close 4-31317, JP-A-4-292414, JP-A-5-155613, JP-A-5-155613. 294616. These are methods in which water is added to a quick suspension of calcium lime or calcium hydroxide and carbon dioxide is introduced to synthesize calcium carbonate. The generated calcium carbonate has a spherical shape, an oval spherical shape, a meteorite shape, and the like. The average particle size is 0.1 to 2.0 μm, and the crystal system is vaterite.
Further, as a method of using an organic solvent as a dispersion medium for calcium carbonate, JP-A 64-4239 and JP-A 64-4240 use glycol as a dispersion medium. In addition, these use the calcium carbonate which surface-treated with the other organic substance beforehand on the calcium carbonate surface.

  The separation and recovery of the calcium carbonate powder dispersed in single particles in the step (3) of the present invention may be performed as desired.

  The method of taking out the inorganic particles synthesized in the aqueous system of the present invention as a single particle powder is not limited to the case where the inorganic particles are calcium carbonate. The present invention can be widely applied to inorganic particles synthesized in water. Hereinafter, examples of other inorganic particles of this type will be described.

An example of another inorganic particle is calcium phosphate.
In general, calcium phosphate (amorphous calcium phosphate, apatite, tricalcium phosphate, etc.) is synthesized by using a water-soluble calcium salt solution or lime milk and a water-soluble phosphate or phosphoric acid solution and an ammonia solution or an alkali metal aqueous solution such as Ca A method is employed in which the reaction is carried out by mixing or dropping under the condition of / P ratio of 1.67 to 1.0. However, in this type of synthesis method, when reacted at a low temperature, colloidal particles of 0.1 μm or less are produced, and it is very difficult to take out as a powder having excellent separability.

Another example of inorganic particles is hydrous silica.
In general, hydrous silica is synthesized by reacting a sodium silicate aqueous solution with a mineral acid (sulfuric acid, etc.) or a sodium silicate aqueous solution and salts (magnesium chloride, etc.) to produce a silicate, and then a mineral acid (sulfuric acid etc.) or carbon dioxide. There is a method of disassembling. Further, in these methods, there are a method of reacting on the acidic side and gelation, and a method of direct precipitation on the alkali side.
In general, primary particles of amorphous hydrous silica are 10 to 50 nm, but secondary particles aggregated in a vine shape are said to be 1 to several hundred μm. Hydrous silica is used as a reinforcing agent for rubber and resin, but it can be partially dispersed to primary particles by applying a strong shearing force such as roll kneading or Banbury, but it is not possible to completely disperse. It is said that it is almost possible.

  Examples of the inorganic powder other than those described above that can be applied to the method of taking out the inorganic particles synthesized in the aqueous system of the present invention as a single particle powder include, for example, magnesium hydroxide, magnesium carbonate, calcium hydroxide, barium sulfate, aluminum hydroxide, Examples thereof include hydrous aluminum silicate, zinc oxide, and titanium oxide.

Hereinafter, the present invention will be described in more detail with reference to examples.
As described above, the present invention has the greatest feature in economically and efficiently producing a single powdery granule of inorganic particles such as calcium carbonate which is highly excellent in dispersibility. Hereinafter, the above-described characteristic points of the present invention will be demonstrated by the degree of dispersion (%) obtained by the following formula (1).
Dispersity (%) = [(specific surface area determined from BET measurement) / (specific surface area determined from calculation formula)] × 100 (1)
The specific surface area obtained from the above calculation formula is obtained by the following formula (2).
S = [6 / (ρ · D)] (2)
In the formula (2), S represents a specific surface area (m ² / g), ρ represents a true specific gravity, and D represents a particle diameter (diameter, μm).
Needless to say, the present invention is not limited to the examples.

A stirring speed of 600 r. p. The carbonation was terminated by introducing 25 vol% carbon dioxide gas at 1600 ml / min. Immediately obtained 50 ml of calcium carbonate emulsion was sealed in a cellulose tube (manufactured by Wako) and immersed in 1000 ml of 99.8% methyl alcohol solution. At this time, 200 g of molecular sieves (manufactured by Wako) was added as a water absorbent and stirred for 12 hours. After completion of solvent replacement, the emulsion was filtered from the cellulose tube and dried at 110 ° C. overnight. The dried product was sieved with a mesh of 100 mesh to obtain about 3 g of dry powder. The powder thus prepared had an average particle diameter of about 0.04 μm by electron microscope observation, a specific surface area of 49.2 m ² / g by BET method, and a dispersity of 88%. An electron micrograph of the powder (magnification of 7000 times) is shown in FIG.

A stirring speed of 600 r. p. The carbonation was terminated by introducing 25 vol% carbon dioxide gas at 1600 ml / min. Immediately after, 50 ml of the obtained calcium carbonate emulsion was sealed in a cellulose tube and immersed in 1000 ml of 99.5% ethyl alcohol solution. This ethyl alcohol was exchanged twice every 3 hours, and at the third ethyl alcohol exchange, 100 g of molecular sieves was added as a moisture absorbent and stirred for 12 hours. After completion of solvent replacement, the emulsion was filtered from the cellulose tube, and 110 Dried overnight at ° C. The dried product was sieved with a mesh of 100 mesh to obtain about 3 g of dry powder. The powder thus prepared had an average particle diameter of about 0.04 μm by electron microscope observation, a specific surface area of 50.1 m ² / g by BET method, and a dispersity of 90%. An electron micrograph of the powder (magnification of 7000 times) is shown in FIG.

To 400 ml of 6% lime milk having a liquid temperature of 15 ° C., a stirring speed of 1000 r. p. m, 25% by volume of carbon dioxide gas was introduced at 600 ml / min to complete the carbonation. Immediately obtained 50 ml of calcium carbonate emulsion was sealed in a cellulose tube and immersed in 1000 ml of 99.8% methyl alcohol solution. At this time, 200 g of molecular sieves as a water absorbent was added and stirred for 12 hours. After completion of solvent replacement, the emulsion was filtered from the cellulose tube and dried at 110 ° C. overnight. The dried product was sieved with a mesh of 100 mesh to obtain about 4 g of dry powder. The powder thus prepared had an average particle diameter of about 0.1 μm as observed by an electron microscope, a specific surface area of 20.8 m ² / g by BET method, and a dispersity of 95%.

400 ml of an aqueous solution in which 47.23 g of calcium nitrate tetrahydrate was dissolved was placed in a 1000 ml container and stirred, while 300 ml of an aqueous solution in which 15.85 g of ammonium dihydrogenphosphate was dissolved in 300 ml and 2.4 ml of aqueous ammonia were dissolved in 300 ml. The aqueous solution was simultaneously added dropwise at a dropping rate of 10 ml / min. At this time, the reaction temperature was set to 10 ° C., and the stirring was continued at the same temperature for 12 hours after completion of the dropping. Immediately after, 100 ml of the obtained calcium phosphate emulsion was sealed in a cellulose tube and immersed in 1000 ml of 99.5% ethyl alcohol solution. . The ethyl alcohol was exchanged twice every 3 hours, and at the third ethyl alcohol exchange, 100 g of molecular sieves was added as a water absorbent and stirred for 12 hours. After completion of solvent substitution, the emulsion was filtered from the cellulose tube, Dried overnight at ° C. The dried product was sieved with a mesh of 100 mesh to obtain about 2 g of dry powder. The powder thus prepared had an average particle size of about 0.02 μm by electron microscope observation, a specific surface area of 99.7 gm ² / g by BET method, and a dispersity of 90%.

400 ml of an aqueous solution in which 44.11 g of calcium chloride dihydrate was dissolved was placed in a 1000 ml container and stirred, while 300 ml of an aqueous solution in which 18.35 g of sodium hexametaphosphate was dissolved in 300 ml and an aqueous solution in which 16.8 g of sodium hydroxide was dissolved in 300 ml. Were simultaneously dropped at a dropping rate of 10 ml / min. The reaction temperature at this time was 10 ° C., and stirring was continued at that temperature for 12 hours after the completion of the dropping. Immediately after completion of the reaction, 50 ml of the calcium phosphate emulsion obtained was sealed in a cellulose tube and immersed in 100 ml of 99.5% ethyl alcohol solution. The ethyl alcohol was exchanged twice every 3 hours, and at the third ethyl alcohol exchange, 100 g of molecular sieves was added as a water absorbent and stirred for 12 hours. After completion of solvent substitution, the emulsion was filtered from the cellulose tube, Dried overnight at ° C. The dried product was sieved with a mesh of 100 mesh to obtain about 39 g of dry powder. The powder thus prepared had an average particle diameter of about 0.02 μm by electron microscope observation, a specific surface area by BET method of 95.4 m ² / g, and a dispersity of 86%.

Comparative Example 1

The same procedure as in Example 1 was performed until a calcium carbonate emulsion was obtained. The resulting calcium carbonate emulsion was immediately filtered and dried at 110 ° C. overnight. The dried product was pulverized with a mortar and sieved with a mesh of 100 mesh to obtain 23 g of dry powder. The powder thus prepared had an average particle diameter of about 0.04 μm by electron microscope observation, a specific surface area by BET method of 28.0 m ² / g, and a dispersity of 51%. This was inferior in monodispersity compared to that in Example 1.

Comparative Example 2

The same procedure as in Example 3 was performed until a calcium carbonate emulsion was obtained. The resulting calcium carbonate emulsion was immediately filtered and dried at 110 ° C. overnight. The dried product was pulverized in a mortar and sieved with a mesh of 100 mesh to obtain 31 g of dry powder. The powder thus prepared had an average particle size of about 0.1 μm as observed with an electron microscope, a specific surface area of 15.3 m ² / g by BET method, and a dispersity of 69%. This was inferior in monodispersity compared to that in Example 3.

Comparative Example 3

400 ml of an aqueous solution in which 47.23 g of calcium nitrate tetrahydrate was dissolved was placed in a 1000 ml container and stirred, while 300 ml of an aqueous solution in which 15.85 g of ammonium dihydrogenphosphate was dissolved in 300 ml and 2.4 ml of aqueous ammonia were dissolved in 300 ml. The aqueous solution was simultaneously added dropwise at a dropping rate of 10 ml / min. The reaction temperature at this time was 10 ° C., and the stirring was continued at the same temperature for 12 hours after completion of the dropping. The obtained calcium phosphate emulsion was immediately filtered, washed with water, and dried at 80 ° C. for 24 hours. The dried product was sieved with a mesh of 100 mesh to obtain 19 g of dry powder. The powder thus prepared had an average particle diameter of about 0.02 μm by electron microscope observation, a specific surface area by BET method of 55.5 m ² / g, and a dispersity of 50%. This was inferior in monodispersibility as compared with Example 4.

Comparative Example 4

400 ml of an aqueous solution in which 44.11 g of calcium chloride dihydrate is dissolved is placed in a 1000 ml container and stirred, while 300 ml of an aqueous solution in which 18.35 g of sodium hexametaphosphate is dissolved in 300 ml and an aqueous solution in which 16.8 g of sodium hydroxide is dissolved in 300 ml. Were simultaneously dropped at a dropping rate of 10 ml / min. The reaction temperature at this time was 10 ° C., and stirring was continued at the temperature for 12 hours after the completion of the dropping. The obtained calcium phosphate emulsion was immediately filtered, washed with water, and dried at 80 ° C. for 24 hours. The dried product was sieved with a mesh of 100 mesh to obtain 29 g of dry powder. The powder thus prepared had an average particle diameter of about 0.02 μm by an electron microscope, a specific surface area by BET method of 64.6 m ² / g, and a dispersity of 58%. This was inferior in monodispersity as compared with Example 5.

It is an EMS (scanning electron microscope) photograph (magnification: 7000 times) of the calcium carbonate powder highly dispersed in single particles prepared in Example 1 of the present invention. It is an EMS (scanning electron microscope) photograph (magnification 7000 times) of the calcium carbonate powder highly dispersed in single particles prepared in Example 2 of the present invention.

Claims (4)

The method of taking out the inorganic particles synthesized in water as a single particle powder,
(1). A step of preparing an aqueous suspension of inorganic particles in an aqueous system;
(2). A step of immediately replacing the aqueous medium with an organic solvent after the step of preparing an aqueous suspension of inorganic particles in the aqueous system,
(3). A step of separating single particle powder of inorganic particles from an organic solvent suspension of inorganic particles obtained by the step (2).
A method for taking out inorganic particles synthesized in an aqueous system as a single particle powder.   (1) The process comprises preparing an aqueous suspension of inorganic particles such as calcium carbonate, calcium phosphate, or hydrous silica having a particle size of 1 μm or less. How to take out as powder.   (2) The method for taking out the inorganic particles synthesized in the aqueous system as a single particle powder according to claim 1, wherein the step of replacing the aqueous medium in the step with an organic solvent is by dialysis or substitution. (2) The organic solvent used in the step is an alcohol or a ketone. The method according to claim 1, wherein the inorganic particles synthesized in the aqueous system are taken out as a single particle powder.

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